SYSTEM AND METHOD FOR GENERATING POWER USING A SUPERCRITICAL FLUID

• US 20130180259A1
• Filed: 11/16/2012
• Published: 07/18/2013
• Est. Priority Date: 01/17/2012
• Status: Active Grant

• Current Assignee: Peregrine Turbine Technologies LLC
• Original Assignee: Peregrine Turbine Technologies LLC
• Inventors: Stapp, David S.
• Granted Patent: US 9,540,999 B2
• Time in Patent Office: Days
• US Class Current: 60/773
• CPC Class Codes: F02C 1/10 Closed cycles
• CPC Class Codes: F02C 3/04 having a turbine driving a compressor power transmission arrangements F02C7/36; control of working fluid flow F02C9/16
• CPC Class Codes: F02C 6/18 using the waste heat of gas-turbine plants outside the plants themselves, e.g. gas-turbine power heat plants using waste heat as source of energy for refrigeration plants F25B27/02; using the waste heat of a gasturbine for steam generation or in a steam cycle see F01K23/10
• CPC Class Codes: F05D 2220/32 in gas turbines
• CPC Class Codes: F05D 2220/70 in combination with
• CPC Class Codes: Y02E 20/14 Combined heat and power generation [CHP]

Abstract

A dual cycle system for generating shaft power using a supercritical fluid and a fossil fuel. The first cycle is an open, air breathing Brayton cycle. The second cycle is a closed, supercritical fluid Brayton cycle. After compression of air in the first cycle, the compressed air flows through a first cross cycle heat exchanger through which the supercritical fluid from the second cycle flows after it has been compressed and then expanded in a turbine. In the first cross cycle heat exchanger, the compressed air is heated and the expanded supercritical fluid is cooled. Prior to expansion in a turbine, the compressed supercritical fluid flows through a second cross cycle heat exchanger through which also flows combustion gas, produced by burning a fossil fuel in the compressed air in the first cycle. In the second cross cycle heat exchanger, the combustion gas is cooled and the compressed supercritical fluid is heated.

Claims

1. A method of generating shaft power in a system comprising an air cycle and supercritical fluid cycle, comprising the steps of:

a) burning a fossil fuel in air so as to produce a combustion gas;

b) expanding said combustion gas in at least a first turbine so as to produce an expanded combustion gas, said expansion of said combustion gas generating shaft power;

c) compressing a supercritical fluid in a first compressor;

d) flowing at least a portion of said compressed supercritical fluid through a first cross cycle heat exchanger, and flowing said combustion gas through said first cross cycle heat exchanger so as to transfer heat from said combustion gas to said compressed supercritical fluid so as to produce a heated compressed supercritical fluid;

e) expanding at least a portion of said heated compressed supercritical fluid in a second turbine so as to produce an expanded supercritical fluid, said expansion of said supercritical fluid generating additional shaft power; and

f) flowing at least a portion of said expanded supercritical fluid through a second cross cycle heat exchanger, and flowing said air through said second cross cycle heat exchanger prior to burning said fossil fuel in said air so as to transfer heat from said expanded supercritical fluid to said air.

2. The method according to claim 1, further comprising the step of compressing said air in a second compressor so as to produce compressed air prior to burning said fossil fuel in said air, wherein said fossil fuel is burned in said compressed air, and wherein at least a portion of said shaft power generated by said first turbine is used to drive said second compressor, and wherein the step of flowing said air through said second cross cycle heat exchanger comprises flowing said compressed air through said second cross cycle heat exchanger so as to transfer heat from said expanded supercritical fluid to said compressed air.

3. The method according to claim 1, wherein the step of flowing said combustion gas through said first cross cycle heat exchanger is performed after the step of expanding said combustion gas in said first turbine.

4. The method according to claim 1, wherein the step of flowing said combustion gas through said first cross cycle heat exchanger is performed before the step of expanding said combustion gas in said first turbine.

5. The method according to claim 1, wherein a first portion of said combustion gas flows through said first cross cycle heat exchanger before the step of expanding said combustion gas in said first turbine and a second portion of said combustion gas flows through said first cross cycle heat exchanger after the step of expanding said combustion gas in said first turbine.

