Energy and Power Engineering, 2013, 5, 157-161
doi:10.4236/epe.2013.54B030 Published Online July 2013 (
Optimization of an Existing Coal-fired Power Plant with
CO2 Capture
Ying Wu, Wenyi Liu, Yong-ping Yang
School of Energy Power and Mechanical Engineering, North China Electric Power University, Beijing, China
Received February, 2013
Nowadays, the worsening environmental issue caused by CO2 emission is greatly aggravated by human activity. Many
CO2 reduction technologies are under fast development. Among these, monoethanolamine (MEA) based CO2 capture
technology has been paid great attention. However, when connecting the CO2 capture process with a coal-fired power
plant, the huge energy and efficiency penalty caused by CO2 capture has become a serious problem for its application.
Thus, it is of great significance to reduce the related energy consumption. Based on an existing coal-fired power plant,
this paper proposes a new way for the decarburized retrofitting of the coal-fired power plant, which helps to improve
the overall efficiency of the power plant with less energy and efficiency penalty. The decarburized retrofitting scheme
proposed will provide a new route for the CO2 capture process in China.
Keywords: MEA; CO2 Capture; Decarburized Retrofitting; Coal-fired Power Plant
1. Introduction
The increased CO2 emission has led to great concern of
people when confronted with today’s environmental
phenomena such as global warming and rising sea levels
[1]. China, one of the world’s largest producers of CO2,
is responsible for approximately one-fifth of the world’s
CO2 emissions and CO2 emitted from coal-fired power
plants accounts for nearly 50% of the to tal CO2 emission.
The CO2 capture and storage (CCS) technology, espe-
cially the monoethanolamine (MEA) based CO2 capture
method is commonly considered as a feasible option for
CO2 reduction[2-3].
However, when connecting CO2 capture with an ex-
isting coal-fired power plant, the huge energy consump-
tion for the CO2 capture process will dramatically reduce
overall efficiency of the power plant, which becomes a
technical barrier for its fast development [4]. Thus, how
to minimize the related energy consumption is of great
significance for CO2 capt ure application[5].
Based on an existing coal-fired power plant, a new
decarburized retrofitting scheme is proposed by fully
utilizing the surplus energy instead of abandoning it,
which provides a new route for the CO2 capture applica-
tion in the thermal power plants.
2. Selected Reference System of the Power
Plant and Capture Process
2.1. A Typical 350 MW Coal-fired Power Plant
in China
The schematic of a typical coal-fired power plant with
350 MW output is selected as the reference system,
which is given in Figure 1.
As shown in the figure, for the steam/water cycle, the
turbines consist of high pressure (HP), intermediate
pressure (IP), and low pressure (LP) turbines connected
to the generator with a common shaft. Steam from the
exhaust of the HP turbine is returned to the boiler for
reheating and then sent to the IP turbine. Exhaust steam
from the IP turbine passes through the one-cylinder/
double-exhaust LP turb ines and flows into the conden ser.
Before recycling back to the boiler, the condensed water
will be heated in the high-pressure and low-pressure re-
generative heaters, in which the thermal heat is supplied
by steam extraction from different turbine cylinders.
For the exhaust flue gas, after leaving selective cata-
lytic reduction (SCR), electrostatic precipitator (ESP)
and flue gas desulphurization (FGD) to get rid of some
toxic gases like NOx and SO2, the flue gas will pass
through the CO2 recovery process, in which about 90%
of CO2 will be absorbed. The treated gas, mostly con-
taining N2, O2 and H2O, will be directly vented to the
2.2. MEA-based CO2 Capture Process
MEA is selected as the absorbent of CO2 capture process
since it has various advantages like stability, fast reaction
rate and large recovery capacity. MEA-based CO2 cap-
ture process, as one of post-combustion CO2 capture
processes, is located between the FGD unit and the flue
stack, which is a comparatively mature technology and
Copyright © 2013 SciRes. EPE
has a bright future to be utilized on a large scale. The
MEA-based CO2 capture process is shown in Figure 2.
