ORIGINAL PAPER

Exergy recuperative CO2 gas separation in pre-combustioncapture

Akira Kishimoto • Yasuki Kansha •

Chihiro Fushimi • Atsushi Tsutsumi

Received: 15 August 2011 / Accepted: 19 October 2011 / Published online: 22 November 2011

� Springer-Verlag 2011

Abstract The integrated coal gasification combined cycle

(IGCC) can achieve higher power generation efficiency

than conventional pulverized coal combustion power plants.

However, a CO2 capture process prevents improving power

generation efficiency of IGCC, because CO2 separation

from gas mixtures requires huge amounts of energy.

Therefore, in this study, we analyzed the CO2 separation

process in the pre-combustion capture process using a

process simulator (PRO/II) in the steady state, and proposed

a new process using a modularity based on self-heat recu-

peration (SHR) technology to decrease energy consump-

tion. Pre-combustion capture was applied in the IGCC

plant, which involved coal gasification and CO-shift con-

version with CO2 capture. The results show that the energy

consumption for the CO2 separation process using SHR was

decreased by two-thirds. This means that the power gen-

eration efficiency can be improved by SHR compared with

conventional IGCC with a CO2 capture process.

Keywords CO2 capture � Coal gasification � Chemical

absorption � Self-heat recuperation

Introduction

The effects of global warming through increasing global

energy consumption are currently becoming more obvious.

Thus, it is necessary to have an adequate discussion about

mitigating global warming. It is believed that anthropogenic

emissions of greenhouse gases (GHGs) are a factor in global

warming, and one of the major gases involved is CO2 gas.

Thus, some approaches for CO2 reduction (Varbanov et al.

2005) have been proposed in industrial processes. Power

generation plants using fossil fuels exhaust large amounts of

CO2 gas (Tofftegard et al. 2010). Among the fossil fuels,

coal has performed an important role as a primary energy

source since the industrial era, because it comprises a stable

energy source for society and the reserves-to-production

ratio (R/P) is greater than oil or natural gas (U.S. IEA

website, 2010). The global demand for coal has been rap-

idly increasing because of the greater demands of devel-

oping nations. Hence, for efficient coal use, many

researchers have paid attention to power plants that employ

the integrated coal gasification combined cycle (IGCC)

(Pruschek et al. 1995; Gottlicher and Pruschek 1997; Wil-

liams et al. 2000; Chiesa et al. 2005; Shoko et al. 2006;

Damen et al. 2006; Rubin et al. 2007). IGCC achieves

higher power generation efficiency compared with con-

ventional pulverized coal-fired power plants and consists of

a gasification/reforming process and a power generation

process. A gas cleaning process for CO2 capture to reduce

emissions is integrated into the IGCC because CO2 emis-

sions from the IGCC are higher than from other power

generation processes using natural gas or oil) (Amman et al.

2009). The power generation efficiency is reduced by

approximately 10% using CO2 capture processes (Ordorica-

Garcia et al. 2005; Decamps et al. 2010; Davison 2007). In

particular, Phent and Henkel (2009) reported that the power

generation efficiency is 48% without CO2 capture and

storage (CCS) but 38.7% with CCS, and that the power

generation efficiency of a conventional pulverized coal

power plant is 46% without CCS and 27.8% with CCS.

Thermal efficiency in IGCC is higher than pulverized coal

combustion, because IGCC power plants can achieve high

A. Kishimoto � Y. Kansha � C. Fushimi � A. Tsutsumi (&)

Collaborative Research Center for Energy Engineering,

Institute of Industrial Science, University of Tokyo,

4-6-1 Komaba, Meguro-Ku, Tokyo 153-8505, Japan

e-mail: a-tsu2mi@iis.u-tokyo.ac.jp

123

Clean Techn Environ Policy (2012) 14:465–474

DOI 10.1007/s10098-011-0428-3

combustion temperatures. Furthermore, the CO2 emissions

of IGCC per unit of generated power (t-CO2/kWh) can be

reduced compared with pulverized coal combustion. How-

ever, the power generation efficiency of IGCC is signifi-

cantly decreased by CCS. Therefore, it is important that the

energy consumption for CCS be reduced.

