Oil and Gas Plants Operation Aspects

ON THE JOB TRAINING MANUALSECTION: 2.5

PROCESS OPERATION DIVISION

AREA 5 (UTILITY: AIR, WATER, NITROGEN…)

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6. OIL & GAS PLANTS OPERATION ASPECTS

6.1 INITIAL OPERATIONS

There is a long distance from Design to Operations.After Design is ready and Legal / Contractual issues solved, Construction can start. But its progress must be continuously checked against Design.(Here come pre-commissioning & commissioning).Even when system is entirely commissioned, it must be started up prior to be operated.Pre-commissioning, commissioning & start-up are often referred to as Initial Operations.

STEPS TO ACHIEVE “OPERATION”

Pre-commissioning = checking ITEMS (purchased)

From bolts & gaskets up to columns and compressors. (Mainly refers to QA/QC papers of purchased items)

starts before construction (from Procurement phase)

Commissioning = checking SYSTEMS (erected)

(System: several items supposed to work together, to fulfill a function) = checking systems’ functionality

(i.e. putting design into practice)Commissioning finishes after construction (Leak Test phase)

Start Up putting the system in operation reaching design parameters reaching design specifications.

CONSTRUCTION SITE

Design of a unit includes: ■ pipelines ■ valves

vessels: columns, separators, tanks, drums;■ static equipment: heaters

heat exchangers etc.

■ dynamic equipment: pumps, compresors, blowers etc. (rotating, reciprocating)■ field instruments■ control loops, software■ buildings etc.

OIL & GAS PLANTS OPERATION ASPECTS (continued)

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Whenever practical, they arrive on site already pre-commissioned. There are some EXCEPTIONS, such as :

big vessels (foundation, internals, cleanliness) furnaces (refractory dry out) pipelines (arrive on site as spools, that must be welded).

Some of the pre-commissioning and all of the commissioning activities are performed on the construction site.

Lots of : ● activities companies HAZARDS

Same SAFETY rules

Same safety goals: 1. Protect life/health

2. Protect equipment 3. Protect environment.

Safety is based on three main pillars:

1. PPE - to be worn daily (helmet, overall, safety shoes) - for special activities ( safety belts, dust mask, face shield, ear plugs)

2. Safety devices ( lifting tools, safety showers, F& G detectors etc).

3. Safety Induction. (Company policy, Rules & Regulations, Records, Permit To Work etc.)

MILESTONES

Each job depends on previous jobs (that should have been completed) and determines future activities.

Failing to perform a job in real time, may result in further delays of several jobs depending on it.

Activities are performed according to SCHEDULES , based on: Ranking priorities Identifying and avoiding “bottlenecks” Using “critical path”.

Schedules are different from project to project – but some main activities are included in any of them.


PRE-COMMISS. COMMISSIONING START UP NORMAL OPERATION

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CONSTRUCTION ACTIVITIES MECHANICAL COMPLETION

FLARE SYSTEM “LIVE”

TEST RUN

Hydrotest Flushing / Blowing Leak Test

Having reached such a milestone means that a certain status of the overall projecthas been achieved.

Hydrotest : start of commissioning; Flushing/Blowing : typical commissioning activities; Mechanical completion : end of commissioning. It is achieved when the system is

tight (= no leaks) when pressurized at a certain pressure (low). Leak tests will continue after Mechanical completion, with pressure increasing

gradually up to Operating pressure.

COMMISSIONING

Is an INTERFACE between Design and Operations – using tools and techniques from both.

Design tools : Block diagrams – one Plant (complex) in one page; PFDs –Process Flow Diagrams - one Unit (process) in one page; P& IDs-Piping & Instrument Diagram – one (max. two) piece of equipment in one page.

Operations techniques: Pressurizing / depressurizing Filling/draining/blowing Heating up/cooling down Lining up etc.

Comments regarding differences between Design and Construction are usually organized in punctual remarks, which can be solved individually.

The official document is referred to as a PUNCH LIST

Handed over to contractor companies, for having the punch list items solved; (when major punch list items are solved, Mechanical completion can be approached).

Punch lists are issued in various moments of the Construction – but each stage has its own critical items to be checked.


ACTIVITY: HYDROTEST FLUSHING/BLOWINGDESCRIPTION Pressurize the system with

water @ p=1.5 x Op.press; Wash the system with water, until water comes out clean –

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monitor pressure maintaining steady for 30 min.

and blow it by air, to make sure water is eliminated.

SYSTEM As much as practical number of pipes that are operating at the same press.(the larger the system – the best).

As much as practical number of interconnecting pipes (regardless operating pressure)

ST

AT

US

OF

:

PIPES Not necessarily installed as per P & ID.

Must be installed as per P& ID.

VESSELS & ROTATING EQPT.

Not included(isolated by TEMPORARY BLINDS)

VALVES Not included. If welded valves – must be fully open.

Included. All – fully open. (Sometimes, check valves must be reversed)

INSTRUMENTS Tie ins plugged. Tie ins opened (one by one)

ACTIVITIES TO BE PERFORMED

FURTHER:

- complete pipes installation, as per P&ID; - install valves and PSVs; - (where necessary) reverse NRVs;-install spacers upstream temporary blinds @ vessels & rotating equip’t.

- remove all temporary blinds; - install check valves in normal position; - install instruments;- close drains and vents;- line up the system for normal operation.- (where necessary) perform chemical cleaning.

Before Hydro test - punch lists should address following items: Line routing; Line size; Line slope; Tie ins.

After Hydro test (before Flushing) – check: Valves and PSVs have been installed; (check PSVs tag numbers). Appropriate bolts and gaskets have been used.

After Flushing/Blowing – check: Temporary blinds have been removed; Checkvalves are in correct direction; Instruments are installed in proper place; Vents & drains are closed, system is lined up.


LEAK TESTSSystems as large as practically possible. All valves open, except :

Vents & drains; Isolation valves of rotating equipment.

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The whole system (including vessels) is pressurized by gas – gradually, up to Operating pressure. Initial gas: utility air; then – nitrogen; then - fuel gas.Note:For most of Utilities (non hydrocarbons) leak-test by air is enough.

When first leak test successful (at about 3 barg): system is mechanically completed.Pressure is further increased, in steps, up to operating value.Air is displaced by N2, N2 displaced by fuel gas – as applicable.

LEAKS must be:- identified (sometimes the system must be segregated into sub-systems)- fixed: ■tight bolts;

■change gaskets (depressurization needed); ■ re-align flanges (re-welding & re-hydro test).

When system is tight, at operating pressure : System operational.

SYSTEMS’ COMPLETION

At one time, various systems are in different stages of completion.(While one is under leak test, another may be under hydro test).

Priorities (UTILITIES FIRST) POWER (if National Grid not available – use Diesel Generators). WATER (initially used to hydro test Fire Water system)

-A. Fire Water-B. Utility Water.

