A method for starting up a fuel cell system at low temperature

Abstract

The present invention discloses a method for starting a fuel cell system at low temperature, which includes a cathode circuit, an anode circuit and a coolant circuit. The cathode circuit consists of a filter, a flow meter, an air compressor, a throttle valve and a fuel cell stack. Inlet air sequentially flows through the filter and the air compressor and enters the fuel cell stack. A throttle valve is provided on the exhaust gas discharge pipeline of the fuel cell stack. The cathode circuit is further provided with a cathode valve. The input end of the cathode valve is connected to the output end of the air compressor, and the output end of the cathode valve is respectively connected to the fuel cell stack and the exhaust gas discharge pipeline. The method includes the following steps: S1. In the coolant circuit of the fuel cell system, heat the coolant; S2. Continuously monitor the coolant temperature, and enter step S3 when the coolant temperature is greater than the preheating temperature; S3. Start preheating the cathode circuit of the fuel cell system; S4. Continuously monitor the coolant temperature, and enter step S5 when the coolant temperature is greater than the starting temperature; S5. Perform hydrogen replacement on the anode circuit of the fuel cell system; S6. After waiting for the hydrogen replacement to be completed, start the cathode purge of the fuel cell system; S7. Determine whether the minimum single-cell voltage of the fuel cell stack of the fuel cell system can reach the starting voltage within a specified time. If it can reach, execute step S8. Otherwise, perform a fault shutdown process and the fuel cell system stops operating; S8. The fuel cell system pulls the idle current, and the fuel cell stack of the fuel cell system starts to operate. By operating components such as the air compressor in the cathode circuit before starting the system, the present invention preheats the cathode circuit of the fuel cell system, raises the temperature of the components in the cathode circuit, and increases the temperature of the air entering the cathode of the stack, thereby avoiding water blockage and icing inside the stack.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cell systems, and particularly to a method for starting a fuel cell system at low temperature. Background Art

[0002] The continuous operation of a fuel cell system (hereinafter referred to as a fuel cell power generation system) requires continuously supplying reaction gases to the anode and cathode of the fuel cell stack, and the gas supply is achieved through the anode circuit and cathode circuit of the fuel cell power generation system. The cathode circuit of the fuel cell power generation system is a structure for supplying air to the fuel cell stack. Figure 1 It is a schematic diagram of a general cathode circuit configuration, including parts such as an air filter, an air flow meter, an air compressor, a throttle valve, and a cathode pressure sensor;

[0003] After the inlet air is filtered by the air filter, it is compressed by the air compressor to become high-pressure air. The flow meter collects the air flow, and the cathode pressure sensor obtains the air pressure entering the stack and feeds it back to the fuel cell system control unit.

[0004] During the operation of the fuel cell power generation system, water is generated through an electrochemical reaction at the cathode of the stack. The greater the current output by the system, the more water is generated by the reaction. If the temperature of the cathode of the stack is relatively low at this time, the generated water will condense, block water, or even freeze inside the stack, resulting in irreversible damage. Therefore, during the operation of the fuel cell power generation system, it is necessary to maintain an appropriate internal temperature of the stack and handle the water generated by the reaction through appropriate means.

[0005] Existing technical solutions heat the coolant by means of auxiliary heating when the fuel cell power generation system is not operating, and raise the temperature of the stack through the circulation of the coolant. When the coolant reaches a certain temperature (such as 5°C), the system is started so that the internal temperature of the fuel cell power generation system is higher than 0°C during operation, avoiding the freezing of the generated water.

[0006] After the system is started, during normal operation, the temperature is continuously increased by the heat generated by the stack, and at the same time, the operation gear and the load current (each operation gear corresponds to one and only one load current) are increased, thereby increasing the output power of the fuel cell power generation system.

[0007] However, in a general fuel cell power generation system, the following problems may be encountered:

[0008] 1. Although the temperature of the coolant and the stack is raised above 0°C by means of auxiliary heating, the air temperature is relatively low. If a large amount of cold air enters the stack during startup, it may cause water blockage and icing at the cathode of the stack, thereby affecting the performance of the fuel cell power generation system.

