A hydrogen fuel cell air compressor recirculation auxiliary system and cold start method

Abstract

The present invention discloses a hydrogen fuel cell air compressor recirculation auxiliary system, which includes an air compressor, an intercooler, a humidifier, a fuel cell stack, a back pressure valve, and a tail exhaust pipe. The outlet of the air compressor is connected to the inlet of the intercooler, the outlet of the intercooler is connected to the inlet of the first side of the humidifier, the outlet of the first side of the humidifier is connected to the cathode inlet of the fuel cell stack, the cathode outlet of the fuel cell stack is connected to the inlet of the back pressure valve, the outlet of the back pressure valve is connected to the inlet of the second side of the humidifier, and the outlet of the second side of the humidifier is connected to the tail exhaust pipe. The system further includes a first regulating valve and a second regulating valve. The two ends of the first regulating valve are respectively connected to the inlet and the outlet of the air compressor, and the two ends of the second regulating valve are respectively connected to the inlet of the air compressor and the outlet of the intercooler. The present invention also discloses a cold start method for the hydrogen fuel cell air compressor recirculation auxiliary system. The present invention improves the success rate of cold start of the fuel cell and controls the cost.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and particularly to a hydrogen fuel cell air compressor recirculation auxiliary system and a cold start method. Background Art

[0002] The proton exchange membrane type hydrogen fuel cell system is the most mature fuel cell technology at present. Under the action of a catalyst, hydrogen loses electrons at the anode to become protons, passes through the proton exchange membrane and enters the cathode, combines with oxygen atoms under the action of the cathode catalyst, and absorbs electrons moving from the external circuit to form water. If hydrogen and oxygen are continuously and stably supplied, and the excess water and heat generated are discharged in time, the fuel cell stack can continuously and stably supply electric energy to the external circuit. The fuel cell stack and all the peripheral accessories together constitute the main part of the hydrogen fuel cell power generation equipment.

[0003] Liquid water plays a key role in the operation of the proton exchange membrane fuel cell stack. During the operation of the fuel cell, water is also continuously generated. In engineering practical applications, the water must be in a reasonable range to ensure that both the performance and reliability goals can be achieved. However, if the fuel cell system is restarted in a low-temperature environment below 0°C, especially after a long-term shutdown, it is very easy for water to freeze, causing difficulties in cold start or even start failure, affecting the user experience of customers, and even causing irreversible damage to the fuel cell stack. The possible mechanisms and reasons are as follows: freezing affects the hydration of protons and hinders them from passing through the proton exchange membrane; freezing causes the proton exchange membrane to be stressed and rupture; freezing covers the catalyst layer, making it difficult for the catalyst to contact the reaction gas and unable to play the role of the catalyst to activate hydrogen and oxygen molecules; freezing blocks the gas channels (including bipolar plates and gas diffusion layers) in the reaction zone, affecting the flow of gas. Therefore, eliminating the influence of water freezing to improve the cold start performance is one of the key issues that need to be considered by technical R & D personnel in this industry at present.

[0004] The existing technologies mainly solve the cold start problem through the following solutions: First, through the purge strategy before shutdown and the optimization of the stack structure, the water remaining in the stack after shutdown is minimized as much as possible, thereby avoiding a large amount of icing during shutdown; Second, for the stack control strategy during cold start, by keeping the stack in a specific working area, the heat generated by the stack itself is increased to quickly raise the temperature of the stack above the freezing point; Third, heat is obtained through other heating methods to help the stack warm up, which is specifically divided into directly heating the stack body structure, or indirectly heating the stack by heating the coolant and the inlet gases of the cathode and anode. The heating method is generally electric heating, and there is also heat generated by the fuel cell system itself during the working process, and part of the heat during the working process is efficiently stored for use during the cold start process. However, the heating methods used in these existing cold start strategies often require adding additional parts, resulting in complex system structures and controls, and limited heat generation, resulting in a relatively long cold start time, affecting the user experience of customers, consuming too much energy, and possibly causing irreversible damage to the stack.

[0005] Therefore, those skilled in the art are committed to providing a hydrogen fuel cell air compressor recirculation auxiliary system and a cold start method to improve the success rate of cold start of hydrogen fuel cells. Summary of the Invention

[0006] In view of the defects in the prior art, the technical problem to be solved by the present invention is how to provide a system and method capable of realizing the cold start of hydrogen fuel cells.

