Efficiency of gas turbine assemblies operating under oxygen enhanced combustion (OEC)

Transcription

1 Efficiency of gas turbine assemblies operating under oygen enhanced combustion (OEC) DeToni Jr, Zimmer, Schneider, Boeira and Maidana The Federal University of Rio Grande do Sul, Brazil

2 Motivation Oy-fuel operation high cost O streams Stoichiometric combustion Oidant stream composition can vary Atmospheric 1%O 79%N Oy-fuel CO replacing N OEC lessncontent OEC Oygen Enhanced Combustion

3 Motivation Is Oygen Enhanced Combustion a feasible alternative for oy-fuel combustion? - Is it possible to run thermal machines on enriched O stream(o/n), cheaper than pure O? - CO concentration on flue gases allows for CCS?

4 SCOPE Theoretical analysis of the performance of a gas turbine running under OEC - Oygen-Enhanced Combustion conditions. Thermodynamic modeling of a gas turbine, considering five different integrations of heat echangers to improve its efficiency.

5 PROBLEM DEFINITION Open Brayton cycle

6 PROBLEM DEFINITION Open Brayton cycle with combustion

7 PROBLEM DEFINITION Open Brayton cycle with OEC

8 PROBLEM DEFINITION Complete assembly with EOC

9 PROBLEM DEFINITION Complete assembly with EOC

10 PROBLEM DEFINITION Complete assembly with EOC

11 PROBLEM DEFINITION Complete assembly with EOC

12 MODELING Mass, species and energy balances with a Newton- Raphson based equation solver Main simplification hypothesis: Power conversion 1) steady state regime ) Variable compressor and turbine efficiencies 3) stagnation properties of the flow streams are negligible 4) pressure drop due to friction flow in piping and equipment is negligible

13 general combustion equation for OEC,,,,,, CO, NO, NO, H, OH, O, N and H

14 general combustion equation for OEC Approach Chemical equilibrium dg = 0 b a d c b a d c b a d c p p y y y y K + = 0 Gibbs function minimization Equilibrium constant K

15 general combustion equation for OEC Species balance n & & + CH 4 = nco n& CO 4n & & & + n& + CH = nh O + n H 4 OH n& H n& & & & & & & + n& + O = nco + nh O + no + nco + nno + n NO OH n& O n & & & & + N = nn + nno + n NO n& N

16 general combustion equation for OEC CO, NO, NO, H, OH, O, N and H spected reactions CO CO + O O N NO + NO + O NO H O H + O H O H + OH O N H O N H

17 general combustion equation for OEC = p p K CO O CO CO ,6,6,6 = p p K N O NO NO 1 0 = p p K NO O NO NO = p p K O H O H H = p p K O H H OH OH 1 0 = p p K O O O 1 0 = p p K N N N 1 0 = p p K H H H Validation CEA (Chemical Equilibrium with Applications NASA)

18 MODELING The general combustion equation for OEC,,,,,,,, For OEC processes an important parameter is the oygen-fuel ratio S instead an air-fuel ratio, as usually adopted on conventional combustion processes

19 MODELING Main simplification hypothesis: Combustion process 1) all chemical species considered as ideal gases; ) fuel composed by pure CH 4

20 operational conditions 1 Constantair mass flow rate m1 Air input 1% O 79% N

21 operational conditions Air input 1% O 79% N Constantnet power output Wn and turbine rotation R

22 operational conditions Air input 1% O 79% N Constantnet power output Wn with variable turbine rotation R

23 operational parameters Fuel consumption (CH4 m10) Air input 1% O 79% N

24 operational parameters Fuel consumption (CH4 m10) net power output (Wnet) Air input 1% O 79% N

25 Oygen demand (m8) Fuel consumption (CH4 m10) net power output (Wnet) Air input 1% O 79% N

26 Total emissions (m13) Oygen demand (m8) Fuel consumption (CH4 m10) Air input 1% O 79% N net power output (Wnet)

27 Case 1 1 Constantair mass flow rate m1 Air input 1% O 79% N

28 Results Constantair mass flow rate m1 Net power output

29 Results Constantair mass flow rate m1 Fuel (CH4)

30 Results Constantair mass flow rate m1 Oygen

31 Results Constantair mass flow rate m1 Specific fuel consumption

32 Results Constantair mass flow rate m1 Specific emissions (CO CO No)

33 Results Constantair mass flow rate m1 NO specific emissions CO specific emissions CO specific emissions

34 Results Constantair mass flow rate m1 CO NO 100 %O 50 %O 1 %O CO

35 Case Air input 1% O 79% N Constantnet power output Wn and turbine rotation R

36 Results Constant net power output Wn and turbine rotation R Fuel CH4

37 Results Constant net power output Wn and turbine rotation R Fuel CH4 Oygen

38 Results Constantair mass flow rate m1

39 case 3 Air input 1% O 79% N Constantnet power output Wn with variable turbine rotation R

40 Results Constant net power output Wn with variable turbine rotation R Air mass flow rate

41 Results Constant net power output Wn with variable turbine rotation R Fuel CH4

42 Results Constant net power output Wn with variable turbine rotation R Fuel CH4 Oygen

43 Results Constant net power output Wn with variable turbine rotation R Specific fuel consumption

44 Results Constant net power output Wn with variable turbine rotation R Specific emissions

45 performance

46 Overall performance

47 DISCUSSION The main disadvantage of the OEC and Oy-fuel is the high cost of a pure oygen injection in the combustion chamber. Assuming 0.5 kwh/ kg O as the energy cost toseparateoygen from air For stoichiometric combustion with 30% of oygen on the oidant stream, pure oygen consumption will be kg O /s, corresponding to an energy cost of 1.78 MW. However, there are several oygen separation processes, like PSA (pressure swing adsorption) and membrane technology, that can yield oygen-enriched stream to the cycle and offset the costs.

48 Thanks for your attention Corresponding author Paulo Smith Schneider