A Solid Oxide Fuel Cell Thermal Equilibrium System and Method for Carbon Capture

Abstract

The present disclosure discloses a thermal balance system for a solid oxide fuel cell for carbon capture, including a pre-reforming module, a solid oxide fuel cell, an oxidation module, a reduction module, a waste heat utilization module, a carbon capture module, and a water treatment module. The present disclosure also discloses a carbon capture method based on the thermal balance of a solid oxide fuel cell, including: using calcium oxide in the pre-reforming module to absorb carbon dioxide generated by reforming, and the reformed product enters the anode of the solid oxide fuel cell for power generation; using the heat released by the reaction in the oxidation module to heat the oxygen-depleted air; using the heat released by the reaction in the reduction module to decompose calcium carbonate and heat the anode exhaust gas of the solid oxide fuel cell, and using the waste heat utilization module to utilize the heat in the exhaust gas to separate cooling water and carbon dioxide, wherein the cooling water enters the water tank for recycling, and the carbon dioxide enters the carbon capture module.

Description

Technical Field

[0001] The present disclosure belongs to the field of solid oxide fuel cells, and particularly relates to a solid oxide fuel cell thermal balance system and method for carbon capture. Background Art

[0002] A solid oxide fuel cell (SOFC) is an all-solid-state power generation device that can convert chemical energy into electrical energy at 600 - 1000 °C. It can use hydrogen, natural gas, methanol, ethanol, etc. as fuels, and the products are carbon dioxide and water. The power generation efficiency of a single cell is greater than 60%.

[0003] The balance of plant (BOP) system is a general term for other devices that assist the operation of solid oxide fuel cells and improve system efficiency. Existing BOP systems only include pre-reformers, burners, fuel preheaters, air preheaters, etc. For hydrocarbon fuels, pre-reforming is generally required before being introduced into the SOFC, that is, converting the hydrocarbon fuel into carbon monoxide and hydrogen and then introducing it into the SOFC anode. To achieve a high fuel conversion rate, the reforming reaction needs to be carried out under high temperature and high pressure (600 - 800 °C, 1 - 4 MPa), and the energy consumption of the reforming device is huge.

[0004] Internal reforming SOFC means introducing hydrocarbon fuel and reforming oxidant into the SOFC anode together, using the anode nickel to achieve internal reforming of the hydrocarbon fuel, turning it into hydrogen and carbon monoxide inside the cell, and then participating in the fuel cell reaction to generate electricity. However, most reforming reactions are strongly endothermic reactions. If the fuel is completely processed by the internal reforming method, the operating temperature of the SOFC will be too low, reducing the electrolyte conductivity, thereby affecting the power generation performance. Secondly, internal reforming makes the SOFC anode prone to carbon deposition, resulting in the electrolyte of the SOFC being covered by carbon and the anode catalyst being poisoned, thereby reducing the battery life.

[0005] In addition, in terms of SOFC tail gas treatment, unreacted fuel usually mixes with the oxygen-depleted air at the SOFC cathode and is completely burned in the combustion chamber. The high-temperature tail gas mainly includes nitrogen, water vapor, and carbon dioxide, which cannot be separated from each other and are directly discharged after passing through the waste heat utilization system, unable to achieve the purpose of emission reduction.

[0006] In summary, there are currently problems in the SOFC combined heat and power generation system, such as high energy consumption of the reforming device and the inability to separate carbon dioxide from the tail gas. Therefore, there is an urgent need in this field to study a new type of SOFC system to achieve energy conservation and emission reduction. Summary of the Invention

[0007] Aiming at the deficiencies in the prior art, the purpose of the present disclosure is to provide a solid oxide fuel cell thermal balance system and method for carbon capture, which can separate carbon dioxide from the tail gas of the solid oxide fuel cell, thereby achieving the capture and storage of carbon dioxide.

