Fuel cell system

Abstract

The invention discloses a fuel cell system which is characterized in that a first inlet of a first fuel input device is used for receiving external fuel, and two outlets of the first fuel input device are respectively connected with a first electrode and a second electrode of a primary electric pile; a first electrode and a second electrode of the primary electric pile are respectively connected with a first inlet and a second inlet of the second fuel input device; a third inlet of the second fuel input device is used for receiving external air, and a fourth inlet of the second fuel input device is connected with a first outlet of the circulating device; and the first outlet and the second outlet of the second fuel input device are respectively connected with the first electrode and the second electrode of the secondary electric pile. According to the technical scheme, performance degradation of the secondary electric pile is avoided, fuel circulation is achieved, the fuel utilization rate and the output power of the primary electric pile and the fuel utilization rate and the output power of the secondary electric pile are taken into consideration at the same time, the fuel utilization rate and the output power meet the system requirements, and the parasitic power consumption and the complexity of the system are reduced.

Description

Technical Field

[0001] The embodiments of the present invention relate to fuel cell technology, and in particular to a fuel cell system. Background Art

[0002] Currently, the power generation efficiency of fuel cells is about 60%. To avoid rapid degradation of the stack performance, a safety margin is generally set for the combustion utilization rate of the stack during system operation. Therefore, the key to improving the power generation efficiency is to improve the system combustion utilization rate as much as possible while ensuring the fuel utilization rate of the stack. Cascade utilization and recycling of combustion are one of the effective methods to improve the system fuel utilization rate.

[0003] In the prior art, the gas discharged from the anode of the first-stage stack is cooled and drained and then enters the second-stage stack. The separated water is mixed with the external fuel and then enters the first-stage stack. The anode tail gas of the second-stage stack is condensed, drained, and then recycled back to the first-stage stack. This not only exacerbates the performance degradation of the second-stage stack, but also reduces the combustion utilization rate of the fuel cell system, and at the same time increases the parasitic power consumption and complexity of the system. Summary of the Invention

[0004] The embodiments of the present invention provide a fuel cell system, which not only avoids the performance degradation of the second-stage stack, realizes the recycling of fuel, but also takes into account the fuel utilization rate and output power of both the first-stage stack and the second-stage stack, enables the fuel utilization rate and output power to meet the system requirements, and reduces the parasitic power consumption and complexity of the system.

[0005] In a first aspect, a fuel cell system provided by the embodiments of the present invention includes: a controller, a first fuel input device, a second fuel input device, a first-stage stack, a second-stage stack, and a recycling device;

[0006] Wherein, the controller is electrically connected to the first fuel input device, the second fuel input device, the first-stage stack, the second-stage stack, and the recycling device;

[0007] The first inlet of the first fuel input device is used to receive external fuel, and the second inlet is used to receive air; the two outlets of the first fuel input device are respectively connected to the first electrode and the second electrode of the first-stage stack;

[0008] The first fuel input device is used to receive external fuel and air, process the external fuel and air, and respectively input fuel to the first electrode of the first-stage stack and input air to the second electrode of the first-stage stack;

[0009] The first electrode and the second electrode of the first-level stack are respectively connected to the first inlet and the second inlet of the second fuel input device; the third inlet of the second fuel input device is used to receive external air, and the fourth inlet of the second fuel input device is connected to the first outlet of the circulation device; the first outlet and the second outlet of the second fuel input device are respectively connected to the first electrode and the second electrode of the second-level stack, and the third outlet of the second fuel input device is connected to the first inlet of the circulation device; the fourth inlet of the second fuel input device is also used to receive external fuel;

[0010] The second outlet of the circulation device is connected to the first inlet of the first fuel input device; the second inlet of the circulation device is used to receive external fuel;

[0011] The second fuel input device is used to receive the exhaust gas from the first electrode of the first-level stack and the exhaust gas from the second electrode of the first-level stack, and is also used to receive external air, input the exhaust gas from the first electrode of the first-level stack into the circulation device, and mix the exhaust gas from the second electrode of the first-level stack with external air and then input it into the second electrode of the second-level stack;

[0012] The controller is used to control the first fuel input device, the second fuel input device, the first-level stack and the second-level stack to start, obtain the output power and fuel utilization rate of the first-level stack, and obtain the output power and fuel utilization rate of the second-level stack, and control the working state of the circulation device according to the output power and fuel utilization rate of the first-level stack and the output power and fuel utilization rate of the second-level stack;

[0013] Among them, the working state of the circulation device includes a first working state and a second working state; in the first working state, the circulation device processes the exhaust gas from the first electrode of the first-level stack and then transmits it to the second fuel input device; in the second working state, the circulation device receives external fuel, processes the exhaust gas from the first electrode of the first-level stack, inputs the processed part of the exhaust gas and external fuel into the first fuel input device, and inputs the processed part of the exhaust gas into the second fuel input device;

[0014] The second fuel input device is also used to process the external fuel and the processed exhaust gas input by the circulation device and then transmit it to the first electrode of the second-level stack.

