Power generation system incorporating multiple Rankine cycles
A power generation system ( 100 ) and a method of generating power. In one embodiment of the system shown in FIG. 1 , a gasification subsystem ( 1 ) is configured to convert a carbonaceous fuel to fuel suitable for combustion in a gas turbine ( 48 ). A first power generation cycle ( 2 ) includes the gas turbine ( 48 ) coupled to receive fuel from a gasifier ( 24 ). A first Rankine cycle ( 3 ) is coupled to receive thermal energy from at least the first power generation cycle ( 2 ) and generate power with a first vapor turbine ( 58 ). A second Rankine cycle ( 4 ) is coupled to receive thermal energy from the gasification subsystem ( 1 ) or the first power generation cycle ( 2 ) and generate power with a second vapor turbine ( 82 ). In an associated method, syngas ( 26 ) is generated and processed to remove components therein. Power is generated in a first turbine ( 48 ) with the processed syngas ( 33 ). Power is generated in a second turbine ( 58 ) with heat recovered from exhaust produced by the first turbine ( 48 ). Power is generated in a third turbine ( 82 ) with heat recovered from the syngas ( 33 ).
1. A method of generating power in a system having a gas turbine subsystem generating a hot exhaust gas, comprising using heat exchangers to derive sensible heat from components within the system and providing the sensible heat to each of at least two Rankine cycles, a first of the Rankine cycles operating a first vapor turbine at a relatively high pressure and a second of the Rankine cycles operating a second vapor turbine at a lower pressure than the relatively high operating pressure of the first vapor turbine, wherein the first vapor turbine is a steam turbine and the second vapor turbine operates with a second working fluid comprising a constituent taken from the group consisting of ammonia, carbon dioxide and hydrocarbon compounds including halocarbon refrigerants.
2. The method of claim 1 wherein sensible heat provided to a first of the Rankine cycles is received from a relatively high temperature source and sensible heat provided to a second of the Rankine cycles is received from multiple heat sources all having a lower temperature than the relatively high temperature source.
3. The method of claim 1 wherein a heat exchanger coupled to the second vapor turbine is optimally designed for the second working fluid.
4. The method of claim 1 wherein heat exchangers heat the second working fluid from heat sources configured to thermodynamically optimize heat recovery.
5. The method of claim 1 wherein the second working fluid operates under supercritical conditions.
6. The method of claim 1 wherein the second Rankine cycle recovers heat from a syngas cooler.