Chiller de Los Chinos Japoneses

석사 학위논문

Master's Thesis

대형 가스 수송선을 위한

엔진 배가스 활용 흡수식 냉동시스템 Absorption Refrigeration System

Utilizing Engine Exhaust Gas for Bulk Gas Carriers

김 기 홍 (金埼弘 Kim, Ki-hong)

기계항공시스템학부 해양시스템공학전공

School of Mechanical, Aerospace and Systems Engineering,

Division of Ocean Systems Engineering

KAIST

2011


엔진 배가스 활용 흡수식 냉동시스템

Absorption Refrigeration System


Absorption Refrigeration System


Advisor : Professor Daejun Chang

by

Kim, Ki-hong

Division of Ocean Systems Engineering

KAIST

A thesis submitted to the faculty of KAIST in partial fulfillment of the re-

quirements for the degree of Master of Science and Engineering in the School

of Mechanical, Aerospace and Systems Engineering, Division of Ocean Sys-

tems Engineering. The study was conducted in accordance with Code of Re-

search Ethics1

2010. 12. 20

Approved by

Professor Chang, Daejun

(Seal or signature)

1 Declaration of Ethical Conduct in Research: I, as a graduate student of KAIST, hereby declare that I have not

committed any acts that may damage the credibility of my research. These include, but are not limited to: falsi-fication, thesis written by someone else, distortion of research findings or plagiarism. I affirm that my thesis contains honest conclusions based on my own careful research under the guidance of my thesis advisor.



김 기 홍

위 논문은 한국과학기술원 석사학위논문으로

학위논문심사위원회에서 심사 통과하였음.

2010 년 12 월 20 일

심사위원장

심사위원

심사위원

장 대 준 (인)

정 상 권 (인)

정 현 (인)

i

MOSE

20093048

김 기 홍. Kim, Ki-hong. Absorption Refrigeration System Utilizing Engine Ex-

haust Gas for Bulk Gas Carriers. 대형 가스 수송선을 위한 엔진 배가스 활용

흡수식 냉동시스템. School of Mechanical, Aerospace and Systems Engineer-

ing, Division of Ocean Systems Engineering. 2011. 47 p. Advisor Prof. Chang,

Daejun.

ABSTRACT

This study demonstrated the feasibility of an absorption refrigeration system (ARS) that is capable of utiliz-

ing the engine exhaust gas of bulk gas carriers as the heat source and generating cooling source either for reli-

quefaction of the boil-off gas or for heating, ventilating and air conditioning (HVAC). The ARS employed an

NH3/H2O mixture as the refrigerant solution. The process was designed and simulated using the properties of

the exhaust gas from the commercially available engines. The coefficient of performance increased with the

temperature of the generated cooling source. A decrease in the engine load resulted in a decrease in the ex-

haust flow rate and, consequently, in a decrease in the cooling capacity. Although the exhaust temperature

reached its minimum near the normal continuous rating, the dependence of the cooling capacity on the engine

load was not significantly affected. A case study for a liquefied natural gas (LNG) carrier verified that the re-

frigeration system afforded a sufficient cooling capacity to satisfy both the required work and the temperature

level needed for reliquefaction of the boil-off gas (BOG).

Keywords: absorption refrigeration; exhaust gas, waste heat, BOG reliquefaction; bulk gas carriers

ii

Table of Contents

List of Figures ..................................................................................................... iii

List of Tables ....................................................................................................... iv

Nomenclature ....................................................................................................... v

Chapter 1. Introduction ...................................................................................... 1

1.1 Background ............................................................................................... 1

1.2 History of Absorption Refrigeration ......................................................... 2

1.3 Principle of Absorption Refrigeration....................................................... 3

1.4 Aims and objectives .................................................................................. 5

1.5 Literature Review ..................................................................................... 8

Chapter 2. System description and model ....................................................... 10

2.1 Concept of ARS utilizing engine exhaust gas ......................................... 10

2.2 Properties of engine exhaust gas ............................................................. 16

Chapter 3. Results and discussion .................................................................... 21

3.1 COP Vs. Cooling Source Temperature ................................................... 21

3.2 Cooling Source Capacity Vs. engine type .............................................. 24

3.3 Cooling Source Capacity Vs. Engine Load for a -30 ℃ Cooling Source

Temperature with 6S60MC6.1 ............................................................... 25

Chapter 4. Case Study ....................................................................................... 26

4.1 Reliquefaction system in LPG carrier ..................................................... 26

4.2 Reliquefaction system in LNG carrier .................................................... 29

4.3 Comparison with conventional systems ................................................. 32

Chapter 5. Conclusion ....................................................................................... 34

Reference ............................................................................................................ 36

iii

List of Figures

Figure 1. Principle of the absorption refrigeration ................................................ 4

Figure 2. Conceptual design of reliquefaction system utilizing ARS ................... 6

Figure 3. Schematic of ans ARS that utilizes engine exhaust gas ....................... 11

Figure 4. Process flow diagram of ans ARS utilizing engine exhaust gas .......... 12

Figure 5. Typical emissions from ans engine of ship .......................................... 16

