Ammonia fuel solid oxide fuel cell system capable of recycling anode tail gas

Abstract

The invention discloses an ammonia fuel solid oxide fuel cell system capable of recycling anode tail gas. The ammonia fuel solid oxide fuel cell system comprises a fuel treatment loop, an air treatment loop, an anode tail gas circulation loop and a combustion tail gas circulation loop, the anode tail gas circulation loop is formed by sequentially connecting a galvanic pile anode outlet, a first electric heating type heat exchanger, a first heat exchanger, a steam-water separator, a booster pump, a hydrogen separator and an afterburner; the hydrogen separator is provided with a separation membrane only allowing hydrogen to pass through in one direction, the separation membrane divides the hydrogen separator into a mixed gas chamber and a hydrogen chamber, an inlet of the mixed gas chamber is connected with an outlet of the booster pump, an outlet of the mixed gas chamber is connected with the afterburner, and an outlet of the hydrogen chamber is connected with the mixer. According to the system, high-grade waste heat and hydrogen in the stack anode tail gas are recycled, the fuel utilization rate and the total thermal efficiency of the system are effectively improved, and the system has a wide market prospect.

Description

Technical Field

[0001] The invention relates to the technical field of power generation equipment, in particular to an ammonia fuel solid oxide fuel cell system for recycling anode tail gas. Background Art

[0002] Solid oxide fuel cells (SOFCs), as an alternative to traditional internal combustion engines, are becoming a promising technology for future mobile power sources, mainly because of their high conversion efficiency and low emissions. SOFCs operate at relatively high temperatures (from 600°C to 1000°C), so they can adapt to a variety of common fuels, including liquefied natural gas, liquefied petroleum gas, ammonia, etc. In addition, its tolerance to fuel impurities solves problems related to hydrogen cleaning, transportation and storage. When using liquefied petroleum gas as a fuel source, the volume of the fuel bottle can be only 1 / 5 of the volume required for high-pressure hydrogen bottles, which is especially important for mobile areas where space is compressed. In addition, studies have shown that SOFCs using ammonia fuel have shown a system efficiency of 50%, exceeding the performance of state-of-the-art PEMFCs, which can typically achieve an efficiency of about 40%.

[0003] Although the ammonia fuel SOFC system has extremely high commercial application value, the main factor restricting its widespread commercialization is the system's operating economy. For example, the anode tail gas usually contains unreacted fuel and high-grade waste heat. If it is discharged directly, it will affect the energy utilization efficiency of the system and cause environmental pollution. Many studies have shown that anode tail gas recycling can improve the system's fuel utilization rate and improve electrical efficiency, but it will reduce thermal efficiency. Therefore, it is necessary to propose a method to improve fuel utilization while ensuring a high thermal utilization efficiency, thereby improving the system's operating economy. Summary of the invention

[0004] In order to solve the deficiencies in the prior art, the present invention provides an ammonia fuel solid oxide fuel cell system for recycling anode tail gas, which can efficiently recycle high-value chemical energy and thermal energy in the anode tail gas of the fuel cell stack while ensuring a high thermal utilization efficiency, thereby improving the economic efficiency of system operation.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] An ammonia fuel solid oxide fuel cell system for recycling anode tail gas, comprising a fuel processing loop, an air processing loop, an anode tail gas circulation loop and a combustion tail gas circulation loop;

[0007] The fuel processing circuit includes a liquid ammonia tank, an expansion valve, a first heat exchanger, a mixer, a first electrically heated heat exchanger, and an inlet of a stack anode, which are connected in sequence;

[0008] The air treatment circuit includes an air compressor, a second heat exchanger, a second electrically heated heat exchanger and an inlet of the cathode of the stack, which are connected in sequence;

[0009] The anode tail gas circulation loop is formed by sequentially connecting the anode outlet of the stack, the first electrically heated heat exchanger, the first heat exchanger, the steam-water separator, the booster pump, the hydrogen separator and the afterburner; the mixed gas chamber in the hydrogen separator is respectively connected to the booster pump and the afterburner, and the hydrogen chamber in the hydrogen separator is connected to the mixer;

[0010] The combustion tail gas circulation loop includes a stack cathode outlet connected to an afterburner, and the outlet of the afterburner is sequentially connected to a second electrically heated heat exchanger, a second heat exchanger and a tail gas treatment device.

