Cold recycle process for gas turbine inlet air cooling

Abstract

Methods and systems for increasing efficiency of combustion in a turbine, methods including expanding in an expansion unit a pressurized fluid stream to form an expanded, cooled fluid stream; exchanging heat between an oxygen containing stream and the expanded, cooled fluid stream to reduce temperature of the oxygen containing stream to a reduced temperature and create a reduced temperature turbine compressor inlet oxygen containing stream; and compressing the reduced temperature turbine compressor inlet oxygen containing stream to an operating pressure of the turbine, where the step of compressing the reduced temperature turbine compressor inlet oxygen containing stream is more efficient than compressing the oxygen containing stream.

Claims

1. A method for increasing power from or efficiency of combustion in a turbine, the method comprising the steps of: concentrating CO.sub.2 in a CO.sub.2 capture system to produce a concentrated CO.sub.2 stream; operating a controller to regulate an amount of the concentrated CO.sub.2 stream to form a pressurized fluid stream; expanding in an expansion unit the pressurized fluid stream to form an expanded, cooled fluid stream; exchanging heat between an oxygen containing stream and the expanded, cooled fluid stream to reduce temperature of the oxygen containing stream to a reduced temperature and create a reduced temperature turbine compressor inlet oxygen containing stream; and compressing the reduced temperature turbine compressor inlet oxygen containing stream to an operating pressure of the turbine, where the step of compressing the reduced temperature turbine compressor inlet oxygen containing stream is more efficient than compressing the oxygen containing stream, where the expanded, cooled fluid stream is at least about 90 mol. % CO.sub.2 and is at about 1 bar pressure, and where the controller regulates the amount of the concentrated CO.sub.2 stream to form the pressurized fluid stream to optimize operation of the turbine depending on ambient temperature of the oxygen containing stream.

2. The method according to claim 1, further comprising the step of combusting a fuel in a combustion chamber of the turbine using the reduced temperature turbine compressor inlet oxygen containing stream, where the step of combusting the fuel with the reduced temperature turbine compressor inlet oxygen containing stream is more efficient than combusting the fuel in the combustion chamber with the oxygen containing stream.

3. The method according to claim 2, where emissions, including nitrogen oxides emissions, of the turbine are reduced compared to combusting the fuel in the combustion chamber with the oxygen containing stream.

4. The method according to claim 2, further comprising the step of applying selective exhaust gas recirculation to at least a portion of exhaust gas produced from the step of combusting the fuel in the combustion chamber of the turbine to recirculate exhaust gas to the oxygen containing stream.

5. The method according to claim 4, where the step of exchanging heat between the oxygen containing stream and the expanded, cooled fluid stream and the step of applying selective exhaust gas recirculation to exhaust gas are performed simultaneously.

6. The method according to claim 1, where the oxygen containing stream comprises air.

7. The method according to claim 1, where the oxygen containing stream comprises an oxygen enriched stream produced from an air separation unit.

8. The method according to claim 1, where the expansion unit comprises a turbine.

9. The method according to claim 1, where compressed CO.sub.2 in the pressurized fluid stream is provided from a carbon capture process capturing carbon dioxide produced in a step of combusting a fuel in a combustion chamber of the turbine.

10. The method according to claim 9, where the compressed CO.sub.2 is cooled before the step of expanding in the expansion unit.

11. The method according to claim 1, where compressed CO.sub.2 in the pressurized fluid stream is provided from a source selected from a group comprising: a carbon capture process capturing carbon dioxide produced in a step of combusting a fuel in a combustion chamber of the turbine; a hydrocarbon-bearing reservoir; a natural gas treatment plant; a CO.sub.2 capture plant comprising CO.sub.2 from combustion products; a CO.sub.2 capture plant comprising CO.sub.2 from air; an industrial process providing CO.sub.2 byproduct; or a combination of any of the foregoing.

12. The method according to claim 1, where the step of exchanging heat between the oxygen containing stream and the expanded, cooled fluid stream is carried out with direct mixing between the oxygen containing stream and the expanded, cooled fluid stream.

13. The method according to claim 1, where the step of exchanging heat between the oxygen containing stream and the expanded, cooled fluid stream is carried out with indirect heat exchange between the oxygen containing stream and the expanded, cooled fluid stream.

