1
The 12th European Conference on Fuel and Energy Research and its Applications
Exergy analysis of a 1000MW single reheat
supercritical CO2 coal-fired power plant
State Key Lab of Coal Combustion (SKLCC)
Huazhong University of Science & Technology (HUST)
Jing Zhou, Sheng Su*, Jun Xu, Kai Xu, Long Jiang, Yi Wang,
Song Hu, Liang Liu, Peng Ling, Jun Xiang*
2
Outline
Background
Model & Methodology
Results & Discussions
Conclusions
3
Steam Rankine cycle (SRC)
S-CO2 Brayton cycle
Advantages： High thermal efficiency
Excellent inheritance of materials
Compact turbine size
S-CO2 coal-fired power plants (SCO2PP) have a broad prospect of development and application
Nuclear energy Solar energy Waste heat energy Coal-fired energy
1、Background: Why do we need S-CO2 coal fired power plant?
Double reheat ultra-supercritical technology 700℃ ultra-supercritical technology
Vapor parameters of 33 MPa/600℃/620℃/620℃ Vapor parameters of 36.65Mpa/700℃/720℃
Unit efficiency of 47.82% Unit efficiency of 51.92%
Difficult to arrange the heating exchange surfaceWeak material development, high investment
cost
4
1、Background: Progress of SCO2PP development
2013 and 2016, Yann Le Moullec, initial concept design
by EDF, France
• Conceptual design and economic evaluation
• Short cut design of the boiler: Reheat cooling wall
(RCW) layout
620℃/30MPa：
Simplified schematic of double reheat S-CO2 boiler using Reheat
cooling wall (RCW) layout
Overall plant net efficiency: 47.8%, 2.4% higher than
traditional steam power plant (TSPP)
2018，Jinliang Xu, by North China Electric Power
University, China
• S-CO2 boiler module design: Partial flow strategy (PFS)
• Efficiency is further improved based on Energy analysis
Overall plant net efficiency: 48.3%
Schematic of double reheat S-CO2 power plants using Partial flow strategy
(PFS) module design
[1] Le Moullec Y. Conceptual study of a high efficiency coal-fired power plant with CO2
capture using a supercritical CO2 Brayton cycle[J]. Energy. 2013, 49(1): 32-46.
[2] Mecheri M, Le Moullec Y. Supercritical CO2 Brayton cycles for coal-fired power
plants[J]. Energy. 2016, 103: 758-771.
[3] Xu J, Sun E, Li M, et al. Key issues and solution strategies for supercritical carbon dioxide
coal fired power plant[J]. Energy. 2018, 157: 227-246.
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1、Background: Progress of S-CO2 coal-fired power plants development
2018，our previous study, Jun Xiang, by SKLCC, China
• Parameter and configuration (Economizer and
Compression) optimization based on exergy analysis
• A comprehensive optimized model for S-CO2 coal-fired
power plant is established.
Schematic of single reheat S-CO2 power plants using exergy analysis
optimization:
2016，Yu Yang, by Xi’an Thermal Power Research Institute,
China
• Numerical simulation of the coupled heat transfer between
combustion and fluid heating
• Design of the heating surface of S-CO2 boiler
Schematic of a 300MW single reheat S-CO2 coal-fired power plant and
temperature distribution of heating surface in S-CO2 boiler:
[4] Yang Y, Bai W, Wang Y, et al. Coupled simulation of the combustion and fluid heating
of a 300 MW supercritical CO 2 boiler[J]. Applied Thermal Engineering. 2017, 113: 259-
267.
[5] Zhou J, Zhang C, Su S, et al. Exergy analysis of a 1000 MW single reheat supercritical CO2
Brayton cycle coal-fired power plant[J]. Energy Conversion and Management. 2018, 173: 348-358.
605℃/603℃/27.4MPa
Overall plant exergy efficiency: 45.4%, improved by 3.5%
compared with TSPP
Reheat cooling wall (RCW) layout
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1、Brief summary
S-CO2 Brayton cycle system remains undetermined
System efficiency needs to be improved.
Energy analysis Exergy analysis
It can accurately characterize the work potential for high-parameter system.
S-CO2 coal-fired power plants has potential for improvement
Optimization method and strategy should be presented and analyzed.