[0008] To achieve the above object, the present disclosure provides the following technical solutions:

[0009] A carbon capture method based on the thermal balance of a solid oxide fuel cell, comprising the following steps:

[0010] S100: Pre-reform a hydrocarbon fuel to generate carbon monoxide, carbon dioxide and hydrogen. Among them, carbon monoxide, hydrogen, and a part of the hydrocarbon fuel that did not participate in the pre-reforming, as well as water vapor, are input into the anode of the solid oxide fuel cell;

[0011] S200: Introduce air into the solid oxide fuel cell. Among them, a part of the air reacts with a part of the carbon monoxide and hydrogen input into the anode of the solid oxide fuel cell to generate carbon dioxide and water vapor. Another part of the air is mixed with the cathode exhaust gas of the solid oxide fuel cell and undergoes an oxidation reaction with a reducible metal to generate a metal oxide, and the heat released during the oxidation reaction is used to heat the oxygen-deficient air to form high-temperature oxygen-deficient air;

[0012] S300: Use the unreacted carbon monoxide, hydrogen, and hydrocarbon fuel in the anode of the solid oxide fuel cell as reducing agents to carry out a reduction reaction with the metal oxide, and use a part of the heat released during the reaction to decompose calcium carbonate to obtain the decomposition product calcium oxide;

[0013] S400: Use the decomposition product calcium oxide to capture the carbon dioxide generated during the pre-reforming of the hydrocarbon fuel, and simultaneously generate calcium carbonate;

[0014] S500: Use another part of the heat released during the reduction reaction to heat the carbon dioxide and water vapor generated in step S200 to form a high-temperature mixed gas;

[0015] S600: Recover the waste heat of the high-temperature oxygen-deficient air in step S200 and the high-temperature mixed gas in step S500. Among them, the water vapor in the high-temperature mixed gas precipitates as liquid water after the waste heat is utilized, and the remaining carbon dioxide is captured.

[0016] Preferably, the hydrocarbon fuel includes alkane compounds and alcohol compounds.

[0017] Preferably, the reducible metal includes any one of the following: Fe, Ni, Co, Cu, Mn, and Cd.

[0018] The present disclosure also provides a solid oxide fuel cell thermal balance system for carbon capture, comprising:

[0019] A pre-reforming module for pre-reforming a hydrocarbon fuel to generate carbon monoxide, carbon dioxide and hydrogen;

[0020] A solid oxide fuel cell for converting the chemical energy of carbon monoxide and hydrogen in a prereforming module into electrical energy;

[0021] An oxidation module for generating metal oxides by an oxidation reaction of oxygen with a reducible metal and heating the oxygen-depleted air by using the heat released from the reaction to form high-temperature oxygen-depleted air;

[0022] A reduction module for performing a reduction reaction of unreacted carbon monoxide, hydrogen, and hydrocarbon fuel in the solid oxide fuel cell with the metal oxide, decomposing calcium carbonate by using a part of the heat released from the reaction to obtain calcium oxide as a decomposition product, capturing carbon dioxide in the prereforming module by using the calcium oxide as the decomposition product, and heating carbon dioxide and water vapor generated during the solid oxide fuel cell and the reduction reaction by using another part of the heat released from the reaction to form a high-temperature mixed gas.

[0023] Preferably, the prereforming module, the oxidation module, and the cathode of the solid oxide fuel cell form a first passage.

[0024] Preferably, the prereforming module, the oxidation module, and the reduction module form a loop.

[0025] Preferably, the prereforming module, the reduction module, and the anode of the solid oxide fuel cell form a second passage.

[0026] Preferably, the system further includes a waste heat utilization module.

[0027] Preferably, the system further includes a capture module.

[0028] Preferably, the system further includes a water treatment module.

[0029] Compared with the prior art, the beneficial effects brought by the present disclosure are as follows:

[0030] 1) Solving the problem of high energy consumption in thermodynamics by a kinetic method. In the present disclosure, calcium oxide absorbs carbon dioxide, so that the reversible reaction equilibrium in the prereforming module continuously moves forward, and a high steam reforming conversion rate is achieved under normal pressure; a large amount of heat is generated when calcium oxide absorbs carbon dioxide, providing a temperature condition for steam reforming and reducing external energy consumption.