Figure 6. Flow rate and temperature of exhaust gas vs. engine power [25] ........ 19

Figure 7. Exhaust gas temperature and flow rate vs. engine load for 6S60MC6.1 [25] 20

Figure 8. COP vs. cooling source temperature .................................................... 21

Figure 9. Cooling source capacity vs. engine type .............................................. 24

Figure 10. Cooling source capacity vs. engine load for a -30℃ cooling source temperature

with 6S60MC6.1 ................................................................................. 25

Figure 11. Conventional BOG of LPG reliquefaction system ............................. 26

Figure 12. BOG of LPG reliquefaction system with ARS .................................. 27

Figure 13. Conventional BOG of LNG reliquefaction system ............................ 29

Figure 14. BOG of LNG reliquefaction system with ARS .................................. 30

Figure 15. Comparison of the reliquefaction systems in conventional system and ARS

application (LPG) ............................................................................... 32


application (LNG) ............................................................................... 33

iv

List of Tables

Table 1. MTA and ΔP values for process simulation ........................................... 13

Table 2. Simulation basis for an ARS ................................................................. 14

Table 3. Engine exhaust gas composition ........................................................... 17

Table 4. Engine power according to the carrier type, cargo capacity and engine type [24] 18

Table 5. Stream properties of an ARS (in Figure 4), producing a -30℃ cooling temperature

for a 6S60MC6.1 engine ..................................................................... 22

Table 6. Energy balance for the ARS in Table 4 ................................................. 23

Table 7. Capability of ARS for LPG carriers ...................................................... 28

Table 8. Capability ARS for LNG carriers .......................................................... 31

v

Nomenclature

ARS Absorption refrigeration system

BOG Boil-off gas

ESP Electrostatic precipitator

LNG Liquefied natural gas

LPLT Low-pressure, Low-temperature

m Mass flow rate, kg/h

MTA Minimum temperature approach

NCR Normal continuous rating

P Pressure, kPa

Q Heat flow rate, kW

QARS Cooling source generated by ARS, kW

QBOG Cooling source required by BOG reliquefaction, kW

RHX Refrigerant heat exchanger

SHX Solution heat exchanger

SMCR Specified maximum continuous rating

T Temperature, ℃

ΔP Pressure drop, kPa

Subscripts

1, 2, 3, etc. system‟s point designation

abs absorber

con condenser

des desorber

ex engine exhaust gas

eva evaporator (cooling source)

in inlet

out outlet

p pump

- 1 -

Chapter 1. Introduction

1.1 Background

Various factors encourage efficiency and quality improvements in ship propulsion systems,

such as the high cost of fuel. Even though shipping remains an economic transport alternative,

fuel consumption is a leading cost component of the operating expenditure. Another factor is

regulation of the engine exhaust gas emissions. Polluting species such as SOx, NOx and par-

ticulate materials are regulated to stay below certain levels [1]. Much effort has been dedicat-

ed to improving the propulsion system. Leu and Huang. [2] investigated ways to enhance en-

gine efficiency and decrease polluting emissions using alternative fuels. Currently, even car-

bon dioxide (the inevitable byproduct of fossil fuel) is being seriously considered for emis-

sion regulation. It is expected that all regulations will become tougher in the future.

The engine exhaust gas is considered to be a potential source for improving the energy effi-

ciency of ships, due to the massive quantity produced and its elevated temperature level. A

popular solution is to generate steam with the hot exhaust gas. Most ships are equipped with

an apparatus, called the economizer, for this purpose. A heat recovery steam generator

(HRSG) can be used to extract even more energy (at higher expense), by absorbing both me-

- 2 -

chanical and thermal energy from the exhaust gas. There are two turbines in this system: an

exhaust gas expansion turbine and a steam turbine. The latter uses the steam generated by the

HRSG, whereas the former makes use of the boosted pressure of the exhaust gas exiting the

engine. While the flue gas is still hot after exiting the gas expansion turbine exhaust, it can be

further used to generate steam and to increase the total steam throughput. Shaft work from

the turbines is either used to generate electric power or connected to a propulsion shaft to re-

duce fuel consumption [3].

1.2 History of Absorption Refrigeration

The theory of absorption refrigeration was established in 1777 by Narine who was French.

Carre from France developed a NH3/H2O type of absorption refrigerator in 1860. In the Unit-

ed States, a H2O/LiCl type of absorption refrigerator was developed in 1929 and became

commercialize in 1945. After that, York, McQuay, Trane and Dunham-Bush put variable type

of absorption refrigerators on the market.

On the other hand, in Japan, a H2O/LiBr type of absorption refrigerator package was devel-

oped and utilized in industry and district heating and cooling system in 1958. Kawasaki

heavy industry developed a double effect type of absorption refrigerator in 1968, so the in-

- 3 -

itiative in the absorption refrigerator has gone over to Japan from the United States.