[0007] To achieve the above object, on the one hand, the present invention provides a hydrogen fuel cell air compressor recirculation auxiliary system, which includes an air compressor, an intercooler, a humidifier, a stack, a back pressure valve, and a tail exhaust pipe. The outlet of the air compressor is connected to the inlet of the intercooler, the outlet of the intercooler is connected to the inlet of the first side of the humidifier, the outlet of the first side of the humidifier is connected to the cathode inlet of the stack, the cathode outlet of the stack is connected to the inlet of the back pressure valve, the outlet of the back pressure valve is connected to the inlet of the second side of the humidifier, and the outlet of the second side of the humidifier is connected to the tail exhaust pipe. The system further includes a first regulating valve and a second regulating valve. The two ends of the first regulating valve are respectively connected to the inlet and the outlet of the air compressor, and the two ends of the second regulating valve are respectively connected to the inlet of the air compressor and the outlet of the intercooler.

[0008] Preferably, the first regulating valve and the second regulating valve are proportional regulating valves.

[0009] Furthermore, a temperature sensor is further included, which is arranged at the outlet of the air compressor for obtaining the gas temperature at the outlet of the air compressor.

[0010] On the other hand, the present invention provides a cold start method for a recirculation auxiliary system of a hydrogen fuel cell air compressor, comprising the following steps:

[0011] Step 1, start the fuel cell system;

[0012] Step 2, obtain the temperature T of the fuel cell stack fs ;

[0013] Step 3, compare the temperature T of the fuel cell stack fs with the threshold temperature T fs1 . If T fs ≥T fs1 , normally start the fuel cell; otherwise, proceed to Step 4;

[0014] Step 4, cold start the fuel cell.

[0015] Further, when normally starting the fuel cell, turn on the fuel cell stack and the air compressor to increase the power of the fuel cell to the rated power point.

[0016] Further, Step 4 includes:

[0017] Step 4.1, partially open the first regulating valve, and close the second regulating valve and the back pressure valve;

[0018] Step 4.2, turn on the air compressor;

[0019] Step 4.3, obtain the temperature value T of the temperature sensor at the outlet of the air compressor 10 , and compare T 10 with the preset temperature T2;

[0020] Step 4.4, if T 10 ≥T2, close the first regulating valve, partially open the second regulating valve and the back pressure valve, and start the fuel cell stack; otherwise, loop Steps 4.2 and 4.3.

[0021] Further, Step 4 further includes:

[0022] Step 4.5, compare the temperature T 10 with the preset temperature T3. If T 10 ≥T3, reduce the speed of the air compressor and decrease the opening degree of the second regulating valve; if T 10 <T3, do not take any action.

[0023] Preferably, the preset temperature T2 is the preheating threshold temperature point of the air compressor, and the preset temperature T3 is the safe operating temperature point of the air compressor.

[0024] Further, Step 4 further includes:

[0025] Step 4.6, compare T 10 with T2. If T10 <When T2, increase the rotational speed of the air compressor and increase the opening degree of the second regulating valve, then return to step 4.5; if T 10 ≥ T2, do nothing;

[0026] Step 4.7: Compare T fs with T fs1 If T fs < T fs1 , then return to step 4.5; if T fs ≥ T fs1 , then the cold start process ends and the normal start process is entered.

[0027] Furthermore, in the said step 4.6, after the cold start ends, the rotational speed of the air compressor returns to the normal operating point, and the first regulating valve and the second regulating valve are closed.

[0028] The present invention has at least the following beneficial technical effects:

[0029] The recirculation auxiliary system and cold start method of the hydrogen fuel cell air compressor of the present invention utilize the air recirculation path and control strategy to realize obtaining the large-flow hot air required for cold start by using the motor power possessed by the air compressor itself, heating the air compressor itself, the coolant and the stack body, which can improve the success rate of cold start, shorten the cold start time, reduce the energy consumed during cold start, reduce the damage to the stack during cold start, and reduce the additional cost consumed by the cold start system.

