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Kongsberg Maritime
Doc.no.: SO-1295-D / 7-Jan-11
Neptune CHS LNG-M User manual
Neptune
CHS
Cargo Handling Simulator
LNG-M Carrier
User’s Manual
Kongsberg Maritime
Doc.no.: SO-1295-D / 7-Jan-11
Neptune CHS LNG-M User manual
Neptune
CHS
Cargo Handling Simulator
LNG-M Carrier
User’s Manual
Steffen Hårstad Jensen (s) Terje Heierstad (s)
Department/Author Approved
2008 KONGSBERG MARITIME AS
All rights reserved
No part of this work covered by the copyright
may be reproduced or otherwise copied
without prior permission from
KONGSBERG MARITIME AS
Kongsberg Maritime
Doc.no.: SO-1295-D / 7-Jan-11
Neptune CHS LNG-M User manual i
DOCUMENT STATUS
Issue No. Date/Year Inc. by Issue No. Date/Year Inc. by
A 18-Jan-06 ABU/beba
B 11-Sep-08 STHJ/BEBA
C 08-Apr-09 STHJ/Beba
D 7-Jan-11 STHJ/beba
CHANGE IN DOCUMENT
Issue
No.
ECO
No.
Paragraph
No.
Paragraph Heading/
Description of Change
B MP-1662 Review & Updates
C MP-1692 Review & Updates
D MP-1749 Updated according to latest revision
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ii Neptune CHS LNG-M User manual
Hazard Warnings
And Cautions
Fire
If a fire condition arises emission of toxic fumes can be
anticipated from burning insulation, printed circuit boards,
ETC.
Dangerous Voltages
This equipment is not fitted with safety interlocks and lethal
voltages are exposed when the cabinets are open. Before
removing any sub-units or component all supplies must be
switched off. No user serviceable parts inside.
Electrostatic sensitive device
Certain semi conductive devices used in this equipment are
liable to damage due to static voltage. Observe all precautions
for handling of semi conductive sensitive devices.
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Neptune CHS LNG-M User manual iii
ESD precautions
Refer service to qualified personnel. Turn power off prior to
opening any of the consoles. Whenever doing work inside the
consoles use an ESD protective wrist strap.
Whenever a printed circuit board is put aside it must be put
into an ESD protective bag or on a grounded ESD mat.
Non-conductive items such as synthetic clothing, plastic
materials, etc. must be kept clear of the working area,
otherwise they may cause damage.
Printed circuit boards must be kept in ESD protective bags at
all times during storage and transport. The bags must only be
opened by qualified personnel using ESD protective
equipment as specified in this section.
Computer system
The simulator contains general purpose computers. Running
non Kongsberg Maritime software in any of them will void the
warranty. Connecting other keyboards, mice or monitors may
also void the warranty.
Notice
The information contained in this document is subject to
change without notice. Kongsberg Maritime shall not be liable
for errors contained herein or for incidental or consequential
damages in connection with the furnishing, performance, or
use of this document.
Kongsberg Maritime
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iv Neptune CHS LNG-M User manual
List of Abbreviations and Terms
AP Aft Peak
AIS Automatic Information System
CBM Cubic Meter
CC Chemical Carrier
CHS Cargo Handling Simulator
COW Crude Oil Washing
CT Center Tank
CTS Custody Transfer System
DO Diesel Oil
DS Dynamic Stability
DW Dead Weight
ECC Error Control Correction
FP Fore Peak
FS Free Surface
FWD Forward
Gb Giga byte
GM Gravity to Metacenter
OG Gas Oil
GZ Righting moment
HFO Heavy Fuel Oil
HMI Human-Machine Interface
Hz Hertz
IFE Institutt For Energiteknikk
IBC International Code for the Construction and the Equipment of
Ships Carrying Dangerous Chemicals in Bulk
IG Inert Gas
IGG Inert Gas Generator
IMDGC International Maritime Dangerous Goods Code
IMO International Maritime Organisation
Kb Kilo byte
LAN Local Area Net
LCG Longitudinal Center of Gravity
LEL Lower Explosion Limit
LNG/C Liquefied Natural Gas Carrier
LOA Length Over All
LPG/C Liquefied Petroleum Gas Carrier
LPP Length between the Perpendiculars
MARPOL International Convention for the Prevention of Pollution from
Ships
Mb Mega byte
MEPC Marine Environment Protection Committee
MFLOPS Million floating point operations pr.sec.
MLC Meter Liquid Column
MIPS Million Instructions pr.sec.
MSC Marine Safety Committee
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Neptune CHS LNG-M User manual v
ODM Oil Discharge Monitor (equipment)
OTISS Operator Training Simulation System
P Port
PC Product Carrier
PPM Parts Per Million
P/V Pressure/Vacuum
RAM Read Access Memory
S Starboard
SAST Special Analysis and Simulation Technology
SL.TK SLOP Tank
SOLAS International Convention for the Safety of Life at Sea
TC Tank Cleaning
UEL Upper Explosion Limit
UTC Universal Time Coordinated
VCG Vertical Center of Gravity
VLCC Very Large Crude oil Carrier
WS Work Station
WT Wing Tank
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vi Neptune CHS LNG-M User manual
TABLE OF CONTENTS
Section Page
1. GENERAL .......................................................................... 1
1.1 Simulation Philosophy ....................................................... 1
1.2 General Training Objectives ............................................... 2
1.3 Specific Training Objectives ............................................... 2
1.4 Concept Description .......................................................... 4
1.5 System Description ........................................................... 5
1.6 Simulator Configuration ..................................................... 6
1.7 Computer System ............................................................. 8
1.8 Getting started ................................................................. 9
1.9 To Start the Simulation ................................................... 10
1.10 Control Functions ............................................................ 11
1.11 Cargo Handling Simulators ............................................... 12
1.12 To Create an Initial Condition ........................................... 12
1.13 To End Simulation ........................................................... 12
1.14 Computer System ........................................................... 13
1.15 Environmental Requirements ........................................... 15
1.15.2 Alarm Section ................................................................ 17
1.15.3 Function buttons at the Operator Section ........................... 18
2. NEPTUNE INSTRUCTOR FUNCTIONALITY ................................. 23
2.1 Neptune Instructor Software Systems ............................... 23
3. FUNCTIONAL DESCRIPTION ................................................. 29
3.1 Graphic Desk-top ............................................................ 29
3.1.1 Pump Models.................................................................. 31
3.1.2 Pipe/Valve Models ........................................................... 34
3.1.3 Tank Models ................................................................... 35
3.1.4 Hull Models .................................................................... 36
3.2 Vessel Particulars ........................................................... 43
3.3 Properties of LNG............................................................ 47
3.3.1 Physical Properties, Composition and Characteristics of LNG 47
3.3.2 Variation of Boiling Point of Methane with Pressure ............. 49
3.3.3 Flammability of Gases ..................................................... 51
3.3.4 Supplementary Characteristics ......................................... 54
3.4 Description of the Ship’s Equipment and Arrangements ....... 57
3.4.1 Design Concept of the Cargo System ................................ 57
3.4.2 Cargo Containment System Principle ................................. 58
3.4.3 Membrane Cargo Containment ......................................... 60
3.4.4 Deterioration or Failure ................................................... 63
3.4.5 Description of Cargo Pumps ............................................. 67
3.4.6 Stripping/Spray Pump ..................................................... 73
3.4.7 Emergency Cargo Pump .................................................. 76
3.4.8 H/D Compressor ............................................................. 79
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3.4.9 L/D Compressor ............................................................. 81
3.4.10 Gas Heater .................................................................... 83
3.4.11 Operation of H/D heater .................................................. 84
3.4.12 Operation of L/D heater .................................................. 85
3.4.13 LNG Vaporizer ................................................................ 86
3.4.14 Operation ...................................................................... 87
3.4.15 Forcing Vaporizer ........................................................... 88
3.4.16 Operation ...................................................................... 89
3.4.17 Nitrogen Generating System ............................................ 90
3.4.18 Inert Gas Generator Plant ................................................ 93
3.4.19 Cargo Control Console (CCC) ........................................... 95
3.4.20 IMS control function ....................................................... 96
3.4.21 BVG management system ............................................... 97
3.4.22 Low duty compressor control ........................................... 98
3.4.23 Control logic .................................................................. 98
3.4.24 Forcing vaporizer control ................................................. 99
3.4.25 High duty compressor control .......................................... 99
3.4.26 Spray Pump Start/Stop .................................................. 101
3.4.27 Spray line Cooldown ...................................................... 103
3.4.28 Cargo Pump Start/Stop .................................................. 104
3.4.29 Discharging .................................................................. 107
3.4.30 Cargo Tank Temperature Control ..................................... 109
3.4.31 Cargo Tank Pressure Control ........................................... 110
3.4.32 Cargo Tank Protection System ........................................ 111
3.4.33 Description of Ballast Tanks and Ballast Pumping .............. 112
3.5 Mimic Diagrams ............................................................ 113
3.5.1 Cargo Tank Overview ..................................................... 114
3.5.2 Ballast Tank Overview .................................................... 115
3.5.3 Bunker/Consumables ..................................................... 116
3.5.4 Shear Force .................................................................. 117
3.5.5 Bending Moment ........................................................... 118
3.5.6 Deflection ..................................................................... 119
3.5.7 Stability ....................................................................... 120
3.5.8 Shore Tanks ................................................................. 121
3.5.9 Ship/Shore Connection ................................................... 122
3.5.10 Deck Lines .................................................................... 124
3.5.11 Cargo Tanks ................................................................. 125
3.5.12 Cofferdams ................................................................... 126
3.5.13 Insulation Spaces Pressure Controller .............................. 127
3.5.14 Compressor Room ......................................................... 128
3.5.15 Low Duty System .......................................................... 129
3.5.16 High Duty System ......................................................... 130
3.5.17 Vapourizers .................................................................. 131
3.5.18 Nitrogen Plant ............................................................... 132
3.5.19 Inert Generator ............................................................. 133
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3.5.20 Ballast Tanks ............................................................... 134
3.5.21 Ballast Pump Room ....................................................... 135
3.5.22 H/D & Spray Control Panel ............................................. 136
3.5.23 Cargo Control Panel ...................................................... 137
3.5.24 Fixed Gas Detection System ........................................... 138
3.5.25 CCTV CAMERA .............................................................. 139
3.5.26 Picture Directory (Load Master) ...................................... 141
3.5.27 Load Master Cargo Tank Overview .................................. 142
3.5.28 Load Master Ballast Tank Overview ................................. 143
3.5.29 Load Master Bunker/Consumables .................................. 144
3.5.30 Load Master Shear Forces .............................................. 145
3.5.31 Load Master Bending Moment ........................................ 146
3.5.32 Load Master Deflection .................................................. 147
3.5.33 Load Master Stability ..................................................... 148
3.5.34 Description of Legends .................................................. 149
4. OPERATION OF THE LNG MEMBRANE TANKER ........................ 151
4.1 Introduction ................................................................. 151
4.2 Insulation Space Tests .................................................. 152
4.2.1 In Service Tests............................................................ 152
4.2.2 Method for Checking the Effectiveness of the Barriers ....... 152
4.2.3 In Service Global Tightness Test ..................................... 153
4.3 Post Dry Dock Operation ................................................ 155
4.3.1 Insulation Space Inerting ............................................... 155
4.3.2 Drying Cargo Tanks ...................................................... 161
4.3.3 Inerting Cargo Tanks .................................................... 165
4.3.4 Gassing-up Cargo Tanks ................................................ 166
4.3.5 Cooling Down Cargo Tanks ............................................ 174
4.3.6 Spraying During Ballast Voyage ...................................... 177
4.3.7 Sloshing ...................................................................... 179
4.4 Loading ....................................................................... 180
4.4.1 Preparations for Loading ................................................ 180
4.4.2 Cargo Lines Cool Down .................................................. 182
4.4.3 To Load Cargo with Vapour Return to Shore ..................... 184
4.4.4 De-Ballasting ............................................................... 187
4.5 Loaded Voyage with Boil-Off Gas Burning ........................ 190
4.5.1 Normal Boil-Off Gas Burning .......................................... 190
4.5.2 Forced Boil-Off Gas Burning ........................................... 192
4.6 Discharging with Gas Return from Shore ......................... 196
4.6.1 Preparations for Unloading ............................................. 197
4.6.2 Liquid Line and Arm Cool down before Discharging ........... 198
4.6.3 Discharging .................................................................. 199
4.6.4 Ballasting .................................................................... 202
4.7 Pre-Dry Dock Operations ............................................... 206
4.7.1 Stripping and Line Draining ............................................ 206
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4.7.2 Tank Warm Up .............................................................. 207
4.7.3 Inerting ........................................................................ 210
4.7.4 Aeration ....................................................................... 211
4.7.5 Limiting Factors ............................................................ 213
4.7.6 Discharge Plans ............................................................. 213
4.7.7 Cargo Handling Training from the Graphic Desk-top ........... 213
4.7.8 Picture Directory General ................................................ 214
4.7.9 Picture Directory LM ...................................................... 215
4.7.10 Pump Flow .................................................................... 218
4.7.11 Ballasting ..................................................................... 219
4.7.12 Inert Gas System .......................................................... 222
4.8 Stress and Stability Calculations ...................................... 224
4.8.1 Online Calculations ........................................................ 224
4.8.2 Offline Calculations ........................................................ 227
5. APPENDIX A ................................................................. 229
5.1 Instructor Station .......................................................... 229
5.2 Student Workstation ...................................................... 229
5.3 Printer ......................................................................... 229
5.4 The Functions of the Major Facilities ................................ 230
5.4.1 Computer System .......................................................... 230
5.4.2 Instructor Workstation ................................................... 231
5.4.3 Student Workstation ...................................................... 232
5.4.4 Printer ......................................................................... 232
5.4.5 Mouse .......................................................................... 232
5.4.6 Keyboard ..................................................................... 233
5.5 Operation ..................................................................... 234
5.5.1 Function buttons & blue pages ........................................ 234
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Neptune CHS LNG-M User manual 1
1. GENERAL This documentation is limited to describing and explaining relevant aspects governed by
the requirements in the Standard for certification of Maritime Simulator Systems. This
documentation is required together with the simulator in order to maintain the type
approval.
1.1 Simulation Philosophy
Over the past years simulator training has proved to be an effective method to train cargo
handling procedures, especially where an error of judgement can endanger life,
environment and property. A dynamic real-time computerised simulator can compress
years of experience into a few weeks, and provide knowledge of the dynamic and
interactive processes typical for real cargo operations.
Proper simulator training will reduce accidents and improve efficiency, and give the
trainees the necessary experience and confidence in their job-situation.
The best way to acquire practical experience is to learn from real life on real ship, but
today the efficiency requirements do not allow for this kind of onboard education, hence
the training can be carried out on a simulator. Practising decision making in a simulator
environment where decisions and their effects are monitored, opens a unique possibility to
evaluate these effects.
The opportunity to experiment on specific problems and get answers on questions such as:
"what happens if ....?" without leading to damaging of components and resultant off hire
costs, is unique. Simulation will give an easy introduction to background theories through
the realistic operation of the simulator.
It is important that the trainees experience life-like conditions on the simulator and that the
tasks they are asked to carry out are recognised as important and relevant in their job-
situation. The trainees shall be challenged at all levels of experience in order to achieve
further expertise and confidence.
Certain training objectives can only be reached properly by means of life-like hands-on
equipment and experience.
For some training objectives it is considered that colour-graphic workstation presentation
and practice will be sufficient. The choice will depend on the abstraction level the trainees
are able to cope with, their experience and the specifics of the training objective.
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1.2 General Training Objectives
The Maritime Training Centre shall be able to train junior officers in basic cargo handling
operations, senior officers in emergency operations and trouble shooting, and to train
senior personnel in optimal operations during cargo handling. This will be achieved by
controlled training, leading to better understanding of the total cargo operation, as a
function of realistic simulation of a LNG carrier cargo system.
In order to fulfil these requirements the simulator shall be suitable for, but not limited to:
- basic and advanced training and education of students leading to professional
qualifications and a higher officer qualification;
- refresher and recurrent training for qualified officers;
- training officers in the operation of a LNG carrier's cargo equipment together with
the most vital auxiliary equipment;
- enabling detailed studies in the different processes of a ship's cargo system.
- training officers to localise faults and deterioration, and to clearly demonstrate the
impact of various types of faults and deterioration on the system's total efficiency;
- study of overall operational economy.
1.3 Specific Training Objectives
Dependent on background knowledge and experience of the trainee, the simulator shall at
least be capable of creating situations ensuring appropriate training in:
System familiarisation:
- tank arrangement
- pipe line arrangement
- pipe line control valves
- cargo compressors (high duty and low duty)
- pumps
- vaporizers
- instrumentation
- controls
- basic procedures
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Neptune CHS LNG-M User manual 3
Special operations and procedures:
- gas freeing
- gassing up
- tank atmosphere evaluation
- use of inert gas system
- use of nitrogen system and purging
- cool down of pipes and tanks
- draining and stripping
- forced vaporizations and boil off to boiler
Cargo and ballast operations:
- general provisions
- ballasting
- de-ballasting
- loading cargo
- discharging cargo
Operational problems:
- normal working conditions
- introduction of
* system faults
* malfunctions
- emergency procedures.
In addition to giving the students operational training, the LNG-M is also a tool for more
intimate theoretical studies for loading/discharging operations, such as:
- Planning the operations by using LNG-M as a load computer
- Run test conditions on the loading computer
- Studying single components
- Studying tank atmosphere
- Studying inert gas in relation to boiler load
- Monitoring the discharge cost and time
- Provide training in operations that the officers will have benefit of later on
- Shows you the results of incorrect operations without damaging the equipment
- Presents all relevant terminology and relates it to associated hardware
- Demonstrates both theoretical aspects and practical results in one and the same
room.
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1.4 Concept Description
The LNG-M is based on the simulator design- and development- system, Operator Training
Simulation System (OTISS) developed by Special Analysis and Simulation Technology
Ltd. (SAST) UK.
The Operator Human-Machine Interface (HMI) is realised using the EMULA Graphic
software Package developed by Institutt For Energiteknikk (IFE) Halden, Norway.
By the simulation of faults and deteriorations, the instructor can create a training situation
that enables the trainee to meet and overcome these problems. This training environment
will give the students experience in dealing with problems that would normally demand
years of seagoing experience.
The third part of the simulator is the instructor station which includes the "simulator
controls" for:
- Changing operational and ambient conditions
- Setting faults and deteriorations, single or in series
- Simulate leaks in cargo lines and tank bulkheads
- Resetting faults
- Logging events and alarms
- General system communication
The LNG-M is designed to train students in cargo handling operation under both normal
and abnormal conditions. It is therefore of utmost importance that the training takes place
in a realistic environment.
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Neptune CHS LNG-M User manual 5
1.5 System Description
As pioneers in the ship automation field, Kongsberg Maritime AS know how modern
technology has improved safety, reliability and economy on board ship.
The improvement has been immense, but it is also known that it is impossible to replace
the proficiency and know how to an experienced engineer, the man who must be present in
the right place at the right time to do things quickly and efficiently.
Kongsberg Maritime AS has designed a dynamic real-time computerised simulator which
can compress years of experience into a few weeks, and provides hands-on training.
The simulator provides the necessary information on dynamic and interactive processes as
found in a real cargo plant.
The LNG-M is designed to meet the demands for basic operational training of junior
officers, fault studies with economy and optimisation studies with the senior officers. It
enables the simulation of individual auxiliary systems (sub-system) and independent
components as well as an efficient simulated presentation of a total plant.
The Cargo Handling Simulator (CHS) includes comprehensive instructor communication
links that allow him to:
- Pre-program and store situations.
- Develop and test new training programs.
- Change operational and ambient conditions.
- Freeze current situations for discussions and clarifications with the trainees.
- Setting of single faults or automatic sequential fault.
The CHS has a layout and instrumentation typical to that of a modern vessel.
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1.6 Simulator Configuration
The CHS Simulator is implemented on a network of desktops with an Instructor Station.
When fitted the Cargo Control Consoles and -Panels are connected to the same Ethernet
via a serial link converter.
Figure 1-1 Computer Configuration
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Example of a typical room layout
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1.7 Computer System
All computers run on WINDOWS.
The instructor station will be the server
for all other computers. Together with the
student workstations it forms a complete
simulator computer system.
This concept is well proven and
extremely efficient for simulation
purposes. All new generations of cargo
handling simulators are based on this
concept.
Both the instructor- and the student
stations are based on the workstation.
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1.8 Getting started
The cargo system can be started at different operating conditions dependent on the training
objectives.
1. If not starting via the Neptune Instructor System you can continue to point 2.
2. If not already running, double-click the simulator program icon to start the program.
3. The Picture Directory window appears normally, but sometimes the Initial Condition
window starts up first. In that case jump to 5.
4. Click once inside the Picture Directory window.
5. Use Shift+F6 to display the Initial Conditions window.
6. Select one of the available conditions by clicking on it.
7. The condition is loaded and the simulator is ready for training.
Note: Initial conditions can only be changed while the simulator is in freeze.
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1.9 To Start the Simulation
The simulator will always be in Freeze mode when the simulator is started and the Initial
Condition is loaded.
1. Push F1 to start the simulation.
2. Running is displayed in the upper left corner.
3. Push Home to display the Picture Directory.
4. Push any picture name to display the corresponding process diagram.
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1.10 Control Functions
The simulator allows you to control pumps, valves, and controllers etc. as follows:
• Valves: Click to open, right-click to close (colour changes to indicate open condition).
• Valves: Some valves are adjustable. Enter an opening value in percent (colour changes
to indicate open condition).
• Pumps: Click to start, right-click to stop (colour changes to indicate running).
• Fans: In some cases there is a panel to be used for starting and stopping (colour
changes to indicate running).
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1.11 Cargo Handling Simulators
In the Picture Directory the picture number background is colour coded as follows:
• Green: Indicates processes taking place in the tank system.
• Beige: Indicates control panels, ship views and various printed diagrams.
1.12 To Create an Initial Condition
The simulation can at any time be stopped and the current situation saved for later use.
1. To freeze the simulation push F2.
2. Push Shift+F6 to display the Initial Conditions.
3. Push the Create button, select an unused button and type in a name for the new
condition.
4. Push Enter.
1.13 To End Simulation
To end the simulation and stop the simulation program do the following:
1. To end the simulation push F3.
2. Click the YES button and the simulator exits.
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1.14 Computer System
On the operator stations, the operator/student(s) can view mimic pages representing the
various simulated systems. These graphic mimic process diagrams are interactive, i.e. the
process can be both monitored and controlled.
In principle, all the graphic desktops can be configured as instructor stations. Whenever a
desktop is going to be used in part task mode, the student using it will act as his own
instructor, meaning that he will have the instructor’s privilege to start/pause the simulation.
Each individual can run the exercise at his own pace.
The following pages comprise a functional description of the main cargo handling systems
and related sub-systems. The process diagrams with corresponding information such as
temperature, flow, pressure, set points, etc. are presented on the colour graphic desktop.
Additional diagrams and information giving insight to the simulated models are available
and can be addressed by using the functional keyboard.
The Process Diagrams presented have the following colour code for pipelines:
- White: Nitrogen
- Blue: Fresh Water
- Green: Sea Water
- Grey: Inert gas
- Orange: Lube Oil
- Light blue: Steam
- Blue: Liquid Cargo and Spray lines
- Red: Vapour line and Vapour build up pressure line
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The Process Diagrams comprises a lot of green numbers with a letter in front. The letter is
used to identify the type of value the number represent. Here is the meaning of these
letters:
T: Temperature
G: Flow
P: Pressure
N: Rpm
Q: Force
I: Ampere
U: Voltage
F: Frequency
E: Electrical Power
V: Valve
L: Level
X: Position
Z: Signal/Concentration
W: Viscosity
c: Constant
d: Density
H: Heat Transfer
M: Mass
R: Pump, Fan Status
By moving your mouse over the figures, a text will pop up at the bottom of the page giving
you the tag name for this value as well as a description of the figure:
G02114 is the tag name.
3973, 26 m3/h is the value with the measuring unit
COP1 FLOW is the description of the tag.
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1.15 Environmental Requirements
Local climate conditions and the system configuration determine the requirements for
heating, ventilation and air-conditioning. The heating, ventilation and air - conditioning
system must provide air flow to keep the ambient conditions within the specified
temperature and humidity range.
- Ideal temperature: 23°C± 3°C
- Ideal relative humidity: 50% ± 10%
- Dust: Air pressure in the simulator rooms should be higher than
the pressure outside. Special demands are made on the air-
conditioning units filter if the air includes corrosive gases,
salts, conductive particles or other unusual particles of
dust.
Minimum and maximum operational requirements:
- Minimum temperature : 10°C
- Maximum temperature : 30°C
- Relative humidity : 15% to 80%
If the humidity is lower than 40%, static electricity may become a problem.
In order to ensure reliable operation of the air-conditioning unit, preventive maintenance
should be carried out regularly.
Thermostats must be installed in each room to allow temperatures to be controlled
individually.
NOTE! The Air-conditioning equipment must include an automatic restart after a
power failure.
It is necessary to maintain air-conditioning even when equipment is shut down, because
parts of the system remain energized. If the humidity specifications are not maintained,
condensation may accumulate which can cause damage to circuits when power is
reapplied.
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1.15.1.1 Running (F1)
Starts simulation after having frozen the simulation. The time starts running, and the
student(s) can proceed with the exercise. When the RUNNING button is pressed, a
message will inform that the simulation has started.
1.15.1.2 Freeze (F2)
Freezes simulation during breaks or when situation needs time-out for evaluation. When
FREEZE button is pushed, a message will inform that simulation is halted. The simulator
must be in FREEZE before loading an Initial Condition or a Scenario.
1.15.1.3 Stop (F3)
Ends simulation after a message. Pressing STOP and typing "yes" after prompt will log out
of simulator completely, and the desktop will return to the simulator model login-window.
To restart, proceed according to the following steps:
Type the user's name in the LOGIN picture (i.e. student1) and press ENTER. After a while
a new display appears, and by means of the left push button, select the LNG-M simulation
plant. A complete start up takes about 2 - 3 minutes. When finished, the instructor picture
Init Condition appears. Load the exercise wanted by pressing the middle button of the
mouse at the Init Condition, and proceed by pressing RUNNING.
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1.15.2 Alarm Section
1.15.2.1 Alarm Pages
The alarm system has several groups with a corresponding red alarm indicator numbered
from 1 through 28. Normally, all alarm lamps are turned off. As soon as an alarm occurs,
one of the alarm lamps starts flashing. Additional information is obtained by choosing the
group with the left mouse button.
Each lamp covers alarm points from dedicated sub systems. The alarm point exceeded
normal values, turns into a flashing mode.
The Alarm point (displayed in the MD picture) turns to steady condition as soon as the
operator moves the cursor to its location and resets the alarm by using the left hand side
push button of the mouse.
As appropriate actions are carried out, the alarm point previously indicated alarm
condition, turns off.
Measured values are displayed together with tag no, tag name, engineering units, and
upper/lower limits for alarms. The limits can be altered from Instructor mode by point and
click with left mouse button at limit and then type in new value, press “Enter” (Carriage
Return).
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1.15.3 Function buttons at the Operator Section
This section comprises all remedies for the student to conduct an exercise independent on
the Instructor or other students. From this section, the student has access to the
Malfunction List, Variable List, Alarm List, Picture Directory and other useful features.
The following pages contain information on how to utilise these functions.
1.15.3.1 Malfunction List (F9)
Most of the Model Drawings comprises one or more buttons marked M. By clicking at one
of these buttons with the left push-button of the mouse, a new window will appear at the
monitor containing the Malfunction List directory. (The M-buttons turn yellow when
malfunctions are activated (in Instructor mode only!)). When in operator mode (student),
all malfunctions are displayed, but there is no indication of which fault is introduced. In
instructor mode, the same window shows active malfunctions and in addition their settings.
Malfunctions are activated by the left hand side push-button of the mouse, while resetting
of malfunctions introduced is carried out by use of the right hand side push-button at the
mouse.
To rectify a suspected fault, move the cursor to the variable in the Malfunction List (ex
M1301), and press the right hand push-button of the Mouse. The response from the
computer will either be "Repair Attempt" or "Malfunction Reset". If the Malfunction log is
turned on, all attempts on repairing the fault are printed.
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1.15.3.2 Variable List (F10)
Displays a window with a list of all variables in the simulator. All related information is
organised in groups. This means that all variables from the Cargo line 1 system are located
at pages starting at 0010 until 0017. The List can be scrolled, moved or removed by using
the mouse and cursor.
After pushing VARIABLE LIST, identify sub system and press selected system. Displayed
window will then be identical to the variables found in the corresponding Model Drawing
ex. MD 02 at the monitor. Tag details and measured values will be displayed. Displayed
data can be changed after clicking on values with left mouse button. After typing in new
values and pressing enter new data is entered.
There are several ways to change the value of a model variable (ex. start/stop of pumps).
One of them is using the Variable List. (Any pump or valve can be operated from this part
of the simulator.) As the component to be operated is found, move the cursor to the
corresponding variable, press the select button at the unit and type the new value and
terminate by pressing "Enter" (Carriage Return).
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1.15.3.3 Alarm List (F11)
The Alarm List contains alarm groups displaying information of actual value, alarm limits
and alarm status. After recognition of the desired Alarm group in the Alarm group
directory, use the select button to display the desired alarm group. List can be scrolled,
moved or removed with cursor and left mouse button to find desired alarm.
After having pressed the ALARM LIST and identified the sub system, window with list of
alarms will be displayed.
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1.15.3.4 Picture Directory (Home)
Displays the directory of all Model Drawings (MD's). After recognition of system, click
with the left mouse button on the actual Model Drawing, and seconds later, the subsystem
is displayed on the screen.
1.15.3.5 Mark Picture (Shift+F7)
When pressing Mark Picture, the displayed Model drawing can be saved, and easily
recalled by using the Recall Marked Picture (F7). After clicking Mark Picture enter a
chosen number between 0 and 9. After clicking Recall Marked Picture, followed by the
same number, the previously MD is displayed again.
1.15.3.6 Select Picture (Shift+Home)
Allows selection of a Model Drawing after typing: MD and its corresponding number (in
one word). Enter MD and the MD's number without space, i.e. MD 101 and "Enter".
1.15.3.7 Previous Picture/Next Picture (PageUp/PageDown)
Allows scrolling to next/previous model drawing (ex.MD 07 MD 08 and MD 09) in line as
listed in picture directory.
1.15.3.8 Alarm Acknowledge
Acknowledges the alarm being pointed at with the cursor. Use the left mouse button.
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1.15.3.9 Alarm Log (F8)
Displays pages of all present alarms. Press the "PageUp" or “PageDown” key to get the
next page of alarms.
1.15.3.10 Alarm Silence (F12)
Resets alarm horn (where installed) in the Cargo Control Room and the internal buzzer.
1.15.3.11 Print Report
The "Print report" field is on the lower part of the VDU and by pressing this soft button a
complete printout of the alarm status is initiated.
1.15.3.12 Unit Conversion
The "Unit Conversion" field is on the lower part of the VDU and by pressing this soft
button a menu of different conversions "pops up" (Length, Volume, Area, etc.). Press one
of the soft keys in the menu. Press the middle button on the mouse and type the value of
the specific unit you want to be converted. And read the converted values in the other
fields.
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2. NEPTUNE INSTRUCTOR FUNCTIONALITY Kongsberg Maritime simulators have released for the Engine Room and Cargo Handling
Simulators the “State of the Art” Instructor, Monitoring and Assessment system.
Kongsberg in close cooperation with experienced world wide instructors, Norwegian
Maritime Directorate and Dot Norske VERITAS (DEN), have designed and developed an
Instructor, Monitoring and Assessment System that is excellent with regards to user-
friendliness and efficiency.
This chapter list available features that can be delivered along with this simulator.
2.1 Neptune Instructor Software Systems
The following will be provided:
Item Content Neptune
Instructorless
Neptune Instructorless gives instructor and students the option to
run readymade exercises, where following features are included.
Includes:
All configurations includes well proven models
Load simulation model on each station
Run simulation
Freeze simulation
Stop simulation
Load initial conditions
Create new initial conditions
Students can run the simulation independently
Insertion of malfunctions
Access to alarm list
Access to variable list.
Neptune Basic Includes:
Neptune Instructorless; as previously listed
Power-up all student stations
Recording of the complete exercise
Replay the whole exercises
Go back to any point in time for restart
-Create exercises including Initial conditions
Deploy exercises to student stations
-Centralized Run/Freeze control of all student stations
Connect student stations in clusters for team training
Send Instant Messages to student(s)
Send Instant Actions (Malfunctions or Events)
Recording of the complete exercise
Power shut-down of student stations
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Item Content Neptune
Professional
Includes:
Neptune Basic; as previously listed
Student Station (Access) Configuration
Exercise development, incl. triggers and actions
E-Coach, Electronic guidance system to students
Assessment
Item Description Instructor
Station
Classroom
View
Monitor and control the
students in the classroom (or
full mission simulator).