[0015] A fuel cell system provided by an embodiment of the present invention includes: a controller, a first fuel input device, a second fuel input device, a primary fuel cell stack, a secondary fuel cell stack, and a circulation device. The controller is electrically connected to the first fuel input device, the second fuel input device, the primary fuel cell stack, the secondary fuel cell stack, and the circulation device. A first inlet of the first fuel input device is used to receive external fuel, and a second inlet is used to receive air. Two outlets of the first fuel input device are respectively connected to a first electrode and a second electrode of the primary fuel cell stack. The first fuel input device is used to receive external fuel and air, process the external fuel and air, and respectively input fuel to the first electrode of the primary fuel cell stack and input air to the second electrode of the primary fuel cell stack. The first electrode and the second electrode of the primary fuel cell stack are respectively connected to a first inlet and a second inlet of the second fuel input device. A third inlet of the second fuel input device is used to receive external air, a fourth inlet of the second fuel input device is connected to a first outlet of the circulation device, a first outlet and a second outlet of the second fuel input device are respectively connected to a first electrode and a second electrode of the secondary fuel cell stack, a third outlet of the second fuel input device is connected to a first inlet of the circulation device, and the fourth inlet of the second fuel input device is further used to receive external fuel. A second outlet of the circulation device is connected to a first inlet of the first fuel input device. A second inlet of the circulation device is used to receive external fuel. The second fuel input device is used to receive the tail gas of the first electrode of the primary fuel cell stack and the tail gas of the second electrode of the primary fuel cell stack, and is further used to receive external air, input the tail gas of the first electrode of the primary fuel cell stack into the circulation device, and mix the tail gas of the second electrode of the primary fuel cell stack with external air and then input it to the second electrode of the secondary fuel cell stack. The controller is used to, after controlling the first fuel input device, the second fuel input device, the primary fuel cell stack, and the secondary fuel cell stack to start, obtain the output power and fuel utilization rate of the primary fuel cell stack, and obtain the output power and fuel utilization rate of the secondary fuel cell stack, and control the working state of the circulation device according to the output power and fuel utilization rate of the primary fuel cell stack, and the output power and fuel utilization rate of the secondary fuel cell stack. The fuel cell system of this embodiment includes a controller, a first fuel input device, a second fuel input device, a primary fuel cell stack, a secondary fuel cell stack, and a circulation device. After the controller controls the first fuel input device, the second fuel input device, the primary fuel cell stack, and the secondary fuel cell stack to start, it obtains the output power and fuel utilization rate of the primary fuel cell stack, and obtains the output power and fuel utilization rate of the secondary fuel cell stack, and controls the working state of the circulation device according to the output power and fuel utilization rate of the primary fuel cell stack, and the output power and fuel utilization rate of the secondary fuel cell stack.In this embodiment, the working state of the circulation device is adjusted according to the fuel utilization rate and output power of the first-stage stack and the second-stage stack. The circulation device can process the tail gas of the first electrode of the first-stage stack in the first working state, so that the tail gas of the first electrode of the first-stage stack can be reused by the second-stage stack. The circulation device can process the tail gas of the first electrode of the first-stage stack in the second working state, so that the tail gas of the first electrode of the first-stage stack can be reused by the first-stage stack and the second-stage stack. This not only avoids the performance degradation of the second-stage stack, realizes the recycling of fuel, but also takes into account the fuel utilization rate and output power of both the first-stage stack and the second-stage stack, making the fuel utilization rate and output power meet the system requirements, and reducing the parasitic power consumption and complexity of the system.

[0016] It should be understood that the content described in this part is not intended to identify the key or important features of the embodiments of the present invention, nor is it used to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0018] Figure 1 is a schematic structural diagram of a fuel cell system provided by an embodiment of the present invention;

[0019] Figure 2 is a schematic structural diagram of the power output and controller configuration of the fuel cell system provided by an embodiment of the present invention;

[0020] Figure 3 is a schematic diagram of the ejector regulation structure provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] In order to enable those skilled in the art to better understand the solution of the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0022] It should be noted that the terms "first", "second", etc. in the description, claims and above-mentioned drawings of the present invention are used to distinguish similar objects and do not necessarily describe a specific order or sequence. It should be understood that such data used can be interchanged under appropriate circumstances so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0023] Figure 1 is a schematic structural diagram of a fuel cell system provided by an embodiment of the present invention. Figure 2 is a schematic structural diagram of the power output and controller configuration of the fuel cell system provided by an embodiment of the present invention. Refer to Figure 1 and Figure 2 This fuel cell system includes: a controller 23, a first fuel input device 14, a second fuel input device 15, a primary fuel cell stack 11, a secondary fuel cell stack 12, and a circulation device 13. Among them, the controller is electrically connected to the first fuel input device 14, the second fuel input device 15, the primary fuel cell stack 11, the secondary fuel cell stack 12, and the circulation device 13.

[0024] The first inlet of the first fuel input device 14 is used to receive external fuel 1, the second inlet is used to receive air, and the two outlets of the first fuel input device 14 are respectively connected to the first electrode and the second electrode of the primary fuel cell stack 11. The first fuel input device 14 is used to receive external fuel and air, process the external fuel and air, and respectively input fuel to the first electrode of the primary fuel cell stack and air to the second electrode of the primary fuel cell stack 11.

[0025] The first electrode and the second electrode of the primary fuel cell stack 11 are respectively connected to the first inlet and the second inlet of the second fuel input device 15. The third inlet of the second fuel input device 15 is used to receive external air, the fourth inlet of the second fuel input device 15 is connected to the first outlet of the circulation device 13, the first outlet and the second outlet of the second fuel input device 15 are respectively connected to the first electrode and the second electrode of the secondary fuel cell stack 12, and the third outlet of the second fuel input device 15 is connected to the first inlet of the circulation device 13; the fourth inlet of the second fuel input device 15 is also used to receive external fuel.

[0026] The second outlet of the circulation device 13 is connected to the first inlet of the first fuel input device 14; the second inlet of the circulation device 13 is used to receive external fuel 2.

[0027] The second fuel input device 15 is used to receive the exhaust gas from the first electrode of the primary stack 11 and the exhaust gas from the second electrode of the primary stack 11, and is also used to receive external air. It inputs the exhaust gas from the first electrode of the primary stack 11 into the circulation device, and mixes the exhaust gas from the second electrode of the primary stack 11 with the external air and then inputs it into the second electrode of the secondary stack 12.

[0028] The controller 23 is used to control the first fuel input device 14, the second fuel input device 15, the primary stack 11 and the secondary stack 12 to start. After that, it obtains the output power and fuel utilization rate of the primary stack 11, and obtains the output power and fuel utilization rate of the secondary stack 12. According to the output power and fuel utilization rate of the primary stack 11, and the output power and fuel utilization rate of the secondary stack 12, it controls the working state of the circulation device 13.

[0029] Among them, the working state of the circulation device 13 includes a first working state and a second working state. In the first working state, the circulation device 13 processes the exhaust gas from the first electrode of the primary stack 11 and then transmits it to the second fuel input device 15. In the second working state, the circulation device 13 receives external fuel, processes the exhaust gas from the first electrode of the primary stack 11, inputs the processed part of the exhaust gas and the external fuel into the first fuel input device 14, and inputs the processed part of the exhaust gas into the second fuel input device 15.

[0030] The second fuel input device 15 is also used to process the external fuel and the processed exhaust gas input by the circulation device 13 and then transmit it to the first electrode of the secondary stack 12.

