Natural gas-based combined hydrogen and power production (CHEP) system and method with renewable energy integration

Abstract

A method and system for integrating renewable power with a natural gas hydrogen production plant is provided. An exemplary method includes generating electricity and a reformed hydrogen stream in a solid oxide fuel cell (SOFC) stack and supplying the power to an electrolyzer to generate an electrolytic hydrogen stream. When renewable energy is available, a second electrical power stream is generated at the renewable energy facility and supplied to the electrolyzer to increase production of the electrolytic hydrogen stream.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Patent Application No. 17 / 894,720, filed August 24, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to systems and methods for integrating renewable energy sources with combined hydrogen and power production (CHEP) utilizing natural gas. [Background technology]

[0003] The amount of carbon dioxide (CO2) in the atmosphere is steadily increasing, which is causing environmental problems such as climate change and ocean acidification. Carbon dioxide alone accounts for more than 75% of greenhouse gas emissions. To mitigate this, scientific research is focusing on capturing and converting CO2 from industry.

[0004] Hydrogen is a well-established and growing global business. Currently, approximately 70 million tons of hydrogen are produced annually (4.5 million barrels of oil equivalent per day, MMboed). The chemical and petroleum refining industries are the largest producers and consumers of hydrogen, controlling more than 90% of global hydrogen demand. With fuel cell electric vehicles likely to soon become commercially viable, hydrogen demand for transportation may surpass the chemical and petroleum refining industries. Hydrogen use is also expected to increase in power generation, industry, and building heat and power. Many companies and countries are pursuing the expansion of hydrogen production and use to establish robust and commercially viable hydrogen supply chains, for example, by creating hydrogen markets.

[0005] Furthermore, with the potential to reduce CO2 emissions by 80 gigatons by 2050, the use of hydrogen has significantly increased the likelihood of achieving net-zero emissions. To achieve this goal, both low-carbon hydrogen, known as blue hydrogen, and renewable hydrogen, known as green hydrogen, are needed, with the former playing a leading role in the short to medium term until renewable hydrogen becomes cost-competitive. A clear, integrated technology concept that can maximize the benefits of low-carbon and green hydrogen production methods would enable the acceleration of hydrogen use as a viable decarbonization energy vector. However, renewable energy is intermittent, requires electricity and hydrogen storage capacity, and integration is complex. Summary of the Invention

[0006] Embodiments described herein provide a method for integrating renewable electrical power with a natural gas hydrogen production plant. The method includes generating electrical power and a reformed hydrogen stream in a solid oxide fuel cell (SOFC) stack and supplying the electrical power to an electrolyzer to produce an electrolytic hydrogen stream. When renewable energy is available, a second electrical power stream is generated at the renewable energy facility and supplied to the electrolyzer to increase production of the electrolytic hydrogen stream.

[0007] Another embodiment described herein provides an integrated hydrogen production system. The integrated hydrogen production system includes a solid oxide fuel cell (SOFC), at least a portion of which is operable as a solid oxide electrolysis cell (SOEC), and an electrolyzer electrically coupled to a power supply line from the SOFC. A carbon dioxide capture system is fluidly coupled to an exhaust line from the SOFC. A steam source is fluidly coupled to the SOFC. A hydrocarbon source is fluidly coupled to the SOFC to provide a gaseous hydrocarbon feed to the SOFC, and a renewable energy source is coupled to the electrolyzer to a power supply line from the renewable energy source. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of a solid oxide fuel cell (SOFC) used to provide hydrogen and electricity. [Figure 2] FIG. 1 is a schematic diagram of an integrated hydrogen production system during normal operation. [Figure 3] FIG. 1 is a schematic diagram of an integrated hydrogen production system operating on low renewable energy. [Figure 4] FIG. 1 is a schematic diagram of an integrated hydrogen production system utilizing surplus renewable electricity. [Figure 5] FIG. 1 is a schematic diagram of an integrated hydrogen production system utilizing excess renewable electricity. [Figure 6] FIG. 1 is a schematic diagram of an integrated hydrogen production system that switches between operating modes based on renewable energy availability. [Figure 7] FIG. 1 is a process flow diagram of a method for integrating energy flows from renewable energy sources and solid oxide fuel cells. DETAILED DESCRIPTION OF THE INVENTION

