Indirect cascade type fuel cell system and power generation equipment

Abstract

The invention discloses an indirect cascade type fuel cell system and power generation equipment. The indirect cascade type fuel cell system comprises an ammonia gas supply device, a throttle valve, a three-way valve, a heat exchange unit, an ammonia decomposition reactor, an electric pile, an afterburner, a fan, an organic Rankine cycle unit and a flow monitoring controller, the flow monitoring controller is used in the system, and the flow of the air inlet and the flow of the cathode outlet of the first-stage galvanic pile are measured at the same time, so that the temperature of combined gas at the cathode inlet of the second-stage galvanic pile is constant, and meanwhile, the utilization efficiency of cathode gas of the first-stage galvanic pile is improved; the system is coupled with an organic Rankine cycle unit, cathode tail gas and heat of the tail gas are used for generating electricity, and the electric efficiency of the system is improved; and meanwhile, high-temperature waste heat in combustion tail gas is fully utilized as a heating source of fuel gas and a working medium of the organic Rankine cycle unit, and the heat utilization efficiency of the whole system is improved. Therefore, the invention has the advantages of high fuel utilization rate, high safety coefficient, environmental friendliness, high electric efficiency and thermal efficiency, and wide market prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of power generation equipment, in particular to an indirect cascade fuel cell system and power generation equipment. Background Art

[0002] With the world attaching great importance to climate change and carbon dioxide emission reduction, fuel cells, as an efficient and clean energy technology, are gradually becoming a hot topic in research and application. Among them, solid oxide fuel cells (SOFCs) stand out due to their unique advantages. SOFCs operate at high temperatures, typically between 600 and 1000°C, and have strong fuel adaptability and impurity tolerance. They can not only use pure H2 as fuel, but also use synthesis gas / reformed gas (mainly H2, CO, CO2 and H2O) generated in situ from hydrocarbon fuels without strictly removing non-H2 substances. Compared with other types of fuel cells, SOFCs usually operate at higher temperatures and use solid oxides as electrolytes, do not rely on precious metal catalysts, and are more efficient. Therefore, the development of SOFC-based vehicle power or auxiliary power systems is of extremely important strategic significance for promoting energy conservation and emission reduction goals in the transportation sector.

[0003] At present, the application technology of ammonia fuel in SOFC stacks is not yet fully mature, which may lead to insufficient fuel utilization, resulting in a large amount of unreacted fuel remaining in the exhaust gas. At the same time, the high-temperature waste heat of the stack exhaust gas cannot be effectively utilized, thereby reducing the energy utilization efficiency of the entire system.

[0004] The existing solution to these problems involves decomposing ammonia fuel into 75% hydrogen and 25% nitrogen over a nickel- or ruthenium-based porous catalyst, which is then directly fed into the SOFC stack for power generation. Alternatively, anode off-gas recycling (AOGR) is implemented, where the anode off-gas is recirculated back to the ammonia decomposer at a pre-designed ratio, mixed with the fuel, and then fed back into the stack. Another alternative is cathode off-gas recycling (COGR), where the cathode off-gas is recirculated back to the cathode inlet at a pre-designed ratio for reuse. However, while waste heat recovery from the exhaust is often achieved through coupling with a gas turbine or ORC (Organic Rankine Cycle), these solutions often overlook the cooling step required during the cathode off-gas recycling process. This failure to fully tap the waste heat potential of the recycled cathode off-gas leads to inefficient utilization of this waste heat, impacting the energy efficiency and economic viability of the entire system. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide an indirect cascade fuel cell system, which adopts a two-stage stack and combines anode exhaust gas recycling (AOGR) with cathode exhaust gas recycling (COGR) to solve the problems of insufficient fuel utilization during system use, resulting in a large amount of fuel in the exhaust gas and unutilized high-temperature waste heat of the anode and cathode exhaust gases of the stack; and provides a coupled ORC system, which utilizes the heat in the cathode circulating exhaust gas and the afterburner exhaust gas to improve the energy utilization efficiency of the system.

