Thesis Compression cooling vs Absorption cooling (Jos Slotema Wu8 0832917).pdf

8/9/2019 Thesis Compression cooling vs Absorption cooling (Jos Slotema Wu8 0832917).pdf

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2014

Jos Slotema (0832917) Wu8

Mentor: Mr. van den Brink

Project cordinator: Mr. H. de Klerk

Company supervisor: Mr. S. de Leeuw

Department: Mechanical Engineering

Capelle aan den IJssel

5/13/2014

Thesis: Compression Cooling Vs.

Absorption Cooling


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Jos Slotema Graduation Internship at Technip-EPG

Prefix

This report was written as part of the graduation assignment, which is the conclusion of the Bachelor

of mechanical engineering study at Hogeschool Rotterdam.

The thesis is the result of a research to an existing compression cooling system with R134a refrigerant

and an absorption cooling system with R717 (Ammonia) refrigerant. To understand this report some

experience or knowledge of cooling systems is necessary.

The thesis was developed in consultation with my dual study supervisor and the lead engineer from

the mechanical department of Technip-EPG. The choice for the Energy Technologythesis fits well

with my interest for the cooling industry.

I want to thank Simon de Leeuw for giving me this opportunity, Johan van den Brink for the guidance,

Ms. Molt for the English check and specially Hein de Klerk for his corrections, patience and hours of

beer talk.

Cheers,

Jos Slotema

Rotterdam, May 2014


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Table Of Contents

Prefix ..................................................................................................................................................2

1. Abstract ......................................................................................................................................4

2. Project backgrounds....................................................................................................................5

2.1 Company .............................................................................................................................5

2.2 Client ...................................................................................................................................6

2.3 Situation ..............................................................................................................................6

2.4 Project .................................................................................................................................6

3 Existing cooling system................................................................................................................7

3.1 What are Fluoro-polymers / carbons. ..................................................................................7

3.2 Analysis of the existing cooling system including backup .....................................................7

3.3 Brine system ........................................................................................................................8

3.4 Connection between -30C and -45C system ......................................................................8

4 Calculations existing -30C R134a system ...................................................................................9

4.1 Log_P-h diagram R134a .......................................................................................................9

4.2 Evaporator ........................................................................................................................ 10

4.3 Compressor ....................................................................................................................... 11

4.4 Condenser ......................................................................................................................... 13

4.5 Hot Gas Bypass .................................................................................................................. 15

4.6 Economizer........................................................................................................................ 15

4.7 Energy balance .................................................................................................................. 16

4.8 Check Brine pump capacity ................................................................................................ 17

5 Explanation absorption cooling process..................................................................................... 18

5.1 LogP-h R717 ...................................................................................................................... 19

5.2 Calculations ....................................................................................................................... 20

6 Comparison both systems ......................................................................................................... 26

7 Conclusion ................................................................................................................................ 27

8 Recommendations .................................................................................................................... 27

9 References ................................................................................................................................ 28

9.1 Text References ................................................................................................................. 28

9.2 Figure References .............................................................................................................. 28

10 Appendices ........................................................................................................................... 29


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1.AbstractFor the production of Fluorocarbons a cooling system is necessary. The production plant at the

Dordrecht site is using the cooling system for multiple products. This cooling system is split up in a

primary and a secondary system. The primary system consist of a compression cooling system to cool

the brine in the secondary system. This system is a circulation system connected to the different

process users. The existing primary compression cooling system needs to be replaced due to aging

and reliability.

An economic comparison should be made for a new absorption cooler fed by waste heat versus a new

compression cooling system with comparable specifications. Which system is preferable after all

conditions are taken into consideration?

The existing -30C R134a refrigeration system at the DuPont site in Dordrecht has been analyzed.

Calculations have been made and compared with a new absorption cooling system equipped with R717

or ammonia refrigerant. The result is that if there is enough waste heat to generate the needed amount

of steam the absorption cooler is in operating conditions cheaper than the existing compression cooler.

After the results of comparing both systems the energy level of waste heat, necessary to operate the

absorption system, should be determined.

In this report the lubrication and the purge unit are not taken in to account for the efficiency of the

compression cooler. The lubrication for the rotating part is very important for especially the

compressor. For future calculations this must be taken into account.


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2. Project backgrounds

2.1 Company

Technip is a world leader in design, engineering, supply and construction of facilities in the oil & gas

and (petro) chemical industry. Technip-EPG is part of the umbrella organization Technip-Group which

also includes Technip Benelux BV in Zoetermeer. Technip Group is represented in 48 countries across

five continents and employs more than 30,000 people. The main business segments in which the

Technip-Group is active are: Subsea, Offshore and Onshore. Technip boasts a fleet of 34 vessels of

which five are now being built (1).

Technip-EPG

Technip-EPG was acquired by Technip-Group in July 2008 to strengthen Technip Benelux. At that time

the company EPG (Engineering Project Group) had 35 years of experience in designing plant

modifications such as modernization and capacity expansion. EPG has 2 locations: Capelle aan den

IJssel and s-Hertogenbosch. This multidisciplinary engineering company has 150 employees who work

on fixed or temporary contracts (2).