Pinch technology has been applied to many industrial

processes to reduce energy consumption since the 1970s

(Kemp 2007; Linnhoff 1993; Eastop and Croft 1990).

Although pinch technology can reduce energy consumption

by 20–30% in chemical processes through heat integration

and heat circulation (Linnhoff and Hindmarsh 1983),

whole process heat cannot be re-circulated without any

heat addition in these processes. Thus, it can be said that

these processes have some potential for further energy

saving. Nord et al. (2009) and Falcke et al. (2011) applied

pinch analysis to pre-combustion capture. Although these

studies provided significant information for analyzing the

energy loss, they did not provide a method that would

enable improvements over conventional systems (Nord

et al. 2009; Falcke et al. 2011).

Recently, an innovative exergy recuperation technology

has been developed for industrial processes: gasification pro-

cesses based on exergy recuperative gasification (Tsutsumi

2004), heating and cooling thermal processes based on self-

heat recuperation (SHR, Kansha et al. 2009), and distillation

processes based on SHR (Kansha et al. 2010a, b; Matsuda

et al. 2011). Kansha et al. reported that the energy require-

ments of thermal processes could be markedly reduced to

1/3–1/22 using SHR (2009) and that the modularity based

on SHR for the distillation processes was found to reduce

the required energy by more than 75% compared with

conventional distillation processes (2010a, b). Furthermore,

Kishimoto et al. (2011) developed a way to reduce the energy

consumption of post-combustion CO2 capture by about 60%

using chemical absorption based on SHR compared with

conventional processes. However, IGCC with pre-combustion

was not considered so clearly it did not account for CO-shift

conversion in pre-combustion capture.

In this article, exergy recuperation technology was applied

to gas cleaning process to reduce the energy consumption for

pre-combustion capture. The gas cleaning process consists of

a CO-shift conversion and a CO2 gas capture process. Thus, a

process modularity based on SHR technology was applied to

the CO-shift conversion and the CO2 gas chemical absorp-

tion process, which can achieve a considerable reduction in

energy consumption. The process simulation for exergy

recuperative gas cleaning in the pre-combustion capture was

conducted using a process simulator, PRO/II (Invensys plc.),

to analyze the energy input/output and compare it to a con-

ventional gas cleaning process.

Description of the IGCC with pre-combustion CO2

separation

Figure 1 shows a schematic diagram of a conventional

IGCC process with pre-combustion CO2 capture. Coal is

gasified using air or O2-rich gas in a gasification section. The

O2-rich gas is produced from an air separation unit (ASU),

which ordinarily uses a cryogenic separation system. After

the gasification section, synthesis gas is fed into a gas

cleaning section, which consists of the CO-shift conversion

and CO2 capture processes. In the CO-shift conversion

CoalGas cleaningGasification

CO2

Gas turbine

HRSG Steam turbine

HRSG: Heat Recovery Steam Generators

H2

Pre-combustion

CO2

CO-shift conversion

CO2

capture

Steam 3.2 GJ/t-CO2

(from HRSG)

H2

Steam 4.1 GJ/t-CO2

(from HRSG)

Exhaust

Steam1.3 GJ/t-CO2

Gas cleaning

Air orO2 rich gas

H2O Steam

Wastegas

H2O

Fig. 1 Diagram of the

conventional IGCC process

with pre-combustion CO2

capture

466 A. Kishimoto et al.

123

process, steam is supplied from heat recovery steam gener-

ators (HRSG) to produce shifted gas. There are two different

separation steps for the CO shift conversion: before sulfur

removal (sour shift) or after sulfur removal (sweet shift). In

both steps, CO2 gas is captured from the shifted gas in the

CO2 capture process. In many cases, chemical absorption

(e.g., monoethanolamine, MEA; methyldiethanolamine,

MDEA) or a physical absorption (e.g., Selexol) is used for

the CO2 capture (Babdyopadhyay 2011).