6. The method according to claim 1, further comprising the step of compressing said air in a second compressor so as to produce compressed air prior to burning said fossil fuel in said air, and wherein said second compressor is operated at a pressure ratio of no more than about 2.0.

7. The method according to claim 1, wherein said supercritical fluid comprises supercritical carbon dioxide.

8. The method according to claim 1, wherein sufficient heat is transferred from said expanded supercritical fluid to said air in said second cross cycle heat exchanger to cool said expanded supercritical fluid to approximately the critical temperature of said supercritical fluid.

9. The method according to claim 8, wherein said air is cooled prior to said air flowing through said second cross cycle heat exchanger.

10. The method according to claim 9, wherein the amount of cooling of said air prior to said air flowing through said second cross cycle heat exchanger is adjusted so as to control the amount of heat transferred from said expanded supercritical fluid to said air in said second cross cycle heat exchanger so as to cool said expanded supercritical fluid to approximately the critical temperature of said supercritical fluid.

11. The method according to claim 1, further comprising the step of further expanding at least a first portion of said expanded supercritical fluid in a third turbine so as to produce a further expanded supercritical fluid, said further expansion of said supercritical fluid generating additional shaft power.

12. The method according to claim 11, wherein said step of further expanding at least said first portion of said expanded supercritical fluid in said third turbine is performed on said supercritical fluid prior to said supercritical fluid flowing through said second cross cycle heat exchanger.

13. The method according to claim 11, further comprising the step of expanding a second portion of said expanded supercritical fluid in a nozzle, said second portion of said expanded supercritical fluid bypassing said third turbine.

14. The method according to claim 1, further comprising the steps of (i) further expanding at least a first portion of said expanded supercritical fluid in a third turbine so as to produce a further expanded supercritical fluid, and (ii) reheating at least a portion of supercritical fluid prior to further expanding said supercritical fluid in said third turbine.

15. The method according to claim 14, wherein the step of reheating at least said portion of said supercritical fluid comprises flowing said portion of said supercritical fluid through said first cross cycle heat exchanger a second time, so as to transfer heat from said combustion gas to said portion of said compressed supercritical fluid thereby reheating said supercritical fluid.

16. The method according to claim 1, further comprising the step of reheating at least a portion of said combustion gas after expanding said combustion gas in said first turbine.

17. The method according to claim 1, further comprising the step of reheating at least a portion of said combustion gas after flowing said combustion gas through said first cross cycle heat exchanger.

18. The method according to claim 17, wherein the step of reheating said combustion gas comprises burning additional fossil fuel in said combustion gas.

19. The method according to claim 1, further comprising the steps of providing a supply of water and transferring heat from said expanded combustion gas from said first turbine to said water so as to generate steam.

20. The method according to claim 19, further comprising the step of transferring heat from said supercritical fluid to said steam so as to superheat said steam.

21. The method according to claim 19, further comprising the step of introducing said steam into said combustion gas.

22. The method according to claim 1, further comprising the step of intercooling said supercritical fluid during compression thereof in said first compressor.

23. The method according to claim 22, wherein the step of intercooling said supercritical fluid during compression thereof in said first compressor comprises flowing said supercritical fluid through an intercooler heat exchanger and flowing water through said intercooler heat exchanger so as to transfer heat from said supercritical fluid to said water, thereby cooling said supercritical fluid and heating said water.

24. The method according to claim 23, further comprising the steps of (i) compressing said air in a second compressor so as to produce compressed air prior to burning said fossil fuel in said air, wherein said fossil fuel is burned in said compressed air, and (ii) cooling said compressed air after compression thereof in said first compressor by transferring heat to said water prior to flowing said water through said intercooler heat exchanger.

25. The method according to claim 1, further comprising the step of flowing said supercritical fluid to said first compressor for entry and compression therein in step (d).

26. The method according to claim 25, further comprising the step of controlling said temperature of said supercritical fluid entering said first compressor.

27. The method according to claim 26, wherein the step of controlling said temperature of said supercritical fluid entering said first compressor comprises controlling said temperature to within ±

2°

K of the critical temperature of said supercritical fluid entering said first compressor.