The market segments in which Technip-EPG is active:

1. Oil and Gas

2. (Petro) Chemicals

3. Energy and Water

4. Industry

5. Utility

To manage the projects, the project team is divided into the disciplines mentioned below, each withtheir own specialties.

Project

HVAC (Heating Ventilation Air Conditioning)

Electrical & Instrument

Civil

Structural

Pipe stress

Process

Piping

Mechanical

Document Control


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2.2 Client

Du Pont de Nemours (Nederland) B.V. is part of the global E. I. Du Pont de Nemours and Company.

DuPont is a science-based products and services company. Founded in 1802, DuPont puts science to

work by creating sustainable solutions essential to a better, safer, healthier life for people everywhere.Operating in more than 70 countries, DuPont offers a wide range of innovative products and services

for markets including agriculture and food; building and construction; communications; and

transportation.

The DuPont sites in the Netherlands are situated in Dordrecht, Breda and Landgraaf. DuPont

Netherlands employs approximately 950 people.

Dordrecht is one of the largest production sites of DuPont in Europe and it is the companys eldest site

in the Netherlands. The site is home to nine manufacturing plants where the synthetic resins Delrin

and Surlyn are made, the refrigerants Isceon and Suva and the Fluorocarbons Teflon and Viton.

The Teodur Powder Coatings sales organization and the DuPont Crop Protection marketing

organization are located in Dordrecht as well. The sales organization of Standox automotive

refinishing paints is located in Breda. The Landgraaf site manufactures filaments for the toothbrush

industry.

All production sites of DuPont in the Netherlands are certified according to ISO-9001 (quality) and ISO

14001 (environment).

2.3 Situation

The graduate student is working for the mechanical department of Technip-EPG Capelle aan den IJssel

as draftsman. During the project the student works solitary. Guidance is provided if necessary. The

mentor who is guiding this project works for the same department and keeps track of the planning and

the progress of the project.

2.4 Project

For the production of Fluorocarbons a cooling system is necessary. The production plant at the

Dordrecht site is using the cooling system for multiple products. This cooling system is split up in a

primary and a secondary system. The primary system consist of a compression cooling system to cool

the brine in the secondary system. This system is a circulation system connected to the differentprocess users. The existing primary compression cooling system needs to be replaced due to aging

and reliability. An economic comparison should be made for a new absorption cooler fed by waste

heat versus a new compression cooling system with comparable specifications. The following must be

taken into account:

Safety

Environment

Operational costs


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3 Existing cooling system

3.1 What are Fluoro-polymers / carbons.

Fluorocarbons are the result of the chemical connection between fluorine and carbon particles. This

gas is commonly used in Fluoropolymers, refrigerants, solvents and anesthetics.1) A mixture of

fluorspar, hydrofluoric acid and chloroform (TFE tetrafluorethylene) is heated between 600 and 900C.

To remove any impurities the gas needs to be distilled. During the distillation process the gas is heated

and in a special distillation vessel which guide the heated gas thru a pipe system cooled by brine. The

purified gas condensates and is collected in storage vessels. To store this gas it needs to be at very low

temperature and pressure to maintain the liquid state of the material. TFE is colorless, odorless and

extremely flammable (4).

Fluoropolymers are the result of polymerized TFE. The polymerization process makes long strings of

the molecules in TFE. To initiate the polymerization process the TFE is guided to special drums

containing purified water and a small amount of initiators. When the TFE comes in contact with the

initiator the process is started. The strings of material are formed to grains of PTFE. The grains are

suspended in the water/initiator solution and will float on the surface. To increase the productivity the

drum is shaken to mix the water mixture with un-used TFE gas to the mixture. The chemical process is

producing heat that must be cooled by the brine system that flows thru the jacket of the drum. The

grains can be sold as bulk or molded into billets (5).

3.2 Analysis of the existing cooling system including backup

The cooling system used for the production of fluoro -polymers and carbons is divided into a primary

and a secondary system as shown in the Process Flow Diagram in figure 1.

Figure 1: PFD R134a -30C

The heat produced by the chemical polymerization processes needs to be absorbed and controlled by

the secondary cooling system (9). The different end users pump their heated cooling medium to a heat

exchanger which transfers the heat to the brine in the secondary cooling system (1). Because the

temperature of the brine is lower than the processed cooling medium the cooled brine extracts the

heat from the cooling medium which can be re-used by the end users.