[0009] 2. If the fuel cell power generation system fails to shut down and complete purging due to abnormal reasons, there may be a relatively large amount of liquid water inside the stack. If it is not processed after re-powering and the system is directly started, it may cause water blockage and icing inside the stack, thereby affecting the performance of the fuel cell power generation system.

[0010] 3. When the internal temperature of the fuel cell stack is relatively low, the water generated by the electrochemical reaction is more likely to condense inside the fuel cell stack, which may cause water blockage inside the fuel cell stack, thereby affecting the performance of the fuel cell system. Summary of the Invention

[0011] The purpose of the present invention is to provide a method for starting a fuel cell system at low temperature to overcome the deficiencies in the prior art.

[0012] To achieve the above object, the present invention provides the following technical solutions:

[0013] The present application discloses a method for starting a fuel cell system at low temperature, including a cathode circuit, an anode circuit, and a coolant circuit. The cathode circuit consists of a filter, a flow meter, an air compressor, a throttle valve, and a fuel cell stack. The inlet air sequentially flows through the filter and the air compressor and enters the fuel cell stack. A throttle valve is provided on the tail gas discharge pipeline of the fuel cell stack. The cathode circuit is also provided with a cathode valve. The input end of the cathode valve is connected to the output end of the air compressor, and the output end of the cathode valve is respectively connected to the fuel cell stack and the tail gas discharge pipeline. The method includes the following steps:

[0014] S1. In the coolant circuit of the fuel cell system, heat the coolant.

[0015] S2. Continuously monitor the coolant temperature. When the coolant temperature is greater than the preheating temperature, enter step S3.

[0016] S3. Start preheating the cathode circuit of the fuel cell system.

[0017] S4. Continuously monitor the coolant temperature. When the coolant temperature is greater than the starting temperature, enter step S5.

[0018] S5. Perform hydrogen replacement on the anode circuit of the fuel cell system.

[0019] S6. After waiting for the hydrogen replacement to be completed, start the cathode purge of the fuel cell system.

[0020] S7. Determine whether the minimum single cell voltage of the fuel cell stack of the fuel cell system can reach the starting voltage within a specified time. If it can reach, execute step S8. Otherwise, perform a fault shutdown process and the fuel cell system stops running.

[0021] S8. The fuel cell system pulls the load idle current, and the fuel cell stack of the fuel cell system starts to run.

[0022] Preferably, the specific operations for starting the auxiliary heating in step S1 include: starting the cooling water pump, turning on the heater, and adjusting the opening degree of the thermostat.

[0023] Preferably, the preheating temperature in step S2 is 0°C, and the starting temperature in step S4 is 5°C.

[0024] Preferably, step S3 specifically includes the following operations:

[0025] S31. Adjust the cathode valve so that the flow rate at the output end of the cathode valve all flows to the tail gas discharge pipe;

[0026] S32. Close the throttle valve and turn on the air compressor.

[0027] Preferably, in step S5, while performing hydrogen replacement in the anode circuit, it is judged whether the last shutdown of the fuel cell system has completed purging. If the purging is not completed, the cathode purge is turned on. Otherwise, step S6 is entered.

[0028] Preferably, the cathode purge includes the following steps:

[0029] S61. Adjust the cathode valve so that the flow rate at the output end of the cathode valve all flows to the fuel cell stack;

[0030] S62. Open the throttle valve and turn on the air compressor.

[0031] Preferably, the specified time in step S7 is 5 seconds, the starting voltage is 800 mV, and the idle current in step S8 is 40 A;

[0032] Preferably, step S8 further includes the following sub-steps:

[0033] S81. Judge whether the coolant temperature is greater than the normal operating temperature. If it is greater, stop heating the coolant, and the fuel cell system operates normally; otherwise, the fuel cell system starts low-temperature operation and enters step S82;

[0034] S82. Increase the air flow rate in the cathode circuit, and limit the operating gear according to the stack inlet temperature of the fuel cell system, and return to step S81.