Instructor can tailor the view
according to site layout
Instructor
Station
Classroom
View
-Start exercises on Pac’s in the
classroom
-Run/pause exercises in the
classroom
-“Client Connect” to exercises
in the classroom
-Set up groups for team
training
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Item Description New Exercise
Structure
Exercise Structure comprises:
Initial Condition and
Scenario Modules
based on:
Triggers
E-Coach Messages
Actions
Assessment
Instructor
Controlled
configuration
for each of
the Student
Stations
Configuration of stations is
part of the exercise. It is
possible to add new stations to
an ongoing exercise “on the
fly”.
Trigger
Overview
Displays the state (Active/Not
Active) of all the triggers in
the module.
Displays users of the trigger
(other triggers, actions,
assessment and e-coach
messages)
Link to editors
Instructor control of triggers
(on the fly).
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Item Description Logic Block
Based Trigger
Editor
Building block used in e-coach
messages, actions and
assessments
Graphical editor
Flexible and powerful
Calculates output
(true/false) based on input
and logic blocks.
Configurable input
E-Coach
Overview
Displays the state (sent/ not
sent) of all e-coach messages
Link to trigger and
message editor
Possible for the instructor
to disable messages
(online).
E-Coach
Editor
Initiated by trigger
From “virtual instructor”
or other “outside world”
(e.g. Captain, VETS)
To a selected screen or all
screens.
Action and
Malfunction
Editor
Activated by trigger:
Additional triggers to
specify on/off conditions
for the criterion
Possible to select between
different types of scoring
(illustrated graphically)
Possible to define “critical”
criteria Action and
Malfunction
Editor
Malfunction introduced as
on/off. Instructor can freely
decide when and for how long
the malfunction shall be
activated
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Item Description Action and
Malfunction
Editor
Malfunction introduced as
repeating on/ off.
Action and
Malfunction
Editor
Malfunction introduced as a
repeating sine shape, where
Amplitude and Time period is
adjustable.
Action and
Malfunction
Editor
Malfunction introduced where
intensity and duration is
randomly selected.
Assessment
Overview
Overview of all assessment
criteria
Calculates total score
Instructor can define
parameters for overall
scoring
Pass and Fail evaluation is
completely based on
objective criteria
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3. FUNCTIONAL DESCRIPTION
3.1 Graphic Desk-top
Graphic Desk-tops are available at the instructor station, trainees desk-top and in the full-
mission consoles in engine control room.
In principle the stations are identical and the functions present on each similar.
On the operator stations, the operator/student(s) can view mimic pages representing the
various simulated systems. These graphic mimic process diagrams are interactive, i.e. the
process can be both monitored and controlled.
In principle, all the graphic desk-tops can be configured as instructor stations. Whenever a
desk-top is going to be used in part task mode, the student using it will act as his own
instructor, meaning that he will have the instructor’s privilege to start/pause the simulation.
Each individual can run the exercise at his own pace.
The colours, symbols and abbreviations used in the mimic diagrams are common
throughout all pictures and are described and explained in MD 150 Description of Legends.
Models
The main element in the CHS Cargo Handling Simulator is a set of dynamic models.
The models are based on physical laws and are updated at regular intervals thereby
yielding a dynamic behaviour. The various models are linked together and replicate the
mutual interactions and dependencies that can be experienced in real life.
For overview, the models are grouped together into:
- pump modells
- pipe/valve modells
- tank modells
- Hull models
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Open Valve/Start Pump
Flowto / fromtanks
Change in:-tank content-tank level
Change in: Change in:-draught-trim-heel
-load distr.-shear force-bend. moment-hull deflection
HULLMODELS
TANKMODELS
PIPE / VALVEMODELS
PUMPMODELS
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3.1.1 Pump Models
3.1.1.1 The Centrifugal Pump
The relationship between discharge head, flow and pump speed for centrifugal pumps can
be expressed as follows:
H = k0*n2 + k1*n*q + K2*q2
Where H = discharge head (delivery pressure)
n = relative pump speed
q = relative volume flow
k0, k1 and K2 are design related constants
H
q
n1
n2n3
Flow resistance
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Model variables & constants The model variables H, n and q are currently and
dynamically updated during the simulation, while the
model constants k0, k
1 and k2 are set initially, thereby
'designing' the capacity and the performance of the
pump.
El. power The deep well pumps are hydraulically driven, which
means that electric power has to be available. This is
provided from the engine room (instructor).
Cavitation Even with deep well pumps cavitation may occur.
This happens if the pump inlet pressure, pinlet, is
getting lower than the vaporization pressure, pvap., for the actual fluid pumped. Then gas bubbles are
generated in the fluid, resulting in fluctuating pump
speed, unsteady flow and increasing bearing
temperature. The dynamic inlet pressure, pinlet, is
dependent on the static inlet pressure and the flow
velocity (Net Positive Suction Head - NPSH).
Cavitation precautions The best way to avoid cavitation conditions when the
static inlet pressure is reduced due to low liquid level
is to reduce the liquid flow rate, either by reducing
the pump speed or by throttling the pump discharge
valve.
Pvap The vaporization pressure, Pvap., will vary from fluid
to fluid. Thus the Pvap. for crude oil and refined
products will be sufficiently high to cause cavitation
problems, whilst the Pvap for ballast water will be
below any critical limit.
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3.1.1.2 The Stripping Eductor
Stripping eductors are used complementary to conventional centrifugal pumps to remove
the last parts of the liquid that remain in the tank (tank stripping).
B AC
D
Drivingflow
Suctionflow
The eductor works on the principle that the total sum of energy in a liquid flow is constant
(Bernoulli's Law).
When the liquid flows from A to B, and when it is constricted in C, a higher velocity is
gained in this point. The kinetic energy will then increase in this point, too. Because of the
fact that the total sum of energy is constant, the static energy is reduced accordingly,
yielding a lower static pressure in C. This will create a suction flow through D. Thus an
increased driving flow rate will result in a higher suction flow rate.
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3.1.2 Pipe/Valve Models
A flow through a pipeline is caused by different pressures in the two ends (nodes) of the
pipeline. Flow is increased by increased pressure drop across the pipeline and reduced by
increased resistance in the pipeline. The resistance may be caused by reduced pipe
dimensions, bends, orifices or throttling valves.
q = cv p
where q = flow
1/cv = flow resistance
p = pressure drop
= specific density
Often the various pipelines are connected in nodes. The flow is then distributed on various
branches dependent on the actual difference in pressures and flow restrictions.
p0
q0
cv1
cv2
cv3
p1
q1
p2
q2
p3q3
q1 = cv1 p1 ; p1 = p0 - p1
q2 = cv2 p2 ; p2 = p0 - p2
q3 = cv3 p2 ; p3 = p0 - p3
q0 = q1 + q2 + q3
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3.1.3 Tank Models
3.1.3.1 Modelling Of Tank Levels
Based on tables containing the tank geometry the actual tank levels are calculated currently
from the actual contents of liquids in the tanks. The actual contents of liquids in the tanks
are based on the current flows to or from the tanks as computed by the Pipe/Valve Models.
Tank Level Gauging The tank levels are measured directly. I.e., Changing the
weight of the cargo/ballast without changing the volume (i.e.
changing the specific density) will not change the actual level.
Changing the volume without changing the total weight (e.g.
due to variations in temperature) will result in changed levels.
Sensor Location The sensors are located aft and in the centrelines of the tanks.
I.e.: The level measured are influenced by the ship's trim, but
not by the heel.
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3.1.4 Hull Models
The content of liquids in the tanks will have an inevitable impact on the hull condition in
terms of:
- hydrostatic conditions:
- draught
- trim
- heel
- intact stability
- meta centre height
- hull stress
- shear force
- bending moment
- hull deflection
3.1.4.1 Hydrostatic Conditions
Draught The draught is adjusted until the weight of the displaced water,
WD, equalizes the light ship weight, WLS, and the cargo weight,
WC.
WD = WLS + WC = *
where = specific gravity of water
= volume of displaced water
G
B dt
A W
T
When the weight of the cargo is changed the draught will be changed accordingly. The
change in draught can be estimated from the formula for displacement (Tons) Per. Cm
draught:
dWD = rAW * 0.01(Tons/Cm)
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This can be found in the tables and curve sheet for the hydrostatics.
t
W D
dWD
T
Trim Trim is adjusted until the trimming moment from the gravity forces
(light ship weight + cargo weight) equalizes the buoyancy moment
from the displaced water.
The trimming moment is calculated with the basis in the Longitudinal
Centre of Flotation (LCF) and the trimming takes place around this
point.
The location of the LCF is given by the shape and area of the hull's
water plane at the actual draught, as the total longitudinal moment of
the water plane-area is to be equal to zero at this point.
F
a
M 1
g
WL 1
WL0
S
The amount of trimming can be estimated by means of the Moment to Trim 1 Cm. formula:
MT = I L
L
This can be found in the hydrostatics tables.
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Heel The heel is adjusted until the heeling moment is equalized by the
buoyancy moment of the displaced water.
The heel will always take place along the water plane’s
longitudinal centre line.
B (x)
dx
x
LCF
L
Water - plane area
L L
AW = _ dAW = _ B(x) dx
0 0
Water - plane moment of area (longitudinal)
L L
FL = _ xdAW = _ B(x)x dx
0 0
Water moment of inertia (longitudinal)
L L
IL = _ x2dAW = _ B(x)x2 dx
0 0
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3.1.4.2 Intact Stability
As long as the vessel lies in upright position there will always be equilibrium between the
weight forces (light ship + cargo) acting through the gravity centre, G, and the total
buoyancy forces acting through the buoyancy centre, B.
G and B will always be located on the same vertical line at a distance KG and KB from the
keel respectively.
G
B
K
Ships heeling When the ship is inclined due to a heeling moment, the
buoyancy centre will move to a new position due to the
displacement's volume and shape.
Meta Centre The vertical line through B will cut the ship's centre line at an
angle, in the point M. At small angles of heeling the point M
is denoted the Initial Meta Centre.
The horizontal distance between the centre of gravity, G, and
the vertical line through the new centre of buoyancy, B', is
denoted GZ and represents the arm of righting moment.
G
B
K
B'
M
ZØ
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Meta Centre The distance between the Centre of Gravity, G, and the Meta
Height, GM Centre, M, is denoted the Meta Centre Height, GM.
Thus:
When GM > 0:
The heel will be counteracted by a righting moment.
The ship is said to be stable.
When GM = 0:
The heel will remain.
The ship is said to be indifferent.
When GM < 0:
The heel will increase.
The ship is said to be unstable.
Variable GM /
variable GZ
Hydrostatic considerations will show that the meta centre
height, GM, will decrease with increasing draught, T.
The GM will be further reduced if free surfaces occur in one
or more tanks. The change in GM will inevitably have impact
on the righting arm, GZ, which is the most relevant parameter
for the intact stability.
15 degr.
30 degr.
45 degr.
60 degr.GZ
Displacement (draught)
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3.1.4.3 Hull Stresses
Load Distribution The forces acting on a ship's hull will be the distributed
weight forces (lightship + cargo) and the distributed buoyancy
forces. As long as the ship lies still in water the sum of these
forces balances each other. However, the resulting forces may
be uneven distributed. This is particular the case during the
loading and discharging operation.
Shear Forces As a result of the uneven distribution of load along the hull,
shear forces will appear.
Mathematically, shear forces can be described as the integral
of the distributed load.
L
Q = q dL Q = shear force
0 q = distributed load
L = ships (hulls) length
Shear forces will act as vertical cutting forces onto the hull
structure and should be kept within the limits of the hull
construction's tensile strength.
Bending Moment The distributed shear forces will result in a bending moment
for the hull.
Mathematically, hull bending moment can be described as
the integral of the distributed shear forces.
L
M = Q dL M = longitudinal bending moment
0 Q = distributed shear force
L = ships (hulls) length
Longitudinal bending moment will cause strains in the hull
construction and should be kept within pre-set limits.
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The relationship between load distribution, shear forces and
bending moment is schematically shown in the figure below.
q Q
-+ +
-
M
0
q: load distribution
Q: shear force
M: bending moment
Hull deflection As the steel in the hull is elastic the longitudinal bending
moment will result in a certain deflection of the hull. The hull
deflection curve will have the same shape as the bending
moment curve.
Thermal deflection In addition to the deflection caused by the bending moment
the hull may be subjected to thermal deflection too. This is the
case in tropical waters where the sun is heating the deck and
the superstructure, while the submerged part of the hull is
cooled by the water.
In these circumstances it should be noted that the deflection
caused by the hogging moment in ballasted or unloaded
condition will be superimposed on the thermal deflection.
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3.2 Vessel Particulars
The modelling of the Cargo Handling Simulator CHS – LNG-M is based on a
vessel with double hull and double bottom.
Ships name LNG Membrane
Signal letters ZCDN9
IMO number 9266962
Port of registry HAMILTON
Flag Bermuda
Builder Ship No. 22xx, Daewoo Shipbuilding &
Marine Engineering Co, South Korea
Length overall 285,40 m
Length between perpendiculars 274,40 m
Breadth moulded 43,40 m
Depth moulded main deck 26,00 m
Draught design 11,35 m
Draught scantling 12,35 m
Service Speed at MCR with 15% S.M. 19,75 Knots
Deadweight 83067,7 MT
Gross tonnage (Int.) 97561 GT
Net tonnage (Int.) 29268 NT
Displacement 114153,4 MT
Class Lloyd’s Register of Shipping:
+100A1. Liquefied Gas Tanker. Ship type
2G. Methane in Membrane Tanks. Max
Vapour Pressure 0.25 bar,
Min.Temperature -163°, ShipRight
(SDA), *IWS, LI, +LMC, UMS, NAV1,
IBS, HCM, TCM with descriptive notes
Pt. Higher Tensile, ETA, ShipRight
(FDA, CM, BWMP(S), SCM), EP
Cargo Tank capacities:
Compartment Capacity @ 98,5 % and –163 C
Cargo Tank no 1 21628,7 m³
Cargo Tank no 2 42403,0 m³
Cargo Tank no 3 42403,6 m³
Cargo Tank no 4 37290,3 m³
Total all tanks 143725,7 m³
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Ballast Tank capacities:
Capacity (m³)
F.P. tk 1355,9
FWD DEEP W.B. TK(P) 1581,8
FWD DEEP W.B. TK(S) 1581,8
FWD DEEP W.B. TK(C) 1748,6
No 1 W.B. TK (P) 5877,8
No 1 W.B. TK (S) 5877,8
No 2 W.B. TK (P) 6145,9
No 2 W.B. TK (S) 6145,9
No 3 W.B. TK (P) 6262,4
No 3 W.B. TK (S) 6262,4
No 4 W.B. TK (P) 5233,1
No 4 W.B. TK (S) 5233,1
E/R W.B. TK (P) 1025,8
E/R W.B. TK (S) 1025,8
A. P. tank 1145,8
TOTAL 56503,9
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Cargo pumps:
8 sets
Type Vert. Centrifugal submerged
Capacity 1650 m3/h x 150 mlc
Drive Electric
Stripping/Spray pumps:
5 sets
Type Vert. Centrifugal submerged
Capacity 50 m3/h x 135 mlc
Drive Electric
Emergency Cargo pump:
1 set
Type Vert. Centrifugal submerged
Capacity 550 m3/h x 150 mlc
Drive Electric
Vacuum pumps:
2 sets
Type Rotary vane
Capacity 1250 m3/h
Drive Electric
High duty compressor
2 sets
Type Horizontal Centrifugal
Suction capacity 18000 m3/h
Delivery condition 196 kPaA
Drive Electric
Low duty compressor
2 sets
Type Horizontal Centrifugal
Suction capacity 3000 m3/h
Delivery condition 196 kPaA
Drive Electric
High duty heater
1 sets
Type Shell/tube
Heating capacity 3200 kW
Low duty heater
1 sets
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Type Shell/tube
Heating capacity 480 kW
LNG Vapourizer
1 sets
Type Shell/tube
LNG Vaporization 3200 kW
Forcing Vaporizer
1 sets
Type Shell/tube
LNG Vaporization 1400 kW
Ballast pumps
3
Type Vert. Centrifugal
Capacity 3100 m3/h – 30 mTH
Drive Electric
Ballast stripping eductor
1
Type Ballast stripping eductor
Capacity 300 m3/h
Drive Water spray pump
Inert gas generator
1
Type I.G. generating
Capacity 14500 m3/h 25 kPag
N2 generator system
2
Type Membrane separation low pressure
Capacity 125 Nm3/h
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3.3 Properties of LNG
3.3.1 Physical Properties, Composition and Characteristics of LNG
Natural gas is a mixture of hydrocarbons which, when liquefied, form a clear colourless
and odourless liquid; LNG is usually transported and stored at a temperature very close to
its boiling point at atmospheric pressure (approximately -160 °C).
The actual LNG composition of each loading terminal such as Qatar and Oman will vary
depending on its source and on the liquefaction process, but the main constituent will
always be methane; other constituents will be small percentages of heavier hydrocarbons,
e.g. ethane, propane, butane, pentane, and possibly a small percentage of nitrogen.
The physical properties of the major constituent gases are given below:
Methane Ethane Propane Butane Pentane Nitrogen
CH4 C2H6 C3H8 C4H10 C5H12 N2
Molecular Weight 16,042 30,068 44,094 58,120 72,150 28,016
Boiling point at 1 bar
abs.
°C -161,5 -88,6 -42,5 -5 36,1 -196
Liquid Density at
boiling point
Kg/m3
426,0 544,1 580,7 601,8 610,2 808,6
Vapour SG at 15°C
and 1 bar absolute
0,554 1,046 1,540 2,07 2,49 0,97
Gas volume/liquid
volume ratio at boiling
point and 1 bar abs.
619 619 413 311 311 205
Flammable limits in
air by volume
% 5,3 - 14 3 - 12,5 2,1 - 9,5 2 - 9,5 3 – 12,4 N/A
Auto-ignition temp °C 595 510 510/583 510/583
Gross Heating value at
15°C -normal
-iso
kJ/kg
55550
51916
50367
49530
49404
49069
48944
Vaporization heat at
boiling point
kJ/kg 510,4 489,9 426,2 385,2 357,5 199,3
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..and a typical composition of LNG is given here:
Ras Laffan Das Island Standard
Methane CH4 90,28% 84,5% 89,63%
Ethane C2H6 6,33% 12,9% 6,32%
Propane n-C3H8 2,49% 1,5% 2,16%
Butane n-C4H10 0,49% 0,5% 1,2%
Iso-Butane i-C4H10 0,00% 0,00% 0,00%
Pentane n-C5H12 0,02% 0,00% 0,00%
Iso-Pentane i-C5H12 0,00% 0,00% 0,00%
Nitrogen N2 0,41% 0,6% 0,69%
Average Mol. Weight 17,88 18,56 18,12
Boiling point at atmospheric pressure -160,8 -161,0 -160,9
Density kg/m3
461,8 456,8 459,4
Higher specific energy kJ/kg 54,414 54,031 54,090
For most engineering calculations (e.g. piping pressure losses) it can be assumed that the
physical properties of pure methane represent those of LNG. However, for custody transfer
purposes when accurate calculation of the heating value and density is required, the
specific properties based on actual component analysis must be used.
During a normal sea voyage, heat is transferred to the LNG cargo through the cargo tank
insulation, causing vaporization of part of the cargo, i.e. boil-off.
The composition of the LNG is changed by this boil-off because the lighter components,
having lower boiling points at atmospheric pressure, vaporizer first.
Therefore the discharged LNG has a lower percentage content of nitrogen and methane
than the LNG as loaded, and a slightly higher percentage of ethane, propane and butane,
due to methane and nitrogen boiling off in preference to the heavier gases.
The flammability range of methane in air (21% oxygen) is approximately 5.3 to 14% (by
volume). To reduce this range, the air is diluted with nitrogen until the oxygen content is
reduced to 2% prior to loading after dry dock. In theory, an explosion cannot occur if the 02
content of the mixture is below 13% regardless of the percentage of methane, but for
practical safety reasons’, purging is continued until the 02 content is below 2%. This safety
aspect is explained in detail later in this section.
The boil-off vapour from LNG is lighter than air at vapour temperatures above -110°C or
higher depending on LNG composition, therefore when vapour is vented to atmosphere;
the vapour will tend to rise above the vent outlet and will be rapidly dispersed. When cold
vapour is mixed with ambient air the vapour-air mixture will appear as a readily visible
white cloud due to the condensation of the moisture in the air. It is normally safe to assume
that the flammable range of vapour-air mixture does not extend significantly beyond the
perimeter of the white cloud.
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The auto ignition temperature of methane, i.e. the lowest temperature to which the gas
needs to be heated to cause self-sustained combustion without ignition by a spark or flame,
is 595°C.
3.3.2 Variation of Boiling Point of Methane with Pressure
The boiling point of methane increases with pressure and this variation is shown in the
diagram for pure methane over the normal range of pressures on board the vessel. The
presence of the heavier components in LNG increases the boiling point of the cargo for a
given pressure.
The relationship between boiling point and pressure of LNG will approximately follow a
line parallel to that shown for 100% methane.
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Boiling point of methane with pressure.
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3.3.3 Flammability of Gases
Flammability of Methane, Oxygen and Nitrogen Mixtures
The ship must be operated in such a way that a flammable mixture of methane and air is
avoided at all times. The relationship between gas/air composition and flammability for all
possible mixtures of methane, air and nitrogen is shown on the diagram above.
The vertical axis A-B represents oxygen-nitrogen mixtures with no methane present,
ranging from 0% oxygen (100% nitrogen) at point A, to 21% oxygen (79% nitrogen) at
point B. The latter point represents the composition of atmospheric air.
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The horizontal axis A-C represents methane-nitrogen mixtures with no oxygen present,
ranging from 0% methane (100% nitrogen) at point A, lo 100% methane (0% nitrogen) at
point C.
Any single point on the diagram within the triangle ABC represents a mixture of all three
components, methane, oxygen and nitrogen, each present in specific proportion of the total
volume. The proportions of the three components represented by a single point can be read
off the diagram.
For example, at point D:
Methane: 6.0% (read on axis A-C)
Oxygen: 12.2% (read on axis A-B)
Nitrogen: 81.3% (remainder)
The diagram consists of three major sectors:
1. The Flammable Zone Area EDF. Any mixture whose composition is represented by a
point which lies within this area is flammable.
2. Area HDFC. Any mixture whose composition is represented by a point which lies
within this area is capable of forming a flammable mixture when mixed with air, but
contains too much methane to ignite.
3. Area ABEDH. Any mixture whose composition is represented by a point which lies
within this area is not capable of forming a flammable mixture when mixed with air.
3.3.3.1 Using the Diagram
Assume that point Y on the oxygen-nitrogen axis is joined by a straight line to point Z on
the methane-nitrogen axis. If an oxygen-nitrogen mixture of composition Y is mixed with a
methane-nitrogen mixture of composition Z, the composition of the resulting mixture will,
at all times, be represented by point X, which will move from Y to Z as increasing quantities
of mixture Z are added.
Note!
In this example point X, representing changing composition passes through the flammable
zone EDF, that is, when the methane content of the mixture is between 5.5% at point M,
and 9.0% at point N.
Applying this to the process of inerting a cargo tank prior to cool down, assume that the
tank is initially full of air at point B. Nitrogen is added until the oxygen content is reduced
to 13% at point G. The addition of methane will cause the mixture composition to change
along the line GDC which, it will be noted, does not pass through the flammable zone, but
is tangential to it at point D. If the oxygen content is reduced further, before the addition of
methane, to any point between 0% and 13%, that is, between points A and G, the change in
composition with the addition of methane will not pass through the flammable zone.
Theoretically, therefore, it is only necessary to add nitrogen to air when inerting until the
oxygen content is reduced to 13%. However, the oxygen content is reduced to 2% during
inerting because, in practice, complete mixing of air and nitrogen may not occur.
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When a tank full of methane gas is to be inerted with nitrogen prior to aeration, a similar
procedure is followed. Assume that nitrogen is added to the tank containing methane at
point C until the methane content is reduced to about 14% at point H. As air is added, the
mixture composition will change along line HDB, which, as before, is tangential at D to the
flammable zone, but does not pass through it. For the same reasons as when inerting from a
tank containing air, when inerting a tank full of methane it is necessary to go well below
the theoretical figure to a methane content of 5% because complete mixing of methane and
nitrogen may not occur in practice.
The procedures for avoiding flammable mixtures in cargo tanks and piping are summarised
as follows:
1. Tanks and piping containing air are to be inerted with nitrogen before admitting
methane until all sampling points indicate 5% or less oxygen content;
2. Tanks and piping containing methane are to be inerted with nitrogen before admitting
air until all sampling points indicate 5% methane.
It should be noted that some portable instruments for measuring methane content are based
on oxidising the sample over a heated platinum wire and measuring the increased
temperature from this combustion. This type of analyzer will not work with methane-
nitrogen mixtures that do not contain oxygen. For this reason, special portable instruments
of the infrared type have been developed and supplied to the ship for this purpose.
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3.3.4 Supplementary Characteristics
3.3.4.1 When Spilled on Water
1. Boiling of LNG is rapid, due to the large temperature difference between the product
and water.
2. LNG continuously spreads over an indefinitely large area; it results in a
magnification of its rate of evaporation until vaporization is complete.
3. No coherent ice layer forms on the water.
4. Under particular circumstances, with a methane concentration below 40%. flameless
explosions are possible when the LNG strikes the water. It results from an interfacial
phenomenon in which LNG becomes locally superheated at a maximum limit until a
rapid boiling occurs. However, commercial LNG is far richer in methane than 40%
and would require lengthy storage before ageing to that concentration.
5. The flammable cloud of LNG and air may extend for large distances downward (only
methane when warmer than -100°C is lighter than air) because of the absence of
topographic features which normally promote turbulent mixing.
3.3.4.2 Vapour Clouds
1. If there is no immediate ignition of an LNG spill, a vapour cloud may form. The
vapour cloud is long, thin; cigar shaped and, under certain meteorological conditions,
may travel a considerable distance before its concentration falls below the lower
flammable limit. This concentration is important, for the cloud could ignite and burn,
with the flame travelling back towards the originating pool. The cold vapour is
denser than air and thus, at least initially, hugs the surface. Weather conditions
largely determine the cloud dilution rate, with a thermal inversion greatly
lengthening the distance travelled before the cloud becomes non-flammable.
2. The major danger from an LNG vapour cloud occurs when it is ignited. The heat
from such a fire is a major problem. A deflagrating (simple burning) is probably fatal
to those within the cloud and outside buildings but is not a major threat to those
beyond the cloud, though there will be burns from thermal radiations.
3. When loaded in the cargo tanks, the pressure of the vapour phase is maintained as
substantially constant, slightly above atmospheric pressure.
4. The external heat passing through the tank insulation generates convection currents
within the bulk cargo; heated LNG rises to the surface and boils.
5. The heat necessary for the vaporization comes from the LNG and, as long as the
vapour is continuously removed by maintaining the pressure as substantially
constant, the LNG remains at its boiling temperature.
6. If the vapour pressure is reduced by removing more vapour than generated, the LNG
temperature will decrease. In order to make up the equilibrium pressure
corresponding to its temperature, the vaporization of LNG is accelerated, resulting in
an increased heat transfer from LNG to vapour.
3.3.4.3 Reactivity
Methane is an asphyxiant in high concentrations because it dilutes the amount of oxygen in
the air below that necessary to maintain life. Due to its inactivity, methane is not a
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significant air pollutant and, due to its insolubility, inactivity, and volatility, it is not
considered a water pollutant.
3.3.4.4 Cryogenic Temperatures
Contact with LNG or with materials chilled to its temperature of about -160°C will damage
living tissue. Most metals lose their ductility at these temperatures; LNG may cause the
brittle fracture of many materials. In case of LNG spillage on the ship's deck, the high
thermal stresses generated from the restricted possibilities of contraction of the plating will
result in the fracture of the steel.
3.3.4.5 Behaviour of LNG in the Cargo Tanks
When loaded in the cargo tanks, the pressure of the vapour phase is maintained
substantially constant, slightly above atmospheric pressure.
The external heat passing through the tank insulation generates convection currents within
the bulk cargo, causing heated LNG to rise to the surface and is then boiled-off.
The heat necessary for vaporization comes from the LNG, and as long as the vapour is
continuously removed by maintaining the pressure as substantially constant, the LNG
remains at its boiling temperature.
If the vapour pressure is reduced by removing more vapour than is generated, the LNG
temperature will decrease. In order to make up the equilibrium pressure corresponding to
its temperature, the vaporization of LNG is accelerated, resulting in an increased heat
transfer from LNG to vapour.
If the vapour pressure is increased by removing less vapour than is generated, the LNG
temperature will increase. In order to reduce the pressure to a level corresponding to the
equilibrium with its temperature, the vaporization of LNG is slowed down and the heat
transfer from LNG to vapour is reduced.
LNG is a mixture of several components with different physical properties, particularly the
vaporization rates; the more volatile fraction of the cargo vapourizers at a greater rate than
the less volatile fraction. The vapour generated by the boiling of the cargo contains a
higher concentration of the more volatile fraction than the LNG.
The properties of the LNG, i.e. the boiling point, density and heating value, have a
tendency to increase during the voyage.
3.3.4.6 Avoidance of Cold Shock to Metal
Structural steels suffer brittle fracture at low temperatures. Such failures can be
catastrophic because, in brittle steel, little energy is required to propagate a fracture once it
has been initiated. Conversely, in a tough material, the energy necessary to propagate a
crack will be insufficient to sustain it when it runs into sufficiently tough material.
Plain carbon structural steels have a brittle to ductile behaviour transition which occurs
generally in the range -50°C to +30°C. This, unfortunately, precludes their use as LNG
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materials (carriage temperature -162°C). The effect is usually monitored by measuring the
energy absorbed in breaking a notched bar and a transition curve.
For this reason, materials which do not show such sharp transition from ductile to brittle
fracture as the temperature is lowered, have found obvious application for use in cryogenic
situations in general and particularly in liquid methane carriers, for example, invar (36%
nickel-iron alloy), austenitic stainless steel, 9% nickel steel and some aluminium alloys
such as 5083 alloy. All of these materials behave in a ductile manner at -162°C, so that the
chance of an unstable brittle fracture propagating, even if the materials were overloaded, is
negligible.
In order to avoid brittle fracture occurring, measures must be taken to ensure that LNG and
liquid nitrogen do not come into contact with the steel structure of the vessel. In addition,
various equipment is provided to deal with any leakages which may occur.
The manifold areas are equipped with a stainless steel drip tray, which collects any spillage
and drains it overboard. The ship, in way of the manifolds, is provided with a water curtain
which is supplied by the deck fire main. The fire main must always be pressurized and the
manifold water curtain in operation when undertaking any cargo operation. Additionally,
fire hoses must be laid out to each liquid dome to deal with any small leakages which may
develop at valves and flanges. Permanent drip trays are fitted underneath the items most
likely to cause problems and portable drip trays are provided for any other needs.
During any type of cargo transfer, and particularly whilst loading and discharging, constant
patrolling must be conducted on deck to ensure that no leakages have developed.
In the event of a spillage or leakage, water spray should be directed at the spillage to
disperse and evaporate the liquid and to protect the steelwork. The leak must be stopped,
suspending cargo operations if necessary.
In the event of a major leakage or spillage, the cargo operations must be stopped
immediately, the general alarm sounded and the emergency deck water spray system put
into operation.
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3.4 Description of the Ship’s Equipment and
Arrangements
This section contains all particulars of the ship’s equipment and arrangements necessary to
enable the crew to follow the operational procedures set out in sections 3 and 4. This
description is based on real vessels data, so there are some points in the descriptions which
not are implemented in the simulator, but we have kept it for guidance only.
3.4.1 Design Concept of the Cargo System
3.4.1.1 General Description
The Cargo Containment System consists of four double insulated cargo tanks encased
within the inner hull and situated in-line from forward to aft.
The spaces between the inner hull and outer hull are used for ballast and will also protect
the tanks in the event of an emergency situation, such as collision or grounding.
The cargo tanks arc separated from other compartments, and from each other, by five
transverse cofferdams which are all dry compartments.
The ballast spaces around the cargo tanks are divided into two double bottom wing tanks,
port and starboard for each cargo tank. The double bottom tanks extend to the side of the
cargo tanks as far up as the trunk ways.
The LNG to be transported is stored in the four cargo tanks numbered 1 to 4, from fore to
aft. All cargo tanks have an octagonal transverse section matching with the supporting
inner hull.
Between the two transverse bulkheads, each tank is composed of a prism placed in a
direction parallel to the keel plate.
The boundaries of the tanks are as follows:
1. One flat bottom, parallel to the keel plate raised along the ship's plating by two
inclined plates, one on each side.
2. Two vertical wails each extended at their upper parts by an inclined plate, in order to
limit the liquid free surface effect when the tanks are full.
3. One flat top parallel to the trunk bottom.
Cargo tank No. l is slightly different in shape due to its position in the ship. It has a
polygonal section and the lengthwise wails are almost parallel to the ship's plating.
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3.4.2 Cargo Containment System Principle
The cargo tanks are of double membrane, Gas Transport No.96-2 Evolution System design.
