Supercritical CO.SUB.2 .cycle coupled to chemical looping arrangement

Abstract

Systems and methods for coupling a chemical looping arrangement and a supercritical CO.sub.2 cycle are provided. The system includes a fuel reactor, an air reactor, a compressor, first and second heat exchangers, and a turbine. The fuel reactor is configured to heat fuel and oxygen carriers resulting in reformed or combusted fuel and reduced oxygen carriers. The air reactor is configured to re-oxidize the reduced oxygen carriers via an air stream. The air stream, fuel, and oxygen carriers are heated via a series of preheaters prior to their entry into the air and fuel reactors. The compressor is configured to increase the pressure of a CO.sub.2 stream to create a supercritical CO.sub.2 stream. The first and second heat exchangers are configured to heat the supercritical CO.sub.2 stream, and the turbine is configured to expand the heated supercritical CO.sub.2 stream to generate power.

Claims

1. A system for employing a supercritical CO.sub.2 cycle, wherein the supercritical CO.sub.2 cycle is coupled to a fuel reactor and an air reactor fluidly connected to the fuel reactor, wherein fuel reacts with oxygen carriers in the fuel reactor to form reformed or combusted fuel and reduced oxygen carriers, and wherein the reduced oxygen carriers are oxidized via an air stream in the air reactor to form re-oxidized oxygen carriers and oxygen-depleted air, the system comprising: a compressor configured to receive a CO.sub.2 stream from a CO.sub.2 source, wherein the compressor is configured to increase the pressure of the CO.sub.2 stream thereby creating a high pressure supercritical CO.sub.2 stream; a first heat exchanger in fluid communication with the compressor and the fuel reactor, the first heat exchanger being configured to receive and heat the supercritical CO.sub.2 stream, and being configured to receive at least a portion of the reformed or combusted fuel from the fuel reactor, wherein the energy from the reformed or combusted fuel is used to heat the supercritical CO.sub.2 stream; a second heat exchanger in fluid communication with the first heat exchanger and the air reactor, the second heat exchanger being configured to receive and further heat the supercritical CO.sub.2 stream received from the first heat exchanger, and being configured to receive the oxygen-depleted air and a portion of the re-oxidized oxygen carriers from the air reactor, wherein the energy from the oxygen-depleted air and the portion of the re-oxidized oxygen carriers is used to heat the supercritical CO.sub.2 stream; and a turbine in fluid communication with the second heat exchanger, the turbine being configured to receive the supercritical CO.sub.2 stream from the second heat exchanger and expand the supercritical CO.sub.2, whereby the expansion of the supercritical CO.sub.2 generates power, and wherein the turbine comprises an outlet for the expanded supercritical CO.sub.2.

2. The system of claim 1, wherein the expanded supercritical CO.sub.2 is used to heat the fuel and the air stream prior to their respective deliveries to the fuel reactor and the air reactor.

3. The system of claim 2, further comprising: a first conduit in fluid communication with the turbine and configured to receive a first portion of the expanded supercritical CO.sub.2 from the turbine; a second conduit in fluid communication with the turbine and configured to receive a second portion of the expanded supercritical CO.sub.2 from the turbine; an air preheater in fluid communication with the first conduit, an air source for the air stream, and the air reactor, the air preheater being configured to heat the air stream using the energy of the first portion of the expanded supercritical CO.sub.2 prior to delivery of the air stream to the air reactor; and a first fuel preheater in fluid communication with the second conduit, a fuel source for the fuel, and the fuel reactor, the first fuel preheater being configured to heat the fuel using the energy of the second portion of the expanded supercritical CO.sub.2 prior to delivery of the fuel to the fuel reactor, wherein the heating of the air stream in the air preheater and the fuel in the first fuel preheater by the respective portions of expanded supercritical CO.sub.2 results in respective low-pressure streams of CO.sub.2.

4. The system of claim 3, further comprising: a cooler in fluid communication with the air preheater and the first fuel preheater, the cooler being configured to receive the respective low-pressure streams of CO.sub.2 from the air preheater and the first fuel preheater and cool the received low pressure CO.sub.2, and a third conduit in fluid communication with the cooler and the compressor, the third conduit being configured to receive the cooled low-pressure CO.sub.2 and transfer the cooled low-pressure CO.sub.2 to the compressor.

5. The system of claim 3, further comprising a second fuel preheater in fluid communication with the fuel reactor, the first fuel preheater and the first heat exchanger, the second fuel preheater being configured to: receive the fuel delivered from the first fuel preheater and at least a portion of the reformed or combusted fuel from the fuel reactor; and further heat the fuel via energy from the reformed or combusted fuel prior to the delivery of the fuel to the fuel reactor.

6. The system of claim 1, further comprising a solids preheater in fluid communication with the fuel reactor, the solids preheater being configured to receive a portion of the reformed or combusted fuel from the fuel reactor and to heat the oxygen carriers using the energy of the reformed or combusted fuel prior to delivery of the oxygen carriers to the fuel reactor.

7. The system of claim 6, wherein the resulting fuel following reaction in the fuel reactor is a reformed fuel, and wherein the system further comprises: a fuel cooler in fluid communication with the solids preheater and the first heat exchanger, the fuel cooler being configured to receive the reformed fuel from the solids preheater and the first heat exchanger, and to cool the received reformed fuel to about ambient temperature; a second compressor in fluid communication with the fuel cooler, the second compressor being configured to compress the ambient temperature reformed fuel received from the fuel cooler; a combustion chamber in fluid communication with the second compressor and the turbine, the combustion chamber being configured to combust the compressed reformed fuel received from the second compressor to generate a stream of CO.sub.2 and water vapor, and to feed the stream of generated CO.sub.2 and water vapor to the turbine; and a gas processing unit in fluid communication with the turbine and downstream of the fuel cooler, the gas processing unit being configured to separate the stream of generated CO.sub.2 and the water vapor received from the turbine from a low pressure CO.sub.2 stream received from the turbine.

