Oxygen-enriched combustion for natural gas combined cycle operation
Systems and methods are provided for operating a combined cycle power plant while enhancing the CO 2 content of the flue gas generated by the power plant. The CO 2 content is enhanced by using a combination of exhaust gas recycle and oxygen-enriched combustion. The oxygen-containing flow for performing the oxygen-enriched combustion can be generated by an integrated pressure swing adsorption process that allows for production of a commercial grade nitrogen stream (95 vol % or more of N 2 ) while also providing an oxygen-containing stream with an oxygen content between 25 vol % and 48 vol % with high O 2 recovery.
1 . A method for operating a power generation process, comprising:
separating air using a pressure swing adsorption process to form a nitrogen-containing stream comprising 95 vol % or more of N 2 and an oxygen-containing stream comprising 25 vol % to 48 vol % of O 2 ;
combusting a fuel with O 2 from at least a portion of the oxygen-containing stream in the presence of a recycle stream in a combustion chamber of a turbine to form a flue gas, the O 2 from the at least a portion of the oxygen-containing stream comprising 16 vol % to 35 vol % of a combined volume of i) the fuel, ii) the at least a portion of the oxygen-containing stream, and iii) the recycle stream, the flue gas comprising 12 vol % or more of CO 2 ;
forming the recycle stream from one or more first portions of the flue gas; and
performing post-combustion capture on at least a second portion of the flue gas to form a CO 2 -containing product stream and one or more CO 2 -depleted flue gas streams, the one or more CO 2 -depleted flue gas streams comprising 30 vol % or less of the CO 2 from the at least a second portion of the flue gas,
wherein the pressure swing adsorption process comprises:
exposing air to a sorbent having kinetic selectivity for O 2 relative to N 2 in a sorbent environment at a pressure of 200 kPa-a to 800 kPa-a to form an adsorption effluent comprising the nitrogen-containing stream;
exhausting a blowdown effluent from the sorbent environment;
purging the sorbent environment with at least a portion of the blowdown effluent to form the oxygen-containing stream; and
purging the sorbent environment with a portion of the adsorption effluent.
2 . The method of claim 1 , wherein the oxygen-containing stream further comprises 50 vol % or more of N 2 .
3 . The method of claim 1 , wherein the sorbent having kinetic selectivity for O 2 relative to N 2 comprises at least one of a carbon molecular sieve and ITQ-55.
4 . The method of claim 1 , wherein the blowdown effluent is exhausted from the same end of the sorbent environment as the adsorption effluent.
5 . The method of claim 1 , wherein the pressure swing adsorption process is performed in a plurality of sorbent environments, the pressure swing adsorption process further comprising equalizing a pressure of a first sorbent environment after exposing air to a first sorbent with a pressure of a second sorbent environment after purging the second sorbent environment with a portion of the adsorption effluent.
6 . The method of claim 1 , wherein the recycle stream is mixed with the oxygen-containing stream prior to entering the combustion chamber.
7 . The method of claim 6 , wherein the recycle stream is at a pressure of 90 kPa-a to 115 kPa-a when mixed with the oxygen-containing stream.
8 . The method of claim 1 , wherein the flue gas comprises a CO 2 content of 16 vol % or more.
9 . The method of claim 1 , wherein the CO 2 -containing product stream comprises 80 vol % or more of CO 2 .
10 . The method of claim 1 , wherein forming the recycle stream from one or more first portions of the flue gas comprises forming the recycle stream from the CO 2 -containing product stream.
11 . The method of claim 1 , wherein performing post-combustion capture on the at least a second portion of the flue gas comprises separating the at least a second portion of the flue gas using a membrane separator, an amine scrubber, a liquid phase sorbent where the liquid is at least partially in the form of liquid droplets or a thin liquid film, or a combination thereof.
12 . The method of claim 1 , wherein performing post-combustion capture on the at least a second portion of the flue gas comprises exposing the at least a second portion of the flue gas to a solid sorbent to sorb CO 2 on the solid sorbent, and desorbing at least a portion of the sorbed CO 2 by direct displacement, a pressure swing, a temperature swing, or a combination thereof.
13 . The method of claim 1 , wherein performing post-combustion capture on the at least a second portion of the flue gas comprises forming a cathode input flow comprising the at least a second portion of the flue gas, passing the cathode input flow into a cathode of a molten carbonate fuel cell, and operating the molten carbonate fuel cell to generate electrical power, an anode output flow, and a cathode output flow corresponding to the CO 2 -depleted stream.
14 . The method of claim 1 , wherein the oxygen-containing stream comprises 35 vol % or more of O 2 .
15 . The method of claim 1 , further comprising passing the at least a second portion of the flue gas through a heat recovery steam generator to generate electrical power prior to performing post-combustion capture on the at least a second portion of the flue gas.
16 . The method of claim 1 , further comprising adding fuel to the at least a second portion of the flue gas; and performing supplemental combustion on the at least a second portion of the flue gas prior to performing post-combustion capture on the at least a portion of the flue gas.
17 . The method of claim 1 , wherein the separating air using a pressure swing adsorption process comprises a kinetic separation process.
18 . The method of claim 1 , wherein the fuel comprises natural gas.
19 . The method of claim 1 , wherein the CO 2 -containing product stream comprises 80 vol % or more of the CO 2 from the at least a second portion of the flue gas.
20 . The method of claim 1 , wherein the turbine comprises a compressor, the combustion chamber, an expander, and shaft coupling the expander to the compressor.