The inner hull, i.e. the outer shell of each of the cargo tanks, is lined internally with the
Gas Transport integrated tank containment and insulation system.
This consists of a thin, flexible membrane called the primary membrane, which is in
contact with the cargo, a layer of plywood boxes filled with Perlite called the Primary
insulation, a second flexible membrane similar to the first one called the secondary
membrane and a second layer of boxes also filled with Perlite in contact with the inner hull
called the Secondary insulation. The double membrane system meets the requirement of
the relevant regulations on the Cargo Containment System to provide two different
“barriers” to prevent cargo leakage.
The tank lining thus consists of two identical layers of membranes and insulation so that in
the event of a leak in the primary barrier, the cargo will be contained indefinitely by the
secondary barrier. This system ensures that the whole of the cargo hydrostatic loads are
transmitted through the membranes and insulation to the inner hull plating of the ship.
The function of the membranes is to prevent leakage, while the insulation supports and
transmits the loads and, in addition, minimizing heat exchange between the cargo and the
inner hull. The secondary membrane, sandwiched between the two layers of insulation, not
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only provides a safety barrier between the two layers of insulation, but also reduces the
convection currents within the insulation.
The primary and secondary insulation spaces are under a pressure controlled nitrogen
atmosphere. The primary space's pressure must never exceed the cargo tank pressure in
order to prevent the primary membrane from collapsing inwards. In normal operation, the
pressure in the primary and secondary insulation spaces shall be maintained between 2
mbar and 0.4 mbar.
3.4.2.1 Construction of the Insulation and Barriers
The primary and secondary barriers are identical and are fabricated from cryogenic invar (a
36% nickel steel, with a very low coefficient of thermal expansion, 0.7 mm thick).
The composition of invar is:
Ni : 35 - 36.5%
C : < 0.04%
Si : < 0.25%
Mn : < 0.2 to 0.4%
S : < 0.0015%
P : < 0.008%
Fe : Remainder
Thermal expansion coefficient = (1.5±0.5) 10-6
mm/°C
between 0°C and -180 °C
(about ten times less than for stainless steel AISI 304 type)
Charpy Test at -196 °C, > 120 J/cm2
The coefficient of thermal expansion is low enough to enable flat, rather than corrugated
sheets, to be used. The entire surface area of the membrane is thus in contact with the
supporting insulation, so that the load which the system is able to carry is limited only by
the load bearing capacity of the insulation.
The primary and secondary insulation spaces are made up of boxes fabricated from
plywood and filled with expanded Perlite. This insulation system allows free circulation of
nitrogen and therefore permits gas freeing or inerting to be carried out in the barrier spaces
without difficulty.
Perlite is obtained from a vitreous rock of volcanic origin which, when heated to a high
temperature (above 800°C), is transformed into very small balls. These balls have
diameters that measure between a few hundredths to a few tenths of a millimetre. The
cellular structure so obtained from the process gives the expanded Perlite its lightness and
thus its excellent insulation properties. The water repellence of the Perlite is reduced by a
silicon treatment.
The insulation is distributed over the hull in two specific areas:
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1. Reinforced area located in the upper part of the tank and covering approximately
30% of the total tank height (including the tank ceilings). This area is fitted with
reinforced type boxes.
2. Standard area (or non-reinforced area) covering approximately 70% of the tank
height (including the tank bottom). This area is fitted with normal boxes (Refer to
Illustration 6.3.la).
The secondary and primary boxes in the reinforced area are specially built with thicker
internal stiffeners to resist the impacts which can be created by the liquid sloshing inside
the tanks. The primary reinforced boxes have two 12 mm thick plywood covers stapled on
it.
The secondary insulation is 300 mm thick, whereas the primary insulation is 230 mm is
thick. (The designed boil-off rate i.e. 0.15% of the total cargo tanks volume per day
governs the thickness.)
3.4.3 Membrane Cargo Containment
The plywood boxes forming the secondary insulation are laid on the ship's inner hull
through the transition of a hard epoxy bearing product deposited on the box in the shape of
ropes by means of an automatic depositing machine. These ropes are of adjustable
thickness and compensate for the flatness defects of the inner hull. The boxes are held in
position by stainless steel coupler rods anchored to the inner hull through their welded
sockets. To absorb the ship's hull deformation, each coupler is fitted with an elastic
coupling made up of several spring washers tightened down on the setting plates for
secondary boxes by securing nuts.
Construction of Containment system – Securing of insulation boxes.
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The number of spring washers used depends on the location of the box. Boxes on the
ballast boundaries have a higher number of spring washers (5) because the hull
deformation has the largest effect on this area.
A continuous invar tongue is held in slots running along the whole length of each
secondary box cover. The secondary membrane strakes are resistance seam welded with
the continuous tongues in between.
The primary boxes are secured in position by collar studs. The collar studs are screwed into
setting (clamp) plates for collar studs linked to the setting plate for secondary boxes by two
securing screws. A plywood bridge is installed between the two setting plates to limit any
thermal conduction through the box fixations.
To allow some flexibility, each collar stud is fitted with elastic coupling, similar to those
on the secondary boxes.
Each collar stud is fitted with a single spring washer and tightened down on the setting
plate for primary boxes by securing nuts.
The primary insulation boxes have lipped invar tongues stapled along slots running
lengthwise. Continuous invar tongues are positioned in the lip of the fixed tongues on the
boxes. The primary membrane strakes are resistance seam welded with these tongues in
between.
Each primary and secondary membrane strake terminates on an invar angle structure, 1.5
mm thick, fitted around the perimeter of each transverse bulkhead and welded to it. Due to
their superposition, the secondary and primary membranes cross each other in both ways,
forming a square tube. This is prefabricated to allow an easier creation process and
attached to the double hull by 4 anchoring bars.
With this system, the membranes are directly connected to the inner hull so that any
membrane tension is directly and uniformly taken by the ship's structure.
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Construction of containment system – Flat area
Construction of containment system – Corner
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In the secondary and primary insulation spaces respectively, the gaps between the
secondary boxes and the primary boxes are insulated with a combination of rigid insulating
materials and glass wool.
3.4.3.1 Cargo Tank Outfitting
A vapour dome is located near the geometrical centre of each cargo tank ceiling.
Each vapour dome is provided with:
1. A vapour supply/return line to supply vapour to the tank when discharging, vent
vapour from the tank whilst loading and also vent the boil-off when the tank contains
cargo.
2. Spray line arrangement for cool down purposes.
3. Two pressure/vacuum relief valves set at 250 mbar and -10 mbar vacuum, venting to
the nearest vent mast riser.
4. Pick-up for pressure sensors
5. Liquid line safety valves exhaust.
In addition, each cargo tank has a liquid dome located near the ship's centre line at the aft
part of the tank. The liquid dome supports a tripod mast made of stainless steel (304 L),
suspended from the liquid dome and held in position at the bottom of the tank by a sliding
bearing to allow for thermal expansion or contraction depending on the tank environment.
The tripod mast consists of the main discharging pipes and emergency pump well, in the
form of a three-legged trellis structure and is used to support the tank access ladder and
other piping and instrumentation equipment.
The instrumentation includes temperature and level sensors, independent high level alarm
sensors and cargo pump electric cables. The two main cargo pumps are mounted on the
base plate of the tripod mast, while the stripping/spray pump is mounted on the pump
tower support. An emergency pump column, float gauge column and the filling line are
also located in the liquid dome.
The four cargo tanks are connected with each other by the liquid, vapour and
stripping/spray headers which are located on the trunk deck. The nitrogen mains supplying
the primary and secondary insulation spaces, and other services directly associated with the
cargo system, arc also located on the trunk deck together with the fire main and deck spray
main.
3.4.4 Deterioration or Failure
The insulation system is designed to maintain the boil-off losses from the cargo at an
acceptable level, and to protect the inner hull steel from the effect of excessively low
temperature. If the insulation efficiency should deteriorate for any reason, the effect may
be a lowering of the inner hull steel temperature, i.e. a cold spot and an increase in boil-off
from the affected tank. Increased boil-off gas may be vented to the atmosphere via No.1
vent mast. The inner hull steel temperature must, however, be maintained within
acceptable limits to prevent possible brittle fracture.
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Thermocouples are distributed over the surface of the inner hull, but unless a cold spot
occurs immediately adjacent to a sensor, these can only serve as a general indication of
steel temperature. To date, the only reliable way of detecting cold spots is by frequent
visual inspections of the ballast spaces on the loaded voyage.
The grade of steel required for the inner hull of the vessel is governed by the minimum
temperature this steel will reach at minimum ambient temperature, assuming that the
primary barrier has failed, so that the LNG is in contact with the secondary membrane.
With sea and air temperatures of 0°C and failure of the primary barrier, the minimum
temperature of the inner hull steel will be about -8°C. For these conditions, Classification
Societies require a steel grade distribution as shown in the next illustration, where the tank
top and top longitudinal chamfer are in grade 'E' steel, and the remaining longitudinal
steelwork grade 'DH', both grades having a minimum operating temperature of -10°C. The
transverse watertight bulkheads between cargo tanks are of grade 'A' with glycol water
heating system.
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In addition to failure of the membrane, local cold spots can occur due to failure of the
insulation.
While the inner hull steel quality has been chosen to withstand the minimum temperature
likely to occur in service, prolonged operation at steel temperatures below 0°C will cause
ice build-up on the plating, which in turn will cause a further lowering of steel temperature
due to the insulating effect of the ice.
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To avoid this, glycol heating coils are fitted in the cofferdam spaces, of sufficient capacity
to maintain the inner hull steel temperature at 0°C under the worst conditions.
If a cold spot is detected either by the inner hull temperature measurement system, or by
visual inspection, the extent and location of the ice formation should be recorded. Small
local cold spots are not critical and, provided a close watch and record are kept as a check
against further deterioration and spreading of the ice formation, no further action is
required.
If the cold spot is extensive, or tending to spread rapidly, salt water spraying should be
carried out. In the unlikely event that this remedy is insufficient and it is considered unsafe
to delay discharge of cargo until arrival at the discharge port, the final recourse will be to
jettison the cargo via a spool piece fitted at the cargo liquid manifold, using a single main
cargo pump.
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3.4.5 Description of Cargo Pumps
3.4.5.1 General
The ship is fitted with submerged, electric, single-stage (the stripping/spray pumps are
two-stage), centrifugal cargo pumps manufactured by Ebara Cryodynamics. They are
installed at the bottom of each tank.
Two sizes of pump, main cargo and stripping/spray pumps are installed as fixed units, i.e.
two main cargo pumps and one stripping/spray pump per tank.
In addition, provision is made at each tank to introduce an emergency cargo pump in case
of total cargo pump failure. Only one emergency pump is available.
3.4.5.2 Description
Particulars
Liquid pumped LNG (S.G.=0.5)
Capacity (rated flow) 1700 m³/h
Dis. head (rated) 155.0 m
Power required (rated) 448,4 kW (Motor rated at 522,2 kW)
Efficiency 80,8%
Rotational speed 1780 rpm
Minimum starting level 0,89 m
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Main pump
The cargo pumps are started and stopped from the Cargo Control Room (CCR). They will
be automatically stopped in the event of various shut down trips being activated both in
relation to the cargo system and the pumps themselves.
Each cargo pump electric motor is protected from:
Overload (over current)
Low-current (no load operation)
Imbalance between phases (single-phasing)
Too long starting
The main cargo pumps are direct on-line started. Swing check valves are installed inside
the tanks just down steam of the cargo pump discharge flange.
These valves assist in the reduction of any excessive liquid hammer that can occur if the
pumps are not started in accordance with the steps outlined in this section.
The power supply to the cargo pump motors is made available via cargo switch boards
which are arranged in two independent sections that are normally operated as coupled, via
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bus-tie connection, or independently. No.1 cargo switchboard supplies the No.1 pumps in
all four tanks, while No.2 cargo switchboard supplies the No.2 cargo pumps.
Each of the cargo switchboards can be supplied by either, or both, of the main
switchboards.
Due to high electrical load imposed on the cargo switchboards by the running of main
cargo pumps, there is a limitation on the number of pumps that can be run depending on
the electrical power management system (start block).
The pumps should be started individually and sequentially, as required, with the pump
discharge valve open (approximately min. 5% to max. 25%).
If the pump discharge valve position docs not open to min. 5%, pump will not be started
due to starting interlock function.
3.4.5.3 Starting Procedure for the Main Cargo Pumps
a) Check to confirm that no pumps are in starting phase.
b) Open the discharge valve to 25% (maximum).
c) Start the associated main cargo pump.
Once the pump has started (the pump symbol changes from black “stop” to “run” blue),
open the discharge valve gradually from the operator station, to give the required flow-rate.
The discharge pressure and pump motor amps are monitored and adjusted to ensure the
most efficient operation as indicated on the pump performance graph, with due regard
being taken of the head of liquid on the pump discharge flange.
The manifold On-Off valves are controlled from the mimic screen, the states of which are
indicated from limit switches.
Note!
The starting duration is 7 seconds for each pump.
Each main cargo pump is rated to discharge 1,700 m3/h at 155 m head of LNG. For
optimum discharge results, bulk discharge will be carried out with 8 pumps running in
parallel.
The pump discharge valves will be throttled to ensure optimum performance as indicated
by the pump performance graph.
During the course of discharge, changes in flow rate and tank levels will alter these
readings and the discharge valve will have to be readjusted accordingly.
Under normal conditions it should be possible to maintain the full discharge rate until the
tank level approaches approximately 2.3 m, at which time the pump will start to cavitate
and lose suction as indicated by fluctuations in the discharge pressure and ammeter
readings.
The discharge valves should be throttled to stabilise conditions and one pump stopped if
necessary. The remaining pump should be progressively throttled in to maintain suction
and to prevent the operation of the low discharge pressure trip, until a level of
approximately 0.37 m is reached.
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By trimming the vessel 1 meter or more by the stem, it should be possible to reduce the
amount of liquid remaining in the tanks before the pumps are stopped. Adjust the trim
carefully at the end of discharging cargo to give an even keel for gauging.
The cargo pumps may be run in closed circuit on their own tanks by opening the loading
valve. This may be required if the discharge is temporarily halted when the tanks are at low
level, thereby avoiding the problems of restarting with low level and low discharge
pressure.
The pump shall be tested before arrival discharge port on calm sea condition, and during
loading when the tank level is about 4-5 m subject to terminal's acceptance.
The cargo pumps will be automatically stopped should any of the following occur:
1) Cargo tank pressure below or equal to, primary insulation space pressure plus 5 mbar
(ESDS: Cargo Tank Protection).
2) Vapour header pressure below or equal to atmospheric pressure plus 3 mbar.
3) Extreme high level in cargo tank (99% volume).
4) Activation of emergency shut down trip
(10 push buttons and 12 fusible elements) (ESDS: Stage 1)
5) Activation of ship/shore pneumatic, fibre-optic or electrical shutdown (ESDS: Stage I)
6) Motor single-phasing
7) Low motor current
8) High motor current (electrical overload)
9) Low discharge pressure with time delay at starting
10) Cargo Control Room stop
1 1) Activation of ESDS stage 2
12) Cargo tank level low
ESDS signifies that all cargo plant is shut down in addition to the pump(s) on the tank(s) in
question.
Note An insulation test of all pumps is to be carried out before arrival loading and discharging
port in order to establish that all pumps are operational and to allow time for the
installation of the emergency cargo pump should it be necessary.
Note Pump should not be started or operated against closed discharge valve due to potential
damage which may result due to insufficient cooling and lubrication for the motor and
bearing and excessive vibration levels associated with zero flow conditions.
Restart of pumps in normal operation is restricted depending on the liquid level above the
submerged electric motor.
Pumps may not be restarted with tank liquid level below at 0.89 m.
1. Normal start-up
- 1st restart : minimum 5minutes after shut down
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- 2nd restart : 15 minutes after lst restart
- 3rd restart : 15 minutes after 2nd restart
No more than 4 restarts within one hour
2. Emergency start-up
For liquid level below motor centreline (approximately 1.5 m liquid in tank), restart
after 30 minutes and not more than 2 restarts within one hour.
Note
In case of a sustained locked rotor start, attempt to restart only after 30 minutes and with
no more than 2 restarts total.
Quantities of cargo remaining in tanks after stripping refer to chapt. 3.6.3 discharging.
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3.4.6 Stripping/Spray Pump
3.4.6.1 General
One spray pump is installed in each cargo tank (total 4 spray pumps), and one complete set
is provided as spare.
The spray pump is of the electric motor-driven, two-stages, centrifugal type. The spray
pump is a submerged type and must be operated in LNG liquid. Do not operate when dry.
Pump bearings are lubricated by LNG drawn in by the LNG pump.
3.4.6.2 Description
Particulars
Number of stages 2
Liquid pumped LNG (S.G.=0.5)
Capacity (rated flow) 50 m³/h
Dis. head (rated) 135.0 m
Power required (rated) 6.9 kW (Motor rated at 22,4 kW)
Efficiency 54,4%
Rotational speed 3560 rpm
Minimum starting level 0,3 m
Stripping pump
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The instances when these pumps can be used are:
1. To cool down the liquid header prior to discharging.
2. To cool the cargo tank during ballast voyage prior to arrival at the loading terminal
by discharging LNG to the spray rails in the tanks.
3. To pump LNG from the tanks to the forcing vaporizer or LNG Vaporizer (emergency
case) when forced vaporization of LNG in the boilers is required.
4. To enable each cargo tank to be stripped as dry as possible for reasons such as
technical stop involving cargo tank entry.
Whenever possible the stripping/spray pump should be started early enough to avoid
possible starting problems due to very low tank levels (about 0.5 m minimum).
The stripping/spray pumps will be stopped automatically should any of the following
occur:
1. Cargo tank pressure below or equal to primary insulation space pressure plus 5 mbar
(ESDS: Cargo tank protection).
2. Vapour header pressure below or equal to atmospheric pressure plus 3 mbar (ESDS:
Stage I).
3. Extreme high level in cargo tank (99% volume)
4. Activation of Emergency Shut Down System trip
(10 push-buttons and 12 fusible elements) (ESDS: Stage 1)
5. Activation of ship/shore pneumatic, fibre-optic or electrical shutdown (ESDS: Stage
1)
6. Motor single-phasing
7. Low motor current
8. High motor current (Electrical overload)
9. Low discharge pressure with time delay at starting
10. Cargo Control Room stop
11. Activation of ESDS stage 2
12. Cargo tank level low low
Note An insulation resistance test of all pumps is to be carried out before arrival loading and
discharging port in order to establish that all pumps are operational and to allow time for
the installation of the emergency cargo pump should it be necessary.
Restart of pumps in normal operation is restricted depending on the liquid level above the
submerged electric motor.
Pumps may not be restarted with tank liquid level below at 0.3 m.
1. Normal start-up
- 1st restart : minimum 5minutes after shut down
- 2nd restart : 15 minutes after 1st restart
- 3rd restart : 15 minutes after 2nd restart
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No more than 4 restarts within one hour
2. Emergency start-up
For liquid level below motor centreline (approximately 0.56 m liquid in tank), restart
after 30minutes and not more than 2 restarts within one hour.
Note
In case of a sustained locked rotor start, attempt to restart only after 30 minutes and with
no more than 2 restarts total.
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3.4.7 Emergency Cargo Pump
3.4.7.1 General
One spray pump is installed in each cargo tank (total 4 spray pumps), and one complete set
is provided as spare.
The spray pump is of the electric motor-driven, two-stages, centrifugal type. The spray
pump is a submerged type and must be operated in LNG liquid. Do not operate when dry.
Pump bearings are lubricated by LNG drawn in by the LNG pump.
3.4.7.2 Description
Particulars
Liquid pumped LNG (S.G.=0.5)
Capacity (rated flow) 550 m³/h
Dis. head (rated) 155.0 m
Power required (rated) 171 kW (Motor rated at 223,8 kW)
Efficiency 67,8%
Rotational speed 3560 rpm
Minimum starting level 0,86 m
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Emergency discharge pump
Each cargo tank is equipped with an emergency pump well or column.
This pump well has a foot valve which is held in the closed position by highly loaded
springs.
Should a failure of either one or both main cargo pumps in one tank require the use of the
emergency pump, the emergency pump is lowered into the emergency pump well after the
well has been purged with nitrogen.
The weight of the emergency pump overcomes the compression of the springs to open the
foot valve.
A small flow of nitrogen should be maintained whilst the pump is being installed.
Note Before undertaking this operation it is important to reduce the tank pressure to near
atmosphere pressure and to keep it at this level throughout the entire operation.
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Electrical connections are made to the fixed junction box which is located adjacent to each
pump well.
A dedicated starter is available with one circuit breaker which is placed in No.1 cargo
switchboard. This starter supplies all 4 fixed junction boxes.
All safety devices are transferred to the emergency pump when the circuit breaker is
engaged, as they are the same for the main cargo pumps.
Note An insulation resistance test of all pumps is to be carried out before arrival loading and
discharging port in order to establish that all pumps are operational and to allow time for
the installation of the emergency cargo pump should it be necessary.
Restart of pumps in normal operation is restricted depending on the liquid level above the
submerged electric motor. Pumps may not be restarted with tank liquid level below 0.86 m.
1. Normal start-up
- 1st restart : minimum 5 minutes after shut down
- 2nd restart : 15minutes after 1st restart
- 3rd restart : 15minutes after 2nd restart
No more than 4 restarts within one hour
2. Emergency start-up
For liquid level below motor centreline (approximately 1.6 m liquid in tank), restart
after 30 minutes and not more than two (2) restarts within one hour.
Note
In case of a sustained locked rotor start, attempt to restart only after 30 minutes and with
no more than 2 restarts total.
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3.4.8 H/D Compressor
3.4.8.1 General
Two sets of High Duty (H/D) compressors are provided in the cargo machinery room for
the following purposes:
a) During loading to return LNG vapour to shore
b) During initial coo1 down to return gas/vapour to shore
b) During warm-up to circulate heated cargo vapour through cargo tanks
3.4.8.2 Particulars
Main particulars are as follows:
Type : Horizontal, Turbo-compressor, Electric motor driven
Manufacturer : Atlas Copco Energas GmbH (GTO63 Tl Kl)
Capacity : 24000 m³/h
Suction press. : 104 kPaA
Suction temp : -140 C
Discharge press. : 200 kPa
Electric motor : 760 kW
3.4.8.3 Construction
The H/D compressors are single-stage radial types equipped with a spur gear. The impeller
is arranged in an overhung position on the pinion shaft. The spiral is screwed to the gear by
means of a cast flange. The suction nozzle is arranged axially, and the discharge nozzle
tangentially.
A shaft seal, fitted where the rotor passes through the casing, consists of 5 floating carbon
ring seals and prevents gas leakage. The installed shaft seal has two chambers. Leakage gas
is drawn from. the impeller-side chamber and returned to the suction side. The second
chamber is fed with dry nitrogen, which seals against the leakage gas from the impeller
side. Seal gas pressure is set manually at the reducing valve. Pressure can be set from 20 to
60 kPa. The recommended setting is 30 kPa. Seal gas consumption is approximately
2.5m³/h at 20 C and 0.11 Mpa.
The compressor gearbox is a 2-shaft in volute helical spur with thrust collars. The shafts
are borne in sleeve bearings. The thrust collars transfer the axial thrust of the pinion shaft
to the axial bearing of the low-speed driving shaft. The running speed of the input shaft is
3570 rpm (elec. Motor revolutions) and speed of the output shaft is 9552 rpm constant.
A bulkhead seal assures gas tightness between the cargo machinery room and motor room.
The seal, located in the motor room side of the bulkhead, consists of a system of chambers
with multiple carbon seal rings (consisting of three pieces) held by hose springs. The
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chambers are pressurised with dry air normally (10kPa) and with nitrogen as back up
(5kPa). Consumption is 0.5 m³/h (dry air) and 0.3 m³/h (nitrogen). The seal housing is on
an independent support which allows easy adjustment and attached to the bulkhead with
stainless steel bellows.
Lubricating oil is supplied to the compressor prior to starting by an electric motor driven
auxiliary L.O. pump. After the compressor has started, the auxiliary L.O. pump continues
to run for about 45 seconds and stops automatically. At shutdown, the auxiliary L.O. pump
starts automatically and continues to run for about 55 minutes. If oil pressure falls below
120 kPa, the auxiliary L.O. pump switches on automatically.
The pump and motor units are located in the motor room and serve as a stand-by unit when
the main, shaft driven L.O. pump fails.
An L.O. cooler is provided to keep the L.O. temperature at 48oC. Cooling water for the
L.O. cooler is supplied from the Auxiliary Control Cooling Fresh Water System (60oC). If
the L.O. temperature is low, L.O. in the sump tank can be heated by a steam heater which
is controlled by a temperature control valve (set value 50oC).
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3.4.9 L/D Compressor
3.4.9.1 General
Two Low Duty (L/D) compressors are provided in the cargo machinery room for
maintaining constant cargo tank pressure and for delivering boil-off gas according to the
boiler demand.
Main particulars are as follows:
Type : Horizontal, Turbo-compressor, Electric motor driven
Manufacturer : Atlas Copco Energas GmbH (GTO32 Tl Kl)
Capacity : 8800 m³/h
Suction press. : 104 kPaA
Suction temp : -40 C
Discharge press. : 200 kPaA
Electric motor : 330 kw
3.4.9.2 Construction
The construction and materials are the same as for the high duty (H/D) compressors except
for the compressor capacity control.
The compressor capacity control is as follows:
The capacity of the L/D compressor is controlled by adjusting the inlet guide vane and
motor speed. The inlet guide vane and motor speed are controlled according to main boiler
demand within the respective split ranges that follow:
When the capacity is below 50%, the motor speed is kept at 1775 rpm and the Inlet
Guide Vane (IGV) is adjusted by a pneumatic actuator between –80oC and +20
oC
according to the main boilers demand signal from SSC on the Engine Control
Console (ECC).
When the capacity is above 50%, IGV is full open, the motor speed is adjusted by a
steeples and variable speed static inverter between 1775 rpm and 3550 rpm according
to demand signal from the SSC on the ECC.
The stable operating range of the compressor is restricted by the surge limit. Surges
which may cause damage to a compressor are prevented automatically by increasing
the flow through the compressor by means of a surge control valve on the
compressor discharge. Surge control is achieved by comparing the difference in
pressure between compressor suction and discharge with actual flow measured by
venture in the suction line. If the ratio of the above two signals falls below the set
value, the anti-surge controller will open the surge control valve and allow gas to be
recirculated to the compressor suction. The surge control is independent of the main
control system.
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3.4.9.3 Operation
Compressor starting can be carried out from the Engine Control Console (ECC) using the
start push button. The operational condition can be read on custom group display 2.
After pressing the “RUN” button, the compressor will be controlled by the Single Strategy
Controller (SSC) on the ECC to meet with the boiler demand according to the set value of
SSC.
The compressor can also be started from either a local control panel, a starter in the cargo
switch board room and push button next to motor side. Remote start (from ECC, local
panel and motor side) is possible when the local/remote change-over switch on the starter
is set on “REMOTE”. Setting the switch on “LOCAL” permits the start from the starter.
This change-over switch is normally set on “REMOTE”.
However, the compressor can be stopped from any control position. A normal/lock switch
is also provided next to motor side. This will inhibit motor start from any control position
when “LOCK” is selected.
Note: At free flow operation (motor stops), the aux. lubricating oil pump should be
running.
3.4.9.4 Start-up
Confirm that the gland sealing(not implemented in the simulator) nitrogen gas pressure is
at the present value (30 kPa) and bulkhead sealing air at correct pressure (10 kPa).
Confirm that the inlet guide vanes are at the minimum position (-80 )
Confirm that the surge control valves are open.
Confirm that the compressor L.O. sump tank level is acceptable and L.O. temperature is
above 25°C, start the auxiliary L.O. pump to circulate oil and heat the oil.
Confirm that the L.O. cooler coolant water valves are open.
Open the compressor suction valves from the Engine Control Console (ECC).
Open the compressor discharge valves manually.
When the start-up procedures are completed, the "READY' lamp for the L/D compressor
will light up on the ECC and local control panel.
Confirm that the "READY" lamp is lit.
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3.4.10 Gas Heater
3.4.10.1 General
A High Duty (H/D) gas heater and a Low Duty (L/D) gas heater are located in the cargo
machinery room. They are horizontal shell and U-tube, direct steam heating types.
The heaters are used for the following purposes;
a) H/D heater
Heating LNG vapour to warm-up the cargo tank for tank inverting, gas freeing
and aeration. Back-up of the L/D heater.
b) L/D heater
Heating boil-off gas from cargo tanks to use as gas fuel in the boiler.
3.4.10.2 Particulars
The design capacity of the H/D and L/D heaters is as follows;
H/D Heater L/D Heater
Gas inlet pressure 200 kPaA 200 kPaA
Gas inlet temperature -55oC -70
oC
Gas outlet pressure 180kpaA P=13kPa
Gas outlet temperature +75oC +45
oC
Maximum gas flow 43000Kg/h 8400Kg/h
Heating capacity 12600MJ/h 1900mJ/h
Heating steam pressure 834kPa 834kPa
Heating steam temperature 177oC 177
oC
Supply steam for each heater is fed from the low pressure steam generator (LPSG) in the
engine room. Each heater is provided with a steam condense drain pot and a steam trap.
Condense from each heater is returned to the drain inspection tank in the engine room
through the gas heater drain cooler and the gas heater drain tank.
3.4.10.3 Control System
Each heater has a local control board located near each heater. All control systems and the
local control board are pneumatic operated.
The gas outlet temperature can be set by the temperature controller fitted on the local
control board. Control valves for flow to the heater inlet and by-pass flow to the heater
outlet are adjusted according to the set temperature.
The L/D heater has two control valves (VG-941 & 943), VG-941 controls the flow to the
heater inlet and VG-943 controls the by-pass flow to the heater outlet. The H/D heater has
four control valves (2 pairs of valves). The large valve pair (VG-945 & 947) is used by the
H/D heater (warm-up mode) and the small valve pair (VG-946 & 948) is used for L/D
heater back-up (gas burning mode). The warm-up mode and the gas burning mode can be
selected using the selector switch on the local control board.
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When heating steam condense level is detected in the drain pot, all control valves are
closed to prevent icing in the heater shell. Under normal conditions, the condition indicator
on the local control board shows green. At trip condition, drain pot level is shown by
red/white strips. And the trip condition in also monitored by the Integrated Monitoring
System(IMS).
When tripped, all control valves are closed. They can be reset manually using the reset
switch fitted on the local control board.
The gas heater alarm set points are as follows;
Gas outset temperature high : 90oC
Gas outlet temperature low : 10oC
Drain pot level high : 195mm
(Temp. control valves close)
3.4.11 Operation of H/D heater
3.4.11.1 Start up
Select the operation mode, either WARM-UP or GAS BURN. Set the Auto / Manual
selector switch on the temp. controller to "M". This is done at the local control board.
Ensure that the gas detection system on the gas vent drain tank in operating.
Ensure that the auxiliary central cooling system Is operating and cooling water is being
supplied to the gas heater drain cooler.
Ensure that instrument air is being supplied to the local control board and the system works
well.
Manually open the vent valve on the heater shell.
Open the drain pot steam trap isolating valve.
Open the steam inlet valve and pass heating steam into the heater slowly and gradually.
Close the vent valve when steam begins to spurt out.
Check that the H/D heater outlet valve (VG-916) is open.
Check the H/D heater inlet valve (VG-915) is open.
At local control board, open the temperature control valve (VG-945 & 947 for warm-up,
VG-946 & 948 for L/D heater back up) and adjust the gas outlet temperature.
When the gas outlet temperature is steady, change the operation mode Auto/Manual switch
to “A”.
3.4.11.2 Stop
Change the operation mode Auto Manual switch to 'M' on the local control board.
Close the gas inlet control valve and stop the gas slowly and gradually.
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Close the steam inlet valve slowly so as to prevent icing after the temp. control valves are
closed.
Slowly open the vent valve an the heater shell.
Close the vent valve after the inside temperature of the shell and gas inlet and outlet piping
reach ambient temperature.
Notes:
Heating steam is supplied before gas flow into the heater to prevent icing.
When stopping, the gas flow is stopped before shutting off steam.
Drain in the heater shall be discharged enough after using the heater to avoid drain attack
in the drain pipe.
3.4.12 Operation of L/D heater
The operation of the L/D heater, start up and stop is the same as the H/D heater except the
selection of operation mode. The L/D heater has no operation mode selection switch, the
L/D heater is only used for GAS BURNING.
Notes for H/D heater also apply. Valve No. corresponding to the L/D heater as follows.
Steam inlet valve : V30970 - 3SV~704
Drain pot steam trap isolating valve : 3DV-702 (Not implemented in the simulator)
L/D heater gas master control valve : V30913 - VG-913
L/D heater outlet valve : V30914 - VG-914
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3.4.13 LNG Vaporizer
3.4.13.1 General
The LNG Vaporizer is of horizontal shell and U tube, direct steam heating type. It is
located in the cargo machinery room.
The LNG Vaporizer is used for the following;
Purging inert gas from the cargo tanks prior to cool down. LNG is supplied from the shore
to the vaporizer and the vaporized gas is led to the cargo tanks.
