SUPERCRITICAL CO2 ENERGY CYCLE WITH DRY REFORMING OF METHANE

Abstract

Power plant with supercritical CO2 cycle, comprising: a combustion chamber (12) configured to combust first and second feed components to produce a gas stream; a turbine (14) configured to be rotated by the gas stream; a compressor (16) configured to receive a first portion of the gas stream from the turbine (14) and supply a first stream of compressed gas to the combustion chamber (12); a booster compressor (18) configured to receive a second portion of the gas stream from the turbine (14) and supply a second stream of compressed gas to the combustion chamber (12); an electric generator (30) configured to be driven by the turbine (14); and a methane reforming reactor (64) configured to dry reform methane to provide the first feedstock; further comprising a heat exchanger (66) fluidly disposed between the methane reforming reactor and the combustion chamber (12), the heat exchanger (66) being configured to receive an input of the fuel at a first inlet and an input of the first input component at a second inlet, and the heat exchanger (66) being configured to bring the fuel and the first input component into thermal communication.

Description

[0001] This document generally relates to, but is not limited to, energy cycles used to convert heat into electrical power. In particular, the present application relates to, but is not limited to, supercritical CO2 energy cycles, in which carbon dioxide (CO2) is used in a supercritical state and the liquid and gas phases cannot be distinguished from each other.

[0002] In a combined cycle gas and steam turbine (GTCC) power plant, a gas turbine engine can be operated to directly generate electricity with the aid of a generator and using shaft power. The hot exhaust gas from the gas turbine engine can also be used to generate steam in a heat recovery steam generator (HRSG), which can be used to rotate a steam turbine shaft to further generate electricity. The working fluid for the GTCC typically comprises air and / or gas (for the pre-cycle) and steam and / or water (for the base cycle), with a gaseous or liquid fuel being combusted in the gas turbine engine.

[0003] As renewable energies gain a foothold in energy generation, other types of energy cycles are also being explored. Supercritical CO2-based energy cycles (sCO2 energy cycles) have the potential to provide greater efficiency in converting heat into electricity, high energy density, and simplified operation compared to conventional energy cycles. Furthermore, sCO2 energy cycles can be operated with small turbomachinery due to high pressures and the higher energy density of CO2 compared to air. These factors could make the cycle attractive to a wide range of applications and stakeholders.

[0004] The sCO2 energy cycle can be integrated into indirectly and directly heated (i.e. fired) applications. The indirectly heated energy cycle is suitable for boiler-type plants where the combustion gases and the circulating working fluid are separate. In the directly heated sCO2 energy cycle, the combustion of fuel (natural gas or syngas (CO and H2)) and oxygen (O2) produces a first stream of flue gas and a second stream of CO2 that mixes with the first stream, with the mixed streams being used as the working fluid to drive the turbine and generate electricity. The directly heated sCO2 energy cycle has two main features: a) the turbine can be operated at a higher turbine inlet temperature (T1t) than in the indirectly heated cycle; b) a high-purity CO2 stream can be produced, which does not require expensive and energy-intensive capture or treatment processes.Separation technologies can be stored.

[0005] US 2016 / 0 010 551 A1 discloses systems and methods enabling power generation using predominantly CO2 as the working fluid. In particular, this document proposes using a portion of the compression heat of a CO2 compressor as additional heat required to increase the overall efficiency of a power generation system and method.

[0006] US 2020 / 0 407 298 A1 discloses a process for producing petrochemical compounds using a hydrocarbon fuel cell and comprises the steps of operating the fuel cell to generate electricity, thermal energy and one or more exhaust gas streams, wherein the one or more exhaust gas streams comprise at least one carbon-containing gas and water, reacting at least a portion of the exhaust gas stream with the reactant stream of natural gas to generate one or more petrochemical streams in a reactor and heating one or more reactants using at least a portion of at least one of the electrical and / or thermal energy.

[0007] The present inventor has recognized, among other things, that the problems to be solved in power plants with a sCO2 energy cycle may generally include the need to improve the efficiency of heat-to-electricity conversion in order to reduce emissions, among other things. A symptom of this problem is the generation of energy cycle byproducts and the inefficient use, or even non-use, of these byproducts.

[0008] The present subject matter can help provide solutions to the problem of inefficient power generation and other problems by improving the thermal efficiency of the directly fired sCO2 energy cycle. In examples, a dry methane reforming (DRM) process can be used to react CO2 with methane, thereby improving the thermal efficiency of an sCO2 energy cycle. The DRM process can convert the CO2 and methane fuel into a synthetic fuel (e.g., syngas) for the sCO2 energy cycle, which can provide a higher energy yield during the combustion process. The DRM process can simultaneously utilize an available heat source, such as free heat from solar power or non-free waste heat from an industrial process, to supplement the DRM process.Thus, the overall efficiency of the sCO2 cycle can be increased by combining DRM with the sCO2 cycle itself and with a low-cost or freely available heat source.