8. The system of claim 1, further comprising at least one controller configured to operate the fuel reactor in a temperature range of about 800° C. to about 1100° C. and configured to operate the air reactor in a temperature range of about 900° C. to about 1200° C.

9. The system of claim 1, wherein the compressor is a multistage compressor having intercooling stages, wherein the intercooling stages enable compression of CO.sub.2 from a low-pressure side of the supercritical CO.sub.2 cycle and transfer of the compressed CO.sub.2 to a high-pressure side of the supercritical CO.sub.2 cycle.

10. A method for generating power via a supercritical CO.sub.2 cycle, wherein the supercritical CO.sub.2 cycle is coupled to a fuel reactor and an air reactor fluidly connected to the fuel reactor, wherein fuel reacts with oxygen carriers in the fuel reactor to form reformed or combusted fuel and reduced oxygen carriers, and wherein the reduced oxygen carriers are oxidized via an air stream in the air reactor to form re-oxidized oxygen carriers and oxygen-depleted air, the method comprising: introducing a CO.sub.2 stream into a compressor, wherein the compressor is configured to increase the pressure of the CO.sub.2 stream to create a supercritical CO.sub.2 stream; transferring both the supercritical CO.sub.2 stream from the compressor and the reformed or combusted fuel from the fuel reactor to a first heat exchanger, which operates to transfer heat from the reformed or combusted fuel to the supercritical CO.sub.2 stream; transferring a) the supercritical CO.sub.2 stream from the first heat exchanger, b) the oxygen-depleted air from the air reactor, and c) a portion of the re-oxidized oxygen carriers from the air reactor to a second heat exchanger, which operates to transfer heat from the oxygen-depleted air and the portion of the re-oxidized oxygen carriers to the supercritical CO.sub.2 stream; and receiving, by a turbine, the supercritical CO.sub.2 stream from the second heat exchanger, wherein the turbine operates under conditions to expand the supercritical CO.sub.2 to generate power.

11. The method of claim 10, further comprising: heating, with the expanded supercritical CO.sub.2, the fuel and the air stream prior to their respective deliveries to the fuel reactor and the air reactor.

12. The method of claim 11, wherein the step of heating comprises: transferring a first portion of the expanded supercritical CO.sub.2 from the turbine to a first conduit; transferring a second portion of the expanded supercritical CO.sub.2 from the turbine to a second conduit; receiving, by an air preheater, the first portion of the expanded supercritical CO.sub.2 from the first conduit; and receiving, by a first fuel preheater, the second portion of the expanded supercritical CO.sub.2 from the second conduit, wherein the air preheater is configured to transfer energy of the first portion of the expanded supercritical CO.sub.2 to the air stream to heat the air stream and wherein the first fuel preheater is configured to transfer energy of the second portion of the expanded supercritical CO.sub.2 to the fuel to heat the fuel, and whereby the transfer of energy from the respective portions of expanded supercritical CO.sub.2 results in respective streams of low pressure CO.sub.2.

13. The method of claim 12, further comprising: receiving, by a cooler, the respective streams of low pressure CO.sub.2 from the air preheater and the first fuel preheater, wherein the cooler is operated at conditions to cool the received low pressure CO.sub.2; transferring the cooled low-pressure CO.sub.2 from the cooler to a third conduit; and transferring the cooled low-pressure CO.sub.2 from the third conduit to the compressor.

14. The method of claim 12, further comprising: transferring the fuel from the first fuel preheater to a second fuel preheater; receiving, by the second fuel preheater, at least a portion of the reformed or combusted fuel from the fuel reactor; and heating the fuel in the second fuel preheater by transferring energy from the reformed or combusted fuel to the fuel.

15. The method of claim 10, further comprising: heating the oxygen carriers via a solids preheater prior to delivery of the oxygen carriers to the fuel reactor; and receiving, by the solids preheater, a portion of the reformed or combusted fuel from the fuel reactor, wherein the solids preheater heats the oxygen carriers by transferring energy of the reformed or combusted fuel to the oxygen carriers.

16. The method of claim 15, wherein the fuel resulting from the reaction in the fuel reactor is a reformed fuel, and wherein the method further comprises: cooling, in a fuel cooler, the reformed fuel received from the solids preheater and first heat exchanger; compressing, in a second compressor, the cooled reformed fuel received from the fuel cooler; combusting, in a combustion chamber, the compressed reformed fuel received from the second compressor to produce a stream of CO.sub.2 and water vapor; feeding the produced stream of CO.sub.2 and water vapor to the turbine; and separating, in a gas processing unit, the stream of CO.sub.2 and water vapor received from the turbine from a low pressure CO.sub.2 stream received from the turbine.

17. The method of claim 10, wherein the fuel comprises a sour gas fuel and the oxygen carriers are calcium-based materials, and wherein the reaction between the sour gas fuel and the calcium-based materials causes at least a portion of sulfur in the sour gas fuel to be removed from the fuel.

18. The method of claim 10, wherein the fuel reactor is operated in a temperature range of about 800° C. to about 1100° C., wherein the air reactor is operated in a temperature range of about 900° C. to about 1200° C.

19. The method of claim 10, wherein the compressor is a multistage compressor that comprises intercooling stages that enable compression of CO.sub.2 from a low-pressure side of the supercritical CO.sub.2 cycle and transfer of the compressed CO.sub.2 to a high-pressure side of the supercritical CO.sub.2 cycle, and wherein the low-pressure side of the supercritical CO.sub.2 cycle is operated in a pressure range of about 45 bar to about 90 bar, and the high-pressure side of the supercritical CO.sub.2 cycle is operated in a pressure range of about 200 bar to about 500 bar.