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The brine solution, is pumped (2) to the evaporator (34) to exchange the absorbed heat to the R134a

gas and is recirculated thru the secondary system. The R134a gas in the primary system is overheated

due to the low pressure and temperature difference of the R134a. The overheated gas is compressed

by a 4 stage compressor driven by an E-motor (5). To prevent an unnecessary stop of the compressor,

the compressed vapor can be redirected to the evaporator by the hot gas by-pass. The high pressure

Freon gas flows to the condenser (6) where the cooling water from the cooling tower rapidly cools

down the Freon gas. Condensation of the R134a is realized by the heat exchange in the condenser by

the cooling water from the cooling tower. The high pressure R134a liquid flows thru a pressure control

valve (7) where the flow remains equal but the pressure drops to a level where the Freon almost

evaporates and is transported into the evaporator where the cycle repeats.

To prevent a shutdown of the plant the cooling system is provided with a backup installation to

guaranty a continuous flow of cooling. This -45C system is fully separated from the main cooling

system except for the cooling water produced by the cooling tower Instead of R134a, as used in the -

30C system. Freon 22is used in the -45C refrigeration system. The connection between both systems

is further explained in chapter 3.4 of this document.

3.3 Brine system

The secondary system is filled with a brine solution.Brine is a commonly used fluid used as a secondary

refrigerant in large refrigeration installations for thetransport ofthermal energy from one place to

another. This fluid is easily transported over longer distances and therefore suitable for the use of

cooling multiple process units. The used type of brine for this installation is Methylene Chloride. For

properties see figure 2 below.

Because of the low temperature of -30C a normally used calcium chloride, natrium chloride or

water/glycol solution is not applicable due to freezing of the fluid. Methylene chloride should not be

used with aluminium or zinc and it will attack most rubber compounds and plastics. To make sure a

minimum of temperature is lost during transport the entire system is insulated to maintain the lowtemperature.

3.4 Connection between -30C and -45C system

There are 5 different cooling systems present for the production facilities to cool all the necessary

operations. The -30C and -45C are both connected to the same brine system as previously described.

Both brine systems are connected with valves en piping spools. Both systems run simultaneously but

when one needs to shut down the other takes over to maintain a continuous brine flow. Both systems

have an electrical driven pump which acts as a backup pump for the other system. The complete

diagram with all the connections is found in appendix 1 of this document.

Property

Boiling point 40 C

Freezing point -97 C

Vapor pressure at 25C 57 kPa

Viscosity 0.70 mPa-sec

Specific heat 1.13 kJ/kg.K

Thermal conductivity 0.19 W/m.K

Density 1400 Kg/mFigure 2: Properties Methylene Chloride
http://en.wikipedia.org/wiki/Brinehttp://en.wikipedia.org/wiki/Refrigeranthttp://en.wikipedia.org/wiki/Transporthttp://en.wikipedia.org/wiki/Thermal_energyhttp://en.wikipedia.org/wiki/Calcium_chloridehttp://en.wikipedia.org/wiki/Natrium_chloridehttp://en.wikipedia.org/wiki/Natrium_chloridehttp://en.wikipedia.org/wiki/Calcium_chloridehttp://en.wikipedia.org/wiki/Thermal_energyhttp://en.wikipedia.org/wiki/Transporthttp://en.wikipedia.org/wiki/Refrigeranthttp://en.wikipedia.org/wiki/Brine


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4 Calculations existing -30C R134a systemIn this chapter a closer look will be taken at the specific components of the -30C cooling system. For

further details of the components see appendix 2. The brine should be cooled from -30C to -23,5C.

To be able to analyze the system a Log_P-h diagram should be made.

4.1 Log_P-h diagram R134a

See figure 3 and appendix 3 for completed log_P-h diagram.

Figure 3: Log_P-h diagram -30C system

Step 1 2: Evaporator.

The heated brine evaporates the R134a till an overheated gas is realized. To make sure all the

refrigerant is evaporated the hot gas bypass from the end of the compressor feeds hot vapor at the

inlet of the evaporator. The high temperature will overheat the gas when necessary. When fluid enters

the compressor the rotors will be heavily damaged and the lubrication isnt effective enough to handle

the high speeds of the rotating parts. The enthalpy of the R134a at the inlet of the evaporator is 182

kJ/kg. The evaporation temperature is by pressure drops reduced to -33C so it is able to absorb lots

of heat from the secondary brine system. The pressure of the refrigerant at the outlet of the

evaporator is equal to the suction pressure at the inlet of the compressor. The enthalpy at this point is

385 kJ/kg. The temperature of the refrigerant is overheated by 10C to -23C by absorbing heat from

the brine system. This fully overheated gas is ready to enter the compressor.

Step 2 3: Compressor

The compressor compresses the overheated gas from the evaporator from 0,65 bar at the inlet to 7,3

bar in 4 different stages. The second and third stage are connected with the respectively High and Low

stage of the economizer. The gas produced due to pressure drops in the economizer is entering the

compressor at stage 2 and 3. This gas cools the gas from the previous stages of the compressor. This

helps the compressor increase his efficiency and also prevents the refrigerant from reaching the critical

temperature of 100.95C (3)from which the refrigerant is not able to condensate/recover any more.