[0009] To overcome the intermittent supply of renewable power sources for green hydrogen production, natural gas-based combined hydrogen and electricity production (CHEP) systems employing high-temperature and intermediate-temperature fuel cell technology are integrated with water electrolyzers. Electrolyzers typically have low utilization rates for hydrogen production due to the intermittent nature of renewable power. To ensure consistent hydrogen production, expensive batteries or hydrogen storage and large-scale renewable power generation capacity are required. CHEPs using high-temperature fuel cell technology, such as solid oxide fuel cells (SOFCs), or intermediate-temperature fuel cell technology, such as molten carbonate fuel cells (MCFCs), can simultaneously produce hydrogen and electricity. These fuel cells have the ability to rapidly vary the hydrogen and electricity production ratio. CHEP facilities can be configured to capture carbon dioxide formed from hydrocarbon feedstocks. Coupling a CHEP with a renewable-power-based electrolyzer allows the electrolyzer to operate continuously with the power provided by the CHEP when renewable power availability is limited, such as at night or when wind is insufficient. Additionally, the solid oxide fuel cell unit or module can be operated in an electrolysis mode utilizing renewable energy sources to produce additional hydrogen.

[0010] "Integrating CHEP with renewable energy plants reduces the need for hydrogen and electricity storage and extends the life of electrolyzers by eliminating routine shutdowns. Furthermore, hydrogen production efficiency can be matched to end-user demand, and CHEP efficiency can be increased by mixing oxygen from the electrolyzer with supply air. Thus, the system can supply hydrogen to applications such as hydrogen fuel cell vehicles, utilizing both renewable and non-renewable power sources, with CO2 capture capability."

[0011] FIG. 1 is a schematic diagram of a solid oxide fuel cell (SOFC) 100 in which electrochemical reactions take place at the interface 102 between an anode 104 and an SO electrolyte 106, and at the interface 102 between the SO electrolyte 106 and a cathode 108 to produce electricity.

[0012] In various embodiments, the SO electrolyte is yttria-stabilized zirconia (YSZ), CeO, or other types of oxygen-ion conductors. In contrast to proton exchange membrane fuel cells, which conduct hydrogen cations (protons) from the anode to the cathode through a polymer electrolyte, SOFCs use a solid oxide (SO) electrolyte to conduct oxygen anions from the cathode to the anode. As used herein, the anode 104, SO electrolyte 106, and cathode 108, along with any catalyst layers, form an electrode assembly (EA) 110 supported within a housing 112. The EA 110 forms one unit within a stack in the SOFC 100. For example, the stack can include 10 electrode assemblies, 100 electrode assemblies, or more. As shown in FIG. 1, the housing 112 isolates fluid flow to the EA 110, allowing individual electrode assemblies to be inverted for use as solid oxide electrolytic cells (SOECs).

[0013] An inlet in the housing 112 is used to introduce an oxidizing gas 114, such as oxygen 116, to the cathode 108. In some embodiments, oxygen 116 is supplied to the fuel cell 100 as the oxidizing gas 114 from an electrolyzer. The oxygen 116 reacts with electrons at the cathode 108 to form oxide ions, which are conducted through the SO electrolyte 106 to the anode 104. The half-reaction at the cathode 108 is as follows:

[0014] [ka]

[0015] Excess oxidizing gas 114, which may include an inert gas such as nitrogen, exits housing 112 through an outlet as spent oxidizer stream 118.

[0016] Another inlet in the housing 112 is used to supply fuel 120, particularly fuel 120 such as hydrogen, light hydrocarbons, or syngas, to the anode 104. Depending on the fuel used, a reforming reaction may occur at the anode 104. This reaction may be facilitated by a catalyst 121 disposed on the surface of the anode. The catalyst 121 may include, among other things, a nickel reforming catalyst.