In Korea, Hyundai-Yanghang introduced a production technology of absorption refrigerator

and placed it on the market in 1975. Since then, Kyungwon Century co.,ltd produced and

put Hitachi‟s the single effect type of absorption refrigerator and the double effect type one

on the market. In the past part of the 1980, in Korea, the natural gas as city gas came into

wide use. At that time, the absorption refrigerator market rapidly grew due to the rational

energy supply policy from Korean government and deterioration of the electrical power sit-

uation.

1.3 Principle of Absorption Refrigeration

The Absorption refrigeration differs from the more prevalent mechanical type of refrigera-

tion in that the power source is heat energy, rather than mechanical energy or electric energy.

The simplest absorption refrigerators are residential refrigerators, with a gas flame at the de-

sorber and no electric energy involved. Some absorption refrigerators are more complicated

and larger, but the basic principle is the same.

- 4 -

Figure 1. Principle of the absorption refrigeration

Figure 1 is principle of the absorption refrigeration. There are mainly four sub device,

which are the evaporator, absorber, desorber and condenser.

Firstly, in evaporator, the refrigerant exchanges heat with something (QH1) to need cooling

source and the refrigerant becomes vapor phase owing to losing its latent heat. The vaporized

refrigerant is absorbed by the solution in absorber. When the solution starts to absorb, it cause

an exothermic reaction. So, the low temperature heat source (QL1) assists the solution to ab-

sorb the more refrigerant by cooling the solution during exothermic reaction. The solution

- 5 -

that contains much refrigerant is called a dilute solution and it is unable to absorb the refrige-

rant. On the other word, the solution that has a little refrigerant is called a strong solution. So

obviously it can absorb the refrigerant.

In the desorber, the dilute solution separate into the strong solution and refrigerant by ex-

changing heat with the high temperature heat source (QH2). Basically, this situation utilizes

difference in the boiling points of these fluids. The strong solution from the desorber returns

to the absorber and absorb the refrigerant continually. In the other word, the refrigerant go to

the condenser and exchange heat with low temperature heat source (QL2), thereby becoming

liquid phase. Next, it pass through the expansion valve as a result of the Joule-Thomson ef-

fect, the refrigerant becomes a low-pressure, low-temperature (LPLT) mixture of liquid and

vapor. This circulation is repeated and the energy balance is following equation 1.

2121 LLHH QQQQ (Equation 1)

1.4 Aims and objectives

One new means of utilizing the engine exhaust gas is the absorption refrigeration system

(ARS). Instead of generating shaft power, this system is able to produce a cooling source.

- 6 -

The ARS employs a mixture of NH3/H2O as the refrigerant solution. The hot engine exhaust

gas heats up the mixture and separates the refrigerant from the solution. After providing a

cooling source, the refrigerant is absorbed back into the solution.

Figure 2. Conceptual design of reliquefaction system utilizing ARS

As described above Figure 2, one application of the ARS is reliquefaction of boil-off gas

(BOG) from a cargo containment system of bulk gas carriers, such as LPG, LNG and CO2

carriers. To improve safety and increase the cargo density, these carriers transport cargo at a

low temperature and low pressure. In spite of heavy insulation, external heat ingress is un-

- 7 -

avoidable while generating the BOG, which is then used as propulsion fuel or reliquefied at

the expense of electric power consumption.

For the ARS, reliquefaction of the BOG delivers heat energy recovered from the exhaust gas

directly to the cooling source, whereas the HRSG-based system needs to convert the generat-

ed electric energy to the shaft work for the compressors of the reliquefaction system. As a

result, the former system is simpler and more compact than the latter system if the carrier

transports low-temperature liquefied gas cargo.

There are a couple of alternatives for the refrigerant mixture. A NH3/H2O solution is the

primary choice for the BOG reliquefaction system for bulk gas carriers. A H2O/LiBr solution

provides a higher level of efficiency, but using water as the refrigerant imposes some limita-

tions because the freezing point of water is relatively high at moderate pressure. Conversely,

an ARS using NH3 is capable of generating a cooling source down to -33 ℃ at 1 bar.

- 8 -

1.5 Literature Review

Several studies have explored the possibility of applying an ARS to gas processing with va-

riable power sources. Colonna and Gabrielli. [4] studied an ARS system that utilized waste

heat from a power plant and used the cooling source for various applications, such as the

food, pharmaceutical and ice production industries. Jo et al. [5] proposed an ARS that uti-

lized LNG cold energy as the cooling source. Kalinowski et al. [6] applied an ARS to extract

heat from gas turbines and pre-cool the feed gas for LNG recovery processes. The ARS pro-

posed by Bruno et al. [7] utilized the exhaust gas from a biogas-driven micro gas turbine for

cooling and to reduce the humidity of the combustion air. Rossa and Bazzo. [8] studied a nat-

ural gas micro turbine that used an ARS to replace a natural gas burning system. Abu-Ein et

al. [9] analyzed the performance of an ARS that used solar power as the heat source.

Manzela et al. [10] studied the performance of an ARS that used engine exhaust gas with the

opening rate in the throttle valve of an exhaust gas pipe. Keisuke Takeshita et al. [11] expe-

rimentally evaluated a cogeneration system made up of three turbine systems and an ARS.