[0006] The technical solution for achieving the purpose of the present invention is:

[0007] An indirect cascade fuel cell system includes: an ammonia supply device, a throttle valve, a heat exchange unit, an ammonia decomposition reactor, a first three-way valve, a fuel cell stack, and an afterburner;

[0008] The heat exchange unit includes a first heat exchanger and a second heat exchanger;

[0009] The battery stack includes a first-stage battery stack and a second-stage battery stack;

[0010] The ammonia supply device is sequentially connected to the throttle valve, the first heat exchanger, the ammonia decomposition reactor, the first three-way valve and the anode inlet of the first-stage fuel cell stack;

[0011] The first outlet of the first three-way valve is connected to the anode inlet of the first-stage fuel cell stack, and the second outlet is connected to the anode inlet of the second-stage fuel cell stack;

[0012] The anode outlets of the first-stage fuel cell stack and the second-stage fuel cell stack are connected to the first inlet and the second inlet of the second three-way valve respectively;

[0013] The outlet of the second three-way valve is connected to the heat exchange channel of the ammonia decomposition reactor, the hot end of the first heat exchanger, and the inlet of the fourth three-way valve in sequence;

[0014] The first outlet of the fourth three-way valve is connected to the anode inlet of the second-stage fuel cell stack, and the second outlet of the fourth three-way valve is connected to the inlet of the afterburner.

[0015] Furthermore, it also includes a fan, a third three-way valve and a fifth three-way valve, the fan is connected to the first outlet of the third three-way valve, the second heat exchanger and the cathode inlet of the first-stage fuel cell stack in sequence, the second outlet of the third three-way valve is connected to the first inlet of the fifth three-way valve, and then connected to the cathode inlet of the second-stage fuel cell stack, the cathode outlet of the first-stage fuel cell stack is connected to the second inlet of the fifth three-way valve; the cathode outlet of the second-stage fuel cell stack is connected to the inlet of the afterburner.

[0016] Furthermore, it also includes a flow monitoring controller, which includes a first flow monitoring controller connected between the cathode outlet of the first-stage fuel cell stack and the second inlet of the fifth three-way valve, and a second flow monitoring controller connected between the fan and the inlet of the third three-way valve.

[0017] Furthermore, it also includes an organic Rankine cycle unit, which includes a pump, a steam turbine, a multi-stream heat exchanger, and a water-cooled heat exchanger. The pump is connected to the cold end of the multi-stream heat exchanger, the steam turbine, and the hot end of the water-cooled heat exchanger in sequence. The first hot end of the multi-stream heat exchanger is installed between the cathode outlet of the second-stage fuel cell stack and the inlet of the afterburner, and the second hot end inlet of the multi-stream heat exchanger is connected to the hot end outlet of the second heat exchanger.

[0018] Furthermore, it also includes an inverter, which includes an inverter and an inverter. The current output end of the first-stage fuel cell stack is connected to the inverter, and the current output end of the second-stage fuel cell stack is connected to the inverter.

[0019] Furthermore, a catalytic cracking channel and a heat exchange channel are provided inside the ammonia decomposition reactor. The catalytic cracking channel is connected to the cold end outlet of the first heat exchanger and the first three-way valve, and the heat exchange channel is connected to the second three-way valve and the hot end inlet of the first heat exchanger.

[0020] Furthermore, a catalytic layer is provided in the catalytic cracking channel of the ammonia decomposition reactor, and the material of the catalytic layer is a nickel-based catalyst.

[0021] Furthermore, the temperature target of the ammonia decomposition reactor is set to 650°C to 750°C.

[0022] Furthermore, the first heat exchanger and the second heat exchanger are shell-and-tube heat exchangers.

[0023] Furthermore, the multi-stream heat exchanger and the water-cooled heat exchanger are shell-and-tube heat exchangers.

[0024] A power generation device comprises any one of the above-mentioned indirect cascade fuel cell systems.