[0031] Among them, the first fuel input device 14 may include a steam generator 1, a primary stack steam reformer 2 and a primary stack air preheater 3. The second fuel input device 15 may include a secondary stack air mixer 5 and a secondary stack steam reformer 4. The circulation device 13 may include a condenser 6, a gas-water separator 7 and an ejector 8. The efficiency of the fuel cell system is determined by the fuel utilization rate and output power of the primary stack 11 and the secondary stack 12.

[0032] Specifically, the controller 23 controls the working state of the circulation device 13 according to the output power and fuel utilization rate of the first-stage fuel cell stack 11, and the output power and fuel utilization rate of the second-stage fuel cell stack 12. It can be as follows: when the circulation device 13 is in the first working state, it is judged whether the output power and fuel utilization rate of the first-stage fuel cell stack 11, and the output power and fuel utilization rate of the second-stage fuel cell stack 12 meet the requirements. If they meet the requirements, the controller 23 controls the circulation device 13 to be in the first working state; if they do not meet the requirements, the controller 23 controls the circulation device 13 to enter the second working state. It can also be that when the circulation device is in the second working state, it is judged whether the output power and fuel utilization rate of the first-stage fuel cell stack 11, and the output power and fuel utilization rate of the second-stage fuel cell stack 12 meet the requirements. If they meet the requirements, the controller 23 controls the circulation device 13 to be in the second working state; if they do not meet the requirements, the controller 23 controls the circulation device 13 to enter the first working state.

[0033] Exemplarily, when the fuel cell system is in the startup process, the second-stage fuel cell stack 12 does not undergo an electrochemical reaction, and the set value of the external fuel 2 is 0. At this time, the circulation device 13 is in the first working state (i.e., the first electrode exhaust gas of the first-stage fuel cell stack 11 is not recycled). The external fuel 1 enters the first electrode of the first-stage fuel cell stack 11 after being processed by the first fuel input device 14. The external air 1 is input to the second electrode of the first-stage fuel cell stack 11 after being processed by the first fuel input device 14. The external fuel and air come into contact with each other on the surface of the electrolyte and undergo an electrochemical reaction. At this time, the controller 23 obtains the output power and fuel utilization rate of the first-stage fuel cell stack 11. After the output power of the first-stage fuel cell stack 11 gradually increases to the set value, the controller 23 controls the second-stage fuel cell stack 12 to output current. At this time, the circulation device 13 still remains in the first working state. The first electrode exhaust gas of the first-stage fuel cell stack 11 is input to the circulation device 13 through the second fuel input device 15. After being processed by the circulation device 13, the condensed water obtained is input to the first fuel input device 14, and the gas in the first electrode exhaust gas of the processed first-stage fuel cell stack 11 is input to the first electrode of the second-stage fuel cell stack 12 through the second fuel input device 15. The external fuel 3 also enters the first electrode of the second-stage fuel cell stack 12 after being processed by the second fuel input device 15. The external air 2 is input to the second electrode of the second-stage fuel cell stack 12 after being processed by the second fuel input device 15. The mixed gas of the gas in the processed first electrode exhaust gas of the first-stage fuel cell stack 11 and the external fuel 3 comes into contact with the external air 2 on the surface of the electrolyte and undergoes an electrochemical reaction. At this time, the controller obtains the output power and fuel utilization rate of the second-stage fuel cell stack 12. After the output power of the second-stage fuel cell stack 12 gradually increases to the set value, the entire fuel cell system enters the stable operation state, and the startup process is completed.

[0034] When the fuel cell system is in the operation / regulation process, the controller 23 will judge whether the output power and combustion utilization rate of the primary stack 11 and the secondary stack 12 reach the expected values. If the output power and combustion utilization rate of the primary stack 11 and the secondary stack 12 reach the expectation, there is no need to recycle the tail gas of the first electrode of the primary stack 11, and the control circulation device 13 will be maintained in the first working state. If the output power and combustion utilization rate of the primary stack 11 and the secondary stack 11 do not reach the expectation, the control circulation device 13 will be in the second working state.

[0035] When the output power and combustion utilization rate of the primary stack 11 and the secondary stack 12 do not reach the expectation, set the initial value of the flow rate of the external fuel 2, and reduce the flow rate of the external fuel 1. The reduction amount is the flow rate of the external fuel 2, that is, it is necessary to ensure that the total amount of the external fuel entering the primary stack 11 does not change. The total amount of the external fuel enters the first electrode of the primary stack 11 after being processed by the first fuel input device 14. The external air 1 is input to the second electrode of the primary stack 11 after being processed by the first fuel input device 14. The external fuel and air contact each other on the surface of the electrolyte to generate an electrochemical reaction. After the electrochemical reaction, the tail gas of the first electrode of the primary stack 11 is input to the circulation device 13 through the second fuel input device 15. After being processed by the circulation device 13, the gas in the processed tail gas of the first electrode of the primary stack 11 is mixed with the external fuel 2 and then recycled back to the first electrode of the primary stack 11 after being processed by the first fuel input device 14. The processed condensed water is input to the first electrode of the primary stack 11 through the first fuel input device 14. The gas in the other part of the processed tail gas of the first electrode of the primary stack 11 enters the first electrode of the secondary stack 12 through the second fuel input device 15. The controller 23 controls to slowly increase the flow rate of the external fuel 2 and observes the change of the system efficiency of the fuel cell. If the system efficiency of the fuel cell reaches the expected value before the external fuel 1 is reduced to 0, the adjustment is stopped and the fuel cell system operates stably. If the external fuel 1 is reduced to 0, that is, the circulation rate reaches the maximum and the system efficiency still does not reach the expectation, the controller needs to adjust the combustion utilization rate of the secondary stack 12. The controller controls to slowly increase the output power of the secondary stack 12, that is, to improve the fuel utilization rate of the secondary stack 12 until the fuel cell system reaches the expectation.

