S2.0 S1743967116305992 Main [628918]

Accepted Manuscript
benchmarking of the pre/post combustion CHEMICAL ABSORPTION for THE CO 2
capture
Cristian Dinca, Nela Slavu, Adrian Badea
PII: S1743-9671(16)30599-2
DOI: 10.1016/j.joei.2017.01.008
Reference: JOEI 302
To appear in: Journal of the Energy Institute
Received Date: 10 October 2016
Revised Date: 17 January 2017
Accepted Date: 25 January 2017
Please cite this article as: C. Dinca, N. Slavu, A. Badea, benchmarking of the pre/post combustion
CHEMICAL ABSORPTION for THE CO 2 capture, Journal of the Energy Institute (2017), doi: 10.1016/
j.joei.2017.01.008.
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MANUSCRIPT
ACCEPTED
ACCEPTED MANUSCRIPTBENCHMARKING OF THE PRE/POST COMBUSTION CHEMICAL
ABSORPTION FOR THE CO 2 CAPTURE

Cristian Dinca a, * , Nela Slavu a, Adrian Badea a, b
aThe Power Plant Department, POLITEHNICA University of Bucharest, Bucharest 060042,
Romania
bThe Romanian Academy of Scientists, Bucharest 05009 4, Romania
*Corresponding author: [anonimizat]
Highlights
• Integration of the chemical absorption process in p re- or post-combustion processes
• Increasing the syngas LHV from the coal gasificatio n using the chemical absorption
process for the CO 2 separation
• Parametrical study of the energy system with integr ated chemical absorption

Abstract. The aim of the article was to compare the pre- and post-combustion CO 2 capture
process employing the chemical absorption technolog y. The integration of the chemical
absorption process before or after the coal combust ion has an impact on the power plant
efficiency because, in both cases, the thermal ener gy consumption for solvent regeneration is
provided by the steam extracted from the low pressu re steam turbine. The solvent used in this
study for the CO 2 capture was monoethanolamine (MEA) with a weight c oncentration of
30%. In the case of the pre-combustion integration, the coal gasification was analysed for
different ratios air/fuel (A/F) in order to determi ne its influences on the syngas composition
and consequently on the low heating value (LHV). Th e LHV maximum value (28 MJ/kg)
was obtained for an A/F ratio of 0.5 kg air /kg fuel , for which the carbon dioxide concentration in
the syngas was the highest (17.26%). But, consideri ng the carbon dioxide capture, the useful
energy (the difference between the thermal energy a vailable with the syngas fuel and the
thermal energy required for solvent regeneration) w as minimal. The maximum value (61.59
MJ) for the useful energy was obtained for an A/F r atio of 4 kg air /kg fuel . Also, in both cases,
the chemical absorption pre- and post- combustion p rocess, the power plant efficiency
decreases with the growth of the L/G ratio. In the case of the pre-combustion process,
considering the CO 2 capture efficiency of 90%, the L/G ratio obtained was of 2.55

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ACCEPTED MANUSCRIPTmol solvent /mol syngas and the heat required for the solvent regeneration was of 2.18 GJ/tCO 2. In
the case of the post-combustion CO 2 capture, for the same value of the CO 2 capture
efficiency, the L/G ratio obtained was of 1.13 mol solvent /mol flue gas and the heat required was of
2.80 GJ/tCO 2. However, the integration of the CO 2 capture process in the power plant leads
to reducing the global efficiency to 30 % in the pr e-combustion case and to 38 % to the post-
combustion case.
Keywords: CO 2 capture, chemical absorption, pre-post combustion, monoethanolamine
1. Introduction
At the moment, fossil fuels cover globally an impor tant part of the demand for primary
energy resources. Coal is used frequently worldwide in the energy sector for power
generation, because coal reserves are more signific ant than the ones of natural gas and oil [1,
2].
The current trend in the energy sector aims to redu ce carbon dioxide emissions, especially
regarding coal fired power plants, so that the ener gy technologies which use coal can be
compared with the ones which use natural gas. Incre asing the global efficiency of power
plants is possible only with very large investments which are more or less justified for the
energy units with a life period higher than 20 year s [3]. In this context, one of the solutions
which has a high potential for reducing CO 2 emissions consists in integrating in the CO 2
capture energy units, transport and storage process es [4, 5].
Today, the CO 2 capture process by chemical absorption is validate d technically and
economically for different power plants [6, 7] or i n the cement industry [8], and in the oil
industry for natural gas extraction, respectively [ 9, 10]. Thus, in this study, for separating the
carbon dioxide from different gases, we employed th e CO 2 capture process by chemical
absorption by means of primary amines (e.g. monoeth anolamine).
Although the chemical absorption process was valida ted to an industrial scale, its
integration in a power plant leads to reducing the power plant global efficiency by 8-14
percentage points [11]. Consequently, the parameter s which influence the power plant
efficiency are the following: the CO 2 capture efficiency, the size of power plant, the t ype and
weight concentration of the chemical solvent, and t he solution of regeneration used. The most
used method for chemical solvent regeneration consi sts in extracting a steam flow rate from
the low pressure steam turbine, which could be up t o 30-40% from the initial steam flow of

