evaluation of sco2 power cycles for direct and …unrestricted © siemens ag 2018 • • 2 •
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siemens.com/power-gasUnrestricted © Siemens AG 2018
EVALUATION OF SCO2 POWER CYCLES FOR DIRECT AND WASTE HEAT APPLICATIONSDr. Stefan Glos
2nd European supercritical CO2 ConferenceAugust 30-31, 2018, Essen, Germany
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Introduction/MotivationPotential benefits of supercritical CO2 power cycles
• higher efficiency compared to water/steam• smaller component size, lower costs, higher operating flexibility
Ahn et al. (2015)Dostal (2004)
?? ?
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Agenda
1. Introduction2. Direct heat applications (150 MW CSP)
Efficiency potentials, sensitivities and first component estimations
3. Waste heat applications (CCPP Trent/SGT800)Efficiency potentials, sensitivities and first component estimations
4. Summary and Outlook
Evaluation of sCO2 power cycles for direct and waste heat applications
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Agenda
1. Introduction2. Direct heat applications (150 MW CSP)
Efficiency potentials, sensitivities and first component estimations
3. Waste heat applications (CCPP Trent/SGT800)Efficiency potentials, sensitivities and first component estimations
4. Summary and Outlook
Evaluation of sCO2 power cycles for direct and waste heat applications
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Supercritical CO2 Brayton cycles for direct heatpower cycles (Example: 150 MW CSP)
(1)
(2)
(8)
(7)
(6)
(5)(3)
(4)
sCO2 Water/Steam
Heat sourceHeat sinkRecuperated heatCompressor work
433°C
39°C
Tm heat sourceTm heat sink
Condition (1) behind the pump/ compressorTm: mean temperature
ηcarnot : 56%
(1)
(3)
(4)
(5)
(6)
(7)
(8)
(2)
357°C
36°C
ηcarnot : 51%
• Higher mean temperatur in boiler main driver for better carnot efficiency in sCO2 cycle
ηcarnot =1- 𝑇𝑇𝑚𝑚,ℎ𝑒𝑒𝑒𝑒𝑒𝑒 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑇𝑇𝑚𝑚,ℎ𝑒𝑒𝑒𝑒𝑒𝑒 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑒𝑒
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-2,7% -0,1%
1,4%
5,0%
-4%
0%
4%
8%
12%
Carnot sCO2 Simple recuperated Recompression(25% recompr. mass flow)
Intercooling
η th,
sCO
2̶ η
th,W
/S
Efficiency analysis and comparison to water/steamExample: 150 MW CSP
Recu & Cond. losses reduced
Comp. & Cond. losses reduced
Simple recuperated sCO2 cycle
Intercooledrecompression cycle
Parameter Water/Steam
sCO2
TMS [°C] 545 545
pMS [bar] 140 370
Treheat [°C] 545 545
pReheat [bar] 27 ≈170
CW inlet [°C] 25 25
TTD Cond. [K] 3 3
TTD Recu. [K] - 5
Water/steam„Noor 3“
Higher Tm
Higher lossesin Recu, Compr. &
Cond.
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-5%
-4%
-3%
-2%
-1%
0%
1%
2%
3%
4%
15 25 35 45
η th,
sCO
2 ̶ η
th,W
/S
Cooling water inlet [°C]
Simple Cycle 545 °C
545 °C
545 °C back pressure opt.
605 °C
605 °C back pressure opt.