[0035] Preferably, the normal operating temperature in step S81 is 70°C.

[0036] Preferably, the specific operation of limiting the operating gear according to the stack inlet temperature of the fuel cell system in step S82 is as follows: Determine by the current-temperature function or determine by stage temperature division.

[0037] Advantages of the present invention:

[0038] 1. By operating components such as the cathode circuit air compressor before the system is turned on, the present invention preheats the cathode circuit of the fuel cell system, heats up the components in the cathode circuit, and raises the air temperature entering the cathode of the stack, thereby avoiding water blockage and icing inside the stack.

[0039] 2. When the shutdown fails to complete purging normally, before the next startup of the fuel cell power generation system, the present invention adopts the method of purging the cathode of the stack with a large flow of air to discharge excess moisture, thereby avoiding water blockage and icing inside the stack.

[0040] 3. When the temperature of the stack is relatively low, the present invention increases the cathode flow rate and limits the operating gear to avoid the generation of a large amount of water under excessive current and take away excess condensate water, thereby avoiding water blockage inside the stack.

[0041] The features and advantages of the present invention will be described in detail through embodiments in conjunction with the accompanying drawings. Description of the Drawings

[0042] Figure 1 is a schematic diagram of the general cathode circuit configuration in the prior art;

[0043] Figure 2 is a schematic diagram of the cathode circuit of the present invention;

[0044] Figure 3 is a schematic flowchart of a method for starting up a fuel cell system at low temperature according to the present invention;

[0045] Figure 4 is a schematic flowchart of the cathode circuit starting preheating according to the present invention;

[0046] Figure 5 is a schematic flowchart of the cathode purging according to the present invention;

[0047] Figure 6 is a schematic flowchart of the fuel cell system of the present invention starting to operate at low temperature;

[0048] Figure 7 is a schematic diagram for judging the stage temperature division according to the present invention. Detailed Embodiments

[0049] To make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below through the accompanying drawings and embodiments. However, it should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the scope of the present invention. In addition, in the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention.

[0050] Refer to Figure 2 , the configuration of the cathode circuit includes parts such as an air filter, an air flow meter, an air compressor, a throttle valve, a cathode pressure sensor, and a cathode valve. Among them, the cathode valve is used to adjust the air flow distribution ratio between the air entering the stack and the bypass air entering the tail exhaust. Usually, during operation, all cathode flow enters the stack through the cathode valve to participate in the reaction; in the standby state, all cathode flow directly enters the tail exhaust pipe through the cathode valve and does not participate in the reaction.

[0051] During the operation of the fuel cell system, H2 at the anode of the stack and O2 at the cathode of the stack undergo an electrochemical reaction to discharge, and water is generated at the cathode. If the generated water fails to be discharged from the stack in time, it will accumulate in the cathode flow channel of the stack, causing water blockage, hindering the participation of O2 in the air in the reaction, and thus affecting the normal operation of the system. Further, if the temperature at the cathode of the stack is below zero at this time, the generated water will freeze inside the stack, which may cause permanent damage.

[0052] To avoid such situations, based on the above cathode circuit design, when the system receives a startup command, there are the following control strategies. Refer to Figure 3 ,

[0053] First, turn on the auxiliary heating function of the fuel cell system (heating the coolant in the coolant circuit of the fuel cell system). This step includes operations such as starting the cooling water pump, turning on the heater, and adjusting the opening of the thermostat. After the above operations are completed, judge whether the cooling water temperature reaches the preheating temperature (such as 0 °C). If not, continue to wait for the temperature to rise; if it reaches, turn on the cathode preheating function;

[0054] As Figure 4 shown, during the cathode preheating process, after the air compressor starts, it will compress the air and raise the temperature of the compressed air. When the high-temperature compressed air flows in the cathode circuit, it will heat the components in the entire circuit, thus achieving the effect of cathode preheating. To avoid water blockage and icing caused by low-temperature air entering the stack in subsequent steps.