[0011] Furthermore, the system works in the following way:

[0012] Preheating mode: Start the electric heating heat exchanger, and when its temperature rises to the target operating temperature, introduce ammonia and air, and start the steam-water separator and booster pump at the same time; ignite the mixed gas entering the afterburner, and use the high-temperature exhaust gas generated by combustion to preheat the air, so as to achieve rapid preheating start of the system;

[0013] Working mode: When the temperature of the fuel cell stack stabilizes at the target operating temperature, the fuel cell stack is started to generate electricity; the flow rates of ammonia and air are gradually increased to the set working flow rates, and the electric power of the electric heating heat exchanger is reduced.

[0014] Furthermore, the steam-water separator is a filled structure and is used to remove water vapor in the anode tail gas.

[0015] Furthermore, the booster pump is a horizontal centrifugal pump used for gas pressurization.

[0016] Furthermore, the separation membrane of the hydrogen separator is made of palladium or silicon dioxide material and is used for unidirectional separation of hydrogen.

[0017] Furthermore, the first electrically heated heat exchanger and the second electrically heated heat exchanger are both plate heat exchangers.

[0018] Furthermore, the battery stack is a flat plate structure, and its solid electrolyte material is yttria-stabilized zirconia.

[0019] Furthermore, the current output end of the battery stack is connected to a converter, and the converter is a DC-AC converter.

[0020] Furthermore, the tail gas treatment device adopts an alkaline solution absorption method to remove nitrogen oxides in the combustion products.

[0021] Furthermore, the fuel processing circuit, the air processing circuit, the anode tail gas circulation circuit and the combustion tail gas circulation circuit are all connected by pipelines.

[0022] Beneficial effects of the present invention:

[0023] (1) The present invention provides an ammonia fuel solid oxide fuel cell system for recycling anode tail gas, wherein the anode tail gas passes through a two-stage heat exchanger on the anode side in sequence, and the combustion tail gas passes through a two-stage heat exchanger on the cathode side in sequence, thereby realizing high-temperature waste heat recovery and improving heat utilization efficiency; at the same time, a membrane separator is used to purify the anode tail gas, and the purified hydrogen re-enters the anode for utilization, thereby improving fuel utilization.

[0024] (2) Compared with the prior art, the system of the present invention has a simple design structure, high heat utilization efficiency and fuel utilization efficiency, and has broad market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The present invention is a schematic structural diagram of an embodiment of an ammonia fuel solid oxide fuel cell system for recycling anode tail gas.

[0026] In the figure, 1. liquid ammonia tank, 2. expansion valve, 31. first heat exchanger, 32. second heat exchanger, 4. mixer, 51. first electrically heated heat exchanger, 52. second electrically heated heat exchanger, 6. fuel cell stack, 7. air compressor, 8. steam-water separator, 9. boost pump, 10. hydrogen separator, 11. afterburner, 12. exhaust gas treatment device, 13. converter. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] In the description of this patent, it should be noted that, unless otherwise clearly specified and limited, the terms "connected", "connected", and "set" should be understood in a broad sense, for example, it can be fixedly connected or set, or detachably connected or set, or integrally connected or set. For ordinary technicians in this field, the specific meanings of the above terms in this patent can be understood according to specific circumstances.

[0029] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0030] See attached Figure 1 , the present invention provides an ammonia fuel solid oxide fuel cell system for recycling anode tail gas, including a fuel processing circuit, an air processing circuit, an anode tail gas circulation circuit and a combustion tail gas circulation circuit;

[0031] The fuel processing circuit includes a liquid ammonia tank 1, an expansion valve 2, a first heat exchanger 31, a mixer 4, a first electrically heated heat exchanger 51, and an inlet of an anode of a fuel cell stack 6, which are connected in sequence;

[0032] The air treatment circuit includes an air compressor 7, a second heat exchanger 32, a second electric heating heat exchanger 52 and an inlet of the cathode of the stack 6 which are connected in sequence;

[0033] The anode tail gas circulation loop is formed by connecting the anode outlet of the stack 6, the first electrically heated heat exchanger 51, the first heat exchanger 31, the steam-water separator 8, the booster pump 9, the hydrogen separator 10 and the afterburner 11 in sequence; the hydrogen separator 10 is provided with a separation membrane that only allows hydrogen to pass in one direction, and the separation membrane divides the hydrogen separator 10 into a mixed gas chamber and a hydrogen chamber, the inlet of the mixed gas chamber is connected to the outlet of the booster pump 9, the outlet of the mixed gas chamber is connected to the afterburner 11, and the outlet of the hydrogen chamber is connected to the mixer 4;

[0034] The combustion exhaust gas circulation loop includes a cathode outlet of the fuel cell stack 6 connected to an afterburner 11, and the outlet of the afterburner 11 is connected in sequence to a second electrically heated heat exchanger 52 and a second heat exchanger 32; the afterburner 11 mixes and burns the exhaust gas discharged from the mixing gas chamber of the hydrogen separator 10 and the exhaust gas from the cathode outlet of the fuel cell stack 6, and the exhaust gas after combustion is discharged from the outlet of the afterburner 11 and enters the second electrically heated heat exchanger 52 and the second heat exchanger 32 in sequence for sufficient heat exchange, thereby realizing waste heat utilization; the exhaust gas discharged from the second heat exchanger 32 enters the exhaust gas treatment device 12 for treatment to remove harmful gases such as nitrogen oxides.