20. The method of claim 10, wherein the temperature of the supercritical CO.sub.2 received by the turbine is in a range of about 400° C. to about 1000° C.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

(1) FIG. 1 displays a schematic of an exemplary system that includes a supercritical CO.sub.2 cycle coupled to a chemical looping arrangement in accordance with one or more embodiments;

(2) FIG. 2 displays a pressure and temperature phase diagram for CO.sub.2, including the operating ranges for the high- and low-pressure sides of the supercritical CO.sub.2 cycle in accordance with one or more embodiments; and

(3) FIG. 3 displays a schematic of another exemplary system that includes a supercritical CO.sub.2 cycle coupled to a chemical looping arrangement in accordance with one or more embodiments.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THE INVENTION

(4) The present application describes systems and methods for coupling a chemical looping combustion arrangement and a supercritical CO.sub.2 cycle. The present application targets challenges regarding energy conversion efficiency and excessive water usage associated with conventional systems and provides solutions to such technical challenges among others.

(5) In one or more embodiments, the system comprises a chemical looping combustion arrangement that comprises an air reactor and a fuel reactor. The fuel reactor receives fuel from a fuel source and receives oxygen carriers. The fuel reactor is configured to heat the received fuel and oxygen carriers. As a result, the fuel is oxidized (combusted) or reformed, resulting in combusted fuel or reformed fuel, respectively, as well as reduced oxygen carriers. The air reactor receives an air stream from an air source and the reduced oxygen carriers from the fuel reactor. The air reactor is configured to re-oxidize the reduced oxygen carriers via a reaction between the reduced oxygen carriers and the air stream. This reaction also results in an oxygen-depleted air stream. A first portion of the re-oxidized oxygen carriers is then transported back to the fuel reactor for additional reactions.

(6) The system further comprises a compressor that receives a CO.sub.2 stream from a CO.sub.2 source and that is configured to increase the pressure of the CO.sub.2 stream to create a high pressure supercritical CO.sub.2 stream. The supercritical CO.sub.2 stream is transported to a first heat exchanger, where energy from the reformed fuel/combusted fuel stream is used to heat the supercritical CO.sub.2 stream. The supercritical CO.sub.2 stream is then transported to a second heat exchanger, where energy from the oxygen-depleted air stream and a second portion of the re-oxidized oxygen carrier from the air stream is used to further heat the supercritical CO.sub.2 stream. The heated supercritical CO.sub.2 stream is transported from the second heat exchanger to a turbine, where the turbine is configured to expand the supercritical CO.sub.2 stream to generate power. The expanded supercritical CO.sub.2 stream is then used to heat the fuel stream and the air stream prior to their respective deliveries to the fuel reactor and the air reactor.

(7) Thus, the present systems and methods provide a supercritical CO.sub.2 cycle that is integrated with a chemical looping cycle such that the supercritical CO.sub.2 cycle provides heat to pre-heat the incoming streams into the chemical looping cycle, and where the supercritical CO.sub.2 cycle is removing heat from the streams exiting the chemical looping cycle. In other words, in the present system, the hot fluid of a first thermodynamic system (supercritical CO.sub.2 cycle) exchanges heat with the cold side of a second thermodynamic system (chemical looping cycle), while the cold fluid of the first thermodynamic system receives heat from the hot side of the second thermodynamic system.

(8) As such, relative to conventional systems, the present systems and methods 1) maximize synergy between the supercritical CO.sub.2 cycle and the chemical looping combustion cycle; 2) provides higher energy efficiency, 3) provides increased operation flexibility, 4) provides lower capex, and 5) provides increased power output, including for embodiments in which the fuel is a sour gas fuel. Additionally, the present systems and methods results in less water usage than previous systems as CO.sub.2 is used as medium to produce power in the first thermodynamic system rather than water and steam. Further, the increased efficiency of the present systems allows for their usage with power generation plants with CO.sub.2 emissions constraints, for example.

(9) The referenced systems and methods for coupling a chemical looping combustion arrangement and a supercritical CO.sub.2 cycle are now described more fully with reference to the accompanying drawings, in which one or more illustrated embodiments and/or arrangements of the systems and methods are shown. The systems and methods of the present application are not limited in any way to the illustrated embodiment and/or arrangement. It should be understood that the systems and methods as shown in the accompanying figures are merely exemplary of the systems and methods of the present application, which can be embodied in various forms as appreciated by one skilled in the art. Therefore, it is to be understood that any structural and functional details disclosed herein are not to be interpreted as limiting the systems and methods, but rather are provided as a representative embodiment and/or arrangement for teaching one skilled in the art one or more ways to implement the systems and methods.

(10) FIG. 1 displays a diagram of an exemplary system 100 that includes a supercritical CO.sub.2 cycle coupled to a chemical looping arrangement in accordance with one or more embodiments. The system 100 includes a fuel source 102 and a fuel reactor 104 that receives fuel from the fuel source 102 via at least one conduit. In at least one embodiment, the fuel source 102 can be one or more sour gas fields and as such the fuel can be a sour gas fuel comprising high levels of H.sub.2S or acid gas streams exiting acid removal units.

(11) In one or more embodiments, the fuel can be any type of common gaseous fuels (e.g., natural gas, sour gas, acid gas), liquid fuels (e.g., heavy fuel oil, oil residues, tar, crude oil, crude oil byproducts or distillates), or solid fuels (e.g., coal and petroleum coke). In at least one embodiment, the fuels can be fossil fuel based or carbon containing, renewable based fuel such as biomass or bio-fuels, or a combination of fossil fuels and renewable fuels. In at least one embodiment, the fuel can be a synthetic gas issued from reforming or gasification of any type of feedstocks. The fuel can be fed directly to the system, be emulsified or put in slurry. The system can be particularly efficient for difficult to burn fuels or fuels with high sulfur content that require extensive cleaning or operating at lower temperature to mitigate corrosion issues. As shown in FIG. 1, in at least one embodiment the fuel from the fuel source 102 is transferred to the fuel reactor 104 via conduits 106 and 108. In one or more embodiments, the fuel is transferred to at least one fuel preheater before being transferred to the fuel reactor 104 via conduit 108. As shown in the exemplary system 100 of FIG. 1, in at least one embodiment, the fuel is first transferred from the fuel source 102 to a first fuel preheater 110 to heat the fuel. The heated fuel is then transferred from the first fuel preheater 110 to a second fuel preheater 112 via conduit 106 for further heating. After the additionally heating in second fuel preheater 112, the fuel is transferred from the second fuel preheater 112 to the fuel reactor 104 via conduit 108 that is fluidly connected to the fuel reactor 104 via a fuel inlet.