INSTRUMENT/UTILITY AIR (diesel-ran compressor) NITROGEN FUEL GAS (i.e. “Gas In”; Area should be restricted by safety ribbon). POWER/STEAM GENERATION

* * *

FLARE SYSTEM “LIVE” (Flare lit, slightly positive fuel gas pressure in the Flare System). This involves:

o Hot work to be performed under PTWo All systems operational (including ESD, F&G, control loops, DCS)

Systems not ready must be isolated from Flare.

Flare is the last utility to be ready. Reaching this milestone means that unit is ready to start


START UP

PRE-CONDITIONS: - Mechanical Completion achieved; - Utilities available; - Unit pressurized with Fuel Gas, at lowest operating pressure.

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PRESSURE PROFILE ADJUSTED (Operate PCVs, start compressor).

LEVELS ADJUSTED (Start pumps, “Oil In”).

FLOWS (RATIOS) ADJUSTED (Operate FCVs).

TEMPERATURES ADJUSTED (start Furnace).

Flare PROVISIONS TO UNTIL SPECIFICATIONS ARE MET.

Recycle(via Off-Spec Tank)

6.2 NORMAL & ABNORMAL OPERATION

Oil & Gas operations involve handling of flammable, explosive and toxic mixtures, at high pressures and temperatures – extremely hazardous for health and environment.That’s why they should be conducted in tight enclosures (vessels, pipes).Due to the dynamic nature of oil and gas processing (continuous change of mixtures’ status – by pumping, compressing, heating etc.) risk-free enclosures are not financially achievable.

The system must be designed with emergency stop facilities, and each piece of equipment must have its own safety device.

However, Oil & Gas industry aim goes beyond operating safely. In order to achieve product specifications - parameters such as pressure, level, flow and temperature must be maintained within operating margins, which are much narrower than safety margins.

Emergency Shut Down System and Process Control operate independently.


ESD PROCESS CONTROLAim To handle abnormal operation;

(safety oriented)To carry on normal operation;(profit oriented)

Settings Fixed, from design. Variable, within operating range.(under Operator’s responsibility)

Control room ESD logic Controllers

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toolsField instruments Switches (which initiate trips);

Fire & Gas detectors.Indicators and Transmitters

Valves Shut Down Valves (on / off) Control valves (adjustable opening)

SAFETY VALVES

-to protect individual equipment, by falling in safe position when a parameter reaches the safety limit.-they are self-contained – don’t need any input from the system. Not connected with ESD system.

Safe Position upstream the processing unit (@wellheads and production headers) – safe position of safety

valves is CLOSED. (Pressure is contained inside the well). Within the process unit the safe position is OPEN (pressure is released to the flare).

Safety LimitsBoth high and low values can affect equipment’s safety.

High Pressure Low PressureCan occur In all pressurized equipment Mainly in tanksCan provoke Explosion (cracking) Implosion (collapse)Safety device Pressure Safety Valve (PSV) Vacuum Safety Valve (VSV)Action: Opens to release pressure outside

the vessel (usually to Flare).Opens to admit fuel gas or inert gas into the vessel.

ESD SYSTEM

Performs trip functions, associated with the safety and integrity of the plant.

It is implemented in a dual redundant Programmable Logic Controller.In normal operation, inputs and outputs are energized and no operator intervention is required.A matrix of lamps indicates normal operation and annunciates any abnormal activity and fault situation.


ESD system is “stand alone” type. It has its own:o Primary sensing devices - to monitor:

- operating parameters;- other variables connected with the safety of the plant, such as:

electrical measurements; vibrations; axial movements; Fire & Gas detection.

o Final actuation devices

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- to ensure a safe and speedy shut down, in case that certain parameters reach safety limit;(ESD system is designed to sectionally isolate all hydrocarbon inventories and stop all drives).

- to inhibit start-up of dynamic equipment.

Can be manually actuated through hard-wired push buttons.

ESD trips can be bypassed through:o start up override; (Normally – automatic reset after the process has achieved operating

condition)o maintenance override. To repair / calibrate primary elements without activate the executive

Shut Down action.

ESD actions(according to level of hazard):1. close key valves (which involve stopping any heat input);2. stop key motors;3. start back-up power devices;4. open depressurization valves.

TYPES OF ESD: AFFECTED AREA REST OF THE UNIT ESD ACTIONS

local PIECES OF EQUIPMENT (e.g. pumps)

Normal operation; (stand-by equipment is automatically started)

1 & 2

partial AN INDEPENDENT PART OF THE UNIT (e.g. one production train)

Normal operation, with reduced throughput.

1 & 2

total ALL PLANT Unit stopped, under pressure. Pressure profile preserved. Ready to start after fixing fault.

1 – 3

total – with depressurization.

ALL PLANT Unit stopped - depressurizing according to a logic sequence. Ready to start after fixing fault and inerting.

1 – 4


OPERATING RANGE

In order to ensure product specifications, the measured and controlled parameters are: pressure; level; flow; temperature.

They are also referred to as process variables.Actual values of process variables are continuously changing; they influence each other and all of them influence the product’s quality.

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Performance of the plant depends on measurement accuracy and control efficiency of process variables. To get a best quality product, a set of optimum operating values must be achieved.

Due to the great number of changes of inlet parameters to a unit (while product specifications are supposed to remain the same) – we cannot talk about one sole set of optimum operating parameters.Identifying, maintaining or adjusting the optimum operating parameters is the main task of the operators. A lot of automation is commonly used for achieving this.

6.3 CONTROL VALVES OPERATION

Actual values of process variables (PV), as measured by measuring elements, are continuously monitored by operator.To keep a process variable within operating range at one point in time – means to achieve a certain opening of the appropriate control valve.Since actual values of PV are continuously changing, the opening of the control valve must be continuously adjusted (remote adjustment, via pneumatic or electric transmission systems). This can be carried out by operator ( MANUAL operation) or by a dedicated controller ( AUTO operation).

Due to the great number of parameters to be dealt with in modern processing units, they are normally controlled in AUTO mode. Operator’s approach is to communicate a SET POINT to the controller. So the controller will receive two input signals:

SET POINT (from operator); ACTUAL VALUE OF PV (from the measuring element).

An automatic controller is capable of comparing the two input signals and issuing one output signal – which is a command to the control valve, to increase or reduce opening.

(NOTE: it is generally agreed that OPENING (%) and not closing of valves should be considered. A closed valve is referred to as 0% open.)

The output signal is aimed to minimize the difference between the set point and the process variable. Control valve opening is that way adjusted, to achieve an actual value of PV as close as possible to the set point.


Advantages of AUTO operation : Saves operator’s time and attention for a particular PV. (If system not perturbed) work with good accuracy – in long term more reliable than manual

operation.Disadvantages:

Cannot achieve operating parameters, can only maintain them within operating limits, after they were achieved through manual operation.