[0035] In the present invention, in specific implementation, the steam-water separator 8 is a filling structure, and its function is to remove water vapor in the anode tail gas of the battery stack 6 to prevent water from affecting the separation membrane.

[0036] In the present invention, in a specific implementation, the booster pump 9 is a horizontal centrifugal pump, which is used for gas pressurization, accelerating the water-gas separation process in the steam-water separator 8 and the hydrogen separation process in the hydrogen separator 10, and improving the hydrogen recovery rate.

[0037] In the present invention, in a specific implementation, the separation membrane of the hydrogen separator 10 is made of palladium or silicon dioxide material, which can realize unidirectional separation of hydrogen.

[0038] In the present invention, in specific implementation, the electrically heated heat exchangers 51 and 52 are plate heat exchangers, which can realize electrical heating of fuel or air, and also realize heat exchange between fuel gas / air and tail gas of the fuel cell stack 6, to ensure rapid startup and stable and efficient operation of the system.

[0039] In the present invention, in a specific implementation, the battery stack 6 is a flat plate structure, and its solid electrolyte material is yttria-stabilized zirconia.

[0040] In the present invention, in a specific implementation, the current output end of the battery stack 6 is connected to the converter 13, and the converter 13 is a DC-AC converter that can convert direct current into alternating current that can be used by users.

[0041] In the present invention, in specific implementation, the tail gas treatment device 12 adopts an alkaline solution absorption method to remove nitrogen oxides in the combustion products.

[0042] In the present invention, in a specific implementation, the fuel processing circuit, the air processing circuit, the anode tail gas circulation circuit and the combustion tail gas circulation circuit are all connected by pipelines.

[0043] In the present invention, the function of the expansion valve 2 is to convert the liquid ammonia in the fuel gas cylinder 1 into gaseous ammonia through throttling.

[0044] In the present invention, the function of the heat exchangers 31 and 32 is to achieve heat exchange between the fuel gas / air and the tail gas of the fuel cell stack 6 .

[0045] In the present invention, the function of the air compressor 7 is to supply external air to the fuel cell stack 7 and maintain it under specific pressure conditions to ensure pressure balance.

[0046] In the present invention, the function of the afterburner 11 is to fully mix and burn the tail gas of the fuel cell stack 6, thereby generating high-temperature heat for preheating the air and removing ammonia in the tail gas.

[0047] The working process of the ammonia fuel solid oxide fuel cell system for recycling anode tail gas designed by the present invention is described in detail below:

[0048] 1. Preheating start-up stage: Start the first electrically heated heat exchanger 51 and the second electrically heated heat exchanger 52. When their temperatures rise to the target operating temperature (e.g., 600°C to 1000°C), introduce ammonia and air, and start the steam-water separator 8 and the boost pump 9. Then, ignite the mixed gas entering the afterburner 11, and use the high-temperature exhaust gas generated by the combustion to preheat the air. The steps in this stage can achieve rapid preheating start-up of the system.

[0049] In the afterburner 11, the chemical equation for the combustion of the mixed gas is as follows:

[0050] 4NH3+3O2==2N2+6H2O;

[0051] 4NH3+5O2=4NO+6H20;

[0052] 2H2+O2==2H2O.

[0053] 2. Stable working stage: When the temperature of the stack 6 is stable at the target working temperature (such as 600℃~1000℃), start the stack 6 to generate electricity; gradually increase the flow of ammonia and air to the set working flow, reduce the electric power of the electric heating heat exchangers 51 and 52, so as to reduce the output of the system parasitic energy consumption and improve the system electrical efficiency; in this stage, the electrochemical heat generated by the stack 6, the electric heat of the first electric heating heat exchanger 51 and the second electric heating heat exchanger 52 and the combustion heat of the afterburner 11 are used as the heat source for the stable operation of the system. Among them, the electrochemical reaction equation involved in the stack 6 is as follows:

[0054] At the anode: 2H2+2O2-==4e-+2H2O;

[0055] At cathode: O2-+4e-==2O2-.

