D5.1 : System modelling and findings adopted in system design

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Joshua Brooks
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1 D5.1 : System modelling and findings adopted in system design 1

2 sco2 turbine Work programme WP5, task 5.1 2

3 Why the sco2 cycle Because it is small 10 to 100 times smaller than Rankine Because it is efficient over 30% cycle efficiency achievable Because CO2 is nice fluid GWP : 1 Non flammable Non toxic 3

4 Recuperated Brayton sco2 Cycle Typical recuperated brayton sco2 cycle 4

5 State of the art : SANDIA Labs Expander 5

6 State of the art : SANDIA Labs Expander wheels 6

7 State of the art : SANDIA Labs sco2 test loop 7

8 State of the art : ECHOGEN Transcritical CO2 turbine 8

9 State of the art : ECHOGEN Transcritical sco2 cycle 9

10 Brayton modelling at ENOGIA With perfect gas model With REFPROP good model correlations 10

11 Assumptions For both perfect fluid and REFPROP models : Fixed turbomachinery efficiencies Fixed elec*mec efficiency Fixed exchanger efficiencies 11

12 Varying turbine inlet Cycle real efficiency with turbine inlet from 200 C to 400 C 140 bar 120 bar 110 bar 100 bar 90 bar The higher the turbine inlet temperature the higher the cycle efficiency But the lower the recovery efficiency 12

13 Indeed, higher turbine temp : lower recovery For 1000 C hot gases (example 1000 hot gas source), it is interesting to enhance turbine inlet temperature Cycle real efficiency >30% Total efficiency > 20% 13

14 Effect for lower temp hot source For 600 C hot gases (example 600 hot gas source), it is not so interesting to enhance turbine inlet temperature! Cycle real efficiency approx 25% Total efficiency >14% 14

15 Even lower temperature hot source C It is better to recover more heat by downgrading the sco2 turbine inlet temperature at 260 C Cycle real efficiency falls down to 20%! Total efficiency in the vicinity of 9% not so good over ORC? 15

16 Conclusions Hot gases heat source temp : 1000 C 600 C 400 C Max sco2 cycle efficiency : >30% 25% 20% Total recup x cycle efficiency : 20% 14% 9% Example massflow : kg/h Optimum temperature : > 400 C 320 C 250 C Optimum pressure : > 140 bar 120 bar 110 bar Recuperated thermal power : 150 kwth 140 kwth 150 kwth Shaft mechanical power : > kw Large diesel engines or gas turbine exhaust is in the C range Can be used with bottoming cycle! 16

17 Proposed working point 1 : engine exhaust WHR Temperature : 500 C (simulates large engine or gas turbine) Exhaust gases flowrate : 3000 kg/h (simulates 600 kw class engine) Nominal thermal power : 220 kw Nominal turbine inlet pressure : 100 bar Nominal turbine inlet temperature : 250 C Nominal turbine outlet pressure : 70 bar Cycle efficiency : 19% Shaft power : 41 kw 17

18 Proposed working point 1 : engine exhaust WHR Simulated compressor and turbine wheels : (For 100 bar turbine inlet) Rotating speed 135 krpm Turbine diameter 26 mm Compressor diameter 23 mm Non satisfactory, rotating speed too high, wheels too small 18

19 Proposed net working point 1 : engine exhaust WHR Temperature : 500 C (simulates large engine or gas turbine) Exhaust gases flowrate : 3000 kg/h (simulates 600 kw class engine) Nominal thermal power : 240 kw Nominal turbine inlet pressure : 90 bar Nominal turbine inlet temperature : 235 C Nominal turbine outlet pressure : 70 bar Cycle efficiency : 17% Shaft power : 38,5 kw 19

20 Proposed working point 1 : engine exhaust WHR Simulated compressor and turbine wheels : (For 90 bar turbine inlet) Rotating speed Turbine diameter Compressor diameter Satisfactory on rpm but small wheels 90 krpm 35 mm 29 mm 20

21 Proposed working point 1 Inlet temp : 500 C Inlet massflow : 3000 kg/h Recovered heat : 240 kw Cycle efficiency : 17% Total efficiency (recuperated x cycle) : 11% Shaft output power : 38,5 kw 21

22 Conclusion About recuperated brayton sco2 : Strong dependency to inlet temperature Turbine difficult to engineer because of high rotating speed and small wheels Simulation with BOWMAN TG80 parameters to be done Brayton supercritical recuperated cycle : «Poor» cycle for low temperature applications Highly efficient cycle on high temperature waste streams 22

23 Task 5.2 Micro-Turbine Expander development CAD design Input from system design Preliminary design, CFD, FEA Drawings Prototype manufacturing 23

24 Thanks for your attention 24

Effect of Compressor Inlet Temperature on Cycle Performance for a Supercritical Carbon Dioxide Brayton Cycle

The 6th International Supercritical CO2 Power Cycles Symposium March 27-29, 2018, Pittsburgh, Pennsylvania Effect of Compressor Inlet Temperature on Cycle Performance for a Supercritical Carbon Dioxide