The target of this study is the sweet shift and chemical

absorption process. The chemical absorption sorbent usu-

ally absorb more than physical absorption sorbent at low

feed CO2 pressure. However, chemical absorption requires

more energy than physical absorption because the chemical

bonds are stronger than the weak binding of the CO2 in

physical absorption (Stephens 2005). Thus, in the con-

ventional chemical absorption process, a huge amount of

steam is provided by HRSG to regenerate solution. It is

responsible for loss of power generation efficiency.

After the gas cleaning section, the captured CO2 gas is fed

into a compressor to carry CO2 gas from the ground surface

into a sequestration site. The purified H2 gas is fed into a gas

turbine for electric power generation. Moreover, heat of flue

gas from the gas turbine is recovered to generate steam by

HRSG. Subsequently, the generated steam is fed into a steam

turbine for power generation. To overcome this problem, SHR

can apply the chemical absorption process for pre-combustion

capture as well as post-combustion (Kishimoto et al. 2011).

Conventional CO-shift conversion and CO2 capture

process

A diagram of a conventional CO-shift conversion is shown

in Fig. 2. Synthesis gas is fed into a heating process

(1.69 GJ/t-CO2, 461.7 kW). The heated synthesis gas and

H2O (g) streams are fed into a CO-shift converter (300�C,

2.14 MPa, 0.62 GJ/t-CO2, 170.1 kW). In the CO-shift

conversion process, the CO-shift reaction takes place

(CO ? H2O ? CO2 ? H2 -41.12 kJ/mol). Thus, the

effluent stream was heated by the heat of the exothermic

reaction (300 ? 377�C). This heat can be recovered by

H2O (l) in a heat exchanger (147 ? 300�C, 0.44 MPa,

0.87 GJ/t-CO2, 237.1 kW). This leads to generation of

steam, which is fed into the CO-shift process. Then, the

residual heat of the stream is cooled by cooling water in the

chemical absorption process (157 ? 45�C, 2.14 MPa,

1.43 GJ/t-CO2, 391.1 kW).

Figure 3 shows a diagram of the conventional CO2 gas

capture process. The process consists of an absorber, heat

exchanger (HX) for heat recovery, and a stripper (regen-

erator) with a reboiler. The shifted gas and a ‘‘lean CO2

concentration’’ amine solution (lean amine) are fed into

the absorber, and CO2 gas is absorbed into the lean amine.

This amine solution containing absorbed CO2 is called

‘‘rich CO2 concentration’’ amine solution (rich amine).

Remaining gases (H2, N2) are discharged from the

absorber. The rich amine is fed into the stripper through

the heat exchanger and then lean amine is regenerated by

heating in the reboiler of the stripper. The CO2 gas is

stripped out by steam in the reboiler. Moreover, the heat

for the endothermic desorption reaction is required to

regenerate the solution in the stripper. The sum of the

reboiler duty for stripping and regeneration is 4.10 GJ/

t-CO2. There is a one-to-one ratio of reaction heat required

for regeneration of the solutions to the heat of vaporization

required for stripping. The heat of steam condensation

cannot be used for water vaporization in the reboiler

because of the temperature difference between condenser

and reboiler.

H2O (g)

Synthesis gas( H2, CO, H2O, CO2, N2 (g) )

Heating + CO-shift reaction Heat recovery =1.44 GJ/t-CO2

300 oC

300 oC, 2.14 MPa

45 oC, 2.14 MPa

1.69 GJ/t-CO2

Shifted gas(H2, H2O,CO2, N2)

H2O (l)

0.87 GJ/t-CO2

45 oC, 2.14 MPa

147 oC, 0.44 MPa

H2O (g) 300 oC, 0.44 MPa

0.62 GJ/t-CO2

(heat of condensation: 0.01 GJ/t-CO2,3.6 kW

377 oC 157 oC

Heating CO-sift reaction

Heat recovery

Cooling

(461.7 kW) (237.1 kW)(170.1 kW)