[0036] The fuel cell system of this embodiment includes a controller 23, a first fuel input device 14, a second fuel input device 15, a primary fuel cell stack 11, a secondary fuel cell stack 12, and a circulation device 13. After the controller 23 controls the first fuel input device 14, the second fuel input device 15, the primary fuel cell stack 11, and the secondary fuel cell stack 12 to start, it obtains the output power and fuel utilization rate of the primary fuel cell stack 11, and obtains the output power and fuel utilization rate of the secondary fuel cell stack 12. According to the output power and fuel utilization rate of the primary fuel cell stack 11, and the output power and fuel utilization rate of the secondary fuel cell stack 12, it controls the working state of the circulation device 13. In this embodiment, the working state of the circulation device 13 is adjusted according to the fuel utilization rate and output power of the primary fuel cell stack 11 and the secondary fuel cell stack 12. The circulation device 13 can process the first electrode tail gas of the primary fuel cell stack 11 in the first working state, so that the first electrode tail gas of the primary fuel cell stack 11 can be reused by the secondary fuel cell stack 12. The circulation device 13 can process the first electrode tail gas of the primary fuel cell stack 11 in the second working state, so that the first electrode tail gas of the primary fuel cell stack 11 can be reused by the primary fuel cell stack 11 and the secondary fuel cell stack 12. This not only avoids the performance degradation of the secondary fuel cell stack 12, but also realizes the recycling of fuel, and at the same time takes into account the fuel utilization rate and output power of both the primary fuel cell stack 11 and the secondary fuel cell stack 12, making the fuel utilization rate and output power meet the system requirements, and reducing the parasitic power consumption and complexity of the system.

[0037] Continue to participate Figure 1 and Figure 2 Optionally, on the basis of the above embodiment, the controller 23 is configured to control the circulation device 13 to be in the first working state after the first fuel input device 14, the second fuel input device 15, the primary fuel cell stack 11, and the secondary fuel cell stack 12 are started. When the circulation device 13 is in the first working state, if the output efficiency of the primary fuel cell stack 11 and the secondary fuel cell stack 12 meets the requirements, and the fuel utilization rates of the primary fuel cell stack 11 and the secondary fuel cell stack 12 are both within the safety margin, the controller 23 controls the circulation device 13 to maintain the first working state. When the circulation device 13 is in the first working state, if the fuel utilization rates of the primary fuel cell stack 11 and the secondary fuel cell stack 12 do not meet the requirements, the controller 23 controls the circulation device 13 to enter the second working state.

[0038] Specifically, when the fuel cell system enters the stable operation stage, the controller 23 will determine whether the output efficiencies of the primary fuel cell stack 11 and the secondary fuel cell stack 12 reach the expected values. If they do, it will then determine whether the combustion utilization rates of the primary fuel cell stack 11 and the secondary fuel cell stack 12 are within the safety boundaries. If the output efficiencies of the primary fuel cell stack 11 and the secondary fuel cell stack 12 reach the expected values, and the combustion utilization rates of both the primary fuel cell stack 11 and the secondary fuel cell stack 12 are within the safety boundaries, it indicates that the fuel cell system is operating as expected, and there is no need to recycle the tail gas of the first electrode of the primary fuel cell stack 11 (i.e., there is no need to transfer the tail gas of the first electrode of the primary fuel cell stack 11 to the primary fuel cell stack 11 for reuse). The controller 23 controls the circulation device 13 to be in the first working state. If the fuel utilization rates of the primary fuel cell stack 11 and the secondary fuel cell stack 12 do not meet the requirements, the controller 23 controls the circulation device 13 to enter the second working state.

[0039] In this embodiment of the technical solution, the controller 23 controls whether the circulation device 13 is in the first working state or the second working state by determining whether the output efficiencies of the primary fuel cell stack 11 and the secondary fuel cell stack 12 reach the expected values and whether the fuel utilization rates of the primary fuel cell stack 11 and the secondary fuel cell stack 12 are within the safety boundaries. When the fuel utilization rates of the primary fuel cell stack 11 and the secondary fuel cell stack 12 do not meet the requirements, a part of the tail gas of the first electrode of the primary fuel cell stack 11 is recycled through the circulation device 13, which can ensure that the fuel utilization rate of the system is increased on the premise that the fuel of the primary fuel cell stack 11 is within the safety boundary and improve the combustion utilization rate of the fuel cell system.

[0040] Figure 3 It is a schematic diagram of the ejector regulation structure provided by an embodiment of the present invention. Refer to Figure 1 and Figure 3 , on the basis of the above embodiments, optionally, the circulation device 13 includes a condenser 6, a gas-liquid separator 7, an ejector 8, a water pump 9, an isolation valve 19, and a first flow control valve 20; the controller is electrically connected to the condenser 6, the gas-liquid separator 7, the ejector 8, the water pump 9, the isolation valve 19, and the first flow control valve 20. The inlet of the condenser 6 is connected to the third outlet of the second fuel output device 15, and the outlet of the condenser 6 is connected to the inlet of the gas-liquid separator 7. The first outlet of the gas-liquid separator 7 is connected to the first inlet of the ejector 8, the second outlet of the gas-liquid separator 7 is connected to the inlet of the water pump 9, and the third outlet of the gas-liquid separator 7 is connected to the fourth inlet of the second fuel input device 15. The second inlet of the ejector 8 receives external fuel through the first flow control valve 20, and the outlet of the ejector 8 is connected to the first inlet of the first fuel input device 14 through the isolation valve 19. The outlet of the water pump 9 is connected to the first inlet of the first fuel input device 14.

[0041] The condenser 6 is used to cool the exhaust gas of the first electrode of the primary stack 11. The gas-water separator 7 is used to separate the gas and water from the exhaust gas of the first electrode of the primary stack 11, output the separated condensed water to the water pump 9, and output the separated gas to the ejector 8 and the second fuel output device 15. The ejector 8 is used to transmit the received separated gas and the external fuel 2 to the first fuel input device 14. The water pump 9 is used to transmit the separated condensed water to the first fuel output device 14.

[0042] The controller is used to control the condenser 6, the water pump 9 and the gas-water separator 7 to be turned on, and control the ejector 8, the isolation valve 19 and the first flow control valve 20 to be turned off when the circulation device 13 is in the first working state; when the circulation device is in the second working state, control the condenser 6, the gas-water separator 7, the ejector 8, the water pump 9, the isolation valve 19 and the first flow control valve 20 to be turned on.