(12) The fuel reactor 104 is also configured to receive oxygen carriers from an oxygen carrier source 114. The oxygen carriers can be transferred from the source 114 to the fuel reactor 104 via conduit 116, which is in fluid connection with an oxygen carrier inlet of the fuel reactor 104. The oxygen carriers are generally solid particles. For instance, in at least one embodiment, the oxygen carriers can be a calcium-based material such as CaCO.sub.3 particles. In one or more embodiments, the oxygen carriers can be CaO or magnesium-based materials or a combination of alkaline earth metals or transition metals such as copper oxides. For sulfur-containing fuels, in one or more embodiments it is preferable to use alkaline earth metals to capture the sulfur in the sulfite and sulfate forms such as CaS and CaSO.sub.4. In one or more embodiments, prior to entry into the fuel reactor, the oxygen carriers are first transferred from the oxygen carrier source 114 to a solids preheater 118 for heating, the solids preheater 118 being in fluid connection with the fuel reactor 104. The heated oxygen carriers can then be transferred from the solids preheater 118 to the fuel reactor via conduit 116.

(13) The fuel reactor 104 is generally defined by a housing that defines a hollow interior for receiving the fuel and the oxygen carriers. The fuel reactor is configured to operate at conditions to oxidize (combust) or reform the fuel and oxygen carriers, thereby the resulting in a combusted fuel stream or a reformed fuel stream, respectively, as well as reduced oxygen carriers. The fuel can be either oxidized (combusted) or reformed via this reactor depending on the temperature of the fuel reactor and the composition of the fuel. In other words, the fuel reactor can operate in either a “reforming” mode to produce a reformed fuel stream or a “combust” mode to produce a combusted fuel stream. For example, in embodiments in which the oxygen carriers comprise CaSO.sub.4, the CaSO.sub.4 oxygen carriers react with the fuel to produce a reformed or combusted fuel stream, CaS (reduced oxygen carriers), and CO.sub.2. In embodiments in which the fuel comprises sulfur compounds such as H.sub.2S (e.g., sour gas fuel) and the oxygen carrier is CaCO.sub.3, at least a portion of the CaCO.sub.3 decomposes into CaO and further reacts with the sulfur components of the fuel to produce CaS as the reduced oxygen carriers.

(14) The reformed fuel stream (or combusted fuel stream) and reduced oxygen carriers are then separated from one another and separately exit the fuel reactor 104. In one or more embodiments, a solid-gas separator, such as a cyclone can be used to separate the reformed (or combusted) fuel stream from the reduced oxygen carriers.

(15) The fuel reactor 104 can further include a controller (not shown) configured to operate the fuel reactor in a particular temperature range. For instance, in one or more embodiments, the controller is configured to operate the fuel reactor in a temperature range of about 800° C. to about 1100° C., or in at least one embodiment, in a temperature range of about 850° C. to about 950° C. With regards to the temperature range of the fuel reactor, the term “about” indicates that the ends of the range can vary by plus or minus 5%.

(16) The system 100 further includes an air source 120 and an air reactor 122 having an inlet that receives an air stream from the air source 120 via conduit 124. The air reactor 122 is generally defined by a housing that defines a hollow interior for receiving the air stream and reduced oxygen carriers from the fuel reactor 104. As shown in FIG. 1, in one or more embodiments the air stream from the air source 120 is transferred to an air preheater 126 before being transferred to the air reactor 122 via conduit 124. The air reactor 122 is also configured to receive reduced oxygen carriers (e.g., CaS) from the fuel reactor 104 via conduit 128.

(17) In the air reactor 122, the air stream oxidizes the reduced oxygen carriers, which results in re-oxidized oxygen carriers and an oxygen-depleted air stream. In embodiments in which the reduced oxygen carriers received from the fuel reactor comprise CaS, the subsequent re-oxidized oxygen carriers comprise CaSO.sub.4. The re-oxidized oxygen carriers and the oxygen-depleted air stream then exit the air reactor 122. The air reactor 122 can further include a controller (not shown) configured to operate the air reactor 122 in a particular temperature range. For instance, in one or more embodiments, the controller is configured to operate the air reactor in a temperature range of about 900° C. to about 1200° C., or in at least one embodiment, in a temperature range of about 1050° C. to about 1150° C. With regards to the temperature range of the air reactor, the term “about” indicates that the ends of the range can vary by plus or minus 5%. In certain embodiments, the same controller that controls the temperature of the air reactor 122 controls the temperature of the fuel reactor 104, while in at least one embodiment the fuel reactor 104 and air reactor 122 can have separate controllers. In a particular implementation in which the fuel reactor 104 and the air reactor 122 have separate controllers, the output for the fuel reactor controller (i.e., change in temperature) can be an input for the air reactor controller and/or the output of the air reactor controller can be an input for the fuel reactor controller. Accordingly, in this implementation, the controllers of the air reactor and fuel reactor can work in tandem such that changes in temperature implemented in one of the reactors can result in a signal being sent to the controller of the other reactor such that a corresponding temperature change (if necessary) can be made in that reactor.

(18) In one or more embodiments, the oxygen-depleted air stream and the re-oxidized oxygen carriers can be separated from one another via a solid-gas separator such as a cyclone, and separately exit the air reactor 122. As shown in FIG. 1, in one or more embodiments, a first portion of the re-oxidized oxygen carriers exit the air reactor 122 via conduit 130, which delivers a first portion of re-oxidized oxygen carriers back to the fuel reactor 104. The re-oxidized oxygen carriers received by the fuel reactor 104 are again included in the reaction with the received fuel. Further, in one or more embodiments, a second portion of the re-oxidized oxygen carriers can exit the air reactor 122 via conduit 132. The oxygen-depleted air stream exits the air reactor 122 via conduit 134.