[0055] During cathode preheating, the cooling water temperature will be continuously judged. If it reaches the starting temperature (such as 5 °C), turn on the anode exhaust device of the fuel cell system and turn on the front-stage hydrogen supply. Under the condition of stabilizing the anode pressure in the stack (such as 40 kPa), replace the gas in the anode circuit of the system by exhaust, thereby increasing the hydrogen concentration inside the anode of the stack.

[0056] At the same time, judge whether the last shutdown of the fuel cell system has completed purging. If it has not completed purging, then perform cathode purging; otherwise, directly proceed to the next step;

[0057] As Figure 5 shown, during the cathode purging process, the air entering the cathode of the stack will blow out the liquid water in the cathode flow channel, thus avoiding water blockage inside the stack.

[0058] After waiting for the hydrogen replacement (such as 5 s) to complete, perform cathode purging. The operation content is the same as above. The purpose is to make both sides of the anode and cathode of the stack be filled with reaction gases, preparing for the subsequent fuel cell reaction.

[0059] After the cathode purge is completed, it is judged whether the minimum single-cell voltage of the fuel cell stack can reach the starting voltage (such as 800 mV) within 5 s. If it can reach, the idle current (such as 40 A) is pulled, and the fuel cell stack officially starts to react, and the fuel cell system starts to operate. If it cannot reach, it means that the system startup is abnormal, and a fault shutdown process needs to be carried out, and the fuel cell system stops operating.

[0060] During the operation of the fuel cell system, electrochemical reactions occur at the anode and cathode of the stack to generate water. The greater the current, the more water is generated by the reaction. And when the system temperature is relatively low, the generated water is more likely to condense in the cathode flow channel, as Figure 6 shown in the following treatment to ensure the normal operation of the system at low temperatures:

[0061] Among them, by increasing the air flow rate flowing through the cathode of the stack, the excess water generated by condensation is carried away, thus avoiding water blockage in the cathode flow channel. Specifically, it can be achieved by increasing the speed of the air compressor and the throttle opening;

[0062] By the inlet temperature of the stack cooling, the gears of system operation and current pulling are restricted to avoid pulling too large a current at a relatively low temperature, resulting in too much water production and condensation water blockage. Specifically, there are two implementation methods including but not limited to the following:

[0063] 1) It is judged by the current-temperature function. For example, the following formula can be used (other current-temperature formulas can also be used):

[0064]

[0065] Among them, I is the current maximum pullable current, I0 is the rated gear operation current, T0 is the normal operation temperature, T is the current cooling temperature, and K is a constant. In a typical example, I0 is 700 A, T0 is 65 °C, K is 10. If the cooling temperature T is 30 °C at this time, the current maximum pullable current I is 350 A.

[0066] 2) It is judged by stage temperature division. For example, the following judgment method can be used, as Figure 7 shown,

[0067] Among them, the stage temperature T1 > T2 > …… > T n , and the pull current I1 > I2 > …… > I n > I min . In a typical example, T1 is 70 °C, T2 is 60 °C, T3 is 40 °C, I1 is 700 A, I2 is 500 A, I3 is 300 A, I minIt is 100A. If the cooling temperature is 30°C at this time, the maximum load current of the fuel cell system is limited to 100A; if the cooling temperature is 65°C at this time, the maximum load current of the fuel cell system is limited to 500A.

[0068] Judge whether the cooling water temperature is higher than the normal operating temperature (such as 70°C). If it is not higher, continue to operate at low temperature. During the low-temperature operation of the system, the cooling temperature will be continuously increased through the way of reaction heat release and auxiliary heating; if it is higher, turn off the auxiliary heating function, including operations such as adjusting the opening of the thermostat and turning off the heater.

[0069] The fuel cell system operates normally, no longer limits the load current, and sets the operating parameters of components such as the air compressor and throttle according to the operating gear.

[0070] By preheating the cathode circuit of the fuel cell system before starting up, the present invention heats up the components in the cathode circuit and raises the air temperature entering the cathode of the stack, thereby avoiding water blockage and icing inside the stack.