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Outline
Background
Model & Methodology
Results & Discussions
Conclusions
8
2.1 Model
Combustor
WW-LF
WW-UF
S-SH1 S-SH2 F-SH F-RH1
F-RH2
P-RH2
P-SH
APH-S
APH-PCoal
Superheated flow
Reheated flow
Material flow into the boiler Air flow into the boiler
S-CO2 flow into S-CO2 cycle
P-RH1
ECO
1
2
3
4 5 6
7
8
9
10
11
12
WW-LF: WaterWall of lower furnace
WW-UF: Cooling Wall of upper furnace
P-SH: Primary superheater/ Primary reheater3
S-SH1: Screen superheater1/ Screen reheater1
S-SH2: Screen superheater2
F-SH: Final superheater
F-RH1: Final reheater1
F-RH2: Final reheater2
P-RH2: Primary reheater2
P-RH1: Primary reheater1
ECO: Economizer
FGC: Flue gas cooler
APH-S: Secondary air preheater
APH-P: Primary air preheater
1、 Traditional steam power plants (TSPP)
Flue gas
Outlet temperature ( C)
Referred
values (TSPP)
Simulation
values (TSPP)Error (%)
WW-LF - 1613.1 -
WW-UF - 1225.9 -
P-SH 503.6 500.8 −0.6
S-SH1 1139.8 1119.6 −1.8
S-SH2 1037.8 1020.6 −1.7
F-SH 938.2 923.7 −1.5
F-RH-H 805.5 794.3 −1.4
F-RH-C 839.9 828 −1.4
P-RH2 770.8 760.5 −1.3
P-RH1 456.7 455.1 −0.4
ECO 358.9 358.5 −0.1
APH-S 128.5 127 −1.2
APH-P 128.5 130.3 1.4
Table 1. The main parameters for the simulation of a single-reheat
boiler
Less than 2% error1000MW single-reheat traditional steam coal-fired power plant
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2、 Basic single reheat S-CO2 power plant (Basic SCO2PP )
PC
LTRHTR
BC
MC1
MC2
IC1
Combustor
CW-LF
CW-UF
S-RH1 S-SH2 F-SH F-RH1
F-RH2
P-RH2
P-RH3
ECO2
APH-S
APH-PCoal
HPT
LPT
Superheated flow
Reheated flow
Material flow into the boiler Air flow into the boiler
S-CO2 flow into S-CO2 cycle
P-RH1
ECO1
1
2
3
4 5 6
7
8
9
10
11
12
10*
575.7℃
361.7℃ 457.3℃
487.3℃545.7℃
30℃ temperature pinch
Boiler heating exchange surface layout:
Flue gas cooler (FGC) under Economizer (ECO)
Waste heat utilization ：Cycle internal split flow (CISF) method
PC
LTRHTR
BC
MC1
MC2
IC1
Combustor
CW-L
CW-U
S-SH2 F-SH F-RH1
F-RH2
P-RH2
FGC
APH-S
APH-PCoal
HPT
LPT
Superheated flow
Reheated flow
Material flow into the boiler Air flow into the boiler
S-CO2 flow into S-CO2 cycle
P-RH1
ECO
S-RH1
P-RH3
50%
50%
50%
50%
1
2
3
4 5 6
7
8
9
10
11
12
10*
3、 S-CO2 partial flow power plant (SCO2PFPP)+CISF
Divide into two halves, and pressure drop decreases by 1/8
Heating length 1/2 Mass flow 1/2
Partial flow strategy (PFS) to reduce the pressure drop
S-CO2 partial flow power plant (SCO2PFPP)
2.1 Model
10
PC
LTRHTR1
BC
MC1
MC2
IC1
Combustor
CW-L
CW-U
S-SH2 F-SH F-RH1
F-RH2
P-RH2
APH-S
APH-PCoal
HPT
LPT
Superheated flow
Reheated flow
Material flow into the boiler Air flow into the boiler
S-CO2 flow into top cycle
P-RH1
FGC
CBT
HTR2
S-CO2 flow into bottom cycle
S-RH1
P-RH3
1
2
3
4 5 6
7
8
9
10
11
12
4、 SCO2PFPP+CTBC
PC
LTR
BC
MC1
MC2
IC1
CBT
HTR2S-HeaterR-Heater
FGC
HPTLPT Waste heat utilization：Connected-Top-Bottom cycle
(CTBC) method
Use this part of flue gas
waste heat as the heat source
of the bottom cycle Mass flow rate of
SCO2PP is 8~10 times
compared with TSPP
Main inlet temperature
into CW of SCO2PP
increases by 100~150℃
Items TSPPBasic
SCO2PP
SCO2PFPP
+CISF
SCO2PFPP+
CTBC
Main inlet temperature into
WW or CW / ℃332.0 467.7 451.0 451.0
T10 / ℃ 483.4 575.7 575.7 575.7
T10* / ℃ - 487.0 487.0 -
T11 / ℃ 361.7 361.7 361.7 361.7
Mass flow rate / tonnes·h-1 3101.8 29184.0 27890.9 26416.4
Energy efficiency of the
unit / %43.2 45.7 47.6 49.1