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Step 3 4: Condenser

The gas heated by compression leaves the compressor at 72C and enters the condenser. The cooling

water from the cooling towers which are pumped thru the tubes of the heat exchanger, absorbs the

heat from the gas flowing thru the shell side. To make sure all the gas is condensed the R134a is 3C

sub cooled.

Step 4 1: Economizer/Choke Valve

The high pressure R134a liquid is flowing in to the first high pressure stage of the economizer. The

pressure drop will partially evaporate the R134a condensate. The pressure drops from 7,3 bar to 3 bar

(Step 4 4). The evaporated R134a flows to the inlet of the third compressor stage. The Condensate

is then guided to the second low pressure stage of the economizer by a level control valve. The

pressure drops from 3 to 1,6 bar and the gas flows to the 2ndstage of the compressor (Step 4 4).

The last stage is the choke valve where the pressure drops to 0,75 bar (Step 4 1). The temperature

at this point of the cycle is -33C and enters the evaporator to repeat the entire process.

4.2 Evaporator

The chiller used in the -30C cooling system is a shell and tube heat exchanger fabricated by Johnson

Hunt. During normal operation the evaporator absorbs 1880 kW heat from the brine system.

Figure 4: Evaporator -30C cooling system.

The absorbed energy from the brine system is 1880 kW (kJ/s).

is 385-182= 203 kJ/kg. The formula used for calculating the mass-flow is: ( ) = (

) \

= = =9.26 / = 33.34 ton/h


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4.3 Compressor

The compressor used in the closed circuit R134a refrigeration system is powered by an electric motor

thru a gearbox. See figure 5 for layout. To prevent excessive wear of the compressor and its

components the lubrication is closely monitored and controlled.

Figure 5: Compressor, engine and gear box assembly -30C cooling system.

The Compressor uses 4 stages to compress the overheated gas from the evaporator from 0,65 bar to

7,3 bar. See appendix 3 for the Log_P-h diagram. Each vane as seen in figure 6 is specifically shaped

to increase the pressure at each stage.

Figure 6: Inside compressor rotor assembly.


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Figure 7: Connections of the compressor

The first compressor stage is connected to the outlet of the evaporator and takes in the overheated

gas at -23C. The calculated flow of the vapor is 9,26 kg/s as determined in chapter 4.2 of this

document. The enthalpy is 392 kJ/kg at the end of this stage and the pressure 1,22 bar. At the end of

the first stage is the released gas from the low pressure side of the economizer added to the gas

from the first stage. This realizes a temperature drop of +/- 7C, see figure 3.

Compression ratio for the first stage is:

1.220.65 =1.877

The second stage compresses the new gas mixture to 2,45 bar. At the end of the stage the vaporized

refrigerant from the high pressure stage of the economizer is added to the mixture. The temperature

drop of the total mixture is +/- 9C for this stage of the compression, see figure 3.

Compression ratio for the second stage is:

2.451.22 =2.008

The third and fourth stages is straight forward with no additional input.

Compression ratio for the third stage is:

4.32.45 =1.755

Compression ratio for the second stage is:

7.34.3 =1.697


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The power consumption of the compressor is calculated with the compressor specifications in

Appendix 2.

Following formula is used:

= 3

= 6600 = 114 .=0.893is used because a three phase power supply is used.= 6 6 0 0 1 1 4 0 .8 9 3 = 1160 The efficiency of the compressor is calculated by dividing the input by the output of the compressor.

=

Poutis 1120 kW according specifications in Appendix 2.

= 11201160 =0.96

4.4 CondenserThe condenser should be able to condensate all the compressed vapor which leaves the compressor.

To make sure there is no vapor left the refrigerant is sub cooled 3C. the water from the cooling towers

is led thru the tubes of the heat exchanger (Shell/Tube type). The gas is fed into the topside of the

condenser in the center shell part. The condensed refrigerant falls to the bottom of the shell. The

temperature difference of the cooling water between the inlet and the outlet of the condenser is 4.7C.

Figure 8: Condensor -30C cooling system


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To make the condenser more efficient a two passes system is used. This means that the cooling water

in the tubes enters in the bottom half of the exchanger redirected thru top part of the condenser. See

figure 9.

Figure 9: Inside Condenser during maintenance.

To calculate the mass-flow of refrigerant thru the condenser the needed capacity from the

specifications is used, see Appendix 2. The enthalpy is derived from the Log_P-h diagram in appendix

3.

The formula used for calculating the mass-flow of the refrigerant is:

( ) = ( ) \

= 3000

= = 4 3 8 2 3 5 = 2 0 3 =

= = 14.78 / = 53.2 ton/h

Cooling water consumption

=

= 3 0 0 0 = 4 .1 8 Specific heat of water at 44C(6) = 7 Assumed temperature drop = 30004.187 =102

102 3600 = 367.200 /

Density of water at 44C= 990 kg/m (6)

376.200/990 = 371 m/h


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Figure 10: Cooling water towers used on the plantsite.