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ACCEPTED MANUSCRIPTthe steam turbine [12]. After integrating the CO 2 capture technology in the power plant, the
cost of the electricity produced increases from 50 to 90 (€/MWh) [13].
In this study, we analysed the consequences of the chemical absorption integration in pre- or
post- combustion processes in order to reduce its t echnical and economic effects resulted
from integrating it in a power plant. Therefore, tw o cases were considered: a) post-
combustion CO 2 capture by chemical absorption; b) pre-combustion CO 2 capture by
chemical absorption. Case “ a” was considered as reference. The first case is an alysed in
different studies: C. Dinca et al. designed the abs orber unit in order to separate the CO 2 from
the flue gases resulted from coal combustion whose design model was made for various types
of packages using plastic, ceramic or metal rings [ 14], A. Lawal et al. studied the dynamic
responses of a post-combustion CO 2 capture plant by modelling and simulation [15], Se
Young Oha et al. constructed, in the UniSim simulat or process, a superstructure including the
conventional amine-based CO 2 capture configuration and four different types of structural
modifications [16], L. Duan et al. studied the effe cts of the key parameters on the MEA
regeneration in order to reduce the thermal energy consumption [17]. The integration of the
pre-combustion chemical absorption is studied only in a few papers: M. Asif et al. modelled
and simulated a large-scale of an IGCC system in th ree configurations: IGCC without CO 2
capture, IGCC with pre-combustion capture by chemic al absorption, and IGCC with post-
combustion capture by chemical absorption finally o btaining the optimal IGCC system [18],
M. Kawabata et al. studied two CO 2 capture options: pre-combustion by a mixture of
dimethyl ethers of polyethylene glycol (DEPG) and p ost-combustion by monoethanolamine
(MEA), which were assessed to compare the power pla nt global efficiency and the necessity
for implementing future technologies [19]. In both cases, for the solvent regeneration there is
used a part of the steam flow generated in the stea m turbine.
On the other hand, the pre-combustion CO 2 capture is studied for analysing different CO 2
capture techniques, Sung Ho Park et al. conducted redesign and modeling of the two-stage
pre-combustion CO 2 capture process, using three different physical so lvents (Selexol,
Rectisol, Purisol). The Selexol process was evaluat ed as the most efficient pre-combustion
CO 2 capture process from the points of electric/therma l energy consumption [20]. See Hoon
Lee et al. developed a pilot scale water gas shift reactor with multi-layer membrane module
for to maximize CO 2 capture and H 2 recovery in integrated gasification combined cycle
(IGCC) [21]. Anna Skorek-Osikowska et al. studied t wo methods of CO 2 capture pre-
combustion, by chemical absorption and membrane CO 2 separation, a comparison of the
energy intensity of both processes shows that the m embrane separation has a much lower, by