[0043] Specifically, when the circulation device 13 is in the first working state, the controller controls the ejector 8 to be turned off, the isolation valve 19 and the first flow control valve 20 to be turned off, controls the condenser 6, the water pump 9 and the gas-water separator 7 to be turned on. All the external fuel entering the primary stack 11 is provided by the external fuel 1. The external fuel 1 generates a gas-water mixture through the first fuel input device 14, and after undergoing a reforming reaction, it is input to the first electrode of the primary stack 11. The external air 1 is heated through the first fuel input device 14 and then input to the second electrode of the primary stack 11 to undergo an electrochemical reaction with the external fuel. After that, the exhaust gas of the first electrode of the primary stack 11 is input to the condenser 6 through the second fuel input device 15. The condenser 6 condenses the exhaust gas of the first electrode of the primary stack 11 and then inputs it to the gas-water separator 7. The gas-water separator 7 separates the gas and water from the condensed exhaust gas. The separated condensed water is input to the first fuel input device 14 through the water pump 9, and then input to the first electrode of the primary stack 11 through the first fuel input device 14. The separated gas is output to the second fuel input device 15 and input to the first electrode of the secondary stack 12 together with the external fuel 3, and undergoes an electrochemical reaction with the external air of the second electrode of the secondary stack 12.

[0044] When the circulation device 13 is in the second working state, the controller controls the ejector 8 to operate, controls the isolation valve 19 and the first flow control valve 20 to open, and controls the condenser 6, the water pump 9 and the gas-water separator 7 to open. At this time, the fuel entering the first-stage stack 11 is provided by the external fuel 1, the external fuel 2, and a part of the gas in the tail gas of the first electrode of the first-stage stack separated by the circulation device 13. The fuel passes through the first fuel input device 14 to generate a gas-water mixture, and after a reforming reaction, it is input to the first electrode of the first-stage stack 11. The external air 1 is heated by the first fuel input device 14 and then input to the second electrode of the first-stage stack 11, where it undergoes an electrochemical reaction with the external fuel at the first electrode of the first-stage stack 11. Then, the tail gas of the first electrode of the first-stage stack 11 is input to the condenser 6 through the second fuel input device 15. The condenser 6 condenses the tail gas of the first electrode of the first-stage stack 11 and then inputs it to the gas-water separator 7. The gas-water separator 7 separates out a part of the gas and inputs it to the ejector 8, and the ejector 8 inputs it and the external fuel 2 to the first fuel input device 14. Another part of the gas separated by the gas-water separator 7 is input to the first electrode of the second-stage stack 12 through the second fuel input device 15.

[0045] In the technical solution provided in this embodiment, when the circulation device 13 is in the first working state, the controller controls the condenser 6, the water pump 9 and the gas-water separator 7 to open, and controls the ejector 8, the isolation valve 19 and the first flow control valve 20 to close, thereby realizing the condensation and gas-water separation of the tail gas of the first electrode of the first-stage stack. When the circulation device 13 is in the second working state, by controlling the condenser 6, the gas-water separator 7, the ejector 8, the water pump 9, the isolation valve 19 and the first flow control valve 20 to open, not only can the condensation and gas-water separation of the first electrode of the first-stage stack be realized, but also the recirculation of the tail gas of the first electrode of the first-stage stack by the operation of the ejector 8 is beneficial to improving the fuel utilization rate of the system on the premise of ensuring the safety margin of the first-stage stack.

[0046] Continue to refer to Figure 1 and Figure 3 Based on the above embodiments, optionally, the fuel cell system further includes: a second flow control valve 21, a first mixing valve 17 and a second mixing valve 16. The second flow control valve 21 is electrically connected to the controller. The input end of the second flow control valve 21 is used to receive the external fuel 1, and the output end is connected to the first end of the first mixing valve 17. The second end of the first mixing valve 17 is connected to the outlet of the ejector 8, and the third end is connected to the first end of the second mixing valve 16. The second end of the second mixing valve 16 is connected to the outlet of the water pump 9, and the third end is connected to the first inlet of the first fuel input device 14.

[0047] The controller is used to adjust the opening degrees of the first flow control valve 20 and the second flow control valve 21 according to the output power of the first fuel cell stack 11 and the output power of the second fuel cell stack 12 when the circulation device 13 is in the second working state, so as to adjust the flow rate of the external fuel 2 input by the first flow control valve 20 and the flow rate of the external fuel 1 input by the second flow control valve 21. Wherein, the sum of the flow rate of the external fuel 2 input by the first flow control valve 20 and the flow rate of the external fuel 1 input by the second flow control valve 21 is a fixed value.

[0048] Specifically, when the circulation device 13 is in the first working state, the controller controls the second flow control valve 21 to open, and all the external fuel entering the fuel cell system is provided by the external fuel 1. The controller determines whether the output power and combustion utilization rate of the first fuel cell stack 11 and the second fuel cell stack 12 reach the expectation. If the output power and fuel utilization rate of the first fuel cell stack 11 and the second fuel cell stack 12 do not reach the expectation, the circulation device 13 enters the second working state. The controller controls the first flow control valve 20 and the isolation valve 19 to open, and the external fuel 2 enters the circulation device 13. At the same time, the controller controls the opening degree of the second flow control valve 21 so that the reduction amount of the external fuel 1 is the flow rate of the external fuel 2. That is, it is necessary to ensure that the total amount of external fuel entering the first fuel cell stack does not change. The external fuel 2 is mixed with the external fuel 1 at the first mixing valve 17 and then enters the first fuel input device through the second mixing valve 16, and then enters the first electrode of the first fuel cell stack 11 through the first fuel input device 14 for reaction.

[0049] In the technical solution of this embodiment, the performance of the ejector 8 is regulated by regulating the flow rate of the external fuel 2, so that a part of the exhaust gas from the first electrode of the first fuel cell stack 11 is recycled, thereby improving the efficiency of the fuel cell system.

[0050] Continue to refer to Figure 1 and Figure 3 , on the basis of the above embodiments, optionally, the controller is used to stop adjusting the opening degrees of the first flow control valve 20 and the second flow control valve 21 when the output power of the first fuel cell stack 11 and the output power of the second fuel cell stack 12 meet the requirements. When the opening degree of the second flow control valve 21 is adjusted to zero, if the output power of the first fuel cell stack 11 and the output power of the second fuel cell stack 12 do not meet the requirements, the output power of the second fuel cell stack 12 is increased.