28. The method according to claim 26, wherein the step of controlling said temperature of said supercritical fluid entering said first compressor comprises the step of controlling the temperature of said air flowing to said second cross cycle heat exchanger.

29. The method according to claim 28, wherein the step of controlling the temperature of said air flowing to said second cross cycle heat exchanger comprises the step of flowing said air through a cooler.

30. The method according to claim 25, wherein said first compressor has an inlet for receiving said supercritical fluid, and further comprising the step of measuring the temperature of said flow of supercritical fluid proximate the inlet of said first compressor.

31. The method according to claim 30, wherein the step of measuring the temperature of said flow of supercritical fluid comprises the step of determining the speed of sound of said supercritical fluid.

32. The method according to claim 30, wherein the step of measuring the temperature of said flow of supercritical fluid comprises the step of determining the specific heat of said supercritical fluid.

33. The method according to claim 1, wherein at least a portion of said shaft power from said expansion of said supercritical fluid is used to drive said first compressor.

34. The method according to claim 1, wherein said second turbine drives a first shaft, and further comprising the step of transmitting torque from said first shaft to a second shaft without contact between said first and second shafts.

35. The method according to claim 34, wherein the step of transmitting torque from said first shaft to a second shaft comprises transmitting said torque via an eddy current coupling.

36. The method according to claim 35, further comprising the step of flowing a portion of said compressed supercritical fluid to said eddy current coupling so as to cool said coupling and heat said portion of said compressed supercritical fluid.

37. The method according to claim 36, further comprising flowing said portion of said heated compressed supercritical fluid from said eddy current coupling to said first cross cycle heat exchanger.

38. The method according to claim 1, wherein the step of expanding said combustion gas in said first turbine comprises expanding said combustion gas to a pressure below atmospheric pressure.

39. The method according to claim 38, further comprising the step of compressing said expanded combustion gas to above atmospheric pressure.

40. The method according to claim 1, wherein the step of flowing said combustion gas through said first cross cycle heat exchanger so as to transfer heat from said combustion gas to said compressed supercritical fluid cools said combustion gas so as to produce cooled combustion gas, and further comprising the step of transferring heat from said cooled combustion gas to a flow of water so as to heat said flow of water.

41. The method according to claim 1, wherein the step of flowing said air through said second cross cycle heat exchanger comprises flowing air at ambient temperature and pressure through said second cross cycle heat exchanger.

42. A method for generating shaft power in a system comprising a supercritical fluid cycle and an air cycle, comprising the steps of:

a) burning a fossil fuel in air so as to produce a combustion gas;

b) compressing a supercritical fluid in a first compressor;

c) transferring heat from said combustion gas to said compressed supercritical fluid so as to produce a cooled combustion gas and a heated compressed supercritical fluid;

d) expanding at least a portion of said heated compressed supercritical fluid in a first turbine so as to produce an expanded supercritical fluid, said expansion of said supercritical fluid generating shaft power;

e) returning said expanded supercritical fluid to said first compressor;

f) transferring heat from said expanded supercritical fluid to said air so as to cool said supercritical fluid to approximately its critical temperature, the step of transferring heat from said expanded supercritical fluid to said air being performed prior to burning said fossil fuel in said air and prior to returning said supercritical fluid to said first compressor.

43. The method according to claim 42, wherein the step of transferring heat from said expanded supercritical fluid to said air so as to cool said supercritical fluid comprises cooling said supercritical fluid to with ±

2°

K of its critical temperature.

44. The method according to claim 42, further comprising the step of compressing said air in a second compressor so as to produce compressed air, the step of compressing said air being performed prior to transferring heat from said expanded supercritical fluid to said air, wherein said heat from said expanded supercritical fluid is transferred to said compressed air.

45. The method according to claim 44, further comprising the step of cooling said compressed air prior to the step of transferring heat from said expanded supercritical fluid to said compressed air.

46. The method according to claim 42, further comprising the step of transferring heat from said cooled combustion gas to a flow of water so as to produce a flow of heated water.