4 5 Hot Gas Bypass

If the process cooling demand is, for whatever reasons low, the compressed refrigerant from thecompressor is let thru the hot gas bypass. This controlled piping system feeds the refrigerant back

to the evaporator to avoid shut down of the compressor. The maximum flow thru the hot gas

bypass is as much as the flow during normal operation. By regulating the feed to the evaporator itis not necessary for the compressor to start and stop when the demand is low. It also makes sure

the compressed R134a is overheated. = 14.78 / .

4.6 EconomizerThe economizer used in this system is a horizontal vessel vertically divided in two separate parts. The

total volume of the vessel is 7,8 m and is also used as storage for the refrigerant. The entire system

contains 6200 kg R134a, according specs see appendix 2.

Figure 11: Schematic drawing of the economizer with connections.


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The economizer used in the -30C system uses the earlier explained 2 stages to:

Cool the condensed refrigerant from the condenser.

Cool the compressed gas in the compressor. Increase the enthalpy of the evaporator.

Large volume is a buffer for un-used refrigerant.

The mass flow of refrigerant vapor fed to the compressor is:

= . . =14.789.26 =5.52/The enthalpy gained by the use of the economizer:

4 4" = 2 3 5 1 8 2 = 53 /

4.7 Energy balance

Energy balance IN OUT

Evaporator 1880 kW -

Compressor 1120 kW -

Condenser - 3000 kW

COP:

To calculate the Coefficient Of Performance of the compression cooler the following formula is used:

=

=3.8

Figure 12: Closeup Log_P-h diagram


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4.8 Check Brine pump capacity

The brine pump is situated before the evaporator of the refrigeration system. The following

calculations are only applicable for the brine system connected to the -30C refrigeration system.

To calculate the brine flow the following formula is used:

= According process data is the temperature difference of the brine 6,5C between the inlet and the

outlet of the evaporator of the refrigeration system.

The specific heat and the density of the brine is derived from Figure 2 in chapter 3.3 of this document.

=

= 1 8 8 0

= 1 .1 3 = 6.5 = 18801.136.5 =256

Pump specifications are given in the unit m/h.

256 3600 = 921600 /

Divided by the density of 1400 kg/m gives:

9216001400 =658 /

According to pump specifications in appendix 4 the maximum capacity of the pump is 795 m/h.

658 < 795

The brine pump has enough capacity to circulate the brine through the system.


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5 Explanation absorption cooling processThe compression cooling system will be compared with a single stage absorption cooling system. The

low pressure part of this system is almost identical with the compression type cooler. To compare both

systems the absorption cooler will be able to extract the same amount of energy from the heated

process brine flow. The calculations for the absorption cooler will be done with the refrigerant R717

which is in fact ammonia (NH3). This refrigerant is at 1 bar (atmospheric pressure) liquid at a

temperature of -33C. Therefore is no additional vacuum needed to reach the desired temperature to

cool the brine-flow. During the process NH3 is mixed with water and will the different evaporation

temperature and pressure used to separate the water and the refrigerant. The amount of NH3 vapor

that can be absorbed by the water gets bigger by increased pressure and lowers by the increase of

temperature.

Figure 13: PFD Absorption cooler

The heated process brine enters the evaporator where it evaporates the refrigerant. The refrigerant is

at this stage fully saturated and flows to the absorber. In the absorber the gas is mixed with weak

liquor from the generator. The mix is cooled down by the cooling water from the cooling towers and

the refrigerant will condense. The mixture is now called strong liquor due to the higher concentrate of

refrigerant. In the chapter absorber of this document will the mixing and the strong and weak values

be explained. The strong liquor is then pumped thru a heat exchanger. The cold strong liquor is pre

heated by the heated weak liquor from the generator. This pre heating makes sure that there is less

energy from the steam powered generator needed to evaporate the refrigerant due to a smaller

temperature difference. The pre heated strong liquor flows after this stage into the generator. The

generator uses steam to heat the strong liquor till the biggest part of the refrigerant is evaporated. The

rest of the refrigerant still mixed with water flows thru the previous described heat exchanger and to

the absorber. The evaporated refrigerant is now entering the condenser. The condenser cools down

the refrigerant till it is entirely condensed and at a liquid state but at high pressure. A part of the


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condensate is then led into the generator again and is called reflux. This part will help the generator

to create a constant flow of evaporated refrigerant delivering to the condenser. The rest of the

condensate flows thru a choke valve where the pressure is dropped till atmospheric pressure and

repeats the entire process again. See figure 13 and appendix 9 for the process flow diagram.

5.1 LogP-h R717For support of the calculations with the absorption cooler a log_P-h diagram must be made. Because

this system does not already exists a few realistic assumptions must be made. See figure 14 for

details.

Figure 14: Log_P-h R717 (ammonia, NH3) Refrigerant

Step 1 2: Evaporator.