[0017] As the fuel, i.e., the reformate, passes through the anode 104, it reacts with oxygen ions from the SO electrolyte 106, releasing electrons. If the fuel is a hydrocarbon, it is reformed to synthesis gas containing carbon monoxide 122 and hydrogen 124. In this example, the half-reactions at the anode 104 are as follows:

[0018] [ka]

[0019] The water vapor 126 and carbon dioxide 128 formed at the cathode 108 exit the housing 112 through an outlet. Electricity 130 is supplied to the power and electrolyzer. When the fuel 120 contains only hydrogen 124, only the first half-reaction is relevant. In embodiments where the SOFC 100 is used as a combined hydrogen and power plant (CHEP), the fuel 120 is introduced in excess with the water vapor 126 at the inlet.

[0020] Thus, in some embodiments, the outlet from the anode 104 includes four gases: carbon monoxide 122, hydrogen 124, water vapor 126, and carbon dioxide 128. As described in more detail with respect to Figure 2, the hydrogen 124 is separated to form a product stream. The carbon monoxide 122 can be catalytically converted to carbon dioxide 128, and the carbon dioxide 128 can be recovered for sale or reuse. Because of the recovery of the carbon dioxide 128, the hydrogen 124 is referred to as "blue hydrogen" or low-carbon hydrogen.

[0021] The steam 126 and spent oxidant stream 118 remove some of the heat generated in the SOFC 100, and in some embodiments, the housing includes a cooling system 132 for removing the heat, such as a steam generating coil, an oil cooling coil, etc. Although not shown, in some embodiments, the cooling system 132 includes lines or coils that contact the EA 110 to remove the heat.

[0022] When SOFC100 is used in reversible operation as an SOFC electrolysis cell (SOEC), heat generated during operation as an SOFC can be stored for use during electrolysis. For example, in one embodiment, heat removed by cooling system 132 during operation as SOFC100 is stored in a reservoir as molten salt, which is returned to provide heat during the endothermic electrolysis process. In some embodiments, the heat generated by SOFC100 is utilized in the process, for example, to generate electricity through a Stirling engine or other energy recovery device.

[0023] FIG. 2 is a schematic diagram 200 of an integrated hydrogen production system during normal operation. Similar numbered items are present as described with respect to FIG. 1. The CHEP 202 includes the SOFC 100, as described with respect to FIG. 1. In this embodiment, the CHEP 202 produces captured carbon dioxide 204. As described with respect to FIG. 1, carbon monoxide present in the exhaust stream from the SOFC 100 along with the carbon dioxide can be catalytically converted to carbon dioxide. The carbon dioxide can then be separated from the hydrogen, for example, by a membrane separator, an amine separator, or a cryogenic separator, among others. The captured carbon dioxide 204 can then be supplied to a pipeline as a product stream, for example, for use in enhanced oil recovery, sequestration, or chemical processes, among others. The separated hydrogen can be dried and supplied as blue hydrogen 206, for example, to a product stream pipeline, storage tank, transport tank, etc.

[0024] At least a portion of the oxidizing gas used by the SOFC 100 includes oxygen 116 from the electrolyzer 208. The electrolyzer 208 is powered in part by electricity 130 from the SOFC 100 and electricity 210 from a renewable power plant 212. In various embodiments, the renewable power plant 212 is a photovoltaic power plant, a solar thermal power plant, a wind power plant, or a combination thereof. The renewable power plant 212 may be co-located with the CHEP 202 and a refinery or chemical plant that supplies the fuel 120 and steam 126.

[0025] The water 214 used by the electrolyzer 208 to produce hydrogen and oxygen can be obtained from product water, wastewater, seawater, etc. In some embodiments, the water 214 is purified, for example, by nanofiltration or reverse osmosis, to reduce the concentration of salts. Other electrolytes, such as sodium hydroxide, can be added to the water 214 to increase the yield of hydrogen and oxygen, reduce the potential of electrolysis, and increase efficiency.