Several new ways to utilize an ARS have been proposed. Kang et al. [12] proposed an ener-

gy transportation system that utilized an ARS, the solution transportation absorption system,

- 9 -

whereas Xu et al. [13] proposed combining Rankine cycle with an absorption refrigeration

cycle. Vijayaraghavan et al. [14] attempted to improve the resource utilization efficiency in

the combined power and cooling cycle, and Liu et al. [15] proposed a novel NH3/H2O mix-

ture cycle to cogenerate power and refrigeration. Other researchers [16, 17] have analyzed

the ARS and properties of the NH3/H2O mixture.

There have been some investigations that have focused on optimizing the ARS. Chang [18]

optimized the heat transfer area for a refrigeration plant in a ship, and Zhao et al. [19] opti-

mized the combined compression refrigeration system and the ARS using a NH3/H2O mix-

ture as the working fluid.

This study focuses on an ARS that utilizes the exhaust gas of a ship; this is a system that has

not received much attention. An ARS is designed to use the exhaust gas from various bulk

gas carriers. The performance and capability of the system is revealed for the engines, which

were commercially implemented. Sensitivity studies were conducted for the exhaust gas flow

rate, the cooling water temperature, and the engine load.

- 10 -

Chapter 2. System description and model

2.1 Concept of ARS utilizing engine exhaust gas

An ARS is generally composed of four parts: the condenser, evaporator, absorber, and de-

sorber. This study used NH3 and H2O for the refrigerant and the solution, respectively. Figure

3 is a schematic of an ARS that utilizes engine exhaust gas. The vapor refrigerant (NH3) from

the desorber is liquefied in the condenser through heat exchange with the cooling water. After

expanding through the expansion valve as a result of the Joule-Thomson effect, the refrige-

rant becomes a LPLT mixture of liquid and vapor. The refrigerant is then vaporized, exchang-

ing heat with the cooling source in the evaporator, and is absorbed into the solution (H2O) in

the absorber. Because the absorption process is exothermic, the solution in the absorber be-

comes warmer and loses its absorption capacity. To counteract this effect, cooling water is

supplied to cool down the solution.

- 11 -

Figure 3. Schematic of ans ARS that utilizes engine exhaust gas

The more refrigerant the solution absorbs in the absorber, the lower the concentration of the

solution. Thus, the solution in the absorber is called the dilute solution. This solution is trans-

ferred to the desorber by the pump and separates into the refrigerant and the strong solution.

The separation in the desorber results from the difference in the boiling temperature between

the solution and the refrigerant. When the dilute solution in the desorber exchanges heat with

the exhaust gas, the refrigerant vaporizes favorably and splits from the solution. The mixture

remaining in the liquid phase is rich in the solution and is called the strong solution. The re-

- 12 -

frigerant from the desorber is passed to the condenser while the strong solution is returned to

the absorber.

Figure 4. Process flow diagram of ans ARS utilizing engine exhaust gas

Figure 4 illustrates the detailed features of the ARS process that utilizes the engine exhaust

gas. Note that some additional components are inserted into the schematic in Figure 3. The

rectifier downstream from the desorber is a type of distillation column and acts as a purifier

to increase the refrigerant concentration. The solution heat exchanger (SHX) and the refrige-

- 13 -

rant heat exchanger (RHX) facilitate heat exchange within the process and increase the ener-

gy efficiency.

Table 1. MTA and ΔP values for process simulation

Components MTA,℃ ΔP, kPa

Condenser 5 10

RHX 5 21

Evaporator 5 0

Absorber 5 10

SHX 28 21

Desorber 28 10

The refrigerant concentration, a minimum temperature approach (MTA) and a pressure drop

(ΔP) are assumed in Table 1. The vapor fraction of the refrigerant after the evaporator and the

concentration of the refrigerant from the rectifier are assumed to be 0.99 and 99 %, respec-

tively [20]. This level of purity is achievable with commercially available equipment. The

temperature in the ARS ranges from approximately -30 ℃ to 150 ℃. Of the six heat ex-

change components, the temperatures of the hot stream in the SHX and at the desorber are

much higher than those of the other components. Consequently, it is assumed that the MTA

should be 28 ℃ for these two exchangers and 5 ℃ for the rest.

- 14 -

In case of phase change in these components, it is assumed that the ΔP is 10 kPa. Otherwise,

the ΔP is assumed to be 21 kPa. The evaporator and the absorber comprise one assembly in

the real system. As a result, the absorber is assumed to have only 10 kPa of ΔP. The desorber

is supposed to also have 10 kPa of ΔP because the phase change is active in the distillation

column (desorber).

Table 2. Simulation basis for an ARS

Item Unit Value

Refrigerant / solution - NH3/H2O

Refrigeration temperature, ℃ -30~0

Sea water temperature,

Inlet

℃

25~36

Outlet 35~46

Refrigerant concentration

After Rectifier

%

99

Dilute Solution 26~50

Strong Solution 16~40

Vapor fraction (after evaporator) % 99

Fluid Package - Sour-SRK

- 15 -

Table 2 indicates the simulation basis for ARS. The process was modeled with HYSYS

launched by Aspen Plus. The Sour-SRK equation of state is used as a fluid package to predict

the physical properties of the sour solution precisely [21]. The fluid package is validated by

comparing its predictions with the experimental measurements.