During cargo unloading, if the shore dose not supply return-vapour to the cargo tanks, the
LNG vaporizer produces vapour by bleeding LNG from the main line and supplies it to the
cargo tanks.
In the event that both cargo pumps fail in a cargo tank, emergency discharge by
pressurising the cargo tank is done using the LNG vaporizer. Liquid LNG is supplied to the
vaporizer by a spray pump and the vapour is led to the cargo tank for pressurising.
In the event that the inert gas generator is unable to produce inert gas, the LNG vaporizer
can produce nitrogen gas using liquid nitrogen from the shore.
3.4.13.2 Particulars
The design capacity is as follows;
Inert gas purging Unloading without return gas
Gas evaporation 8500 kg/h 18000 kg/h
LNG inlet temperature -163oC -163
oC
LNG inlet pressure 290 kPa 200 kPa
Gas outlet temperature +20oC -60
oC
Gas outlet pressure 29 kPa 29 kPa
Steam for the LNG vaporizer is supplied from the low pressure steam generator (LPSG) in
the engine room. The vaporizer is provided with a steam condense drain pot and a steam
trap. Condense drain from the vaporizer is returned to the drain inspection tank in the
engine room through the gas heater drain cooler and the gas heater drain tank.
3.4.13.3 Control system
The LNG vaporizer has a local control board located near the vaporizer. Outlet gas
temperature is controlled by the temperature controller fitted on the local control board.
The outlet gas temperature can be set by the temperature controller. A pneumatic operated
control valve (VS-902), is adjusted according to the set temperature. Outlet gas
temperature is monitored by IMS.
The flow rate can be controlled using the remotely operated valve (VS-901). It is adjusted
from the Cargo Control Console (CCC).
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When heating steam condense level is detected in the drain pot, the temperature control
valve and the flow rate control valve are closed to prevent icing in the vaporizer shell.
Under normal conditions, the condition indicator on the local control board shows green.
At trip condition, the drain pot level is shown by red / white strips. The trip condition is
also monitored by the IMS.
If the flow rate control valve is fully closed due to accidental operation at the CCC, then
the temperature control valve is forced closed. This condition is interpreted by the
Integrated Monitoring System (IMS) as a trip condition. The condition indicator on the
local control board also shows red / white strips instead of green.
When tripped, both temperature and flow rate control valves are closed. They must be reset
manually using the reset switch on the local control board.
LNG vaporizer alarm set points are as follows;
Gas outlet temperature high : 80oC
Gas outlet temperature low : -70oC
Drain pot level high : 195mm
3.4.14 Operation
3.4.14.1 Start up
Select the spray nozzle according to the operation mode. These modes are inert gas
purging, unloading without return gas or emergency discharge. In unloading without return
gas mode, use a 1-1/2 inch spray nozzle. Use a 1 inch spray nozzle for the other modes. (a
1 inch spray nozzle is set in the vaporizer at delivery.)
At the local control board, set the Auto / Manual selector switch on the temp controller to
"M.
Ensure that the gas detection system on the gas vent drain tank is operating.
Ensure that the auxiliary central cooling system is operating and cooling water is being
supplied to the gas heater drain cooler.
Ensure that instrument air is being supplied to the local control board and the system works
well.
Manually open the vent valve on the vaporizer shell.
Open the drain pot steam trap Isolating valve (3DV-704)
Open the steam inlet valve (3SV-706) and pass heating steam into the vaporizer slowly and
gradually.
Close the vent valve when steam begins to spout out.
Open the flow control valve (VS-901) using the local valve handle and then open the
temperature control valve (VS-902) using the local temp. controller. Do this slowly and
gradually.
Adjust both flow and temperature control valves locally until gas outlet temperature is
steady.
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When the gas outlet temperature is steady, then change the operation mode Auto / Manual
switch on the temperature controller to "A".
Under normal operating conditions, the flowrate is adjusted by the flow control valve (VS-
501). This is done manually from the CCC in accordance with the cargo tank pressure.
3.4.14.2 Stop
Change the operation mode Auto / Manual switch on the local. temperature controller to
“M”.
Close the flow control valve using the local valve handling and the temperature control
valve using the local temperature controller. Stop the LNG slowly and gradually.
Close the steam inlet valve slowly so as to prevent icing after the flow and temp. control
valves are closed.
Slowly open the vent valve for the vaporizer shell.
Close the vent valve completely after the inside temperature of shell and LNG inlet and
outlet piping reach the ambient temperature.
Notes:
Heating steam is supplied first to prevent icing.
When stopping, the LNG liquid supply is stopped before shutting off steam.
The flow control valve is not closed fully during normal operation.
When exchanging the spray nozzle, the vaporizer is purged with nitrogen gas.
Drain in the heater shall be discharged enough after using the heater to avoid drain attack
in the drain pipe.
Do not start the vaporizer to vaporize LNG unless the drain pot is at operational
temperature.
3.4.15 Forcing Vaporizer
3.4.15.1 General
The forcing vaporizer is a horizontal shel1 and U tube, direct steam heating type. It is
located in the cargo machinery room.
The forcing vaporizer is used for producing LNG vapour to be sent to the main boiler as
fuel gas. The produced LNG vapour is added to natural boil-off gas from cargo tanks.
3.4.15.2 Particulars
The design capacity of the forcing vaporizer is as follows;
Gas evapouration : 6400 kg/h (min. 1000kg/h)
LNG inlet temperature : -163oC
LNG inlet pressure : 290 kPa
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Gas outlet temperature : -40oC
Gas outlet pressure : 25 kPa
Supply steam for the forcing vaporizer is fed from the engine room.
3.4.15.3 Control system
The forcing vaporizer is provided with a local control board located near the vaporizer.
Outlet gas temperature is controlled by the temperature controller fitted on the local control
board.
Outlet gas temperature can be set by the temperature controller and a pneumatic control
valve (V32904, VS-904), is adjusted according to the set temperature. Temperature of the
outlet gas is monitored by the Integrated Monitoring System (IMS).
The outlet gas flow rate is controlled by a PID controller. The control signal of the flow
rate is determined as the additional flow to the natural boil-off gas flow. The control signal
is calculated using the following formula by the SSC: Main boiler gas consumption minus
available gas flow from cargo tanks. The gas flow rate is adjusted by the pneumatic type
flow control valve (V32903, VS-903), according to the signal from the PID.
When the gas temperature in the mist separator becomes too low because of mixing with
the natural boil-off gas, a low temperature signal is sent to the IMS and both temperature
control valve and flow rate control valve are closed as trip condition so as not to send cold
gas, which might include LNG mist, to the gas compressor.
The trip condition must be reset by the reset switch fitted on the local control board after
recovery of trip cause.
Forcing vaporizer alarm/trip set points are as follows;
Gas outlet temperature high : 80oC
Gas outlet temperature low : -70oC
Mist separator temperature low : -145oC
3.4.16 Operation
3.4.16.1 Start up
Change the operation mode of the flow and temp. control valves from "A" to "M". This is
done at the manual loader and temp. controller on the local control board.
Ensure that the heating steam. supply pressure is at 0.3 MPa. Do this by adjusting the
steam inlet valve (V32980, 3SV-801).
Open the valve (V32980, 3SV-801) and pass heating steam into the vaporizer slowly and
gradually.
Open the flow control valve (V32903, VS-903) and the temp. control valve (V32904; VS-
904) using the manual loader and temp. controller. Do this slowly and gradually.
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Adjust both flow and temp. control valves locally until the gas outlet temperature is steady.
When the vaporizer gas outlet temperature is steady, then change the operation mode of the
flow and temp. control valves to "A" on the local control board.
Under normal operating conditions, the flow rate is controlled automatically according to a
control signal from the SSC.
3.4.16.2 Stop
Change the operating mode of the flow and temp. control valves from “A” to “M”. This is
done at the manual loader and temp. controller on the local control board.
Close the flow and temp. control valves (V32904, VS-904 & V32903, VS-903) manually
from the manual loader and temp. controller. Stop the LNG flow slowly and gradually.
Close the steam inlet valve slowly so as to prevent icing after the flow and temp. control
valves are closed.
Open the vent valve for the vaporizer shell slowly.
Close the vent valve completely after the Inside temperatures of the shell, LNG inlet and
outlet piping reach ambient temperature.
Note:
Heating steam is supplied first to prevent icing.
When stopping, LNG liquid supply is stopped before shutting off steam.
Drain in the heater shall be discharged enough after using the heater to avoid drain attack
in the drain pipe.
Do not start vaporizer to vaporize LNG unless the drain pot is at operational temperature.
3.4.17 Nitrogen Generating System
3.4.17.1 General
The nitrogen generating system is installed on the 2nd deck in the engine room.
It is used for the following purposes:
Cargo line purging.
Cargo compressors (H/D,L/D) gland sealing & bulkhead sealing.
Cargo tank insulation space inerting.
Vent riser fire extinguishing.
Engine room gas line purging.
3.4.17.2 Particulars
Nitrogen generator; 2 sets
Type : Membrane permeation
Capacity : 90 Nm3/h
Outlet press. : 490 kPa
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Nitrogen purity : 97% (by vol.N₂+Ar)
Max. outlet temp. : 50oC
Dew point at atm. press. : -65oC
Feed air compressor ; 2 sets
Type : Screw compressor electric motor driven
Capacity : 280 Nm3 /h
Discharge press. : 1450 kPa
N2 buffer tank ; 1 set
Capacity : 10 m3
Working press. : 300 500 kPa
3.4.17.3 Construction
Ambient air is compressed by the water cooled screw compressor. Some condense water
will be. separated in the cyclone separator (F-4A/B) and automatically drained out. Then
the saturated air passes through three filters (F-1A/B,2A/B,3A/B).
The treated compressed air is heated by the electric heater before entering the membranes.
The heated air then passes the membranes and is separated into two streams. One stream is
nitrogen, the other is the remaining gases.
In downstream of the membranes, the nitrogen passes through the flow indicator (F1-
1A/B), the purity control valve (HCV-1A/B) and the back pressure regulator (PCV-1A/B),
and is led to the nitrogen buffer tank. The other gases are discharged to the atmosphere.
This system is simplified in the simulator.
3.4.17.4 Operation
The nitrogen generator (MD340) is started / stopped locally.
Once the system has been started from the local control panel, the feed air compressor is
started and stopped automatically in response to the pressure in the nitrogen buffer tank
(start : 300 kPa, stop : 500 kPa).
When plant is stopped which means that the generator inlet and outlet valves are closed
and vent valves are open, the compressor will continue idling for a few more minutes and
stop.
If the plant has been stopped for several hours, the membranes are cold and will therefore
not separate properly for about 15 minutes after start-up. The nitrogen gas can be sent after
about 15 minutes. This delay is reduced in the simulator.
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Confirm that the oxygen content in the N2 buffer tank is below 3.5% before you open
supply to consuming systems, reduce O2 in the buffer tank by venting the it by opening
V34070.
3.4.17.5 Initial Start-up
Before start-up, check all drain valves(not implemented in the sim)on the filters for the
presence of water.
Open manually operated valves, V34001 & V34051
Switch ON the isolating switch on the El. Heater control panel.
Switch ON the main isolating switch on the Nitrogen system control panel.
Switch ON the oxygen analysers and calibrate in accordance with manufacturer's manual.
Select the process trains and put the selector switch in the position corresponding to the
following operational scenarios.
3.4.17.6 Single train operation
Position 1.:
(Crossover valve invar angle (V34040; XV-4 is CLOSED)
Compressor A operates with side A of the nitrogen generator or compressor B operates
with side B of the nitrogen generator.
Position 2.:
(Crossover valve (V34040; XV-4 is OPENED))
Compressor A operates with side B or compressor B with side A.
Note:
SELECTORS SWITCH
Position 1 COMPR A N2 GEN. A
COMPR B N2 GEN. B
Position 2 COMPR A N2 GEN. B
COMPR B N2 GEN. A
3.4.17.7 Double train operation
Position 1 should always be selected.
Confirm that the manual isolation valves are OPEN.
Confirm that all valves upstream of the nitrogen buffer tank are OPEN.
Put the local panel compressor selector on REMOTE.
Shut-off valve will remain in the "SHUT" position and vent valve in the "OPEN" position
until oxygen content is less than the set point of alarm OAHH-1A (Ref to alarm list).
Once the oxygen content is less than the set point of the alarm, the shut-off valve will
OPEN and start to deliver nitrogen gas to the buffer tank.
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3.4.17.8 Stop
Press the STOP button on the compressor control panel.
Open all filter drain valves.
If the system is to be out of service for a long time, switch off the isolating switches
(Nitrogen system control panel, electric heater panel, oxygen analyser).
3.4.17.9 Safety
Nitrogen is a non-toxic but asphyxiating gas. Its density is slightly lower than air.
3.4.18 Inert Gas Generator Plant
3.4.18.1 General
The inert gas generator plant sends inert gas or dry air to cargo tanks and cargo holds.
The plant consists of two air blowers, an inert gas generator, an Inert gas refrigerating unit
and an inert gas dryer unit (the two latter shown as only one unit).
The inert gas generator plant is in the IGG Room on the 3rd deck of the engine room.
3.4.18.2 Particulars
The design capacity of the IGG is as follows;
Inert gas capacity : 11000 Nm3/h
Discharge pressure : 0.025 MPa
Temperature : Average 30oC (Max 65
oC)
Dewpoint after expansion : Maximum –45oC
to atmospheric pressure
Dry inert gas composition is as follows;
Oxygen O2 : Maximum 1.0 %
Carbon-dioxide CO2 : Maximum 14.0 vol %
Carbon-monoxide CO : Maximum 100 ppm
Sulphur-oxides SOx : Maximum 10 ppm
Nitrogen N2 : balance
3.4.18.3 Construction of the Inert gas generator (IGG)
The inert gas generator consists of a combustion chamber and a cooling/washing tower. In
the combustion chamber, fuel oil and air are burnt and inert gas is generated. Then the inert
gas is sent to the cooling/washing tower. At the cooling/washing tower, a sea water shower
cools the inert gas and washes out sulphur oxides which are contained in the gas.
The NO.3 ballast pump supplies sea water to the cooling/washing tower and the cooling
jacket of the combustion chamber.
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The IGG fuel Oil Pump supplies fuel oil from IGG gas oil tanks. The combustion air is
supplied by roots type air blowers. The final discharge pressure of the dryer unit is
maintained by the air blowers, and the pressure is controlled by a pressure control valve.
3.4.18.4 Inert gas refrigerating unit (Freon R-22)
This is not shown in the simulator
The inert gas refrigerating unit cools the inert gas as the first step of drying.
The inert gas refrigerating unit consists of a freon compressor with capacity control, a
freon condenser, a freon evapourator and a demister.
The freon evapourator is a shell and tube type cooler. Direct expanded freon 'R-22' cools
inert gas and condenses excess water in the inert gas.
3.4.18.5 Inertgas dryer unit
The dryer unit absorbs water in the inert gas with activated alumina.
The inert gas dryer unit has two dryer vessels. When one vessel is working, the other
vessel is regenerating.
The change-over between working/regenerating is carried out automatically every 8 hours.
In the regenerating phase, the vessel is heated by hot air for at least 4 hours, and then
cooled.
The hot air is generated by both electric and steam heaters. The temperature of hot air is
controlled about 220oC by electric heater.
3.4.18.6 Control and monitor
The final discharge pressure (0.25MPa) of the inert gas plant is controlled by the pressure
control valve.
The oxygen content can be adjusted manually by changing the fuel oil/air ratio. (This is
done automatically in the simulator).
When oxygen content rises above the high high level (2 %), the discharge valve will close
and the purge valve will open.
The inert gas is blown-off to the atmosphere.
Dew point is measured continuously by the dew point analyser. If a high high condition (-
40oC) continues for 15 minutes, the inert gas is blown-off too.
3.4.18.7 Preparation of Starting-up
Before starting the system:
Open IGG Scrubber SW overboard valve (V35014)-MD 350 and the Inert Gas Cooling
Water valve (V40142, 2WV-41)-MD 401
Start the No.3 ballast pump(MD401) after lining up for cooling of IG system scrubber.
Line up from the IG system to the tanks or holds in question.
Dryer unit and inert gas refrigerating unit which is shown as one unit will work
automatically, and need no attention here.
Set the O2 analyser to OFF.
Open the valve to above funnel.
3.4.18.8 Inert gas production
Open the fuel supply valve to the burner.
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Line up and start one or two fans.
Switch on the burner.
After the O2 has stabilised at a low level switch ON the O2 analyser and change over from
above funnel to delivery line. Adjust pressure level at the PID control.
3.4.18.9 Dry air production (on cargo tank aeration)
Use the same procedure as for inert gas production, but leave the burner and the O2
analyser OFF.
3.4.18.10 Stop
There is a certain way to shut down the IG plant in real life. On the simulator you may shut
of the different valves for supply, and then shut down the complete plant step by step
without any great concern. Remember to shut down the ballast pump no 3 and its valves as
well.
3.4.19 Cargo Control Console (CCC)
The CCC is in the Cargo Control Room.
3.4.19.1 Composition
The simulator works in a semi mode where all mimic panels are presented on the screen.
Therefore it may act as “real equipment” where the operator are walking on deck and
adjusting the different valves directly. Or it may act as a mimic panel in the CC room
where the operation of the equipment will be remotely controlled.
Most mimic pictures are of this semi type. However the Cargo Control Panels (1-5), and
H/D & Spray Control Panels are looked upon as if they where positioned in the CC room.
These panels are composed of the following equipment for remote operation;
Port and Starboard cargo pumps with discharge control and tank temperature setter control
for each tank.
Cargo tank spray pump and spray header control for each tank.
Control for high duty compressor no 1 & 2.
See also the IMS control.
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3.4.20 IMS control function
3.4.20.1 General
The IMS provides the following control functions.
For machinery:
- Low duty compressor control
- Forcing vaporizer control
For cargo:
- High duty compressor control
- Tank pressure control
- Spray pump start/stop, (Spray pump load control), (spray header press control).
- Spray line cool down
- Equator temperature control
- Cargo pumps start/stop, (Cargo pump load control).
- Discharging
The main components of the control functions are the Signal Strategy Controller (SSC) for
continuous PID control of sequence and logic control.
The Single Strategy Controller (SSC) is a stand alone programmable controller and is
located on the CCC.
The data setter allows setting of variable data for cargo pump stop/striping level.
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3.4.21 BVG management system
3.4.21.1 General
The BVG (Boil-off and Vapour Gas) management system is a total gas flow control from
cargo tanks to main boilers. The total gas flow consists of the following two kind of gas;
Natural boil-off gas (Natural BOG) from cargo tanks.
Forcing boil-off gas (Forcing BOG) generated by forcing vaporizer.
The natural BOG is sent to the main boilers by the L/D compressor through the low duty
heater and the flow rate is controlled by an L/D compressor speed & inlet guide vane
(IGV). If natural BOG does not meet boiler demand, the forcing vaporizer will generate
forcing BOG and add it to the natural BOG for full speed range of ship.
3.4.21.2 System configuration
BVG management system consists of the following control system:
Vent control
The vent valve is operated by the signal from the cargo pressure controller for tank
protection.
The vent valve is opened at 23Kpa in vapour header and closed at 21Kpa.
Tank pressure control
The control system maintains the pressure in cargo tanks at a present value.
The control system calculates the available gas flow and excess gas flow.
Forcing vaporizer control
The control system controls the flow rate of forcing vaporizer.
Gas heater control
The control system controls the outlet temperature of low duty heater at a present
value.
Low Duty (L/D) compressor control
The control system controls the inlet vane opening and revolutions of. The low duty
compressor according to boiler fuel gas demand.
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3.4.22 Low duty compressor control
3.4.22.1 General
This control system controls the inlet vane opening and the revolutions of the low duty
compressor according to boiler fuel gas demand.
3.4.22.2 Operation
Line up for use of the L/D compressor.
Start the aux. L.O. pump of the selected low duty compressor.
Confirm that L.O. temperature and pressure are OK, and that the READY lamp is lit.
Start the low duty compressor on the compressor control panel by pushing START.
After confirming steady running of the low duty compressor, change the control mode of
the PID controller to AUTO mode.
The low duty compressor can be controlled according to the boiler fuel gas demand.
Stop operation
Push the STOP button for the low duty compressor on the control panel.
The Aux. L.O. pump starts automatically and continues running 55min after the stop
signal.
The PID control mode will change to MANUAL automatically when both low duty
compressors are stopped.
3.4.23 Control logic
Boiler fuel gas demand is detected by the boiler gas flow control valve position. The valve
position signal which is selected from NO.1 and NO.2 boilers by high selecter is sent to the
PID controller as the process value (PV).
The difference between the process value and the pre-set value (SP) in the PID controller
becomes the output signal. The out-put signal is divided into two signals; the inlet vane
control signal and the revolution control signal for the low duty compressor.
Inlet vane control 0 35%
Revolution control 35 100%
When the vapour header pressure decreases to the pre-set value (3kpa), the SSC outputs a
F.O. back-up order signal to the boiler automatic combustion control system(ACC). After
confirmation of F.O. burning signal from the ACC, the output signal from the PID
controller is set to minimum, the inlet vane fully closed and revolutions set to minimum.
When both low duty compressors are stopped, the SSC control mode is set to MANUAL
automatically.
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3.4.24 Forcing vaporizer control
3.4.24.1 General
This control system controls the flow rate of the forcing vaporizer based on the difference
between actual boiler gas flow (fuel gas consumption) and available natural Boil Off Gas
(BOG) from cargo tanks.
3.4.24.2 Start operation
Change the operation mode of the flow and temp. control valves from "A" to "M". This is
done at the manual loader and temp. controller on the local control board.
Ensure that the heating steam. supply pressure is at 0.3 MPa. Do this by adjusting the
press. reducing valve (3SV-718).
Open the steam inlet valve (3SV-801) and pass heating steam into the vaporizer slowly and
gradually.
Open the flow control valve (VS-905) and the temp. control valve (VS-904) using the
manual loader and temp. controller. Do this slowly and gradually.
Adjust both flow and temp. control valves locally until the gas outlet temperature is steady.
When the vaporizer gas outlet temperature is steady, then change the operation mode of the
flow and temp. control valves to "A" on the local control board.
Ensure that the PID controller operate in order to help the set value to approach the process
value.
Confirm the forcing vaporizer outlet temperature controller is operating.
Change the control mode to “C”.
3.4.24.3 Stop operation
Change the control mode to “A”.
Change the flow control valve manual loader on the local control board to “M”.
Local operation at the local control board is carried out.
3.4.24.4 Control logic
The total fuel gas consumption for the boiler is measured by the boiler automatic
combustion control (ACC) and is compared with the available BOG flow from cargo tanks.
The difference between those values is sent to the PID controller as set point.
The measured flow signal from the forcing vaporizer is also sent to the PID controller and
the output signal from the PID controller is sent to the forcing vaporizer gas flow control
valve.
3.4.25 High duty compressor control
3.4.25.1 General
Two high duty compressor controllers (SSC) are on the Cargo Control Console (MD500).
The control system controls the inlet vane in the high duty compressor so as to keep the
vapour header pressure constant.
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3.4.25.2 Start operation
Switch to mimic MD 319 and start the aux. L.O. pump for the high duty compressor in
question by clicking with the left mouse button on the LO icon.
Open N2 Supply. Open suction inlet valve and discharge valve. Check that the vane is set
to -80º.
L.O. temperature, pressure and the related valves are confirmed ready.
Ensure that the READY lamp is lit.
Ensure that the START AVAIL lamp on is lit.
Ensure that the SSC is in MAN mode.
Start the high duty compressor by pushing the START button.
Set the vapour header pressure (which is the pressure in the Vapour. line which the
compressors are sucking from). Typical setting is 5-10 kPa.
After confirming that the high duty compressor is running steady, change the control mode
of the SSC to AUTO.
Adjust the set point of vapour header pressure according to the actual vapour header
pressure.
The second high duty compressor is started if necessary.
3.4.25.3 Stop operation
Change the control mode on the SSC to MAN.
Decrease the PID output signal to 0 gradually.
Push the STOP button. The aux. L.O. pump will start automatically and continue running
for 55 min after the stop order.
3.4.25.4 Control logic
The measured vapour header pressure signal is sent to the PID controller as a process
value. The difference between the set point and the process value in the PID controller
becomes the output signal and is sent to the inlet vane actuator.
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3.4.26 Spray Pump Start/Stop
3.4.26.1 General
The spray pump is started and stopped sequentially by controlling a discharge valve and a
return valve.
The spray pumps and the relevant valves are controlled by the spray pump load controller
(SSC) and the spray header pressure controller (SSC).
The flow chart of the control function is shown below.
3.4.26.2 Sequence control
The sequence control will carry out the following operation by choosing AUTO mode.
The spray pump discharge valve opens to the present position (7%)
The tank spray return valve opens to 100%
Spray pump starts
Timer counting (10 sec)
Initial control set point (35% motor load) of the SSC is set.
Initial control set point (Spray header press : 350 kPa) of the SSC is set,
Motor load is controlled by the adjustment of the spray pump discharge valve.
Spray header pressure is controlled by the adjustment of the tank spray return valve.
The control set point of SSC returns to the initial set point just before the finish of PLC.
The sequence control will carry out the following operation by choosing MAN mode.
The tank spray return valve opens to 100%
The spray pump discharge valve closes to 0%
The spray pump will have to be stopped manually by clicking the right mouse button on
the icon.
3.4.26.3 Caution
Spray pump cannot be started at the tank level less than 2.0 m normally.
It is necessary to block the low level alarm (CTS) when the pump is started at the tank
level less then 2.0 m.
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3.4.27 Spray line Cooldown
3.4.27.1 General
Spray line cool down is controlled from the Cargo Control Console (CCC).
Spray line cool down is carried out before spraying, if necessary.
3.4.27.2 Sequence control
The sequence control will carry out the following operation:
All spray valves open.
Time counting (60 sec).
All spray valves close.
Activate chime ring for ten seconds (works only if sound system is enabled).
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3.4.28 Cargo Pump Start/Stop
3.4.28.1 General
The cargo pump is started and stopped sequentially by controlling a discharge valve and a
filling valve.
The flow chart of the control function is shown below.
The cargo pumps and the relevant valves are controlled by the Programmable Logic
Controller (PLC) in combination with the cargo pump load controller (SSC).
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3.4.28.2 Pump stop level
There are two modes for the stop sequence: “STOP MODE” and “STRIPPING MODE”. In
both modes stop level should be input manually.
Each pump will be in the following mode automatically by the stop level input.
Where L01 = stop level for No.1 pump
L02 = stop level for No.2 pump
Mode of pump
No.1 pump No.2 pump
L01 < L02 Stripping Stop
L02 < L01 Stop Stripping
L01 = L02 Stop Stop
Note:
Allowable input level range as follows:
0 L01 15m 0 L02 15m
The cargo pump is protected against low current which will be caused by running at low
tank level.
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3.4.28.3 Sequence control
The sequence controller will carry out the following after pushing the START button on
the Automatic Sequence panel. This manual shows the normal start of cargo pumps in
No.1 cargo tank.
3.4.28.4 Pump start
Confirmation of cargo pump start available
The Cargo Pump Discharge valve opens to the preset position (12%).
The Filling valve opens to 100%.
The Liquid Branch valve (out of the tank) closes to 0%.
Pump starts (No.1 or No.2)
Timer counting
Initial control set point (42.3% motor load) of the SSC is set
In compliance with the set point, the pump discharge valve opens or closes to maintain the
motor current constantly.
(Starting Discharge operation see next page)
3.4.28.5 Pump stop “STOP MODE”
When the tank level reaches the stop level (L1 or L2), the pump discharge valve closes to
the preset position.
Timer counting
Pump stops
The pump discharge valve closes to 0%.
(Required time about 20 30 sec.)
3.4.28.6 Pump stop “STRIPPING MODE”
When the tank level reaches the stop level, chime activates.
Note: In this case the operator must stop cargo pump manually.
3.4.28.7 Caution
The Cargo pumps cannot be started at a tank level less than 2.0m normally.
It is necessary to block the low level alarm (CTS) when the pump is started at a tank level
less then 2.0m. This figure is adjustable by keyboard operation on CTS.
When this sequence control is started when the cargo pump is running, the discharge valve
is returned to the preset position(initial load).
Cargo pump stop sequence control utilises the level signal (0-15 meters) from CTS main
level segment.
3.4.29 Discharging
3.4.29.1 General
The liquid branch valve and filling valve automatically open and close by the
Programmable Logic Controller (PLC).
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3.4.29.2 Sequence control
The sequence controller will carry out the following operation by pushing the START
button on the Automatic Sequence panel. This manual shows the discharging of No.1 tank.
Confirmation of the setting of the Filling valve ( 95 %) and the Liquid branch valve
( 3%).
Liquid branch valve opens to 100%
Timer counting (20 seconds from the open signal of this valve)
The Filling valve closes to 0%.
Note: The CTS measuring system must be on during cargo operations.
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3.4.30 Cargo Tank Temperature Control
3.4.30.1 General
During ballast voyage, the equator temperature of the cargo tank can be maintained at a
present value by automatic control of spraying.
Temperature control is done through the NO.3 spray nozzle valve (nominal capacity 2,35
t/h /tank ) of each tank.
The control temperature is measured by four thermo resistance bulbs (three wire type pt
100 at 0oC) which are provided forward, aft, port and starboard at equator level of each
tank.
“Cargo tank pressure control” stops spraying when the tank pressure reaches the preset
value.
3.4.30.2 Operation
Preparation:
Start spray pump (refer to “Spray pump”)
Cool down spray line
Set the variable value for spray header pressure controller.
Push the “START” button at the Auto Sequence panel on the Tank Temp Setter.
Set the equator temperature.
Caution: Equator temperature should reach below –124oC before starting of normal
loading.
To stop push the “STOP” switch at the Auto Sequence panel on the Tank Temp Setter.
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3.4.31 Cargo Tank Pressure Control
3.4.31.1 General
During ballast or laden voyage, pressure of the cargo tank can be maintained at a present
value by controlling amount of vapour generated by forcing vaporizer.
3.4.31.2 Description
Two sets of controllers are provided for this function. One controls tank pressure by
measuring gauge pressure at the vapour header, and the other controls by measuring
absolute pressure.
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Selection one of the two tank pressure controllers is done using the changeover switch on
the CCC.
The way to control tank pressure in relation with the gas supply and demand condition is as
follows;
Natural BOG > boiler demand Dump, Vent or Pressurising
Natural BOG + spraying > boiler demand Dump, Vent or Pressurising
Natural BOG + forcing + spraying > boiler demand Decrease the flow from vaporizer
Natural BOG + forcing + spraying < boiler demand Increase the flow from vaporizer
Natural BOG + spraying < boiler demand Forcing
Natural BOG < boiler demand Forcing and/or Spraying
Regarding the acceptable pressure range of the cargo tank, refer to "Cargo tank protection
system”.
3.4.32 Cargo Tank Protection System
3.4.32.1 General
An instrumented tank protection system is provided.
In addition to the level measurement, three level alarms for each tank (in the custody
transfer system) are provided, whereof one is adjustable
Thermo-resistance bulbs are provided to monitor the temperature of the cargo tank and
hold.
3.4.32.2 Level alarm and safety
A High level alarm is provided in each cargo tank. It is initiated by a capacitance level
sensor and is set at 97.0% volume.
A High-High level alarm is provided in each cargo tank. It is initiated by a capacitance
level sensor and is set at 99.0 % volume level. The tank filling valve for each cargo tank is
closed automatically by the High-High level signal mentioned above.
Moreover, an Emergency Shut Down system (ESD) is activated by the signal from a
capacitance spot sensor at 99.5 % volume level.
3.4.32.3 Pressure alarm and safety
A High pressure alarm for each cargo tank is provided, and is set at 22 kPa. The vapour
header pressure control valve is opened at 23 kPa. The pilot operated relief valve of each
cargo tank releases excess vapour in the cargo tank to the atmosphere at 25 kPa.
A Low pressure alarm is provided for each cargo tank and is set at 1 kpa. An automatic trip
system for the gas compressors, cargo pumps, spray pumps, IGG, ESD valves, spray inlet
valves and fuel gas master valve is activated when the pressure of any one of the cargo
tanks is equal to the atmosphere.
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A High pressure alarm for each hold is provided, and is set at 12kPa. The pilot operated
relief valves of each hold space release excess air in the atmosphere at 15kPa.
A Low pressure alarm for each hold is provided, and is set at -2kPa.
A Dry air supply request alarm for each hold is provided and set at -2kPa.
The pilot operated relief valves of each hold introduce atmospheric air to the hold space
when the pressure drops to -5kPa.
A high differential pressure alarm for each tank and hold is provided, and is set at 3kPa of
excess pressure in hold. An automatic trip system for gas compressors, cargo pumps, spray
pumps, IGG, spray inlet valves, fuel gas master valve and emergency shut down valves is
activated at 4kPa of excess pressure in the hold.
Moreover differential pressure relief valves (for each hold) release air in the hold to the
atmosphere at 5kPa of excess pressure in the hold.