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ACCEPTED MANUSCRIPTapproximately 15-fold, energy requirement than the amine absorption process. However, the
purity of the separated CO 2 significantly depends on the type and surface of t he membrane
and on the process parameters [22]. Calin-Cristian Cormos investigated the most important
techno-economic and environmental indicators for IG CC with pre-combustion capture using
gas-liquid absorption (Selexol) applied to the shif ted syngas. He is obtained that the carbon
capture penalty is 9.5% for gasification reactor Sh ell and 7.1% for gasification reactor
Siemens for a 90% carbon capture rate [23].
The novelty of this paper consists in adapting the CO 2 capture chemical absorption
process to the pre-combustion processes and in comp aring the results with those obtained in
the benchmark case (the chemical absorption process in the post-combustion processes). The
purpose is to increase the quality of the syngas pr oduced in the IGCC technologies by
separating the CO 2. In this case, the challenge consists in determini ng the energy balance
with considering the heat required for the solvent regeneration and the gain of energy by
syngas treatment. The advantage of using the IGCC t echnology which includes the pre-
combustion CO 2 capture by chemical absorption is to obtain a clea n fuel gas (syngas) (H 2,
CH 4, N 2, CO and H 2S) with a high LHV (low heating value) [19, 24]. Th e syngas
composition obtained depends on the oxidizing agent type (air or oxygen) or the moderator
agent type (water or steam) [25 – 27]. In this stud y, we only analysed the air gasification
process characterized by a lower cost than using wa ter or a steam moderator agent [28].
2. Method
The functional unit is mandatory for all the energy processes analysed. In this paper, the
functional unit was defined by the net amount of el ectricity generated by the power
plant ()yE. The installed power of the power plant ()P and the annual power plant operation
()yp d are required for determining the functional unit.
yp ydPE⋅= (1)
For simplifying the study, the annual power plant o peration is considered constant for
both cases analysed. For maintaining the same funct ional unit, the fuel flow is changed
according to the global efficiency of the systems a nalysed. The coal composition used is
presented in Table 1.

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ACCEPTED MANUSCRIPTTable 1
Coal composition
Elementary Coal Analysis
C
[%] H
[%] N
[%] O
[%] S
[%] W
[%] A
[%] LHV
(kJ/kg)
58 2 1 1.8 0.8 18.1 18.3 21335
The cases studied in the article are the following :
a) The coal power plant without CO 2 capture;
b) The coal power plant with post-combustion CO 2 capture by chemical absorption (case
”2a”);
c) The coal gasification with pre-combustion CO 2 capture by chemical absorption and
syngas conversion in the coal power plant (case ”2b ”).
In Fig. 1 there are presented the processes of the coal power plants equipped with pre- and
post-combustion CO 2 capture. Inside the continuous line there are pres ented the components
of the power plant including the coal gasification with air; the CO 2 capture from the syngas;
and the electricity generation using the clean syng as in the coal power plant. Inside the
dashed line the following processes are presented: coal combustion and electricity generation
in the coal power plant; CO 2 capture from the flue gases.
In the chemical absorption process, the rich loadin g solvent was maintained constant, that
is of 0.21 mol CO2 /mol MEA, both for the pre- and post-combustion process [14] .

Fig. 1. Energy systems with pre- and post-combustion CO 2 capture by chemical absorption
Chemical absorption (Fig. 2) is the process where t he carbon dioxide from the flue
gases/syngas reacts with a chemical solvent to form an intermediate product characterized by
a weak bonding of the molecules. The regeneration o f the rich solvent in the CO 2 is made at
high temperatures, of approximately 120°C, to obtai n a concentrated stream of CO 2 with 95%
purity [29]. The gas stream (flue gases or syngas) resulted from the combustion or the coal
gasification enters the absorber at the bottom, and comes out at the top of it. The chemical

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ACCEPTED MANUSCRIPTsolvent (the amines) is introduced at the top of th e absorber unit, and it is removed at the
bottom of it. In the case of the power plant equipp ed with post-/pre-combustion CO 2 capture,
the amount of thermal energy required for the chemi cal solvent regeneration is obtained by
using a steam ratio from the low pressure steam tur bine. Taking into account the steam ratio
used for the solvent regeneration, the thermal effi ciency of the steam turbine decreases
considerably [12].