The cooling water temperature affects the coefficient of performance (COP) of the ARS.

The COP for this ARS is defined by the following standard equation 2 [20].

gasexhaustfromtransferHeat

sourcecoolingfromreomvedHeat

desorberinaddedHeat

evaporatorinremovedHeatCOP (Equation 2)

The cooling water temperature is closely related to the pressure and temperature of the re-

frigerant in the condenser. As the temperature of the cooling water decreases, the liquid frac-

tion of the refrigerant after the expansion valve increases. The liquid fraction is directly pro-

portional to the cooling capacity of the refrigerant in the evaporator. To reveal the effect of

the cooling water temperature, three levels of cooling water temperature are considered: 25,

32, and 36 ℃.

- 16 -

2.2 Properties of engine exhaust gas

The Figure 5 indicates the typical emissions from an engine of ship. The engine combusts

the fuel with the air and generates the propulsion work. The rest of the combustion energy,

however, is released as heat to the exhaust gas and to the cooling medium. Only half of the

energy contained in the fuel is converted to the population work. A quarter of the combustion

energy is used by the exhaust gas, and the rest is transferred to the jacket water cooler, the air

cooler and the lubricating oil cooler [22].

Figure 5. Typical emissions from ans engine of ship

- 17 -

Table 3. Engine exhaust gas composition

Component Composition, % weight

O2 14.0

N2 76.2

CO2 4.5

H2O 5.1

Others (NOx, SOx, CO, etc.) 0.2

The properties of the exhaust gas depend on the engine itself, the fuel characteristics, and

the air properties. The composition of a representative exhaust gas is indicated in Table 3.

The temperature after the engine is approximately 225 ℃. However, the amount of exhaust

gas depends on the engine capacity.

- 18 -

Table 4. Engine power according to the carrier type, cargo capacity and engine type [24]

Carrier type Cargo capacity, m3 Engine type Engine power in NCR, kW

LPG carrier

30,000 5S60MC6.1 7,500

60,000 6S60MC6.1 9,000

82,000 7S60MC6.1 10,500

LNG carrier

150,000 2*5S70ME-C7.1 22,348

150,000 7K90ME-C6.1 23,521

210,000 2*6S70ME-C7.1 27,452

210,000 7K98ME-C7.1 29,451

250,000 2*7S70ME-C7.1 31,770

250,000 8K98ME-C6.1 33,864

Data from MANBW engines are used in this study because they are available in the public

domain. The normal continuous rating (NCR), which corresponds to 75 % of the specified

maximum continuous rating (SMCR), is considered as the reference case. Table 4 indicates

the engine power, which is intrinsically proportional to the size of the carrier. In general, a

pair of engines provides better propulsion efficiency than does a single engine.

- 19 -

Figure 6. Flow rate and temperature of exhaust gas vs. engine power [25]

Figure 6 indicates the flow rate and the temperature of the exhaust gas from the engines.

The flow rate of the exhaust gas is linearly proportional to the engine power. The temperature,

however, shows no significant effect and ranges from 223.9 ℃ to 226.9 ℃.

- 20 -

Figure 7. Exhaust gas temperature and flow rate vs. engine load for 6S60MC6.1 [25]

The flow rate and temperature of the exhaust gas change with the engine load. Figure 7 in-

dicates the temperature and the flow rate of the exhaust gas according to the engine load for

6S60MC6.1. The flow rate of the engine exhaust gas is almost directly proportional to the

engine load. The tendency of the temperature is not straight, exhibiting a maximum and min-

imum at 35 % and 80 % of SMCR, respectively.

- 21 -

Chapter 3. Results and discussion

3.1 COP Vs. Cooling Source Temperature

The COP increases with both the temperature of the cooling source and the refrigerant

temperature in the evaporator, as indicated in Figure 8. Over a cooling source temperature

range from -30 ℃ to 0 ℃, COP improves by 36 %. As the evaporator temperature increases,

the evaporator pressure increases and the amount of refrigerant absorbed by the solution in-

creases, which reduces the amount of exhaust gas that is required.

Figure 8. COP vs. cooling source temperature

- 22 -

Table 5. Stream properties of an ARS (in Figure 4), producing a -30℃ cooling temperature

for a 6S60MC6.1 engine

Stream P, kPa T, ℃ m, kg/h Vapor fraction NH3 weight fraction

R1 1,167 66.8 2,812 1.00 0.99

R2 1,157 30.0 2,812 0 0.99

R3 1,136 16.3 2,812 0 0.99

R4 114 -30.0 2,812 0.16 0.99

R5 114 1.9 2,812 0.99 0.99

R6 104 25.0 2,812 1.00 0.99

D1 104 52.3 23,340 0.13 0.26

D2 104 30.0 23,340 0 0.26

D3 1,198 30.1 23,340 0 0.26

D4 1,177 106.4 23,340 0 0.26

S1 1,167 145.1 20,530 0 0.16

S2 1,146 58.1 20,530 0 0.16

S3 104 55.9 20,530 0 0.16

EXin 101 226.9 88,700 1.00

EXout 101 134.4 88,700 1.00

W1,in 136 25.0 87,210 0

W1,out 101 35.0 87,210 0

W2,in 136 25.0 169,000 0

W2,out 101 35.0 169,000 0

W3,in 136 25.0 26,670 0

W3,out 101 35.0 26,670 0

- 23 -

Table 6. Energy balance for the ARS in Table 4

Components Heat (kW)