[0009] In one example, a supercritical CO2 cycle power plant may include a combustor configured to combust first and second feedstocks to produce a gas stream; a turbine configured to be rotated by the gas stream; a compressor configured to receive a first portion of the gas stream from the turbine and supply a first stream of compressed gas to the combustor; a booster compressor configured to receive a second portion of the gas stream from the turbine and supply a second stream of compressed gas to the combustor; an electric generator configured to be driven by the turbine; and a methane reforming reactor configured to dry reform methane to provide the first feedstock.

[0010] In another example, a method of operating a supercritical CO2 cycle power plant may include reacting a fuel with CO2 to produce a syngas in a reactor; mixing the syngas with oxygen to perform a combustion process and produce an exhaust gas (e.g., CO2 and steam); rotating a turbine using the exhaust gas; driving an electric generator using the turbine; passing the exhaust gas through a compressor and a booster to produce pressurized gas; and passing the pressurized gas through a two-stage recuperation process to deliver heated and compressed CO2 to the combustor.

[0011] In another example, a method of operating a supercritical CO2 cycle power plant may include operating a supercritical CO2 energy cycle to rotate a turbine; driving an electric generator using the turbine; extracting a CO2 byproduct from the supercritical CO2 energy cycle; reacting a fuel with a portion of the CO2 byproduct to produce a syngas in a dry methane reforming (DRM) reactor; and mixing the syngas with oxygen to perform a combustion process for the supercritical CO2 energy cycle.

[0012] In one example, a supercritical CO2 cycle power plant includes a supercritical CO2 energy cycle configured to generate a gas stream comprising CO2; a turbine configured to be rotated by the gas stream; an electric generator configured to be driven by the turbine; and a methane reforming reactor configured to dry reform methane using CO2 from the gas stream to provide syngas for a combustion process of the supercritical CO2 energy cycle.

[0013] This overview is intended to provide an overview of the subject matter of the present patent application. It is not intended to be an exclusive or exhaustive explanation of the invention. The detailed description serves to provide further information related to the present patent application.

[0014] In other words, the object is achieved by a power plant according to claim 1 or claim 20 and by a method according to claim 9 or 17. The dependent claims relate to further advantageous embodiments of the invention. Fig. Figure 1 is a schematic diagram illustrating a typical supercritical CO2 energy cycle that uses oxygen and natural gas as feedstocks and generates electricity with CO2 as a byproduct. Fig.Figure 2 is a schematic flow diagram illustrating a supercritical CO2 energy cycle with an integrated methane dry reforming reactor for converting CO2 and methane into synthesis gas. Fig. Figure 3 is a schematic diagram showing a graphical representation of the energy level versus temperature for a typical supercritical CO2 energy cycle according to Fig. 1 and for a supercritical CO2 energy cycle with a DRM reactor integrated therein according to Fig. 2 illustrates. Fig. Figure 4 is a line diagram illustrating the steps of methods for operating a supercritical CO2 energy cycle with a DRM reactor integrated therein.

[0015] In the drawings, which are not necessarily to scale, like numbers may describe similar components in different views. Like numbers with different letter suffixes may represent different manifestations of similar components. The drawings generally illustrate, by way of example, various embodiments discussed in this document, but are not limited thereto.

[0016] Fig.1 is a schematic diagram illustrating a supercritical CO2 (sCO2) energy cycle 10. The sCO2 energy cycle may include a combustor 12, a turbine 14, a compressor 16, a booster compressor 18, a high-temperature (HT) recuperator 20, a low-temperature (LT) recuperator 22, and a cooler 24. The combustor 12 may be supplied with oxygen via the oxygen compressor 26, and the combustor 12 may be supplied with natural gas via the fuel compressor 28. As explained in more detail below, oxygen and natural gas may be combusted in the combustor 12 to produce a high-pressure, high-temperature gas to rotate the turbine 14, which may be used to drive the electric generator 30.

[0017] Oxygen and natural gas from the compressors 26 and 28, respectively, can be supplied to the combustion chamber 12. Oxygen and natural gas can be supplied to the compressors 26 and 28 from an external source or from storage containers. The oxygen and natural gas can be combusted, e.g., heated, in the combustion chamber 12 to produce a hot exhaust gas, by means of which the turbine 14 can be driven. The combustion chamber 12 can be configured as a compression-ignition type combustion chamber, which can be operated with a very high temperature of the working medium at the combustion chamber inlet (e.g., ~1000°C). The turbine 14 can be connected to the generator 30 via the shaft 32. Thus, the generator 30 can be driven directly by the turbine 14 and can generate electrical power, for example, for a power grid.

[0018] The turbine 14 may also be connected to the compressor 16 and the booster 18. In examples, the compressor 16 and the booster 18 may be driven directly by the turbine 14 via one or more shafts or shaft systems. After being used to drive the turbine 14, the exhaust gas from the combustor 12 may flow via line 34 through the HT recuperator 20, via line 36 through the LT recuperator 22, and into line 38 to feed the compressor lines 40A and 40B. The exhaust gas may be distributed among lines 40A and 40B to flow separately through the compressor 16 and the booster 18. The exhaust gas from line 40A may flow into the cooler 24, via line 41 into the compressor 16, and then via line 42 into the LT recuperator 22 before entering line 44.The exhaust gas from line 40B can flow into the booster compressor 18 and then via lines 46 and 48 into the high-temperature recuperator 20. Heat can be added to the exhaust gas flowing from line 42 to line 44 using the low-temperature recuperator 22, and heat can be added to the exhaust gas flowing from line 48 to line 50 using the high-temperature recuperator 20. This added heat can improve the efficiency of the sCO2 cycle. The exhaust gas originating from the low-temperature recuperator 22 in line 44 can be recombined with the exhaust gas from line 46 for entry into the high-temperature recuperator 20 via line 48. The heated gas can be recirculated to the combustion chamber 12 via line 50 to be incorporated into the combustion process.