3.4.32.4 Temperature alarm and safety
Ten temperature sensors in each tank are provided. Five are for service and five are for
spare. They are located at bottom, 25% level, 50% level, 75% level and 100% level in each
tank.
Four temperature sensors are provided at the equator level for each tank.
There are four temperature sensors for each hold space (side bulkhead, foundation deck,
double bottom and drip-pan), and three temperature sensors for the forward bulkheads.
A low temperature alarm indicates a cargo leakage or tank insulation failure.
3.4.33 Description of Ballast Tanks and Ballast Pumping
3.4.33.1 Segregated Ballast System
The ship is equipped with a segregated ballast system comprising a total of 15 water ballast
tanks.
All valves in the ballast system are single actuated butterfly valves.
All the valves are hydraulically remote controlled from the cargo control room.
Three electrically driven self priming ballast pumps, with a capacity of 3000 m3/h at 35
mLc (SW) each, are provided.
One ballast ejector with a capacity of 300 m3/h at 20 mLc (SW) is also provided.
The above pumps and ejector cannot be used in the cargo system and consequently they do
not require consideration with Annex II in MARPOL 73/78.
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3.5 Mimic Diagrams
The Picture Directory will give the operator an overview of all process pictures. From this
directory any picture can be selected by clicking on the name field of the picture.
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3.5.1 Cargo Tank Overview
The Cargo Tank Overview will give the operator a total view of the cargo tanks with
information about the cargo and tank level, shown as a bar graph, as well as vital data of
the ship’s condition like trim, list, deadweight, stability and draught. The small picture of
the ship at the bottom of the page makes it possible to quickly change the picture to either
one of the cargo tanks, or holds by just clicking at the corresponding area of the small ship.
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3.5.2 Ballast Tank Overview
The Ballast Tank Overview picture will give an overview of all the ballast tanks with
information about the fillage of the tanks shown as a bar graph. Ship conditions will be
dynamically updated based on tank ullage.
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3.5.3 Bunker/Consumables
The Bunker/Consumables Picture gives an overview of all tanks not related to cargo
operations like HFO, DO, FW and forepeak/aftpeak tanks.
The picture displays both a layout of the tanks as well as an ullage bar graph shown in %.
These tanks can be manually filled or emptied in this picture.
A summary of the tanks will also be shown.
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3.5.4 Shear Force
The Shear Forces are calculated from the load distribution of the ship including the steel
weights of the different hull sections, and the corresponding buoyancy forms.
The graphic picture will display three different curves: yellow shows maximum permitted
shear forces in harbour condition; red curve the maximum permitted shear forces in
seagoing condition and the blue curve is the actual shear forces.
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3.5.5 Bending Moment
The Bending Moments are calculated from the Shear Forces. The actual bending moment
curve is drawn in blue, the yellow and red curves give maximum limits for respectively
harbour and seagoing condition.
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3.5.6 Deflection
The hull´s deflection (from the straight line) is calculated from the bending moments and
from the elasticity of each hull section. Positive deflection represents a hogging hull
condition, negative deflection represents a sagging hull condition.
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3.5.7 Stability
The stability curve in the form of righting arm values is calculated for heel angles ranging
from 0 to 60 degrees. All righting arm values are corrected (reduced) for possible "free
surface" effects. The reduction in meta centric height is specifically given.
The area under the stability curve represents the heel resistance or dynamic stability.
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3.5.8 Shore Tanks
The Shore Tanks picture gives an overview of the shore tanks which we can load from or
discharge to. There is two shore tanks. Note also the Emergency Shutdown Button in the
lower right corner.
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3.5.9 Ship/Shore Connection
Ship/Shore connection shows the shore and the vessel manifold. Shore has two liquid
manifolds and two vapour manifolds. It also indicates a lightering barge/vessel which can
be used.
The manifold all the way to the left in the picture is a ballast discharge manifold on the
vessel and the ballast receiving manifold on the shore side.
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Manifolds
There are four liquid cargo manifold connections, and one vapour line connection on each
side.
But as you can see there is also a thin white nitrogen line connected to the liquid and
vapour lines for inerting of the latter. There are also several measuring points in this
picture shown by the SP buttons. By clicking on one of these a multi-meter is presented:
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3.5.10 Deck Lines
All tanks are connected to the same mainlines onboard, but divides into four tanks in one
end and four manifolds in the other end. There is only one vapour line and manifold
connection.
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3.5.11 Cargo Tanks
There are four tanks. We use tank no 1 as an example here. We have a view of the two
cargo pumps and one spray pump and the position were the emergency pump can be
installed. From the two cargo pumps there is a discharge line connected, each line with a
discharge valve. These lines are then merged into one common line. A filling line is also
shown to the right of the two discharge lines. A vapour line is connected as well. From the
spray pump there is a line going onto the main deck as well as a pipe going back to the tank
and dividing into the two spray line nozzle systems. Control of the cargo pumps and spray
system can be found to the right, where there are four PID controllers. Vital info on the ship
and the tank/cargo is shown to the left. An Emergency Shutdown button is shown in the
lower right corner. A picture of the ship at the lower left makes it possible to quickly
change the picture to one of the other cargo tanks by just clicking at the corresponding area
of the small ship.
Buttons with picture numbers make it possible to quickly change to other pictures in the
simulator.
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3.5.12 Cofferdams
There are five cofferdams although there are only four tanks. The first question that arises
is why do we have cofferdams between the cargo tanks? The reason is quite obvious when
we know a little more. The ship is basically built of ordinary steel. This material becomes
very brittle when cooled down to the temperatures we are talking about for this cargo. If
there were no cofferdams between the cargo tanks, the temperature from the cargo would
also reach the hull structure between the tanks. This would not work, and the hull would be
damaged. Therefore there is a built in heating system in the cofferdams which keeps the
temperature at a value of +5ºC. The heating system is required to manage a minimum of
0ºC under the most critical conditions!
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3.5.13 Insulation Spaces Pressure Controller
This ship has two insulation barriers, and since the membrane in these barriers are very
thin and can not take two much pressure, there is a pressure control system fitted.
The system will also make sure the barriers are free of oxygen/methane whenever needed
by use of the vacuum pumps and the nitrogen supply.
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3.5.14 Compressor Room
This picture gives us an overview of the compressor room, consisting of the H/D and L/D
compressors as well as the heaters (L/D and H/D heaters) and vapourizers (LNG and
forcing vaporizer).
Connections are made to the deck lines as well as to the engine room (boiler supply).
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3.5.15 Low Duty System
The Low Duty System consists of the Low Duty compressors and the Low Duty heater.
The controllers for the L/D compressors are also in this picture, it will not be possible to
start the compressors unless the correct preparation is done. Which is to open for Nitrogen,
start the lub oil pump, open the suction inlet valve and the discharge valve and set the vane
angle to -80 deg. Only after getting the READY signal it will be possible to start the
system.
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3.5.16 High Duty System
The High Duty system consists of the H/D compressors and the H/D heater. The
controllers for the H/D compressors are also in this picture, it will not be possible to start
the compressors unless the correct preparation is done. Which is to open for Nitrogen, start
the lub oil pump, open the suction inlet valve and the discharge valve and set the vane
angle to -80 deg. Only after getting the READY signal will it be possible to start the
system.
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3.5.17 Vapourizers
Under the page of “Vapourizers” we will find the Forcing vaporizer and the LNG
vaporizer as well as a schematic picture of the L/D and the H/D compressors. This is only
to be able to look more into detail on the vapourizers which are positioned in the
Compressor room.
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3.5.18 Nitrogen Plant
The Nitrogen plant consists of two Nitrogen compressor systems delivering Nitrogen
supply to the ship wherever needed.
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3.5.19 Inert Generator
The cargo handling simulator is modelled with an inert gas plant where HFO is burned
effectively and the exhaust gas is directed through the scrubber to the main inert gas deck
line. The capacity of the inert gas plant is approximately 5000 m3/h. The scrubber washes
and cools the flue gas in order to reduce soot and SO2 content.
The inert gas plant is fitted with two air inlets, one for each fan, allowing the plant to take
air instead of inert gas for ventilating and gas-freeing cargo tanks.
The drier unit consists of two units: the refrigerating/cooling unit and a drier unit
containing activated alumina. They are in this model fully automated.
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3.5.20 Ballast Tanks
All ballast tanks are situated in the double bottom. They give a graphic view of the content
of the different tanks as well as the sounding. All connections between the tanks with lines
and valves are shown. In addition we are also given the trim, list and draft measurements.
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3.5.21 Ballast Pump Room
The ballast pump room picture shows a schematic view of the actual ballast pump room. In
this room there are three ballast pumps and an ejector.
These ballast pumps have a capacity of 3000 m3/h – 35 mTH (SW).
The ejector has a capacity of 300 m3/h – 20 mTH (SW).
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3.5.22 H/D & Spray Control Panel
In this panel we are positioned in the cargo control room. We have the control panel for the
Cargo Tank Spray pumps and Spray Header (which are connected and work together) as
well as the control panel for the two H/D compressors positioned in the Compressor Room.
The Spray Sequences are started from these panels.
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3.5.23 Cargo Control Panel
This is another part of the panels in the Cargo Control Room.
From these panels we control the cargo pumps start up, their changeover to discharge and
the temperature setter of the tank which is only used under a voyage.
The Automated Tank measurement system is also started from these panels (CTS).
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3.5.24 Fixed Gas Detection System
This ship has a fixed gas detection system which runs all the time. It is divided in two
parts. The one to the left consists of one metering system which is measuring on 40
different locations onboard. Changing from one to the other automatically. When all 40 has
been checked the system starts from measuring point one again.
The other part to the right will measure in eight different locations continuously, so
whenever there is a gas-leak in these places there will be an immediate alarm.
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3.5.25 CCTV CAMERA
Via the MD page nr 140 you can get up the picture from the CCTV Camera.
You can see either the vessels manifolds or the vessel seen from the dock.
This can be chosen from buttons in the picture.
This is visualizing the connection/disconnection of loading arm or cargo hoses.
If there is a leakage in the manifold connection or blind flange this will also be visible.
Leakages can be triggered either from wrong procedure during disconnection or from a
malfunction set by the instructor.
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From the operation page which is accessed via the “F5” button it is possible to change the
operating scenario. “Weather scenario” and “Ship state” can be changed
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3.5.26 Picture Directory (Load Master)
The purpose of the Load Master Computer is to avoid excessive bending stresses in the hull
structure by offering the stress calculations off-line in advance. These stresses vary with the
cargo distribution throughout the length of the ship. Incorrect loading can damage the ship
and hence the cargo/ballast must be placed according to a carefully calculated plan.
Standard plans are often prepared by the shipyard.
However, it is impossible to foresee all cargo distributions, it is therefore necessary to have
a sophisticated calculator on board which can provide all the appropriate stresses for every
load distribution case which is manually input.
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3.5.27 Load Master Cargo Tank Overview
From this picture it is possible to try out various tank settings, and it does not matter
wether you put in the sounding, the volume (in %) or the mass of the cargo. The load
master will do the right calculation anyway. The corresponding trim and list will change
accordingly.
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3.5.28 Load Master Ballast Tank Overview
Here you may have a look at the different values of the ballast tanks shown as bar graphs.
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3.5.29 Load Master Bunker/Consumables
All consumables may be entered here in a simple way, and the trim and list will change
accordingly. This makes it easy to try out and plan a stowage for a trip.
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3.5.30 Load Master Shear Forces
This picture shows the actual shear forces which will affect the ship in this situation. This
makes it possible to check if the wanted condition is suitable for the ship or not.
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3.5.31 Load Master Bending Moment
This picture shows the actual bending moments which will affect the ship in this situation.
This makes it possible to check if the wanted condition is suitable for the ship or not.
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3.5.32 Load Master Deflection
This picture shows the actual deflection which will affect the ship in this situation. This
makes it possible to check if the wanted condition is suitable for the ship or not.
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3.5.33 Load Master Stability
This picture shows the actual stability of the ship in this situation. This makes it possible to
check if the wanted condition is suitable for the ship or not.
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3.5.34 Description of Legends
In this diagram an explanation is given of all colours, symbols and abbreviations used in
the various mimic diagrams throughout the system.
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3.5.35 Seek tag Functionality
All valves, pump, flows etc in the simulator do have a tag. Consisting of a ‘Capital’ letter
and some numbers. IE: V31756 is a discharge valve in one simulator model.
If you know the Tag name, you can seek for the Tag by pushing “CTRL” + “T”
When typing the tag name and enter, you will be directed to the first page were the
mention tag is present.
If you type a TAG name which not exists, the text “Tag not found” will be displayed in the
bottom of the screen.
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4. OPERATION OF THE LNG MEMBRANE TANKER
4.1 Introduction
This Chapter describes the cargo handling principles and operations relevant to the
simulator. But please be aware that the manual is based on a real vessels manual, so there
might be some functions which is mention but do not exist in the manual!
The normal cycle of tanker operations comprises loading/deballasting, laden voyage,
discharging/ballasting, ballast voyage and reloading.
Loading is accomplished by following directions given in the ship's loading orders.
Discharging is accomplished by discharging the cargo directly into a terminal tank storage
area.
Ballasting is a process whereby sea water is taken aboard into the segregated ballast tanks
to ensure proper stability, propeller immersion and to provide good manoeuvring and sea-
keeping characteristics.
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4.2 Insulation Space Tests
4.2.1 In Service Tests
Classification society regulations require that the barriers of a membrane tank should be
capable of being checked periodically for their effectiveness.
The following covers the practice, recommendations and the precautions which should be
taken during the in-service periodical examination of the primary and secondary
membranes.
Caution
Measurement devices which may otherwise be damaged should be isolated prior to the
commencement of the test. The barrier spaces must at all times be protected against over
pressure, which might otherwise result in membrane failure.
4.2.2 Method for Checking the Effectiveness of the Barriers
Primary Membrane
Since each primary insulated space is provided with a permanently installed gas detection
system capable of measuring gas concentration at intervals not exceeding thirty minutes,
any gas concentration in excess, with regard to the steady rates, would be the indication of
primary membrane damage. It results that each primary membrane is, in terms of tightness,
continuously monitored and a special test would not be required to check its effectiveness.
However that may be, each primary membrane can be tested according to the method
described below for the secondary membrane.
Secondary Membrane
In order to check its effectiveness, the secondary (or primary) membrane is submitted to a
global tightness test, which is the reiteration of the equivalent test, carried out during the
cargo containment building.
Procedure
a) Reduce the insulated space pressure at the back of the membrane to be tested to 200
mbarA.
b) After a stabilising period of about 8 hours, record by means of an accurate measuring
device, the vacuum decay over the next 24 hour period.
c) From the results obtained, the selection of the 10 hours continuous period during
which the temperature variations of the compartments surrounding the tested
membrane are minimum.
d) The allowable limit for vacuum decay of the space is given by the equation:
Δp≤0,8
e
where e = the thickness in meters of the insulated space at the back of the membrane.
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4.2.3 In Service Global Tightness Test
The global test is carried out either during a maintenance period, or when the cargo tanks
have been warmed up and gas freed.
To overcome any doubtful results arising from possible leaks through equipment connected
with the insulated spaces i.e. valves, pressure relief valves, electric cable glands etc, their
effectiveness must be carefully checked, and eventually replaced with blank joints, in so
far as the spaces remain protected against any over-pressure.
Test of Secondary Membrane
a) The pressure of the secondary space is reduced to 200 mbarA, while the primary
space is maintained at a slight vacuum.
(i.e. -100 mbar)
Under these conditions, the secondary membrane is submitted by one side to the
atmospheric pressure existing inside the primary space, by the other to the reduced
pressure existing inside the secondary space.
b) The vacuum decay is carried out on this space only by the method described in
secondary membrane testing b), c) and d).
In spite of the precautions taken for providing against leaks of the equipment, it is
important to check whether the vacuum decay of the secondary barrier space (DPs)
corresponds with a pressure reduction of the primary space (DPp).
If this is not the case, there may be an external leak which must be located and rectified
before another test is conducted.
When comparing (DPp) and (DPs), it is necessary to take into account the primary and
secondary space volumes as shown in the equation below:
ΔPρ=
ΔPxes
ep
Where (es) and (ep) represents the thickness of the secondary and primary spaces.
Primary Membrane Test Procedure
a) The pressure of the primary and secondary barrier spaces is reduced to 200 mbar a
simultaneously, in communication, in order to prevent the potential collapse of the
secondary barrier due to a higher pressure than that of the primary space.
b) The primary and secondary spaces are isolated and the vacuum decay procedure is
followed on the primary space only. The method used is as described in secondary
membrane testing b), c) and d).
Under these conditions, the primary membrane is submitted by one side to the atmospheric
pressure existing inside the tank and by the other to the reduced pressure existing inside the
primary space.
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Since both faces of the secondary membrane are in an equal pressure system, no flow can
be generated through any eventual leak of this membrane; therefore the measured vacuum
decay is the correct figure of the tightness of only the primary membrane.
Caution
Changes in temperature or barometric pressure can produce differentials far in excess of
30 mbar in the insulation spaces which are shut in. With the cargo system out of service
and during inerting, always maintain the primary insulation space pressure at or below
tank pressure and always maintain the secondary insulation space pressure at or below the
primary insulation space pressure. Severe damage to the membranes may occur if the
differentials exceed 30 mbar.
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4.3 Post Dry Dock Operation
4.3.1 Insulation Space Inerting
4.3.1.1 First Step: Evacuation of Insulation Space
Caution
To avoid major damage to the secondary barrier, never evacuate a primary insulation
space whilst leaving the associated secondary space under pressure and never fill a
secondary space whilst the primary space is under vacuum.
Prior to putting a cargo tank into service initially, or after dry docking, it is necessary to
replace the ambient humid air in the insulation space with dry nitrogen.
This is done by evacuating the insulation spaces with the vacuum pumps and refilling them
with nitrogen. The procedure is repeated until the oxygen content is reduced to less than
2%.
Evacuation of all the insulation spaces takes approximately 8 hours. Three cycles are
usually necessary to reduce the oxygen to less than 2% by volume.
Caution
Changes in temperature or barometric pressure can produce differentials far in excess of
30 mbar in the insulation spaces which are shut in. With the cargo system out of service
and during inerting, always maintain the primary insulation space pressure at or below
tank pressure and always maintain the secondary insulation space pressure at or below the
primary insulation space pressure. Severe damage to the membranes may occur if the
differentials exceed 30 mbar.
Before refilling with nitrogen, the insulation spaces arc evacuated to 200 mbar absolute
pressure. The evacuation of the insulation spaces is also used in order to check the integrity
of the barriers during periodical test.
To avoid possible damage to the secondary membrane, the secondary insulation spaces
must be evacuated before the primary insulation spaces. The pipe work at the vacuum
pump's suction has been designed to ensure that the evacuation of the primary spaces
cannot take place without having first evacuated the secondary spaces, or ensuring that
they will be both evacuated simultaneously.
Two electrically driven vacuum pumps, cooled by fresh water, are installed in the cargo
compressor room. They draw from the pressurisation headers and discharge to the vent
riser No.2.
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Operating Procedure All valves are assumed shut. – All valves mention in this procedure is on MD 240
a) Isolate any pressure gauge, transducer or instrument which could be damaged
by the vacuum and install temporary manometers to allow pressures in the
insulation spaces to be monitored.
b) On each tank, open Second.Ins. Space valves (V24014, V24013, V24012 and
V24011) connecting the pressurisation header with the feeder columns of the
secondary insulation spaces.
c) Open the S.Ins.Space.Head to Vacuum pumps Vlv (V24054) and Nitrogen to
Vacuum pump Vlv (V24053), and vacuum pumps suction valves
(V24051&V24052)
d) Prepare the vacuum pumps for use.
e) Start both vacuum pumps.
f) Monitor the secondary insulation space's pressure. When it has been reduced to
200 mbarA, in all the spaces, stop the pumps.
g) Close Second.Ins. Space valves (V24014, V24013, V24012 and V24011) on
the trunk deck.
h) On each tank, open the Primary Ins.Space Valves (V24004, V24003, V24002
& V24001) connected to the pressurisation header with the aft transverse of the
primary insulation spaces.
i) Open the Primary Ins. Space Header to Vacuum valve (V24055)
j) Start both vacuum pumps.
k) Monitor the primary insulation spaces, pressure. When it has been reduced to
200 mbarA, in all the spaces, stop the pumps.
l) Close Primary Ins.Space Valves (V24004, V24003, V24002 and V24001) on
trunk deck.
m) Close valves V24054, V24053, V24055 and valves V24052, V24051 at the
pumps' suction.
n) Stop the vacuum pumps
During the evacuation of the insulation spaces, the tightness of the primary and secondary
insulation spaces relief valves has to be confirmed and if suspected of leaking, blanked
until the operation is completed. Blanks must be clearly marked and notices posted.
General notes on the vacuum pumps:
Ensure that auxiliary fresh water for auxiliary fresh water cooler is available and on.
Ensure that the LO tank is full and the power supply to the pumps is available.
Ensure that the bulkhead seal system is full.
Ensure that the pump is free to rotate.
Ensure that LO is feeding the lubrication points.
Close the pump drains.
(Some of these checkpoints are not possible to do in the simulator, but are kept to show the
full extent of the operation in real life).
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4.3.1.2 Second Step: Initial Filling with Nitrogen
After evacuation, the next step consists of filling the insulation spaces with nitrogen. The
cycle is repeated until the oxygen content in the spaces is less than 2%.
Procedure for Initial Filling With Nitrogen
Depending on the type of vessel there are several ways of supplying N2 to this operation.
Some vessels use liquid N2 supplied from shore to the liquid manifold where it passes to
the stripping/spray header via the appropriate ESDS liquid valve. It is then fed to the LNG
vaporizer and N2 gas produced is passed at +20°C to each insulation spaces.
At this stage, ship's N2 generators are not used due to required capacity for initial filling.
Other vessels use N2 storage tanks to supply the N2 necessary to carry out the operation.
We have chosen to go for the latter version.
It is assumed that all valves are closed prior to use. All valves for below procedure is on
MD 240
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a) Line up from the Nitrogen storage tank. Open Nitrogen supply & reduction valves
V24041, V24042, V24043, V24044 & the Nitrogen Supply Cross over Vlv(V24045)
and Nitrogen main supply Vlv (V24046).
b) Open the nitrogen supply isolation valves (V24027, V24026, V24025 and V24024).
c) Open the Primary & Secondary Exhaust Isolation valves (V24034, V24035, V24036
and V24037).
d) On each tank open the primary space supply valves (V24004, V24003, V24002,
V24001).
e) Adjust the opening of the primary space supply valves for balancing the pressure rise
in all the spaces. In the Simulator they are not adjustable, only open or closed.
During filling, always maintain the pressure in the primary space 100 mbar above the
secondary space.
f) When the pressure in the primary spaces reaches 300 mbarA (100 mbar above the
pressure in the secondary spaces), on each tank open the secondary space supply
valves (V24014, V24013, V24012, V24011). Adjust the opening of these valves for
balancing the pressure rise in all the spaces.
g) Set the controller for the Primary & Secondary space Exhaust valves (V24031 &
V24032) at 4 mbar (0,4 kPa).
Operating Procedure for the Completion of the Nitrogen Filling
a) The final filling of the insulation spaces, up to 2 mbar is carried out at reduced flow
rate. Three cycles are usually necessary.
b) After the final filling, check the oxygen content in all the spaces. If it is higher than
2%, repeat inerting operation. There is also the possibility to check the 02 content at
the vacuum pump discharge.
Caution
Changes in temperature or barometric pressure can produce differentials far in excess of
30 mbar in the insulation spaces which are shut in. With the cargo system out of service
and during inerting, always maintain the primary insulation space pressure at or below
tank pressure and always maintain the secondary insulation space pressure at or below the
primary insulation space pressure. Severe damage to the membranes may occur if the
differentials exceed 30 mbar.
Operating Procedure for Normal Inerting
The primary and secondary insulation spaces are filled with dry nitrogen gas which is
automatically maintained by alternate relief and make-up as the atmospheric pressure or
the temperature rises and falls, under a pressure of between 2 mbar and 4 mbar above
atmospheric.
The nitrogen provides a dry and inert medium for the following purposes:
To prevent formation of a flammable mixture in the event of an LNG leak
To permit easy detection of an LNG leak through a barrier
To prevent corrosion
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Excess nitrogen from the insulation spaces is vented to mast No.2, through the exhaust
regulating valves.
Both primary and secondary insulation spaces of each tank are provided with a pair of
pressure relief valves which open at a pressure, sensed in each space, of 10 mbar above
atmospheric. A manual bypass with a cut out valve and a ball valve is provided from the
primary space to the N2 vent mast for local venting and sweeping of a space if required.
The nitrogen production is maintained in an automatic mode.
a) Adjust the set point of the nitrogen supply regulating valve (V24021) –MD240 to the
secondary header at 2 mbar/0,2 kPa, and the regulating valve (V24022) to the
primary header at 2 mbar/0,2 kPa.
b) At the forward part of the trunk deck, ensure that the Primary & Secondary space
Exhaust Isolating valves (V24034, V24035, V24036 and V24037) are open.
c) Adjust the set point of the Pri.Nitrogen exhaust control valve (V24031) at 4
mbar/0,4 kPa and regulating valve (V24032) (secondary) at 4 mbar/0,4 kPa.
There is a standby exhaust regulating valve (V24033), which can be connected to either the
primary or secondary system in the event of failure of one of the master regulating valves.
The nitrogen supply to the insulation spaces has a standby regulating valve V24023, which
can be connected to either the primary or secondary system in the event of failure of one of
the master regulating valves.
In the event of cargo gas leakage into insulation spaces, this can be swept with a
continuous feed of nitrogen by opening the exhaust from the space, allowing a controlled
purge. Close monitoring of the gas analyser on this space will be necessary during purging.
In cases where other consumers reduce the availability of nitrogen for the insulation
spaces, the pressure may temporarily fall below the atmospheric pressure.
This condition is not critical insofar as the differential pressure (Ps - Pp) between the
secondary spaces pressure (PS) and the primary space pressure (Pp) do not exceed 30
mbar/3 kPa.
(Ps - Pp) < 30 mbar
Warning
When the depression in the primary insulation spaces, relative to the secondary insulation
spaces, reaches 30 mbar, the two insulation spaces shall be immediately inter-connected -
which will involve a manual operation.
When put in communication, and therefore subjected to the same nitrogen pressure, the
primary and secondary insulation spaces can withstand a large depressurisation without
any damage.
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It should be noted that, even with the tanks fully loaded, a pressure lower than atmospheric
pressure in the primary insulation spaces is not harmful to the primary membrane. In this
respect, it should be noted that this membrane is subjected to a -800 mbar vacuum pressure
- both during global testing at the construction stage and also for the insulation spaces'
cycles purging.
4.3.2 Drying Cargo Tanks
During a dry docking or inspection, cargo tanks which have been opened and contain
humid air must be dried to avoid primarily the formation of ice when they are cooled down
and secondly, the formation of corrosive agents if the humidity combines with the sulphur
and nitrogen oxides which might be contained in excess in the inert gas. The tanks are
inerted in order to prevent the possibility of any flammable air/LNG mixture. Normal
humid air is displaced by dry air. Dry air is displaced by inert gas produced from the IGG.
Dry air is introduced at the bottom of the tanks through the filling piping. The air is
displaced from the top of each tank through the dome and the vapour header, and is
discharged from the vent mast No. l.
The operation is carried out when in port or at sea and it will take approximately 20 hours
to reduce the dew point to less than -20°C.
At the same time that the inert gas plant is in operation for drying and inerting the tanks,
the inert gas is also used to dry (below -40°C) and to inert all other LNG and vapour pipe
work. Any pipe work not purged with inert gas must be purged with nitrogen before the
introduction of LNG or vapour.
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Operating Procedure for Drying Tanks
Dry air, with a dew point of -45°C, is produced by the IGG at a flow rate of 14,000 Nm3/h.
a) Prepare the dry air/inert gas plant for use in the dry air mode (the burner is not
started) See IGG Plant operating Instruction Chapter 2.4.18.
b) Open blind flange Hold Gas Free Line/Liquid Line(F12001)-MD121 to connect the
inert gas/dry air feeder line to the liquid header.
In MD121: Open valve Vapour/Inert Gas to Liq Head (V12702), in cgo tank Pictures
1-4 open:
CT 1 Liquid Filling Vlv (V20100) and CT 1 Liquid Isolation Vlv (V20110)-MD201
CT 2 Liquid Filling Vlv (V20200) and CT 2 Liquid Isolation Vlv (V20210)-MD202
CT 3 Liquid Filling Vlv (V20300) and CT 3 Liquid Isolation Vlv (V20310)-MD203
CT 4 Liquid Filling Vlv (V20400) and CT 4 Liquid Isolation Vlv (V20410)-MD204
to supply dry air to the liquid header.
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c) Open the individual tank dome vapour header valves.
CT 1 Vapour Valve (V20170)-MD201
CT 2 Vapour Valve (V20270)-MD202
CT 3 Vapour Valve (V20370)-MD203
CT 4 Vapour Valve (V20470)-MD204
d) Go to MD330 and use the vent control panel to open the Vapour Header Vent Ctrl
Vlv (V12771) (push MAN and set the value to 100%).
e) Go to MD 121, open the Vapour Head Vent Shut off Vlv (V12772) to vent through
the No.1 vent mast. Manually regulate the tank pressure by regulating valve V12771
at MD330. The pressure should not be higher than 10 kPa.
f) Start the dry air production. When the dew point after the drier is -45°C (X35044),
open the valve IG Main Line Supply Vlv 2 (V35042)-MD350 upstream of the two
non-return valves on the dry air/inert gas discharge line.
g) Monitor the dew point of each tank by taking a sample at the vapour domes. When
the dew point is -25°C or less, close the filling and vapour valves of the tank.
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Humid air which may be contained in the discharge lines from the cargo pumps, float level
piping and any associated pipe work in the cargo compressor room must be purged with
dry air.
h) When all the tanks are dried, stop the plant. Remove the Hold Gas Free Line/Liquid
Line flange (F12001) and close the Vapour/Inert Gas to Liq Head supply valve
(V12702) to the LNG header and close the Vapour Head Vent Shut off Vlv (V12772)
to the venting system at the mast riser No. l.
Note It is necessary to lower the tank's dew point by dry air to at least -20°C, before feeding
tanks with inert gas in order to avoid formation of corrosive agents.
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4.3.3 Inerting Cargo Tanks
Inert gas, with an oxygen content of less than 1% and a dew point of -45ºC, is produced by
the IGG with a flow rate of 14,000 m3/h. The inert gas is primarily nitrogen and carbon
dioxide, containing less than 1% oxygen with a dew point of -40°C or below.
Emergency pump wells have to be inerted with nitrogen before inerting the cargo tanks.
(Inerting of emergency wells are not part of the simulator).
Warning
Inert gas from this generator and pure nitrogen will not sustain life. Great care must be
exercised to ensure the safety of all personnel involved with any operation using inert gas
of any description in order to avoid asphyxiation due to oxygen depletion.
a) Prepare the IGG for use in the inert gas mode. See IGG Plant operating instructions
chapter 2.4.18.7
b) Open blind flange Hold Gas Free Line/Liquid Line(F12001)-MD121 to connect the
inert gas/dry air feeder line to the liquid header.
c) Open the Vapour/Inert Gas to Liq Head Vlv (V12702), open:
CT 1 Liquid Filling Vlv (V20100) and CT 1 Liquid Isolation Vlv (V20110)-MD201
CT 2 Liquid Filling Vlv (V20200) and CT 2 Liquid Isolation Vlv (V20210)-MD202
CT 3 Liquid Filling Vlv (V20300) and CT 3 Liquid Isolation Vlv (V20310)-MD203
CT 4 Liquid Filling Vlv (V20400) and CT 4 Liquid Isolation Vlv (V20410)-MD204
to supply inert gas via the liquid header to the cargo tanks.
d) Open the individual tank dome vapour header valves.
CT 1 Vapour Valve (V20170)-MD201
CT 2 Vapour Valve (V20270)-MD202
CT 3 Vapour Valve (V20370)-MD203
CT 4 Vapour Valve (V20470)-MD204
e) Go to MD330 and use the vent control panel to open the Vapour Header Vent Ctrl
Vlv (V12771) (push MAN and set the value to 100%).
f) In MD 121, open the Vapour Head Vent Shut off Vlv (V12772) to vent through the
No.1 vent mast. Regulate the tank pressure by regulating the Vapour Header Vent
Ctrl Vlv (V12771)-MD330. The pressure should not be higher than 10 kPa.
g) Start the inert gas production. When oxygen content is less than 1% and dew point is
-45ºC, open IG Main Line Supply Vlv 2 (V35042)-MD350 upstream of the two non-
return valves on the inert gas discharge line.
h) By sampling at the vapour domes, check the atmosphere of each tank by means of
the portable oxygen analyser. O2 content is to be less than 2% and the dew point less
than -40°C.