[0026] The electrolyzer 208 produces green hydrogen 216 from electricity 210 supplied by a renewable power plant 212. In the embodiment shown in Figure 2, a portion of the green hydrogen 216 is produced by electricity 130 from the SOFC 100 and is considered to be blue hydrogen.

[0027] The CHEP 202 can control the rate of power 130 production while capturing CO2 204 and producing blue hydrogen 206. The CHEP 202 can provide the power 130 needed to operate the electrolyzer 208 when renewable power supply is limited, such as at night or on windless days. Additionally, the CHEP 202 can vary its capacity between producing hydrogen and producing power. For example, when more hydrogen production is needed, e.g., in a high hydrogen production mode, it may be more efficient to reduce power production and increase hydrogen production. When less hydrogen is needed, the CHEP 202 can be used to generate more power in a high power mode, e.g., for use with the utility grid. This is further described with reference to FIG. 5.

[0028] The CHEP 202 can always be on-stream to provide power 130 and blue hydrogen 206 as long as hydrocarbons 120 are being supplied to the SOFC, as further described with reference to FIG.

[0029] Figure 3 is a schematic diagram 300 of an integrated hydrogen production system operating on low renewable energy. Like numbered items are as described in connection with Figures 1 and 2. In this scenario, when renewable power is not available, for example, when it is not sunny or windy, the power 130 required for the electrolyzer 208 is provided by the CHEP 202 to produce additional blue hydrogen 302. As a result, a shutdown of the electrolyzer 208 is not necessary. The CHEP 202 transitions to maximum power generation mode. Some blue hydrogen 206, albeit in a smaller amount, is still produced in the CHEP 202.

[0030] FIG. 4 is a schematic diagram 400 of an integrated hydrogen production system utilizing excess renewable electricity. Like-numbered items are as described in connection with FIGS. 1 and 2. In this scenario, the SOFCs 100 for the CHEP 202 are used to generate electricity 130, but some of the SOFCs 100 units in the stack are operated in reverse and function as solid oxide electrolysis cells (SOECs) 402. In addition to green hydrogen 216 from the electrolyzer 208, excess electricity 210 from the renewable power plant 212 is used to produce additional green hydrogen 404 from the stack of SOECs 402. Steam 406 generated by heat recovery from the remaining operating SOFCs 100 units can be used as feed to the SOECs 402, further improving the overall efficiency of green hydrogen 216 and 404 production.

[0031] FIG. 5 is a schematic diagram 500 of an integrated hydrogen production system utilizing a large excess of renewable electricity. Like-numbered items are as described in connection with FIGS. 1, 2, and 4. As described herein, the CHEP 202 can generate more hydrogen and less electricity, for example, at the operating limit of a high hydrogen production mode. In this scenario, all SOFC 100 units in the CHEP 202 are operated as SOECs 402 to produce green hydrogen 216 and 404 without producing electricity from the SOFCs 100. Thus, renewable electricity 210 is utilized to produce green hydrogen 216 and 404 at a lower cost than other sources. The steam 126 used by the SOECs 402 is produced by existing facilities, such as a refinery or chemical plant, associated with the CHEP 202.

[0032] FIG. 6 is a schematic diagram 600 of an integrated hydrogen production system that switches operating modes based on the availability of renewable energy. Like-numbered items are as described in connection with FIGS. 1-5. Assuming some power is available from a renewable energy plant, normal operation of the integrated system produces products, such as blue hydrogen, green hydrogen, and carbon dioxide, as described in connection with schematic diagram 200 of FIG. 2. When renewable energy is unavailable, such as at night, operation switches to schematic diagram 300 as described in connection with FIG. 3. When excess renewable energy is available, operation switches to the mode shown in schematic diagram 400 of FIG. 4, in which a portion of the SOFC stack switches to function as an SOEC stack. When a large excess of renewable energy is available, the SOFC stack can be completely reversed, with all units functioning as SOECs, and power from the renewable energy plant can be used to produce green hydrogen from both the electrolyzer and the SOEC stack.