14. The method according to claim 1, where the oxygen containing stream is between about 30° C. and about 60° C., the reduced temperature turbine compressor inlet oxygen containing stream is between about 5° C. and about 45° C., and where oxygen level in the reduced temperature turbine compressor inlet oxygen containing stream is maintained at least at about 15 mol. %.

15. The method according to claim 1, further comprising the step of increasing a volume amount of the expanded, cooled fluid stream based on temperature of the oxygen containing stream.

16. The method according to claim 1, further comprising the step of decreasing a volume amount of the expanded, cooled fluid stream based on temperature of the oxygen containing stream.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other features, aspects, and advantages of the present disclosure will become better understood with regard to the following descriptions, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the disclosure and are therefore not to be considered limiting of the disclosure's scope as it can admit to other equally effective embodiments.

(2) FIG. 1 is a schematic for a system exhibiting expanded, cooled fluid recycle to control inlet air temperature in a gas turbine, where the system includes a single column CO.sub.2 absorption system.

(3) FIG. 2 is a schematic for a system exhibiting expanded, cooled fluid recycle to control inlet air temperature in a gas turbine, where the system includes a double column CO.sub.2 absorption system.

(4) FIG. 3 is a schematic for a system exhibiting expanded, cooled fluid recycle to control inlet air temperature in a gas turbine, where the system includes a double column CO.sub.2 absorption system and selective exhaust gas recirculation.

(5) FIG. 4 is a schematic for a system exhibiting expanded, cooled fluid recycle to control inlet air temperature in a gas turbine, where the system includes a double column CO.sub.2 absorption system and selective exhaust gas recirculation.

DETAILED DESCRIPTION

(6) So that the manner in which the features and advantages of the embodiments of apparatus, methods, and systems applying fluid expansion and recycle, in addition to or alternative to selective exhaust gas recirculation, which show efficient, surprising, and unexpected effects on turbine power production efficiency, as well as others, which will become apparent, may be understood in more detail, a more particular description of the embodiments of the present disclosure briefly summarized previously may be had by reference to the various embodiments, which are illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only various embodiments of the disclosure and are therefore not to be considered limiting of the present disclosure's scope, as it may include other effective embodiments as well.

(7) FIG. 1 is a schematic for a system exhibiting expanded, cooled fluid recycle to control inlet air temperature in a gas turbine, where the system includes a single column CO.sub.2 absorption system. In integrated turbine and carbon capture system 100, turbine system 102 and carbon capture system 104 operate together to synergistically increase the performance of turbine system 102 via control of the temperature of inlet air or an inlet oxidizing stream, for example a stream containing above 90 mol. % O.sub.2.

(8) An oxygen rich stream, external air, or a combination thereof for example at ambient outdoor conditions varying with seasonal temperatures, is fed through external air stream 106 into a heat exchange unit 108 where it exchanges heat with and is cooled by an expanded, cooled fluid stream 110. Heat exchange unit 108 can directly mix and comingle external air stream 106 and cooled fluid stream 110, and/or heat exchange unit 108 can indirectly allow for heat exchange between external air stream 106 and expanded, cooled fluid stream 110 to cool external air stream 106. Expanded, cooled fluid stream 110 includes in some embodiments a CO.sub.2-rich gas stream. A cooled intermediate temperature stream 112 results from the mixing of external air and expanded, cooled fluid from stream 110 in heat exchange unit 108, for example an air mixing chamber, and cooled intermediate temperature stream 112 is fed to inlet compressor 114 of the turbine system 102. Mixed, cooled air from cooled intermediate temperature stream 112 is compressed in inlet compressor 114 before entering combustion chamber 116 via stream 118 where it oxidizes or combusts the fuel fed through fuel inlet 120.

(9) Resulting exhaust gases from combustion chamber 116 exit via combustion exhaust stream 122 and expand in turbine 124 to about ambient pressure. Low pressure exhaust gases are conveyed through stream 126 to a waste heat recovery system 128, which includes a heat recovery steam generator to recover the remaining energy and generate steam, which is generally used as utility or expanded to generate power.