[0051] Specifically, when the total external fuel provided by external fuel 1 and external fuel 2 enters the first electrode of the primary electric thruster 11 for an electrochemical reaction, the controller monitors the output powers of the primary stack 11 and the secondary stack 12 in real time, and controls the opening degree of the first flow control valve 20 according to the output powers of the primary stack 11 and the secondary stack 12 to slowly increase the flow rate of external fuel 2. Observe the change in the output power of the fuel cell system. If the efficiency of the fuel cell system reaches the expected value before external fuel 1 drops to 0, then maintain the flow rates of external fuel 1 and external fuel 2 to keep the fuel cell system running stably.

[0052] If external fuel 1 drops to 0, that is, the circulation rate reaches the maximum and the system efficiency still fails to reach the expectation, then it is necessary to adjust the combustion utilization rate of the secondary stack 12. The controller controls to slowly increase the output power of the secondary stack 12, that is, to improve the fuel utilization rate of the secondary stack 12 until the fuel cell system reaches the expectation.

[0053] In the technical solution of the embodiment, when the output powers of the primary stack 11 and the secondary stack 12 of the fuel cell system cannot meet the demand expectation, the operation of the circulation device 13 is used to recycle a part of the tail gas of the first electrode of the primary stack 11 to increase the output power of the primary stack 11. When the circulation rate reaches the maximum and still cannot meet the output powers of the primary stack 11 and the secondary stack 12, then the secondary stack 12 is regulated to improve the fuel utilization rate of the secondary stack 12, thereby further improving the efficiency of the entire fuel cell system.

[0054] See Figure 2 , on the basis of the above embodiments, optionally, the fuel cell system further includes: an output control device, the output control device is electrically connected to the secondary stack 12 and the controller 23, and the output control device is used to adjust the output power of the secondary stack 12 according to the control signal of the controller 23.

[0055] Among them, the output control device includes a primary stack DCDC 24 and a secondary stack DCDC 25, and both the primary stack 11 and the secondary stack 12 are independently controlled through DCDC. During operation, the output current of the primary stack 11 is controlled by the primary stack DCDC 24, and the output current of the secondary stack 12 is controlled by the secondary stack DCDC 25.

[0056] Specifically, when the circulation device 13 is in the second working state, an electrochemical reaction occurs between the external fuel and the external air in the first-stage fuel cell stack 11 to generate current. The controller 23 controls the first-stage fuel cell stack DCDC 24 to adjust the output current of the first-stage fuel cell stack 11 by monitoring the fuel utilization rate of the first-stage fuel cell stack 11. When the total amount of external fuel entering the first-stage fuel cell stack 11 remains unchanged, slowly increase the flow rate of the external fuel 2. If the external fuel 1 drops to 0, that is, when the circulation rate reaches the maximum and the efficiency of the fuel cell system still fails to reach the expected value, it is necessary to adjust the fuel utilization rate of the second-stage fuel cell stack 12. The controller 23 controls the second-stage fuel cell stack DCDC 25 to increase the output current of the second-stage fuel cell stack 12, that is, to improve the fuel utilization rate and output power of the second-stage fuel cell stack 12 until the system efficiency reaches the expected value.

[0057] In the technical solution of this embodiment, the output current of the first-stage fuel cell stack 11 is controlled by the first-stage fuel cell stack DCDC 24, and the output current of the second-stage fuel cell stack 12 is controlled by the second-stage fuel cell stack DCDC 25. Even when the maximum tail gas circulation amount of the first electrode of the first-stage fuel cell stack 11 fails to meet the system efficiency, the fuel utilization rate of the second-stage fuel cell stack 12 is adjusted to improve the efficiency of the fuel cell system.

[0058] See Figure 1 , based on the above embodiments, optionally, the first fuel input device 14 includes a steam generator 1, a first-stage fuel cell stack steam reformer 2, and a first-stage fuel cell stack air preheater 3. The inlet of the first-stage fuel cell stack air preheater 3 is used to receive external air, and the outlet is connected to the first inlet of the first-stage fuel cell stack steam reformer 2. The inlet of the steam generator 1 is connected to the second outlet of the circulation device 13, and the outlet is connected to the second inlet of the first-stage fuel cell stack steam reformer 2. The first outlet of the first-stage fuel cell stack steam reformer 2 is connected to the second electrode of the first-stage fuel cell stack 11, and the second outlet is connected to the first electrode of the first-stage fuel cell stack 11. Among them, the first inlet and the first outlet of the first-stage fuel cell stack steam reformer 2 are interconnected, and the second inlet and the second outlet are interconnected. The steam generator 1 is used to generate a fuel and water vapor mixture. The first-stage fuel cell stack steam reformer 2 is used to cause the fuel and water vapor mixture to undergo a steam reforming reaction under the action of a catalyst. The first-stage fuel cell stack air preheater 3 is used to heat the external air.

[0059] Specifically, when the external fuel enters the first fuel input device 14, a reaction occurs in the steam generator 1 in the first fuel input device 14 to generate a fuel and water vapor mixture, and then it enters the first-stage fuel cell stack steam reformer 2 through the steam generator 1. The external fuel undergoes a steam reforming reaction under the action of a catalyst to generate CO 2 and H 2 . The external air 1 is input into the first-stage fuel cell stack air preheater 3 for heating, and then input into the second electrode of the first-stage fuel cell stack 11.

[0060] In the technical solution of this embodiment, the external fuel and external air entering the first fuel cell stack 11 are pre-treated by the steam generator 1, the first fuel cell stack steam reformer 2, and the first fuel cell stack air preheater 3, which is beneficial to improving the fuel utilization rate of the first fuel cell stack 11.

[0061] Referring to Figure 1 , on the basis of the above embodiments, optionally, the second fuel input device 15 includes a second fuel cell stack steam reformer 4 and a second fuel cell stack air mixer 5. The first inlet of the second fuel cell stack steam reformer 4 is connected to the first electrode of the first fuel cell stack 11, the second inlet is connected to the first outlet of the circulation device 13, the first outlet is connected to the first electrode of the second fuel cell stack 12, and the second outlet is connected to the first inlet of the circulation device 13. The second fuel cell stack steam reformer 4 is used to cause a steam reforming reaction of the fuel before entering the second fuel cell stack 12. The first inlet of the second fuel cell stack air mixer 5 is connected to the second electrode of the first fuel cell stack 11, the second inlet is for receiving external air, and the outlet is connected to the second electrode of the second fuel cell stack 12. The second fuel cell stack air mixer 5 is used to mix the external air and the tail gas of the second electrode of the first fuel cell stack 11.