[0025] After adopting the above technical solution, the present invention has the following positive effects:

[0026] (1) Combination of two-stage fuel cell stack and dual tail gas circulation: A two-stage fuel cell stack structure is adopted, integrating anode tail gas circulation (AOGR) and cathode tail gas circulation (COGR), to solve the problems of low fuel utilization (residual fuel in tail gas) and insufficient utilization of high-temperature waste heat in traditional technologies.

[0027] (2) Optimization of the anode tail gas circulation fuel distribution scheme: After the two-stage stack anode tail gas is combined, it provides heat for the ammonia decomposition reactor and the first heat exchanger, and then is split into two streams, one of which is fed into the second-stage stack anode to continue the reaction; the other is fed into the afterburner, thereby improving the fuel utilization efficiency.

[0028] (3) Intelligent control design: Through the flow monitoring controller, the temperature and flow parameters of the cathode outlet and the fan outlet of the first-stage fuel cell stack are monitored synchronously to realize real-time data monitoring of the system operation status. Based on the real-time monitoring data, the air distribution ratio of the three-way valve is automatically calculated and controlled to ensure that the temperature of the air entering the cathode of the second-stage fuel cell stack meets the temperature requirements. Through the closed-loop process of "monitoring → calculation → control", a complete feedback mechanism from data acquisition to execution and adjustment is formed, thereby improving the stability and reliability of the system.

[0029] (4) Further optimization of energy utilization: ORC (Organic Rankine Cycle Unit): further recovers the heat in the cathode cycle exhaust gas and the afterburner exhaust gas to improve the energy utilization efficiency of the system; Multi-stream heat exchanger: utilizes the waste heat from the cathode outlet of the second-stage fuel cell stack and the afterburner exhaust gas to improve the energy utilization efficiency of the system.

[0030] Therefore, the system of the present invention has high design fuel utilization rate, high electrical efficiency and high system thermal efficiency, and has broad market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments and in conjunction with the accompanying drawings, wherein

[0032] Figure 1 A schematic structural diagram of an embodiment of an indirect cascade fuel cell system according to the present invention;

[0033] Figure 2 FIG. 1 is a structural schematic diagram of another embodiment of an indirect cascade fuel cell system of the present invention.

[0034] The numbers in the accompanying drawings are: 1-ammonia supply device; 2-throttle valve; 31-first heat exchanger; 32-second heat exchanger; 33-water-cooled heat exchanger; 4-ammonia decomposition reactor; 51-first three-way valve; 52-second three-way valve; 53-third three-way valve; 54-fourth three-way valve; 55-fifth three-way valve; 61-first stage fuel cell stack; 62-second stage fuel cell stack; 71-first flow monitoring controller; 72-second flow monitoring controller; 8-afterburner; 91-inverter; 92-inverter; 10-fan; 11-pump; 12-steam turbine; 13-multi-stream heat exchanger. DETAILED DESCRIPTION

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0036] In the description of this patent, it should be noted that, unless otherwise expressly specified or limited, the terms "connected," "connected," and "disposed" should be understood broadly. For example, they can refer to fixed connection or disposition, detachable connection or disposition, or integral connection or disposition. Those skilled in the art will understand the specific meanings of the above terms in this patent based on the specific circumstances.