Heat recovery

(391.1 kW)1.43 GJ/t-CO2

Heat

Fig. 2 Diagram of the

conventional CO-shift

conversion

Exergy recuperative CO2 gas separation 467

123

Design of self-heat recuperative process

As mentioned above, a lot of process heat is wasted in

the cooling water. However, this waste heat can be

disappeared when whole process heat is re-circulate

using SHR technology. A gas cleaning process using the

CO-shift conversion and the chemical adsorption based

on SHR has been proposed for pre-combustion. In the

proposed process, the pairs of feed and effluent streams

are selected to recover the heat. The stream condition is

changed by compression of the process stream and all

the self heat of one stream is exchanged to the other

stream of the pair in heat exchangers, leading to the self

heat of the process stream being recirculated based on

exergy recuperation to reduce the process energy con-

sumption (Kansha et al. 2009). The self-heat recuperative

process consists of such modules, in which all heat of

the streams is recirculated. In each module, heating and

cooling loads are balanced by enthalpy and exergy

analysis.

Simulation

Process simulation was conducted with PRO/II (Invensys

plc.) to calculate the process energy consumption of the gas

cleaning process. The standard amine package model of

PRO/II (Invensys plc.) was used for simulation. In the

thermodynamics package, the liquid enthalpy and liquid

phase density are calculated by an ideal method. Vapor

phase enthalpy, entropy and density are calculated by the

Soave-Redlich-Kwong Modified (SRKM) model. Purity of

recovered CO2 was assumed 95%. The details of the sim-

ulation conditions are given in Table 1.

Result and discussion

Conventional process

Figure 4 shows a flow diagram and temperature heat diagram

for the conventional CO-shift conversion and CO2 capture

processes. In the CO-shift conversion process, streams of

synthesis gas (1) and H2O (3) were heated to 300�C by heaters

(1 ? 2, 3 ? 4), and then these streams were fed into the CO-

shift conversion process (2 and 4 ? 5). A part of the stream

heat was recovered by generating steam (5 ? 6, 7 ? 8:

237.1 kW). A large amount of heat was wasted by cooling

water (6 ? 9: 391.1 kW). Condensed H2O (l) was separated

Stripping(heat of vaporization)

Abs

orbe

r

Str

ippe

r

Reboiler

Condenser(heat of condensation)

Lean amine

Richamine

CO2

H2O

Shifted gas

Heat of exothermicreaction

Remaining gas H2, N2

Regeneration heat (Heat of endothermicreaction)

124 oC

Heat of endothermic reaction + Vaporization heat = 4.10 GJ/t-CO2 (MEA)

45 oC

65 oC 123 oC

4.10 GJ/t-CO2

H2, N2, CO2, H2O

HX

Fig. 3 Diagram of the

conventional CO2 gas capture

process

Table 1 Simulation conditions

Flow rate of synthesis gas 100 kmol/h

Consist of synthesis gas H2 21.0 mol%

CO2 14.5 mol%

CO 7.9 mol%

H2O 19.6 mol%

N2 37.0 mol%

Degree of CO2 removal [99 %

Purity of recovered CO2 [95 %

Concentration of amine 30 wt%

Inlet gas temperature 45 OC

Inlet gas pressure 2.04 MPa

468 A. Kishimoto et al.

123

from mixture in a flash column (9 ? 10, 11). In the con-

ventional CO-shift conversion process, the sum of the heating

load was 631.9 kW (1 ? 2, 3 ? 4; 2.31 GJ/t-CO2) and the

sum of the cooling load was 391.1 kW (6 ? 9; 1.43 GJ/

t-CO2). Net energy consumption was 394.8 kW (631.9 –

237.1 = 394.8, 1.44 GJ/t-CO2) in the shift conversion pro-

cess. The shifted gas (11) was fed into an absorber. CO2 was

absorbed into the lean amine solution (11 ? 13), converting

the lean amine to rich amine. The remaining gases were

discharged from top of the column (11 ? 12). The rich

amine solution was heated in a heat exchanger to recover heat

from the lean amine (13 ? 14, 20 ? 21, 626.6 kW) and the

heated stream was fed into a stripper. In the stripper, the lean

amine was regenerated by endothermic reaction and CO2 was

stripped out with steam. The reboiler duty was 1112.4 kW.