Qdes 2,444

Qeva 973

Wp 11

Qabs 2,081

Qcon 1,018

Qrec 328

Table 5 illustrates the properties of each stream when the cooling source temperature is held

at -30 ℃ for 6S60ME-C7.1. Considering the energy balance in Table 6, the COP is estimated

at 0.398.

- 24 -

3.2 Cooling Source Capacity Vs. engine type

The cooling source capacity increases with the engine power, as indicated by Figure 9. This

effect is expected because the flow rate of the exhaust gas is almost linearly proportional to

the engine power. For a given engine power, the cooling capacity decreases with the cooling

source temperature.

Figure 9. Cooling source capacity vs. engine type

- 25 -

3.3 Cooling Source Capacity Vs. Engine Load for a -30 ℃ Cooling Source Tempera-

ture with 6S60MC6.1

The amount of exhaust gas is proportional to the engine load in the SMCR mode. Neverthe-

less, the temperature of the exhaust gas remains constant. These features are considered in

the process model. Figure 10 indicates the performance of the ARS. Although the cooling

source capacity is proportional to the overall engine load, the temperature of the exhaust gas

introduces a convex downward curve for the capacity.

Figure 10. Cooling source capacity vs. engine load for a -30℃ cooling source temperature

with 6S60MC6.1

- 26 -

Chapter 4. Case Study

4.1 Reliquefaction system in LPG carrier

Figure 11 indicates the conventional BOG of LPG reliquefaction system. The conventional

system is composed of multi compression stages and it means that the BOG of LPG is

compressed until the BOG becomes liquid when it exchanges heat with cooling water. When

the pressure of BOG is roughly 12.5 bar, the condensation temperature is 30 ℃. So, the BOG

can be liquefied to exchange heat with the 25 ℃ cooling water.

LPG to tank

BOG of LPG

Cooling

Water 1

Cooling

Water 2

Cooling

Water 3

Heat

Exchanger

1

Heat

Exchanger

Heat

Exchanger

3Heat

Exchanger

2

Separator

Scrubber 2Scrubber 3

Compressor

1

Compressor

2

Compressor

3

Expansion

Valve

Figure 11. Conventional BOG of LPG reliquefaction system

The ARS is applicable for reliquefaction of the BOG from LPG carriers. The Figure 12

shows that case. The cooling source temperature from the ARS is -30 ℃. However, this

temperature is not sufficiently cold to liquefy the BOG when the cargo is ethylene, which has

- 27 -

a normal condensation temperature of -42 ℃ at 1 bar. When the BOG is compressed to 2.5

bar, the condensation temperature increases to -22 ℃, and the cooling source from the ARS

becomes capable of liquefying the BOG. Condensation of the compressed BOG is typical in

BOG reliquefaction for bulk gas carriers.

LPG to tank

BOG of LPG

Separator

Scrubber 1

Compressor 1Expansion

Valve

ARS

Figure 12. BOG of LPG reliquefaction system with ARS

- 28 -

Table 7. Capability of ARS for LPG carriers

Item Unit Value

Volume LPG carrier m3 30,000 60,000 82,000

Max. BOG rate %/day 0.15 0.15 0.15

BOG mass flow kg/s 0.303 0.606 0.828

Required cooling capacity for reliquefaction,

QBOG

kW 166 331 453

Available cooling capacity, QARS kW 810 973 1,134

Capability of ARS, QBOG / QARS % 20 34 40

Table 7 compares the cooling source capacity with the required BOG of LPG reliquefaction

load, demonstrating that the cooling source from the ARS has enough capacity for BOG of

LPG reliquefaction.

- 29 -

4.2 Reliquefaction system in LNG carrier

The Figure 13 indicates the conventional BOG of LNG reliquefaction system. There are

largely multi compression stages and N2 reverse brayton cycle. The former one makes the

pressure of BOG high, and the condensation temperature becomes low.

In the N2 reverse brayton cycle, the N2 after the expander liquefy the BOG and cools itself

from multi compression stages in the N2 heat exchanger.