47. The method according to claim 42, further comprising the step of expanding said combustion gas in a second turbine so as to generate additional shaft power.

48. The method according to claim 47, wherein the step of expanding said combustion gas in a second turbine so as to generate additional shaft power is performed before the step of transferring heat from said combustion gas to said compressed supercritical fluid.

49. The method according to claim 47, wherein the step of expanding said combustion gas in a second turbine so as to generate additional shaft power is performed after the step of transferring heat from said combustion gas to said compressed supercritical fluid.

50. The method according to claim 42, wherein said supercritical fluid comprises supercritical carbon dioxide.

51. The method according to claim 42, wherein said first turbine drives a first shaft, and further comprising the step of transmitting torque from said first shaft to a second shaft without contact between said first and second shafts.

52. The method according to claim 51, wherein the step of transmitting torque from said first shaft to a second shaft comprises transmitting said torque via an eddy current coupling.

53. The method according to claim 52, wherein first and second portions of said supercritical fluid are compressed in said first compressor, and further comprising the step of flowing said first portion of said compressed supercritical fluid to said eddy current coupling so as to cool said coupling and heat said first portion of said compressed supercritical fluid.

54. The method according to claim 53, further comprising the step of transferring heat from said heated first portion of said compressed supercritical fluid from said eddy current coupling to said second portion of said compressed supercritical fluid.

55. A method of generating shaft power in a system comprising a supercritical fluid cycle and an air cycle, comprising the steps of:

a) burning a fossil fuel in air so as to produce a combustion gas;

b) compressing a first flow of supercritical fluid in a first compressor so as to produce a first flow of compressed supercritical fluid;

c) transferring heat from said combustion gas to said first flow of said compressed supercritical fluid so as to produce a cooled combustion gas and a first flow of heated compressed supercritical fluid;

d) expanding at least a portion of said first flow of heated compressed supercritical fluid in a first turbine so as to produce a first flow of expanded supercritical fluid, said expansion of said first flow of supercritical fluid generating shaft power;

e) returning said first flow of expanded supercritical fluid to said first compressor;

f) transferring heat from said first flow of expanded supercritical fluid to said air, the step of transferring heat from said first flow of expanded supercritical fluid to said air being performed prior to returning said first flow of supercritical fluid to said first compressor;

g) compressing a second flow of supercritical fluid in a second compressor so as to produce a second flow of compressed supercritical fluid;

h) transferring heat from said cooled combustion gas to said second flow of compressed supercritical fluid so as to produce a second flow of heated compressed supercritical fluid;

i) expanding said second flow of heated compressed supercritical fluid in a second turbine so as to produce a second flow of expanded supercritical fluid and so as to generate additional shaft power.

56. The method according to claim 55, further comprising the step of transferring heat from said second flow of expanded supercritical fluid to a flow of water so as to produce a flow of heated water and cooled expanded supercritical fluid.

57. The method according to claim 56, wherein the step of transferring heat from said second flow of expanded supercritical fluid to a flow of water comprising cooling said expanded supercritical fluid to approximately is critical temperature.

58. The method according to claim 55, further comprising the step of compressing said air in a third compressor so as to produce compressed air, the step of compressing said air being performed prior to transferring heat from said first flow of expanded supercritical fluid to said air, wherein said heat from said expanded supercritical fluid is transferred to said compressed air.

59. The method according to claim 58, further comprising the step of cooling said compressed air prior to the step of transferring heat from said first flow of expanded supercritical fluid to said compressed air.

60. The method according to claim 55, wherein the step of transferring heat from said first flow of expanded supercritical fluid to said air comprises cooling said first flow of expanded supercritical fluid to approximately its critical temperature.

61. The method according to claim 60, wherein the step of transferring heat from said first flow of expanded supercritical fluid to said air so as to cool said supercritical fluid comprises cooling said supercritical fluid to with ±

2°

K of its critical temperature.