(19) The air reactor 122 and the fuel reactor 104 are in fluid connection with one another via conduits 128 and 130. Further, the circulation of reduced oxygen carriers and re-oxidized oxygen carriers between the fuel reactor 104 and the air reactor 122 (via conduits 128 and 130, respectively) contribute to temperature management of the fuel reactor 104 and the air reactor 122 as the fuel reactor 104 is an endothermic reactor, and the air reactor 122 is an exothermic reactor.

(20) With continued reference to FIG. 1, the system 100 further comprises a supercritical CO.sub.2 cycle that includes a compressor 136 having an inlet for receiving a CO.sub.2 stream from a CO.sub.2 source 138. The CO.sub.2 source 138 can be used to initially fill the system and provide a CO.sub.2 make-up that would replenish the CO.sub.2 lost through leaks out of the system. The compressor 136 can be configured to increase the pressure of the CO.sub.2 stream to create a high-pressure supercritical CO.sub.2 stream. Supercritical CO.sub.2 is a fluid state of CO.sub.2 in which the CO.sub.2 is at or above its critical temperature (approximately 31° C.) and its critical pressure (approximately 73.8 bar). A pressure and temperature phase diagram for CO.sub.2 is shown at FIG. 2.

(21) In one or more embodiments, the temperature of the CO.sub.2 delivered to the system from the CO.sub.2 source 138 can be at ambient temperature, and therefore above or below the critical temperature of CO.sub.2. When starting to fill the system, the CO.sub.2 delivered to the system from the CO.sub.2 source 138 can be below the critical pressure of CO.sub.2. The pressure of the CO.sub.2 can then be raised above the critical pressure value once the system is fully filled. In one or more embodiments, the in-line make-up of CO.sub.2 can be done at the operating pressure, which can be controlled by an external unit (e.g., a pump, compressor or expansion valve).

(22) In one or more embodiments, the compressor 136 is a multistage compressor with or without intercooling stages. The compressor 136 enables compression of the CO.sub.2 transferring from the low-pressure side of the supercritical CO.sub.2 cycle to the high-pressure side of the supercritical CO.sub.2 cycle. In one or more embodiments, the low-pressure side of the supercritical CO.sub.2 cycle is operated in a pressure range of about 45 bar to about 90 bar, and in at least one embodiment, in a pressure range of about 75 bar to about 80 bar. In one or more embodiments, the high-pressure side of the supercritical CO.sub.2 cycle is operated in a pressure range of about 200 bar to about 500 bar, and in at least one embodiment, in a pressure range of about 300 bar to about 400 bar. The low-pressure side of the supercritical cycle is operated around ambient temperatures, between about −40° C. and about +70° C. The high-pressure side of the supercritical cycle is operated in a temperature range of about 400° C. to about 1200° C. The operating ranges of the high-pressure and low-pressure sides of the supercritical CO.sub.2 cycle are shown in the phase diagram of FIG. 2. With regards to the pressure ranges of the high- and low-pressure sides, the term “about” indicates that the ends of the ranges can vary by plus or minus 5%. In at least one embodiment, the compressor 136 can include a controller (not shown) configured to control the pressure range of the supercritical CO.sub.2 cycle. It should be understood that in one or more embodiments, the system 100 can include one or more sensors for measuring the temperature and pressure of the fluids and/or components of the present system.

(23) In at least one embodiment, the CO.sub.2 compression is done in a first step via a multistage compressor to compress the CO.sub.2 above the CO.sub.2 critical pressure followed by a second step via a dense phase pump to reach the desired supercritical CO.sub.2 pressure. The CO.sub.2 compressor and dense pump can have direct fluid communication or have an intermediate buffer tank to allow for better operability and control.

(24) As mentioned above, the compressor 136 is configured to increase the pressure of the CO.sub.2 stream to create a supercritical CO.sub.2 stream. The compressor 136 is also in fluid communication with a first heat exchanger 140. The supercritical CO.sub.2 stream from the compressor 136 can then be transported to the first heat exchanger 140 via a conduit 142. In the first heat exchanger 140, the supercritical CO.sub.2 stream is heated via heat transferred from the reformed (or combusted) fuel stream. Specifically, the first heat exchanger 140 is also in fluid communication with the fuel reactor 104 via a series of conduits.

(25) As exemplified in the embodiment of FIG. 1, the reformed (or combusted) fuel resulting from the reaction in the fuel reactor exits the fuel reactor via conduit 144 and at least a first portion of the reformed (or combusted) fuel is transferred to conduit 145, which is in fluid communication with the second fuel preheater 112.

(26) More specifically, the first portion reformed (or combusted) fuel is transferred from conduit 144 to the second fuel preheater 112 via conduit 145, and the reformed (or combusted) fuel in the preheater 112 is then used to transfer heat to the fuel stream prior to the fuel stream's entry into the fuel reactor 104. It should be understood that the reformed (or combusted) fuel and the fuel stream are separated within the second fuel preheater 112 (e.g., via a solid wall) such that there is no direct contact between the reformed (or combusted) fuel and the fuel stream.

(27) The reformed (or combusted) fuel is then transferred from the second fuel preheater 112 to the first heat exchanger 140 via conduit 148. In the first heat exchanger 140, the energy of the reformed (or combusted) fuel is transferred to the supercritical CO.sub.2 stream, thereby heating the supercritical CO.sub.2 stream. Again, it should be understood that the reformed (or combusted) fuel and the supercritical CO.sub.2 stream are separated within the first heat exchanger 140 such that there is no direct contact between the reformed (or combusted) fuel and the supercritical CO.sub.2 stream. After transferring heat to the supercritical CO.sub.2 stream, the first portion of reformed (or combusted) fuel exits the first heat exchanger 140 via conduit 150 and exits the system. In one or more embodiments, the first portion of reformed (or combusted) fuel exiting the system via conduit 150 can be further processed for CO.sub.2 removal in instances in which the reformed (or combusted) fuel was the result of complete combustion in the fuel reactor 104. In at least one embodiment, the reformed (or combusted) fuel exiting the system via conduit 150 can be shifted (i.e., shift the CO to CO.sub.2 using steam and producing more hydrogen) and/or purified for hydrogen separation or can be further used in a power generation block to generate steam or power.