[0019] In the sCO2 energy cycle, a fixed or semi-fixed amount of CO2 is recovered using the energy cycle 10. The combustion of fuel, such as natural gas, can result in CO2, which is introduced into the system. However, excess CO2 can be removed at outlet 54. The CO2 can be removed and stored for other external uses or introduced into a pipeline for transport to other locations to maintain the balance of the energy cycle 10. Excess vapor in the system line 41 can be removed after condensation using the cooler 24 at outlet 52. The cooler 24 can be coupled to a source of cold liquid or cold gas to cool the exhaust gas flowing between lines 40A and 41 and reduce the temperature of the working fluid to a temperature near ambient.In examples, pure or nearly pure CO2 may remain as the working medium after the outlet 52, at which water is removed.

[0020] The configuration of a typical directly fired sCO2 energy cycle as used in Fig. 1, differs from a typical Brayton cycle in the combustion chamber. In the sCO2 energy cycle 10, the fuel is burned with pure oxygen, using a slight excess of oxygen as part of an oxyfuel combustion process. In the Brayton cycle, an excess of air is used as part of the combustion process. As shown in Fig.As shown in Figure 1, to achieve higher efficiency, the waste heat from turbine 14 is recovered using recuperators 20 and 22 to heat gas at the outlet of compressor 16. This two-stage recuperation process and the use of booster compressor 18 are designed to improve the heat transfer profile in recuperators 20 and 22, thereby achieving higher energy cycle efficiency.

[0021] The thermal efficiency of a directly fired sCO2 energy cycle is predicted to reach 64% when the combustor inlet pressure and turbine inlet temperature are 300 bar and 1200°C, respectively.

[0022] The present inventor has recognized that the efficiency of sCO2 energy cycles can be increased using the systems and methods described herein. The present inventor has recognized that a typical sCO2 fuel, such as natural gas, may contain a high proportion of methane, i.e., CH4. The present inventor has also recognized that typical sCO2 energy cycles produce CO2 as a byproduct. The present inventor has combined these features of sCO2 energy cycles to improve the overall efficiency of the system. In particular, the present inventor has integrated a dry methane reforming (DRM) reactor into an sCO2 energy cycle to convert a portion of a natural gas fuel fed to an sCO2 energy cycle into a more energy-rich syngas, using the CO2 byproduct of the sCO2 system as the chemical feedstock.Thus, a more energy-rich fuel can be burned in the combustion chamber 12, increasing the efficiency of the energy cycle 10 and reducing greenhouse gas emissions. Furthermore, the present inventor has recognized that a heat exchanger can be used between the inlets and outlets of the DRM reactor to improve the efficiency of the DRM reaction and a compressor receiving the outlets. Furthermore, the heat required by the DRM reactor can be supplied from an external source, which can provide low-cost or free heat.

[0023] Fig. 2 is a schematic diagram showing the supercritical CO2 energy cycle 10 according to Fig.1 with a DRM system 60 integrated therein, creating a combined energy system 62. The DRM system 60 may include a reactor 64, a heat exchanger 66, a heat source 68, and valves 70A, 70B, and 70C. The oxygen compressor 26 may be connected to the combustion chamber 12 via line 72. The fuel compressor 28 may be connected to the combustion chamber 12 via line 74. The heat exchanger 66 may be connected to the inlet of the fuel compressor 28 via line 76. The DRM reactor 64 may be coupled to the heat exchanger 66 via line 78. The outlet 54 for CO2 may be connected to the heat exchanger 66 via line 78. The heat exchanger 66 may be connected to the DRM reactor 64 via line 80. The fuel source 82 may either be connected to the line 78 via the line 84, or may be connected directly to the line 76 via the line 86.Valve 70C may be disposed in line 78 between outlet 54 and line 84. Valve 70A may be disposed in line 84 between line 78 and fuel source 82. Valve 70B may be disposed in line 86 between fuel source 82 and line 76.

[0024] The fuel source 82 may comprise a source of a fuel that can be at least partially reacted in the DRM reactor 64. In examples, the fuel source 82 may supply natural gas to the DRM reactor 64. Natural gas may consist of a mixture of methane, ethane, propane, and butane, as well as combinations thereof. In some examples, the natural gas may comprise exclusively or predominantly methane or may be processed to comprise exclusively or predominantly (e.g., ~95%) methane, which has the chemical composition CH4. In the DRM reactor 64, methane may be used along with carbon dioxide (CO2) from the outlet 54 to produce syngas, which is a mixture of carbon monoxide (CO) and hydrogen (H2).By burning synthesis gas, more energy can be introduced into the combustion chamber 12 than in the case of conventional natural gas, thereby achieving an overall higher efficiency of the combined energy system 62.