[0031] 2) Carbon capture can be performed. The traditional way to treat the tail gas of SOFC is to mix the anode and cathode tail gases and burn them. If the tail gas after combustion needs to be separated, a large cost is required; or replacing the air at the cathode of SOFC with pure oxygen still has a high cost. In the present disclosure, carbon capture is performed by using an intermediate carrier before the fuel enters SOFC and after the SOFC tail gas is burned, realizing the mutual separation of the tail gas components.

[0032] 3) High energy utilization rate. Not only does the conversion rate of hydrocarbon fuels increase through the method of absorbing carbon dioxide, but also the unreacted hydrocarbon fuels and water vapor in the pre-reforming module are further converted into fuels on the SOFC anode. A small amount of hydrocarbon fuels are internally reformed in the anode, which not only utilizes the heat of the SOFC but also controls the maximum temperature of the SOFC, reducing the risk of material failure. The chemical reactions occurring in the pre-reformer, the oxidation device, and the reduction device can basically achieve heat self-sufficiency and require very little external energy supply. In addition, the waste heat utilization module can also make full use of the waste heat of the tail gas.

[0033] 4) High material utilization rate. In the present disclosure, the water in the product can be reused as the raw material of the pre-reforming module, and calcium oxide and reducible metals can be recycled and regenerated in the pre-reforming module, the oxidation module, and the reduction module. Description of the Drawings

[0034] Figure 1 is a flowchart of a carbon capture method based on the thermal balance of a solid oxide fuel cell provided by an embodiment of the present disclosure;

[0035] Figure 2 is a schematic structural diagram of a solid oxide fuel cell thermal balance system for carbon capture provided by an embodiment of the present disclosure;

[0036] The reference numerals in the drawings are described as follows:

[0037] 1. Pre-reforming module; 2. Oxidation module; 3. Reduction module; 4. Waste heat utilization module; 5. Solid oxide fuel cell (SOFC); 6. Water tank; 7. Water pump; 8. Boiler. Detailed Embodiments

[0038] The following will refer to the attached Figures 1 to 2 The specific embodiments of the present disclosure will be described in detail. Although the specific embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present disclosure can be more thoroughly understood and the scope of the present disclosure can be fully conveyed to those skilled in the art.

[0039] It should be noted that in the description and claims, certain terms are used to refer to specific components. Those skilled in the art should understand that technicians may use different terms to refer to the same component. The description and claims in this specification do not distinguish components by the difference in terms, but by the difference in the functions of the components. For example, the terms "comprising" or "including" mentioned throughout the specification and claims are open-ended terms, and should be interpreted as "including but not limited to". The subsequent description in the specification is for the purpose of describing the preferred embodiments of the present disclosure, but it is not intended to limit the scope of the present disclosure. The scope of protection of the present disclosure shall be determined by the claims appended hereto.

[0040] For the convenience of understanding the embodiments of the present disclosure, the following will further explain with specific embodiments in conjunction with the accompanying drawings, and the accompanying drawings do not constitute a limitation to the embodiments of the present disclosure.

[0041] In one embodiment, as Figure 1 shown, the present disclosure provides a solid oxide fuel cell thermal balance system for carbon capture, including:

[0042] A pre-reforming module 1 for pre-reforming a hydrocarbon fuel to generate carbon monoxide, carbon dioxide, and hydrogen;

[0043] A solid oxide fuel cell 5 for converting the chemical energy of carbon monoxide and hydrogen in the pre-reforming module into electrical energy;

[0044] An oxidation module 2 for oxidizing a reducible metal with oxygen to generate a metal oxide, and using the heat released by the reaction to heat the oxygen-depleted air to form high-temperature oxygen-depleted air;

[0045] A reduction module 3 for using the unreacted carbon monoxide, hydrogen, and hydrocarbon fuel in the solid oxide fuel cell to perform a reduction reaction with the metal oxide, using a part of the heat released by the reaction to decompose calcium carbonate to obtain the decomposition product calcium oxide, using the decomposition product calcium oxide to capture carbon dioxide in the pre-reforming module, and using another part of the heat released by the reaction to heat the carbon dioxide and water vapor generated during the solid oxide fuel cell and the reduction reaction to form a high-temperature mixed gas.