[0056] Based on the above technical solutions, it can be known that in the present invention, the waste heat of the high-temperature exhaust gas from the anode of the fuel cell stack 6 and the afterburner 11 is recovered and utilized, and at the same time, the hydrogen in the anode exhaust gas is separated and purified by combining with the hydrogen separator 9, and reused as anode fuel, thereby effectively shortening the startup time of the fuel cell system, and improving the thermal efficiency, electrical efficiency and fuel utilization efficiency of the system, thereby reducing the operating cost of the system.

[0057] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, it should be understood by those skilled in the art that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An ammonia fuel solid oxide fuel cell system with anode tail gas recovery and utilization, characterized in that: It includes a fuel processing circuit, an air processing circuit, an anode tail gas circulation circuit and a combustion tail gas circulation circuit; The fuel processing circuit comprises a liquid ammonia tank (1), an expansion valve (2), a first heat exchanger (31), a mixer (4), a first electrically heated heat exchanger (51), and an inlet of an anode of a fuel cell stack (6) which are connected in sequence; The air processing circuit comprises an air compressor (7), a second heat exchanger (32), a second electrically heated heat exchanger (52) and an inlet of a cathode of a fuel cell stack (6) which are connected in sequence; The anode tail gas circulation loop is formed by sequentially connecting the anode outlet of the stack (6), the first electrically heated heat exchanger (51), the first heat exchanger (31), the steam-water separator (8), the booster pump (9), the hydrogen separator (10) and the afterburner (11); the mixed gas chamber in the hydrogen separator (10) is connected to the booster pump (9) and the afterburner (11), respectively, and the hydrogen chamber in the hydrogen separator (10) is connected to the mixer (4); The combustion exhaust gas circulation loop comprises a cathode outlet of a fuel cell stack (6) connected to an afterburner (11), and an outlet of the afterburner (11) connected in sequence to a second electrically heated heat exchanger (52), a second heat exchanger (32) and an exhaust gas treatment device (12).

2. The ammonia fuel solid oxide fuel cell system for anode tail gas recovery and utilization according to claim 1 is characterized in that: The system works in the following mode: Preheating mode: start the first electrically heated heat exchanger (51) and the second electrically heated heat exchanger (52), and when their temperatures rise to the target operating temperature, introduce ammonia and air, and simultaneously start the steam-water separator (8) and the booster pump (9); ignite the mixed gas entering the afterburner (11), and use the high-temperature exhaust gas generated by the combustion for air preheating, thereby achieving rapid preheating start of the system; Working mode: when the temperature of the fuel cell stack (6) is stabilized at the target working temperature, the fuel cell stack (6) is started to generate electricity; the flow rates of ammonia and air are gradually increased to the set working flow rates, and the electric power of the first electric heating heat exchanger (51) and the second electric heating heat exchanger (52) is reduced.

3. The ammonia fuel solid oxide fuel cell system for anode tail gas recovery and utilization according to claim 1, characterized in that: The steam-water separator (8) is a filling structure and is used to remove water vapor from the anode tail gas.

4. The ammonia fuel solid oxide fuel cell system for anode tail gas recovery and utilization according to claim 3 is characterized in that: The booster pump (9) is a horizontal centrifugal pump used for gas pressurization.

5. The ammonia fuel solid oxide fuel cell system for anode tail gas recovery and utilization according to claim 4, characterized in that: The separation membrane of the hydrogen separator (10) is made of palladium or silicon dioxide material and is used for unidirectional separation of hydrogen.

6. The ammonia fuel solid oxide fuel cell system for anode tail gas recovery and utilization according to claim 5, characterized in that: The first electrically heated heat exchanger (51) and the second electrically heated heat exchanger (52) are plate heat exchangers.

7. The ammonia fuel solid oxide fuel cell system for anode tail gas recovery and utilization according to claim 1, characterized in that: The battery stack (6) is a flat plate structure, and its solid electrolyte material is yttria-stabilized zirconium oxide.

8. The ammonia fuel solid oxide fuel cell system for anode tail gas recovery and utilization according to claim 7, characterized in that: The current output end of the battery stack (6) is connected to a converter (13), and the converter (13) is a DC-AC converter.

9. The ammonia fuel solid oxide fuel cell system for anode tail gas recovery and utilization according to claim 1, characterized in that: The tail gas treatment device (12) adopts an alkaline solution absorption method to remove nitrogen oxides in the combustion products.

10. The ammonia fuel solid oxide fuel cell system for anode tail gas recovery and utilization according to claim 1, characterized in that: The fuel processing loop, the air processing loop, the anode tail gas circulation loop and the combustion tail gas circulation loop are all connected by pipelines.

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