From Figure 2, the MEA-based CO2 capture process
can be summarized as follows: (1) The flue gas is com-
pressed by a booster fan; (2) The CO2 in the flue gas is
absorbed by MEA in an absorber and the treated flue gas
will be directly vented to the atmosphere; (3) The rich
amine solution with CO2 is delivered to a heat exchanger
by a pump; (4) The rich amine solution will release CO2
and lean ammonia solution in the stripper by reboiler
operation; (5) The high-purity CO2 will be flashed in a
CO2 cooler, and later compressed and cooled for trans-
port and storage; (6) Contrary to the rich amine solution,
the lean ammonia solution leaving from the stripper will
release energy in the heat exchanger and be recycled
back to the absorber. (7) The makeup MEA solution is
also added into the absorber. The main parameter of the
MEA-based CO2 capture process is shown in Table 1.
Figure 1. A typical 1000 MW coal-fired power plant in China.
Figure 2. MEA-based CO2 capture process.
Copyright © 2013 SciRes. EPE
Y. WU ET AL. 159
Usually, the energy for the reboiler duty, with 3.4
MJ/kg CO2, is provided by the steam extraction from the
power generation unit, which leads to great energy and
efficiency penalty of the power plant.
3. The Decarburized Retrofitting of the
Coal-fired Power Plant
3.1. Scheme 1: The Conventional Decarburized
The conventional decarburized retrofitting of the coal-
fired power plant is given in Figure 3. When 90% of
CO2 in the flue gas is separated, the steam extraction for
CO2 capture process may account for over half of the
total steam flow with pressure of 2bar-4bar. Due to the
structural constraints of the LP turbine, it is impossible to
extract so much steam within the LP turbine. Thus, the
cross pipe between IP turbine and LP turbine is the only
feasible extraction point to provide so much steam ex-
traction. The average temperature for the regeneration of
MEA absorbent is about 115℃. In practice, the highest
temperature of the extracted steam for absorbent regen-
eration should not exceed 140℃. Otherwise, MEA deg-
radation and corrosion issue will be sharply aggravated.
Unfortunately, the steam parameter in the extraction
point is usually higher than needed. Thus, the extracted
steam needs to be throttled and cooled to a suitable pres-
sure and temperature by a couple of throttling valve and
cooling equipment. The exhausted water out of the re-
boiler is recycled back into the condenser.
Table 1. Main parameters of the MEA-based CO2 capture process.
Item Value
Stripper pressure (bar) 2.1
Average temperature of reboiler (°C) 115
CO2 recovery ratio (% ) 90
CO2 lean loading (molCO2/molMEA) 0.3
CO2 rich loading (molCO2/molMEA) 0.45
Energy consumption of reboiler (MJ/kg CO 2) 3.4
Mass purity of sep a rated CO2 (%) 99.8
Mole purity of separated CO2 (%) 99.6
Figure 3. The original decarburized retrofitting scheme of the coal-fired power plant.
Copyright © 2013 SciRes. EPE
3.2. Scheme 2: Optimization of the Decarburized
The decarburized system in Section 3.1 realizes the CO2
capture in cost of great energy consumptio n. Suppose the
surplus energy in the extracted steam can be utilized, it
will be certain to improve the thermal performan ce of th e
decarburized system.
Thus, to recover the surplus pressure of the extracted
steam, a new letdown steam turbine generator (LSTG) is
installed to recover the surplus energy of the extracted
steam in the new decarburized system, as shown in Fig-
ure 4. Such improvement is really simple and easy to
implement while it is very effective to retrieve the sur-
plus pressure and temperature, which can also make the
output p ower gre a t ly increase t o a certain de g r e e.
3.3. Performance Evaluation of the Two Capture
Performance evaluation of the two capture systems is
conducted in Table 2.
It is easy to find that, with the help of new LSTG, the
net power generation is increased from 211.25 MW to
230.36 MW. The efficiency of the new decarburized sys-
tem has increased to 28.01% with 12.03% efficiency
penalty compared to 14.35% of the original decarburized
system. Thus, the energy-saving effects in the steam ex-
traction point are obvious.