Limited capability to react to changes; cannot work without operator’s supervision.

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A control loop consists of a measuring element, a transmitter and a control valve - which acts according to the received signal, to minimize the difference between the actual value and desired value of a process variable.If the operation is in AUTO mode, the signal comes from a controller, which decides the valve’s opening considering the SET POINT received from the operator.If the operation is in MANUAL mode, the signal comes straight from the operator (operator plays the part of controller).

From construction point of view -all controllers have proportional, integrative and derivative characteristics (PID) which influence the controller’s response to input changes (actual values or Set points).These can be individually adjusted by qualified Instrument Technicians to suit process needs. (faster or delayed response).Since in an operating plant there are hundreds of controllers and switches – an overall adjustment ( Tuning) is necessary – to achieve optimum operating conditions in the unit. Dedicated softwares are available on the market, for assistance in performing this job.

Level and Flow Control.(e.g. in a Separator)

Even if the oil flow coming out of a Separator is maintained constant - due to the fact that the incoming flow to the Separator is not constant, the level in the drum will continuously change.Within some limits, the level’s fluctuations can be accepted, considering the size of the drum.However, both low and high values of the level could seriously affect Plant’s safety.

The oil level is controlled by LIC, which displays the readings of LT.As long as the cascade is not activated, the controller is only indicating the level’s actual value – and gives alarms for high and low (LAH, LAL).Should not any proper action be taken, the level may escape out of the working range of the operation LT - and go into the area controlled by LT-s belonging to the ESD system (for high values or low values). These LTs don’t report to the controller, but to level switches (LSHHand LSLL) - which will operate appropriate SDVs, according to ESD logic.


Cascade Control.In order to prevent abnormal operation, the oil level must be continuously monitored.Even if the outgoing flow is controlled at the desired value, it may be necessary sometimes to modify controller’s set point in order to comply with level requirements.

Separator’s oil level depends both on Feed Flow and Outgoing Flow. Since feed flow cannot be too much adjusted (or it may be affecting the Separator’s condition) – then the outgoing flow must be adjusted.Physically, any changes in the Outgoing Flow values depend on FCV opening.The FCV must now receive signals that take into account stability of the level, and not the desired flow rate.

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(Changing the flow only affects production, while changing the level may affect Plant’s safety)

The change of FIC Set Point can be done by the operator – or by the dedicated level controller. The arrangement in which a controller’s set point is supplied by another controller is referred to as cascade control.

Controllers working in Cascade observe a “master / slave “ hierarchy.In the example given, the Level controller is the master and the Flow controller the slave.LIC is the one which will receive Set Point from the operator (usually 50%), will compare it with the actual value of level transmitted by LT – and will issue a Set Point to FIC.

FCV will act upon signals received as usually from FIC; (a Level controller cannot operate a Flow valve). But the signal issued by the Flow controller will be dictated by the Level.It’s operator’s responsibility to decide if and when the cascade control should be activated.

In some other applications the “slave controller” has more independence, within some limits.Only when one particular parameter escapes outside the range, the “slave” is overridden by another controller (or switch) which takes over.

Pressure control

Pressure is normally controlled in drums, such as Separators. The principle of pressure control is that the higher pressure from upstream the drum is reduced to a lower, desired, value - by releasing gas, in a controlled manner, from the top of the drum.

Pressure control valves (PCV) release as much gas as necessary to keep the required pressure in the drum, opening as per the signal received from Pressure Indicators & Controllers (PIC) – which compare the given Set Point with the actual value of the pressure, transmitted by pressure transmitters.For calculating of the appropriate opening of the valve, the PIC is provided with a dedicated algorithm, according to the constructive type of PCV. PCVs cannot be replaced by FCVs and vice versa.


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Simplified Pressure Control Loop

Split range controlThe gas from a Separator can be usually sent to 2 locations:

To the downstream process; To the Flare system.

The pressure in the separator is controlled by a PIC, operating two valves, PCV-“A” and PCV-“B”.Any increase of the pressure measured in the separator determines an increased opening of the control valve, PCV-“A”.When the amount of gas is unusually high – and the separator’s pressure remains high even when the control valve PCV-“A” is fully open – the second control valve, PCV-“B” will start to open, diverting the excess gas to the Flare.PCV-“B” receives the signal from the same PIC,

but only after it has already opened fully the PCV-“A”.The two valves are operated in series (B opens after “A” was already opened).The PIC operating in series the control valves “A” and “B”, is a split range controller.In normal operating condition, valve “B” is expected to remain closed – and the PIC should operate only the PCV – “A”, like any common controller.


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Temperature control

The principle of temperature control in a heat exchanger is based on an excess of hot stream which flows through a bypass line across the exchanger. By including or excluding a certain amount of this stream in the heat exchange, the outlet temperature of the stream getting heated can be controlled.

Simplified Temperature Control Loop

Parallel range controllersSplit range controllers are mainly used for controlling the pressure, while parallel range controllers are used to control the temperature in heat exchangers.The temperature element, located on the cold stream’s outlet from the exchangertransmits the actual value measurement to a temperature controller, which operates two valves,located on hot stream lines:

o one on the straight line, going through exchanger;o the other one on the bypass line.

The valves will be operated in the same time (in parallel) – but in opposite directions: If the measured temperature of the stream to be heated is higher than the set point:

o the valve supplying heating agent will reduce opening;o the bypass valve will open more.


If the stream getting heated leaves the exchanger colder than the set point

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o the supply valve will open more;o the bypass valve will reduce opening.

Feed back control

See the sketch below for a simple diagram of a cascade control loop (the tag number for the loop is 4)

The control loop is controlling the temperature at tray number 5 in a process distillation tower.The temperature is sensed at tray 5.The temperature transmitter (TT-4) converts the temperature into a signal.The temperature signal is transmitted to the temperature controller. (TIRC-4)This controller (known as the "master") has a set point temperature that has been set by the plant operator.The output signal from the master controller is obtained by comparing the set point temperature with the process temperature – and becomes the set point for the “ slave" controller, FIC-4.

The output signal from the slave controller is the input signal to the control valve.The control valve adjusts the steam flow as needed.

It can be seen that a cascade control loop measures a process variable (PV).It also measures a second PV, which will have an effect on the first PV (in this case the flow of steam).


This way, all the factors that affect the first PV are used for producing the control signal for the final control element – which thus will react faster to changes in the PV.

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However, after the flow valve on the hot stream will increase opening, it will take some time until the temperature will really increase - due to delayed response of the system.

The degree of accuracy of any process control system can be maximised by reducing the lags. When the response time for the system is not suitable for the process requirements, design changes are usually made. These design changes can include the addition of booster relays or the modification of the control loop to maximise the degree of system accuracy.In all the examples described above, the value of an outlet variable was adjusted by changing the value of another outlet variable. The difference between the actual and the desired value of a parameter was only corrected after its occurrence (feed back control) – hence a certain delay.