Heat of vaporization was then wasted in the condenser

(15 ? 16,17, 623.1 kW), and additionally, a large amount of

heat was wasted in the cooler (21 ? 22, 477.9 kW).

Proposed process

Figure 5 shows CO-shift conversion process based on the

SHR. Feed streams of synthesis gas (1) and H2O (3) were

heated to 300�C in heat exchangers by effluent streams

(feed streams 1 ? 2, 3 ? 4; effluent streams 12 ? 13,

24 ? 25), and a part of heat of synthesis gas was supplied in

the heater (28), because differential quantity of heat between

feed and effluent streams was needed by the CO-shift con-

version. These heated streams were fed into the CO-shift

conversion process, and these streams were converted into

shifted gas (2 and 4 ? 5). The shifted gas was fed into H2O

separation module. In the module, stream of shifted gas was

separated into two streams (synthesis gas (11) and H2O

(23)). To separate H2O from the shifted gas stream (5),

compressor was applied to the H2O separation module

(5 ? 6), and the additional work (30; 128.4 kW) was then

wasted by a cooler (8 ? 9). Heat of effluent streams was

recovered by heat exchanger (feed stream: 6 ? 7; effluent

streams: 10 ? 11, 22 ? 23). These effluent streams were

compressed by compressors (11 ? 12, 23 ? 24) to recover

the heat of streams in heat exchangers (12 ? 13, 24 ? 25).

The shifted gas stream (13) was separated into shifted gas

and H2O by a separator (13 ? 14 and 19). The shifted gas

(14) and liquid H2O stream were fed into an expander

(14 ? 15) and a valve (19 ? 20), and then expanded,

respectively. These streams were fed into coolers, and

Abs

orbe

r

Str

ippe

r

Reboiler

CondenserLean amine

Rich amine

CO2

H2O

Shifted gas

H2, N2

124 oC

45 oC

H2, N2, CO2, H2O

H2O (g)

Synthesis gas( H2, CO, H2O, CO2, N2 (g) )

300 oC

300 oC, 2.14 MPa

45 oC, 2.14 MPa

H2O (l)

45 oC, 2.14 MPa147 oC, 0.44 MPa

H2O (g) 300 oC, 0.44 MPa

377 oC 157 oC

Heat

2

5

4

6 9

Con

vert

er

H2O(l)

45 oC,2.14 MPa

19

16

14

22

1320

300 oC

Heat

H2O (l)45 oC, 2.14 MPa

170.2 kW

461.7 kW

237.1 kW626.6 kW

21

623.1 kW

477.9 kW

391.1 kW

7

8

1

3

11

12

1018

15

17

1112.4 kW

Fig. 4 T–Q diagram of the

conventional CO-shift

conversion and CO2 gas capture

processes

Exergy recuperative CO2 gas separation 469

123

cooled (15 ? 16, 20 ? 21). Shifted gas stream was sepa-

rated into two streams by a separator (16 ? 17 and 18). The

H2O stream (25) was depressed by a valve (25 ? 26) and

cooled by cooler (26 ? 27). Net energy consumption for

the CO-shift conversion was 153.9 kW (0.57 GJ/t-CO2).

The process reduced the energy requirement by SHR tech-

nology compared with the conventional CO-shift conversion

process (394.7 kW, 1.44 GJ/t-CO2 (cf. Fig. 2)). The

majority of energy in the CO-shift conversion process was

consumed in the H2O separation module (128.4 kW). The

amount of condensation heat for H2O in the H2O separation

module is balanced with the amount of inflow enthalpy for

H2O into the CO-shift converter. It was important to balance

the amount of H2O heat between the inflow enthalpy for H2O

and the amount of condensed H2O. The self-heat recupera-

tive pre-combustion process is constructed on the basis of

process modularity, which can explain about the energy and

material flow, and the modularity can make pairing of heats

in these streams. These whole process heat was reused and

recirculated as a result of modularity based on SHR.