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i) During tank inerting, purge for about 5 minutes the air contained in the lines and
equipment by using valves and purge sample points (not fitted in the simulator).
j) When the inerting of the tanks, lines and equipment is completed, regulate Vapour
Header Vent Ctrl Vlv (V12771)-MD330, so that all the tanks are pressurised to 15
kPa.
k) When the operation is completed, stop the supply of inert gas and close the IG Main
Line Supply Vlv 2 (V35042)-MD350, close the Vapour/Inert Gas to Liq Head Vlv
(V12702)-MD121 close the Hold Gas Free Line/Liquid Line blind flange (F12001)-
MD 121. An then close on the cargo tanks:
CT 1 Liquid Filling Vlv (V20100) and CT 1 Liquid Isolation Vlv (V20110)-MD201
CT 2 Liquid Filling Vlv (V20200) and CT 2 Liquid Isolation Vlv (V20210)-MD202
CT 3 Liquid Filling Vlv (V20300) and CT 3 Liquid Isolation Vlv (V20310)-MD203
CT 4 Liquid Filling Vlv (V20400) and CT 4 Liquid Isolation Vlv (V20410)-MD204
Note Until the ship is ready to load LNG for gas filling, the tanks may be maintained under inert
gas as long as necessary. If required pressurise the tanks to 20 mbar/ 2 kPa above
atmosphere pressure and, to reduce leakage, isolate all the valves at the forward venting
system.
The inert gas is purged and replaced by natural gas (NG) produced by the LNG vaporizer
(+20ºC outlet temperature) fed with LNG supplied by the loading terminal. One point eight
(l,8) complete volume changes are required for displacing the inert gas and attaining a CO2
content ≤ 1% by volume. This operation is complete in 20 hours.
4.3.4 Gassing-up Cargo Tanks
Introduction
After lay-up or dry dock, the cargo tanks are filled with inert gas or nitrogen. If the purging
has been done with inert gas, the cargo tanks have to be purged and cooled down when the
vessel arrives at the loading terminal. This is because, unlike nitrogen, inert gas contains
15% carbon dioxide (CO2), which will freeze at around -60°C and produces a white
powder which can block valves, filters and nozzles.
During purging, the inert gas in the cargo tanks is replaced with warm LNG vapour. This is
done to remove any gases which can freeze, such as carbon dioxide, and to complete the
drying of the tanks.
Description
LNG liquid is supplied from the terminal to the liquid manifold where it passes to the
stripping/spray header via the appropriate ESDS liquid valve. It is then fed to the LNG
vaporizer and the LNG vapour produced is passed at +20°C to the vapour header and into
each tank via the vapour domes.
At the start of the operation to fill the cargo tanks, the piping system and LNG vaporizer
are vapour locked. The stripping/spray header can be purged into the cargo tanks via the
vapour dome through the arrangement of spray valves containing the control valve until
liquid reaches the LNG vaporizer. The LNG vapour is lighter than the inert gas, which
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allows the inert gases in the cargo tanks to be exhausted up the tank filling line to the liquid
header. The inert gas then vents to the atmosphere via the No. l vent mast.
When 5% methane (the percentage figure will be specified by the particular port authority)
is detected at No.1 vent mast riser, the exhaust gas is directed ashore via the HD
compressors by-pass line, or to the boilers through the gas burning line.
This operation can be done without the compressors, subject to existing back pressure, or
with one or both HD compressors in service. If possible, it is better not to use compressors
to avoid creating turbulence inside the tanks.
The operation is considered complete when the CH content, as measured at the top of the
cargo filling pipe, exceeds 98% by volume.
The target values for N2 gas and inert gas CO2 is equal or less than 1%. These values
should be matched with the LNG terminal requirements.
This normally entails approximately 2.0 changes of the volume of the atmosphere in the
cargo tank.
On completion of purging, the cargo tanks will normally be cooled down.
There are exceptional cases where it may be necessary to undertake the purging of one or
more tanks at sea using LNG liquid already on board. In this case the liquid will be
supplied to the LNG vaporizer via the stripping/spray header using the stripping/spray
pump of a cargo tank containing LNG liquid. Due to local regulations on venting methane
gas to the atmosphere, some port authorities may require the entire operation to be carried
out with the exhaust gases being returned to shore facilities.
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Operating Procedures to Purge the Cargo Tanks with LNG Vapour.
Stage One
It is assumed, though unlikely, that all valves are closed prior to use. The vessel is docked
with port side to and the 3P manifold is connected, purged and ready.
l) Install the following spool pieces:
Liquid line –Vapour Line Flange F12002 (MD 121)header to compressors (only if
compressors are required),
Vapour Line - Liquid Line Flange F12000 to No.1 vent mast (MD121)
m) Prepare the LNG vaporizer for use. (MD 329), open the LNG Vapourizer steam inlet
valve (V32970) to supply heat to the vaporizer and set capacity to 100%. Then open
the LNG Vapourizer Flow Control Valve (V32901)
n) Adjust the set point of the output temperature controller(Z32910) . This regulates the
Temp Ctrl. Valve(V32902) to +20°C.
o) Regulate the tank pressure by regulating valve V12771 at MD330. The pressure
should not be higher than 60 mbar/6 kPa (or required value).
p) At No.1 vent mast, open the Vapour Head Vent Shut Off Vlv (V12772) MD 121
q) Open valve the LNG Vapourizer Supply Vlv (V12056) MD 121, to the manifold.
Open the Vapour/Inert Gas to Liq. Head Vlv (V12702)
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r) In the cargo machinery room (MD300 or MD 329 open LNG Vaporizer Outlet Vlv
(V32918).
s) Open the LNG/Vap/Vapour Head Conn. Vlv V30605(MD 300) to supply vapour
from the vaporizer to the vapour header.
t) Open the individual tank dome vapour header valves.
CT 1 Vapour Valve (V20170)-MD201
CT 2 Vapour Valve (V20270)-MD202
CT 3 Vapour Valve (V20370)-MD203
CT 4 Vapour Valve (V20470)-MD204
For safety reasons, ensure that the hull water curtain on the connected side is in operation.
The water curtain is not shown in the manifold pictures but there is a Water Spray Disch.
Vlv (V40144) to the system in the ballast pump room picture - MD401
u) Open Liq. Manif. Cooldown Vlv (V12065) -MD120 or MD121(if using the after
liquid manifold on the port side), or the Starboard Liq. Manif . Vlv (V12066)-MD
120 (if you are using the starboard side), the isolating valve to the LNG vaporizer
supply line.
v) Open the individual tank dome liquid filling & liquid isolating loading valves.
CT 1 Liquid Filling Vlv (V20100) and CT 1 Liquid Isolation Vlv (V20110)-MD201
CT 2 Liquid Filling Vlv (V20200) and CT 2 Liquid Isolation Vlv (V20210)-MD202
CT 3 Liquid Filling Vlv (V20300) and CT 3 Liquid Isolation Vlv (V20310)-MD203
CT 4 Liquid Filling Vlv (V20400) and CT 4 Liquid Isolation Vlv (V20410)-MD204
w) Open the Liq. Manif 3P ESD Vlv (V12031)-MD 120 or MD 121, the liquid
manifold valve on the port side. Request the terminal to commence supply of
LNG liquid to the ship at a constant pressure of 2 bar/200 kPa.-MD110. (Start
up the shore side pump with the liquid loading rate set at 10% capacity. Open
the Shore Tank Isolation Valve (V11002) and Shore Line 3 Shut Off Valve
(V11031)-MD110
x) Set the controller at No. 1 vent mast to AUTO this will control the Vapour Head.
Vent.Ctrl Vlv (V12771)-MD 330. The Automatic set point is at 230 mbar/23 kPa .
y) Monitor the inert exhausting gas at each liquid dome. Also monitor the inert
exhausted gas at No.1 vent mast by using the sample point at MD 201(upper right
corner)
z) When 5% methane, (or the quantity the port authority will allow) is detected at No.1
vent mast and at each vapour dome, request permission from the terminal personnel
to direct exhaust gas to the terminal facilities. Verify that your Vapour Manif. P Flange to Shore is connected and OPEN.
Shore side should open the Shore Vapour Line Shut off Valve (V11071) and Flare
Vapour Return Valve (V11073)-MD 110, each 100%.
At the manifold, fully open the Vapour Manif. P ESD Vlv (V12071)-MD121
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Finally, fully open (100%) the Vapour Crossover Block Valve(V12079)-MD121.
The vapour from the tanks now has a path to shore.
Close the Vapour Header Vent Shut Off Vlv (V12772) and the Vapour Header Vent
Control Vlv (V12771)-MD121. This will secure shipboard venting.
aa) Now you can safely remove the spool piece installed between Liquid main and
Vapour Main line (F12000)-MD121.
Natural Gas Total Required
1.8 x 145.914 m3 (100% of Total Volume) = 262.646 m3 OF NG
Required LNG
LNG Total Requirement = 1,8 x V(100 %) x ρ NG
= 1,8 x 145.914 x 0.8120
= 213.268,6 kg
= 454,7 m3 of LNG
(Density ρ NG = 0.8120 kg/m3 AT +20ºC and 1,060 mbara)
Required Heat Energy at Initial Purging
Tank Tk Volume
(m3)
Required
NG (m3)
Required
LNG (kg)
Required
LNG (m3)
Heat Energy
(MMBTU)
No.1 21958 39524,6 32094,0 68,4 1649,6
No.2 43049 77487,8 62920,1 134,2 3234,1
No.3 43049 77488,9 62921,0 134,2 3234,1
No.4 37858 68144,8 55333,5 118,0 2844,1
Total 145914 262646,1 213268,6 454,7 10962,0
Note
I) LNG Density: 469,0 kg/m3
2) LNG Heating Value: 51,400 MMBTU/ton
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Stage Two
Inert gas condition CO2: equal to or less than 1%.
Nitrogen gas condition N2: equal to or less than 1%.
When 5% CH content (or the quantity of port authority is allowed) is detected at No.1 vent
mast and each vapour dome, request permission from the terminal personnel to direct
exhaust gas to the terminal facilities as flare stack.
Normally HD compressor shall not be used to avoid creating turbulence inside the tanks.
Cargo tank pressure shall not be maintained in steady condition due to the back pressure
from shore side; in that case the HD compressor shall be used for the operation.
a) Prepare both HD compressors for use. See Chapter 2.4.8
b) Install the spool piece connecting the liquid line to the suction for the HD
compressors (F12002)-MD121
c) On the HD compressors (MD 319)open the following valves:
Inlet to No.1 HD compressor (V31907)
Outlet from No. l HD compressor (V31909)
Inlet to No.2 HD compressor (V31910)
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Outlet from No.2 HD compressor (V31912)
d) Open the following valves:
Open the Vapour/Inert Gas to Liq. Head Vlv (V12702)-MD 121, and Hot Vapour
Compressor suction Vlv (V30603)-MD 300 and the Vapour return Throttling Vlv
(V31900)-MD300, compressor supply to the manifold.
e) Open the vapour manifold ESD valve (V12071)- port side MD120 or MD121. This
will enable a free flow of gas to the terminal and is a check that the pipeline layout
on board has been arranged correctly.
f) Make sure the lube oil is started, there is N2 supply to the compressor, and that the
vane is set to -80 to get “Start available”. Start the compressors and adjust the
pressure set point of both HD compressors’ flow control, to around 6-7 kPa.
g) Once the flow to the terminal has been established, close the Liq.Head to No 1 Vent
Mast Vlv (12000)- MD 121. Close the No.1 mast riser control valve (V12771)-MD
330, and open the Vapour Header Vent Shut Off Vlv (V12772)-MD121.
h) If the tank pressure increases too much, start one or both of the compressors as
necessary.
i) Monitor the pressure inside the tanks.
If the pressure increases, request the terminal to reduce the supply of LNG, or increase the
flow through the HD compressor by adjusting the set point on both HD compressors to be
controlled by pressure set point.
If the pressure decreases, reduce the flow through the HD compressors by adjusting the set
point of both HD compressor's. Alternatively, shut down one of the compressors as
necessary, or request the terminal to increase the LNG liquid supply to the LNG vaporizer.
But normally HD compressors may not be used.
When the cargo tank CH content reaches 98%, throttle in the individual tank loading valve
until it is only just cracked open.
During the change of atmosphere, purge the following sections for about 5 minutes each:
a) All sections of the stripping/spray header and tank connections, via the valves at each
vapour dome:
CT.1 Spray By Pass Vlv(V20156), low & upper spray Vlv (V20151 & V20152)
CT.2 Spray By Pass Vlv(V20256), low & upper spray Vlv (V20251 & V20252)
CT.3 Spray By Pass Vlv(V20356), low & upper spray Vlv (V20351 &V20352)
CT.4 Spray By Pass Vlv(V20456), low & upper spray Vlv (V20451 &V20452)
b) Purge manual valves and ESD valves. The manifold bypass valves are not in use.
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The operation is considered complete when all four cargo tanks have at least a 98% CH
content and the acceptable CO2 content and/or N2 content as requested by the terminal.
c) Purge the following lines and equipment for five minutes each:
No.1 and 2 boil-off/warm-up heater, forcing vaporizer, (normal venting via the
sampling cocks, but these are not available in the simulator).
HD and LD compressors with the compressor inlet and outlet valves. Make
sure to thoroughly purge each compressor in turn.
Vapour crossover Starboard & Port manifold purge Valves (V12078 and
V12077)- MD120, venting through the manifold flanges (V12072 and
V12071).
Cargo pump lines, stripping/spray pump lines and emergency cargo pump well
via the appropriate line valve and purge sample point (no emergency pump
well or purge sample points on the simulator).
Extremities of vapour header via sample points (no sample points on the
simulator.
d) Request the terminal to stop the supply of LNG liquid.
e) Stop both HD compressors, if operated.
f) Close the LNG Vaporizer Supply Vlv(V12056)-MD 120 or MD 121, to isolate the
stripping/spray lines.
g) Do not shut down the LNG vaporizer until it has been warmed through to the
ambient temperature.
h) Remove any spool pieces after purging with nitrogen and testing the gas content.
i) Prepare the cargo system for cool down.
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4.3.5 Cooling Down Cargo Tanks
Introduction
Arriving at the loading terminal to load the first cargo after refit or when repairs require the
vessel to be gas free, the cargo tanks will be inert and at ambient temperature. After the
cargo system has been purge-dried and gassed up, the headers and tanks must be cooled
down before loading can commence. The cool down operation follows immediately after
the completion of gas filling, using LNG supplied from the terminal.
The rate of cool down is limited for the following reasons:
To avoid excessive pump tower stress.
Vapour generation must remain within the capabilities of the HD compressors to maintain
the cargo tanks at a pressure of 70 mbar/7 kPa (about 1083 mbarA).
To remain within the capacity of the nitrogen system to maintain the primary and
secondary insulation spaces at the required pressures.
Unlike rigid cargo tank designs, vertical thermal gradients in the tank walls are not a
significant limitation on the rate of cool down.
LNG is supplied from the terminal to the manifold cool down line and from there directly
to the spray header which is open to the cargo tanks. Once the cargo tank cool down is
nearing completion, the liquid manifold cross-overs, liquid header and loading lines are
cooled down.
Cool down of the cargo tanks is considered complete when the mean temperature except
two(2) top sensors in each tank indicate temperatures of -130°C or lower. When these
temperatures have been reached, and the CTS registers the presence of liquid, bulk loading
can begin. (GTT defines that target LNG loading is possible when mean temperature of the
cargo tank is lower than -80°C.) But GTT recommends to carry on the cool down operation
of the cargo tanks to -130°C as per LNG terminal requirement.
Vapour generated during the cool down of the tanks is returned to the terminal via the HD
compressors (or free flow) and the vapour manifold, as in the normal manner for loading.
During cool down, nitrogen flow to the primary and secondary spaces will significantly
increase. It is essential that the rate of cool down is controlled so that it remains within the
limits of the nitrogen system to maintain the primary and secondary insulation space
pressures between 2 mbar and 4 mbar (0,2 and 0,4 kPa).
Once cool down is completed and the build up to bulk loading has commenced, the lank
membrane will be at, or near to, liquid cargo temperature and it will take some hours to
establish fully cooled down temperature gradients through the insulation. Consequently
boil-off from the cargo will be higher than normal.
Cooling down the cargo tanks from +40°C to -130°C, over a period of 10 hours will
require a total of about 800 m3 of LNG to be vaporized. Cool down rate in the cargo tank
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and insulation spaces is depended on amount of spraying LNG. As typical data taken at gas
trial for the vessel refer to attached chart.
Preparation for Tank Cool Down
Place in service the heating system for the cofferdams.
a) Prepare the records for the tank, secondary barrier and hull temperatures.
b) Check that the nitrogen pressurisation system for the insulation spaces is in automatic
operation and lined up to supply the additional nitrogen necessary to compensate for
the contraction from cooling of the tanks. Prior to the cooling down, the nitrogen
pressure inside the primary insulation spaces will be raised to 6 mbar. Pressurise the
buffer tank at maximum pressure.
c) Check that the gas detection system is in normal operation.
d) Prepare the nitrogen generators for use.
Operating Procedure -Gas Return Through Vapour Header
Assume that the ship is ready to prepare for cool down after the completion of gas filling.
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As reported by several ship operators, it seems accepted that the vapour return through the
liquid header instead of the vapour header, makes the cool down operation more efficient
and prevents liquid droplets in the vapour stream. Alternatively, the procedure for cooling
down cargo tanks with gas return via the vapour header is as follows:
a) Arrange the nitrogen piping to preferentially feed the primary insulation spaces.
b) Adjust the set point of the nitrogen supply regulating valvesV24022(MD240), and
V24021 at 2 mbar/0,2 kPa.
c) Adjust the set point of the nitrogen exhaust regulating valvesV24032(MD240) and
V24031 at 4 mbar/0,4 kPa.
d) Open valve V12050 (MD 121)connecting the stripping/spray header with the forward
manifold and V12751, V12752, V12053 and V12055 on the stripping/spray header.
e) Open V12065(MD 120 or MD 121) to supply LNG from the liquid manifold.
f) At each vapour dome open the spray valves V20155, V20151, V20152,V20255,
V20251,V20252,V20355,V20351,V20352,V20455,V20451,V20452.
g) Open vapour valves on each tank:
h)
CT 1 Vapour Valve (V20170)-MD201
CT 2 Vapour Valve (V20270)-MD202
CT 3 Vapour Valve (V20370)-MD203
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CT 4 Vapour Valve (V20470)-MD204
i) At No.1 vent mast, open V12771(MD 330). Adjust the valve V12771 to keep at
pressure of 200 mbar/20 kPa.
j) Open the HD compressor's suction discharge and valves(V31907, V31909, V31910,
V31912) - MD319.
k) Open the HD compressor's suction from the vapour header V30601 (MD300)and
discharge valve V31900 (MD 300) to the vapour manifold.
l) Open vapour manifold valve V12071 (MD 121 or MD120)
m) When shore is ready to supply LNG, open ESDS valve V12031 ( MD 121 or
MD120)
n) After cooling down the lines, request the terminal to supply a pressure of 2 bar/200
kPa at the ship's rail. Monitor the tank's pressure and the cooling down rate.
o) Adjust the flow to the spray bars in order to obtain an average temperature fall of
20°C per hour in the first five hours and then 10-15°C per hour thereafter.
p) Start one HD compressor (or both as necessary) in order to maintain the tank
pressure at about 100 mbar/10 kPa.
q) Check the nitrogen pressure inside the insulation spaces. If it has a tendency to fall,
reduce the cooling down rate.
In cases where other consumers reduce the availability of nitrogen for the insulated spaces,
the pressure may temporarily fall below atmospheric pressure. This condition is not critical
insofar as the differential (Ps-Pp) between the secondary space pressure (Ps) and the
primary space pressure (Pp) do not exceed 30 mbar/3 kPa.
(Ps - Pp ≤30 mbar)
r) When the average of the temperatures shown by the sensors installed on the pump
towers is -130°C, request the terminal to stop LNG supply, and close V12031. The
other valves should remain open until the lines have warmed up.
s) Stop the compressor(s) if loading does not take place after cool down.
4.3.6 Spraying During Ballast Voyage
It is one of the operating schemes during ballast voyage.
After increasing cargo tank pressure, accumulated gas shall be used as fuel.
We assume that a single tank is to be cooled down, using heel from that tank.
It is assumed that all valves are closed prior to use, and we are using tank No.4.
Prepare the LD compressor(s) to supply the engine room with boil-off gas for the boilers.
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Make sure the pressure is 150 mbar/15 kPa by manually regulating of the forward mast
riser valve (V12771) at MD330.
Check the nitrogen system for high flow operation.
Confirm the set point of N2 supply regulating valve to 2 mbar/0,2 kPa.
Confirm the set point of N2 Exhaust regulating valve to 4 mbar/0,4 kPa.
a) Open vapour dome outlet valves to the vapour header:
CT 1 Vapour Valve (V20170)-MD201
CT 2 Vapour Valve (V20270)-MD202
CT 3 Vapour Valve (V20370)-MD203
CT 4 Vapour Valve (V20470)-MD204
b) Fully open the spray inlet valves to No.4 tank (V20451 and V20452). Partially open
the spray isolating valve (V20455) to the spray line - MD 204
c) Start No.4 spray pump and open the spray discharge valve (V20450 and V20455)
to allow minimum flow and to cool down the spray header. Pressure in stripping /
spray main line shall be controlled by the Spray Return Valve(V20454).
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d) Once cool down of the spray header to No.4 tank is complete, open up the Spray
Isolation Valve (V20455) and increase the flow rate by adjusting the spray pump
discharge valve to allow an even cool down and control of vapour pressure.
Care should be taken to maintain control of vapour pressure either by use in the boilers as
fuel, or venting to atmosphere via the forward riser.
e) On completion of cool down leave the spray header valves open to allow the spray
line to warm up to ambient temperature before closing them.
The above operation can be repeated for each individual tank.
4.3.7 Sloshing
Sloshing effect is not implemented in the simulator. From the experience gained on the
first LNG ships put into service and from a large number of model tests and computer
analyses, Gas Transport have designed new tanks which are reasonably free from any
sloshing risk.
The ship's cargo tanks are designed to limit the impact forces and the safety margin has
been considerably enlarged. However, operators should always be aware of the potential
risks to the cargo containment system and also on the tank equipment due to sloshing.
Precautions to Avoid Damage Due to Sloshing
Cargo tank levels:
The first precaution is to maintain the level of the tanks within the required limits i.e.:
Lower than a level corresponding to 10% of the length of the tank
Or
Higher than a level corresponding to normally 80% of the height of the tank.
Ship's movement:
The second precaution is to try to limit the ship's movement, which would generate
sloshing in the tanks.
The amplitude of sloshing depends on the condition of sea (wave pattern), the trim and the
speed of the ship.
No sloshing effect is implemented in the Simulator
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4.4 Loading
4.4.1 Preparations for Loading
It is assumed that all preparatory tests and trials have been carried out as per section 3.3 on
the ballast voyage prior to arrival at the loading terminal.
The loading of LNG cargo and simultaneous de-ballasting are carried out in a sequence to
satisfy the following:
1. The cargo tanks are filled at a uniform rate.
2. List and trim are controlled by the ballast tanks.
3. The cargo tanks are to be topped off at the fill heights given by the loading tables.
4. During topping off, the ship should have a trim limited to 1m by the stern, but if
possible kept on an even keel.
5. During the loading, the ship may be trimmed according to the terminal maximum
draught, in order to assist in emptying the ballast tanks.
6. The structural loading and stability, as determined by the loading computer, must
remain within safe limits.
An officer responsible for the operation must be present in the CCR when cargo is being
transferred. A deck watch is required for routine checking and/or any emergency
procedures that must be carried out on deck during the operation.
During the loading operations, communications must be maintained between the ship's
CCR and the terminal, and a telephone/agreed signals for the automatic actuation of the
Emergency Shutdown from or to the ship must be established.
At all times when the ship is in service with LNG and mainly during loading, the following
are required:
The pressurization system of the insulation spaces must be in operation with its automatic
pressure controls.
The secondary Level Indicating system should be maintained ready for operation.
The temperature recording system and alarms for the cargo tank barriers and double hull
structure should be in continuous operation.
The gas detection system and alarms must be in continuous operation.
Normally when loading cargo, vapour is returned to the terminal by means of the HD
compressors or shore compressor. The pressure in the ship's vapour header is maintained
by adjusting the compressor flow.
The cargo tanks must be maintained in communication with the vapour header on deck,
with the vapour valve on each tank dome open.
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The vent mast No.1 is maintained ready during the loading operation, for automatic
venting.
If the tanks have not been previously cooled down, LNG spraying is carried out.
Alongside of Terminal
a) Connect and bolt up the shore ground cable.
b) Connect and test the shore communication cable.
c) Test the telephone for normal communication with the terminal.
d) Test the back-up communication arrangements with the terminal.
e) Change over the blocking switch for the shut down signal from the terminal, from the
blocked to the terminal position.
f) Connect the terminal loading arms to the four LNG crossovers and one vapour
crossover. This operation is done by the terminal personnel.
g) Check that the coupling bolts or QCDC (Quick Connection and Disconnection) are
lubricated and have the correct torque.
h) In the cargo control room (CCR), switch on the cargo tank level alarms and level
shutdowns which are blocked at sea.
i) Switch the independent level alarms from blocked to normal on each tank.
j) Switch the derived level alarms from blocked to normal on each tank.
k) Verify that alarms for level shut downs blocked are cleared.
l) Connect the nitrogen purge hoses to the crossover connections and purge the air from
each loading arm, or using N2 gas from shore.
m) Pressurize each loading arm with full nitrogen pressure through the purge valve, and
soap test each coupling for tightness.
n) Bring the ship to a condition of no list and trim, and record the arrival conditions for
custody transfer documentation. Official representatives of both buyer and seller are
present when the printouts are run.
This list is in this manual mainly to give a clue as to what is happening when going
alongside the terminal. It is not possible to do all these operations on the simulator.
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4.4.2 Cargo Lines Cool Down
Assuming the ship has the port side alongside.
a) Open the following valves on the spray line: (V12055, V12053, V12752, V12751) -
MD121), and the Liquid isolation valves on the tanks:
CT 1 Liquid Isolation Vlv (V20110)-MD201
CT 2 Liquid Isolation Vlv (V20210)-MD202
CT 3 Liquid Isolation Vlv (V20310)-MD203
CT 4 Liquid Isolation Vlv (V20410)-MD204
b) On each vapour dome, open the following valves to allow the supply of LNG to the
spray rings:
CT 1 (V20155, V20151, V20152) - MD201
CT 2 (V20255, V20251, V20252) - MD201
CT 3 (V20355, V20351, V20352) - MD201
CT 4 (V20455, V20451, V20452) - MD204
c) Open the vapour manifold valve(V12071)MD120 or MD121.
d) Open manifold valve on liquid manifold 3P (V12031) and liquid manifold cool down
valve (V12065), which will allow liquid into the stripping/spray main via crossover
valve (V12050) MD120 or MD121-, if necessary for additional cool down in the
tanks.
e) Assuming that the aft loading arm 4P is the first to be cooled down:
Crack open the CT1 & CT4 liquid filling valves (V20100 & V20400)-
MD 201 & MD 204.
f) Inform the terminal that the ship is ready to receive LNG.
Open the LNG quick closing valve(V12041)-MD 120 or MD 121 on the liquid
manifold.
The terminal should be instructed to begin pumping at a slow rate for approximately 15
minutes, in order to gradually cool down the terminal piping and the ship's headers.
g) Open valve 4P Liquid Double Shut of Vlv(V12043).
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Slowly increase the terminal pumping rate until the liquid main and spray headers have
cooled down (approximately 15 to 20 minutes).
Note
In order to avoid the possibility of pipe sections hogging, the liquid header and crossovers
must be cooled down and filled as quickly as possible.
h) Open the filling valves to the tanks;
CT 1 Liquid Filling Vlv (V20100) -MD201
CT 2 Liquid Filling Vlv (V20200) -MD202
CT 3 Liquid Filling Vlv (V20300) -MD203
CT 4 Liquid Filling Vlv (V20400) -MD204
fully on completion of the loading arm's cool down.
i) Open liquid manifold valves: (V12033, V12013, V12023) and the LNG manifold
quick closing valves (V12031, V12021and V12011)-MD120 or MD121
j) Inform the terminal to increase the loading rate to the ship's maximum capacity.
k) Close Liq. Manif Cool Down valve (V12065) - MD120 or MD121.
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On each tank keep open the stripping/spray valves to the spray rings in order to avoid over-
pressure due to line warm up.
l) Start one HD compressor and adjust the flow rate to maintain the tank vapour
pressure at 50 mbar/5 kPa.
4.4.3 To Load Cargo with Vapour Return to Shore
It is assumed for clarity of the description that all valves are closed prior to use and that the
ship is port side alongside.
Checks to be made before cargo operation:
a) Test the remote operation of all tank valves and manifold crossover valves.
b) Test the remote operation of ballast valves. Test the HD compressors, ballast pumps,
safety systems and glycol heating systems.
Safety precautions:
a) Ensure that the hull water curtain is in operation on the port side, if the ship loading
from portside.
b) Prepare the fire fighting equipment, water hoses and protective clothing for use. In
particular, the manifold dry powder monitors should be correctly aligned ready for
remote operation. Ensure the water spray system on deck is ready for operation,
filters installed and off shore blanks removed.
c) Prepare both HD compressors for use with seal gas and the lube oil system in
operation.
Nitrogen system:
a) Ensure that the nitrogen storage tank is at maximum pressure and that the two
nitrogen production plants are ready for use.
b) Arrange nitrogen piping to preferentially feed the primary insulation spaces.
c) Check the additional supply valve (V24023)-MD 240 as stand-by.
d) Adjust the set point of the nitrogen supply regulating valves(V24022) & (V24021) -
MD240 at 2 mbar/0,2 kPa.
e) Adjust the set point of the nitrogen exhaust pressure control valves,
primary insulation space (V24032 at 4 mbar/0,4 kPa
secondary insulation space( V24031 at 4 mbar/0,4 kPa.
f) Switch on the unblocking level alarms in the Custody Transfer. CTS should be open
before loading arm cool down operation.
g) Open gas outlet valves on tank gas domes (normally these valves are left open).
MD 201 – MD204
Tank No.l V20170
Tank No.2 V20270
Tank No.3 V20370
Tank No.4 V20470
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h) On HD gas compressors open valves(V31907, V31909, V31910 & V31912)-MD
319.
i) Check:
Optical fibre(shore) system, operates from Variable Page 11003
Connection of liquid and vapour arms
Communications with shore
Ship/shore electrical and pneumatic connection and safety devices
ESDS
j) Carry out safety inspections.
k) Complete the relevant ship/shore safety checklist.
l) Open filling valve of tank No.4 and tank No.1 fully, (V20400 and V20100)-
MD 204& MD 201.
Open filling valves of tank No.2: (V20200, & tank No.3:V20300)- MD 202 &
MD203
(See cargo line cool down)
m) Increase the loading rate.
n) Start the de-ballasting program. Keep draught, him and hull stresses within
permissible limits by controlling de-ballasting.
Refer to trim and stability data provided.
o) Start bulkhead heating in the cofferdams. This should already be running in
automatic.
p) Monitor tank pressures in order to achieve a pressure of about 80 mbar/8 kPa. Open
valve the Comp.Suct.Vlv (V30601)-MD300 and Vap.Ret Throttling Vlv(V31900)
(MD300) on the compressor's discharge side. Start one or both HD compressors as
necessary.
q) Adjust the opening of the tank filling valves to maintain an even distribution.
r) Ease in the filling valve of each tank as the tank approaches full capacity. Arrange to
terminate tanks at 15 minute intervals.
s) High level alarms. When any tank approaches 95% capacity inform the shore.
t) High/High level alarm. Standby valve before level approaches about 98% (signal
from main segment).
Close valve at correct filling limit capacity.
Very High level alarm will sound at 98.5% capacity and filling valve concerned will
automatically close (signal from independent sensor).
Extreme High level alarm will operate at 99% capacity and will initiate the
Emergency Shut Down System (signal from independent sensor).
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Warning
Extreme and very high level alarms and shut downs are emergency devices only, and
should on no account be used as part of the normal topping-off operation.
u) Before topping-off the first tank, request shore to reduce loading rate and continue
reducing when topping off each following tank. When a tank is at its required level,
close the corresponding loading valve tank No.1 V20100, tank No.2 V20200, and
tank No.3 V20300. It is convenient to finish loading by the use of tank No.4 for ease
of line draining. Leave a capacity of 50 m3 for this purpose.
v) Stop loading when the final tank reaches a capacity according to the filling chart,
minus an allowance for line draining and leave tank No.4 loading valve open
(V20400).
w) Liquid lines, including the horizontal part of the crossover, will automatically drain
to tank No.4. The inclined parts of the manifold are purged inboard with nitrogen.
x) On completion of draining loading arms, close the liquid manifold ESDS valves. The
shore lines are now pressurized at 2 to 3 bar with nitrogen.
y) Open the liquid manifold valves (V12011, V12021, V12031 and V12041)-MD 120
or MD 121 to allow the nitrogen to flush the liquid into No.4 tank. Close the valves
when the nitrogen pressure has fallen to 0 bar. Repeat the operation 3 times, or until
no liquid remains in the manifold lines. If there is a problem opening the valves due
to filling height in the tanks, go to variable page 54000 were the ESD system may be
shut off. Remember to turn it back on when the operation is finished!
z) The purging of the liquid lines should be carried out one at a time.
aa) When gas readings obtained from an explosimeter are less than 50% LEL at the vent
cocks, all valves are closed and the loading arms are ready to be disconnected.
bb) Leave loading valve of tank No.4 (V20400) open until the piping has returned to the
ambient temperature.