4. Techno-economic Analysis of the Two
Capture Systems
Techno-economic analysis of the original power plant
and two retrofitting schemes is conducted in Table 3.
As shown in the table, the total plant investment of
reference system (230.52 M$) are estimated according to
the related data of typical 350 MW coal-fired power
plants in China with specific plant investment of ap-
proximately 700 $/kW. The total investment of CO2 cap-
ture process, estimated based on some demonstration
plant in China, reaches 92.15 M$. Due to the connection
with the CO2 capture process, the total plant investment
of scheme 1 has reached up to 322.67 M$ with specific
plant investment of 1527.43 $/kW. For scheme 2, al-
though the total plant investment is further increased to
324.27 M$ with consideration of the added LSTG and
the related retrofitting cost, its specific plant investment
is reduced to 1407.67 $/kW because of the increased net
power generation.
Figure 4. The new decarburized retrofitting scheme of the coal-fired power plant.
Table 2. Overall performance of two capture system.
Item Original New
HP, IP & LP power output (MW) 260.37 260.37
LSTG power output ( % ) - 19.11
Gross power output (MW) 260.37 279.48
Internal power consumption (MW) 17.33 17.33
Power for CO2 capture process (MW) 31.79 31.79
Net power generation (MW) 211.25 230.36
Total energy of coal input (LHV) 822.39 822.39
Net plant efficiency (%) 25.69% 28.01%
Original plant effic iency (%) 40.04% 40.04%
Efficiency penalty (%) 14.35% 12.03%
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Y. WU ET AL. 161
Table 3. Techno-economic analysis results.
Item Reference Scheme 1 Scheme 2
Net plant efficiency (%) 40.04% 25.69% 28.01%
Net power generation (MW) 329.32 211.25 230.36
Total plant investment (M$) 230.52 322.67 324.27
Specific plant investment ($/kW) 700.00 1527.43 1407.67
Cost of electricity (COE, $/MWh) 57.75 103.49 94.70
CO2 emission rate (tCO2/MWh) 0.87 0.14 0.12
CO2 avoided rate (tCO2/MWh) 0 0.73 0.75
Cost of CO2 avoided ($/t CO2) 0 62.66 49.27
For cost of electricity (COE) and cost of CO2 avoided,
both of two parameters have the same trend. Their values
in scheme 1 are increased when compared to the refer-
ence system. However, for scheme 2, due to the in-
creased net power generation, their values are reduced
compared to scheme 1.
To sum up, with the added LSTG, the net efficiency
and net electricity generation of the new retrofitting
scheme increases while its specific plant investment,
COE and th e cost of CO2 avoided reduces, which reflects
the economic advantage of the new retrofitting scheme.
5. Conclusions
This paper carries out the decarburized retrofitting study
of an existing coal-fired power plant in China. Since the
energy consumption of the CO2 capture process is ex-
tremely huge, the energy and efficiency penalty caused
by CO2 capture process becomes a technical barrier for
the large-scale CO2 capture application.
Optimization measures are conducted in the conven-
tional decarburized retrofitting scheme. Based on the
conventional scheme, a new LSTG is added to recover
the surplus energy existed in the extracted steam. Per-
formance results also show its benefits. The added LSTG
helps the improvements of the overall performance of the
power plant and provides a new route for the CO2 cap-
ture application in coal-fired power plants.
Finally, techno-economic results are also conducted.
From the results, it is easy to find that the net efficiency
and net electricity generation of the new retrofitting
scheme increases while its specific plant investment,
COE and th e cost of CO2 avoided reduces, which reflects
economic benefits of the new retrofitting scheme.
6. Acknowledgements
This study has been supported by the National Key
Technology R&D Program of China (2012BAC24B01),
National Nature Science Foundation Project (51006034,
51061130538), the Fundamental Research Funds for the
Central Universities (11 MG04) and Internation al Science
and Technology Cooperation Project (2010DFA 72760-
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