Cycle efficiency comparison for 150MW CSP @ varying cooling water temperatures
• Efficiency of simple sCO2 cycle behind w/s optimization necessary
• Decreasing efficiency advantage @ high cooling water inlet temperature
can be compensated with optimal back pressure
• Benefit of sCO2 cycle is reduced by optimization of w/s cycle (e.g. supercritical process)
reco
mpr
.&
inte
rcoo
led
65 bar 75 bar
95 bar 105 bar
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6753 mm
Turbine comparison sCO2 vs. water/steamExample: 150 MW CSP with reheat
sCO2 Turbines based on H60 & H70 modules / Rotormass = 17,7 t
Water/Steam Turbine BH50 & CH80-6.3 / Rotormass = 39,3 t
2268 mmGear-box
• ~ 55% lower rotor mass for sCO2 turbine • Significant smaller sCO2 turbine exhaust compared to w/s• High wall thickness due to high pressures
2850 mm2520 mm
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Component dimensions and sensitivity analysis− Recuperator:
-5%
-4%
-3%
-2%
-1%
0%
5 10 15 20 25
∆ηth
TTD [K]
0
0,2
0,4
0,6
0,8
1
5 10 15 20 25
A / A
ref,5
K
TTD [K]
LTR HTR Sum
ηth,w/s(TTD=5K)
Aw/s(TTD=5K)
Sensitivity for recompressed & intercooled sCO2 cycle @ 370 bar, 605°C, 75 bar, 25°C
• Larger heat exchanger surfaces in sCO2 cycle compared to w/s
• High pressure levels (e.g. 370bar/75bar) at both sides of recuperator
Water/SteamsCO2
Recompressed & Intercooled
Recuperated heat [MW] 79 505
kA LP / LTR [MW/K] 3,8 23
kA HP / HTR [MW/K] 3,4 10,5
Chordia et al. [1], [2]
LTR HTR
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Component dimensions and sensitivity analysis− Recompression bypass ratio:
0 %
1 %
2 %
3 %
4 %
5 %
0 % 5 % 10 % 15 % 20 % 25 %
∆ηth
Bypass ratio
1
2
3
4
5
0 % 5 % 10 % 15 % 20 % 25 %
A /
A ref
Bypass ratio
LTR HTR Sum
• Higher bypass ratio decreases the exergy losses
25 % bypass ratio10 % bypass ratio
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Component dimensions and sensitivity analysis
− High pressure piping:
-6%-5%-4%-3%-2%-1%0%1%
3 6 9 12 15 18 21 24 27 30 33 36
∆ηth
∆pHP-path [%]
ηth,w/s
sCO2∆pHP = 12%
sCO2∆pHP = 6%
δ
da
δ
da
• Efficiency/Performance strongly dependent on pressure losses
Reduction in specific weight: ~26%
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Agenda
1. Introduction2. Direct heat applications (150 MW CSP)
Efficiency potentials, sensitivities and first component estimations
3. Waste heat applications (CCPP Trent/SGT800)Efficiency potentials, sensitivities and first component estimations
4. Summary and Outlook
Evaluation of sCO2 power cycles for direct and waste heat applications
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Supercritical CO2 Brayton cycles for waste heat applications(bottoming cycle)
T [°C]
Q [MW]
flue gas
~ Exergy flue gas
T [°C]
Q [MW]
~ Exergy losses
T [°C]
Q [MW]
sCO2
• Lower losses in HRSG in sCO2 bottoming cycle
T [°C]
Q [MW]
flue gas
water/steam
~ Exergy water/steam
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OverviewT,s – Diagram of bottoming cycle (Trent 60)
Heat sourceHeat sink
Reuperated heatTurbomachinery work
Water/steam
Tem
pera
ture
[°C
]
Entropy [kJ/kg∙K]3,00 6,00 9,00
100
200
300
400
00
40 bar
0,074 bar
(1)
(2)
(3)
(4)
(5)
(6)
(7)
Tem
pera
ture
[°C
]
1,00 2,00 3,00
100
200
300
400
sCO2
240 bar
75 bar
0
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)0
Critical Point:• pCrit = 73,75 bar• TCrit = 31 °C
Entropy [kJ/kg∙K]
qrecu
qrecu
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Cycle analysis – Trent 60TGT-Exhaust = 431 °C
Baseline: Trent 60 CCPP (2P)
sCO2**Dual Rail cycle
∆ CC efficiency [%pkt] + 1,2
∆ Pnet [MW] + 1,4
Bottoming cycle – sCO2:
*) Water tank, Steam drums**) optimized parameters
ExhaustParameter Water/Steam sCO2
TTurbine, in [°C] 400 387
pTurbine, in [bar] 40 220
pCond, out [bar] 0,074 78
TCooling, in/out [°C] 15 / 35 15 / 35
TTDCond [K] 5 5
ηTurbine [%] 83 86; 79,5
ηCompressor [%] 80 80
100%
54%
15%14%
0,1% 11% 7% 0,2%
0%
25%
50%
75%
100%
Exer
gy [%
]
Water/steam
100%
57%
7% 8%4% 10%
7% 8%
0%
25%
50%
75%
100%
Exer
gy[%
]
sCO2
• Lower exergy losses at stack & HRSG compared to w/s higher ηCC & Pnet