[0025] When the sCO2 energy cycle 10 is operated exclusively, valves 70A and 70C may be closed and valve 70B may be open. In this way, fuel from the fuel source 82 can be supplied directly to the fuel compressor 28, bypassing the DRM reactor 64 and the heat exchanger 66. The energy cycle 10 can be configured to operate in a configuration in which the DRM system 60 is not operating due to maintenance or the heat source 68 is unavailable. The heat source 68 can, for example, comprise a solar energy source that is unavailable due to weather conditions. The heat source 68 can also comprise an industrial process that is temporarily not operating. The heat source 68 is explained in more detail below.

[0026] To operate the sCO2 energy cycle 10 in combination with the DRM reactor 64, valve 70B may be closed and valves 70A and 70C may be open. In this way, the fuel cannot bypass the DRM reactor 64 via line 86. Accordingly, the fuel is supplied to the DRM reactor 64 via line 78. In one example, the fuel is supplied to the DRM reactor 64 at ambient temperature. The fuel is added to a CO2 stream already present in line 78 leading from the outlet 54. The mixture of fuel and CO2 is first passed through the heat exchanger 66 before being introduced into the DRM reactor 64. The heat exchanger 66 may bring the inputs of the DRM reactor 64 into a heat exchange relationship with the outputs of the DRM reactor 64.In examples, the heat exchanger 66 is configured to transfer heat from the outputs of the DRM reactor 64 to the inputs of the DRM reactor 64 to reduce the temperature of the fuel in the line 76, which may, for example, benefit the compression process of the fuel compressor 28. Reducing the operating load of the compressor 28 may increase the overall efficiency of the energy cycle 10. Thus, in various examples, the integration of the heat exchanger 66 into the DRM system 60 may enable efficient integration of the energy cycle 10 into the DRM system 60.

[0027] Once in the DRM reactor, the CO2 and methane components of the natural gas can be reacted with each other according to equation [1]. CH4+CO2↔2CO+2H2:ΔHf0= +247.05 kJ / mol

[0028] Equation [1] shows that under the addition of heat (ΔH f 0) the combination of methane (CH4) and an inert (e.g., non-combustible) component (CO2) can be converted into two combustible components (CO and H2). CO and H2 thus have a higher potential energy as fuel for the combustion chamber 12. If the heat source 68 can be combined with the DRM reactor 64, the overall efficiency of the combined energy system 62 can be improved due to the provision of a more energy-rich fuel.

[0029] To prevent coking, the reaction temperature is typically above 700°C. However, a recent study suggests that low-temperature DRM can be achieved using a plasmonic Ni / Al2O3 photocatalyst and a fixed-bed flow reactor at 200°C. Low-temperature DRM processes may facilitate integration into sCO2 systems as described herein.

[0030] As can be seen from equation [1], the DRM reaction process consumes CO2, thereby reducing greenhouse gas emissions. Equation [1] also suggests that it is a highly endothermic reaction, meaning energy is absorbed. To compensate for the energy required for the DRM reaction, heat source 68 may supply heat to DRM reactor 64 accordingly. Heat source 68 may comprise a heat-releasing industrial process. In examples, heat source 68 may comprise heat from the environment, such as solar thermal heat or geothermal heat. In further examples, heat source 68 may comprise steam from a nearby power plant, such as low-pressure steam or steam from a heat recovery steam generator (HRSG).The transfer of heat from the synthesis gas at the outlet of the DRM reactor 64 on line 78 to the natural gas and CO2 inputs of the DRM reactor by means of the heat exchanger 66 not only reduces the operating load of the compressor 28, but also reduces the amount of heat required from the heat source 68 to drive the reaction.

[0031] In examples, the DRM reactor 64 may comprise part of an industrial process. Such industrial processes may be used, for example, for energy conversions such as Fischer-Tropsch (FT), carbonylation, and hydroformylation, as well as for the synthesis of high-value fuels and chemicals. The DRM reactor 64 may be located upstream of the fuel compressor 28 and may be operated at a pressure close to the pressure of a natural gas pipeline.

[0032] In the combined energy system 62, a certain amount of heat energy is required for the DRM reaction. This endothermic reaction may occur at 200°C, so the external heat source, as explained above with reference to the heat source 68, may be of a low-quality level, e.g., inexpensive or readily available. In examples, the heat exchanger 66 may be configured to heat the DRM reactor 64 to approximately 200°C for the reaction, such as using the aforementioned plasmonic Ni / Al2O3 photocatalyst process. The heat exchanger 66 may be used to increase the temperature of the fuel for the DRM reactor 64 and facilitate this process, thereby reducing the amount of external heat supplied by the heat source 68.