BOG of LNG

Cooling

Water 1

Cooling

Water 2

Cooling

Water 3

Heat

Exchanger

1

Heat

Exchanger

Heat

Exchanger

3Heat

Exchanger

2


Compressor

1

Compressor

2

Compressor

3

GCUGCU/BOG

Header

Scrubber 4

Expansion

Valve

Scrubber 5

To Cargo Tank

P-34

Scrubber 1

N2

Compressor 1N2 Heat

Exchanger 1

Cooling

Water 4

N2

Compressor 2 N2 Heat

Exchanger 2

Cooling

Water 5

N2


Exchanger 3

Cooling

Water 6

Expander

P-50

N2 Heat

Exchanger

Figure 13. Conventional BOG of LNG reliquefaction system

In the case of BOG of LNG, the ARS is not used for liquefaction directly. A cascaded BOG

- 30 -

reliquefaction system can utilize the ARS as a pre-cooling component rather than the propane

cycle. In the reverse N2 expansion type, the ARS is partially utilized to cool N2 such as

Figure 14.

BOG of LNG

Cooling

Water 1

Cooling

Water 2

Cooling

Water 3

Heat

Exchanger

1

Heat

Exchanger

Heat

Exchanger

3Heat

Exchanger

2


Compressor

1

Compressor

2

Compressor

3

GCUGCU/BOG

Header

Scrubber 4

Expansion

Valve

Scrubber 5

To Cargo Tank

Scrubber 1

N2

Compressor 1N2 Heat

Exchanger 1

Cooling

Water 4

N2


Exchanger 2

Cooling

Water 5

N2

Compressor 3

Expander

N2 Heat

Exchanger

ARS

Figure 14. BOG of LNG reliquefaction system with ARS

- 31 -

Table 8. Capability ARS for LNG carriers

Item Unit Value

Volume LNG carrier m3 150,000 210,000 250,000

Max. BOG rate %/day 0.15 0.15 0.15

BOG mass flow kg/s 1.33 1.862 2.216

Required cooling capacity for reliquefaction,

QBOG

kW 1,546 3,291 3,774

Available cooling capacity, QARS kW 2,700 3,291 3,774

Capability of ARS, QBOG / QARS % 57.3 65.8 68.3

Table 8 compares the cooling source capacity with the required BOG of LNG reliquefaction

load, demonstrating that the cooling source of the ARS has enough capacity to use the N2 sub

cooling in the reliquefaction system.

- 32 -

4.3 Comparison with conventional systems

The Figure 15 indicates comparison of the BOG of LPG reliquefaction systems and the

Figure 16 is LNG one. While the ARS application for LPG can save approximately 70 % of

energy consumptions. It for LNG can save only 14 % of energy consumptions. The ARS is

more useful for LPG reliquefaction than it is for LNG reliquefaction. This gap starts with the

temperature difference between cooling source temperature and LNG or LPG‟s condensation

temperature.


application (LPG)

- 33 -


application (LNG)

- 34 -

Chapter 5. Conclusion

This study demonstrated the feasibility of the NH3/H2O ARS application for bulk gas carri-

ers utilizing the exhaust gas of engines. The flow rate and the temperature level of the engine

exhaust gas were sufficient to generate the cold source, even for reliquefaction of the BOG.

By employing an ARS, a bulk gas carrier experiences significant improvement in its fuel ef-

ficiency, removing the necessity of electric power generation for BOG reliquefaction. A con-

ventional mechanical type refrigerator can be replaced by an ARS that uses NH3 as the refri-

gerant.

There are still some challenges for the realization of an ARS. One challenge is the effect of

ship motion because the system contains some parts that are sensitive to motion. For example,

the desorber is a type of distillation column and must be horizontal. When the ship is subject

to the movement caused by waves, the performance of the desorber may deteriorate. Note

that the BOG generated may be increased under these conditions because the stratification of

the cargo tanks would be disturbed.

Another challenge is the layout. The ARS requires heat exchange between the solution and

- 35 -

the exhaust gas surrounding the desorber. Two methods are conceivable: one method is to

inhale the exhaust gas within the desorber (as indicated in Figure 4) and the other is to pass

the solution through a heat exchanger placed in the stack. Both of these solutions require

complicated piping.

The last challenge is the safety risk posed by an ammonia leak, which would be hazardous to

the crew. A leak may result in the rapid evaporation of ammonia from the solution, especially

from the pressurized part of the system. One solution to this problem would be to install the

ARS on the deck rather than in the engine room. Detailed risk assessments should be per-

formed.

- 36 -

Reference

[1] Marine Environment Protection Committee. (2008). Report of the

Marine Environment Protection Committee on its Fifty-English Ses-

sion, IMO, London, MEPC 58/23/add.1, ANNEX 13.

[2] Leu, J.-H., Huang, M.-Y. (2009). “Alternative fuel test study of a

diesel engine fed by synthetic fuel derived from waste bilge oil.” Jour-

nal of marine science and technology, 17(1):7-12.

[3] http://www.mhi.co.jp/en/products/detail/mers.html

[4] Piero Colonna, Sandro Gabrielli. (2003). “Industial trigeneration

using ammonia-water absorption refrigeration systems.” Applied ther-

mal engineering, 23:381-396.

[5] Young Kyoung Jo, Jin-Kyeong Kim, Soon Geul Lee, Yong Tae

Kang. (2007). “Development of type 2 solution transportation absorp-

tion system for utilizing LNG cold energy.” International journal of

refrigeration, 30: 978-985.