With the advent of computer science, microprocessors started to be used, and feed forward control loops have been devised.

Feed Forward control

A feed forward loop controls the PV on the outlet by measuring process variables on the input. If it detects changes in the inlet process variables it takes action immediately before the liquid enters the process vessel.

Above is represented a Feed Forward Control Loop for a Heat Exchanger - where a process liquid is heated by steam .The process variable to be controlled is the process liquid outlet temperature; the desired value is T2.The set point for the feed forward controller is therefore the same temperature, T2.


For controlling the process liquid outlet temperature, the steam flowrate F2 is adjusted by a standard flow controller, (FC). This flow controller gets its "set point" from the feed forward controller.The feed forward controller receives also information on the temperature T1 and the flow rate F1 of the process liquid, as it comes in.

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So, any changes in the inlet flow are detected before it affects the outlet temperature.Such controllers require having a microprocessor incorporated.

Multi - Variable control loops

In the previous example, the feed forward controllers receives information on two process variables (flow rate and temperature of the inlet stream ).Following the progress in Information Technology, complex controllers could be achieved, that receive information on many variables.They are often used to control centrifugal compressor systems which are driven by large gas turbines.

A typical example is the anti-surge controller of a centrifugal gas compressor.The controller’s output to the recycle control valve depends on the inputs from six different transmitters.The controller normally uses proportional, integral and derivative control action (PID control). These values are set using a computer software programme.

Control Room

Oil & Gas plants are typically running around the clock, operated by teams working on shift.All data regarding parameters’ evolution and any particular events occurred must be recorded and handed over to the next shift.They also should be available anytime for further reports and statistic studies – as well as for analyzing causes of any unwanted event.

To manage a plant operation – a central location is required (currently referred to as “Control room”) – where all operating data should be available, so that situations could be assessed and appropriate action could be decided. The advent of Information Technology regarding remote transmission of signals and data processing was extensively used to improve the possibilities of plants control and operation.


6.4 INDUSTRIAL CONTROL SYSTEMS

Industrial Control Systems are typically used in industries such as electrical, water, oil & gas. Based on information received from from remote stations, automated or operatory-driven supervisory commands can be transmitted to field devices.

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Field devices control local operations such as opening and closing valves and breakers, collecting data from sensor systems and monitoring the local environment for alarm conditions. For achieving an analysis on a continuous basis (i.e. computer data logging), the Process Variable (PV), in its way to the controller, had to be intercepted by a computer.In a real unit there are many thousands of PV data points; one signal at a time must be made available for the computer. This can be achieved by introducing a device known as multiplexer (MUX).The signal arrived to and from the MUX is still in analogue form (1→5 Volt range). Since computers deal only with digital signals, an Analogue to Digital Converter (ADC) had to be used.

Process line ControlValve

Transmitter TX Controller

Printer

MUX

AdressBus

ADC

Computer

(Operator’s interface with computer: Visual Display Unit –VDU)

Computer Supervisory Control (CSC)Operator, when changing Set Point to one control loop (e.g. flowrate to a vessel) must also watch the interactions with the vessel’s level, pressure, temperature.Computer is already monitoring the PVs – so, it can monitor the interactions taking place – with additional electronics. It can also adjust the SP.

Process line Control Valve

TX Controller

MUX

Adr

ess

Bus

DEMUX

ADC DAC

Computer


Set Point adjustment is calculated better and faster by the computer.Disadvantage: Controllers must be capable of receiving a computer-generated set-point.

Direct Digital Control (DDC)

Process line Control Valve

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TX

MUX DEMUX

ADC DAC

Computer

Computer is programmed to perform the Controller function.Each PV is sampled on a regular basis, every few mili-seconds.Advantage: Removal of controllers. Reduced maintenance. Better energy management.Disadvantages:

Extended data lines. Data integrity is jeopardized; Complex software required (individually tailored to the process to be controlled); Computer’s failure causes process loss. (Additional computers required, and additional data

lines – which is too expensive).

Distributed Control System (DCS)

Several controllers, microprocessor – based. Memory attached to microprocessor – configured for the individual control loops associated with that controller.Communication Operator ↔ Controller can be carried out through data link (≈ network), via single coaxial cable. Normally two cables are used: one over which communication is passed and one to listen only. The cables are able to automatically switch roles.

Controllers may be sited as close as possible to their end elements (transmitters & control valves), so data path is as short as possible (data corruption: limited). However, circuit boxes (which are not intrinsically safe) will require to be housed in a safe area (pressurized box). Data signals to and from circuit boxes need to be routed through Zener barriers, as a protection from hazardous areas.

Distributed Control Systems are used extensively in process-based industries, such as oil & gas refineries, electric power generation and automotive production.They are provided with a control architecture containing a supervisory level of control – overseeing multiple, integrated sub-systems that are responsible for controlling the details of a localized process. Product and process control are usually achieved by deploying feed back or feed forward control loops whereby key product or process conditions are automatically maintained around a desired set point.


The large plants are subdivided in several Local Control Units.The single control loops in each unit are all controlled by one Local Control Unit.The information that the control room operator needs is sent by a single cable (data highway) from the Local Control Unit to the Central Control Room (CCR).

This information is shown on a Video Display Unit (VDU) in the Central Control Room.

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The operator in the Central Control Room can change the set points in the control loops and open or close motor-operated valves on the plant. He does this by sending signals back along the same data highways.

There are 5 levels at which the system can be controlled or monitored. Basically, the system includes everyone from the lowest plant operator to the Managing Director.

Level 1- Field. The input devices (transmitters) and output devices (control valves) are connected to Input/Output units. (I/0 Units). The I/0 units convert the signals received from the transmitters to specially coded signals. (The signals are sent in a special code because the data bus highway must handle many signals at the same time).The field bus data highway is co-axial cable (like a TV antenna cable). It can transmit many signals in two directions at the same time. The specially coded signals leave the I/0 Units along the field, bus data highway to level 2.

Level 2- Local Control Unit.

The I/0 units also receive specially coded signals from level 2 on the same field bus highway.Those incoming signals are converted by the I/0 units into output signals which can be used to operate the final control devices.

This is the Local Control Unit level.The Control Processor (CP) uses data from the field bus to control individual control loops. It can control several loops at the same time.The control parameters (PID settings) are set in the CP by using a computer software programme.


In the figure below it is showed a CP with 5 control loops; the I/0 Units are shown as two separate units.

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The data on the field bus contains all the information for each loop input and output.

The control parameters (PID settings) for each loop are separately programmed.

The CP controls each loop in turn, i.e. 1,2,3,4,5,1,2,3,4 etc. It only takes milliseconds to switch from one loop to the next.The CP switches so fast that it seems as if it is controlling all the loops at the same time.

Level 3- Central Control Room.