2.1 Model
Table 2. Simulation values of four different coal-fired power plants
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2.2 Methodology
EA
EB
Es,in
Es,out
ER,outER,in
Efg
Ir
B , , , ,E E E E E E EA s in R in s out R out r fgI
S-CO2 boiler system exergy analysis method:Boiler system exergy balance equation:
Boiler system exergy efficiency: , , , ,eE E E E
E
s out s in R out R in
b
A BE
+
Fuel exergy:
Heating exchange exergy loss:
Flue gas exergy loss:
S-CO2 cycle system exergy analysis method:
, , , ,E E E E Ws out R out s in R in rI
S-CO2 cycle system exergy balance equation:
Es,in Es,out
ER,outER,in
W
rI
S-CO2 cycle system exergy efficiency: e
sc
, , , ,
W
E E E Es out s in R out R in
+
12
Outline
Background
Model & Methodology
Results & Discussions
Conclusions
13
3.1.1 Exergy distribution analysis of different 1000MW coal-fired power plants
Fig. 1. Exergy analysis of different coal-fired power plants
Table 3. Exergy distribution analysis of different coal-fired power plants
SCO2PFPP(CTBC) has better comprehensive performance, including higher exergy efficiency of the boiler and S-CO2
cycle due to its lowest exergy loss ratio of heat exchange surface.
The exergy loss ratio of the S-CO2 boiler system is as high as about 82%, in which the exergy loss ratio of the furnace
combustion accounts for about 50% and the heat exchange surface for about 29%.
The exergy loss of the heat exchange surface has more remarkable effect on the unit exergy efficiency.
Items
Exergy loss (MW) Exergy loss ratio (%)
TSPPBasic
SCO2PP
SCO2PFPP
+CISF
SCO2PFPP
+CTBCTSPP
Basic
SCO2P
P
SCO2P
FPP+CI
SF
SCO2P
FPP+C
TBC
Input exergy to the unit 2444.8 2444.8 2444.8 2444.8 - - - -
Furnace combustion 662.5 662.5 662.5 662.5 46.7 48.7 50.4 51.8
Heat exchanger surface
in boiler472.6 402.0 403.3 357.9 33.3 29.6 30.7 28.0
Traditional steam cycle
or S-CO2 cycle246.8 232.7 224.0 234.9 17.4 17.1 17.1 18.4
Others 36.4 62.3 23.6 22.7 2.6 4.6 1.8 1.8
Sum of exergy loss 1418.3 1359.5 1313.4 1278.0 100.0 100.0 100.0 100.0
Output effective exergy 1027.0 1085.3 1131.4 1166.8 - - - -
Exergy efficiency of the
boiler (%)52.1 53.9 55.4 57.3
Exergy efficiency of the
cycle (%)80.7 82.4 83.5 83.2 - - - -
Exergy efficiency of the
unit (%)42.0 44.4 46.3 47.7 - - - -
TSPPBasic SCO2PP
SCO2PFPP+CISF
SCO2PFPP+CTBC40
45
50
55
Ex
erg
y e
ffic
ien
cy o
f th
e u
nit
/ %
Exergy efficiency of the unit
Exergy loss ratio of furnace combustion
Exergy loss ratio of heat exchanger surface in boiler
Exergy loss ratio of the steam cycle or S-CO2 cycle
Exergy loss ratio of the others
0
10
20
30
40
50
60
70
80
Ex
erg
y l
oss
rat
io /
%
Boiler
Cycle
Unit
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3.1.2 Exergy analysis of the heating exchange surface between TSPP and basic SCO2PP
8. Final reheater2
9. Primary reheater2
10. Primary reheater1
11. Economizer
12. Flue gas cooler
13. Secondary air preheater
14. Primary air preheater
1. Waterwall or cooling Wall of lower furnace
2. Waterwall or cooling Wall of upper furnace
3. Primary superheater/ Primary reheater3
4. Screen superheater1/ Screen reheater1
5. Screen superheater2
6. Final superheater
7. Final reheater1
Fig. 2. Exergy analysis of the heating exchange surface between TSPP and basic SCO2PP
Compared with TSPP, the increase in exergy efficiency of basic SCO2PP is mainly due to the decreasing
exergy loss ratio of the heat exchange surface.