62. The method according to claim 55, wherein said supercritical fluid comprises supercritical carbon dioxide.

63. A system for generating shaft power using a supercritical fluid cycle and an air cycle, comprising:

a) a first flow path for directing the flow of a first fluid therethrough, said first fluid comprising air, said first flow path comprising;

(i) a combustor connected to said first flow path so as to receive at least a portion of said air, said combustor supplied with a fossil fuel for combustion in said air, wherein said combustion of said fossil fuel in said air produces heated combustion gas;

(ii) a first turbine connected to said first flow path;

b) a second flow path for directing the flow of a second fluid therethrough, said second fluid comprising a supercritical fluid, said second flow path separate from said first flow path so as to prevent mixing of said air and said supercritical fluids, said second flow path comprising;

(i) a first compressor connected to said second flow path so as to receive said supercritical fluid for compression therein and to discharge said compressed supercritical fluid into said second flow path;

(ii) a second turbine for expansion of said supercritical fluid therein, said second turbine connected to said second flow path so as to discharge said expanded supercritical fluid into said second flow path;

c) a first cross cycle heat exchanger connected to said first and second flow paths,

(i) said first cross cycle heat exchanger connected to said first flow path so as to (1) receive at least a portion of said air for transfer of heat thereto so as to heat said portion of said air prior to said portion of said air being received by said combustor, and (2) discharge said heated air into said first flow path;

(ii) said first cross cycle heat exchanger connected to said second flow path so as to (1) receive at least a portion of said expanded supercritical fluid discharged from said second turbine for transfer of heat therefrom so as to cool at least said portion of said expanded supercritical fluid, and (2) discharge said cooled expanded supercritical fluid into said second flow path, wherein said expanded supercritical fluid transfers heat to said air;

d) a second cross cycle heat exchanger connected to said first and second flow paths,

(i) said second cross cycle heat exchanger connected to said first flow path so as to (1) receive at least a portion of said combustion gas produced by said combustor for transfer of heat therefrom so as to cool said combustion gas, and (2) discharge said cooled combustion gas into said first flow path;

(ii) said second cross cycle heat exchanger connected to said second flow path so as to (1) receive at least a portion of said compressed supercritical fluid from said first compressor for the transfer of heat thereto so as to heat at least said portion of said compressed supercritical fluid and (2) discharge said heated supercritical fluid into said second flow path, wherein said combustion gas transfers heat from said compressed supercritical fluid;

e) said first turbine connected to said first flow path so as to (1) receive at least a portion of said combustion gas produced by said combustor for expansion therein, and (2) discharge said expanded combustion gas to said first flow path;

f) said second turbine connected to said second flow path so as to receive said heated supercritical fluid discharged from said second cross cycle heat exchanger, said second turbine having a second shaft, whereby said expansion of said compressed supercritical fluid in said second turbine drives rotation of said second shaft.

64. The system according to claim 63, wherein said first flow path further comprises a second compressor connected to said first flow path so as to receive said air for compression therein and to discharge said compressed air into said first flow path, said second compressor connected so as to receive and compress said air prior to said air being received by said combustor, wherein said fossil fuel is combusted in said compressed air from said second compressor, and wherein said air received by said first cross cycle heat exchanger is said compressed air from said second compressor.

65. The system according to claim 63, wherein said second cross cycle heat exchanger is connected to said first flow path so as to receive at least said portion of said combustion gas produced by said combustor after expansion of said combustion gas in said first turbine.

66. The system according to claim 63, wherein said second cross cycle heat exchanger is connected to said first flow path so as to receive at least said portion of said combustion gas produced by said combustor before expansion of said combustion gas in said first turbine.

67. The system according to claim 63, wherein said first flow path further comprising a second compressor connected to said first flow path so as to receive said air for compression therein and to discharge said compressed air into said first flow path, said second compressor connected so as to receive and compress said air prior to said air being received by said combustor, and wherein said air received by said first cross cycle heat exchanger is said compressed air from said second compressor, and wherein said first flow path further comprises a cooler connected to said first flow path so as to received said compressed air discharged from said first compressor for cooling therein prior to said compressed air being received by said first cross cycle heat exchanger.