This is the top level of control at the plant.The information which is needed for each loop is displayed on a Video Display Unit (VDU) at a work station.The workstation supervisor can change set points in the control loops or change from automatic to manual control, etc.The supervisor does this by using the keyboard at the workstation. (Similar to a computer keyboard).These commands are sent to the CP's at Level 2 through data link (≈ network). Other controllers, units etc. can simply be joined on to the network (provided that network communication is not overloaded).

Large control systems may have many workstations.- which display information from many Local Control Units around the plant.


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Notes1. - The control loops are actually controlled by the Control Processor at Level 2.Therefore, a fault on a CCR workstation (level 3) does not mean that control of a plant unit has been lost.2. – Other controllers, units etc. can be simply joined into the network (provided network communication is not overloaded).


Level 4 - Area Management.

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At this level the process can be monitored but there is no direct control.An applications processor (AP) at level 3 takes selected signals from the CP's.The AP converts the signals into a digital code so that they can be sent one way over a higher level data highway.This allows information about how the plant unit is operating to be displayed on VDU's in the plant manager's office.

Level 5 – Group Management.Located at Company’s Head Office (which may be located at hundreds of miles away from the plant).Selected signals from the AP at level 3 are converted into a different code . These converted signals can then be sent by microwave link to the head office.Level 4 & level 5 give information only. The process can not be controlled from these levels.

DCS is a control system which allows the processes in the plant to be monitored and controlled from different points at the same time.

Supervisory Control And Data Acquisition (SCADA)

SCADA usually refers to a central system that monitors and controls a system spread out over a long distance (kilometers/miles).The system consists of Remote Terminal Units and a Master Station.

RTU is the equipment that regularly scans the process parameters and reports alarm and change conditions to the Master Station. It contains a central processor which has the appropriate programs loaded into it for effecting the scanning and processing of defined analogue and digital signals.RTU sends data when interrogated by the Master Station (usually, every two seconds). The RTUs are passive devices (i.e. they don’t send unsolicited messages to master station).If alarm conditions occur between two scan cycles, it is stored in RTU’s data base - and reported as soon as addressed by Master Station.RTU can also receive ESD commands from Master Station.Types of digital signals handled by an RTU:

o valves’ status (open / closed);o pumps’ trips;o low levels at tanks;o emergency shut down.

Types of analogue signals transmitted by RTUs. A. Measurements : pressures, flows, temperatures; B. Status of Utility and Safety systems. (Power or Software faults).


An important part of most SCADA implementations are alarms.

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An alarm is a digital status point that has either the value normal or alarm. The SCADA opertator’s attention is drawn to the part of the system requiring attention by the alarm. Alarms can be created in such a way that when their requirements are met, they are activated.Lately, the use of “smart” RTUs or Programmable Logic Controllers (PLCs), which are capable of autonomously executing simple logic processes without involving the master computer, is increasing.The SCADA system gathers information from the PLCs and other controllers via some form of network – and combines and formats the information – for providing trending and diagnostic data and management information such as scheduled maintenance procedures or expert-system troubleshooting guides.SCADA solutions often have Distributed Control System (DCS) components.

Programmable Logic Controllers (PLC)

PLCs are computer-based solid state devices that control industrial equipment and processes.They provide boolean logic operations ( i.e.are able to control a sequence of actions), timers and (in some models) continuous control.Their basic function is to control a sequence of actions. They provide electronic switching operations and are mainly used in safety systems (to shut down a plant in an emergency).

When the plant is in normal operation, the PLC is energised.When the PLC is energised an electrical digital signal holds the micro processor in the "operating" mode.The micro processor holds all the switches in the "energised" mode.If there is an emergency, the PLC operates the switching sequence which shuts down the plant. The micro processor in the PLC de-energises the switches sequentially (time delays are built in to the system where necessary).

7. PERMIT TO WORK (PTW)

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The Permit to Work is a written document that authorizes a Job Performer to carry out commisioning or maintenance activities on a turned over system.Permit to Work activities are controlled and performed in a manner meant to ensure the safety of Personnel and Plant. PTW operations are coordinated – in order to avoid conflict of access or activities.By signing a Permit to Work, one guarantees safe conditions at the work place for the whole duration of the work; he is also responsible that the work place does not become a source of danger for the other parts of the plant.

The Area Coordinator (who is, usually, also the job originator) issues the PTW in the area under his coordination / responsibility. He will fill out the PTW check lists and clearly instruct all the involved personnel about the operating and safety requirements to be taken, as well as associated restrictions.If necessary, he will request “Gas Test Certificate” or “Isolation Certificate”- which are parts of the Permit To Work system and must be attached to the work permit as the case may be.Area Coordinator will write his name in printed letters and sign the PTW when he is satisfied with the handing over of the job.He will keep the record of open and closed PTWs – as well as isolations, tags and locks.

The Job Performer applies for a PTW 24 hrs prior to the day on which the work is scheduled to start. He fills in the first part of the Work Permit form, indicating the names of the persons who will perform the job, starting date and time, equipment and tools to be used etc.He will also sign the Work Permit, to state that he understands all the precaution to be taken during the execution.He is responsible for advising the personnel performing the work about these precautions – as well as about the safe manner in which each detail of the job should be carried out (“toolbos talk”).He will notify the PTW issuing authority about work completion.

Several types of work permits are currently in use: Hot Work (involving the use of any naked flames, such as welding, grinding, drilling etc). Cold Work (which may include work at high elevations, in confined space etc). Radiographic Work (use of x-rays or gamma-rays for tests and inspections). Excavation Work.

The Job performer will ensure that the PTW, prepared in four copies, is distributed as follows:

the original with the personnel actively engaged in the work; the first copy on the job site, displayed by the PTW engineer on the Permit Board, in the

Control Room (or site office). the second copy to the HSE department; the third copy to Area Coordinator’s file.

Work permits have a normal validity of maximum seven days and must be sanctioned daily., at the beginning of each shift. (When Gas Test is required, the maximum validity will be one day).On job completion, the Job performer will return the original to the PTW engineer, who will sign it off (if satisfactory).More details about PTW can be found in Petroconsult HSE manual, Level two, volume II.

PERMIT TO WORK (continued)

S.C.PETROTEL LUKOIL S.A.SECTION №WORKSHOP Date

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UNIT

Fill in all the fields Delete the fields that are not nrcessary.