[0033] 7 is a process flow diagram of a method 700 for integrating energy flows from renewable energy sources and solid oxide fuel cells. The method begins at block 702, where electrical power and a reformed hydrogen stream are produced in a solid oxide fuel cell. Carbon dioxide produced in the SOFC is recovered for use in other processes. At block 704, electrical power is supplied to an electrolyzer to produce an electrolytic hydrogen stream.

[0034] If renewable energy is available, a second power stream is generated in the renewable energy facility in block 706. If renewable energy is not available, all of the power used to operate the electrolyzer is supplied by the SOFC.

[0035] In block 708, a second power stream is supplied to the electrolyzer to increase production of the electrolytic hydrogen stream. If excess power from the renewable energy facility is available, a portion of the SOFC stack is operated as a solid oxide electrolysis cell (SOEC) stack. The excess power from the renewable energy facility is supplied to the SOEC stack to produce hydrogen. If sufficient excess power is available, the entire SOFC stack is operated as an SOEC stack. Power is supplied from the renewable energy facility to power both the electrolyzer and the SOEC stack, both of which produce an electrolytic hydrogen stream. As described herein, this can be referred to as a high hydrogen operating mode of the CHEP.

[0036] Embodiment

[0006] Embodiments described herein provide a method for integrating renewable electrical power with a natural gas hydrogen production plant. The method includes generating electrical power and a reformed hydrogen stream in a solid oxide fuel cell (SOFC) stack and supplying the electrical power to an electrolyzer to produce an electrolytic hydrogen stream. When renewable energy is available, a second electrical power stream is generated at the renewable energy facility and supplied to the electrolyzer to increase production of the electrolytic hydrogen stream.

[0037] In one embodiment, the method includes powering an electrolyzer with power from the SOFC to produce an electrolytic hydrogen stream when renewable energy is not available.

[0038] In one aspect, the method includes operating a portion of the SOFC stack as a solid oxide electrolysis cell (SOEC) stack when excess power from the second power stream is available, and supplying the excess power from the second power stream to the portion of the SOFC stack operating as the SOEC stack.

[0039] In one aspect, the method includes operating all of the SOFC stacks as SOEC stacks; powering both the electrolyzer and the SOEC stacks with power from a second power stream; and producing electrolytic hydrogen streams in both the electrolyzer and the SOEC stack.

[0040] In one embodiment, the method includes supplying steam to the SOEC stack from a SOFC stack.In one embodiment, the method includes supplying steam to the SOEC stack from a chemical plant or refinery plant.

[0041] In one embodiment, the method includes capturing carbon dioxide produced in the SOFC. In one embodiment, the method includes providing the carbon dioxide as a product stream. In one embodiment, the method includes utilizing the carbon dioxide for enhanced oil recovery.

[0042] In one embodiment, the method comprises supplying a stream of oxygen produced in an electrolyzer to a SOFC.

[0043] In one embodiment, the method includes providing a stream of water vapor to the SOFC.

[0044] In one embodiment, the method includes supplying a natural gas stream to the SOFC.

[0045] Another embodiment described herein provides an integrated hydrogen production system. The integrated hydrogen production system includes a solid oxide fuel cell (SOFC), at least a portion of which is operable as a solid oxide electrolysis cell (SOEC), and an electrolyzer electrically coupled to a power supply line from the SOFC. A carbon dioxide capture system is fluidly coupled to an exhaust line from the SOFC. A steam source is fluidly coupled to the SOFC. A hydrocarbon source is fluidly coupled to the SOFC to provide a gaseous hydrocarbon feed to the SOFC, and a renewable energy source is coupled to the electrolyzer to a power supply line from the renewable energy source.

[0046] In one embodiment, the integrated hydrogen production system includes an oxygen supply line from the electrolyzer to the SOFC.

[0047] In one aspect, the steam source comprises a refinery plant, a chemical plant, or both.

[0048] In one embodiment, an integrated hydrogen production system includes a power supply line from a renewable energy source to a portion of the SOFC operating as an SOEC.

[0049] In one embodiment, the hydrocarbon source comprises a gas plant and the gaseous hydrocarbon feed comprises natural gas.