Fig. 2. The chemical absorption process [11]
The reactions between the CO 2 and MEA solution have been described in the litera ture by
two mechanisms, namely the zwitterion mechanism and the thermo molecular mechanism
[30].
Further there is presented the zwitterion mechanism . Reactions 2-14 may occur when the
CO 2 absorbs into and reacts with the aqueous MEA. All the species represented are in
aqueous solution [30].
Ionization of water:
+ −+↔ OHOH HK
3 21
2 (2)
Dissociation of the dissolved CO 2 in carbonic acid:
+ −+ ↔ +−
OHHCO OHCO Kk k
33,,
22222
2 (3)
Dissociation of bicarbonate:
+ − −+ ↔+ OHCO OHHCO K
32
3 233 (4)

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ACCEPTED MANUSCRIPTZwitterion formation from the MEA and CO 2 reaction:
−+−
↔ + COO RNH RNH CO Kk k
2,,
2 2444 (5)
Carbamate formation by deprotonation of the zwitter ion:
− + −++ ↔ +−
RNHCOO RNH RNH COO RNH Kk k
3,,
2 2555 (6)
− + −++ ↔ +−
RNHCOO OH OHCOO RNH Kk k
3,,
2 2666 (7)
− −++ ↔+−
RNHCOO OH OH COO RNH Kk k
2,,
2777 (8)
Carbamate reversion to bicarbonate (hydrolysis reac tion):
− −++ ↔ +−
3 2,,
2 2888
HCO RNH OHCOO RNH Kk k
(9)
Dissociation of the protonated MEA:
+ ++ ↔ +−
OHRNH OH RNH Kk k
32,,
23999 (10)
Bicarbonate formation:
− −−
↔ +3,,
210 10 10
HCO HO CO Kkk
(11)
− − −++ ↔ +−
RNHCOO CO H HCO COO RNH Kkk
32,,
3 211 11 11 (12)
− − − −++ ↔ +−
RNHCOO HCO CO COO RNH Kkk
3,,2
3 212 12 12 (13)
Based on this reaction scheme, the general rate of reaction of the CO 2 with MEA via the
zwitterion mechanism could be described as in the f ollowing equation:
∑∑ ∑
−+
−−
−
−+−=]) [ /(/ 1]) [/ ][]( [/]][ [
444442 2
2BkkkkBk BH k RNHCOO kk RNH CO r
bb b
MEA CO (14)

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ACCEPTED MANUSCRIPTwhere B designates any species in the solution whic h can act as a base to abstract the proton
from the zwitterion. In this case, the expected spe cies for a loaded MEA solution are the
following: ][2RNH , ][2OH, ][−OH , ][3−HCO , ][3=CO .
The global thermal energy (heat duty) required for regenerating the solvent represents the
sum of the following: the energy required for break ing the chemical bond between the solvent
and the CO 2 molecule, the energy required for heating the solv ent ) (sensible Q and the energy
required for water vaporization )(dilution Q. In order to determine each component of the
global energy, the following mathematical relations are used (15, 16) [29]:
) (),(),(
2 2 , min CO wea lean rich rich in p rich in
CO sensible
MCT Tc T
mQ
⋅⋅−Δ ⋅ ⋅
=γγγ γρ (15)
where: ) (sensible Q is the energy needed to heat the chemical solvent solution to the boiling
point, in [kJ]; 2CO mis the mass of CO 2; pc is the specific heat for the rich chemical solvent
solution, in [kJ/(kg K)]; ρis the density of the rich chemical solvent solutio n, in [kg/m 3];
TΔis the difference between the inlet temperature in T and the boiling temperature of the CO 2
rich feed, in [K]; ) (lean rich γγ− is the mole fraction CO 2 sent to compression per mole
chemical solvent; eaCmin is the concentration of the chemical solvent in t he rich solvent
solution, in [kmol/m 3]; 2CO m is the mass of CO 2, in [kg]; and 2,CO wM is the mole weight
CO 2, in [kg/kmol].
)(),()(
2
2 22 2
2 ,in vap
O HCO w rich in CO O H in sat
O H
CO diluation THM TpxTp
mQΔ ⋅⋅⋅
=γ (16)
where: )(dilution Q is the heat required to keep the 2 2CO sat
CO pp>, in [kJ]; vap
OHH
2Δ is the energy
required to evaporate the water, in [kJ/kmol]; OHx2 is the fraction of liquid water, sat
OHp
2 is
the water saturation pressure, in [bar], 2CO p is the partial pressure of the CO 2, in [bar].
The required global energy is procured from the hea t recovery of the flue gases or the
syngas ( sg fg Q/) and from the electrical re-boiler (boiler re Q−). Each of these was determined
using the equations listed below (17, 18) [29].
st gas pgas ex
gas sg fg TTcTVQ
Δ ⋅ ⋅⋅= )()(/ρη (17)