[0033] As previously mentioned, the heat exchanger 66 can simultaneously reduce the temperature of the synthesis gas and unreacted methane, thereby reducing, for example, the energy consumption of the fuel compressor 28. Since, according to equation [1], the volumetric flow rate of fuel increases (due to a lower number of moles of gas on the left than on the right side of the reaction equation), the fuel compressor can consume more energy than the standalone sCO2 energy cycle. The use of the heat exchanger 66 reduces the energy requirements of both the compressor 28 and the heat source 68, thereby synergistically increasing the efficiency of the combined energy system 62.The combustion chamber 12 can be designed to accommodate different fuel properties, such as the combustion of a mixture of unconverted natural gas and synthesis gas compared to pure natural gas for the stand-alone sCO2 energy cycle, as well as different volumetric flow rates. TABLE 1 cases 1 sCO2 cycle 2 sCO2 cycle + DRM Gross energy tax MW 500 500 Efficiency of the sCO2 cycle %, LHV 64 64 Heat input into the combustion chamber MWth, LHV 781.3 781.3 Heat input to natural gas fuel MWth, LHV 781.3 736 Gross overall efficiency %, LHV 64 67.9 Increasing the gross efficiency % points, LHV - 3.9 additional energy of the fuel compressor MW - 3.9 Overall efficiency - free heat %, LHV 64 67.4 Increase in overall efficiency - free heat % points, LHV - 3.4 additional / equivalent energy by Qext MW - 10 Overall efficiency - taking Qext into account %, LHV 64 66 Increasing overall efficiency - taking Qext into account % points, LHV - 2 Performance comparison between sCO2 cycle and sCO2 cycle + DRM with and without free heat

[0034] Table 1 shows calculations for the operation of the energy cycle 10 alone (1) compared to the operation of the energy cycle 10 with a DRM system 60 integrated therein (2). Table 1 shows an equivalent gross energy output for processes (1) and (2), which are operated with the same electrical generator 30. Accordingly, the heat input into the combustion chamber is identical, which is to be expected since both processes use the same components, such as the turbine 14, the compressor 16, the booster compressor 18, and the recuperators 20 and 22. Thus, the efficiency of the sCO2 energy cycle 10 is identical in both processes. However, energy savings are achieved due to the reduced use of natural gas in process (2) with the combined energy system 62.This means that the DRM reactor 64 converts the combination of natural gas and CO2 into a more energy-rich fuel (syngas), and that less natural gas (736 MWth) is used as input to supply the same amount of heat energy (781.3 MWth) to the combustor 12. Furthermore, Table 1 shows that the theoretical process efficiency decreases from 67.9% to 67.4% because process (2) involves an increase in compressor energy consumption of 3.9 MW. As described herein, the use of heat exchanger 66 reduces compressor energy consumption. If Qext is freely available as waste heat from another industrial process or from solar energy, the combined heat and power system according to process (2) shows an increase in overall efficiency of 3.4 percentage points, LHV.However, if Qext is not freely available and the costs of external heat, such as heat source 68, are taken into account, the overall efficiency increases by only 2 percentage points, LHV. In other words, Table 1 shows that Case 2 is significantly more efficient than Case 1, and that the overall efficiency increases by 3.4 percentage points (the load from Qext is not taken into account) and 2.0 percentage points (the load from Qext is taken into account).

[0035] Note that the calculations for Table 1 are based on calculations for the DRM process, which show that, in one example, 45.2 MWth of external heat energy is required for the DRM reaction, corresponding to 6.1% of the natural gas heat input. These calculations are based on the following assumptions: 1) a typical sCO2 energy cycle has a gross energy output of 500 MW and an efficiency of 64%; 2) the conversion rate of CH4 within the DRM reactor is 20%; and 3) the natural gas used as fuel is 100% CH4.

[0036] Fig.Figure 3 is a schematic diagram illustrating a graph 100 of the energy level (A) as a function of temperature (t) for a supercritical CO2 energy cycle 10 and for a supercritical CO2 energy cycle 10 with a DRM reactor 64 integrated therein. The x-axis of the graph 100 indicates the temperature (t) in degrees Celsius. The y-axis of the graph 100 indicates the energy level (A).

[0037] From an exergy analysis perspective, a gas turbine (GT) combustor typically results in the highest exergy destruction. Minimizing exergy destruction in a GT combustor offers the greatest potential for performance improvement. The higher efficiency of Case 2 can be reasonably explained using a cascade utilization principle with a combination of chemical and physical exergy.

[0038] In Fig.3, the Δt coordinates represent the energy level and temperature, respectively. The area above the Carnot efficiency curve (ηC) 102 illustrates the chemical exergy, while the area below shows the physical exergy. The cascade utilization of physical exergy is achieved by optimizing the sCO2 energy cycle 10 based on the thermal energy levels. Regarding the chemical exergy of hydrocarbon fuels during combustion, their energy levels (Δf) could be as high as 1.0 (case 1), while the energy level of syngas fuel (Δsyn) has a value of 0.83 to 0.9 (case 2) and depends on the composition of the syngas. Accordingly, it is possible to effectively utilize the chemical exergy of fuels with different energy levels, similar to the cascade utilization of physical energy in the energy cycle.

[0039] The chemical exergy of hydrocarbon fuels is traditionally released through direct combustion and utilized as a form of thermal exergy. Consequently, the higher energy level of hydrocarbon fuels Af is immediately reduced to the energy level of thermal energy Ath, resulting in greater exergy destruction during fuel combustion (Af - Ath) than in Case 1.