In CCR
a) Tank level alarms. Inhibit independent level alarms prior to proceeding to sea.
b) Complete the de-ballasting operation to obtain an even keel situation for final
measurement. When measurement is completed, adjust the ballast tank levels for
sailing condition.
c) Stop the HD compressors just prior to sailing, before closing vapour manifold ESDS
valve (V12071) MD120 or MD121 (Ship is loading from portside) for nitrogen
purging and disconnecting the loading arms. If departure is delayed, the vapour
return to shore should be continued. Close CTS by independent surveyor
d) Disconnect the vapour arms.
e) Prepare the cargo system for gas burning at sea.
f) Open valves necessary to allow warming up. These are normally the filling valves
and spray valves on the tank domes.
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4.4.4 De-Ballasting
Operating Procedures
It is assumed that the main sea water crossover pipe is already in use, supplying other sea
water systems, e.g. the main circulating system, the sea water service system and that the
cargo and ballast valve hydraulic system is also in service.
To De-Ballast the Ship By Gravity
Caution
Mal-operation of the ballast system will cause damage to the GRP pipe work. Damage is
generally caused by a pressure surge due to sudden changes in the flow rates. During the
de-ballasting operation this can be caused by the opening of a full or partly full tank into
the main lines when under vacuum.
Under no circumstances should a vacuum be drawn on closed ballast main. Before starting
deballasting operations, the main lines must be purged of any air pockets in the following
manner.
a) Open the overboard discharge crossover line valves (V40103 and V40104)- MD 401.
Open also the suction valves (V40111, V40112), filling & discharge valves(V40133,
and V40134). Open overboard discharge valve (V40110).
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b) Open the forward deep ballast tank valves port and starboard (V40011, V40021) –
MD 400, or No. l ballast tanks port and starboard (V40012, V40022), if the forward
ballast tanks do not have sufficient head of water to gravity flow .
A flow will now be established
c) Open the valves on the tank(s) to be emptied as per the deballasting plan.
Deep tank port V40011
Deep tank starboard V40021
Deep tank centre V40001
No. l port V40012
No. l starboard V40022
No.2 port V40013
No.2 Starboard V40023
No.3 port V40014
No.3 starboard V40024
No.4 port V40015
No.4 starboard V40025
Engine room port V40016
Engine room stb'd V40026
After peak tank V40109 (if applied)
Fore peak tank V40000 (if applied)
When it becomes necessary to start the ballast pumps:
d) Close BW Suction Aft valves (V40112 and V40122) –MD 401.
e) Check that the ballast tank valves are open - MD 400
f) Start the ballast pump(s).
g) Open the pump(s) discharge valve (V40114 (N0.1)), (V40124 (N0.2)).
h) If you feel you need the third pump, start this one as well in the same manner.
i) As the tank reaches the required level, open the valves on the next tank before
closing the valves on the first tank.
j) When suction has been lost on all tanks, close the discharge valves on the pumps
(V40114 (N0.1), V40124 (N0.2)) and stop the pumps.
k) Close all tank valves, ballast crossover valves (V40103 and V40104), and the
overboard discharge valves V40110.
l) Strip the ballast tanks as required (see below).
To Strip the Ballast Tanks Using a Ballast Eductor
Using the GS pump and the ballast eductor
a) Open the eductor drive water overboard discharge valve (V40141)- MD401.
b) Open the drive water supply from the GS pump, valve (V40143)-MD401.
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c) Open the Low Suction Sea Chest Vlv(V40108).
d) Start the GS pump (R40105).
e) Open eductor suction valves (V40101 and V40102).
f) Open the valve on the tank to be stripped.
g) When one tank has been stripped, ensure the next tank valve is opened before closing
the previous tank.
h) When all tanks have been stripped, close the eductor suction valves( V40101 and
V40102).
i) Stop the GS pump (R40105).
j) Close the eductor drive water valve (V40143).
k) Close the eductor overboard discharge valve (V40141 and the Low Suction Sea
Chest V40108.)
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4.5 Loaded Voyage with Boil-Off Gas Burning
4.5.1 Normal Boil-Off Gas Burning
Introduction
During a sea passage when the cargo tanks contain LNG, the boil-off from the tanks is
burned in the ship's boilers. The operation is started on deck and controlled by the ship's
engineers in the CCR and Engine Control Room. If for any reason the boil-off cannot be
used for gas burning, or if the volume is too great for the boilers to handle, any excess
vapour is vented to atmosphere via No. l vent mast.
Operation The cargo tank boil-off gas enters the vapour header via the cargo tank vapour domes. It is
then directed to one of the LD compressors, which pump the gas to the boil-off/warm-up
heater. The heated gas is delivered to the boilers at a temperature of +35°C via the Fuel
Gas Master Vlv (V30610). The compressors speed and inlet guide vane position is
governed by fuel demand from the boiler(s) and cargo tank's pressure. The system is
designed to burn all boil-off gas normally produced by a full cargo, and to maintain the
cargo tank pressure (i.e. temperatures) at a predetermined level.
If the propulsion plant steam consumption is not sufficient to burn the required amount of
boil-off, the tank pressure will increase and eventually the steam dump will open, dumping
steam directly to the main condenser. The main dump is designed to dump sufficient steam
to allow the boiler to use all the boil-off produced, even when the ship is stopped.
The flow of gas through the LD compressors is controlled by adjusting the compressor's
speed and inlet guide vane position. This is directed by the boiler combustion control when
gas burning is initiated. The normal boil-off in the boiler combustion control has to be
selected as well as the maximum and minimum allowed tank pressures and the tank
pressure at which the main dump operates.
For normal operation the normal boil-off valve is selected at 60% boil-off provides 60% of
the fuel required to produce 90% of the boiler full steam capacity, and the minimum and
maximum tank pressures are selected at l050 and 1090 mbarA (105 – 109 KpaA).
If the normal boil off valve has been correctly adjusted, the tank pressures will remain
within the selected values. Should the selected normal boil off value be too large, the tank
pressure will slowly be reduced until it reaches the minimum value selected. If the tank
pressure value reduces to below the minimum value selected, the normal boil-off value will
be reduced until the tank pressure has increased again above the selected value.
If the selected normal boil-off value is too small, the tank pressure will slowly, increase
until it reaches the maximum value selected. If the tank pressure value increases above the
maximum selected value, the normal boil-off value will be increased until the tank pressure
reduces again below the selected value.
If the tank pressure continues to increase because the steam consumption is not sufficient
to burn all the required boil-off, the steam dump will open.
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The steam dump is designed to open when the normal boil-off valve is 5% above the
original selected value and when the tank pressure has reached the pre-selected dump
operating pressure.
With the present setting, an increase of 5% of the normal boil-off corresponds
approximately to an increase of tank pressure by 40 mbar above the maximum tank
pressure selected.
The cargo and gas burning piping system is arranged so that excess boil-off can be vented
should there be any inadvertent stopping of gas burning in the ship's boilers. The automatic
Vapour Header Vent control valve (V12771)–MD 330 at No.1 vent mast is set at 230
mbar to vent the excess vapour to atmosphere as tank protection system.
If the gas header pressure falls to less than 40 mbar above the primary insulation space
pressure, an alarm will sound.
In the event of automatic or manual shut down of the gas burning system (or if the tank
pressure falls to 5 mbar above the insulation space's the Fuel Gas Master Vlv V30610 will
close and the gas burning supply line to the engine room will be purged with nitrogen.
Operating Procedures
It is assumed that all valves are closed prior to use.
a) Prepare LD compressors No.1 and 2, the boil-off heaters and the engine room gas
burning plant for use.
b) Open Vapour Head Vent Shut Off Vlv (V12772)-MD 121 to No.1 Vent Mast.
c) Check that the following valves on the vapour domes are open and locked in
position:
CT No.1: Open and lock in position valve V20170 – MD201
CT No.2: Open and lock in position valve V20270 – MD202.
CT No.3: Open and lock in position valve V20370 – MD203.
CT No.4: Open and lock in position valve V20470 – MD204.
The valves should already be locked in the open position.
d) Open vapour supply to the LD compressors valves (V30601)- MD300 and gas
heaters via the mist separator (V30901,V30903, V30904, V30906)- MD309.
e) Open heater inlet and outlet valves (V30913 & V30914) –MD309, At No. 1 boil-
off/warm-up heater (L/D Heater)
.
Open steam supply Vlv (V30970) to the heater.
f) In MD330 there are quite a few controllers that work in series. First choose LADEN
or BALLAST on the “Tank Press Controller”. Set the LD Compressor Controller in
Cascade (meaning it will get its set point from the “Tank Press Controller”. The only
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place to set the flow now is on the controller in the engine room. Set the set point to
the desired consumption in the range of 0 to 10 t/h.
When the engine room is ready to start gas burning, ensure that there is sufficient nitrogen
to purge the lines to the boiler i.e. > 5 bar in the buffer tank.
g) Ensure that the gas outlet temperature of the heater is approximately 35°C. Open the
Fuel Gas Master Vlv (V30610) and start the LD compressor(s).
Note
If the volume of boil-off exceeds demand in the boilers, the steam dump should be put into
operation.
Should the system shut down for any reason, valve V30610(MD330) will close
automatically.
Trip causes:
Boiler manual trip ( ECR, and local ) : Not implemented
Both boiler trip : Not implemented
Gas content High-High at common vent hood : Not implemented
Fuel gas temperature Low-Low : Not implemented
ESDS activated : This Trip is implemented
Vent duct exhaust fan stop : Not implemented
Remote/manual close from local, CCR and ECR : Not implemented
Fire detection in ER : Not implemented
When stopping gas burning for any reason;
h) Stop the LD compressor(s), shut down the boil-off heater. Close the Fuel Gas Master
Vlv (V30610) gas supply to engine room and adjust the set point of vent mast
control (V12771) to l l00 mbarA.
4.5.2 Forced Boil-Off Gas Burning
Introduction
Consideration must be given to the economics of gas versus fuel oil burning before
undertaking forced boil-Off.
If, during a loaded passage, additional fuel gas from the cargo tanks is required to be
burned in the ship's boilers, it can be made available by forced vaporization using the
equipment on board.
The above operation, called Forced Boil-Off will be used to complement gas burning up to
100% of the boiler's fuel requirement.
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Operation
The normal gas burning arrangement is maintained and the forcing vaporizer is brought
into operation.
A single stripping/spray pump is used to pump LNG to the forcing vaporizer. The excess
flow from the pump is returned to the tank through the stripping header pressure control
valves (V20154, V20254, V20354, V20454).
Note
In normal operation the controlled return is directed back to the same tank where the
liquid is being drawn from.
After vaporization, the LNG vapour produced passes through the demister where the
possibility of liquid LNG carryover is eliminated. The vapour then combines with the
natural boil-off gas from the vapour header before being drawn into the suction of the LD
compressors.
One LD compressor is used for this operation.
The flow of gas through the compressors is controlled via the boiler combustion control
unit by adjusting the opening of the inlet guide vanes and motor speed.
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The split control is as follows:
Low load: Inlet guide vane control (-80 to +20 deg).
High load: Motor speed control (30-60Hz).
The boiler combustion control has to be switched to Forced Boil-off (FBO) mode, This
control is not implemented in the Simulator
The amount of forced boil-off to be produced is controlled by the throttling of the FCV to
the forcing vaporizer operated by the Boiler Combustion Control.
When changing over to 100% gas burning, the fuel oil flow through the FO rails is adjusted
to minimum. The FO supply to the burners will then be cut out and the FO system put on
recirculation. The FO combustion control loops are maintained energized to enable re-
lighting of FO burners in an emergency.
In the event of automatic or manual shut down of the gas burning system (or if the tank
pressure falls to 3 mbar above the insulation spaces pressure), valve Fuel Gas Master Vlv
(V30610) will close and the gas burning supply line to the engine room will be purged with
nitrogen. FO booster devices are incorporated in the control loop to allow a quick
changeover should the gas burning be tripped.
Operating Procedures
The cargo piping system is arranged for normal gas burning during loaded voyage.
It is assumed that all valves are closed prior to use.
a) Prepare the forcing vaporizer for use.
b) Open the stripping/spray header isolating valve for the tank/s to be used –MD121
If Using CT No.1: V12752, V12751, V12055
If Using CT No.2: V12752, V12751
If Using CT No.3: V12752
If Using CT No.4: V12053
If cargo tanks No.1 is used, open stripping/spray header isolating valve V12752, V12751,
V12055. If tank No.2 is used open stripping/spray header isolating valve V12752, V12751.
If No.3 tank is used open stripping/spray header isolating valve V12752. And if No.4 tank
is used open stripping/spray header isolating valve V12053.
c) Open stripping/spray header supply valve (V12054)-MD121 to the forcing vaporizer.
d) Open stripping pump discharge valves (V20150, V20250, V20350, V20450 and
stripping isolation valves V20155, V20255, V20355 and V20455). Start
stripping/spray pump and adjust the return flow to the tank through the stripping
header pressure control valves (V20154, V20254, V20354, V20454).
e) Run up the forcing vaporizer
f) Set the boiler combustion control on FBO mode, not implemented in the sim.
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g) Start No.1 LD compressor depending on gas demand.
h) Set control of liquid supply to the vaporizer and LD compressor control to auto
mode.
Cargo tank pressure control, 'Gas Management System'
Pressure range at ballast and laden voyage:
Ballast voyage: 47-67 mbar/4,7-6,7 kPa
Laden voyage: 1,050-1,080 mbarA/105-108 kPaA
Set point of safety valve and alarm point
Set point of safety valve: Pressure 25 mbar
Vacuum -10 mbar
Alarms:
Vent valve open 230 mbar/23 kPa
Vent valve close 210 mbar/21 kPa
High pressure alarm 200 mbar (For./LNG Vap. trip)
FO back-up order ON 30 mbar/3 kPa
Low pressure alarm 10 mbar/1 kPa
Low Low pressure alarm 3 mbar/0,3 kPa
Set point controller:
Set point of tank press. Control 70 mbar
Set point of tank protection control 50 mbar
Min. gas flow of F/V control 1,400 kg/h (20- 100%)
Set temperature of BOG temp. control 40°C
Preferred FGV position of LD comp. control 87%
Permissible range: 10-230 mbar
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4.6 Discharging with Gas Return from Shore Introduction
During a normal discharge, only the main cargo pumps will be used and a quantity of cargo
will be retained on board for cold maintenance of the cargo tanks.
The quantity to be retained is according to voyage duration of ballast passage.
If the ship has to warm-up tanks for technical reasons, the stripping/spray pumps will be
used to discharge the remaining cargo on completion of the bulk discharge with the main
cargo pumps.
During cargo discharge, LNG vapour is supplied from shore to maintain pressure in the
cargo tanks.
Operation
The main cargo pumps discharge LNG to the liquid header and then to shore via the mid-
ship liquid crossover manifold connections.
After an initial rise, the pressure in the tanks decreases. It then becomes necessary to
supply vapour from shore via the manifold and crossover to the vapour header into the
cargo tank gas domes in order to maintain a pressure of 1,090 mbarA/109 kPaA.
Should the vapour return supply from shore be insufficient to maintain tank pressures,
other means of supplying vapour to the tanks, either by using the tank sprayers or the LNG
vaporizer, have to be used.
The boil-off gas heater should be prepared and lined up for use in order to avoid venting
cold LNG vapour through No.1 vent mast.
Note All LNG terminals prohibit venting of flammable gas.
Ballasting is undertaken concurrently with discharging. The ballasting operation is
programmed to keep the vessel within the required limit of draught, trim, hull stress and
stability following indications obtained from the loading computer.
During the discharge period, the ship is kept on an even keel. If it is required to empty a
cargo tank, the ship is trimmed according to terminal maximum draught by the stern to
assist in stripping the tank.
Each tank is normally discharged down to a level of about 0.37 m. The quantity being
retained in the tanks varies according to the length of the ballast voyage, the expected
elapsed time before loading and the volume of boil-off that is estimated to be burned in the
ship's boilers.
One pump is stopped at a level of approximately 1.0 m to avoid excessive turbulence at the
tank bottom which creates disturbance at the suction of both pumps.
If the vessel is to warm up one or more tanks for technical reasons, the ship shall be
trimmed according to the terminal's maximum draught. The cargo remaining in the tanks to
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be warmed up will be discharged to shore or to other tanks using the stripping/spray pumps
on completion of bulk discharge.
The stripping pump is run together with the remaining main pump until the main pump
stops on low discharge cut-out.
On completion of discharge, the loading arms and pipelines are purged and drained to No.
4 cargo tank and the arms are then gas freed and disconnected. Due to the manifold
configuration, it is necessary to purge the cargo lines using nitrogen at a pressure of at least
3 bar. This is done several times to ensure successful draining at the manifold connections.
The vapour arm remains connected until just before sailing if a delay is expected.
4.6.1 Preparations for Unloading
It is assumed that all valves are closed prior to starting.
Preliminary preparation:
a) Checks to be made prior to starting cargo operations.
Test remote operation of all tank discharge valves and manifold
ESD valves.
Test remote operation of ballast valves.
Test operation of Emergency Shut Down Systems (ESDS).
b) Safety precautions:
Ensure that hull water curtain at mid-ship is in operation.
Prepare fire fighting equipment, water hoses and protective clothing for use.
c) Cargo tanks level arms:
Switch on high level alarms.
d) Tank vapour domes - confirm that:
Open and lock in position valve V20170 (Tank No.1)
Open and lock in position valve V20270 (Tank No.2)
Open and lock in position valve V20370 (Tank No.3)
Open and lock in position valve V20470 (Tank No.4)
These valves must be locked open at all times when the ship has cargo on board,
unless a tank is isolated and vented for any reason.
e) : Open Vapour crossover block valve (V12079) -MD120 or MD121.
f) Cargo pumps:
Check insulation resistance of electric motor and related cables prior to supplying
power to the cargo pumps. (This can not be done in the Simulator)
g) Check connections of liquid and vapour arms.
Check communications with shore.
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Check ship/shore link.
h) Purge the manifold connections with nitrogen to be supplied from shore when shore
is ready.
If shore agrees:
i) Open Vapour manifold ESD valve (V12071)-MD120 or MD121
j) Liquid connections:
Open manifold ESD valves (V12011, V12021, V12031, and V12041).
k) Test Emergency Shut down System (ESDS) from shore and from the ship as
required. Re-open liquid and vapour ESD valves.
When it is agreed with shore, then the cool down may commence.
4.6.2 Liquid Line and Arm Cool down before Discharging
To cool down the cargo discharge lines proceed as follows: assuming that No.3
stripping/spray pump is being used, all manifold lines and the ESD valves are open, having
been purged with nitrogen.
a) Open No.3 stripping/spray pump discharge valve(V20350) from to 30%.
b) Open the Spray Cross Over & Spray Header Iso valves (V12050, V12751, V12752),
the Liq. Manif. Cool D. Vlv’s(V12061, V12063, V12065, V12067) at the port
manifold.
c) Start the stripping/spray pump.
d) When hard-arms and shore side lines have cooled down to -100°C, open Spray
Header Iso Vlv(V12053), CT 4 Spray Isolation Vlv & CT 4 Spray By Pass
Vlv(V20455, V20456) & CT4 Liq Iso Vlv (V20410), Liq Manif Double Shut Off
Vlv’s( V12013, V12023, V12033and V12043). This will now cool down the ship's
liquid line.
The cooling down is complete when the manifold and ship's liquid line is
approximately - 130°C.
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e) Stop the stripping/spray pump.
Shut valves (V12053, V20455, V20456, V12061, V12063, V12065 and V12067)
Open valves (V20353 and V20354) to drain the line back to No.3 tank.
f) When spray line has warmed up, close valves (V12050, V12751, V20353 and
V20354)
On completion of cool down and when shore is ready for discharge, proceed with
unloading.
4.6.3 Discharging
Before starting the main cargo pumps for No.2 and 3 tanks (these being the first tanks from
which to commence discharge) it is necessary to fill the discharge column with LNG to
avoid a pressure surge in the lines. The spray pump for each tank is used for this operation.
When the discharge column is filled up, the vessel in ready to start discharge.
Inform the Engine Control Room that a main cargo pump is about to be started.
After preparation for start of cargo pump, sequence consol is to be operated. This is found
in MD 503. Make sure the CTS is turned on.
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a) Push start at the first pump (normally port) at the automatic sequence control.
b) The discharge valve will open to 12% and the loading valve will open to 100%, then
the pump will start and the sequence goes into AUTO mode.
c) Start the next pump in the same way with the automatic sequence.
d) After steady condition of the two cargo pumps start the automatic discharge sequence
controller. The liquid isolation valve will open fully, and the filling valve will close.
e) Adjust the set point of the two cargo pump controllers to increase the discharge flow.
Normal set point is around 450 A.
The preferred sequence of cargo pump starting, to obtain a stable discharge operation is as
follows: Tank No.3 → Tank No.2 →Tank No.4 → Tank No. 1.
f) Monitor the tank's pressure.
g) Request the vapour return from shore and continue to monitor the pressure to
confirm that it stabilises.
h) As the discharge pressure and flow rate increase, continue to monitor the pipe work
and loading arms for leakage.
i) Adjust the pump set points of the pumps to obtain optimum performance as indicated
by current, discharge pressure and pump graph.
j) It is important to maintain the tanks at a pressure of at least 100 mbar/10 kPa in order
to avoid cavitation and to have good suction at the pumps. If the tank's pressure falls
to 60 mbar/6 kPa request shore to increase the gas return.
If shore can no longer supply gas return, the LNG vaporizer will have to be started to
restore the tanks pressure.
k) Start ballasting operations. Keep draught, trim and hull stresses within permissible
limits by controlling the various ballast tank levels. Refer to trim and stability data
provided.
l) Continue to monitor the tank's pressure and the cargo pump's current and discharge
pressures.
Stop the main cargo pumps in each tank at approximately 1.1 m in tank No.4 and 0.3 m in
tanks No. l, 2 and 3. The above data is for reference only. Actual liquid level to be stopped
cargo pump shall be depended on selection of coolant storage tank and amount of required
heel for cooling down before along side of loading terminal.
Requirement of LNG for cooling down operation refer to Guidance Manual for reference.
Quantities of cargo remaining in the tanks after stripping refer to Guidance Manual for
reference.
Throttle in the main cargo pump discharge valve to 40% by adjusting the set point before
stopping the pump. If two main cargo pumps are in use in a tank, when the level reaches
1.1 m, throttle in the discharge valve on one pump to 40% and stop that pump. This is in
order to reduce turbulence around the pump suction.
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On completion of the final tank and after all cargo pumps have been stopped:
m) Drain the liquid line.
n) Stop the gas return from shore.
If stripping of tanks ashore is required use the forward manifold connection.
Purging and Draining of Loading Arms
When the shore terminal is ready to inject nitrogen and the pressure at the manifold is 2.5
bar.
a) Close the liquid ESDS manifold valves.
Purging is carried out one line at a time.
b) Open manifold Liq Manif 1P Vlv (V12011). If the ESD is active it will have to be
shut off at Variable page 54000. Remember to activate it again when finished.
c) Close the valve when the pressure on the manifold drops to 0 bar. Repeat the
operation twice. For the last operation, shut the bypass valve at approximately 1 bar,
in order to eliminate the risk of liquid back flow from ship's liquid line.
d) Repeat procedure b) to c) for each line.
Open the test drain valve on the loading arm(not implemented in the sim) to ensure that
there is no liquid present. When the required amount of methane (usually less than 1%) is
showing at the drain valve, close the shore terminal ESDS valves.
e) When purging is completed, proceed with the disconnection of the liquid arms.
f) Complete the ballasting operations for final measurement and for sailing condition.
Shortly before departure:
g) Vapour line connection:
Purge the vapour line with nitrogen from the shore terminal at a pressure of 2 bar.
Close the Vapour Manif Port Vlv(V12071), confirm that the gas content is less than
1% by volume at the drain valve.
After confirming that the gas content is less than 1% volume:
h) Disconnect the vapour arm.
i) Prepare the cargo system for gas burning at sea.
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4.6.4 Ballasting
Operating Procedures
It is assumed that the main sea water crossover pipe is already in use, supplying other sea
water systems, e.g. the main circulating system, sea water service system and that the cargo
and ballast valve hydraulic system is also in service.
To Ballast the Ship
Caution
Incorrect operation of the ballast system will cause damage to the GRP pipe work.
Damage is generally caused by a pressure surge due to sudden changes in the flow and the
presence of air pockets. During the ballasting operation great care must be taken to ensure
that flow rates are adjusted smoothly and progressively. In particular, the pumping rate
should be reduced to one pump when filling only one tank and make use of the discharge to
sea to further reduce the rate before shutting the final tank valve.
It is necessary to eliminate the air pockets that may be present in the piping before
proceeding with the normal ballasting operations. This is achieved by running ballast into
either of the Deep ballast or No.1 ballast tanks.
It is important not to compress any air in the system. To achieve this, the valve admitting
water to the system should be opened last.
Fill by Gravity
a) Open the WBDS Valves (V40021 and V40011)-MD 400 on the deep ballast tanks.
b) Check that the BW crossover valves (V40103 and V40104) –MD 301 are open.
c) Open the ballast Aft Suction Valves (V40122 and V40112).(suction aft for Pump 1 &
2)
d) Open the Sea Chest Valve (V 40108)
e) Open the Suction Forward valves f (V40111 and V40121). When a flow has been
established to the deep ballast tanks, the WBDS Valves (V40021 and V40011) can
be shut.
f) Open the valve(s) on the tank(s) to be filled as per the ballast plan.
Deep tank port V40011
Deep tank starboard V40021
Deep tank centre V40001
No. l port V40012
No. l starboard V40022
No.2 port V40013
No.2 Starboard V40023
No.3 port V40014
No.3 starboard V40024
No.4 port V40015
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No.4 starboard V40025
Engine room port V40016
Engine room stb'd V40026
After peak tank V40109 (if applied)
Fore peak tank V40000 (if applied)
g) As each tank reaches the required level, open the valve of the next tank before
closing the valve of the full tank.
h) When all the tanks are at their correct level, shut the tank valves, ballast main valves
and gravity filling valves (V40021, V40011, V40022 and V40012).
Note
The speed when filling by gravity will sharply decrease as the level of the water line is
approached. The tanks will require to be filled to their capacity with the ballast pump.
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To Ballast the Ship Using the NO.l Ballast Pump
a) Open the valve(s) on the tanks to be filled as required by the ballast plan.
Deep tank port V40011
Deep tank starboard V40021
Deep tank centre V40001
No. l port V40012
No. l starboard V40022
No.2 port V40013
No.2 Starboard V40023
No.3 port V40014
No.3 starboard V40024
No.4 port V40015
No.4 starboard V40025
Engine room port V40016
Engine room stb'd V40026
After peak tank V40109 (if applied)
Fore peak tank V40000 (if applied)
b) Open the sea water crossover valves (V40103 and V40104)-MD401
c) Open sea water suction valve to the No.1 pump (V40112).
d) Start the No. 1 ballast pump.
e) Open the pump discharge valve (V40113).
f) As each tank reaches the required level, open the valve of the next tank before
closing the valve of the tank which is full.
g) Close the final tank valve when the required level is reached.
h) Close the pump discharge valve (V40113) and stop the pump.
i) Close all other valves.
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To Ballast the Ship Using the N0.2 Ballast Pump
a) Follow operations a) to b) inclusive.
b) Open sea water suction valve (V40122) to the No. 2 ballast pump.
c) Start the pump.
d) Open pump discharge valve (V40123).
e) As each tank reaches the required level, open the valve of the next tank before
closing the valve of the tank which is full.
f) Close the pump discharge valve (V40123) and stop the pump.
g) Close all other valves.
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4.7 Pre-Dry Dock Operations
During the last loaded voyage before refit, a full inner hull inspection of all ballast tanks
and cofferdams must be carried out and a report sent to the Ship-owner company. This is a
Class requirement, to confirm the absence or presence of any cold spots. A Class surveyor
may attend the last discharge before refit, to inspect selected ballast tanks and cofferdam
spaces.
The ship will carry out a maximum discharge. The tank levels should be reduced to the
point where the main cargo pumps trip on low current. Then, using the stripping/spray
pumps, remove the last of the cargo until they also trip on low current. The ship will then
proceed to sea and commence the warm up, inerting and aerating, prior to arrival at the
refit yard.
4.7.1 Stripping and Line Draining
It is assumed that the cargo tanks have been discharged to their maximum with the main
cargo pumps which have been shut down. Discharge via the port side manifold.
Note Stripping/spray pump should be started at higher level than minimum start level (300 mm)
for the pump.
a) At manifold crossover:
Open valve 2P Liq Manif Cool Down Vlv(V12063)-MD120 or MD121
Close Liq Manif Shut Off Vlv’s (V12013, V12023, V12033, V12043) and 1P,3P &
4P Liq Manif ESD Vls (V12011, V12031, V12041)
b) Stripping/spray header:
Open Isolating Valves (V12053, V12751, V12751 and V12055)- MD 121.
Open stripping/spray header to liquid manifold crossover Vlv (V12050).
c) At required tanks:
Open stripping/spray discharge valves from individual tanks to give the required
performance, (V20150, V20250, V20350 and V20450).
Start stripping/spray pump(s).
On completion:
d) Stop final pump:
Close 2P Liq Manif Cool Down Vlv (V12063) and Liq Manif 2p ESD Vlv(V12021)
Open valves Spray Iso Vlv & Spray Return Vlv (V20454 and V20455)-MD204, to
drain down the header line to tank No.4.
e) When completed:
Leave open Spray header Iso. Valves (V12055, V12053, V12752 and V12751) in
order to warm up the line. When the line has warmed up, close the valves.
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Purging and Draining of Loading Arms
Purging is carried out one line at a time.
When the shore terminal is ready to inject nitrogen and the pressure at the manifold is 2.5
bar:
a) Open 1P manifold valve (V12011). If the ESD is active it will have to be shut of at
Variable page 54000. Remember to activate it again when finished.
b) Close the bypass valve when pressure on manifold drops to 0 bar.
Repeat the operation a further twice. On the last operation shut the bypass valve at
approximately 1 bar, in order to eliminate the risk of liquid back flow from ship's
liquid line.
Open the test drain valve on the loading arm to ensure that there is no liquid present. When
the required amount of methane (usually less than 1%) is showing at the drain valve, close
the shore terminal ESDS valves.
c) When purging is completed, proceed with the disconnection of the liquid arms.
d) Complete the ballasting operations for the final measurement and for the sailing
condition.
Shortly before departure:
e) Vapour line connection:
Purge the vapour line with nitrogen from the shore terminal at a pressure of 2 bar.
Close Vapour Manif. port ESD valve (V12071) and Vapour Cross over Block
Vlv(V12079)–MD 120 or MD 121.
Confirm that the gas content is less than 1% by volume at drain valve.
f) After confirming that the gas content is less than 1% volume:
Disconnect the vapour arm.
g) Prepare the cargo system for warming up the cargo tanks.
4.7.2 Tank Warm Up
Tank warm up is part of the gas freeing operations carried out prior to a dry docking or
when preparing tanks for inspection purposes.
The tanks are warmed up by recirculation heated LNG vapour. The vapour is recirculated
with the two HD compressors and heated with the cargo heaters to a preset value. (1st
stage: 0°C, 2nd stage: 75°C).
In a first step, hot vapour is introduced through the filling lines to the bottom of the tanks
to facilitate the evaporation of any liquid remaining in the tanks. In a second step, when the
temperatures have a tendency to stabilize, hot vapour is introduced through the vapour
piping at the top of the tanks.
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Excess vapour generated during the warm up operation is vented to atmosphere when at
sea, or returned to shore if in port. (The instructions that follow apply to the normal
situation, venting to atmosphere at sea).
The warm up operation continues until the temperature at the coldest point of the
secondary barrier of each tank reaches 5°C.
The warm up operation requires a period of time dependent on both the amount and the
composition of liquid remaining in the tanks and the temperature of the tanks and
insulation spaces. Generally, the warm up will require about 48 hours after vaporizing the
remaining liquid.
Initially, the tank temperatures will rise slowly as evaporation of the LNG proceeds,
accompanied by high vapour generation and venting. A venting rate of approximately
8,000 m3/h at 60% can be expected. On completion of evaporation, tank temperatures will
rise rapidly and the rate on venting will fall to between 1,000 and 2,000 m3/h at steadily
increasing temperatures.
Rolling and pitching of the vessel will assist evaporation. Temperature sensors at the aft
end of the tank give a good indication of the progress of warm-up. Slight listing of the
vessel will assist in correcting uneven warm-up in any one tank.
Gas burning should continue as long as possible, normally until all the liquid has
evaporated, venting ceased and tank pressures start to fall.