(28) In at least one embodiment, a second portion of the reformed (or combusted) fuel is transferred from conduit 144 to a conduit 146, which is in fluid communication with the solids preheater 118. The solids preheater 118 is configured to transfer heat from the second portion of the reformed (or combusted) fuel to the oxygen carriers prior to entry of the oxygen carriers into the fuel reactor 104. In at least one embodiment, the oxygen carriers and the second portion of the reformed (or combusted) fuel are separated within the solids preheater 118 such that there is no direct contact between the reformed (or combusted) fuel and the oxygen carriers. In at least one embodiment, the oxygen carriers and the second portion of the reformed (or combusted) fuel are in intimate contact within the solids preheater 118 such that there is a direct contact between the reformed (or combusted) fuel and the oxygen carriers. In such a configuration, a solid/gas separator (e.g., cyclone) is used to separate the oxygen carrier solid stream from the gaseous reformed (or combusted) fuel stream. After transfer of heat to the oxygen carriers, the second portion of the reformed (or combusted) fuel exit the solids preheater 118 and can be purged from the system 100 via conduit 151. In one or more embodiments, the reformed (or combusted) fuel exiting the system at conduit 151 can be merged with the reformed (or combusted) fuel stream of conduit 150 or can exit the system separately. In either configuration, the exiting reformed (or combusted) fuel from conduit 151 can then be further processed for CO.sub.2 removal in instances in which the reformed (or combusted) fuel was the result of complete combustion in the fuel reactor 104. In at least one embodiment, the reformed (or combusted) fuel exiting the system via conduit 151 can be shifted (i.e., shift the CO to CO.sub.2 using steam and producing more hydrogen) and/or purified for hydrogen separation or can be further used in a power generation block to generate steam or power.

(29) Returning to the supercritical CO.sub.2 cycle, the heated supercritical CO.sub.2 stream exits the first heat exchanger 140 via conduit 152. Conduit 152 is also in fluid communication with a second heat exchanger 154 such that the supercritical CO.sub.2 stream is transferred from conduit 152 to the second heat exchanger 154.

(30) In the second heat exchanger 154, the supercritical CO.sub.2 stream is further heated. The supercritical CO.sub.2 stream receives heat transferred from a second portion of re-oxidized oxygen carriers delivered from the air reactor 122 and/or a stream of oxygen-depleted air delivered from the air reactor 122. As shown in the embodiment of FIG. 1, the oxygen-depleted air stream exits the air reactor 122 via conduit 134, which is in fluid communication with the second heat exchanger 154. Similarly, the second portion of the re-oxidized oxygen carriers exits the air reactor 122 via conduit 132, which is also in fluid communication with the second heat exchanger 154. In the second heat exchanger 154, the energy from the oxygen-depleted air stream and/or the second portion of re-oxidized oxygen carriers is transferred to the supercritical CO.sub.2 stream to further heat the supercritical CO.sub.2 stream. In the second heat exchanger 154, the supercritical CO.sub.2 stream, the oxygen-depleted air stream, and the re-oxidized oxygen carriers can be separated such that there is no direct contact between them. After the heat transfer, the oxygen-depleted air stream exits the second heat exchanger 154 via conduit 156, which directs the oxygen-depleted air stream out of the system 100. Likewise, the second portion of re-oxidized oxygen carriers exits the second heat exchanger 154 via conduit 158, which directs the second portion of re-oxidized oxygen carriers out of the system 100.

(31) As shown in the embodiment of FIG. 1, the second heat exchanger 154 can be single multi-channel heat exchanger with three streams. In at least one embodiment, the second heat exchanger can be two separate heat exchangers operating in parallel: one between the supercritical CO.sub.2 stream and the second portion of re-oxidized oxygen carrier, and another between the supercritical CO.sub.2 stream and the oxygen-depleted air stream.

(32) The heated supercritical CO.sub.2 stream exits the second heat exchanger 154 via conduit 160 which is in fluid communication with a turbine 162. In one or more embodiments, the heated supercritical CO.sub.2 stream exits the second heat exchanger 154 at a temperature in the range of about 400° C. to about 1200° C., and in at least one embodiment, at a temperature in the range of about 550° C. to about 850° C. With regards to the temperature range of the heated supercritical CO.sub.2 stream exiting the heat exchanger 154, the term “about” indicates that the ends of the range can vary by plus or minus 5%. The heated supercritical CO.sub.2 stream enters the turbine 162, and in the turbine 162 the supercritical CO.sub.2 stream is expanded. The expansion of the supercritical CO.sub.2 stream in the turbine 162 generates power that is used to drive the compressor 136. In at least one embodiment, the generated power in the turbine 162 can also be used to generate electricity through an electric generator (not shown). Alternatively or additionally, the generated power in the turbine 162 can be used to generate mechanical power to drive process equipment.

(33) Expansion of the supercritical CO.sub.2 stream and generation of power by the turbine 162 lowers the pressure of the CO.sub.2 stream, and in certain embodiments can lower the pressure of the CO.sub.2 stream below its critical pressure value (approximately 73.8 bar) when ambient temperature allows it (e.g., when ambient temperature is below the CO.sub.2 critical point temperature or when adding external cooling to reduce the low pressure CO.sub.2 stream temperature below the critical point temperature). Otherwise, the low pressure CO.sub.2 stream remains in supercritical conditions. The reduced pressure CO.sub.2 stream exits the turbine 162 via conduit 164. In one or more embodiments, conduit 164 splits into two conduits 166 and 168, such that a first portion of the reduced pressure CO.sub.2 stream enters conduit 166 and a second portion of the reduced pressure CO.sub.2 stream enters conduit 168. Conduit 166 is in fluid communication with the first fuel preheater 110 such that the first portion of the reduced pressure CO.sub.2 stream is used in the first fuel preheater 110 to transfer heat to the fuel prior to entry of the fuel into the fuel reactor 104. Similarly, conduit 168 is in fluid communication with the air preheater 126 such that the second portion of the reduced pressure CO.sub.2 stream is used in the air preheater 126 to transfer heat to the air stream prior to entry of the air into the air reactor. The first portion of the reduced pressure CO.sub.2 stream exits the first fuel preheater 110 via conduit 170 and the second portion of the reduced pressure CO.sub.2 stream exits the air preheater 126 via conduit 172.