(10) In some embodiments, temperature of stream 110 can range between about −76° C. and about 40° C., and in some embodiments between about 0° C. and about 30° C. Stream 112 temperature can be between about 2 K to 40 K below stream 106 temperature, and preferably being about 5 K to about 15 K below stream 106 temperature. Depending on turbine size and configuration, a decrease in stream 112 temperature of 10 K can yield efficiency increase above 1% for turbine system 102. Compression energy required decreases as colder air is compressed, and thus the overall efficiency of the system increases.

(11) In certain embodiments, turbine system 102 includes a gas turbine, and fuel inlet 120 accepts natural gas. In some embodiments, other fossil fuels such as synthetic fuels, oils, and oil derivatives can be used in a turbine system. In turbine system 102, the system can incorporate one or more different types of gas turbines such as heavy-duty, industrial, or aero-derivative gas turbines. A gas turbine can be designed to operate in a simple cycle, in multi-generation, or in a combined cycle, and can be used either for mechanical drive applications or power generation.

(12) In embodiments of turbine system 102 where a gas turbine is operated in a simple cycle or as a mechanical drive, waste heat recovery system 128 can be applied in turbine system 102, as it is generally part of a combined cycle configuration or multi-generation configuration. In other embodiments, a waste heat recovery system is not required. One of ordinary skill understands different configurations for and different uses of turbine systems, such as turbine system 102.

(13) Carbon capture system 104 represents an example of a solvent based post-combustion CO.sub.2 capture system comprising an absorption tower 130 and a CO.sub.2 solvent regenerator 132, for example a stripper column. Carbon capture system 104 can incorporate in different embodiments any suitable CO.sub.2 solvent, such as for example amine-based solvents or ionic liquids. In some embodiments, carbon capture systems, such as carbon capture system 104, can include adsorption-based CO.sub.2 capture units, such as temperature or pressure swing adsorption units, or cryogenic CO.sub.2 separation, and membrane-based separation units. A person of ordinary skill will realize that a variety of carbon capture technologies exist for incorporation into carbon capture systems.

(14) Stream 134 exits waste heat recovery system 128 and is fed to an exhaust conditioning unit 136 before entering the absorption tower 130 via stream 138. Exhaust conditioning unit 136 in the embodiment shown includes a water quench and polishing step, which allow the exhaust gases to meet the requirements of the carbon capture system 104, in particular for this example the absorption tower 130 and the CO.sub.2-absorbing solvent. In FIG. 1, 100% of stream 134 exiting waste heat recovery system 128 is sent to carbon capture system 104. In other embodiments where CO.sub.2 capture/sequestration is not required beyond internal usage for inlet air cooling, an optional split stream 164 from stream 134 would be vented rather than all exhaust being fed to carbon capture system 104 to reduce energy usage of carbon capture system 104.

(15) Absorption tower 130 is fed a CO.sub.2-lean solvent via stream 140 that is contacted with exhaust gas in absorption tower 130, where the exhaust gas exits exhaust conditioning unit 136 via stream 138 and is input into absorption tower 130 for mixing with the CO.sub.2-lean solvent stream. Carbon dioxide is absorbed by the CO.sub.2-lean solvent and exits absorption tower 130 via a CO.sub.2-rich solvent stream 142. CO.sub.2 capture rate is partly a function of the design of absorption tower 130 and what solvent or combination of solvents is used. In some embodiments, about 90% of the CO.sub.2 from stream 138 is captured.

(16) CO.sub.2-lean exhaust gases are vented out of absorption tower 130 through stream 144. The CO.sub.2-rich solvent stream 142 in some embodiments is compressed by a pump and circulated through internal heat exchangers 146 where it is heated before its introduction into the CO.sub.2 solvent regenerator 132 via stream 148. Heat is applied to the CO.sub.2 solvent regenerator 132, and CO.sub.2 is desorbed from the CO.sub.2-rich solvent to exit CO.sub.2 solvent regenerator 132 via stream 150. Heated CO.sub.2-lean solvent is conveyed out of CO.sub.2 solvent regenerator 132 via line 152 and through internal heat exchangers 146 before CO.sub.2-lean solvent is recycled and fed again to the absorption tower 130 via stream 140.

