EVALUATION OF SCO 2 POWER CYCLES FOR DIRECT AND WASTE HEAT APPLICATIONS Dr. Stefan Glos

Transcription

1 EVALUATION OF SCO 2 POWER CYCLES FOR DIRECT AND WASTE HEAT APPLICATIONS Dr. Stefan Glos 2 nd European supercritical CO2 Conference August 30-31, 2018, Essen, Germany siemens.com/power-gas

2 Introduction/Motivation Potential benefits of supercritical CO2 power cycles higher efficiency compared to water/steam smaller component size, lower costs, higher operating flexibility??? Dostal (2004) Ahn et al. (2015) Page 2

3 Agenda Evaluation of sco 2 power cycles for direct and waste heat applications 1. Introduction 2. 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 Page 3

4 Agenda Evaluation of sco 2 power cycles for direct and waste heat applications 1. Introduction 2. 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 Page 4

5 Supercritical CO2 Brayton cycles for direct heat power cycles (Example: 150 MW CSP) sco2 Water/Steam η carnot : 56% (3) (5) η carnot : 51% (3) (5) Heat source Heat sink Recuperated heat Compressor work 433 C (2) (4) (6) η carnot =1- TT mm,heeeeee ssssssss TT mm,heeeeee ssssssssssss 357 C (2) (4) (6) T m heat source T m heat sink 39 C (1) (7) (1) 36 C (7) (8) (8) Higher mean temperatur in boiler main driver for better carnot efficiency in sco2 cycle Page 5 Condition (1) behind the pump/ compressor T m : mean temperature

6 Efficiency analysis and comparison to water/steam Example: 150 MW CSP Parameter Water/ Steam sco2 12% T MS [ C] p MS [bar] T reheat [ C] % 5,0% Higher T m p Reheat [bar] CW inlet [ C] TTD Cond. [K] 3 3 TTD Recu. [K] - 5 η th,sco2 η th,w/s 4% 0% Higher losses in Recu, Compr. & Cond. Recu & Cond. losses reduced -2,7% -0,1% Comp. & Cond. losses reduced 1,4% -4% Carnot sco2 Simple recuperated Recompression (25% recompr. mass flow) Intercooling Page 6 Water/steam Noor 3 Simple recuperated sco2 cycle Intercooled recompression cycle

7 Cycle efficiency comparison for 150MW varying cooling water temperatures 4% 3% 65 bar 75 bar 95 bar 105 bar η th,sco2 η th,w/s 2% 1% 0% -1% -2% -3% -4% Simple Cycle 545 C 545 C 545 C back pressure opt. 605 C 605 C back pressure opt. recompr. & intercooled -5% Cooling water inlet [ C] Efficiency of simple sco 2 cycle behind w/s optimization necessary Decreasing efficiency high cooling water inlet temperature can be compensated with optimal back pressure Benefit of sco 2 cycle is reduced by optimization of w/s cycle (e.g. supercritical process) Page 7

8 Turbine comparison sco 2 vs. water/steam Example: 150 MW CSP with reheat sco 2 Turbines based on H60 & H70 modules / Rotormass = 17,7 t 2850 mm 2520 mm Water/Steam Turbine BH50 & CH / Rotormass = 39,3 t Page mm Gear-box ~ 55% lower rotor mass for sco 2 turbine Significant smaller sco 2 turbine exhaust compared to w/s High wall thickness due to high pressures 6753 mm

9 Component dimensions and sensitivity analysis Recuperator: Water/Steam sco 2 Recompressed & Intercooled Recuperated heat [MW] ka LP / LTR [MW/K] 3,8 23 ka HP / HTR [MW/K] 3,4 10,5 LTR HTR Larger heat exchanger surfaces in sco 2 cycle compared to w/s High pressure levels (e.g. 370bar/75bar) at both sides of recuperator Chordia et al. [1], [2] η th 0% -1% -2% -3% η th,w/s (TTD=5K) -4% -5% TTD [K] Page 9 Sensitivity for recompressed & intercooled sco2 370 bar, 605 C, 75 bar, 25 C A / A ref,5k 1 LTR 0,8 HTR Sum 0,6 0,4 0,2 A w/s (TTD=5K) TTD [K]

10 Component dimensions and sensitivity analysis Recompression bypass ratio: η th 5 % 4 % 3 % 2 % 1 % A / A ref LTR HTR Sum 0 % 0 % 5 % 10 % 15 % 20 % 25 % Bypass ratio 1 0 % 5 % 10 % 15 % 20 % 25 % Bypass ratio 10 % bypass ratio 25 % bypass ratio Page 10 Higher bypass ratio decreases the exergy losses

11 Component dimensions and sensitivity analysis High pressure piping: 1% 0% sco 2 p HP = 6% sco 2 p HP = 12% -1% η th -2% -3% η th,w/s δ δ -4% -5% d a d a -6% p HP-path [%] Reduction in specific weight: ~26% Efficiency/Performance strongly dependent on pressure losses Page 11

12 Agenda Evaluation of sco 2 power cycles for direct and waste heat applications 1. Introduction 2. 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 Page 12