In the evaporator the process brine heat is absorbed and evaporates the R717. A correction must be

made at the start point of the evaporator the value is derived from figure 14. This correction is used

with values below 0C. The difference in enthalpy between 0C and -40C is 180 kJ/kg (8). This difference

must be subtracted from the value of the condensate after the condenser. This brings the start value

for the evaporator to:

1=11801=4081801 = 228 /The enthalpy when fully saturated =1417 kJ/kg at 1 bar and -33C.

Step 2 3: Generator+ Absorber

For this step the assumption is made that the temperature of the vapor must be at least 165C when

it enters the condenser. The next assumption is that the temperature at the exit of the condenser is

44C. The line derived with these values gives an enthalpy of 1829 kJ/kg at 17.3 bar.

Step 3 4: Condenser

At the exit of the condenser at the assumed temperature of 44C the enthalpy is 408 kJ/kg.

Step 4 1: Choke valve and correction

The pressure is relieved of the condensate.

4

1 1

2

3


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5.2 Calculations

All calculations in this chapter are according the book: Kents Mechanical Engineers Handbook,

Power Volume by J. Kenneth Salisbury 12thedition. All Imperial units are converted into Metric units

and used in the formulas (8).

Evaporator

The evaporator must be able to absorb 1880 kW heat from the brine system.

Figure 15: Schematic drawing evaporator absorption cool system.

To calculate the mass-flow of R717 refrigerant the following formula is used:

( ) = ( ) \

=

=

=1417228 = 1189 /

3 = =1.58 / = 5.69 ton/h

Absorber

The absorber mixes the weak liquor and the condensed refrigerant by condensing the refrigerant

with cooling water. The amount of strong liquid is calculated in this chapter. The percentages are

derived from the table in appendix 5.

(S) Strong liquor = 26% NH3 dissolved in water (74%H2O)

(W) Weak liquor = 15% NH3 dissolved in water (85% H2O)

3 + = The formula for the mixing point is:

S 0 .7 4 = W 0 .8 5S = 1 . 1 4 9 W

Figure 16: Schematic drawing absorberabsorption cool system.


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3 + = 1.149 1.149 = 0.149=1.58

= 1.580.149 = 10.6 /

This result is filled in in the formula for the mixing point to calculate the flow of strong liquor.

S 0 .7 4 = W 0 .8 5S0.74=10.60.85

S = 9.010.74 = 12.18 /

The capacity to condense the flow of vaporized refrigerant is calculated with the following formula:

= = 1.58 / = =1490405=1085 /

= 1.58 1085 = 1714

To calculate the needed amount of cooling water to condensate the refrigerant, the following

formula is used:

= Rewritten for mass flow

=

= 1 7 1 4

= 4 ,1 8

Specific heat of water at 44

C(6)

= 7 Assumed temperature drop = 17144.187 =58,6

58,6 3600 = 210.881 /

Density of water at 44C= 990 kg/m (6)210.881/990 = 213 m/h


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Pump

To calculate the needed capacity of the pump the following formula is used:

=

= 17.3 = 1730000 /= estimated efficiency of 0,75= 2+3 3 = 681.9 /`at -33C (7)

2 = 1000 /

3 12.18 = 26% 3 = 12.18 0.26 = 3.17 = 0.00464

2 12.18 = 74% 2 = 12.18 0.74 = 9.01 =0.009

= 0.009 + 0.00464 = 0.0136

= 0.013617300000.75

= 31,37

Figure 17: Absorption cooler pump


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Generator

The strong liquor is pre heated in the heat exchanger by the weak liquor. After evaporation is a part of

the refrigerant sent back as reflux. So there are 2 inputs and 3 outputs with different temperatures.

Figure 18: Schematic drawing generator absorption cool system.

First the reflux must be determined. According to appendix 5 the minimum amount of reflux ratio is

0,7. To make the value is not at the bare minimum an assumed safety factor of 1,2 is applied. This

makes the reflux ratio 0,7*1.2= 0,84. This means that 84% of the high pressure condensate is

redirected to the generator.

The next step is to calculate the temperature of the strong liquor at the inlet of the compressor. The

assumed temperature of 165C is still present in the weak liquor that flows into the heat exchanger

point 1 on figure 18. The insert temperature of the weak liquor in the generator at point 2 is assumed

45C. The entrance temperature of the strong liquor in the heat exchanger is assumed 35C at point 3.

The temperature at point 4 is calculated as follows:

=

= = 10.6 /=16545=120C = 12.1 / = 35Filled in in the formula gives:

10.6120=12.1 35

1 2

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127212.1 + 3 5 =

=140CCondenser

To calculate the needed cooling capacity for the condenser the mass-flow of NH3 at the exit of the

condenser must be determined.

85% reflux is what enters the generator and 1,58 kg/s is what enters the evaporator. So 100% NH3 l

at the exit of the condenser 3is :1,58*1.85 =2.92 kg/s.

Figure 19: Schematic drawing Condenser absorption cool system.