(17) Stream 150 is mostly composed of CO.sub.2 saturated with water vapor when it leaves CO.sub.2 solvent regenerator 132. As for example, in amine-based solvent regeneration units, the CO.sub.2 and water vapor stream leaves the regenerator at a pressure of about 2 bar (about 1 to 5 bar range), a temperature of about 120° C., and a water vapor content that can be above 50 mol %. Regeneration columns include heat exchangers to cool down the temperature of the exiting stream close to a cold sink temperature to condense water and knock it out of the stream for recirculation back in the solvent loop. In the case where CO.sub.2 capture system 104 provides a CO.sub.2 rich stream 150 at temperatures above an ambient sink temperature, a heat exchanger can be incorporated in the system to exchange heat with the ambient sink and cool down stream 150 to near ambient temperatures. The remaining gaseous stream then is a highly concentrated CO.sub.2 stream (typically above 90 mol. %) saturated with some water vapor. In another example using a methanol based absorption system, stream 150 would be at pressures between about 2 to 10 bar and temperatures between about −50 to −30° C.

(18) Stream 150 is fed to controller 154, which regulates the amount of CO.sub.2-rich stream to be recycled to turbine system 102 via streams 156 and 110. CO.sub.2 is split between streams 156 and stream 158. Remaining CO.sub.2 exits controller 154 via stream 158 to CO.sub.2 dehydration and compression station 160. Depending on the water vapor content in stream 156 along with stream 156 pressure and temperature, in some embodiments stream 156 is cooled and dehydrated before expansion to avoid water frost formation after expansion. Operating temperatures and pressures of different CO.sub.2 capture systems and CO.sub.2 streams exiting these systems are well known to persons having ordinary skill in the art, and therefore the design of controller 154, the requirements for further treatment of stream 156 before entering the expansion unit 162, and the design of the expansion unit 162 would be based, in part, on the composition, temperature, and pressure of stream 150.

(19) CO.sub.2 enters an expansion unit 162 where it is expanded and cooled below ambient air temperature, or below the temperature of an oxidation stream to a turbine compressor inlet. CO.sub.2, in addition to or alternative to other fluids such as for example water vapor, are expanded in expansion unit 162, and are therefore cooled in temperature. Expanded, cooled fluid stream 110 is recycled to heat exchange unit 108. Expansion unit 162 in some embodiments comprises one or more turbines of any suitable type; in another embodiment, it can comprise one or more nozzles or expansion valves, optionally in series with one or more turbines. The amount and temperature of recirculated fluids, such as CO.sub.2-rich gases, in streams 110, 156 are controlled to optimize the operation of turbine system 102 depending on the ambient temperature of external air stream 106. If for example external air stream 106 is at a greater temperature, a greater recirculation rate is used, while still keeping the O.sub.2 content in the combustion chamber 116 above about 16 or 17 mol. % to prevent flame instabilities and poor combustion performance.

(20) In an example, stream 110 temperature can be in a range between about −76° C. and 40° C., and in some embodiments between about 0° C. and 30° C. Stream 112 temperature can be about 2 K to about 40 K below stream 106 temperature and preferably being 5 K to 15 K below stream 106 temperature.

(21) As noted, in other embodiments where CO.sub.2 capture is not required beyond internal usage for inlet air cooling, an optional split stream 164 from stream 134 would be vented rather than all exhaust being fed to carbon capture system 104. Captured CO.sub.2 in carbon capture system 104 would then be conveyed through stream 156 to the expansion unit 162; in such a configuration, carbon capture system 104 would be smaller and optimized for the specific purpose of inlet air cooling, rather than capturing all CO.sub.2 produced by a turbine system.

(22) Carbon capture system 104 can be designed to capture and recirculate only CO.sub.2 required to cool external air stream 106, when there is no requirement to reduce the emissions from a power plant generally. In such an embodiment CO.sub.2 dehydration and compression station 160 would not be required. In such an embodiment, control of the system is performed in part by controlling the amount of flue gas entering the CO.sub.2 capture system through stream 134, and in part using the CO.sub.2 solvent regenerator 132 column reboiler duty. Increasing the reboiler duty can increase solvent regeneration and therefore the recoverable CO.sub.2 from the CO.sub.2 solvent, while reducing the reboiler duty would reduce the recoverable CO.sub.2 from the solvent.