[0040] Alternatively, the chemical exergy difference between Af and Asyn is used to first convert methane fuel into syngas, followed by combustion of the syngas (indirect fuel combustion), releasing the chemical exergy Asyn to the thermal energy level of Ath. The energy level reduction from chemical energy to thermal energy is significantly smaller (Asyn - Ath) than in Case 2. In the examples, only 20% of the methane is converted to syngas in the DRM reactor 64 (as explained in Section 2.2), so the reduction in exergy loss refers to this portion of the fuel.

[0041] According to Fig.3, it should also be noted that in Case 2, both the fuel energy Qf and the external heat energy Qext are supplied to the combustion chamber. Due to the cascade utilization of the fuel's chemical exergy, the external heat energy Qext is increased from the lower value AQext (0.22) to the higher energy level Asyn (0.83-0.9). This leads to a reduction in fuel consumption, resulting in a significant improvement in the overall efficiency for Case 2.

[0042] In summary, Fig.3, that low-grade heat according to point 104 has a lower energy level (AQext = 0.22), while pure methane fuel according to point 106 has the highest energy level (Af = ~1.0) and syngas has a reduced energy level (Asyn = 0.83 to 0.9). Exergy is lost during the combustion of any type of fuel in combustion chamber 12. Thus, during the combustion of methane fuel (Af) in combustion chamber 12, point 106 drops to point 110 (Ath). Meanwhile, during the combustion of syngas (Asyn) in combustion chamber 12, point 108 drops to point 110 (Ath). Thus, the exergy loss when decreasing from point 108 to point 110 is lower than when decreasing from point 106 to point 110, indicating that the combustion of syngas is more effectively converted into usable energy in case 2.

[0043] Fig.4 is a line diagram illustrating the steps of a method 200 for operating the combined energy system 62 having a supercritical CO2 energy cycle 10 and a DRM system 60 integrated therein according to the present disclosure.

[0044] In step 202, CO2 may be provided as an inventory component for a DRM reaction process. As explained below, the CO2 may be supplied using method 200.

[0045] In step 204, fuel may be provided as an inventory component for the DRM reaction process. The fuel, which may include natural gas, may be supplied from an external source, such as a pipeline or storage tanks. The CO2 from step 202 may be added to the fuel from step 204 for mixing in the DRM reaction process.

[0046] In step 206, heat may be supplied to the DRM reactor 64. As explained above, this heat, e.g., Qext, may be provided by heat source 68, where heat source 68 may comprise free energy, such as solar energy, or non-free energy, such as heat from an industrial process or energy system.

[0047] In step 208, the CO2 and fuel mixture from steps 202 and 204 and the heat from step 206 may be combined to perform a DRM process in the DRM reactor 64 to produce synthesis gas (CO and H2) and methane (unreacted fuel).

[0048] In step 210, the outputs of the DRM reactor 64, i.e., synthesis gas and methane, are cooled in the heat exchanger 66, thereby reducing the compression work of the fuel compressor 28. At the same time, the CO2 and fuel mixture from steps 202 and 204 can be heated in the heat exchanger 66 before entering the DRM reactor 64, thereby facilitating efficient operation of the DRM reactor 64 and reducing the external heat quantity Qext required to drive the DRM reaction. Synthesis gas, methane, and CO2 are then fed to the combustion chamber 12. The fuel compressor 28 can be used to supply fuel to the combustion chamber 12 at a pressure desired for combustion.

[0049] In step 212, oxygen (O2) may be supplied to the combustion chamber 12, along with the fuel, for a combustion process. The oxygen may be supplied from an external source, such as a pipeline or storage vessel. The oxygen may be compressed using the oxygen compressor 26 to be supplied to the combustion chamber 12 at a pressure desired for combustion.

[0050] In step 214, the syngas, methane, and oxygen may be combusted in the combustion chamber 12, generating an exhaust gas. The combustion of syngas and methane may benefit from the fact that more energy is introduced into the combustion chamber during the DRM reaction than when natural gas is burned alone, thereby improving the overall efficiency of the sCO2 energy cycle 10.

[0051] In step 216, high-pressure, high-temperature gas, primarily comprising CO2 and steam, may be used to rotate turbine 14. The rotation of turbine 14 may be used to operate a generator (see step 230), compressor 16, and booster compressor 18.

[0052] In step 218, the exhaust gas may be passed through a first recuperator. In one example, the first recuperator may comprise a high-temperature recuperator 20. The first recuperator may supply heat to the operating fluid of the energy cycle 10 (e.g., CO2) entering the combustion chamber 12.

[0053] In step 220, the exhaust gas may be passed through a second recuperator. In one example, the second recuperator may comprise a low-temperature recuperator 22. The second recuperator may supply heat to the operating fluid of the energy cycle 10 (e.g., CO2) entering the first (high-temperature) recuperator 20.

[0054] The recuperator 20 can be referred to as a “high-temperature recuperator” because the exhaust gas passing through the recuperator 20 originates directly from the turbine 14 and is therefore hotter than the exhaust gas entering the recuperator 22, the “low-temperature recuperator”.

[0055] In step 222, a first portion of the exhaust gas exiting the recuperator 22 may enter the cooler 24. The cooler 24 may be used to condense steam present in the working medium of the energy circuit 10 into water.