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ACCEPTED MANUSCRIPTwhere: sg fg Q/ is the heat which is recovered from the flue gases or syngas, in [kJ]; gas V is
the volume of gas, in [m 3]; ex η is the heat exchanger efficiency; pc is the specific heat for
the gases, in [kJ/(kg K)]; ρ is the density of the rich chemical solvent soluti on, in [kg/m 3];
st TΔ is the difference between the flue gas temperature in and out the stripper, in [K].
2, min ) (),(),(
CO wea lean rich r rich MEA prich MEA
MEA boiler re
MCT Tc T
mQ
⋅⋅−Δ ⋅ ⋅
=−
γγγ γρ (18)
where: boiler re Q− is the heat produced at the re-boiler, in [kJ]; MEA m is the amount of
chemical solvent, in [kg]; pc is the specific heat for the rich chemical solvent solution, in
[kJ/(kg K)]; ρ is the density of the rich chemical solvent soluti on, in [kg/m 3]; rTΔ is the
difference between the flue gas temperature in and out of the electrical re-boiler, in [K].
The separation process by chemical absorption appli ed to the cases studied is analysed
according to several parameters such as: the CO 2 capture efficiency, the CO 2 lean/rich
loading solvent, the L/G ratio (solvent flow/ flue gases or syngas flow) and the concentration
of amine in the solvent.
Fig. 3 shows the process of case “2a”: power plant with CO 2 capture by chemical
absorption.

Fig. 3. Coal power plant with post-combustion chemical abso rption [31]
The characteristics of the power plant are presente d in Table 2. The parameters, also
presented in Table 2, are specified for the power p lant without CO 2 capture. Once the CO 2
capture is integrated, the net power installed decr eases due to the mechanical work used for
solvent regeneration. The steam used for the solven t regeneration is extracted at a pressure of
2.25 bar (for both pre- and post-combustion cases).
The process of the power plant with pre-combustion CO 2 capture is presented in Fig. 4.

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Fig. 4. Coal power plant with pre-combustion chemical absor ption [31]
The main data for the chemical absorption process u sed in the pre- and post- combustion
case are presented in the second part of Table 2. O ne observes that the power installed
decreases from 250 MW (the power plant without CO 2 capture) to 217.3 MW (the power
plant with CO 2 capture using an L/G ratio of 1.8 mol solvent /mol flue gases ). The size of the
absorption and desorption unit is maintained consta nt in both cases: pre- and post-
combustion.
Table 2
Main data of the coal power plant with chemical abs orption
Coal power plant operating parameters
Power installed, MW 250
Net power plant efficiency, % 37.6
Air equivalence ratio 1.55
HP steam, °C/bar 560/170
MP steam, °C/bar 557/34
LP steam, °C/bar 282/4.84
Steam turbine isentropic efficiency HP/IP/LP, % 85/ 92.5/86.5
Condenser pressure, bar 0.05

Chemical absorption with MEA – post-combustion
Absorber/stripper stages number 10/15
MEA concentration, wt. % 30
Lean solvent temperature, oC 40
Rich solvent temperature, oC ~ 120
L/G ratio 1 .. 1.8
Specific heat at reboiler, GJ/tCO 2 1.77 .. 3.62
CO 2 capture efficiency, % 84.6 .. 99.2
Net power, MW 233.7 .. 217.3

Chemical absorption with MEA – pre-combustion
A/F ratio 0.5; 0.8; 1.15
L/G ratio 2.55; 1.7; 1.08
Specific heat at reboiler, GJ/tCO 2 2.18; 2.15; 2.13

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ACCEPTED MANUSCRIPTCO 2 capture efficiency, % ~ 90
Net power, MW 248, 247, 246