(23) In other embodiments, stream 134 entering carbon capture system 104 can include CO.sub.2 from one or more external CO.sub.2 sources (other than turbine system 102), such as for example another gas turbine, a boiler, a gas plant, or subterranean CO.sub.2 storage. In some embodiments, carbon capture system 104 is an external system that is providing at its battery limits stream 156, comprising CO.sub.2, feeding the expansion unit 162. CO.sub.2 provided through stream 156 can be in a gaseous state, a liquid state, a two-phase state, or a supercritical state. Expansion unit 162 is selected from commercially-available technologies based upon, in part, maintaining appropriate pressure levels, pressure ratio, and physical state of the CO.sub.2 streams at the inlet and outlet of the device. In one example embodiment, stream 156 can include a liquid CO.sub.2 stream or a supercritical CO.sub.2 stream feeding an expansion valve in expansion unit 162. In other example embodiments, stream 156 can include a gaseous CO.sub.2 stream or supercritical CO.sub.2 stream feeding a turbine in expansion unit 162.

(24) An external system providing CO.sub.2 at its battery limits can be a CO.sub.2 capture system in a gas plant or in a power plant, or can be a chemical process with CO.sub.2 as a byproduct such as ethylene glycol plants or reforming plants with hydrogen membrane separation, or can be CO.sub.2 recovered from acid gas enrichment plants. In other instances, CO.sub.2 can be produced from subterranean CO.sub.2 storage and hydrocarbon-bearing reservoirs.

(25) In some embodiments, systems use CO.sub.2 that is captured in gas plants from CO.sub.2 removal from natural gas inlet streams for meeting the inlet quality requirements for the natural gas streams. In such cases, the CO.sub.2 is generally captured by absorption systems operating at high pressure, and therefore CO.sub.2 is initially at higher pressure when compared to CO.sub.2 captured from exhaust gases. If CO.sub.2 pressure exiting the CO.sub.2 solvent regenerator 132 is not sufficient to provide the necessary cooling, in some embodiments a smaller regenerator is installed that is operated specifically at higher pressure to meet the cooling requirements as is the case described further with regard to FIG. 2.

(26) Raw natural gas is usually processed in gas plants at elevated pressures (for example about 10 to about 100 bar) compared to power plant flue gases operating around atmospheric pressure. In some embodiments CO.sub.2 solvent can be regenerated in a reboiler at higher pressure compared to the classical regeneration scheme in order to collect the CO.sub.2 at higher pressure. In such a setup, the steam required for the regeneration is at higher pressure compared to the classical regeneration scheme.

(27) Stream 156, which can be provided by an external CO.sub.2 system described previously in addition to or alternative to CO.sub.2 exiting CO.sub.2 solvent regenerator 132, in some embodiments has a pressure between about 1.5 bar and about 200 bar, or between about 1.5 bar and about 15 bar, or between about 3 bar and about 7 bar. In an embodiment where amine-based solvent is used for the capture of CO.sub.2, the pressure in regenerator 132 would range between about 1 and 5 bar, and typically be about 3 bar. In one embodiment, CO.sub.2 is collected from one or more carbon capture systems, such as carbon capture system 104, and is expanded in a single turbine of expansion unit 162 to about 1 bar. In some embodiments, the CO.sub.2 is then distributed to separate or more than one turbine systems, such as for example turbine system 102, working in parallel, and in other embodiments recirculated CO.sub.2 can be distributed to dedicated smaller turbines of expansion unit 162 before feeding a corresponding gas turbine mixing chamber, such as for example heat exchange unit 108. In such cases, the carbon capture system is sized and designed specifically for this application.

(28) In some embodiments, expanded, cooled fluid stream 110 is cooled entirely or substantially completely intrinsically, or without external energy and without external coolers to below ambient temperatures. For example, the energy required for compression of CO.sub.2 in carbon capture system 104 allows for the later expansion and cooling of CO.sub.2 in expansion unit 162 to less than ambient temperature, and thus cooling energy is provided intrinsically in system 100 by compression of carbon capture system 104, as is the case of vapor compression refrigeration systems. Optionally, a compressed CO.sub.2 stream can itself be cooled by an available heat sink to near ambient temperatures prior to expansion and temperature decrease to less than ambient temperature. The CO.sub.2 in streams 156 and 110 for recycle in some embodiments is about 50 mol. % CO.sub.2, is about 80 mol. % CO.sub.2, in some embodiments is about 90 mol. % CO.sub.2, and in some embodiments is about 95 mol. % CO.sub.2. In some embodiments, after expansion unit 162, stream 110 is expanded to about ambient pressure, or about 1 bar. Inlet compressors such as inlet compressor 114 typically accept inlet air at or near about 1 bar. Standard gas turbine flue gas (exhaust) generally contains about 5 mol. % CO.sub.2.