[0062] Specifically, when the tail gas of the first electrode of the first fuel cell stack 11 enters the second fuel input device 15, it enters the circulation device 13 through the second fuel cell stack steam reformer 4 in the second fuel input device 15. After being condensed and drained by the circulation device 13, it enters the second fuel cell stack steam reformer 4 again, and reacts with the external fuel 3 through the second fuel cell stack steam reformer 4 to generate CO 2 and H 2， and enters the first electrode of the second fuel cell stack 12. The external air enters the second fuel cell stack air mixer 5, and together with the tail gas of the second electrode of the first fuel cell stack 11, enters the second electrode of the second fuel cell stack 12 after being heated by the second fuel cell stack air mixer 5.

[0063] In the technical solution of this embodiment, the external fuel and external air entering the second fuel cell stack 12 are pre-treated by the second fuel cell stack steam reformer 4 and the second fuel cell stack air mixer 5, which is beneficial to improving the fuel utilization rate of the second fuel cell stack 12.

[0064] Continuing to refer to Figure 1 , on the basis of the above embodiments, optionally, the fuel cell system further includes: a third flow control valve 22 and a third mixing valve 18. The first end of the third mixing valve 18 is connected to the second outlet of the circulation device 13, the second end is connected to the fourth inlet of the second fuel input device 15, and the third end is connected to the first end of the third flow control valve 22. The second end of the third flow control valve 22 is for receiving external fuel. The third flow control valve 22 is electrically connected to the controller. The controller is used to control the opening degree of the third flow control valve 22.

[0065] Specifically, the controller controls the opening degree of the third flow control valve 22 according to the input power of the secondary stack 12 and the combustion utilization rate. The external fuel 3 enters the second fuel input device 15 through the third mixing valve 18, and then enters the secondary stack 12 through the second fuel input device 15, and undergoes an electrochemical reaction with the external air between the first electrode and the second electrode of the secondary stack 12.

[0066] In this embodiment, the controller controls the opening degree of the third flow control valve 22 to adjust the flow rate of the external fuel 3, replenishes new external fuel for the secondary stack 12, ensures that the fuel utilization rate of the secondary stack 12 is within the safety margin, and is beneficial to improving the output power of the secondary stack 12.

[0067] Continue to refer to Figure 1 , on the basis of the above embodiments, optionally, the fuel cell system further includes: a burner 10, the inlet of the burner 10 is connected to the first electrode and the second electrode of the secondary stack 12, and the outlet is connected to the steam generator 1 and the primary stack air preheater 3. The burner 10 is used to provide heat for the steam generator 1 and the primary stack air preheater 3.

[0068] Specifically, the external fuel 3 input to the first electrode of the secondary stack 12 and the tail gas of the first electrode of the primary stack 11 react electrochemically with the external air of the second electrode of the secondary stack 12. The unconsumed tail gas of the first electrode of the secondary stack 12 and the unconsumed tail gas of the second electrode of the secondary stack 12 enter the fuel burner 10 to burn, and the generated heat is input to the steam generator 1 and the primary stack air preheater 3.

[0069] In the technical solution of this embodiment, the unconsumed tail gas of the first electrode of the secondary stack 12 and the tail gas of the second electrode of the secondary stack 12 burn in the burner 10 to provide heat for the steam generator 1 and the primary stack air preheater 3, which is beneficial to improving the fuel utilization rate of the primary stack 11 and the secondary stack 12.

[0070] It should be understood that various forms of the processes shown above can be used, steps can be reordered, added or deleted. For example, the steps described in the present invention can be executed in parallel, sequentially, or in a different order, as long as the desired results of the technical solution of the present invention can be achieved, and no limitation is made herein.

[0071] The above specific embodiments do not constitute a limitation to the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub - combinations and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A fuel cell system, characterized in that: include: A controller, a first fuel input device, a second fuel input device, a primary fuel stack, a secondary fuel stack and a circulation device; Wherein, the controller is electrically connected to the first fuel input device, the second fuel input device, the first-stage fuel cell stack, the second-stage fuel cell stack and the circulation device; The first inlet of the first fuel input device is used to receive external fuel, and the second inlet is used to receive air; the two outlets of the first fuel input device are respectively connected to the first electrode and the second electrode of the first-level fuel cell stack; The first fuel input device is used to receive external fuel and air, process the external fuel and air, and input fuel to the first electrode of the first-level stack and input air to the second electrode of the first-level stack respectively; The first electrode and the second electrode of the first-stage fuel stack are connected to the first inlet and the second inlet of the second fuel input device, respectively; the third inlet of the second fuel input device is used to receive external air, and the fourth inlet of the second fuel input device is connected to the first outlet of the circulation device; the first outlet and the second outlet of the second fuel input device are connected to the first electrode and the second electrode of the second-stage fuel stack, respectively, and the third outlet of the second fuel input device is connected to the first inlet of the circulation device; the fourth inlet of the second fuel input device is also used to receive external fuel; The second outlet of the circulation device is connected to the first inlet of the first fuel input device; the second inlet of the circulation device is used to receive external fuel; The second fuel input device is used to receive the tail gas of the first electrode of the first-stage stack and the tail gas of the second electrode of the first-stage stack, and is also used to receive external air, and input the tail gas of the first electrode of the first-stage stack into the circulation device, and mix the tail gas of the second electrode of the first-stage stack with the external air and then input it into the second electrode of the second-stage stack; The controller is used to control the first fuel input device, the second fuel input device, the first-level fuel stack and the second-level fuel stack to start up, obtain the output power and fuel utilization rate of the first-level fuel stack, and obtain the output power and fuel utilization rate of the second-level fuel stack, and control the working state of the circulation device according to the output power and fuel utilization rate of the first-level fuel stack and the output power and fuel utilization rate of the second-level fuel stack; Wherein, the working state of the circulation device includes a first working state and a second working state; in the first working state, the circulation device processes the tail gas of the first electrode of the first-level fuel cell stack and transmits it to the second fuel input device; in the second working state, the circulation device receives external fuel, processes the tail gas of the first electrode of the first-level fuel cell stack, inputs part of the treated tail gas and the external fuel into the first fuel input device, and inputs part of the treated tail gas into the second fuel input device; The second fuel input device is also used to process the external fuel and the treated exhaust gas input by the circulation device and then transmit them to the first electrode of the secondary fuel cell stack.