[0046] In this embodiment, the hydrocarbon fuel includes various alkane compounds such as methane and ethane, as well as various alcohol compounds such as methanol and ethanol. Specifically, methane is taken as an example in this embodiment. In the pre-reforming module, the hydrocarbon fuel and water vapor undergo a steam reforming reaction to generate carbon monoxide and hydrogen, and carbon monoxide and water vapor undergo a water gas shift reaction to generate carbon dioxide and hydrogen. The specific chemical reactions are as follows:

[0047] ΔH = 206 kJ / mol

[0048] ΔH = -41 kJ / mol

[0049] It should be noted that methane and steam do not react completely, and a small part enters the anode of the solid oxide fuel cell (SOFC) together with the generated carbon monoxide and hydrogen. Methane and steam undergo steam reforming and water-gas shift reactions on the SOFC anode to continue generating carbon monoxide, carbon dioxide, and hydrogen. The hydrogen and carbon monoxide generated on the SOFC anode, together with the hydrogen and carbon monoxide entering the SOFC anode from the pre-reforming module, are supplemented to the SOFC anode and undergo an electrochemical reaction with the oxygen in the air at the SOFC cathode to generate steam and carbon dioxide. The specific chemical reactions are as follows:

[0050] H2 + 0.5O2 = H2O ΔH = -286 kJ / mol

[0051] CO + 0.5O2 = CO2 ΔH = -283 kJ / mol

[0052] Since a large amount of the oxygen supplemented to the SOFC is consumed in the anode, only a large amount of nitrogen and a small amount of oxygen are contained in the SOFC cathode. This mixed gas is called oxygen-depleted air, which is mixed with another stream of fresh air and enters the oxidation module to react with metallic copper (in addition to metallic copper, metals such as Fe, Ni, Co, Mn, and Cd are also applicable to this method) to generate copper oxide. The specific chemical reaction is as follows:

[0053] Cu + 0.5O2 = CuO ΔH = -156 kJ / mol

[0054] While generating copper oxide, the oxidation reaction releases a large amount of heat to heat the oxygen-depleted air, thus forming high-temperature oxygen-depleted air and entering the waste heat utilization module from the oxidation module.

[0055] After the above reactions, a small amount of methane, carbon monoxide, and hydrogen, as well as a large amount of carbon dioxide and water, remain in the SOFC anode. Among them, methane, carbon monoxide, and hydrogen can act as reducing gases and react with copper oxide in the reduction module to produce metallic copper, while generating carbon dioxide and water. The specific chemical equations are as follows:

[0056] 4CuO + CH4 = 4Cu + CO2 + 2H2O ΔH = -170 kJ / mol

[0057] CuO + H2 = Cu + H2O ΔH = -86 kJ / mol

[0058] CuO + CO = Cu + CO2 ΔH = -127 kJ / mol

[0059] Meanwhile, a part of the heat released during the reduction process (the reduction of copper oxide) can be used to decompose calcium carbonate in the reduction module. The specific chemical reaction is as follows:

[0060] CaCO3 = CaO + CO2 ΔH = 178 kJ / mol

[0061] The calcium oxide generated after decomposition and the metallic copper obtained after reduction are transported to the pre-reforming module. Among them, calcium oxide absorbs the carbon dioxide generated by the reforming reaction of methane and steam in the pre-reforming module to form calcium carbonate solid. The specific chemical reaction is as follows:

[0062] CO2 + CaO = CaCO3 ΔH = -178 kJ / mol

[0063] It can be seen from the above reaction process that the pre-reforming module, the oxidation module, and the reduction module form a loop, enabling the conversion between calcium carbonate and its decomposition product calcium oxide to cyclically absorb carbon dioxide in the pre-reforming module. Moreover, since a large amount of heat is generated when calcium oxide cyclically absorbs carbon dioxide, it can also continuously reduce the external energy consumption.