(29) FIG. 2 is a schematic for a system exhibiting expanded, cooled fluid recycle to control inlet air temperature in a gas turbine, where the system includes a double column CO.sub.2 absorption system. Similarly labeled units are the same as those described with respect to FIG. 1. FIG. 2 shows an embodiment where regeneration of CO.sub.2-capturing solvent is performed in two stages. Integrated turbine and carbon capture system 200 in FIG. 2 is similar system 100 in FIG. 1; however, carbon capture system 105 in FIG. 2 includes two CO.sub.2 solvent regenerators 132, 133, for example regeneration columns or stripper columns.

(30) In carbon capture system 105, CO.sub.2 exiting CO.sub.2 solvent regenerator 132 via stream 151 is directed directly to CO.sub.2 dehydration and compression station 160. A slip stream of CO.sub.2-rich solvent 149 is taken either or both from stream 148 or lower stages of CO.sub.2 solvent regenerator 132, and stream 149 is further compressed by pump 153 to enter via stream 155 second CO.sub.2 solvent regenerator 133, which operates at higher pressure than first CO.sub.2 solvent regenerator 132. CO.sub.2 is stripped from solvent at higher pressure in CO.sub.2 solvent regenerator 133 and is conveyed via stream 157 to the expansion unit 162. Stream 157 can be subjected to further cooling if its temperature is higher than that required by expansion unit 162.

(31) In one example, pressure in regenerator 132 is about 3 bar while the pressure in regenerator 133 can be up to about 10 bar, preferably up to about 7 bar. Pump 153 can be designed to compress the CO.sub.2 rich solvent stream 149 from its pressure in line 148 or regenerator 132 to about the pressure of the regenerator 133.

(32) In the embodiment of FIG. 2 where the CO.sub.2 capture system is an amine-based solvent system, stream 157 can exit regenerator 133 at temperatures above about 130° C., and therefore can require cooling to near ambient temperature or the temperature of a cooling water source to allow for further cooling when expanded through expansion unit 162, such as a turbine or expansion valve for example.

(33) Greater pressure in CO.sub.2 solvent regenerator 133 leads to greater pressure CO.sub.2 in stream 157, and thus more work and more cooling is available as stream 157 passes through expansion unit 162. Stream 110 is conveyed back to heat exchange unit 108 to reduce the temperature of external air stream 106. Integrated turbine and carbon capture systems of FIGS. 1 and 2 can in other embodiments include selective exhaust gas recirculation, shown and described in more detail with respect to FIGS. 3 and 4. FIG. 3 shows a configuration with selective exhaust gas recirculation in parallel, and FIG. 4 shows a configuration in series.

(34) In the system of FIG. 2, the recirculated CO.sub.2 can be obtained at greater pressure with a lower energy penalty compared to other embodiments, requiring a lesser recirculation rate to achieve the same inlet air cooling. Carbon capture system 105 of FIG. 2 is controlled, in part, by varying the amount of solvent sent to CO.sub.2 solvent regenerator 133 and by varying operating parameters of CO.sub.2 solvent regenerator 133. The systems and methods described with respect to FIGS. 1 and 2 increase CO.sub.2 concentration in exhaust gases and achieve certain benefits sought in systems applying selective exhaust gas recirculation. Stream 157 exits CO.sub.2 solvent regenerator 133 at between about 1.5 bar and about 15 bar, or between about 3 bar and about 7 bar. Regenerated solvent stream 159 is returned from CO.sub.2 solvent regenerator 133 to CO.sub.2 solvent regenerator 132.

(35) A lower energy penalty in the embodiment as presented in FIG. 2 derives in part from the usage of high pressure steam only to regenerate the CO.sub.2 that is required for the recirculation in CO.sub.2 solvent regenerator 133, while the bulk of the CO.sub.2 is regenerated at lower pressure and would be requiring lower quality, lower pressure steam in solvent regenerator 132.