2. The fuel cell system according to claim 1, characterized in that: The controller is used to: After the first fuel input device, the second fuel input device, the first-stage fuel cell stack and the second-stage fuel cell stack are started, the circulation device is controlled to be in the first working state, and when the circulation device is in the first working state, if the output efficiency of the first-stage fuel cell stack and the second-stage fuel cell stack meets the requirements, and the fuel utilization rates of the first-stage fuel cell stack and the second-stage fuel cell stack are within the safety margin, the circulation device is controlled to maintain the first working state; When the circulation device is in the first working state, if the fuel utilization rates of the primary fuel cell stack and the secondary fuel cell stack do not meet the requirements, the circulation device is controlled to enter the second working state.

3. The fuel cell system according to claim 1 or 2, characterized in that: The circulation device comprises a condenser, an air-water separator, an ejector, a water pump, an isolation valve and a first flow control valve; the controller is electrically connected to the condenser, the air-water separator, the ejector, the water pump, the isolation valve and the first flow control valve; The inlet of the condenser is connected to the third outlet of the second fuel output device, and the outlet of the condenser is connected to the inlet of the gas-water separator; The first outlet of the gas-water separator is connected to the first inlet of the ejector, the second outlet of the gas-water separator is connected to the inlet of the water pump, and the third outlet of the gas-water separator is connected to the fourth inlet of the second fuel input device; The second inlet of the ejector receives external fuel through a first flow control valve, and the outlet of the ejector is connected to the first inlet of the first fuel input device through an isolation valve; The outlet of the water pump is connected to the first inlet of the first fuel input device; The condenser is used to cool the tail gas of the first electrode of the first-stage fuel cell stack; The gas-water separator is used to separate gas and water from the tail gas of the first electrode of the first-stage fuel cell stack, and output the separated condensed water to the water pump, and output the separated gas to the ejector and the second fuel output device; The ejector is used to transfer the received separated gas and external fuel to the first fuel input device; The water pump is used to transfer the separated condensed water to the first fuel output device; The controller is used to control the condenser, the water pump and the gas-water separator to open, and control the ejector, the isolation valve and the first flow control valve to close when the circulation device is in the first working state; when the circulation device is in the second working state, control the condenser, the gas-water separator, the ejector, the water pump, the isolation valve and the first flow control valve to open.

4. The fuel cell system according to claim 3, characterized in that: Also includes: a second flow control valve, a first mixing valve, and a second mixing valve; The second flow control valve is electrically connected to the controller; The input end of the second flow control valve is used to receive external fuel, and the output end is connected to the first end of the first mixing valve; The second end of the first mixing valve is connected to the outlet of the ejector, and the third end is connected to the first end of the second mixing valve; The second end of the second mixing valve is connected to the outlet of the water pump, and the third end is connected to the first inlet of the first fuel input device; The controller is used to adjust the opening of the first flow control valve and the second flow control valve according to the output power of the first-stage fuel cell stack and the output power of the second-stage fuel cell stack when the circulation device is in the second working state, so as to adjust the flow rate of the external fuel input by the first flow control valve and the flow rate of the external fuel input by the second flow control valve; The sum of the flow rate of the external fuel input by the first flow control valve and the flow rate of the external fuel input by the second flow control valve is a constant value.

5. The fuel cell system according to claim 4, characterized in that: The controller is used to: When the output power of the primary fuel cell stack and the output power of the secondary fuel cell stack meet the requirements, stop adjusting the openings of the first flow control valve and the second flow control valve; When the opening of the second flow control valve is adjusted to zero, if the output power of the primary fuel cell stack and the output power of the secondary fuel cell stack do not meet the requirements, the output power of the secondary fuel cell stack is increased.

6. The fuel cell system according to claim 5, characterized in that: Also includes: Output control device; The output control device is electrically connected to the secondary battery stack and the controller; The output control device is used to adjust the output power of the secondary fuel cell stack according to the control signal of the controller.

7. The fuel cell system according to claim 1, characterized in that: The first fuel output device includes a steam generator, a primary stack steam reformer and a primary stack air preheater; The inlet of the primary stack air preheater is used to receive external air, and the outlet is connected to the first inlet of the primary stack steam reformer; The inlet of the steam generator is connected to the second outlet of the circulation device, and the outlet is connected to the second inlet of the primary stack steam reformer; The first outlet of the primary stack steam reformer is connected to the second electrode of the primary stack, and the second outlet is connected to the first electrode of the primary stack; wherein the first inlet and the first outlet of the primary stack steam reformer are interconnected, and the second inlet and the second outlet are interconnected; The steam generator is used to generate a mixed gas of fuel and water vapor; The first-stage stack steam reformer is used to cause a mixed gas of fuel and steam to undergo a steam reforming reaction under the action of a catalyst; The first-stage stack air preheater is used to heat the external air.

8. The fuel cell system according to claim 1, characterized in that: The second fuel input device includes a secondary stack steam reformer and a secondary stack air mixer; The first inlet of the secondary stack steam reformer is connected to the first electrode of the primary stack, the second inlet is connected to the first outlet of the circulation device, the first outlet is connected to the first electrode of the secondary stack, and the second outlet is connected to the first inlet of the circulation device; The secondary stack steam reformer is used to cause the fuel to undergo a steam reforming reaction before entering the secondary stack; The first inlet of the secondary stack air mixer is connected to the second electrode of the primary stack, the second inlet is used to receive external air, and the outlet is connected to the second electrode of the secondary stack; The secondary stack air mixer is used to mix external air and the tail gas of the second electrode of the primary stack.

9. The fuel cell system according to claim 1, characterized in that: Also includes: a third flow control valve and a third mixing valve; The first end of the third mixing valve is connected to the second outlet of the circulation device, the second end is connected to the fourth inlet of the second fuel input device, and the third end is connected to the first end of the third flow control valve; The second end of the third flow control valve is used to receive external fuel; The third flow control valve is electrically connected to the controller; The controller is used to control the opening degree of the third flow control valve.

10. The fuel cell system according to claim 7, characterized in that: Also includes: Burner; The inlet of the burner is connected to the first electrode and the second electrode of the secondary stack, and the outlet is connected to the steam generator and the air preheater of the primary stack; The burner is used to provide heat for the steam generator and the primary stack air preheater.

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