WORK PERMITFor REPAIRS AND INTERVENTION

WORK IN CONFINED SPACEWORK IN SEWERS AND TRENCHESACCESS FOR MEASUREMENTS

WORK DESCRIPTION

WORK DURATION: STARTING WITH……………HRS……... ENDING ON….…………HRS……WORKPLACE:JOB PERFORMER:

(name, surname, position, trade/company)NAME AND TRADE OF WORKTEAM MEMBERS

PRELIMINARY SAFETY MEASURES AT THE START OF THE WORKS

SAFETY MEASURE DESCRIPTION NAME AND POSITION SIGNATURE0 1 2

1 INLET AND OUTLET PIPELINES HAVE BEEN BLINDED / DISCONNECTED

TECHNICAL TEAM LEADER

2 THE UNIT, EQUIPMENT OR VESSEL HAS BEEN EMPTIED, PURGED, CLEANED AND VENTED.

TECHNICAL TEAM LEADER

3 ELECTRICAL OR THERMAL POWER WILL BE DISCONNECTED.

ELECTRICIAN, FOREMAN

4 MECHANICALLY ACTUATED SYSTEMS WILL BE SHUT DOWN.

TEAM COORDINATOR

5 IT HAS BEEN ESTABLISHED THAT TOXIC GASES AR MISSING AT THE WORK PLACE AND OXYGEN CONTENT IS ≥ 18 %

GAS TEST CERTIFICATE(S), ENDORSED BY LAB. TECHNICIAN

6 PROPER VENTILATION IS AVAILABLE FOREMAN7 SPECIFIC SAFETY INDUCTION HAS BEEN

DONE TO ALL THE PERSONNEL PARTICIPATING IN THE WORK

TECHNICAL TEAM LEADER,

FOREMAN8 THE CONDITION OF LIFTING

EQUIPMENT PLANNED TO BE USED IN THE OPERATION HAS BEEN CHECKED.

CRANE OPERATOR


0 1 2

9 THE CONDITION OF ACCESS MEANS (SCAFFOLDING, STAIRS, LADDERS, PLATFORMS) HAS BEEN CHECKED.

WORK COORDINATOR

10 PROPER TOOLS AND SPECIFIC SAFETY TEAM LEADER,

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EQUIPMENT AND DEVICES HAVE BEEN DISTRIBUTED.

FOREMAN

11 WORK CAPABILITY OF THE PERSONNEL HAS BEEN CHECKED.

TEAM LEADER, FOREMAN

12 PERSONAL PROTECTION EQUIPMENT HAS BEEN CHECKED.

TEAM LEADER, FOREMAN

13 LOW VOLTAGE LIGHTING WAS SUPPLIED.

ELECTRICIAN

14 THE AREA HAS BEEN MARKED BY SAFETY RIBBON AND RESTRICTION INDICATORS.

WORK COORDINATOR

15 THE STATUS OF THE SAFETY AND LIFE SAVING EQUIPMENT HAS BEEN CHECKED.

WORK COORDINATOR

16 OTHER SAFETY MEASURES SPECIFIC TO THE WORK

ALL THE FORESEEN MEASURES WERE ACOMPLISHEDPROCESS FOREMAN………………………….. TEAM LEADER……………………………………

THE WORK MAY START AT……………………………………………………………..(DATE) (HOUR)

PERMIT ISSUER (PLANT SUPERINTENDENT)(NAME:) (SIGNATURE)

APPROVED BY (AREA COORDINATOR)(NAME:) (SIGNATURE)

RECEIVED BY (JOB PERFORMER)(NAME:) (SIGNATURE)

THE WORK DOES (NOT) COMPLY WITH THE SAFETY MEASURES. THE UNIT WILL BE (NOT) PUT INTO OPERATION.PLANT SUPERINTENDENT

(NAME:) (SIGNATURE)

EXTENSIONALL THE MEASURES WILL BE RE-CHECKED AND AS EFFECT THE WORK MAY CONTINUE UNTILL………………………………………………………………………………………………………..TECHNICAL TEAM LEADER

(NAME:) (SIGNATURE)JOB PERFORMER

(NAME:) (SIGNATURE)EXTENSION APPROVAL (AREA COORDINATOR)

(NAME:) (SIGNATURE)

PERMIT TO WORK (continued)S.C.PETROTEL LUKOIL S.A.SECTION Annex № 1WORKSHOP to Decision № 82/11.02.2000UNIT

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EXCAVATION PERMIT№……………………….Date ………………………

1.Mr. ,in the capacity of JOB PERFORMER, leading the team(Name) (Surname)

1 52 63 74 8

is authorized to execute excavation (manually / mechanized) foron route limited byuntil

2. Measures:a) before the start of work

b) during the work

c) at the interruption of the work

d) at work completion

e) special measures

3. The work was requested by the Department

4. SIGNATURESHead of Department who requested the work Head of department where the work is being

done

5. Department Responsible Persons who are keeping the evidenceA) Electric cables D) Sewerage systemsB) Phone cables E) Gas pipelinesC) Distance measuring cables F) Water pipelines

6. Will be authorized to continue the work

№ Year Month Day AUTHORIZED PERSONNEL SIGNATURESHead of Department Job Performer HSE representative


INSTRUCTIONS

1. The excavation permit shall be issued by the Head of Department who requests the operation – in three copies:

one to the issuer;

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one to the Utilities department; one to the Job performer.

The permit shall be filed by the labour department of the job originator.2. The Head of Department has the obligation to identify the competent personnel for

authorizing the excavation permits.3. Before starting the work, the Job Performer will train the team regarding the rules and

regulations to be followed and will have a “toolbox talk” regarding details for safely carying out of each step.

4. It is Job Performer’s responsibility to ensure that all personnel involved is provided with proper safety equipment.

5. If ,during the excavation job, any pipelines or bricks are found, indicating the presence of cables that haven’t been marked on the sketch – the work will be stopped and the job originator will be acknowledged immediately. The job originator is responsible for advising the department supervisors involved in the operation, and establish the steps to be further followed. The additional precautions will be included as an annex to the work permit.

6. It is mandatory that excavation should be performed in such a manner that the excavation walls, the cable layouts or pipelines are protected.

7. The job originator will organize the work to be done in such a way that access in case of emergency situations should not be blocked.

8. The excavation work re-starting is subject to daily authorization.9. It’s Job Performer’s responsibility to install safety ribbon and safety tags (visible day and

night) delimitating the working area.10. At work completion, the trench will be filled up and the area will be levelled.11. Authorization by responsible persons mentioned at § 5 a), b) and c)is mandatory for any

kind of excavation. Authorization by responsible persons mentioned at § 5 d) & e) is mandatory only in case of mechanized excavation.

Acknowledged by the Job Performer,Name ……………Surname………………Signature.

Sketch place:

Job originator’s representative in charge with sketch accuracy,Name ……………Surname………………Signature.

8. QUESTIONS8.1 WATER SYSTEMS

1. Filters’ regeneration completion is confirmed by analyzing:A) Diluted acid outlet;B) Water outlet stream (normal operation);C) Final washing water.

2. When does one of the following samples turns red?

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A) The sample from Strong Acid Filters, when some drops of methyl-orange are poured in it;

B) The sample from Strong Basic Filters, with 2-3 drops of phenol-ftaleine, after titration with NaOH solution 0.1N;

C) The sample from Weak Acid Filters, with 2-3 drops of methyl-orange, after titration with HCl solution 0.1 N.