(36) As noted, the integration of expanded, cooled CO.sub.2 recycle with selective exhaust gas recirculation is possible and discussed in detail with respect to FIGS. 3 and 4. An expanded, cooled CO.sub.2 recycle loop and a selective exhaust gas recirculation loop can be operated individually or simultaneously to optimize system performance and meet load demand on an electricity grid. For example, a system can operate a cooled, expanded CO.sub.2 recycle loop at greater ambient temperatures (summer), such as temperatures above about 20° C. or 30° C., and the selective exhaust gas recirculation at lesser ambient temperature (winter), below about 20° C.

(37) FIG. 3 is a schematic for a system exhibiting expanded, cooled fluid recycle to control inlet air temperature in a gas turbine, where the system includes a double column CO.sub.2 absorption system and selective exhaust gas recirculation. The system of FIG. 3 is similar to that of FIGS. 1 and 2, and similarly labeled units represent the same units as in previous figures. In carbon capture system 109 of integrated turbine and carbon capture system 300, stream 139 exiting exhaust conditioning unit 136 is split into stream 141 and stream 143. Stream 141 is fed to absorption tower 130 to follow the same operating schematic of carbon capture system 105 in FIG. 2.

(38) Stream 143 is fed to a selective CO.sub.2 transfer unit 145 which transfers exhaust CO.sub.2 from stream 143 to the external air stream 147 resulting in a CO.sub.2-rich inlet air stream 107 feeding heat exchange unit 108. CO.sub.2 transfer unit 145 vents CO.sub.2-lean exhaust and air via stream 161.

(39) Selective CO.sub.2 transfer unit 145 could be a set of membranes permeable to CO.sub.2 or other devices and systems where CO.sub.2 transfer occurs indirectly through the usage of an intermediate media as for example an adsorption or absorption system.

(40) FIG. 4 is a schematic for a system exhibiting expanded, cooled fluid recycle to control inlet air temperature in a gas turbine, where the system includes a double column CO.sub.2 absorption system and selective exhaust gas recirculation.

(41) Integrated turbine and carbon capture system 400 includes carbon capture system 111, and stream 163 exiting absorption tower 130 is fed to a selective CO.sub.2 transfer unit 145 which transfers exhaust CO.sub.2 from stream 163 to the external air stream 147 resulting in a CO.sub.2-rich inlet air stream 107 feeding heat exchange unit 108. In some embodiments, a portion of the flue gases are recycled to the air compressor inlet via stream 163 while the remaining portion of the flue gases exit the system through the stack via stream 131. CO.sub.2 transfer unit 145 vents CO.sub.2-lean exhaust and air via stream 161. In such a configuration, the carbon capture system 111 is designed and operated to increase CO.sub.2 in stream 163 leaving the absorption tower 130 to allow for CO.sub.2 transfer in the CO.sub.2 transfer unit 145. In certain embodiments of the present disclosure, expanded, cooled recycle streams comprising concentrated CO.sub.2 are used to cool turbine inlet air in the absence of or without selective exhaust gas recycle.

(42) By allowing selective exhaust gas recycle to operate in parallel with a cold CO.sub.2 recycle loop, systems can reduce energy requirements by maintaining a specific concentration of CO.sub.2 in the inlet stream to a turbine compressor thereby controlling emissions when the inlet air temperature is at intermediate levels. In some instances, energy requirements for the cold CO.sub.2 recycle might be more than the energy requirements for the selective exhaust gas recirculation. Having both systems available allows for optimization of energy use of the system.

(43) The singular forms “a,” “an,” and “the” include plural referents, unless the context clearly dictates otherwise.

(44) The term “about” when used with respect to a value and/or range refers to values including plus and minus 5% of the given value and/or range.

(45) In the drawings and specification, there have been disclosed embodiments of apparatus, systems, and methods for expanded, cooled fluid recycle, as well as others, and although specific terms are employed, the terms are used in a descriptive sense only and not for purposes of limitation. The embodiments of the present disclosure have been described in considerable detail with specific reference to these illustrated embodiments. It will be apparent, however, that various modifications and changes can be made within the spirit and scope of the disclosure as described in the foregoing specification, and such modifications and changes are to be considered equivalents and part of this disclosure.