[0064] In the pre-reforming module, since the carbon dioxide generated by the reforming reaction of methane and steam is absorbed, the concentration of carbon dioxide decreases, and the equilibrium of the aforementioned water-gas shift reaction will shift forward, resulting in a decrease in the concentration of carbon monoxide and an increase in the concentration of hydrogen. Both carbon monoxide and hydrogen are products of the steam reforming reaction. According to the principle of chemical kinetics, the promotion of the steam reforming reaction by the reduction of carbon monoxide is greater than the inhibition of the steam reforming reaction by the increase in hydrogen (the reforming reaction of methane is a first-order reaction and accounts for the main position, while the water-gas shift is a second-order reaction and accounts for the secondary position. The second-order reaction consumes the products of the first-order reaction and promotes the first-order reaction. However, the products of the second-order reaction are the same as those of the first-order reaction and inhibit the first-order reaction. However, the order of magnitude of the products of the second-order reaction is much smaller than that of the first-order reaction. Therefore, the promotion of the second-order reaction to the first-order reaction is greater than the inhibition). Therefore, the conversion rate of methane is increased. At the same time, a large amount of heat is generated when calcium oxide absorbs carbon dioxide, thus providing the temperature condition for steam reforming and reducing the energy consumption.

[0065] In addition, another part of the heat released during the reduction process is absorbed by the carbon dioxide and steam input from the SOFC anode to the reduction module and the carbon dioxide and steam generated during the reduction process in the reduction module, enabling the reduction module to output a mixed gas formed by high-temperature carbon dioxide and steam.

[0066] At this point, since the pre-reforming module, the SOFC cathode, and the oxidation module form a separate path, lean oxygen air can enter the waste heat utilization module after being heated by the oxidation module; since the pre-reforming module, the SOFC anode, and the reduction module form another separate path, carbon dioxide can be heated and discharged through the reduction module, so that carbon dioxide can be separated from nitrogen and captured and stored separately.

[0067] In another embodiment, the system further includes a waste heat utilization module 4.

[0068] In this embodiment, the lean oxygen air discharged from the oxidation module and the mixed gas discharged from the reduction module are both high-temperature gases. Therefore, a waste heat utilization module can be provided at the tails of the oxidation module and the reduction module to utilize the high-temperature gases. After the heat in the high-temperature mixed gas discharged from the reduction module is utilized, the water vapor condenses into liquid water, so that it can be separated from carbon dioxide. Among them, the separated carbon dioxide is captured and stored. The liquid water then enters the water treatment module composed of a water tank 6, a water pump 7, and a boiler. Specifically, the liquid water first enters the water tank 6 for storage, and then is pumped into the boiler 8 by the water pump 7, heated and re-evaporated into water vapor in the boiler 8, and then enters the pre-reforming module to carry out a pre-reforming reaction with the hydrocarbon fuel again.

[0069] In another embodiment, the system further includes a capture module (not shown in the figure).

[0070] In this embodiment, the capture module is connected to the waste heat utilization module and is used to capture the carbon dioxide separated by the waste heat utilization module.

[0071] It should be noted that the focus of the present disclosure is how to separate carbon dioxide from the tail gas of the fuel cell through a certain process method. The structures of the various modules in the system are not included in the scope of this protection. Therefore, the structures of the various modules in the system are not limited, and any existing device that can achieve the corresponding functions can be used in the system described in the present disclosure.

[0072] Thus, the above embodiments constitute a complete technical solution of the present disclosure. The traditional method for treating the SOFC tail gas is to burn the anode and cathode tail gases together. If the tail gas is to be separated, a large cost is required; or the air at the cathode of the SOFC is replaced with pure oxygen, and the cost is still very high. Compared with the traditional method for treating the SOFC tail gas, the method described in the present disclosure has the following characteristics: 1. Calcium oxide and metallic copper are used as intermediate carriers to achieve carbon capture before the fuel enters the SOFC and after the SOFC tail gas is burned, which is convenient for further carbon dioxide capture and storage. 2. The conversion rate of the hydrocarbon fuel in the pre-reforming module can be increased by absorbing carbon dioxide, and the unreacted hydrocarbon fuel and water vapor in the pre-reforming module are further converted into fuel on the SOFC anode. The internal reforming of a small amount of methane in the anode not only utilizes the heat of the SOFC, but also controls the maximum temperature of the SOFC, reducing the risk of material failure; 3. The condensed liquid water can be reused as a raw material for the pre-reforming module, and calcium oxide and metallic copper can be recycled and regenerated in the pre-reforming module, oxidation module, and reduction module.