Figure 6 shows the material and energy balance for the

self-heat recuperative CO-shift conversion process based

on modularity. The boxes show units, while solid, dashed

and chain lines show material, heat and chemical or work

flows, respectively.

In Fig. 6a, streams of synthesis gas (1) and H2O (3) were

heated by heaters, and then these streams were fed into heat

receivers (1 ? 2, 3 ? 4), which received heat (34, 39)

from the heat transmitters (12 ? 13, 24 ? 25), respec-

tively. The heated streams were fed into a CO-shift

converter and then an exothermic reaction took place

(2, 4 ? 5). Thus, the temperature of the shifted gas was

raised from 300 to 377�C by heat from the exothermic

reaction (83.8 kW). This stream was fed into an H2O

separation module (Fig. 6b), to which compression work

(31, 128.4 kW) was supplied to separate H2O from the

shifted gas (5 ? 11 and 23). In the module, the process

heat (6) was recirculated by self-heat transmitter (6 ? 7)

and receivers (10 ? 11, 22 ? 23). These H2O and the

shifted gas streams from the H2O separation module were

compressed (33, 31.4 kW; 38, 3.3 kW) to recover the heat

between the heat transmitters (12 ? 13, 24 ? 25) and the

heat receivers (1 ? 2, 3 ? 4). The H2O stream was de-

pressurized by a valve and cooled by a cooler

(25 ? 26 ? 27). The other stream was separated by H2O

separator (13 ? 14 and 19). These streams expanded by an

expander and cooled by a cooler (14 ? 15 ? 16 ? 17

and 18, 19 ? 20 ? 21). In the expander, power can be

recovered (35, 12.8 kW) and in the coolers (15 ? 16,

20 ? 21, 26 ? 27), the sum of wasted heat was 21.9 kW

(4.4 ? 3.9 ? 13.6 = 21.9 kW; 36, 37, 40). Furthermore,

input energy for compression in the H2O separation module

was wasted by cooling water (32).

A self-heat recuperative CO2 gas separation process is

shown in Fig. 7. Figure 7a shows the CO2 gas capture

process. The heat of condensation from the steam was

recovered by compression work (105.1 kW) as heat of

vaporization. The condensed steam was separated from the

mixed stream (H2O and CO2) in the H2O separation

module, which is shown in Fig. 7b. The additional com-

pression work (42–1 (g) ? 42–2 (g), 111.7 kW) was

wasted in a cooler (42–4(l,g) ? 42–5(1,g), 111.7 kW).

The heat energy for separation, including sensible heat and

latent heat, was exchanged in heat exchangers (633.2 kW).

Compression work for recovering the heat of vaporization

can be reduced by applying the H2O separation module.

CO

-shi

ft

conv

erto

r

Total: Compression + heating Expansion =153.9 kW (0.57 GJ/t-CO2)

H2O (l)

492 oC

378 oC

Shifted gas(H2, H2O (g),CO2, N2)

45 oC, 2.14 MPa

45 oC, 2.14 MPa

378 oC

12.8 kW 128.4 kW

406 oC,2.59 MPa

410 oC,2.63 MPa

21.9 kW

31.4 kW

3.3 kW

376.7 oC

128.4 kW

34.7 kW

H2O separation module

128.4 kW

99 oC

62 oC

3.6 kW

H2O (l)

45 oC,2.14 MPa

Synthesis gas45 oC, 2.14 MPa

300 oC

127.8 oC

50 oC

300 oC1

528

3 4

6 7 8

10

22

9

11

23

12

1516

2

27 2526

13

24

14

202119

17

18H2O (l)

45 oC, 2.14 MPa

45 oC

38

33

30

32

3536

37

40

Fig. 5 The self-heat

recuperative CO-shift

conversion process

470 A. Kishimoto et al.

123

Furthermore, wasted heat of exothermic reaction can be

recovered by reaction heat transformer (RHT) and supplied

as heat for the endothermic reaction. This RHT has the role

of a heat pump to recover reaction heat by compression

work using a volatile fluid.

