System and method for high efficiency power generation using a carbon dioxide circulating working fluid
The present invention provides methods and system for power generation using a high efficiency combustor in combination with a CO 2 circulating fluid. The methods and systems advantageously can make use of a low pressure ratio power turbine and an economizer heat exchanger in specific embodiments. Additional low grade heat from an external source can be used to provide part of an amount of heat needed for heating the recycle CO 2 circulating fluid. Fuel derived CO 2 can be captured and delivered at pipeline pressure. Other impurities can be captured.
1. A method of power generation comprising:
expanding a CO 2 -containing stream from a pressure of at least about 12 MPa and from a temperature of at least about 750° C. across a series of a first turbine and a last turbine so as to output from the last turbine a last turbine discharge stream comprising CO 2 ;
passing the last turbine discharge stream though a recuperator heat exchanger to withdraw heat therefrom as a heating source and form a cooled turbine discharge stream;
isolating at least a portion of the CO 2 from the cooled turbine discharge stream to form a recycle CO 2 stream;
compressing the recycle CO 2 stream to a pressure of at least about 12 MPa to form a compressed recycle CO 2 stream;
heating a first portion of the compressed recycle CO 2 stream with the heat withdrawn from the last turbine discharge stream in the recuperator heat exchanger, heating a second portion of the compressed recycle CO 2 stream with heat from a source other than the heat withdrawn from the last turbine discharge stream, and combining the first portion and the second portion to form a combined heated, compressed recycle CO 2 stream;
passing the combined heated, compressed recycle CO 2 stream to a combustor wherein a hydrocarbon or carbonaceous fuel is combusted in the presence of an oxidant and the combined heated, compressed recycle CO 2 stream to further heat the combined heated, compressed recycle CO 2 stream so as to form the CO 2 -containing stream; and
passing the CO 2 -containing stream to the first turbine in the series.
2. The method of claim 1 , further comprising adding further heat to the CO 2 -containing stream between the first turbine and the last turbine.
3. The method of claim 2 , wherein the further heat is provided in a further combustor wherein a hydrocarbon or carbonaceous fuel is combusted in the presence of an oxidant and the CO 2 -containing stream.
4. The method of claim 1 , further comprising withdrawing a side stream from the compressed recycle CO 2 stream.
5. The method of claim 4 , wherein withdrawn side stream of compressed recycle CO 2 comprises the second portion.
6. The method of claim 1 , wherein the heating of the first portion and the heating of the second portion is sufficient so that the temperature of the combined heated, compressed recycle CO 2 stream entering the combustor is less than the temperature of the last turbine discharge stream by no more than about 50° C.
7. The method of claim 1 , wherein the source of the heat that is not withdrawn from the last turbine discharge stream is an air separation unit.
8. The method of claim 1 , wherein the source of the heat that is not withdrawn from the last turbine discharge stream is a steam supply.
9. The method of claim 1 , wherein the source of the heat that is not withdrawn from the last turbine discharge stream is a hot exhaust gas from a conventional open cycle gas turbine.
10. The method of claim 1 , wherein the recuperator heat exchanger comprises a series of at least two heat exchangers.
11. The method of claim 1 , wherein the step of passing the turbine discharge stream though a recuperator heat exchanger comprises passing the turbine discharge stream sequentially through a first heat exchanger, a second heat exchanger, and a third heat exchanger.
12. The method of claim 11 , wherein the second portion of the compressed recycle CO 2 stream is heated by passing through a side heater.
13. The method of claim 12 , wherein the side heater utilizes heat withdrawn from the adiabatic stages of air compressors in a cryogenic air separation unit.
14. The method of claim 12 , wherein the side heater comprises a cryogenic air separation unit with two compressors, both of which are operated adiabatically, and wherein the method comprises removing the heat of compression in after-coolers against a circulating heat transfer fluid which transfers the heat of compression.
15. The method of claim 1 , wherein the second portion is also heated with the heat withdrawn from the last turbine discharge stream.