(34) Conduits 170 and 172 both feed into conduit 174, such that both portions of the reduced pressure CO.sub.2 stream are transferred into conduit 174. Conduit 174 then transfers the reduced pressure CO.sub.2 stream into a cooler 176. In the cooler 176, the reduced pressure CO.sub.2 stream is cooled to near ambient temperature. The cooled CO.sub.2 stream then exits the cooler 176 via a conduit 178, which is in fluid communication with the compressor 136. Thus, via conduit 178, the cooled CO.sub.2 stream is transferred back to the compressor 136 to complete the supercritical CO.sub.2 cycle. In other words, the cooled CO.sub.2 stream is recycled back to the compressor 136 to continue the supercritical CO.sub.2 cycle.

(35) While the systems and methods of the present application have been described above in reference to FIG. 1, the present systems and methods are not limited to such a configuration. For example, in at least one embodiment the turbine 162 can have a medium pressure CO.sub.2 extraction point. The extracted, medium-pressure CO.sub.2 stream can then be re-heated in one of the air reactor 122 or fuel reactor 104 or one or more of conduits 132, 134, and 144 before its re-introduction into the turbine 162 for higher output. In this configuration, the turbine is considered a turbine with a single-stage re-heat. Other embodiments can include a turbine with double re-heat, in which two CO.sub.2 streams exit the turbine via separate extraction points at two different intermediate pressures. The two CO.sub.2 streams are both re-heated before injection back into the turbine for more power production.

(36) In at least one embodiment, the supercritical CO.sub.2 cycle can include two or three stages in which a re-cycle compressor could be added to the existing CO.sub.2 cycle to improve its efficiency.

(37) In at least one embodiment, the supercritical CO.sub.2 cycle can include a CO.sub.2 compressor coupled directly or via an intermediate vessel tank to a CO.sub.2 dense phase pump allowing for the compression of the CO.sub.2 to high pressure supercritical state.

(38) In one or more embodiments, the supercritical CO.sub.2 cycle can include a regenerator that exchanges heat between the high pressure-low temperature CO.sub.2 stream (conduit 142) and low pressure-high temperature CO.sub.2 stream (conduit 164). In this embodiment, the regenerator is designed to reduce the temperature pinch in the system and help heat exchangers 140 and 154 on one side, and air preheater 126 and first fuel preheater 110 on the other side.

(39) In at least one embodiment, the high temperature CO.sub.2 stream (conduit 164) can exchange heat directly with the fuel reactor 104 through an embedded heat exchanger before feeding the air preheater 126. Similarly, in at least one embodiment, the high-pressure CO.sub.2 stream (conduit 160 and/or conduit 152) can be further heated in the air reactor 122 through a heat exchanger embedded in the air reactor 122.

(40) FIG. 3 discloses a schematic of another embodiment of the exemplary system that includes a supercritical CO.sub.2 cycle coupled to a chemical looping arrangement in accordance with one or more embodiments. As shown in FIG. 3, the system 300 has a similar configuration as compared with system 100 (with a few additional features) and the common features of system 100 and system 300 operate in substantially the same fashion as described above in reference to system 100 (FIG. 1). As such, aspects of the system that are common to systems 100 and 300 are displayed in FIG. 3 with the same numbers that are used to denote them in FIG. 1.

(41) In system 300, the fuel reactor 104 operates in “reforming mode” (i.e., the fuel stream is reformed, not combusted, in the fuel reactor) such that a reformed fuel stream (e.g., synthetic gas stream) is produced. The reformed fuel stream exits the fuel reactor 104 via conduit 144. The reformed fuel stream is then split into two portion that passed through the same routes as shown in FIG. 1 (i.e., via conduits 145 and 146). Specifically, the first portion of the reformed fuel is transferred from conduit 144 to the second fuel preheater 112 via conduit 145, and the reformed fuel in the preheater 112 is then used to transfer heat to the fuel stream prior to the fuel stream's entry into the fuel reactor 104. The reformed fuel is then transferred from the second fuel preheater 112 to the first heat exchanger 140 via conduit 148. In the first heat exchanger 140, the energy of the reformed fuel is transferred to the supercritical CO.sub.2 stream, thereby heating the supercritical CO.sub.2 stream. After transferring heat to the supercritical CO.sub.2 stream, the first portion of reformed fuel exits the first heat exchanger 140 via conduit 150.

(42) Similarly, the second portion of the reformed fuel is transferred from conduit 144 to a conduit 146, which is in fluid communication with the solids preheater 118. The solids preheater 118 is configured to transfer heat from the second portion of the reformed fuel to the oxygen carriers prior to entry of the oxygen carriers into the fuel reactor 104. After transferring heat to the oxygen carriers, the second portion of reformed fuel exits the solid preheater 118 via conduit 151, which then flows into conduit 147.

(43) As such, both portions of reformed fuel transfer heat to other streams after leaving the fuel reactor 104 and are thereby cooled. The conduits 150 and 147 then merge into conduit 149 such that the two cooled streams of reformed fuel are combined back into one stream. Conduit 149 then feeds into a fuel cooler 202, which runs at ambient conditions (similar to cooler 176). The fuel cooler 202 is configured to further cool the combined stream of reformed fuel to about ambient temperature. The reformed fuel at ambient temperature exits fuel cooler 202 via conduit 157 and is fed to a compressor 203, which causes the pressure of the reformed fuel stream to increase.