The CO 2 capture efficiency was calculated using the follow ing equation:
100
22 2
2⋅−=
in ex in CO CO CO CO Ef (19)
where: 2CO Ef is the CO 2 capture efficiency, in [%]; in CO 2 is the amount of CO 2 from the flue
gases/syngas, in [kg]; ex CO 2is the amount of CO 2 released in the atmosphere, in [kg].
The power plant efficiency (the global efficiency) is calculated using equation (20), where
the global efficiency was defined as the ratio betw een the net electricity generation ()el E and
the primary energy content in the fuel extracted ()pE. The primary energy content in the fuel
was calculated with the formula presented below, wh ere the amount of fuel extracted ()fuel M
is introduced in kg and the LHV (low heating value) is introduced in kJ/kg.
6 p10 6 . 3E ,100 ⋅⋅= ⋅=fuel
pel
gl MLHV
EEη (20)
In the chemical absorption process, the solvent use d for the CO 2 capture was the
monoethanolamine (MEA) with a MEA weight concentratio n of 30%. The weight
concentration was restricted to 30 % due to the cor rosion of the equipment’s metal surfaces
[32]. In the scientific literature, for the weight concentration chosen, the CO 2 capture
efficiency was of 90% for a heat amount required of 3.2 GJ/tCO 2 [14].
3. Results and Discussion
The chemical absorption process was compared from t he energy consumption point of
view for post- and pre-combustion. In both cases, t he energy consumption is provided by the
steam extracted from the steam turbine at the press ure of 2.25 bar. In the pre-combustion
case, the amount of solvent used (L) is lower, for the same electricity amount generation, than
in the post-combustion case because the syngas flow has a higher LHV (due to the lack of the
inert components such as CO 2) than the coal fuel.

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For different ratios A/F the syngas composition is shown in Table 3 in volume
concentration. One observes that by increasing the A/F ratio of 0.5 kg air /kg fuel , the quantity of
H2 increases; after this value, the content of H 2 begins to decrease. Instead, the quantity of
CH 4 decreases with increasing the air/fuel ratio and t he CO and H 2S increase. The volume
concentration of CO 2 decreases to an A/F ratio of 3.5 kg air /kg fuel ; after this ratio it begins to
increase, because by increasing the amount of air i ntroduced to the gasification unit, the
gasification process is replaced with the combustio n process.
The useful energy was calculated as the difference between the energy content of syngas
and the global thermal energy (heat duty) required for regenerating the solvent.
Table 3
Syngas composition for various ratios A/F
Syngas composition
Air/Fuel
(m ai r/m fuel ) H2
(%) CH 4
(%) N2
(%) CO
(%) CO 2
(%) H2S
(%) LHV
(kJ/kg)
0.3 15.30 4.99 57.43 0.78 21.35 0.14 21113.02
0.35 19.00 3.33 55.00 1.92 20.61 0.14 24869.78
0.4 20.87 2.36 53.65 3.40 19.59 0.13 26789.72
0.5 22.05 1.35 52.54 6.67 17.26 0.13 28043.98
0.6 21.85 0.89 52.37 9.73 15.03 0.14 27878.92
0.7 21.23 0.63 52.54 12.38 13.09 0.14 27270.65
0.8 20.51 0.47 52.84 14.62 11.43 0.14 26542.07
0.9 19.78 0.37 53.17 16.52 10.02 0.14 25809.14
1.15 18.19 0.22 54.00 20.13 7.31 0.15 24176.01
1.4 16.91 0.14 54.75 22.63 5.42 0.15 22834.24
1.7 15.69 0.09 55.53 24.71 3.83 0.15 21548.98
2.3 13.95 0.05 56.80 27.11 1.95 0.15 19663.49
2.8 12.92 0.03 57.69 28.0 1.12 0.15 18502.77
3.5 11.82 0.02 58.77 28.69 0.55 0.15 17234.44
3.7 10.96 0 60.27 27.25 1.37 0.15 16041.41
4 9.38 0 62.85 25.00 2.62 0.15 13901.40
4.3 7.85 0 65.31 22.98 3.72 0.14 11837.32
4.7 6.00 0 68.31 20.42 5.13 0.13 9347.25
5 4.82 0 70.31 18.54 6.19 0.12 7729.91

Consequently, the low heating value variation of th e syngas is heavily dependent on the
air/fuel ratio. For values of the ratio between 0.3 ..1.7 kg air /kg fuel , the low heating value of the
syngas is higher than that of the coal.
The simulation of the CO 2 capture processes by pre-/post-combustion chemical
absorption was made in Chemcad, version 6.0.1.