Exergy loss ratio of almost all the heat exchange
surface of basic SCO2PP is lower than that of TSPP
due to their relatively higher exergy efficiency, except
Flue gas cooler (FGC).
The exergy loss ratio of FGC is as high as 3.7%, which
takes up relatively high proportion. And its exergy
efficiency is lowest.(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)(11)(12)(13)(14)
0
2
4
6
8
10
12
14
16
18
20
Exergy loss ratio in TSPP
Exergy loss ratio in basic SCO2PP
Exergy efficiency in TSPP
Exergy efficiency in basic SCO2PP
0
20
40
60
80
100
Ex
ergy l
oss
rat
io /
%
Ex
ergy e
ffic
iency
/ %
15
MC1MC1
MC2MC2 BC BC
HPTHPT
LPTLPT
CBTLTR
LTRHTR1
HTRHTR2
Coolers
Coolers
0
1
2
3
4
5
6
7
8
****** ***
Ex
ergy l
oss
rat
io /
%
Exergy loss ratio of SCO2 cycle
Exergy efficiency of SCO2 cycle
*80.0
82.5
85.0
87.5
90.0
92.5
95.0
97.5
100.0
Exer
gy e
ffic
iency
/ %
3.1.3 Exergy analysis of CISF and CTBC units
Between SCO2PFPP+CISF and SCO2PFPP+CTBC, the main variations occur in the heat exchange surface
and the S-CO2 cycle.
Fig. 3. Exergy analysis of the heating exchange surface between CISF and CTBC units Fig. 4. Exergy analysis of S-CO2 cycle betweenCISF and CTBC units
Exergy efficiency of the heat exchange surface between
CISF and CTBC units is almost the same, except FGC.
The exergy loss ratio of FGC in the CTBC unit suffers
much lower than that of the CISF unit.
The exergy loss ratio of HTR is the highest and takes up
the majority of the S-CO2 cycle.
Connected-bottom-cycle turbine (CBT) has relatively
lower exergy efficiency compared with HPT and LPT in
CTBC units , due to its lower inlet parameters.
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)(11)(12)(13)(14)0
2
4
6
8
10
12
14
16
18
20
Ex
erg
y l
oss
rat
io /
%
Exergy loss ratio in SCO2PFPP+CISF
Exergy loss ratio in SCO2PFPP+CTBC
Exergy efficiency in SCO2PFPP+CISF
Exergy efficiency in SCO2PFPP+CTBC
0
20
40
60
80
100
Ex
erg
y e
ffic
ien
cy /
%
16
3.2.1 ADFGC layout for SCO2PFPP+CISF
Optimization for SCO2PFPP +CISF
Fig. 5. The effect of the FGC split ratio on HTR performance
Fig. 6. The effect of the FGC split ratio on unit performance
HTR temperature difference decrease
Improve HTR exergy efficiency
Exergy efficiency:48.22%
Improved by 1.94%
PC
LTR
HTR
BC
MC1
MC2
IC1CW-L
CW-U
S-SH2 F-SH F-RH1
F-RH2
P-RH2
FGC1
APH-S
APH-P
HPT
LPT
P-RH1
S-RH1
P-RH3
50%
50%
50%
50%
1
2
3
4 5 6
7
8
9
10
11
12
FGC2
575.7℃
361.7℃191.5℃
476.1 ℃
Optimization method：Adjacent double flue gas cooler (ADFGC) layout
Analyze HTR separately
Split from the inlet high-pressure side
of HTR
0.00 0.02 0.04 0.06 0.08 0.1040
45
50
55
Ex
erg
y e
ffic
ien
cy o
f th
e u
nit
/ %
Split flow ratio to FGC
Exergy efficiency of the unit
Exergy loss ratio of furnace combustion
Exergy loss ratio of heat exchanger surface in boiler
Exergy loss ratio of the steam cycle or S-CO2 cycle
Exergy loss ratio of the others
0
10
20
30
40
50
60
70
80
Ex
erg
y l
oss
rat
io /
%
0.0 0.2 0.4 0.6 0.8 1.00
10
20
30
40
50
60
Split flow ratio to FGC
χ=0.14, ηe=97.70%
χ=0.10, ηe=96.82%
χ=0.05, ηe=95.70%
Ho
t an
d c
old
str
eam
s te
mp
erat
ure
dif
fere
nce
in
HT
R /
oC
Cumulative thermal duty ratio in HTR
χ=0, ηe=94.66%
Analyze the SCO2PFPP unit
17
CW-L
CW-U
S-SH2 F-SH F-RH1
F-RH2
P-RH2
FGC1
APH-S
APH-P
HPT
LPT
P-RH1
S-RH1
P-RH3
50%
50%
50%
50%
1
2
3
4 5 6
7
8
9
10
11
12
PC
LTR
BC
MC1
MC2
IC1
CBT
HTR2
FGC2
Optimization for SCO2PFPP +CTBC
Exergy efficiency:47.95%（600℃）Optimization method：Staggered double flue gas cooler (SDFGC) layout
450 500 550 600 65040
45
50
55
Ex
erg
y e
ffic
ien
cy o
f th
e u