[6] Paul Kalinowski, Yunho Hwang, Reinhard Radermacher, Saleh Al

Hashimi, Peter Rodgers. (2009). „Application of waste heat powered

absorption refrigeration system to the LNG recovery process.” Interna-

tional journal of refrigeration, 32: 687-694.

[7] Joan Carles Bruno, Victor Ortega-Lopez, Alberto Coronas. (2009).

http://www.mhi.co.jp/en/products/detail/mers.html

- 37 -

“Integration of absorption cooling systems into micro gas turbine tri-

generation systems using biogas: Case study of a sewage treatment

plant.” Applied energy , 86: 837-847.

[8] Janilson Arcangelo Rossa and Edson Bazzo. (2009). “Thermody-

namic modeling of an ammonia-water absorption system associated

with a microturbine.” International journal of thermodynamics,

12(1):38-43.

[9] Suleiman Qaseem Abu-Ein, Sayel M. Fayyad, Waleed Momani,

Mamdouh Al-Bousoul. (2009). “Performance analysis of solar po-

wered absorption refrigeration system.” Heat mass transfer, 46(2):

137-145.

[10] Andre Aleixo Manzela, Sergio Morais Hanriot, Luben Cabezas-

Gomez, Jose Ricardo Sodre. (2010). “Using engine exhaust gas as

energy source for an absorption refrigeration system.” Applied energy,

87(4): 1141-1148.

[11] Keisuke Takeshita, Yoshiharu Amano, Takumi Hashizume. (2005).

“Experimental study of advanced cogeneration system with ammonia-

water mixture cycles at bottoming.” Energy, 30:247-160.

[12] Y.T. Kang, A. Akisawa, Y. Sambe, T. Kashiwagi. (2000). “Absorp-

tion heat pump systems for solution transportation at ambient tempera-

ture-STA cycle.” Energy, 25: 335-370.

[13] Feng Xu, D. Yogi Goswami, Sunil S. Bhagwat. (2000). “A com-

bined power/cooling cycle.” Energy, 25:233-246.

- 38 -

[14] S. Vijayaraghavan, D.Y. Goswami. (2006). “A combined power

and cooling cycle modified to improve resource utilization efficiency

using a distillation stage.” Energy, 31:1177-1196.

[15] Meng Liu, Na Zhang. (2007). “Proposal and analysis of a novel

ammonia-water cycle for power and refrigeration cogeneration.” Ener-

gy, 32:961-970.

[16] A. Vidal, R. Best, R. Rivero, J. Cervantes. (2006). “Analysis of a

combined power and refrigeration cycle by the exergy method.” Ener-

gy, 31:3401-3414.

[17] Feng Xu, D. Yogi Goswami. (1997). “Thermodynamic properties

of ammonia-water mixtures for power-cycle applications.” Energy,

24:525-536.

[18] Chang, T.-B..(2007). “Optimal allocation of heat transfer area for

a refrigeration plant.” Journal of marine science and technology,

15(1):41-46.

[19] Yang Zhao, Zhang Shigang, Zhao Haibe.(2003). “Optimization

study of combined refrigeration cycles driven by an engine.” Applied

energy, 76:379-389.

[20] Keith E. Herold, Reinhard Radermacher, Sanford A. Klein. (1996)

Absorption chillers and heat pumps. CRC press, Boca Raton, 329 pag-

es.

[21] Aspen Technology. (2009). Aspen HYSYS Tutorial and Applica-

tions. Aspen Technology, Burlington, 561 pages.

- 39 -

[22] MAN B&W Diesel A/S. (2009). Soot Deposits and Fires in Ex-

haust Gas Boiler. MAN B&W Diesel, Copenhagen, 21 pages.

[23] MAN Diesel A/S. (2010). LNG Carriers with ME-GI Engine and

High Pressure Gas Supply System. MAN Diesel A/S, Copenhagen,

37pages.

[24] MAN Diesel & Turbo, Main Engine Room Data.

(www.manbw.dk/ceas/erd).

http://www.manbw.dk/

- 40 -

요 약 문



본 논문은 엔진 배가스 이용 흡수식 냉동시스템에 관한 것으로, 대형 가스운반선에서

나오는 증발 가스를 흡수식 냉동시스템을 이용하여 재액화하는 시스템의 실현가능성을

증명한다. 이러한 흡수식 냉동시스템은 냉매와 흡수제로 각각 암모니아/물을 이용하며 실제

상용화된 엔진에서 나오는 배가스의 물성치를 사용하여 시물레이션을 하였다. 성능계수는

배가스의 온도가 높을수록, 엔진 로드가 커질수록 높아진다. 사례연구를 통해 LPG 및 LNG

운반선의 엔진에서 나오는 배가스로 LPG 및 LNG 증발가스를 각각 직접, 간접 방법으로

재액화가 충분히 가능하며 기존의 시스템 보다 효율이 높다는 것을 확인 하였다.

핵심어: absorption refrigeration; exhaust gas, waste heat, BOG reliquefaction; bulk gas carriers

Chiller de Los Chinos Japoneses

Documents

Transcript of Chiller de Los Chinos Japoneses