[0030] The following will further illustrate the concept, specific structure and technical effects generated by the present invention with reference to the accompanying drawings, so as to fully understand the purpose, features and effects of the present invention. Brief Description of the Drawings

[0031] Figure 1 is a schematic diagram of the recirculation auxiliary system of the hydrogen fuel cell air compressor according to an embodiment of the present invention;

[0032] Figure 2 is a cold start flow chart of the recirculation auxiliary system of the hydrogen fuel cell air compressor according to an embodiment of the present invention;

[0033] Figure 3 is a schematic diagram of the cold start operating point according to an embodiment of the present invention.

[0034] In the figure, 1 - air filter, 2 - air compressor, 3 - intercooler, 4 - humidifier, 5 - stack, 6 - back pressure valve, 7 - tail exhaust pipe, 8 - first regulating valve, 9 - second regulating valve, 10 - temperature sensor;

[0035] Point a: shutdown point, no pressure, no flow;

[0036] Point b: a small flow rate point near the surge boundary of the air compressor at a selected high rotational speed; the purpose is to ensure low efficiency and high motor power to generate high heat, and at the same time, it can reduce the recirculation flow rate of the system to reduce the flow area of the first regulating valve;

[0037] Point c: a large flow rate point near the blockage boundary of the air compressor at a selected high rotational speed; it can ensure low efficiency and high motor power to generate high heat, but because it needs to take into account the sum of the working flow rate requirements after the start-up of the fuel cell system and the working flow rate requirements of the self-circulation of the air compressor, its flow rate is increased compared with point b, so it is selected in the blockage area;

[0038] Point d: the rated operating point during normal operation, generally the highest efficiency area designed;

[0039] T 10 : the temperature of the gas at the outlet of the air compressor

[0040] T2: the preheating threshold temperature point of the air compressor

[0041] T3: the safe operating temperature point of the air compressor

[0042] T fs : the temperature of the fuel cell stack

[0043] T fs1 : the cold start threshold temperature point of the fuel cell stack. Specific embodiments

[0044] The following introduces the preferred embodiments of the present invention to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the protection scope of the present invention is not limited to the embodiments mentioned in the text.

[0045] In the drawings, components with the same structure are denoted by the same numerical reference signs, and components with similar structures or functions are denoted by similar numerical reference signs. The size and thickness of each component shown in the drawings are arbitrarily shown, and the present invention does not limit the size and thickness of each component. In order to make the drawings clearer, the thickness of some parts in the drawings is appropriately exaggerated.

[0046] The present invention provides a hydrogen fuel cell air compressor recirculation auxiliary system and a cold start method for a hydrogen fuel cell, which utilize the air recirculation path and control strategy to realize obtaining a large flow rate of hot air for cold start by using the relatively large motor power possessed by the air compressor itself, so that no additional device is required, the cost of the hydrogen fuel cell is controlled, and the heating effect is better.

[0047] An embodiment of the present invention provides a hydrogen fuel cell air compressor recirculation auxiliary system, as Figure 1As shown, it has an air compressor 2, an intercooler 3, a humidifier 4, an electrolytic stack 5, a back pressure valve 6, and an exhaust pipe 7. Air is inhaled at the inlet of the air compressor 2 and compressed by the air compressor 2. The outlet of the air compressor 2 is connected to the inlet of the intercooler 3, and the compressed air exchanges heat in the intercooler 3 to heat the coolant. The outlet of the intercooler 3 is connected to the inlet of the first side of the humidifier 4, so that the compressed air is humidity-adjusted in the humidifier 4. The outlet of the first side of the humidifier 4 is connected to the cathode inlet of the electrolytic stack 5, so that the compressed air enters the electrolytic stack 5 to participate in the reaction. The cathode outlet of the electrolytic stack 5 is connected to one end of the back pressure valve 6, and the other end of the back pressure valve 6 is connected to the exhaust pipe 7, so that the waste gas in the electrolytic stack 5 is discharged. The improvement of this embodiment lies in that a first regulating valve 8 and a second regulating valve 9 are also provided. The two ends of the first regulating valve 8 are respectively connected to the inlet and the outlet of the air compressor 2, and the two ends of the second regulating valve 9 are respectively connected to the inlet of the air compressor 2 and the outlet of the intercooler 3. Through the first regulating valve 8 and the second regulating valve 9, part of the air is recycled between the inlet and the outlet of the air compressor, so that the air compressor 2 repeatedly heats the recycled air, which not only ensures that the normal flow passes through the air compressor to avoid problems such as surging, but also can significantly increase the temperature of this part of the air to heat the electrolytic stack and meet the cold start requirements.