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Exhaust
Bottoming cycle – sCO2:
Baseline: Trent 60 CCPP (2P)
sCO2**Dual Rail cycle
∆ CC efficiency [%pkt] + 0,5
∆ Pnet [MW] + 0,9
100%
65%
5% 7% 3% 6% 7% 1% 5%
0%
25%
50%
75%
100%
Exer
gy [%
]
sCO2
100%
63%
13%10%
0,1% 6%7% 1%
0%
25%
50%
75%
100%
Exer
gy [%
]
Water/steam
Cycle analysis – SGT 800TGT-Exhaust = 567 °C
*) Water tank, Steam drums, fuel preheater
**) optimized parameters• Lower exergy losses at stack & HRSG compared to w/s higher ηCC & Pnet
Fuel preheating
Parameter Water/Steam sCO2
TTurbine, in [°C] 551 516
pTurbine, in [bar] 80 255
pCond, out [bar] 0,045 68
TCooling, in/out [°C] 15 / 35 15 / 35
TTDCond [K] 5 5
ηTurbine [%] 90; 87,3 89; 86
ηCompressor [%] 80 80
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-4%
-3%
-2%
-1%
0%
1%
10 15 20 25 30 35 40
η CC
, sC
O2
-ηC
C, w
/s[ %
]
Inlet temperature cooling water [°C]
sCO2
-1%
0%
1%
2%
3%
10 15 20 25 30 35 40
η CC
, sC
O2
-ηC
C, w
/s[ %
]
Inlet temperature cooling water [°C]
sCO265 bar
75 bar
85 bar
(Bestpoints)
95 bar
65 bar
75 bar
85 bar
Impact of cold endCooling water & back pressureTrent 60 (431 °C) SGT 800 (567 °C)
• Backpressure optimization to reduce exergy losses at higher ambient temperatures
• Higher potential of sCO2 for low GT exhaust temperatures
95 bar
(Bestpoints)
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-0,40,00,40,81,21,6
5 10 15 20 25
∆P n
et[M
W]
TTD [K]
sCO2 - HRSG sCO2 - Recuperator
Component dimensions and sensitivity analysis
− Heat exchanger:
Sensitivity for sCO2 cycle @ Trent; 220 bar, 400°C, 75 bar, 15°C
W/S sCO2 (400°C*)
Net output: 14,6 MWel 16,0 MWel
Heat source: 53,1 MWth 62,3 MWth
Heat sink: 38,5 MWth 46,3 MWth
Recuperator: - 61,7 MWth * Turbine inlet temperature
0%
100%
200%
300%
400%
W/S sCO2, 10K sCO2, 20KHRSG
sCO2, 20KRecuperator
A/A W
/S[%
]
Condenser
Recuperator
HRSGPnet,w/s (TTD=10K)
ΔTln [K] W/S sCO2 (400 °C*)
Condenser 12 8
HRSG 34 / 48** 13
Recuperator - 15** LP/HP
• Higher amount of waste heat is used
• Lower ΔTln leading to considerably higher heat exchanger surface
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− Piping:
Component dimensions and sensitivity analysis
-0,5
0,0
0,5
1,0
1,5
2,0
4 6 8 10 12 14
∆P n
et[M
W]
Pressure drop (HRSG) [%]
sCO2, HP & LP sCO2, HP only
Pnet,w/s
Sensitivity for sCO2 cycle @ 220 bar, 400°C, 75 bar, 15°C
sCO2∆pHP = 13%
sCO2∆pHP = 6%
δ
da
δ
da
• Efficiency/Performance strongly dependent on pressure losses
Reduction in specific weight: ~36%
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Agenda
1. Introduction2. Direct heat applications (150 MW CSP)
Efficiency potentials, sensitivities and first component estimations
3. Waste heat applications (CCPP Trent/SGT800)Efficiency potentials, sensitivities and first component estimations
4. Summary and Outlook
Evaluation of sCO2 power cycles for direct and waste heat applications
Unrestricted © Siemens AG 201803.08.2018Page 22 Glos / PG PR R&D SU
Summary
Benefits Challenges
• Simple & compact cycle structure
• Potential for better performance compared to w/s
especially @ cold cooling conditions• Potential for lower turbomaschinery cost
• Large heat exchanger surfaces due to small TTD
• Thick walled piping & casings due to high pressures
• Turbine and compressor concepts including
advanced sealing technologies
• Operational concepts
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Outlook
Envisaged development project:
• Scientific technological fundamentals• Potential analysis and assessment of process architectures for optimized LCOE• Development of numerical methods for enhanced design tools• Development of high temperature test facility for basic experiments and component test
• Development of a sCO2 demonstration plant • Turbine and compressor concepts, new sealing technologies, advanced blade
technology • High pressure low cost heat exchangers, waste heat recovery units considering limited
space, limited pressure drop• operational concepts, I&C technology
• Consortium
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Thank youfor
your attention !
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