To calculate the needed cooling capacity the following formula is used:

( ) = (

) \ = 44C (See figure 20)

= 1490.8405.7 = 1085.1 /=2.921085.1=2.921085.1 = 3,17

Figure 20: Saturation table R717 at 44

To calculate the needed amount of cooling water to condensate the refrigerant, the following

formula is used:

= Rewritten for mass flow

=


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= 3 1 7 0 = 4 .1 8 Specific heat of water at 44C(6) = 7 Assumed temperature drop

= 31704.187 =108

108 3600 = 390.020 /

Density of water at 44C= 990 kg/m (6)390.020/990 = 394 m/h

Steam consumption

To calculate the steam consumption in the generator a separation is made between the capacities IN

and OUT. The generator is in fact a kind of heat exchanger so the formula used is:

= 35 45 3 44

+ = + 3 +The values for the weak and strong liquor are derived from appendix 5 in kJ/kg

+5626.5= 7155+366+3170= 7155+366+31705626.5=5065 The amount of steam necessary for evaporating in the generator is calculated with the following

formula:

=

To derive the enthalpy specific for steam at 165Cthe enthalpy for gas and liquid is derived from thetable in appendix 6. = 5065 = =2762697=2065 /

= =50652065 = 2,45 /

Total steam consumption = 8,8 ton/h


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6 Comparison both systemsThe price of a full year of operation is calculated to compare both systems. The prices are estimated

and the year counts 365 days. The values are in operating condition that means without startup

Cost Unit

Cooling water 1000 m 33

E- Power kWh 0,17

Steam ton 18

Compression cooler

Consumption hour year

Cooling water 371 m/h 3249960 m 107.248

E-Power 1160 kW 10,161.600 kWh 1.727.472

Total 1.834.720

Absorption cooler

Consumption hour year

Cooling water 607 m/h 5.317.320 175.471

E-Power 31,37 kW 274.801 46.716

Steam 8820 kg 77.263.200 1.390.737

Total 1.612.924

With a difference of 221.796 the absorption cooler is cheaper in operational costs.

The environmental load of the absorption system is bigger due to toxic NH3 levels.

Maintenance costs are much lower for the absorption cooler because there are fewer rotating parts

that need close monitoring of wear tear and lubrication


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7 ConclusionThe Absorption cool system is during a year of 365 days 221.769 cheaper in operational costs than

the compression cooler. The price for the steam used by the generator is only acceptable if the steam

can be derived from waste heat from the chemical process.

8 RecommendationsIn this report the lubrication and the purge unit are not taken in to account for the efficiency of the

compression cooler. The lubrication for the rotating part is very important for especially the

compressor. For future calculations this must be taken into account.

The available waste heat should be calculated.

The prices used to calculate the operational costs are estimated. For more accurate results the actual

prices need to be used. Unfortunately I did not had access to these prices.

Other absorption refrigerants can be calculated for use in the cooling system.

Multiple stage absorption coolers can be calculated.

If the absorption cooler is installed proper steps should be taken to prevent the refrigerant to spill in

the environment due to high toxic levels. The operators must be instructed properly for the use of the

absorption system.

Maintenance costs are a big factor in the total costs of the systems so they can be calculated to be

more accurate.


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9 References

9.1 Text References

1) Site TP Group,http://www.technip.com/en/about-us/company-profile/technip-glance

2)

Site TPEPG,http://www.epg.nl/organisatie/index.php

3)

Site Dupont NL,

http://www2.dupont.com/Dordrecht_Plant_Site/nl_NL/sites_products/ddt/dordrecht.html

4)

Fluorocarbons information site,http://en.wikipedia.org/wiki/Fluorocarbon

5) Teflon information site,http://www.madehow.com/Volume-7/Teflon.html

6) Water properties, Information site,http://www.engineeringtoolbox.com/water-thermal-

properties-d_162.html

7) Log_P-h diagram R717, Appendix 7

8) Kents Mechanical Engineers Handbook, Power Volume by J. Kenneth Salisbury 12thedition

chapter 11 Absorption refrigeration, John Wiley & Sons Inc.

9.2 Figure References

Figure 1: PFD R134a -30C, Screenshot appendix 8, By J.Slotema

Figure 2: Properties Methylene Chloride,http://www.inchem.org/documents/pims/chemical

/pim343.htm

Figure 3: Log_P-h diagram -30C system, CoolPack program, Microsoft Word, by J.Slotema

Figure 4: Evaporator -30C system, Picture site visit 3-4-2014

Figure 5: Compressor, engine and gearbox assembly -30C system, picture site visit 3-4-2014

Figure 6: Inside compressor rotor assembly, Picture Maintenance 23-9-2009

Figure 7: Connections of the compressor, Appendix 10, Bentley MicroStation, by J.Slotema Figure 8: Condenser -30C system, Picture site visit 3-4-2014

Figure 9: Inside Condenser during maintenance, Picture Maintenance 23-9-2009

Figure 10: Cooling water towers used on the plantsite, picture site visit 3-4-2014

Figure 11: Schematic drawing of the economizer with connections, Appendix 10, Bentley