3. Which sample, and when, changes the colour from strong yellow to faded pink?A) The sample from Weak Acid Filters, with methyl-orange, while being titrated with HCl

0.1N;B) The sample from Medium Basic Filters, with phenol-ftaleine, while being titrated with

HCl 0.1N;C) The sample from Strong Acid Filters, with methyl-orange, while being titrated with

NaOH 0.1N;4. The Methyl-Orange indicator reacts to:

A) NaOH 0.1 N;B) HCl 0.1N;C) Reacts only if pH is higher than 8.3.

5. In which situation the titration is carried out until the sample becomes colourless:A) During the “-m” test, while using methyl-orange;B) During the “m” test, while using phenol-ftaleine;C) During the “p” test, while using phenol-ftaleine.

6. What is the significance of a sample turning blue ?A) There is no acidity in the outlet stream from Weak Acid Filters (indicator: methyl-

orange);B) There is no hardness in the outlet stream from NaK Filters (Indicator: eryochrome);C) There is high alcalinity in the outlet stream from Strong Basic Filters (Indicator: phenol-

ftaleine).7. What is the similitude between the “m” and the “-m” test ?

A) Both are carried out for de-anionized water;B) Both use the same indicator;C) Both use the same chemical for titration.

8. What is the purpose of the Natrium-cationic Filters?A) To remove cations from the Raw Water;B) To reduce hardness;C) To adjust the pH of the condensate.

9. What is the content of the Mechanical Filters used for condensate filtering ?A) Acid resin in the first stage and Alkaline resin in the second stage;B) Mixed beds in both stages;C) Activated Carbon in both stages.

8.1 WATER SYSTEMS (continued)

10. Which stream is known as “decarbonated water” ?

A) The stream feeding the Acid Filters;B) The stream feeding the Basic Filters;C) The stream feeding the NaK Filters.

11. Which kind of Boilers require a lower conductivity of the Feed Water ?

A) Those boilers operating at a higher temperature;B) Those boilers operating at a higher flow;

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C) Those boilers operating at a higher pressure.12. In the Weak Acid Filters:

A) Ca2+ and Mg2+ cations are removed from sulfates and nitrates;B) Ca2+ and Mg2+ cations are removed from bicarbonates;C) Chlorides and sulfates are retained on the resin.

13. The CO2 is removed from water:A) By air- blowers;B) By Weak Acid Resins;C) By Medium Basic Resins.

14. What is the reason for allowing water to overflow through the vent valve of the Filters, prior to putting them in operation?A) To make sure that no air was trapped inside;B) To be able to control a flowrate of max. 50 m3/h through the Filters;C) There is no reason; this is an operating mistake, which will result in resin being lost in

the sewage.15. Which Filters, prior to be put in operation, require washing until reaching an “m” value of

0.5 mval/l?A) Strong Acid Filters;B) Medium Basic Filters;C) Weak Acid Filters.

16. What is the purpose of performing the “p” alkalinity test ?A) For finding out if the Strong Basic Filter washing is completed;B) For finding out if the Strong Basic Filter is exhausted;C) For finding out if the serial regeneration from Strong Basic Filter to Medium Basic Filter

may be lined up.17. What is the meaning of a pH value higher than 6 in the outlet stream from Medium Basic

Filter?A) The Filter may be put in service, because the washing is completed;B) The Filter is not yet exhausted;C) It has no special meaning.

18. What is the meaning of a SiO2 content lower than 0.2 mg/l in the outlet stream from the Strong Basic Filter?A) The filter is exhausted ;B) There is no special meaning, the filter is in normal operation.C) No meaning - samples from Strong Basic Filters are not analyzed for SiO2 content.

8.1 WATER SYSTEMS (continued)

19. What is the function of the layer of quartz installed on the bottom of the Filters?

A) To prevent the resin from being entrained with water during normal operation;B) To ensure a better distribution for backwash water;C) To prevent the resin from being entrained with water during the backwash;

20. The Backwash sequence for the Mixed bed Filters goes as follows:A) The cationic resin is backwashed first and the anionic resin is backwashed next;B) There is a sole, common backwash for both resins;C) The anionic resin is backwashed first and the cationic resin is backwashed next;.

21. When is the air bubbled through the Mixed Bed Filters ?

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A) After the cationic resin Final washing ;B) After the anionic resin Final washing;C) Before the common Final washing.

8.2 STEAM & CONDENSATE

22. Why is it necessary to drain frequently the Steam lines, when putting them in operation ?A) In order to remove the condensed steam;B) In order to remove Oxygen;C) For preventing line’s over-pressurizing, as there is no PCV in the Steam Distribution

section.23. How is distributed the steam coming from the units which are also steam users (such as FCC and CCR-

Platforming)?A) Through branched pipes;B) Through ring-type network;C) Through individual, two-ways flow pipes.

24. Describe the role of Steam-traps and how do they work.25. What is the purpose of installing a brass plate at the end of a steam header under preparation

for starting up?A) For protecting the Battery Limit Valve against the solid particulates, while air-blowing

the pipe;B) For protecting the Process Unit downstream the Battery Limit against warming up;C) For witnessing the efficiency of steaming out the pipe.

26. What actions are recommended, in the Lukoil Operating Instructions, for stopping severe hammering on a steam pipeline?

27. What are Superheated Steam and Saturated Steam used for?

28. Describe what is the purpose of a Pressurization Bypass Valve and in which steps of the Steam Header’s Start-Up is it used.

29. What is the reason for condensate generation in the steam lines?A) Steam cooling down against the walls of the pipe;B) Pressure drop due to elbows and valves;C) Malfunctions at Steam Generation units;

30. In normal operation, condensate is drained from the steam lines:A) When steam parameters are below specifications;B) When hammering is experienced in the steam lines;C) Continuously, through the steam traps .

8.2 STEAM & CONDENSATE (continued)

31. How can tube ruptures in a heat exchanger be fixed ?A) By isolating the equipment and monitoring tubeside vs. shellside pressure;B) By chemical cleaning;C) By plugging those tubes found leaking.

32. Why are the Condensate Drums installed at a higher elevation than the condensate pumps?A) To ensure condensate flowing freely into the pumps;B) To ensure the required NPSH at pumps’ sucction;C) To allow pressure equalizing between MP and LP Condensate Drums.

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33. Describe the steps for starting up of the condensate pumps.34. Describe the steps for starting up of a heat exchanger .35. Describe the steps for having up a condensate pump repaired.

8.3 FUEL GAS & FUEL OIL

36. Flash Point can be defined as:A) The temperature of the burning fuel;B) The lowest temperature at which a fuel can form an ignitable mixture with air;C) The temperature of the ignition source;

37. Which of the following statements is true?A) Dew point increases with increased ambient pressure;B) Boiling point of an isomer is higher than the boiling point of the normal(linear)

hydrocarbon;C) The boiling temperature decreases when operating presure increases.