68. The system according to claim 63, wherein said second flow path further comprises a third turbine connected to said second flow path so as to (1) receive at least a first portion of said expanded supercritical fluid discharged from said second turbine for further expansion therein prior to said expanded supercritical fluid being received by said first cross cycle heat exchanger, and (2) discharge said further expanded supercritical fluid to said first cross cycle heat exchanger.

69. The system according to claim 68, wherein said second flow path further comprises an expansion nozzle connected to said second flow path so as to (1) receive a second portion of said expanded supercritical fluid discharged from said second turbine for further expansion therein, whereby said second portion of said expanded supercritical fluid bypasses said third turbine, and (2) discharge said second portion of said further expanded supercritical fluid into said second flow path, wherein said further expanded supercritical fluid from said nozzle is received by said first cross cycle heat exchanger.

70. The system according to claim 68, wherein said second cross cycle heat exchanger is connected to said second flow path so as to receive at least said first portion of said expanded supercritical fluid discharged from said second turbine for transfer of heat thereto prior to said portion of said expanded supercritical fluid being further expanded in said third turbine.

71. The system according to claim 63, wherein said second flow path further comprises an expansion nozzle connected to said second flow path so as to (1) receive at least a portion of said heated supercritical fluid discharged from said second cross cycle heat exchanger for expansion therein, and (2) discharge said portion of said expanded supercritical fluid into said second flow path, wherein said portion of said expanded supercritical fluid is received by said first cross cycle heat exchanger.

72. The system according to claim 63, wherein said second shaft is coupled to said first compressor, whereby expansion of said supercritical fluid in said second turbine drives said first compressor.

73. The system according to claim 63, wherein said first flow path further comprises a second combustor connected to said first flow path so as to receive at least a portion of said cooled combustion gas discharged from said second cross cycle heat exchanger, said second combustor supplied with additional fossil fuel for combustion in said cooled combustion gas, wherein said combustion of said fossil fuel in said cooled combustion gas produces reheated combustion gas.

74. The system according to claim 63, wherein said second flow path further comprises a third turbine connected to said second flow path so as to (1) receive at least a portion of said expanded supercritical fluid discharged from said second turbine for further expansion therein prior to said expanded supercritical fluid being received by said first cross cycle heat exchanger, and (2) discharge said further expanded supercritical fluid to said first cross cycle heat exchanger;

and

wherein said first flow path further comprises a second combustor connected to said first flow path so as to receive said at least a portion of said cooled combustion gas discharged from said second cross cycle heat exchanger, said second combustor supplied with additional fossil fuel for combustion in said cooled combustion gas, wherein said combustion of said additional fossil fuel in said cooled combustion gas produces reheated combustion gas, and

further comprising a third cross cycle heat exchanger connected to said first and second flow paths,

a) said third cross cycle heat exchanger connected to said first flow path so as to receive said reheated combustion gas from said second combustor for transfer of heat therefrom so as to cool said reheated combustion gas,

b) said third cross cycle heat exchanger connected to said second flow path so as to receive at least a portion of said supercritical fluid discharged from said second turbine so as to transfer heat thereto prior to said expansion in said third turbine.

75. The system according to claim 63, further comprising a boiler supplied with water, said boiler connected to said first flow path to receive said expanded combustion gas discharged from said first turbine so as to transfer heat therefrom to said water so as to generate steam.

76. The system according to claim 75, wherein boiler is connected to said combustor so as to direct said steam generated in said boiler into said combustor.

77. The system according to claim 76, further comprising a superheater connected to said second flow path so as to receive at least a portion of said supercritical fluid discharged from said second turbine.

78. The system according to claim 63, wherein at least a portion of said expanded combustion gas discharged into said first flow path from said first turbine is discharged from said first flow path to the atmosphere.

79. The system according to claim 63, wherein said supercritical fluid comprises supercritical carbon dioxide.

80. The system according to claim 63, further comprising a third shaft driven by said second shaft, said second shaft not in contact with said third shaft.

81. The system according to claim 80, wherein said second shaft is coupled to said third shaft by an eddy current coupling.