[0037] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0038] In one embodiment, see the attached Figure 1 The present invention provides an indirect cascade fuel cell system, comprising an ammonia supply device 1, a throttle valve 2, a heat exchange unit, an ammonia decomposition reactor 4, a plurality of three-way valves, a fuel cell stack, and an afterburner 8; the fuel cell stack comprises a first-stage fuel cell stack 61 and a second-stage fuel cell stack 62; the heat exchange unit comprises a first heat exchanger 31 and a second heat exchanger 32, which fully utilizes the high-temperature waste heat in the combustion exhaust as a heat source for fuel gas, air, and the system, thereby improving the heat utilization efficiency of the entire system; the ammonia supply device 1 is connected to the throttle valve 2, the cold end of the first heat exchanger 31, the ammonia decomposition reactor 4, and the inlet of the first three-way valve 51 in sequence; the cold end of the first heat exchanger 31 is connected to the throttle valve 2 and the ammonia decomposition reactor 4 in sequence, and the first heat exchanger 31 is connected to the throttle valve 2 and the ammonia decomposition reactor 4 in sequence. The hot end is connected to the exhaust gas outlet in the ammonia decomposition reactor 4 and the fourth three-way valve 54 in sequence; the first outlet of the first three-way valve 51 is connected to the anode inlet of the first-stage fuel cell stack 61, and the second outlet of the first three-way valve 51 is connected to the anode inlet of the second-stage fuel cell stack 62; the anode outlets of the first-stage fuel cell stack 61 and the second-stage fuel cell stack 62 are respectively connected to the first inlet and the second inlet of the second three-way valve 52; the outlet of the second three-way valve 52 is connected to the heat exchange channel of the ammonia decomposition reactor 4, the hot end of the first heat exchanger 31, and the inlet of the fourth three-way valve 54 in sequence; the first outlet of the fourth three-way valve 54 is connected to the anode inlet of the second-stage fuel cell stack 62, and the second outlet of the fourth three-way valve 54 is connected to the inlet of the afterburner 8.

[0039] In this embodiment, the ammonia supply device 1 may be an ammonia tank or an ammonia cylinder, which is used to provide ammonia fuel.

[0040] In this embodiment, the ammonia decomposition reactor 4 decomposes the ammonia fuel so that the mixed gas entering the ammonia decomposition reactor 4 for combustion is mainly hydrogen, thereby avoiding the pollution of the environment by the generation of nitrogen oxides.

[0041] In this embodiment, ammonia decomposition reactor 4 is internally provided with a catalytic cracking channel and a heat exchange channel. The heat exchange channel supplies heat to the catalytic cracking process, enabling the complete cracking of ammonia into H2 and N2. The catalytic cracking channel is sequentially connected to the cold outlet of the first heat exchanger 31 and the first three-way valve 51. The heat exchange channel is sequentially connected to the second three-way valve 52 and the hot inlet of the first heat exchanger 31.

[0042] In this embodiment, it also includes a fan 10, a third three-way valve 53 and a fifth three-way valve 55; the fan 10 is connected to the inlet of the third three-way valve 53; the first outlet of the third three-way valve 53 is connected to the cold end inlet of the second heat exchanger 32, and then connected to the cathode inlet of the first-stage fuel cell stack 61, and the second outlet of the third three-way valve 53 is connected to the first inlet of the fifth three-way valve 55; the cathode outlet of the first-stage fuel cell stack 61 is connected to the second inlet of the fifth three-way valve 55; the outlet of the fifth three-way valve 55 is connected to the anode inlet of the second-stage fuel cell stack 62; the cathode outlet of the second-stage fuel cell stack 62 is connected to the inlet of the afterburner 8; the hot end inlet of the second heat exchanger 32 is connected to the outlet of the afterburner 8.

[0043] In this embodiment, the first flow monitoring controller 71 is connected between the cathode outlet of the first-stage fuel cell stack 61 and the second inlet of the fifth three-way valve 55, and the second flow monitoring controller 72 is connected between the fan 10 and the inlet of the third three-way valve 53. It can monitor the temperature and flow at the cathode outlet of the first-stage fuel cell stack and the fan outlet, and then control the proportion of air distributed by the three-way valve to the second-stage fuel cell stack so that the temperature of the air entering the cathode of the second-stage fuel cell stack meets the temperature requirement. Specifically, the air inlet flow and the flow at the cathode outlet of the first-stage fuel cell stack are measured at the same time, so that the combined gas temperature at the cathode inlet of the second-stage fuel cell stack is constant, the cathode exhaust gas of the first-stage fuel cell stack is reused, and the utilization efficiency of the cathode gas of the first-stage fuel cell stack is improved.