nit
/ %
CBT inlet temperature / ℃
Exergy efficiency of the unit
Exergy loss ratio of furnace combustion
Exergy loss ratio of heat exchanger surface in boiler
Exergy loss ratio of the steam cycle or S-CO2 cycle
Exergy loss ratio of the others
0
10
20
30
40
50
60
70
80
Ex
erg
y l
oss
rat
io /
%
Fig. 7. The effect of CBT inlet temperature on unit performance
3.2.2 SDFGC layout for SCO2PFPP+CISF
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Outline
Background
Model & Methodology
Results & Discussions
Conclusions
19
Conclusion
The exergy loss ratio of S-CO2 power plants units from high to low is mainly concentrated
on furnace combustion, furnace heat transfer surface, followed by S-CO2 cycle and exhaust
gas waste heat.
The CISF and CTBC method can solve the waste heat utilization of the S-CO2 boiler.
However, the exergy loss of FGC and HTR takes up considerably high percentages in CISF
unit and connected-bottom-cycle turbine (CBT) has relatively lower exergy efficiency in
CTBC unit.
For optimization of SCO2PFPP+CISF, an innovative adjacent double flue gas cooler
(ADFGC) layout is presented. The unit exergy efficiency is 48.22%, improved by 1.94%.
For optimization of SCO2PFPP+CTBC, an innovative staggered double flue gas cooler
(SDFGC) layout is presented. The unit exergy efficiency is 47.95% as the CBT inlet
temperature is 600℃.
A comprehensive exergy analysis and optimization method for S-CO2 partial
flow power plant (SCO2PFPP) using cycle-internal-split-flow (CISF) and
connected-top-bottom-cycle (CTBC) method are constructed.
20
Acknowledgments
The authors would like to acknowledge the support from the National Key R&D program of China (No. 2017YFB0601802)
and National Science Foundation of China (NSFC) (Nos. 51576081, 51576086) for this research.
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A:Model input parameter and logic framework
Parameter ValueS
HPT inlet pressure/temperature 274bar/605 C
LPT inlet pressure/temperature 177bar/603 C
MC1 inlet flow pressure/temperature 76bar/32 C
MC2 inlet flow pressure/temperature 90bar/32 C
Optimum split ratio to BC 0.28
Components' pressure drop of S-CO2 cycle 0.1
Superheat or reheat exchange surface‘s
pressure drop in boiler 1.0
Compressor isentropic efficiency 89.00%
Compressor motor efficiency 99.60%
Turbine isentropic efficiency 93.00%
Recuperator pinch temperature difference 5 C
Flue gas and CO2 pinch temperature
difference 30 C
Flue gas outlet temperature 129 C
Table 1. Main input parameters during the simulation of the single-reheat S-CO2 power
plants
Input: T5, P5, P6, PHTR, PLTR, PHeater, PCoole r, T1
Calculate P5: P2=P5+ PHTR+ PLTR+ PHeater;
Calculate P1: P1=P6- PHTR- PLTR- PCoole r ;
Calculate P2: P2=P3+ PLTR ;
Assume T8
HTR hot stream outlet temperature T7 is calculated
to equalize mixing flow temperatures at point 3.
The split flow ratio before the point 8 is then fixed
to make the temperature difference (T7-T3) equal to
the HTR temperature-pinch chosen value.
The split flow ratio before the point 8 is then fixed
to make the temperature difference (T7-T3) equal to
the HTR temperature-pinch chosen value.
Calculate each point temperature on the high
pressure side of LTR: Ti=Ti-1+ Qi/(mCO2cpi×(1-x));
Calculate each point temperature on the low
pressure side of LTR: Tj=Tj-1+ Qi/(mCO2cpj);
Calculate Tn: Tn=Tj-Ti;
Tn,min= LTR temperature-pinch
chosen value?
Y
N
Adjusting the mass flow rate of the cycle to ensure
the boiler heat duty equal to traditional steam boiler ,
and assign heat to each heat exchange surface.
End