82. The system according to claim 81, wherein said eddy current coupling is connected said second flow path so as to (1) receive a portion of said compressed supercritical fluid, wherein said compressed supercritical fluid absorbs heat from said eddy current coupling so as to heat said compressed supercritical fluid and cool said eddy current coupling, and (2) to return said compressed supercritical fluid to said second flow path after said heating of compressed supercritical fluid in said eddy current coupling.

83. The system according to claim 63, further comprising an apparatus for measuring temperature of said supercritical fluid received by said second compressor.

84. The system according to claim 83, wherein said temperature measuring apparatus comprises a heat source for introducing heat into said supercritical fluid at a first location, and first and second temperature measuring means for the temperature of said supercritical fluid upstream and downstream, respectively of said first location.

85. The system according to claim 83, further comprising means for generating sound waves in said supercritical fluid and means for detecting said sound waves.

86. A system for generating shaft power using a supercritical fluid cycle and an air cycle, comprising:

a) a combustor for burning a fossil fuel in air so as to produce a combustion gas;

b) a first compressor for compressing a supercritical fluid so as to produce a compressed supercritical fluid;

c) a first cross cycle heat exchanger for transferring heat from said combustion gas to said compressed supercritical fluid so as to produce a cooled combustion gas and a heated compressed supercritical fluid;

d) a first turbine for expanding at least a portion of said heated compressed supercritical fluid so as to produce an expanded supercritical fluid, said expansion of said supercritical fluid generating shaft power;

e) a flow path for returning said expanded supercritical fluid to said first compressor;

f) a second cross cycle heat exchanger for transferring heat from said expanded supercritical fluid to said air so as to cool said supercritical fluid to approximately its critical temperature prior to burning said fossil fuel in said air in said combustor and prior to returning said supercritical fluid to said first compressor.

87. The system according to claim 86, wherein said second cross cycle heat exchanger is capable of cooling said expanded supercritical fluid to with ±

2°

K of its critical temperature.

88. A system generating shaft power using a supercritical fluid cycle and an air cycle, comprising:

a) a combustor for burning a fossil fuel in air so as to produce a combustion gas;

b) a first compressor for compressing a first flow of supercritical fluid so as to produce a first flow of compressed supercritical fluid;

c) a first heat exchanger for transferring heat from said combustion gas to said first flow of said compressed supercritical fluid so as to produce a cooled combustion gas and a first flow of heated compressed supercritical fluid;

d) a first turbine for expanding at least a portion of said first flow of heated compressed supercritical fluid so as to produce a first flow of expanded supercritical fluid, said expansion of said first flow of supercritical fluid generating shaft power;

e) a flow path for returning said first flow of expanded supercritical fluid to said first compressor;

f) a second heat exchanger for transferring heat from said first flow of expanded supercritical fluid to said air prior to returning said first flow of supercritical fluid to said first compressor;

g) a second compressor for compressing a second flow of supercritical fluid so as to produce a second flow of compressed supercritical fluid;

h) a third heat exchanger for transferring heat from said cooled combustion gas to said second flow of compressed supercritical fluid so as to produce a second flow of heated compressed supercritical fluid;

i) a second turbine for expanding said second flow of heated compressed supercritical fluid so as to produce a second flow of expanded supercritical fluid and so as to generate additional shaft power.

89. In a system for generating shaft power by expanding a supercritical fluid in a turbine having a shaft, a coupling from transmitting torque from said turbine shaft to a drive shaft, said coupling comprising:

a) an induction rotor adapted to be connected to said turbine shaft so as to rotate with said turbine shaft;

b) first and second armatures adapted to be connected to said drive shaft so as to rotate with said drive shaft;

c) a magnet creating a magnetic flux within said coupling, said magnet connected to said first and second armatures so as to rotate with said armatures, whereby rotation of said induction rotor imparts torque to said first and second armatures that causes rotation of said drive shaft;

d) a first flow path for directing a portion of said supercritical fluid to said induction rotor for cooling said induction rotor, whereby said portion of said supercritical fluid is heated;

e) a second flow path for directing said heated supercritical fluid to said turbine for expansion therein.

90. The coupling according to claim 89, further comprising a pressure membrane disposed between said induction rotor and said first and second armatures, said pressure membrane having an approximately spherically shaped surface.