evaluation of sco2 power cycles for direct and …unrestricted © siemens ag 2018 • • 2 •

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

Unrestricted © Siemens AG 201803.08.2018 Glos / PG PR R&D SU

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)

?? ?


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


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


-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.


-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


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


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


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


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%


Agenda







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


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


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


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


-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)

Unrestricted © Siemens AG 201803.08.2018Page 19 Glos / PG PR R&D SU

-0,40,00,40,81,21,6

5 10 15 20 25

∆P n

et[M

W]

TTD [K]

sCO2 - HRSG sCO2 - Recuperator


− 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


− Piping:


-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%


Agenda







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


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


Thank youfor

your attention !


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TRENT® and RB211® are registered trade marks of and used under license from Rolls-Royce plc. Trent, RB211, 501 and Avon are trade marks of and used under license of Rolls-Royce plc.

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