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ACCEPTED MANUSCRIPTWhen the A/F ratio increases, the useful energy of the syngas has had a maximum for the
A/F ratio of 4 kg air /kg fuel (Fig.5). On the contrary, the L/G ratio presented a minimum value
for an A/F ratio of 2.2 kg air /kg fuel .

Fig. 5. The A/F ratio influence on the energy content of th e syngas
For a CO 2 capture efficiency of 90%, there was determined th e energy content of the
syngas (Table 4) according to the A/F ratio. The sy ngas energy content in the case without
(w/o) CO 2 capture was calculated as the product of the synga s flow and its LHV; in the same
way, there was determined the syngas energy content in the case with CO 2 capture. The
useful energy after the chemical absorbtion process integration is the difference between the
syngas energy content, E syngas , (in the case of CO 2 capture) and the heat duty required, Q, for
the solvent regeneration (equation 21).
Q E Useful syngas energy − = , [GJ/h] (21)
Table 4
The energy content of the syngas before and after t he CO 2 capture technology integration
A/F
ratio Syngas
flow
w/o CO 2
capture LHV
syngas
w/o CO 2
capture Syngas
flow
with
CO 2
capture LHV
syngas
with CO 2
capture Syngas
energy
w/o CO 2
capture Syngas
energy
with
CO 2
capture Heat
duty Useful
energy
(kg/kg ) (kg/h) (kJ/kg) (kg/h) (kJ/kg) (GJ/h) (GJ/h) (GJ/h) (GJ/h)
0.3 385.51 21113.02 264.46 26135.84 8.14 6.91 0.34 6.57
0.35 454.16 24869.78 311.20 30519.49 11.29 9.50 0.40 9.10
0.4 521.33 26789.72 361.95 32550.41 13.97 11.78 0.45 11.33
0.5 650.85 28043.98 471.97 33215.46 18.25 15.68 0.50 15.18
0.6 775.80 27878.92 587.06 32280.23 21.63 18.95 0.53 18.42
0.7 897.80 27270.65 707.99 30914.92 24.48 21.89 0.53 21.36
0.8 1017.91 26542.07 829.03 29596.81 27.02 24.54 0.53 24.01
0.9 1136.73 25809.14 952.31 28365.98 29.34 27.01 0.52 26.50

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1.4 1720.09 22834.24 1568.78 23996.78 39.28 37.65 0.43 37.22
1.7 2065.25 21548.98 1937.03 22311.67 44.50 43.22 0.37 42.85
2.3 2749.01 19663.49 2662.75 20007.71 54.06 53.28 0.25 53.03
2.8 3313.44 18502.77 3253.29 18687.78 61.31 60.80 0.17 60.62
3.5 4097.12 17234.44 4060.88 17317.04 70.61 70.32 0.10 70.22
3.7 4283.09 16041.41 4191.32 16241.47 68.71 68.07 0.28 67.80
4 4545.39 13901.40 4362.53 14239.06 63.19 62.12 0.53 61.59
4.3 4805.46 11837.32 4536.85 12249.91 56.88 55.58 0.77 54.81
4.7 5154.09 9347.25 4770.25 9798.60 48.18 46.74 1.0 8 45.66
5 5419.11 7729.91 4941.62 8183.51 41.89 40.44 1.35 39.09

We can see (Fig. 6) that the pre-combustion CO 2 capture integration by chemical
absorption does not significantly influence the ene rgy content of the syngas, the energy
penalty (the heat duty) for regenerating the solven t being small as compared with the useful
energy of the syngas in the benchmark case. This is an advantage of the pre-combustion CO 2
capture integration compared with the post-combusti on one.
In the future, it is preferable to use the syngas p roduced by removing the CO 2, in different
energetic power plants in order to reduce the amoun t of the CO 2 generated.

Fig 6. Useful energy of the syngas w/o and w/ CO 2 capture according to the A/F ratio
For comparing the pre- and post-combustion chemical absorption, the influence of the
L/G ratio on the power plant and on the CO 2 capture efficiency was determined (Fig. 7). For
all the three cases (A/F = 0.5; 0.8 and 1.15 kg air /kg fuel ), the L/G ratio was established
considering the CO 2 capture efficiency of approximately 90%. In the pr e-combustion case,
the global efficiency also takes into account the c oal gasification efficiency. The pre-
combustion global efficiency is much lower than in the post-combustion case due to the
lower efficiency of the coal gasification process ( 30 – 35 %) [33]. Also, the power plant

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ACCEPTED MANUSCRIPTefficiency decreases as the L/G ratio increases due to the higher thermal energy required for
the solvent regeneration.