38. How must be handled the liquid level built up in a Fuel Gas KO Drum?A) Must be completely drained, because a HH level in the drum will trip the boiler;B) A small level must be maintained in the drum, for ensuring the hydraulic closure towards

the Closed Drain system; C) The level built up in the drum depends solely on the operation of the pressure controller.

39. Discuss the difference between combustion and explosion.40. Mention at least three causes for a Heater’s trip.41. Why is necessary that a flame should be continuously maintained on the

top of the flare stack 42. Which of the following is the normal source of fuel for PLK users?

A) Natural gas;B) Fuel Oil;C) Refinery gas.

43. When are the TPS boilers shifted from Natural Gas to Refinery Gas consumption?A) when there is a shortage or trip in the natural gas network;B) when the Process units achieve normal operation, after start-up;C) when there is a need of Fuel Oil consumption to the other PLK users.

44. Which of the following could be a reason for shifting the burners to Fuel Oil consumption?A) Increase of total fuel demand;B) The need of higher caloric value at burners;C) Decrease of fuel gas production.

8.3 FUEL GAS & FUEL OIL (continued)

45. Mention at least seven of the analyzes required for the characterization of a Fuel Oil.46. Describe the operation of a fuel oil burner

8.4 AIR SYSTEMS

47. Why do we need to cool down the outlet stream from the1st stage of compression?A) because atmospheric air is too hot in summer time;B) because in the1st stage of compression is achieved a higher Δp than in the 2nd stage;

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C) because air becomes overheated due to compression.48. Which one of the Air system streams has a higher dew point?

A) Instrument Air, because it is produced at a higher pressure;B) Plant Air, because it is not passed through dryers;C) Instrument Air, because it is passed through dryers.

8.5 MISCELLANEOUS

49. Mention at least three actions by which a plant can be operated from Control Room.50. Mention the five levels of the Distributed Control System.51. How is the adjusted opening of a Control Valve, in Manual Operation?

A) Physically, on the field, by the operator;B) Remotely, by the operator, through pneumatic or electric transmission systems;C) For Manual Operation, the operator takes the responsibility of fixing the controller’s Set

Point.52. A Controller is expected to compare:

A) Actual value with desired value (of the Process Variable);B) Desired value with the set point;C) Actual value of the Process Variable with the opening of the valve.

53. In a Level / Flow cascade, which controller is the master ?A) The Level Controller, because it is dictating the set point;B) The Flow Controller, because it is operating the Control Valve;C) The Operator may select any of them, according to operating needs.

54. What is the purpose of a Hydro test ?A) To wash the system with water, for checking if it is clean;B) To check the quality of welding;C) To check the tightness of flanged connections.

55. When are flow meters supposed to be installed on pipelines?A) Immediately after the Hydro test;B) After systems’ flushing and blowing;C) Before the Hydro test.

56. When performing a job in open air, under a Hot Work Permit, one might use:A) Breathing apparatus;B) Anti spark tools;C) Face shield / safety glasses.

8.5 MISCELLANEOUS (continued)

57. What is the purpose of purging the lines with nitrogen, when shutting down the Fuel Gas system?A) To displace Fuel Gas to Flare;B) To reduce Oxygen content below 2%, for preventing explosive mixtures building up;C) To vent Fuel Gas and Oxygen out of the header, in order to achieve an inert atmosphere

inside the system.58. Why are Diesel Generators used in Oil & Gas Plants ?

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A) Because power supplied by Diesel is cheaper;B) As an alternative source of power, for short time operations;C) As an independent source of power, for emergency situations.

59. A system prepared for flushing consists of :A) Pipelines operating at the same pressure (not necessarily installed as per P&ID);B) Interconnected pipelines, installed as per P&ID (regardless operating pressure);C) Spool pieces of pipelines that are prepared for Hydro test.

60. Mention three conditions which may cause a Plant’s shut down.

9. ANSWERS

1. C 17. B 42. C 2. A 18. B 43. B 3. A 19. A 44. A,C4. A,B 20. B 47. C5. C 21. C 48. B6. B 22. A 51. B7. B 23. C 52. A8. B 25. C 53. A9. C 29. A 54. B

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10. B 30. C 55. B

11. C 31. C 56. C12. B 32. B 57. A13. A 36. B 58. C14. A 37. A 59. B15. C 38. B16. A,C

24. To ensure full condensing of the steam. They open to admit a batch of steam and keep it trapped until complete condensing.

They must be installed in the diresction of flow.

26. Close all drainvalves of the affected line. Isolate the affected line: close first the inlet and then the outlet valve. Allow cooling down of the pipe, then drain.

27. Superheated: work transfer (turbines and pumps). Saturated: heat exchange.

28. Can be controlled much easier by the operator, than the isolation valve – in terms of gradually opening. Steam throttling through the valve is minimized so the seat will not be dammaged. It is used for Steaming Out and Warming Up.

33. Check out pump’s integrity / check lube oil / open suction valve and prime the pump / crack-open the discharge valve / start the pump / keep the discharge valve throttled until the full discharge pressure is reached.

34. Close drains on shell side & tube side / Open inlet & outlet valve of the cold stream, prime and fill the circuit / Open inlet & outlet valve of the hot stream, prime and fill the circuit / Adjust flows and temperatures as required.

35. Stop pump / Close suction & discharge valves / Allow pump’s cooling down/ Depressurize & drain the pump / Ask electricians to disconnect pump’s motor in the substation / Issue work permit / Blind suction and discharge valves.

39. Explosion involves a sudden increase in volume and releasing of energy in a violent manner (pressure waves are produced, besides the heat). It occurs if too much fuel is available when combustion is initiated.

40. HH temp. on heater’s outlet line; LL fuel gas pressure; HH level at fuel gas KO drum; Loss of pilots’ flame.

41. To act as an instant source of ignition in case of any hydrocarbon release; to prevent atmospheric air from entering the flare system.

45. Viscozity curve● Gravity● Flash point● Caloric value● Thermal conductivity and stability● Specific heat curve● Pour point● Asphaltenes● Metallic impurities● Sulfur.

46. Concentrical tubes with common top nozzle: fuel oil flowing inside and steam outside of the central tube. Atomizing steam contributes to the reduction of liquid into an uniform spray, for improved combustion. A small portion of steam is passed through the fuel oil burners even when they are not in operation, for keeping not in operation, for keeping them hot.

49. Select “MANUAL” or “AUTO” mode of operation● Change set points of the control loops● open or close motor-operated

valves● start or stop pumps.

50. Field● Local Control Unit● Central Control Room● Area Management● Group Management.

60. High-High Level in the Flare K.O. Drum; Low –Low Instrument Air pressure; Total Power failure (Black-Out).

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Documents

Oil and Gas Plants Operation Aspects