[0048] In this embodiment, unless otherwise specified, the connections between components are all connected through pipelines. The air compressor 2 is electric and its speed is adjustable. The first regulating valve 8 and the second regulating valve 9 are proportional regulating valves, and their opening degrees are adjustable; the opening degree of the back pressure valve 6 is also adjustable. In order to improve the quality of the compressed air, an air filter 1 is also provided at the inlet of the air compressor 2 to remove impurities such as dust in the air. In order to realize the measurement and control of the recirculation auxiliary system, a temperature sensor 10 is provided at the outlet of the air compressor 2 to measure the temperature of the compressed air at the outlet of the compressor 2.

[0049] In the hydrogen fuel cell air compressor recirculation auxiliary system of this embodiment, through recirculation, a part of the hot air flows back to the inlet of the air compressor 2, which can increase the inlet temperature, thereby further increasing the outlet temperature. After the air compressor 2 enters the low compression efficiency area, more electric energy can be converted into heat energy to increase the temperature of the compressed gas. The recirculation method also solves the contradiction between the large flow rate of the air compressor 2 and the small flow rate required by the electrolytic stack 5. It neither loses compressed air nor can it give full play to the large motor power of the air compressor 2 to increase the heating effect.

[0050] Another embodiment of the present invention provides a cold start method for a hydrogen fuel cell air compressor recirculation auxiliary system, as Figure 2 and Figure 3 shown. The cold start process of this embodiment is as follows:

[0051] 1) Start the fuel cell system;

[0052] 2) Detect the temperature T inside the stack fs , and compare it with the set critical temperature T fs1 :

[0053] When T fs ≥T fs1 , the system starts normally, turns on the air compressor 2, the water pump, and the hydrogen circulation pump, and opens the valves at the cathode outlet and inlet of the stack 5, the valves at the anode outlet and inlet, turns on the fuel cell stack 5 and supplies power to the air compressor 2 and the hydrogen circulation pump. The fuel cell quickly rises to the rated power point, and the startup is completed.

[0054] When T fs <T fs1 , enter the cold startup procedure.

[0055] 3) During cold startup, the stack 5 does not start. First, start the air compressor 2 and let the air compressor 2 work to point b;

[0056] At this time, the first regulating valve 8 is partially opened, the second regulating valve 9 is fully closed, and the back pressure valve 6 is fully closed, so that all compressed air can flow back to the inlet of the air compressor 2, realizing repeated heating and continuous temperature rise and avoiding surge, while quickly increasing the temperature of the air compressor 2 itself.

[0057] 4) Monitor the temperature T of the temperature sensor 10 at the outlet of the air compressor 2 10 , when the temperature of the compressed gas rises to the preset temperature value T2:

[0058] Adjust the working point of the air compressor 2 to c;

[0059] Start the stack 5, close the first regulating valve 8, partially open the second regulating valve 9 and the back pressure valve 6, so that after the compressed air flows through the intercooler 3 and the humidifier 4, a part of the air enters the stack according to the pressure and flow required by the stack 5, and the remaining air flows back to the inlet of the air compressor 2 through the second regulating valve 9 to complete the recirculation. At this time, from the perspective of heating, part of the heat of the compressed air is used to maintain the temperature of the air compressor 2, part is used to heat the coolant in the intercooler 3, and the rest is used to heat the cathode of the stack 5.

[0060] 5) During the cold startup of the stack, continuously monitor the temperature T of the gas at the outlet of the air compressor 2 10 , and adjust:

[0061] When the temperature T 10 is too high and exceeds the preset value T3, there is a risk of damaging the air compressor 2. At this time, reduce the speed of the air compressor 2 and reduce the opening of the second regulating valve 9 to reduce the recirculation air flow, but ensure that the air volume entering the cathode of the stack 5 is constant;

[0062] When the temperature T 10When it is too low, lower than T2, the heating effect cannot be fully exerted. At this time, the rotation speed of the air compressor 2 is increased, and the opening degree of the second regulating valve 9 is increased to increase the recirculated air flow, but ensure that the air volume entering the cathode of the fuel cell stack 5 is constant.