[0044] In this embodiment, an inverter is also included, which includes an inverter 91 and an inverter 92. The current output end of the first-stage fuel cell stack 61 is connected to the inverter 91, and the current output end of the second-stage fuel cell stack 62 is connected to the inverter 92 to convert direct current into alternating current that can be used by users.

[0045] In this embodiment, the ammonia supply device 1, the throttle valve 2, the heat exchange unit, the ammonia decomposition reactor 4, multiple three-way valves, the fuel cell stack, the flow monitoring controller, the afterburner 8, the inverter, the fan 10 and the organic Rankine cycle unit are connected by pipelines.

[0046] In this embodiment, the first heat exchanger 31 and the second heat exchanger 32 are shell-and-tube heat exchangers.

[0047] In this embodiment, the multi-stream heat exchanger 13 and the water-cooled heat exchanger 33 are both shell-and-tube heat exchangers.

[0048] In this embodiment, a catalytic layer is provided in the catalytic cracking channel of the ammonia decomposition reactor 4 , and the catalytic layer material is a nickel-based catalyst.

[0049] In this embodiment, the target temperature of the ammonia decomposition reactor 4 is set to 650°C to 750°C, so that the ammonia decomposition reaction occurs under the action of the catalyst and meets the minimum temperature required for entering the fuel cell stack. For example, the target temperature can be set to 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C, or 750°C.

[0050] In another embodiment, see the attached Figure 2 , also includes an organic Rankine cycle unit, which includes a pump 11, a steam turbine 12, a multi-stream heat exchanger 13, and a water-cooled heat exchanger 33. The pump 11 is connected in sequence to the cold end of the multi-stream heat exchanger 13, the steam turbine 12, and the hot end of the water-cooled heat exchanger 3. The first hot end of the multi-stream heat exchanger 13 is installed between the cathode outlet of the second-stage fuel cell stack 2 and the inlet of the afterburner 8, and the second hot end inlet of the multi-stream heat exchanger 13 is connected to the hot end outlet of the second heat exchanger 32. The multi-stream heat exchanger 13 utilizes the waste heat from the cathode outlet of the second-stage fuel cell stack and the afterburner exhaust, improving the energy efficiency of the system. Pipelines connect the pump 11, steam turbine 12, multi-stream heat exchanger 13, water-cooled heat exchanger 33, and the fuel cell stack system.

[0051] In another embodiment, a power generation device includes any of the above-mentioned indirect cascade fuel cell systems.

[0052] The working process of the above-mentioned indirect cascade fuel cell system is as follows:

[0053] 1. Ammonia cracking and entering the anodes of the two fuel cell stacks: Ammonia from the ammonia supply device 1 passes through the throttle valve 2 and enters the first heat exchanger 31. After the temperature is raised to 650°C to 750°C, it enters the catalytic cracking channel of the ammonia decomposition reactor 4, decomposing into nitrogen and hydrogen. The two gases then enter the first-stage fuel cell stack 61 and the second-stage fuel cell stack 62 in a ratio of 6:4, participating in the electrochemical reactions within the fuel cell stacks. Specifically, the temperature of the ammonia gas must be raised to 650°C to 750°C upon entering the first heat exchanger 31. The heat supply to the ammonia decomposition reactor 4 in the subsequent process is intended to maintain this temperature range.

[0054] II. Treatment of the two stack anode tail gases: The two stack anode tail gases enter the second three-way valve 52, merge into a single stream, and then flow into the heat exchange channel of the ammonia decomposition reactor 4 to provide heat for catalytic cracking of the ammonia. They then enter the first heat exchanger 31 to provide heat for ammonia preheating. They then enter the fourth three-way valve 54 and enter the anode of the second-stage stack 62 and the afterburner 8 in a ratio of 4:6.