Likewise, the heat of the exothermic reaction can be

supplied for the heat of the endothermic reaction (Fig. 7a)

using an RHT. In this simulation, the coefficient of per-

formance (COP) for the RHT is defined as follows:

COP ¼ Q=W ð1Þ

Compression work

H2O (l)

Synthesis gas

45 oC,2.14 MPa

45 oC, 2.14 MPa

H2O (g) 300 oC

300 oC

377 oC

378 oC, 2.14 MPa

Reaction heat

128.4 kW

170.2 kW

458.0 kW

83.8 kW

410 oCHeat

receiver

Heat receiver

Heat transmitter

Heat transmitter

1

3

2

4

5

13

25

3429

39

12

24

3.3kW

2.63 MPa

2.59 MPa406 oC

128.4 kWWasted heat (cooling water)

Compressor

Compressor

31.4 kW

H2Oseparation

module

Shifted gas (H2, H2O,CO2, N2)45 oC, 2.14 MPa

45 oC, 2.14 MPa

13.6 kW

valve99 oC

HeatChemical, Work

13

25 2726

H2OSeparator

H2O (l)

H2O (l)

Material

Cooler

62 oC

99 oC

3.7 kW 28

30

11

23

33

38

CO-shift converter

40

heat

3212.8 kW

50 oC

1615

4.4 kW

Expander Cooler

35

36

14

20

H2OSeparator

H2O (l)

17

18

21

3.9 kW

Cooler

37

valve99 oC

19H2O (l)

Compressor valveSelf-heattransmitter

cooler

Self-heatreceiver

Self-heatreceiverH2O

Separator

5 6 7 8 9

9

10 11

2322

128.4 kW

377 oC, 2.14 MPa

492 oC4.32 MPa 128.4 kW

H2/H2O/CO2/N2

238.0 kW

159.6 kW

378 oC

378 oC

128 oC

146 oC2.14 MPa397.6 kW

167 oC

31(b)

(a)

32 33

32

32

Fig. 6 Modularity of the self-

heat recuperative CO-shift

conversion process

Exergy recuperative CO2 gas separation 471

123

where Q is the heat received from the heat of the exothermic

reaction and W is the compression work in the RHT. In this

study, COP = 3 was assumed. Then, the regeneration heat can

be recovered by RHT (161.9 kW). Furthermore, the stripping

module based on SHR technology can recover the heat of

condensation by compression work. Therefore, by installing

the RHT, not only the process heat but also the reaction heat

can be recovered in the self-heat recuperative CO2 gas

capture process. The net energy consumption in the proposed

process was 378.7 kW (1.39 GJ/t-CO2). The energy

consumption of the CO2 capture process was reduced to

approximately 1/3 that of the conventional CO2 capture

process.

The modularity of CO2 capture process based on SHR

technology is shown in Fig. 8. This process has three

modules: absorption, heating and cooling, and stripping

modules. The shifted gas (17) from the CO-shift conver-

sion process and the lean amine (38) were fed into the

absorption module. In the absorption module, CO2 was

absorbed by lean amine and simultaneously exothermic

reaction took place (46; 350.8 kW). The rich amine (40)

was discharged from the absorption module and was fed

into the heating module (47; 977.5 kW, 106�C). The heated

rich amine was fed into a stripping module where lean

amine was regenerated by heat (48 and 49; 485.8 kW) and

at the same time CO2 (42) was stripped out by heat

42-3 (l,g)

42-6 (g)

42-9 (l)

109.0 oC

111.7 kW

108.3 oC

633.2 kW

42-1 (g)

128.7oC 44.8 oC

42-2 (g)

277.0 oC901 kPa

338 kW

42-4 (l,g)

42-5 (l,g)

44.8 oC79.9 oC101 kPa

44.8 oC

111.7 kW

42-7(g)

42 (g)

120.7 oC201 kPa

128.7 oC42-10 (g)