[0056] In step 224, the first portion of the exhaust gas exiting the cooler 24 may enter the compressor 16. The first portion of the exhaust gas exiting the compressor 16 may enter the recuperator 22 before passing through the recuperator 20, which is to be placed in thermal communication with the original exhaust gas stream from step 218. The recuperators 22 and 20 may heat the first portion of the exhaust gas before it enters the combustion chamber 12.

[0057] In step 226, a second portion of the exhaust gas exiting the recuperator 22 may enter the booster compressor 18. The second portion of the exhaust gas exiting the recuperator 22 and the booster compressor 18 may enter the high-temperature recuperator 20, which is to be brought into thermal communication with the original exhaust gas stream from step 218. The recuperator 20 may heat the second portion of the exhaust gas before it enters the combustion chamber 12.

[0058] In step 228, water, e.g., liquid H2O, can be extracted from the first portion of the exhaust gas for external use. In one application example, the H2O can be stored. Removing water from the working fluid can make it possible to obtain pure or nearly pure CO2 in step 229.

[0059] In step 229, CO2 may be extracted from the first portion of the exhaust gas for use in an external application. The external application may include simple storage for use in another process at the site of the energy cycle 10, or may include storage in containers for transport to another location. In examples, the application may include direct use in another application without storage, such as in an industrial process. In one example, the CO2 may be used in a tertiary oil recovery (EOR) process. However, a portion of the CO2 may be recycled to the process 200 for use in the DRM reactor in step 202.

[0060] In step 230, the generator 30 can be driven by the turbine 14 via the shaft 32. The generator 30 can be used to generate electrical power, which can be fed into a power grid, for example.

[0061] The present disclosure demonstrates that the combined energy system 62, e.g., the combination of the sCO2 energy cycle 10 and the DRM system 60, can achieve a significant performance improvement compared to operating an sCO2 energy cycle alone. The overall efficiency can be increased by 3.4 percentage points (Qext load not considered) or by 2.0 percentage points (Qext load considered).

[0062] The performance calculation of Fig.2 is based on: a) an sCO2 energy cycle efficiency of 64% at 1200°C T1t; b) a CH4 conversion rate within the DRM reactor of 20%. However, the sCO2 energy cycle efficiency can be further increased at higher T1t. The CH4 conversion rate within the DRM reactor could be higher if a new catalyst were developed. Based on the calculations, the efficiency increase could be 5.7% and 3.6%, respectively, assuming an sCO2 energy cycle efficiency of 70% and a CH4 conversion rate of 30%. Accordingly, even greater potential for power improvement can be predicted for the application of this new concept.

[0063] The study is based on a typical sCO2 energy cycle system, as presented herein. It is understood that there are a variety of energy cycle systems using CO2 as a working fluid (supercritical CO2 cycles or subcritical CO2 cycles) to which the proposed integration concept should be applicable.

[0064] The foregoing detailed description includes references to the accompanying drawings, which form a part of this detailed description. The drawings illustrate specific embodiments in which the invention may be practiced. These embodiments are also referred to herein as "examples." Such examples may include elements other than those shown or described. However, the present inventor also contemplates examples in which only the elements shown or described are provided.Furthermore, the present inventor also contemplates examples in which any combination or permutation of the elements shown or described (or one or more aspects thereof) is used, either with respect to a particular example (or one or more aspects thereof) or with respect to other examples shown or described herein (or one or more aspects thereof).

[0065] In case of conflicting usages between this document and the documents incorporated by reference, the usage in this document shall prevail.

[0066] Throughout this document, the term "a / an" is used, as is customary in patent documents, to include one or more than one object, regardless of other cases or the use of "at least one" or "one or more." Throughout this document, the term "or" is used to denote a non-exclusive "or," such that "A or B" includes "A but not B," "B but not A," and "A and B," unless otherwise specified. Throughout this document, the terms "including" and "in which" are used as simple English equivalents of the respective terms "comprising" and "wherein."In the following claims, the terms "including" and "comprising" are to be interpreted broadly; this means that a system, apparatus, product, composition, formulation, or method that includes elements in addition to those listed after such a term in a claim is still considered to fall within the scope of the claim. Furthermore, the terms "first," "second," "third," etc., are used in the following claims merely as identifiers and are not intended to impose numerical requirements on their objects.

[0067] The foregoing description is illustrative and not limiting. For example, the examples described above (or one or more aspects thereof) may be used in combination with one another. Other embodiments may also be utilized, as would be apparent to one skilled in the art upon reviewing the foregoing description. The Abstract is provided in accordance with 37 CFR §1.72(b) to enable the reader to quickly appreciate the nature of the technical disclosure. It is presented with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Further, in the foregoing Detailed Description, various features may be grouped together for the purpose of streamlining the disclosure. This should not be construed to imply that an unclaimed disclosed feature is essential to a claim.Rather, inventive subject matter may reside in fewer than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated by reference as examples or embodiments of the detailed description, each claim being considered to represent a separate embodiment, and it is contemplated that such embodiments may be combined in various combinations or permutations. The scope of the invention should be determined by reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