[0050] In one aspect, the integrated hydrogen production system includes a pyrolysis unit, and the gaseous hydrocarbon feed includes pyrolysis gas.

[0051] In one embodiment, the integrated hydrogen production system includes a water-gas shift reactor, and the gaseous hydrocarbon feed includes water gas.

[0052] In one aspect, the renewable energy source comprises a solar power plant. In one aspect, the renewable energy source comprises a wind power facility.

[0053] Other implementations are also within the scope of the following claims.

Claims

1. 1. A method for integrating renewable electricity with a natural gas hydrogen production plant, comprising: generating electrical power and a reformed hydrogen stream in a solid oxide fuel cell (SOFC) stack; supplying said electrical power to an electrolyzer to produce an electrolytic hydrogen stream; generating a second power flow at the renewable energy facility when renewable energy is available; supplying the second electrical power stream to the electrolyzer to increase production of the electrolytic hydrogen stream; A method comprising:

2. 10. The method of claim 1, comprising providing the power from the SOFC to operate the electrolyzer to produce the electrolytic hydrogen stream when renewable energy is not available.

3. if excess power is available from the second power stream; operating a portion of the SOFC stack as a solid oxide electrolysis cell (SOEC) stack; supplying the excess power from the second power stream to a portion of the SOFC stack operating as an SOEC stack; The method of claim 1 , comprising:

4. operating all of the SOFC stacks as SOEC stacks; providing the power from the second power stream to power both the electrolyzer and the SOEC stack; generating the electrolytic hydrogen stream at both the electrolyzer and the SOEC stack; The method of claim 3, comprising:

5. The method of claim 3 , comprising supplying water vapor from the SOFC stack to the SOEC stack.

6. 5. The method of claim 4, comprising supplying steam to the SOEC stack from a chemical or refinery plant.

7. The method of claim 1 , comprising capturing carbon dioxide produced in the SOFC.

8. 8. The method of claim 7, comprising providing the carbon dioxide as a product stream.

9. 8. The method of claim 7, comprising utilizing the carbon dioxide for enhanced oil recovery.

10. 10. The method of claim 1, comprising supplying a stream of oxygen produced in the electrolyzer to the SOFC.

11. The method of claim 1 , comprising providing a stream of water vapor to the SOFC.

12. The method of claim 1 , comprising supplying a natural gas stream to the SOFC.

13. a solid oxide fuel cell (SOFC), at least a portion of which is operable as a solid oxide electrolysis cell (SOEC); an electrolyzer electrically coupled to a power supply line from the SOFC; a carbon dioxide capture system fluidly coupled to an exhaust line from the SOFC; a water vapor source fluidly coupled to the SOFC; a hydrocarbon source fluidly coupled to the SOFC for providing a gaseous hydrocarbon feed to the SOFC; a renewable energy source, wherein the electrolyzer is coupled to a power supply line from the renewable energy source; An integrated hydrogen production system comprising:

14. 14. The integrated hydrogen production system of claim 13, comprising an oxygen supply line from the electrolyzer to the SOFC.

15. The integrated hydrogen production system of claim 13 , wherein the water vapor source comprises a refinery plant, a chemical plant, or both.

16. 14. The integrated hydrogen production system of claim 13, comprising a power supply line from the renewable energy source to the portion of the SOFC operating as an SOEC.

17. 14. The integrated hydrogen production system of claim 13, wherein the hydrocarbon source comprises a gas plant and the gaseous hydrocarbon feed comprises natural gas.

18. 14. The integrated hydrogen production system of claim 13, comprising a pyrolysis unit, wherein the gaseous hydrocarbon feed comprises pyrolysis gas.

19. 14. The integrated hydrogen production system of claim 13, comprising a water-gas shift reactor, wherein the gaseous hydrocarbon feed comprises water gas.

20. The integrated hydrogen production system of claim 13 , wherein the renewable energy source comprises a solar power plant.

21. The integrated hydrogen production system of claim 13 , wherein the renewable energy source comprises a wind power generation facility.

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