[0071] If the last shutdown fails to complete the purge normally, before starting the fuel cell system, purge the cathode of the stack with a large flow of air to discharge the excess water, thereby avoiding water blockage and icing inside the stack.

[0072] When the temperature of the stack is relatively low, by increasing the cathode flow rate entering the stack, while heating up the stack with a large flow of hot air, the excess condensed water is carried away, thereby avoiding water blockage inside the stack.

[0073] When the temperature of the stack is relatively low, by restricting the operating gear and load current of the fuel cell system, the large amount of water generation under excessive current is avoided, thereby avoiding water blockage inside the stack.

[0074] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements or improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for starting up a fuel cell system at low temperature, comprising a cathode circuit, an anode circuit and a coolant circuit. The cathode circuit consists of a filter, a flowmeter, an air compressor, a throttle valve and a fuel cell stack. Inlet air sequentially flows through the filter and the air compressor and enters the fuel cell stack. A throttle valve is provided on the tail gas discharge pipeline of the fuel cell stack. It is characterized in that: The cathode circuit is also provided with a cathode valve. The input end of the cathode valve is connected to the output end of an air compressor, and the output end of the cathode valve is respectively connected to a fuel cell stack and an exhaust gas discharge pipeline. The method includes the following steps: S1. In the coolant circuit of the fuel cell system, heat the coolant. S2. Continuously monitor the coolant temperature. When the coolant temperature is greater than the preheating temperature, proceed to step S3. S3. Start preheating the cathode circuit of the fuel cell system. S4. Continuously monitor the coolant temperature. When the coolant temperature is greater than the starting temperature, proceed to step S5. S5. Conduct hydrogen replacement in the anode circuit of the fuel cell system. S6. After waiting for the hydrogen replacement to be completed, start the cathode purge of the fuel cell system. S7. Determine whether the minimum single-cell voltage of the fuel cell stack of the fuel cell system can reach the starting voltage within the specified time. If it can reach, execute step S8; otherwise, perform a fault shutdown process and the fuel cell system stops running. S8. The fuel cell system pulls the idle current, and the fuel cell stack of the fuel cell system starts to operate. In step S2, the preheating temperature is 0°C, and in step S4, the starting temperature is 5°C. In step S7, the specified time is 5 seconds, the starting voltage is 800 mV, and the idle current in step S8 is 40 A. Step S8 also includes the following sub-steps: S81. Determine whether the coolant temperature is greater than the normal operating temperature. If it is greater, stop heating the coolant, and the fuel cell system operates normally. Otherwise, the fuel cell system starts low-temperature operation and proceeds to step S82. S82. Increase the air flow in the cathode circuit and limit the operating gear according to the inlet temperature of the fuel cell stack of the fuel cell system, and return to step S81. In step S81, the normal operating temperature is 70°C. The specific operation of limiting the operating gear according to the inlet temperature of the fuel cell stack of the fuel cell system in step S82 is as follows: Determine by the current-temperature function or by stage temperature division.

2. The low-temperature startup method of a fuel cell system according to claim 1, wherein: The specific operation of starting the auxiliary heating in step S1 includes the following: Start the cooling water pump, turn on the heater, and adjust the opening of the thermostat.

3. A method for cold starting a fuel cell system according to claim 1, characterized in that: Step S3 specifically includes the following operations: S31. Adjust the cathode valve so that all the flow at the output end of the cathode valve flows to the exhaust gas discharge pipeline. S32. Close the throttle valve and turn on the air compressor.

4. A method for cold start of a fuel cell system according to claim 1, characterized in that: In step S5, while conducting hydrogen replacement in the anode circuit, determine whether the previous shutdown of the fuel cell system has completed the purge. If the purge has not been completed, start the cathode purge; otherwise, proceed to step S6.

5. A method for cold starting a fuel cell system according to claim 1 or 4, characterized in that: The cathode purge includes the following steps: S61. Adjust the cathode valve so that all the flow at the output end of the cathode valve flows to the fuel cell stack. S62. Open the throttle valve and turn on the air compressor.

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