Preparation for Tank Warm up
a) Strip all possible LNG from all tanks.
b) When discharging the final cargo, remove the maximum LNG with the
stripping/spray pumps.
c) If discharge of LNG to shore is not possible, vaporize it in the LNG vaporizer and
vent the vapour to the atmosphere through the No.1 vent mast.
d) If venting to the atmosphere is not permitted, the vapour must be burned in the
boilers.
e) For maximum stripping, the ship should have zero list and should be trimmed down
at least 2.6 m by the stem.
f) Run the stripping pumps until trip by low current.
g) Remove the emergency pump that may have been placed in a cargo tank.
Operating Procedure
During the tank warm up, gas burning may be used by directing some vapour from the
heater outlet, to the boilers and by controlling manually this operation.
a) Install the spool piece Liquid Line/ Vapour Line (F12002) and open the
Vapour/Inertgas to Liqid Header Vlv (V12702) to discharge heated vapour to the
liquid header.
b) Prepare LD and HD gas heaters for use.
c) Adjust the temperature set point to between 20 and 25°C.
d) Prepare No.1 and 2 HD compressors for use.
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e) At vent mast No.1, open Vapour Header Vent Shut of valve (V12772)- MD121.
f) Manually adjust the pressure by use of the Vapour Header Vent Control Vlv
(V12771)- MD330 to 160 mbar/16 kPa.
g) Open the Compressor Suction valve (V30601)- MD 300, the compressor(s) suction
from the vapour header.
h) Open the compressor inlet and outlet valves (V31907, V31909, V31910 and
V31912)- MD 319.
i) Open the heater inlet and outlet valves (V31913, V31914, V31915, V31916)- MD
319, and the L/D, H/D Comp disch cross valve (V30920).
j) Open the vapour valves on each tank:
CT 1 Vapour Valve (V20170)-MD201
CT 2 Vapour Valve (V20270)-MD202
CT 3 Vapour Valve (V20370)-MD203
CT 4 Vapour Valve (V20470)-MD204
k) Open the filling valves on each tank:
CT 1 Liquid Filling Vlv (V20100) and CT 1 Liquid Isolation Vlv (V20110)-MD201
CT 2 Liquid Filling Vlv (V20200) and CT 2 Liquid Isolation Vlv (V20210)-MD202
CT 3 Liquid Filling Vlv (V20300) and CT 3 Liquid Isolation Vlv (V20310)-MD203
CT 4 Liquid Filling Vlv (V20400) and CT 4 Liquid Isolation Vlv (V20410)-MD204
l) Start both HD compressors and run the compressors in manual. Gradually increase
flow by the inlet guide vane position.
m) Monitor the tank pressure and adjust the compressor flow for maintaining the tank
pressure at about 160 mbar/16 kPa. It is possible to control tank pressure by (V12771
via valve V12772). Pressure build-up line may be used to exhaust excess vapour to
No. l vent mast through Pressure B. Up to Vent/Liq Conn Vlv (V12770). Liquid
main shall be normally used for warming up operation.
n) Check that the pressure in the insulation spaces, which have a tendency to increase,
remains inside the preset limits.
o) Monitor the temperatures in each tank and adjust the opening of the filling valve to
make uniform the temperature progression in all the tanks.
p) After twenty/twenty-four hours, the temperature progression slows down.
Eventually, the procedure of the second method described below, may be more
efficient.
q) Purge the emergency pump column with N2 to remove liquid in the column.
r) At the end of the operation, when the coldest temperature of the secondary barrier is
at least +5°C, or before switching to the second step, stop and shut down gas burning
system if used. Stop both HD compressors, shut the filling valves on all tanks and
restore the normal venting from the vapour header.
s) As alternative operation, the target temperature in the cargo tank is at least +5°C
when inerting with hot inert gas is applied. In this case total operating time for
warming up and inerting has taken approximately 58 hours.
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4.7.3 Inerting
After the tanks have been warmed up, the LNG vapour is displaced with inert gas.
Inert gas from the inert gas plant is introduced at the bottom of the tanks through the LNG
filling piping. Gas from the tanks is vented from the top of the tank through the vapour
header to the vent mast No.1, or to shore if in port. (The instructions which follow apply to
the normal situation, venting to the atmosphere at sea.)
Inerting is necessary to prevent the possibility of having an air/LNG vapour mixture in the
flammable range. The operation is continued until the hydrocarbon content is reduced to
less than 1.5%. The operation requires about 20 hours.
In addition to the cargo tanks, all pipe work and fittings must be gas freed. This is best
done with inert gas or nitrogen, while the plant is in operation for gas freeing the tanks.
Operating Procedure
a) Prepare the inert gas plant for use in the inert gas mode.
b) Open the vapour on each tank
CT 1 Vapour Valve (V20170)-MD201
CT 2 Vapour Valve (V20270)-MD202
CT 3 Vapour Valve (V20370)-MD203
CT 4 Vapour Valve (V20470)-MD204
c) At vent mast No.1 open valve (V12772)-MD121 and adjust the set point to 2.0 bar.
d) Install the Hold Gas Free/ liquid Line spool pieces( F12001)-MD121 connecting the
IG line to the LNG liquid header. Open the Vapour/ Inert Gas to Liq Head valve
(V12702).
e) Open the filling valves each tank
CT 1 Liquid Filling Vlv (V20100) and CT 1 Liquid Isolation Vlv (V20110)-MD201
CT 2 Liquid Filling Vlv (V20200) and CT 2 Liquid Isolation Vlv (V20210)-MD202
CT 3 Liquid Filling Vlv (V20300) and CT 3 Liquid Isolation Vlv (V20310)-MD203
CT 4 Liquid Filling Vlv (V20400) and CT 4 Liquid Isolation Vlv (V20410)-MD204
f) Start the inert gas generator and run it until the oxygen content and dew point are
acceptable.
g) On the dry air/inert gas discharge line, open the IG Main line Supply valve(V35042)
-MD350, supplying inert gas to deck.
h) Monitor tank pressures and adjust the opening of the fill valves to maintain a uniform
pressure in all the tanks. Ensure that the tank pressures are always higher than the
insulation space pressures by at least 10 mbar/1 kPa, but that the tank pressures do
not exceed 180 mbar/18 kPa above atmospheric pressure. In any case, during gas
freeing the pressure in the tanks must be kept low, to maximize the piston effect.
i) Approximately once an hour, take samples of the discharge from the vapour dome at
the top of each tank and test for hydrocarbon content. Also verify that the oxygen
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content of the inert gas remains below 1%. by testing at a purge valve at the filling
line of one of the tanks being inerted.
j) Purge for 5 minutes all the unused sections of pipelines, machines, equipment and
instrumentation lines.
k) When the hydrocarbon content sampled from a tank outlet falls below 1.5%, isolate
and shut off the tank. On completion of tank and pipeline inerting, stop the inert gas
supply and shut down the inert gas plant. Reset the valve system for aerating.
l) If the tanks remain inerted without aerating, shut Vapour Head Vent Shut Off valve
(V12772), raise the pressure to 100 mbar/10 kpa, then shut off the tanks.
Warning
If any piping or components are to be opened, the inert gas or nitrogen must first be
flushed out with dry air. Take precautions to avoid concentrations of inert gas or nitrogen
in confined spaces which could be hazardous to personnel.
4.7.4 Aeration
Introduction
Prior to entry into the cargo tanks the inert gas must be replaced with air.
With the Inert Gas and Dry-Air System in Dry-Air production mode, the cargo tanks are
purged with dry air until a reading of 20% oxygen by volume is reached.
Operation
The Inert Gas and Dry-Air System produces dry air with a dew point of -45°C.
The dry-air enters the cargo tanks via the vapour header, to the individual vapour domes.
The inert gas/dry-air mixture is exhausted from the bottom of the tanks to the atmosphere
at No.1 vent mast via the tank filling pipes, the liquid header, and spool piece and Vapour
Line/ Liquid Line valve (V12000). During aerating, the pressure in the tanks must be kept
low to maximize a piston effect.
The operation is complete when all the tanks have a 20% oxygen value and a methane
content of less than 0.2% by volume (or whatever is required by the relevant authorities)
and a dew point below -40°C.
Before entry, test for traces of noxious gases (carbon dioxide less than 0.5% by volume,
and carbon monoxide less than 50ppm) which may have been constituents of the inert gas.
In addition, take appropriate precautions as given in the Tanker Safely Guide and other
relevant publications.
The pressure in the tanks is adjusted to 120 mbar/12 kPa.
Aeration carried out at sea as a continuation of gas freeing will take approximately 20
hours.
Warning
Take precautions to avoid concentrations of inert gas or nitrogen in confined spaces,
which could be hazardous to personnel. Before entering any such areas, test for sufficient
oxygen > 20% and for traces of noxious gases; CO2 < 0,5% and CO < 50 ppm.
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Operating Procedure
a) Prepare the inert gas plant for use in the dry-air mode.
b) Install the Vapour Line/Liquid Line spool piece ( F12000) for venting the mixture of
inert gas/dry-air from the liquid header. Adjust the Vapour Header Vent Ctrl Vlv
(V12771) at a pressure of 160 mbar/16 kPa above atmospheric pressure.
c) Open the filling valves on each tank
CT 1 Liquid Filling Vlv (V20100) and CT 1 Liquid Isolation Vlv (V20110)-MD201
CT 2 Liquid Filling Vlv (V20200) and CT 2 Liquid Isolation Vlv (V20210)-MD202
CT 3 Liquid Filling Vlv (V20300) and CT 3 Liquid Isolation Vlv (V20310)-MD203
CT 4 Liquid Filling Vlv (V20400) and CT 4 Liquid Isolation Vlv (V20410)-MD204
d) Open the vapour valves on each tank.
CT 1 Vapour Valve (V20170)-MD201
CT 2 Vapour Valve (V20270)-MD202
CT 3 Vapour Valve (V20370)-MD203
CT 4 Vapour Valve (V20470)-MD204
e) Fit the spool piece Hold Gas Free/Liquid Line (F12001) and Liquid Line/Vapour
Line (F12002), and open the IG Main Line Ssupply Vlv( V35042) on the dry-
air/inert gas discharge line on MD350.
f) Start the dry air generator.
g) Open the valves (V12702)-MD121, V30601 and V30603 (MD300) to supply dry air
to the vapour header.
h) Observe the tank pressures and insulation space pressures, to ensure that the tank
pressures are higher than the space pressures by 10 mbar at all times.
i) Approximately once an hour, take samples from the filling pipe test connections to
test the discharge from the bottom of the tanks for oxygen content.
j) When the oxygen content reaches 20%, isolate and shut in the tank.
k) When all the tanks are completed and all piping has been aired out, raise the pressure
to 100 mbar in each tank and shut the filling and vapour valves on each tank. Restore
the tank pressure controls and valves to vent from the vapour header.
l) During the time that dry air from the inert gas plant is supplied to the tanks, use the
dry air to flush out inert gas from vaporizers, compressors, gas heaters, crossovers,
pump risers and emergency pump wells. Piping containing significant amounts of
inert gas should be flushed out. Smaller piping may be left filled with inert gas or
nitrogen.
m) During the time a tank is opened for inspection, dry air will be permanently blown
through the vapour header line in order to prevent the entry of humidity from the
ambient air.
n) The insulation spaces are to be maintained in a vacuum condition during cargo tank
maintenance.
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4.7.5 Limiting Factors
Temperature It is vital that the tank temperatures are kept as close as possible to the temperature of the
cargo since this will hamper the loading and/or discharging time.
Berth Time
Some terminals limit berth time. In order to fully outturn cargo it may be necessary to
reduce ballasting time by taking on reduced ballast alongside and ballasting in river
passage, or ballasting during discharge.
Stress The vessel must not exceed maximum stress limits (harbour condition) at any time during
cargo operations.
The vessel may also have operating constraints such as: leaking pipelines, failing valves,
inoperative pumps. These difficulties may be overcome during the discharging by a
carefully planned operation which compensates for them.
4.7.6 Discharge Plans
These plans are to be prepared prior to the vessel's arrival and should include instructions
on:
- Cargo stowage and quantity.
- Discharge rate.
- Permissible pump pressure.
- Approximate discharge time.
- Ventilation method.
- Emptying of loading arms and lines.
- Ballasting.
- Method of how to stop cargo pumps and to raise alarm in case of fire or pollution.
Copy of the discharge plan should be given to Terminal representative.
4.7.7 Cargo Handling Training from the Graphic Desk-top
Cargo handling training with the CHS LNG-M can be performed from the graphic desk-top
by means of mimic pictures or from the cargo consoles by means of the cargo operation
panels. All operations are similar in both versions, the only difference is the presentation
method to the trainee.
In the case of the graphic desk-top presentation it is essential to have the correct mimic
diagram available. The directory pages have to be used for such.
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4.7.8 Picture Directory General
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4.7.9 Picture Directory LM
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Layout
As the LNG-M is equipped with two pumps in each tank, there is no central cargo pump
room. From the manifold all cargo and vapour is distributed to/from the tanks via the
network of cargo/vapour deck lines and cargo/vapour crossover lines.
Commands controlled by the use of the mouse buttons:
- Start/Stop Pumps
- Open/Close Valves.
Trim
The trim is changed by changing the load moments of the fore and aft halves of the ship.
NOTE: This change may cause another load distribution which results in
different distribution of shear forces, bending moments and hull deflection.
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Heel (list)
The heel (list) is changed by changing the load moments to/from the side ballast tanks.
Manifold
Only the pressure at the manifold connections can be monitored just as you would onboard
a real ship.
These figures will give information about the functioning of the pumps, leaking
connections etc.
The flow will be possible to monitor at the different tank pictures.
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4.7.10 Pump Flow
The pump flow is generated by starting the pump and opening the discharge valve(s). This
ship requires that the cargo pump system is started and controlled by a sequence controller.
The flow rate will depend on:
- The pump speed
- The flow resistance caused by pipe characteristics
- Valve characteristics and valve settings
- The suction head (cavitation)
- The liquid density
- Tank pressure
Open/Close The discharge valve setting is controlled by means of clicking on the screen at the
individual tank picture.
The pump flow and the pump pressure are controlled by the PID controller.
Cavitation
If the suction head is too low, the pump will start cavitation. The critical suction head for
cavitation will depend on the vaporizing pressure of the liquid to be pumped and the
current NPSH (Net Positive Suction Head) of the pump. Cavitation will occur on the cargo
pumps, but not on the ballast pump.
Stopping
The pump is stopped by Automatic Sequence controller. Depending on stop mode, the
pump will be stopped by the controller, or will have to be stopped manually. After the
electric supply is stopped, the pump is brought to a complete stop after a while.
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4.7.11 Ballasting
The LNG-M is fitted with a double bottom in which ballast tanks are located.
These tanks are interconnected by means of a separate set of ballast water lines.
The ballast water pumps (3) are located in the ballast pump room (picture MD 401).
Ballasting is a process where sea water is loaded into segregated ballast tanks to ensure
proper immersion and to provide good manoeuvring and stability characteristics. In order
to lessen hull immersion and thus reduce fuel consumption, minimum quantities of ballast
should be taken. However, the quantity must be sufficient to submerge the propeller,
maintain vessel manoeuvrability, to avoid excessive vibration, to operate within approved
stress limits and to retain sufficient bow immersion.
Ballast should be evenly distributed to minimize stress. Tanks should be either empty or
full. Partially full or slack tanks should be avoided.
Start-up The appropriate ballast tanks are chosen and the ballast tank valves are opened by clicking
on the symbols.
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Sounding During the ballast operation the tank soundings can be monitored on the level indicator.
The total content can be viewed on the Bunker/consumables picture (MD 103).
Heel/Trim Furthermore the changes in heel and trim of the vessel will be shown on the indicators on
the same mimic picture.
Pumps The pump room can be viewed by clicking on the symbol for the ballast pump room (MD
401).
Starting Procedure The pumps can be started/stopped by use of the left/right mouse buttons.
The following is normal start procedure for centrifugal type pumps:
- Close the discharging valve.
- Open the suction valve.
- Fill the pump with liquid.
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- Start the pump.
- Open the discharging valve.
Segregated Ballast
The Segregated Ballast Tanks (SBT) is completely separate from the cargo and fuel system
and is permanently allocated to the carriage of ballast water only. SBT require separate
pumps and pipes dedicated to handling ballast water only.
Segregated ballast may be retained on board in order to restrict the air draught if it is
necessary because of weather conditions or restrictions of loading arms or shore gangway.
However, care must be taken not to exceed the maximum draught for the Terminal or for
hull stress.
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4.7.12 Inert Gas System
From the Inert Generator and distribution pictures the operator can carry out and control
the following operations:
- Operation of inert gas generator.
- Inerting of cargo tanks.
- Ventilation (gas freeing) of cargo tanks
Start-up Procedures The Inert generator is ready for operation as long as the burner is on.
1. Ensure that the oxygen analyzer and Inert Gas pressure indicator are working.
2. Open valves and start scrubber pump.
3. Start the blowers and open inlet valves.
4. Start burner by pushing "on" after opening fuel supply.
5. Open Inert Gas main valve on deck.
6. The Inert Gas-plant is now ready to deliver gas to the cargo tanks or the cargo
holds.
Shutdown Procedures 1. Close the Inert Gas main valve on deck.
2. Shut down the burner.
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3. Close the blower discharge valves and stop blowers.
4. Keep full water supply on the scrubber for a minimum of 1 hour.
Inerting/Venting The operator can choose inerting or air venting by either starting the burner or leaving the
burner off.
NOTE: Before commencing ventilation by fresh air, the tanks must be measured
for hydro carbon gas concentration. If the readings indicate gas
concentration above 2 % by volume, the tanks are to be purged with Inert
Gas until the hydrocarbon gas concentration has decreased to less than 2
% by volume. This will ensure that the atmosphere is kept below the
lower explosion limit throughout the ventilation process.
Inert Press/Flow The current Main Line Inert Gas Pressure and Flow can be read from separate indicators on
the Inert Gas plant picture.
Distribution
From the Inert Gas plant there is a network of deck lines to all tanks and holds for the
distribution of Inert Gas.
Tank Pressure
The tank pressure is indicated at each tank and should be closely watched in order to avoid
over-pressure or under-pressure when discharging or loading cargo.
It can also happen that due to temperature change of the cargo a pressure difference is
created which will have to be compensated by either the spray system or the H/D
compressor(s).
Pressure
During cargo operations the tank pressures are shown in order to monitor the variations.
Vapour return lines are connected to shore at the manifold so as to take away excess
vapour.
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4.8 Stress and Stability Calculations
For the purpose of calculating permissible stresses and stability the Cargo Handling
Simulator both in full-mission as well as desk-top version is equipped with both an
"online" and an "offline" LoadMaster load computer.
4.8.1 Online Calculations
During simulation the online LoadMaster load computer will constantly calculate and show
in the respective mimic pictures the results that occur from loading, discharging, ballasting
or any other changes in the vessels weight distribution.
The relevant mimic diagrams are given in the picture directory nos.:
104 Shear Forces
105 Bending Moment
106 Deflection
107 Stability
These can be called up in the normal way, but not be influenced during the running of the
simulation. Actual weights, volumes and levels can be read in the mimic diagrams:
101 Cargo Tank Overview
102 Ballast Tank Overview
103 Bunker/Consumables
Care should be taken when running simulation in fast speed. As the amount of calculations
for the stress and stability are numerous there can be a back lag in the updating of the
pictures in the mimic diagrams. This holds the danger of temporary inaccurate values being
represented in the various graphs thus resulting in wrong conclusions being drawn.
After resuming normal speed simulation again the correct graphical representations will
appear again on the mimic diagram displays.
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4.8.2 Offline Calculations
In order to perform preloading/discharging calculations as is common practice to ensure no
critical limit values are exceeded during the loading or discharging operations the system is
equipped with an offline LoadMaster load computer.
This feature is represented by the mimic diagrams nos.
601 LM Cargo Tank Overview
602 LM Ballast Tank Overview
603 LM Bunker/Consumables
604 LM Shear Forces
605 LM Bending Moment
606 LM Deflection
607 LM Stability
Once the cargo loading or discharging plan has been drawn up and the tank sequence
chosen, the values can be entered in the cargo bar graph and tank diagrams. As this can be
done step by step and tank by tank it is possible to monitor and check the values of shear
force and bending moment against the allowable limits indicated in the respective screens.
The input of the values for cargo should be done on the mimic diagram of the cargo
bargraph. Underneath each tank a changeable value for "% full" is given. A value entered
here will result in an indicative bar in the tank.
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Switching then to the shear force and bending moment graphs will show the actual status
blue curve. This status curve can then be compared with the yellow harbour condition and
the red open sea condition curves.
If at any stage the yellow curve should be exceeded and the simulator is in harbour
condition an alarm will sound and a flashing indicator will appear at the bulkhead
concerned. The same will happen if the simulator is in sea condition for exceeding of the
red curve.
Damage Stability
To check the vessels damage stability it is possible to simulate how the stability will
become if you get water ingress into the engine room or into hold spaces. This can be seen
at the off line load calculator.
In the Variable page Directory you can find a line called “Damage Stability”.
From here you can choose which compartment there is damage to. If the damage is in the
engine room, you can set the amount of water inside.
If the damage is in the ballast tanks the water level in the damaged tank will be decided
by the actual loading condition you have in the Load Calculator
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5. APPENDIX A The following pages will describe operation of the mouse and the keyboard, the old
Instructor-, the Alarm- and the Operator sections which is included in the simulator.
This can be used if the simulator is running without the Neptune Instructor System
5.1 Instructor Station
The instructor station includes the following equipment:
- Computer
- Hard disk
- Monitor
- Mouse and keyboard
- Printer
The instructor has full access to the model.
5.2 Student Workstation
The student workstation includes the following equipment:
- Computer
- Monitor
- Mouse and keyboard
- Printer (depending on configuration)
The student station has instructor controlled limitations to the model.
5.3 Printer
The printer is used as an alarm and event log.
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5.4 The Functions of the Major Facilities
5.4.1 Computer System
The instructor workstation manages the software and use of peripherals, simulation
components and, allows real time simulations and recording, as well as exercise replay.
The real time simulation functions will provide the following:
- Operation of workstations.
- Operation of instructor station.
- Recording of:
- Simulation data
- Student action data
The simulating software is written in C language running under the WINDOWS operating
system.
The instructor workstation and the other simulator and computing units will be linked
using Ethernet, which is a Local Area Network (LAN). This LAN enables the computers to
share the disk systems using the Network File System (NFS) and a computing task may be
routed to any computer having spare capacity. Future extensions will easily be integrated
into the existing system because of the standardised LAN communication.
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5.4.2 Instructor Workstation
The instructor workstation and the student workstations are connected together in Ethernet
and are exactly of the same type. All workstations have a standard mouse and keyboard
with dedicated instructor function-keys.
The instructor workstation will be the host computer and act as a server for all other
computers. The instructor functions are divided in two groups, the primary- and the
secondary functions.
The primary functions are:
- Start of simulator
- Stop simulator
- Select scenario
- Run simulator
- Freeze simulator
The secondary functions are:
- Change scenario
- Alphanumeric pages of variables
- Alphanumeric pages of malfunctions
- Alphanumeric pages of alarms
- Operating conditions
- Snapshots
- Replay
- Simulation speed (relative real time)
- Sound control
- Inhibit control of alarm systems
- Access control of input
The instructor has full control of the simulator and the training session through the above
listed functions. He can whenever he likes, change the environment during a scenario, and
evaluate the operators handling of the situation.
The log printer acts as:
- Event log
- Alarm log
- Malfunction log
The instructor can select each of these logs. If more than one is selected, all the requested
events are printed out in chronological order. These logs are also available
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5.4.3 Student Workstation
The student workstation is provided as the central training device. The following
familiarisation, procedural training and experience will be possible:
- Familiarisation with piping and equipment layout
- Studies of process optimising and fuel economy
- Separately studies and tuning of control loops; temperature, level and pressure
- Familiarisation with the load calculator
- Preparation for port arrival/ departure
- Preparation dock set/ departure
- Preparation for loading and discharging
- Preparation for sea voyage
During each of these conditions, a number of systems must be tuned to function properly.
Economic and safe operation of the ship is based on reliable equipment and skilled officers
who can take correct decisions at the right time. These simulations are partly made possible
by a well developed man-machine interface.
The system design facilities in the KONGSBERG MARITIME CARGO HANDLING
SIMULATOR concept, has taken all these factors into consideration during design and
engineering. The result is a comprehensive system that allows the students to work under
conditions close to real ship environment.
The student workstation may be run in the full simulation or part task simulation mode:
- In full simulation mode the workstation reflects the behaviour of the total current
simulator scenario for the student to observe and to influence or change.
- When operated in part task mode the student has full control of the simulation
program and scenario he has selected to run, completely independent of the simulator
itself.
5.4.4 Printer
The printer acts as:
- Event log
- Alarm log
- Malfunction log (only accessible by instructor)
Each of these logs can be selected by the student/instructor. If more than one is selected, all
the requested events are printed in chronological order.
5.4.5 Mouse
Connected to the Desktop station is a standard mouse. The mouse moves the cursor on the
screen.
Function of left button is: START pump/compressor or open valve.
It will also utilise operation of buttons in the model drawings, retrieval of new sub systems
or call display windows.
The push button on the right hand side, is used for execution of commands to STOP
pumps/compressors, CLOSE valves or reset of malfunctions introduced.
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5.4.6 Keyboard
The keyboard is used to:
- change set point of controllers
- call new model drawings
- change variables in the variable list
- change intensity of malfunctions
- type text strings in connection with creation of scenarios and initial conditions
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5.5 Operation
5.5.1 Function buttons & blue pages
The functions are only accessible when in Instructor mode (all except the RUNNING,
FREEZE, STOP and SCENARIO which can be selected from Operator Mode).
Keyboard Key Function
F1 Run simulation
F2 Freeze simulation
F3 Stop the simulator
F4 Make Snapshot
F4+shift Snapshot Directory
F5 Operating Condition
F6 Scenario
F6+shift Init Condition
F7 Recall Picture
F7+shift Mark Picture
F8 Alarm Log Summary Display
F8+shift Page Acknowledge
F9 Malfunction List
F10 Variable List
F11 Alarm List
F12 Alarm Silence
F12+Alt Toggle window decorations
Home Directory
Home+shift Select Picture
Page Up Previous picture
Page Down Next picture
Ctrl + P Print hardcopy to default printer
Ctrl + L Display Message Log
This list may vary dependent of type of Desktop/Operating system and age of installation.
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5.5.1.1 Scenario (F6)
A scenario is a predefined list of actions and or malfunctions that will take place during the
simulation when Running is activated. Almost any action and malfunction available in the
simulator can be included in a scenario. The scenario push button, when activated, displays
a directory of the scenarios already created. This feature allows the instructor to load an
already existing scenario or creating a new one.
To create a scenario, enter scenario by pressing SCENARIO button. Prompts on the screen
will guide you through the preparation required. Point and click the software button
CREATE at the lower part of the screen, and then point and click at the position where to
locate the new scenario (S01 to S20).
After prompt and having typed the name of the scenario, press ENTER. A prompt will then
ask for an INITIAL condition which will be the basis for the scenario. Type in the
appropriate initial condition (101 to 160) and press enter. If accepted, prompt line will add
initial condition name and colour changes.
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5.5.1.2 Initial Condition Directory (Shift+F6)
An Initial Condition is a specific condition of the total simulation plant, comprising a
complete set of data and variables. When activating the Init Condition push button, a list of
all created initial conditions appears.
To store an initial condition to later use, the following procedure must be carried out.
Press Freeze. Choose display INIT CONDITION and click on software button CREATE.
Type in name of the exercise to be saved in one of the vacant locations and press enter.
During the process of creating the exercise its name starts flashing. After few seconds, the
new initial condition is made, and the simulation can proceed by pressing Running.
To load an Init Condition, press Freeze and click with left mouse button, on the Init
Condition selected. Loading is completed when the name of the exercise turns steady.
From this step the simulation can start on condition that Running is pressed.
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5.5.1.3 Operating Condition (F5)
This function allows the instructor to vary the external parameters, the ship dynamics as
well as internal processes. In addition the instructor can introduce fixed values of selected
variables.
By pressing this button, an Instructor picture called Operating Condition is displayed. This
picture is divided into several groups where the following parameter can be altered.
Access: Different access levels can be set.
Sound Control: Allows the Instructor to control the volume of the Sound System in the
Cargo control room where the full-mission simulator is installed if applicable.
Fixed process: Instructor can introduce fixed process values for some of the major
parameters in the systems. Independent of consumption, the fixed values will remain the
same. The fixed process is valid for the following systems:
Boiler isolation sets the steam pressure to cargo pumps at 15 bar.
Inert gas fixed sets the flue gas oxygen content to 3,5 %
Inhibit: The demand for realism with regard to what kind of alarm indication to be most
appropriate, depends on the training situation and the number of students present. The
functions are disabled when pressed. For the maximum version, the following functions are
available.
Alarm Horn (and alarm lamp), operational only.
Keyboard Buzzer.
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Log printer 1: Determines which events or alarms to be logged on the printer. If required,
all buttons can be activated. Press the appropriate push button(s) to satisfy the exercise to
be run. The actual event/ alarm is printed together with the time it took place.
The choice is as follows:
Alarm: In general all alarms that occur are printed.
Event: All actions from the student are printed, like start/stop of pumps, opening or
closing valves.
DataChief: All actions from the Electrical Power Plant will be printed. (If connected)
Malfunction: Setting and Resetting of Malfunctions.
Instructor: Not in use
-Log printer 2: For future use.
-Log printer 3: For future use.
Snapshot: A snapshot represents the condition of the simulation at the time it was created.
If the student fails to run the simulation properly and for instance this results in a black out
or any other abnormal condition, the situation can be corrected by simply retrieve a
snapshot prior to the "accident". Each Snapshot is identified by the time it was created,
manually or automatically. When generated automatically, the interval between each
snapshot has to be specified. See also description of Snapshot push button.
5.5.1.4 Malfunction Editor
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Gives ability for editing and creating of malfunctions prior to start or during the simulation.
It is a prerequisite that a scenario is loaded into the desktop. To create a malfunction, click
on software button CREATE and click at one of the buttons M01 to M40 and type in a
descriptive name of the malfunction.
IMPORTANT: When a malfunction name has been typed and ENTERED, a prompt
will ask you which TAG name from the Malfunction List is wanted.
This tag name must be written with full style name and number directly copied from
Malfunction List. In addition, type in _S. Otherwise tag will not enter. When prompt
changes colour, it will be written ex.. M1301_S, and you are allowed to continue.
In the section VALUE
The active and passive values are entered. When prompted, type in values either
digital (0,1,2 etc.) or analogue in percentage of max. value.
In the section ACTIVE
The value entered is the new default as the fault is activated. Selection of how the
malfunction will be introduced; continuo’s fault or repeating fault in the section
“AUTOMATIC MODE”.
In the section PASSIVE
The value entered is starting level at the time when the malfunction is activated.
UNIT
Engineering unit or percentage. Not necessary to be entered.
Under column AUTOMATIC MODE:
Activating this will make fault go active, and stay active, when
entered time is reached.
Activating this button will make fault go active, and then off
again when time limits entered are reached.
Activated, this button will make fault go on and off repeatedly within
specified time limits, as long as scenario is run.
When activated, time ramp for fault to develop can be specified.
Common for all four function buttons are that faults can be simulated after entering a
scenario only when buttons are activated. When active, buttons change colour. Ramp
function can be active together with any of three other buttons.
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Actions to be created in the same way as malfunction editor. Input of tag names similar to
malfunctions editor, adding underscore S after the Malfunction tag.
When starting a scenario, malfunctions and actions which are activated during the
simulation, must be chosen by clicking on software buttons. Changing colours will indicate
which buttons are activated. In front of each button there is a light with 2 circles.
Outer circle lit means action is activated, but waiting for set time interval to be reached in
order to switch action on.
Inner circle lit means that READING is active, meaning set intervals are reached, and
action started. On the bottom half of screen (buttons A41 to A80) is event malfunctions.
Used and created as malfunction, but triggering actions instead of malfunctions. Such as
closing of valves.
5.5.1.5 Sound
Toggles sound system on/off. Valid for operational simulator only.
5.5.1.6 Time Editor
Allows altering the time for which the malfunctions or actions to take place.
Clicking on CHANGE TIMEPHASE software button enters a line on time section of
picture. Use the inner scroll buttons to increase or decrease the time between actions or
events to take place. Outer scroll buttons to changes time phase.
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5.5.1.7 Event Editor
Used to supervise and allows adjusting events and event conditions.
5.5.1.8 Snapshot (F4)
Takes a snapshot of simulation for later reference. Places snapshot in snapshot directory is
referred to by time.
NOTE! As soon a new Initial Condition is loaded, all snapshots are deleted. However, a
snapshot can be stored as an Init Condition (has to be done before loading a new initial
condition).
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5.5.1.9 Evaluation Editor
For evaluation of the student throughout the exercise taking place. Input of specified
measuring variables under tag name. Specify upper and lower limits. Will evaluate how the
process is maintained by the student during the simulation. Evaluation criteria is whether
student is able to maintain process within specified limits.