[0055] 3. Air enters the cathodes of the two stacks: Air passes through fan 10, second flow monitoring controller 72, and third three-way valve 53. According to the ratio calculated by flow monitoring controller 72, a portion enters second heat exchanger 32, where it is heated to 650°C to 750°C. It then enters the cathode of first-stage stack 61. The remaining portion enters fifth three-way valve 55, combines with the cathode exhaust of first-stage stack 61, and enters the cathode of second-stage stack 62, participating in the electrochemical reaction in the stack. The generated current is converted from DC to AC via inverter 9.

[0056] 4. Afterburner working process: The cathode tail gas of the second-stage fuel cell stack 62 enters the afterburner 8 and is burned together with the flow from the second outlet of the fourth three-way valve 54, then enters the second heat exchanger 32 to provide heat for heating the air, and is finally discharged into the air.

[0057] V. Operation of Flow Monitoring Controller 7: Monitors the temperature and flow at the cathode outlet of first-stage stack 61 and at the outlet of blower 10, and automatically calculates and controls the air distribution ratio of third three-way valve 53 to the second-stage stack, ensuring that the air temperature entering the cathode of second-stage stack 62 meets the required temperature. Specifically, the flow monitoring controller can simultaneously monitor the temperature and flow at the cathode outlet of first-stage stack 61 and at the outlet of blower 10, enabling real-time data monitoring of the system's operating status. Based on this real-time monitoring data, the air distribution ratio of the three-way valve is automatically calculated and controlled. This closed-loop process of "monitoring → calculation → control" forms a complete feedback mechanism from data acquisition to regulation execution, improving system stability and reliability.

[0058] For example, the first flow monitoring controller 71 monitors the temperature T at the cathode outlet of the first-stage fuel cell stack 61. a and flow rate n aThe second flow monitoring controller 72 monitors the temperature T at the outlet of the fan 10 b and flow rate n b Assume that the ratio of the air distributed by the third three-way valve 53 to the second-stage stack 62 is x, and the inlet temperature of the second-stage stack 62 is known to be T 入口 , then the following formula is satisfied.

[0059]

[0060] Solving for x yields:

[0061]

[0062] This realizes the closed-loop process of "monitoring → calculation → control". It should be noted that, in addition to the above content, other control logic, methods and program control codes involved can refer to the existing technology and will not be elaborated here. VI. ORC (Organic Rankine Cycle Unit) Working Process: See Figure 2 After passing through pump 11, the isobutane increases in pressure. It then flows through multi-stream heat exchanger 13, absorbing heat from the cathode exhaust of the second-stage stack 62 and the exhaust of the afterburner 8, raising its temperature. It then passes through the steam turbine to generate electricity, reducing its pressure. Finally, it passes through the water-cooled heat exchanger 33, where its temperature is lowered, before re-entering pump 11, completing the cycle. In other words, the multi-stream heat exchanger 13 utilizes the waste heat from the cathode outlet of the second-stage stack 6 and the exhaust of the afterburner 8, improving the system's energy efficiency. This can be understood as a fuel cell system coupled with an organic Rankine cycle unit, further utilizing the heat from the cathode and exhaust gases to generate electricity, improving the system's electrical efficiency. Furthermore, the high-temperature waste heat from the combustion exhaust is fully utilized as a heating source for the fuel gas and the organic Rankine cycle working fluid, improving the overall system's thermal efficiency. Therefore, the system design of the present invention offers high fuel efficiency, a high safety factor, environmental friendliness, high electrical and thermal efficiency, and broad market prospects.

[0063] 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 various embodiments of the present invention.