13 Supercritical CO2 Brayton cycles for waste heat applications (bottoming cycle) T [ C] flue gas T [ C] flue gas water/steam T [ C] ~ Exergy losses ~ Exergy flue gas ~ Exergy water/steam Q [MW] Q [MW] Q [MW] T [ C] sco2 Lower losses in HRSG in sco2 bottoming cycle Q [MW] Page 13

14 Overview T,s Diagram of bottoming cycle (Trent 60) sco 2 Water/steam 400 Critical Point: p Crit = 73,75 bar T Crit = 31 C 240 bar (4) 75 bar bar (2) Temperature [ C] (2) (3) (6) q recu (5) Temperature [ C] (4) (5) (1) q recu (7) (8) 1,00 2,00 3,00 Entropy [kj/kg K] (1) (7) (3) (6) 0,074 bar 3,00 6,00 9,00 Entropy [kj/kg K] Page 14 Heat source Heat sink Reuperated heat Turbomachinery work

15 Cycle analysis Trent 60 T GT-Exhaust = 431 C Parameter Water/ Steam T Turbine, in [ C] sco2 Bottoming cycle sco 2 : Exhaust 100% 100% Water/steam 15% 14% 0,1% 11% p Turbine, in [bar] p Cond, out [bar] 0, T Cooling, in/out [ C] 15 / / 35 TTD Cond [K] 5 5 Exergy [%] 75% 50% 25% 0% 7% 0,2% 54% η Turbine [%] 83 86; 79,5 η Compressor [%] sco 2 Baseline: Trent 60 CCPP (2P) sco2** Dual Rail cycle CC efficiency [%pkt] + 1,2 P net [MW] + 1,4 Exergy [%] 100% 75% 50% 25% 0% 100% 7% 8% 4% 10% 7% 8% 57% Page 15 Lower exergy losses at stack & HRSG compared to w/s higher η CC & P net *) Water tank, Steam drums **) optimized parameters

16 Cycle analysis SGT 800 T GT-Exhaust = 567 C Parameter Water/ Steam T Turbine, in [ C] p Turbine, in [bar] p Cond, out [bar] 0, sco2 T Cooling, in/out [ C] 15 / / 35 Bottoming cycle sco 2 : Exhaust Exergy [%] 100% 75% 50% 25% 0% 100% Water/steam 13% 10% 0,1% 6% 7% 1% 63% TTD Cond [K] 5 5 η Turbine [%] 90; 87,3 89; 86 η Compressor [%] Fuel preheating sco 2 Baseline: Trent 60 CCPP (2P) sco2** Dual Rail cycle CC efficiency [%pkt] + 0,5 P net [MW] + 0,9 Exergy [%] 100% 75% 50% 25% 0% 100% 5% 7% 3% 6% 7% 1% 5% 65% Page 16 Lower exergy losses at stack & HRSG compared to w/s higher η CC & P net *) Water tank, Steam drums, fuel preheater **) optimized parameters

17 Impact of cold end Cooling water & back pressure Trent 60 (431 C) SGT 800 (567 C) η CC, sco2 - η CC, w/s [ %] 3% 65 bar sco2 (Bestpoints) 2% 75 bar 1% 85 bar 0% 95 bar -1% η CC, sco2 - η CC, w/s [ %] 65 bar 1% sco2 (Bestpoints) 0% 75 bar -1% 85 bar -2% 95 bar -3% -4% Inlet temperature cooling water [ C] Inlet temperature cooling water [ C] Backpressure optimization to reduce exergy losses at higher ambient temperatures Higher potential of sco 2 for low GT exhaust temperatures Page 17

18 Component dimensions and sensitivity analysis Heat exchanger: W/S sco 2 (400 C*) ΔT ln [K] W/S sco 2 (400 C*) Net output: 14,6 MWel 16,0 MWel Condenser 12 8 Heat source: 53,1 MWth 62,3 MWth HRSG 34 / 48** 13 Heat sink: 38,5 MWth 46,3 MWth Recuperator - 15 Recuperator: - 61,7 MWth * Turbine inlet temperature ** LP/HP Higher amount of waste heat is used Lower ΔT ln leading to considerably higher heat exchanger surface P net [MW] Page 19 1,6 1,2 0,8 0,4 0,0-0,4 sco2 - HRSG TTD [K] sco2 - Recuperator P net,w/s (TTD=10K) A/A W/S [%] 400% 300% 200% 100% 0% Sensitivity for sco2 Trent; 220 bar, 400 C, 75 bar, W/S sco2, 10K sco2, 20K HRSG sco2, 20K Recuperator Condenser Recuperator HRSG

19 Component dimensions and sensitivity analysis Piping: P net [MW] 2,0 1,5 1,0 0,5 0,0 sco2, HP & LP sco2, HP only P net,w/s sco 2 p HP = 6% d a δ sco 2 p HP = 13% d a δ -0, Pressure drop (HRSG) [%] Reduction in specific weight: ~36% Efficiency/Performance strongly dependent on pressure losses Page 20 Sensitivity for sco2 220 bar, 400 C, 75 bar, 15 C

20 Agenda Evaluation of sco 2 power cycles for direct and waste heat applications 1. Introduction 2. 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 Page 21

21 Summary Benefits Simple & compact cycle structure Potential for better performance compared to w/s cold cooling conditions Potential for lower turbomaschinery cost Challenges 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 Page 22

22 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 sco 2 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 Page 23

23 Thank you for your attention! Page 24

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