[0063] 6) When the system determines that the cold start is over, that is, when T fs ≥T fs1 is satisfied, it enters the normal working state; at this time, the rotation speed of the air compressor 2 is restored to the preset value d of the normal working point, and the first regulating valve 8 and the second regulating valve 9 are completely closed.

[0064] The hydrogen fuel cell air compressor recirculation auxiliary system and cold start method of the present invention utilize the air recirculation path and control strategy to realize obtaining the large-flow hot air required for cold start by using the motor power possessed by the air compressor itself, which can improve the success rate of cold start, shorten the cold start time, reduce the energy consumed during cold start, reduce the damage to the fuel cell stack during cold start, and reduce the additional cost consumed by the cold start system.

[0065] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations according to the concept of the present invention without creative labor. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field of the present invention based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art should be within the protection scope determined by the claims.

Claims

1. A hydrogen fuel cell air compressor recirculation auxiliary system, comprising an air compressor, an intercooler, a humidifier, an electric stack, a back pressure valve, and a tail exhaust pipe. The outlet of the air compressor is connected to the inlet of the intercooler, the outlet of the intercooler is connected to the inlet of the first side of the humidifier, the outlet of the first side of the humidifier is connected to the cathode inlet of the electric stack, the cathode outlet of the electric stack is connected to the inlet of the back pressure valve, the outlet of the back pressure valve is connected to the inlet of the second side of the humidifier, and the outlet of the second side of the humidifier is connected to the tail exhaust pipe. It is characterized in that, It further includes a first regulating valve and a second regulating valve. Two ends of the first regulating valve are respectively connected to an inlet and an outlet of the air compressor, and two ends of the second regulating valve are respectively connected to the inlet of the air compressor and an outlet of the intercooler. It further includes a temperature sensor. The temperature sensor is arranged at the outlet of the air compressor and is used for obtaining the gas temperature at the outlet of the air compressor. The cold start method of the hydrogen fuel cell air compressor recirculation auxiliary system includes the following steps: Step 1: Start the fuel cell system. Step 2, obtain the temperature T of the stack fs ; Step 3: Compare the stack temperature T fs with the threshold temperature T fs1 . If T fs ≥T fs1 , start the fuel cell normally; otherwise, go to Step 4; Step 4: Cold start the fuel cell. The said Step 4 includes: Step 4.1: Partially open the first regulating valve and close the second regulating valve and the back pressure valve. Step 4.2: Start the air compressor and let the air compressor work to point b. The operating point b is a small flow point near the surge boundary of the air compressor at a selected high speed. Step 4.3: Obtain the temperature value T of the air compressor outlet temperature sensor 10 , and compare T 10 with the preset temperature T2; Step 4.4: If T 10 ≥ T2, close the first regulating valve, partially open the second regulating valve and the back pressure valve, start the stack, and adjust the operating point of the air compressor to c, where c is a large flow rate point near the blockage boundary of the air compressor at a selected high speed; otherwise, loop through steps 4.2 and 4.

3. Step 4.7, compare T fs with T fs1 . If T fs ≥ T fs1 , the cold start process ends, and the normal start process is entered. The air compressor speed returns to the normal operating point, and the first regulating valve and the second regulating valve are closed. The normal operating point is the rated operating point during normal operation and is the designed highest efficiency area.

2. The recirculation auxiliary system of the hydrogen fuel cell air compressor according to claim 1, characterized in that When normally starting the fuel cell, start the stack and the air compressor to make the fuel cell increase its power to the rated power point.

3. The recirculation auxiliary system of a hydrogen fuel cell air compressor according to claim 1, characterized in that The said Step 4 further includes: Step 4.5, compare the temperature T 10 with the preset temperature T3. If T 10 ≥ T3, reduce the rotational speed of the air compressor and decrease the opening degree of the second regulating valve; if T 10 < T3, do not take any action.

4. The recirculation auxiliary system of the hydrogen fuel cell air compressor according to claim 3, wherein The preset temperature T2 is the preheating threshold temperature point of the air compressor, and the preset temperature T3 is the safe operating temperature point of the air compressor.

5. The recirculation auxiliary system of a hydrogen fuel cell air compressor according to claim 4, wherein The said Step 4 further includes: Step 4.6: Compare T 10 with T2. If T 10 < T2, increase the rotational speed of the air compressor and the opening degree of the second regulating valve, and return to Step 4.

5. If T 10 ≥ T2, do not take any action.

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