Fig. 7. The L/G ratio influence on the power plant efficien cy and on the CO 2 capture process
The heat duty required for the solvent regeneration according to the A/F ratio, is
presented in Fig. 8. We mention that the syngas flo w (G) is maintained constant. So, the L/G
ratio increases only if the solvent flow increases.

Fig. 8. The effect of A/F ratio on the heat duty and L/G ra tio
A lower amount of thermal energy is required for th e solvent regeneration in the pre-
combustion case due to the small amount of the syng as flow compared to the flue gases
amount (the post-combustion case). When the A/F rat io increases, the L/G ratio for a CO 2
capture efficiency of 90% decreases because the A/F ratio influences the carbon dioxide
concentration in the syngas produced, consequently the thermal energy has a small
decreasement .

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ACCEPTED MANUSCRIPT3. Case ”2b” – chemical absorption process in post-co mbustion
The influence of the L/G ratio on the power plant p erformance was determined following
the simulations performed in Aspen Hysys (Fig. 9), highlighting the heat required for the
solvent regeneration. This heat required for the so lvent regeneration comes from the steam
extracted from the low pressure steam turbine in bo th cases (pre- and post-combustion).
One observed that with increasing the L/G ratio (an d obviously the CO 2 capture
efficiency), the power plant efficiency decreased. For a CO 2 capture efficiency of 90% (for an
L/G ratio of 1.13 mol solvent /mol flue gas ), the power plant efficiency was of approximately 37%.

Fig. 9. The effects of L/G ratio on the power plant and CO 2 capture process efficiency

Fig. 10. The effects of L/G ratio on the heat duty
In this paper, for a CO 2 capture process efficiency of 90 % (for an L/G rat io of 1.13
mol solvent /mol flue gas ) the heat duty required was of 2.5 GJ/tCO 2 (Fig. 10).
In the pre-combustion process, the CO 2 capture efficiency was maintained of 90 % for
each A/F ratio of 0.5; 0.8 and 1.15 kg air /kg fuel , and for the L/G ratio of 2.55, 1.7, 1.08
mol solvent /mol syngas . For each case represented by the A/F ratio, the h eat duty required was of
2.18; 2.15; 2.13 GJ/tCO 2.

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ACCEPTED MANUSCRIPT4. Conclusions
In this paper a benchmarking analysis was made betw een the pre- and post-combustion
process for CO 2 capture by chemical absorption. To highlight the d ifferences between the two
ways, the chemical absorption was integrated in the pre-combustion (considering the coal
gasification process before the coal power plant) a nd in the post-combustion in a coal fired
power plant. The syngas obtained after the treatmen t has a higher LHV compared to the coal
used, thus, a smaller amount of syngas is required for producing the same amount of
electricity. However, in the post-combustion case, for a CO 2 capture efficiency of 90 %, the
L/G ratio is higher than in the pre-combustion case only for an A/F ratio bigger than
0.8kg air /kg fuel . In the pre-combustion case, the heat duty used fo r the solvent regeneration is
smaller than in the post-combustion case due to the smaller amounts of syngas employed.
However, considering the CO 2 capture efficiency of 90 %, the CO 2 flow generated in the
environment is higher in the pre-combustion case (7 .08 kg/s) than in the post-combustion
case (3.48 kg/s) due to the carbon dioxide oxidatio n in the syngas combustion process (after
the pre-combustion case, a rest of 2 % of CO 2 is found in the syngas).
For estimating in which way (pre- or post-combustio n technology) it is better to use the
chemical absorption for the CO 2 mitigation in the power plants, an economical meth od will
be analysed in the future studies.
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ACCEPTED MANUSCRIPTHighlights
• Integration of the chemical absorption process in p re- or post-combustion processes
• Increasing the syngas LHV from the coal gasificatio n using the chemical absorption
process for the CO 2 separation
• Parametrical study of the energy system with integr ated chemical absorption