Claims

1. An indirect cascade fuel cell system, characterized in that: include: An ammonia supply device (1), a throttle valve (2), a heat exchange unit, an ammonia decomposition reactor (4), a first three-way valve (51), a fuel cell stack, and an afterburner (8); The heat exchange unit comprises a first heat exchanger (31) and a second heat exchanger (32); The battery stack comprises a first-stage battery stack (61) and a second-stage battery stack (62); The ammonia supply device (1) is sequentially connected to the throttle valve (2), the first heat exchanger (31), the ammonia decomposition reactor (4), the first three-way valve (51), and the anode inlet of the first-stage fuel cell stack (61); The first outlet of the first three-way valve (51) is connected to the anode inlet of the first-stage fuel cell stack (61), and the second outlet is connected to the anode inlet of the second-stage fuel cell stack (62); The anode outlets of the first-stage battery stack (61) and the second-stage battery stack (62) are respectively connected to the first inlet and the second inlet of the second three-way valve (52); The outlet of the second three-way valve (52) is connected in sequence to the heat exchange channel of the ammonia decomposition reactor (4), the hot end of the first heat exchanger (31), and the inlet of the fourth three-way valve (54); The first outlet of the fourth three-way valve (54) is connected to the anode inlet of the second-stage fuel cell stack (62), and the second outlet of the fourth three-way valve (54) is connected to the inlet of the afterburner (8).

2. The indirect cascade fuel cell system according to claim 1, characterized in that: The invention also includes a fan (10), a third three-way valve (53) and a fifth three-way valve (55), wherein the fan (10) is connected in sequence to the first outlet of the third three-way valve (53), the second heat exchanger (32) and the cathode inlet of the first-stage fuel cell stack (61); the second outlet of the third three-way valve (53) is connected to the first inlet of the fifth three-way valve (55), and then connected to the cathode inlet of the second-stage fuel cell stack (62); the cathode outlet of the first-stage fuel cell stack (61) is connected to the second inlet of the fifth three-way valve (55); and the cathode outlet of the second-stage fuel cell stack (62) is connected to the inlet of the afterburner (8).

3. The indirect cascade fuel cell system according to claim 2, characterized in that: The system also includes a flow monitoring controller, which includes a first flow monitoring controller (71) connected between the cathode outlet of the first-stage fuel cell stack (61) and the second inlet of the fifth three-way valve (55), and a second flow monitoring controller (72) connected between the fan (10) and the inlet of the third three-way valve (53).

4. The indirect cascade fuel cell system according to claim 1, characterized in that: The organic Rankine cycle unit includes a pump (11), a steam turbine (12), a multi-stream heat exchanger (13), and a water-cooled heat exchanger (33). The pump (11) is connected to the cold end of the multi-stream heat exchanger (13), the steam turbine (12), and the hot end of the water-cooled heat exchanger (33) in sequence. The first hot end of the multi-stream heat exchanger (13) is installed between the cathode outlet of the second-stage fuel cell stack (62) and the inlet of the afterburner (8). The second hot end inlet of the multi-stream heat exchanger (13) is connected to the hot end outlet of the second heat exchanger (32).

5. The indirect cascade fuel cell system according to claim 1, characterized in that: The invention also includes an inverter, wherein the inverter includes an inverter (91) and an inverter (92), the current output end of the first-stage battery stack (61) is connected to the inverter (91), and the current output end of the second-stage battery stack (62) is connected to the inverter (92).

6. The indirect cascade fuel cell system according to claim 1, characterized in that: A catalytic cracking channel and a heat exchange channel are provided inside the ammonia decomposition reactor (4); the catalytic cracking channel is connected to the cold end outlet of the first heat exchanger (31) and the first three-way valve (51); and the heat exchange channel is connected to the second three-way valve (52) and the hot end inlet of the first heat exchanger (31).

7. The indirect cascade fuel cell system according to claim 6, characterized in that: A catalytic layer is provided in the catalytic cracking channel of the ammonia decomposition reactor (4), and the material of the catalytic layer is a nickel-based catalyst.

8. The indirect cascade fuel cell system according to claim 1, characterized in that: The temperature target of the ammonia decomposition reactor (4) is set to 650°C to 750°C.

9. The indirect cascade fuel cell system according to claim 4, characterized in that: The first heat exchanger (31), the second heat exchanger (32), the multi-stream heat exchanger (13) and the water-cooled heat exchanger (33) are shell-and-tube heat exchangers.

10. A power generation device, characterized in that: An indirect cascade fuel cell system comprising any one of claims 1 to 9.

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