MicroStation, by J.Slotema

Figure 12: Close-up Log_P-h diagram, Appendix 3, by J.Slotema

Figure 13: PFD Absorption cooler, Appendix 9, Bentley MicroStation, by J.Slotema

Figure 14: Log_P-h R717 refrigerant, Appendix 7,CoolPack program, Microsoft Word, by

J.Slotema

Figure 15: Schematic drawing evaporator absorption cooling system, Appendix 9

Figure 16: Schematic drawing absorber absorption cooling system, Appendix 9

Figure 17: Schematic drawing pump absorption cooling system, Appendix 9

Figure 18: Schematic drawing pump generator cooling system, Appendix 9

Figure 19: Schematic drawing pump condenser cooling system, Appendix 9

Figure 20: Saturation table R717 at 44C, screenshot CoolPack program
http://www.technip.com/en/about-us/company-profile/technip-glancehttp://www.technip.com/en/about-us/company-profile/technip-glancehttp://www.technip.com/en/about-us/company-profile/technip-glancehttp://www.epg.nl/organisatie/index.phphttp://www.epg.nl/organisatie/index.phphttp://www.epg.nl/organisatie/index.phphttp://www2.dupont.com/Dordrecht_Plant_Site/nl_NL/sites_products/ddt/dordrecht.htmlhttp://www2.dupont.com/Dordrecht_Plant_Site/nl_NL/sites_products/ddt/dordrecht.htmlhttp://en.wikipedia.org/wiki/Fluorocarbonhttp://en.wikipedia.org/wiki/Fluorocarbonhttp://en.wikipedia.org/wiki/Fluorocarbonhttp://www.madehow.com/Volume-7/Teflon.htmlhttp://www.madehow.com/Volume-7/Teflon.htmlhttp://www.madehow.com/Volume-7/Teflon.htmlhttp://www.engineeringtoolbox.com/water-thermal-properties-d_162.htmlhttp://www.engineeringtoolbox.com/water-thermal-properties-d_162.htmlhttp://www.engineeringtoolbox.com/water-thermal-properties-d_162.htmlhttp://www.engineeringtoolbox.com/water-thermal-properties-d_162.htmlhttp://www.inchem.org/documents/pims/chemical%20%20/pim343.htmhttp://www.inchem.org/documents/pims/chemical%20%20/pim343.htmhttp://www.inchem.org/documents/pims/chemical%20%20/pim343.htmhttp://www.inchem.org/documents/pims/chemical%20%20/pim343.htmhttp://www.inchem.org/documents/pims/chemical%20%20/pim343.htmhttp://www.inchem.org/documents/pims/chemical%20%20/pim343.htmhttp://www.engineeringtoolbox.com/water-thermal-properties-d_162.htmlhttp://www.engineeringtoolbox.com/water-thermal-properties-d_162.htmlhttp://www.madehow.com/Volume-7/Teflon.htmlhttp://en.wikipedia.org/wiki/Fluorocarbonhttp://www2.dupont.com/Dordrecht_Plant_Site/nl_NL/sites_products/ddt/dordrecht.htmlhttp://www.epg.nl/organisatie/index.phphttp://www.technip.com/en/about-us/company-profile/technip-glance


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10Appendices

Appendix 1: Routing diagram between cooling systems.................. 30

Appendix 2: Component description -30C cooler.. 31-32

Appendix 3: Log_P-h diagram -30C cooler

.. 33

Appendix 4: Brine circulation pump specifications.. 34

Appendix 5: Aqua Ammonia chart .. 35

Appendix 6: Steam Saturation table .. 36

Appendix 7: Log_P-h R717................. 37

Appendix 8: PFD Compression cooler... 38

Appendix 9: PFD Absorption cooler.................39

Appendix 10: PFD Compressor, Economizer.... 40


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Appendix 1: Routing diagram between cooling systems.

Information obtained from site visit 3-4-2014, Drawing DuPont.


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Appendix 2: Component description -30C cooler.

Information obtained from site visit 3-4-2014


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Appendix 3: Log_P-h diagram -30C cooler.

CoolPack program, Microsoft Word and Excel


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Appendix 4: Brine circulation pump specifications.

Information obtained from site visit 3-4-2014


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Appendix 5: Aqua Ammonia chart.

Kents Mechanical Engineers Handbook, Power Volume by J. Kenneth Salisbury 12thedition, figure 19

page 11-32


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Appendix 6: Steam Saturation table

http://www.stoommachine.info/tabel.html
http://www.stoommachine.info/tabel.htmlhttp://www.stoommachine.info/tabel.htmlhttp://www.stoommachine.info/tabel.html


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Appendix 7: Log_P-h R717

CoolPack program, Microsoft Word and Excel


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Appendix 8: PFD Compression cooler

Bentley MicroStation, By J.Slotema


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Appendix 9: PFD Absorption cooler



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Appendix 10: PFD Compressor, Economizer


Documents

Thesis Compression cooling vs Absorption cooling (Jos Slotema Wu8 0832917).pdf