[1] Power plant with supercritical CO2 cycle, comprising: a combustion chamber (12) configured to combust first and second feed components to produce a gas stream; a turbine (14) configured to be rotated by the gas stream; a compressor (16) configured to receive a first portion of the gas stream from the turbine (14) and supply a first stream of compressed gas to the combustion chamber (12); a booster compressor (18) configured to receive a second portion of the gas stream from the turbine (14) and supply a second stream of compressed gas to the combustion chamber (12); an electric generator (30) configured to be driven by the turbine (14); and a methane reforming reactor (64) configured to dry reform methane to provide the first feedstock; further comprising a heat exchanger (66) fluidly disposed between the methane reforming reactor and the combustion chamber (12), the heat exchanger (66) being configured to receive an input of the fuel at a first inlet and an input of the first input component at a second inlet, and the heat exchanger (66) being configured to bring the fuel and the first input component into thermal communication. [2] A supercritical CO2 cycle power plant according to claim 1, wherein the heat exchanger (66) transfers heat of the first feed component to the fuel, thereby decreasing the temperature of the first feed component and increasing the temperature of the fuel. [3] A supercritical CO2 cycle power plant according to claim 1, further comprising: an outlet (52, 54) for removing CO2 from the power plant; and a flow line (78) connecting the outlet (52, 54) to the first inlet of the heat exchanger (66). [4] A supercritical CO2 cycle power plant according to claim 3, wherein the fuel comprises natural gas and the methane reforming reactor (64) is configured to produce the first feedstock comprising CO and H2 from CO2 and natural gas. [5] The supercritical CO2 cycle power plant of claim 1, further comprising a heat source (68) configured to supply heat to the methane reforming reactor (64). [6] A supercritical CO2 cycle power plant according to claim 5, wherein the heat source (68) comprises heat from an industrial process or steam from a power plant. [7] A supercritical CO2 cycle power plant according to claim 1, further comprising: a first recuperator (20) configured to exchange heat between the gas stream and the second stream of compressed gas; and a second recuperator (22) configured to exchange heat between the gas stream and a recombination of the first stream of compressed gas and the second stream of compressed gas. [8] A supercritical CO2 cycle power plant according to claim 1, further comprising: a cooler (24) configured to cool the first portion of the gas stream; and an outlet (52, 54) for removing separated water from the power plant downstream of the cooler (24). [9] A method for operating a power plant with a supercritical CO2 cycle, the method comprising: reacting a fuel with CO2 to produce a synthesis gas in a reactor (64); mixing the synthesis gas with oxygen to carry out a combustion process and produce an exhaust gas; rotating a turbine (14) using the exhaust gas; driving an electric generator (30) by means of the turbine (14); passing the exhaust gas through a compressor (16) and a booster compressor (18) to produce pressurized gas; and passing the pressurised gas through a two-stage recuperation process to supply heated and compressed CO2 to the combustion chamber (12); further comprising exchanging heat between the synthesis gas and the fuel upstream of the combustion chamber (12). [10] The method of claim 9, further comprising returning a portion of the CO2 from the exhaust gas to the reactor (64). [11] A method according to claim 9, wherein the fuel is heated using the synthesis gas. [12] The method of claim 9, further comprising supplying heat to the reactor (64) from an external source. [13] A method according to claim 12, wherein the external source comprises heat from an industrial process or steam from a power plant. [14] A method according to claim 9, wherein the two-stage recuperation process comprises: a first recuperator (20) configured to exchange heat between the exhaust gas and a portion of the pressurized gas; and a second recuperator (22) configured to exchange heat between the exhaust gas and the total pressurized gas. [15] The method of claim 9, further comprising bypassing the reactor (64) with the fuel introduced into the combustion chamber (12). [16] The method of claim 9, further comprising: removing part of the CO2 from the exhaust gas of the energy cycle (10); and condensing moisture from the exhaust gas to separate water from the energy cycle (10). [17] A method for operating a power plant with a supercritical CO2 cycle, the method comprising: operating a supercritical CO2 energy cycle to rotate a turbine (14); driving an electric generator (30) by means of the turbine (14); the removal of a CO2 by-product from the supercritical CO2 energy cycle; reacting a fuel with a portion of the CO2 by-product to produce a synthesis gas in a dry methane reforming (DRM) reactor (64); and mixing the synthesis gas with oxygen to carry out a combustion process for the supercritical CO2 energy cycle further comprising the exchange of heat between the synthesis gas and the fuel before the combustion process. [18] A method according to claim 17, wherein heat is transferred from the synthesis gas to the fuel, thereby reducing the temperature of the synthesis gas and increasing the temperature of the fuel. [19] The method of claim 17, further comprising supplying heat to the DRM reactor (64) from an external source. [20] Power plant with supercritical CO2 cycle, comprising: a supercritical CO2 energy cycle configured to produce a gas stream comprising CO2; a turbine (14) configured to be rotated by the gas stream; an electric generator (30) configured to be driven by the turbine (14); and a methane reforming reactor (64) configured to dry reform methane using CO2 from the gas stream to provide synthesis gas for a combustion process of the supercritical CO2 energy cycle; furthermore, the exchange of heat between the synthesis gas and the methane before the combustion process. [21] The power plant of claim 20, further comprising supplying heat to the methane reforming reactor (64) from an external source.

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