(44) The reformed fuel stream exits the compressor 203 via conduit 159, which then feeds the reformed fuel stream to a combustion chamber 201. Additional fuel can be supplied to the combustion chamber 201 through supply line 190. The additional fuel supplied through line 190 can be a portion of the fuel provided from fuel source 102 or can be a separate fuel stream. The fuel supplied through line 190 can be a liquid or gas fuel of the type(s) discussed above with regards to the fuel of fuel source 102. Oxygen can be supplied to the combustion chamber 201 via conduit 180. The oxygen supplied to combustion chamber 201 enables oxy-combustion firing of the reformed fuel stream (synthetic gas stream). As such, the combustion of the reformed fuel stream in the combustion chamber 201 results in the generation of CO.sub.2 and water vapor. In one or more configurations, the oxygen delivered to the combustion chamber 201 via conduit 180 can be preheated by transfer of heat from one or both of conduits 156 and 158. In at least one configuration, the oxygen of conduit 180 can be further preheated by a transfer of heat from a conduit stemming off from conduit 134. In one or more embodiments, the combustion chamber 201 is operated in a temperature range of about 1000° C. to about 2000° C. In at least one embodiment, the combustion chamber is operated in a temperature range of about 1300° C. to about 1800° C. In one or more embodiments, the temperature of the combustion chamber 201 is controlled, at least in part, by the flow rate of recycle CO.sub.2 stream 187. In one or more embodiments, the supercritical CO.sub.2 stream of conduit 160 from the second heat exchanger 154 also passes to the combustion chamber 201 and is combusted.

(45) The flue gas (e.g., CO.sub.2 and water vapor) and the supercritical CO.sub.2 stream exit the combustion chamber 201 via conduit 161, which feeds to turbine 162. In the turbine the CO.sub.2 is expanded and its pressure is reduced. The flue gas and resulting reduced pressure CO.sub.2 stream then follow substantially the same route(s) as the reduced pressure CO.sub.2 stream in system 100 of FIG. 1. In particular, at least one portion of the flue gas and the reduced pressure CO.sub.2 stream exits the turbine 162 and is fed to air preheater 126, where it is used to transfer heat to the air stream prior to entry of the air into the air reactor. Similarly, another portion of the flue gas and reduced pressure CO.sub.2 stream exits the turbine 162 and is fed to the first fuel preheater 110, where it is used to transfer heat to the fuel prior to its entry into the fuel reactor. Both portions of the flue gas and reduced pressure CO.sub.2 stream are then re-combined in conduit 174 and transferred to cooler 176 for cooling to near ambient temperature. The cooled flue gas/reduced pressure CO.sub.2 stream then exits the cooler 176 via a conduit 178.

(46) With continued reference to FIG. 3, conduit 178 then feeds the cooled flue gas/reduced pressure CO.sub.2 stream to a gas processing unit 204 that is configured to separate the flue gas (water vapor and CO.sub.2) from the main stream of reduced pressure CO.sub.2. In one or more embodiments, the gas processing unit 204 can be further configured to provide a CO.sub.2 stream of a specified purity for one or more downstream applications (e.g., CO.sub.2 conversion technologies, CO.sub.2 purity requirements, CO.sub.2 sequestration). Off gases and water exit the processing unit 204 via conduits 183 and/or 184. In one or more embodiments, the gas processing unit 204 can be an adsorption-based unit, a cryogenic type unit, or any type of unit that is typically used in oxy-combustion CO.sub.2 capture technologies. The main stream of cooled reduced pressure CO.sub.2 exits the processing unit 204 via conduit 187, which returns it to the compressor 136. The flow rate of the stream of reduced pressure CO.sub.2 in conduit 187 can be regulated to keep the temperature in the combustion chamber 201 within the specified range. Thus, via conduit 187, the reduced pressure CO.sub.2 stream is transferred back to the compressor 136 to complete the supercritical CO.sub.2 cycle. In other words, the reduced pressure CO.sub.2 stream is recycled back to the compressor 136 to continue the supercritical CO.sub.2 cycle.

(47) In one or more embodiments, there is a thermal linkage between conduit 160 and conduit 164, as the temperature of the flue gases exiting the turbine 162 is very high. In at least one embodiment, conduit 164 can have a thermal linkage to transfer heat to a bottoming cycle based on steam generation or supercritical CO.sub.2 to produce power in the combined cycle. In at least one embodiment, conduit 164 can have a thermal language with gas process unit 204.

(48) Thus, in a salient aspect, the present systems and methods provide a supercritical CO.sub.2 cycle that is integrated with a chemical looping cycle such that the supercritical CO.sub.2 cycle provides heat to pre-heat the incoming streams into the chemical looping cycle, and where the supercritical CO.sub.2 cycle is removing heat from the streams exiting the chemical looping cycle. In other words, in the present system, the hot fluid of a first thermodynamic system (supercritical CO.sub.2 cycle) exchanges heat with the cold side of a second thermodynamic system (chemical looping cycle), while the cold fluid of the first thermodynamic system receives heat from the hot side of the second thermodynamic system. While other systems have combined a chemical looping cycle with a supercritical CO.sub.2 cycle, these other systems comprise heat exchangers that are only exchanging heat within the thermodynamic system in which it is located. Accordingly, these other systems do not exchange a significant amount of heat between the two thermodynamic systems (chemical looping cycle and supercritical CO.sub.2 cycle), and moreover, do not exchange a significant amount of heat in both directions between the two thermodynamic systems.

(49) Although much of the foregoing description has been directed to systems and methods for chemical looping and supercritical CO.sub.2 cycles, the system and methods disclosed herein can be similarly deployed and/or implemented in scenarios, situations, and settings far beyond the referenced scenarios. It should be further understood that any such implementation and/or deployment is within the scope of the system and methods described herein.

(50) It is to be further understood that like numerals in the drawings represent like elements through the several figures, and that not all components and/or steps described and illustrated with reference to the figures are required for all embodiments or arrangements. Further, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms ““including,” “comprising,” or “having,” “containing,” “involving,” and variations thereof herein, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

(51) It should be noted that use of ordinal terms such as “first,” “second,” “third,” etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

(52) The subject matter described above is provided by way of illustration only and should not be construed as limiting. Various modifications and changes can be made to the subject matter described herein without following the example embodiments and applications illustrated and described, and without departing from the true spirit and scope of the present invention, which is set forth in the following claims.