(b)

(a)

H2O separation module

Total: Compression = 111.7 kW (0.41 GJ/t-CO2 )

Fig. 7 The self-heat

recuperative CO2 gas capture

process. a CO2 gas capture

process and b H2O separation

module

472 A. Kishimoto et al.

123

(50, 626.6 kW), and then cooled (52). The lean amine

(44; 124�C) was discharged from the stripping module and

fed into the cooling module (44 ? 45), and the lean amine

stream was then cooled (53, 1104.3 kW). Note that the

cooling module was selected to pair with the heating

module. The heat of lean amine (53) was exchanged with

the sensible heat of the rich amine (47). The lean amine

was pumped and then fed into the absorber (45 ? 38).

Furthermore, the heat of exothermic reaction (46) was

supplied to the heat of endothermic reaction (49). Note that

the heat of the endothermic reaction is larger than the heat

of the exothermic reaction. Thus, it is necessary to supply

additional heat (48) to the rich amine for regeneration,

which is wasted in the cooling water (8.2 (52) ? 1104.3

(53) - 977.5 (47) = 135.0 kW). In addition, the regener-

ation heat (48) can recover from wasted heat in cooling

water (53). The temperature–heat diagram for the proposed

process is shown in Fig. 9. It can be seen that process heat

was recovered and re-circulated by compression work

based on SHR technology.

Table 2 shows a summary of a comparison of the energy

consumption between the conventional CO-shift and CO2

separation processes and the proposed process. The pro-

posed process can reduce the amount of energy required by

about two-thirds compared with the conventional process

for the shift conversion and CO2 capture process.

Conclusion

In this article, energy saving CO-shift conversion and CO2

chemical absorption processes based on SHR technology

were proposed to reduce energy consumption for pre-

combustion. In IGCC, the self-heat recuperative pre-com-

bustion process is constructed on the basis of process

modularity, which can explain about the energy and

material flow, and can make pairing of heats in these

streams. These whole process heats were reused and re-

circulated as a result of modularity based on SHR. The

amount of energy consumption of the proposed process

using a commercial process simulator was evaluated and

compared it with that required for a conventional CO2 gas

Absorption Heating Stripping Cooling

Heat (pre-heating)

Heat (endothermic reaction)

Heat (stripping)

Heat of exothermic reaction

Material

Heat

Wasted heat

Chemical, Work

Shifted gas

Fuel (H2, N2)

CO2

Leanamine

Rich amine

Lean amine

Rich amine

Leanamine

45 oC, 2.14 MPa

45 oC, 2.14 MPa

45 oC, 2.14 MPa,

45 oC106 oC 124 oC 45 oC

350.8 kW

45 oC, 201 kPa

623 kW

1104.3 kW

977.5 kW

626.6 kW

350.8 kW

201 kPa

135.0 kWHeat (endothermic reaction)

17

46

38

39

40 41 44 45

47

48

49

50

51

43

53

Cooling

8.2 kW5245 oC

42

Fig. 8 Modularity of the self-

heat recuperative CO2 gas

capture process

100

265

Absorption

155

210

320

45Q [ kW ]

375

Stripping

Rich amine

Heating Cooling

Rich amine

H2O,CO2

T [ oC ]

CO2 captureCO-Shift conversionHeating Cooling

Lean amine

4144

4849

Reboiler duty

50

17,38 17,18

50

453

4

524

12

25

2713

17,18,21

430

2

Fig. 9 T–Q diagram based on self-heat recuperation technology

(based on Figs. 5, 7)

Table 2 Simulation results

Shift conversion

process

CO2 capture

process

Sum

Conventional process 1.44 4.10 5.54

Proposed process 0.57 1.39 1.96

Unit GJ/t-CO2

Exergy recuperative CO2 gas separation 473

123

separation process. The energy consumption of the pro-

posed process based on SHR technology can greatly reduce

the amount of energy required by 2/3 compared with the

conventional process. This means that the electric power

generation can be improved by SHR compared with con-

ventional IGCC with a CO2 capture process.

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