[0073] The above uses specific embodiments to elaborate on the present disclosure, which is only used to help understand the present disclosure and is not used to limit the present disclosure. Any partial modification or replacement by those skilled in the art within the technical scope disclosed by the present disclosure should be covered within the scope of the present disclosure.

Claims

1. A carbon capture method based on the thermal balance of a solid oxide fuel cell, comprising the following steps: S100: Pre-reform the hydrocarbon fuel to generate carbon monoxide, carbon dioxide and hydrogen, where Carbon monoxide, hydrogen, a part of the hydrocarbon fuel that has not participated in pre-reforming, and water vapor are input into the anode of the solid oxide fuel cell; S200: Air is introduced into the solid oxide fuel cell. Among them, a part of the air reacts with a part of the carbon monoxide and hydrogen input into the anode of the solid oxide fuel cell to generate carbon dioxide and water vapor. Another part of the air is mixed with the cathode exhaust gas of the solid oxide fuel cell and undergoes an oxidation reaction with the reducible metal to generate metal oxide, and the heat released during the oxidation reaction is used to heat the oxygen-deficient air to form high-temperature oxygen-deficient air; S300: The unreacted carbon monoxide, hydrogen, and hydrocarbon fuel in the anode of the solid oxide fuel cell are used as reducing agents to react with the metal oxide, and a part of the heat released during the reaction is used to decompose calcium carbonate to obtain the decomposition product calcium oxide; S400: The decomposition product calcium oxide is used to capture the carbon dioxide generated during the pre-reforming of the hydrocarbon fuel, and at the same time calcium carbonate is generated; S500: Another part of the heat released during the reaction in step S300 is used to heat the carbon dioxide and water vapor generated in step S200 to form a high-temperature mixed gas; S600: The high-temperature oxygen-deficient air in step S200 and the high-temperature mixed gas in step S500 are used for waste heat utilization. Among them, the water vapor in the high-temperature mixed gas is condensed into liquid water after waste heat utilization, and the remaining carbon dioxide is captured.

2. The method according to claim 1, wherein The hydrocarbon fuel includes alkane compounds and alcohol compounds.

3. The method according to claim 1, wherein The reducible metal includes any one of the following: Fe, Ni, Co, Cu, Mn, and Cd.

4. A solid oxide fuel cell thermal balance system for carbon capture, comprising: A pre-reforming module for pre-reforming the hydrocarbon fuel to generate carbon monoxide, carbon dioxide, and hydrogen; A solid oxide fuel cell for converting the chemical energy of carbon monoxide and hydrogen in the pre-reforming module into electrical energy; An oxidation module for generating metal oxide by the oxidation reaction of oxygen with the reducible metal, and using the heat released by the reaction to heat the oxygen-deficient air to form high-temperature oxygen-deficient air; A reduction module for using the unreacted carbon monoxide, hydrogen, and hydrocarbon fuel in the solid oxide fuel cell to react with the metal oxide, using a part of the heat released by the reaction to decompose calcium carbonate to obtain the decomposition product calcium oxide, using the decomposition product calcium oxide to capture the carbon dioxide in the pre-reforming module, and using another part of the heat released by the reaction to heat the carbon dioxide and water vapor generated during the solid oxide fuel cell and the reduction reaction to form a high-temperature mixed gas.

5. The system according to claim 4, wherein, The pre-reforming module, the oxidation module, and the cathode of the solid oxide fuel cell form a first path.

6. The system according to claim 4, wherein, The pre-reforming module, the oxidation module, and the reduction module form a loop.

7. The system according to claim 4, wherein, The pre-reforming module, the reduction module, and the anode of the solid oxide fuel cell form a second path.

8. The system according to claim 4, wherein The system further includes a waste heat utilization module.

9. The system according to claim 4, wherein, The system further includes a capture module.

10. The system according to claim 4, wherein, The system further includes a water treatment module.

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