A method for cryogenic storage shutdown and purging of a fuel cell system

Abstract

This invention belongs to the field of fuel cell technology, and specifically relates to a method for low-temperature storage shutdown purging of a fuel cell system. The invention includes the following steps: calculating the water production W2 within the fuel cell stack based on the on-load purging current I during shutdown; and calculating the target water content λ of the membrane electrode assembly at low temperatures. i Corresponding to the appropriate amount of water stored in the stack W3; according to the total amount of air out of the stack Q 出 , stack air pressure P 出 , air humidity RH 出 and the outflow air temperature T 出 , calculate the water content W4 in the stack gas; according to the water content mass conservation W1+W2=W3+W4, calculate the total water volume W1 required for the stack; according to the air pressure P 入 , air humidity RH 入 , air temperature entering the pile T 入 The total amount of water required for the stack W1 is used to calculate the required purge gas volume Q 入 ; According to the calculated purge gas volume Q 入 The invention provides a method for shutting down and purging a fuel cell system, which takes into account ambient temperature and humidity to precisely control the amount of purging gas and ensure low-temperature, damage-free storage. The method involves invoking a corresponding purging strategy and performing purging.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell technology, and specifically relates to a method for low-temperature storage shutdown and purging of a fuel cell system. Background Technology

[0002] Within its operating temperature range, proton exchange membrane fuel cells (PEMFCs) generate both gaseous and liquid water in the reaction zone due to the electrochemical and chemical reactions of hydrogen and oxygen. In practical applications, the startup process below 0°C is referred to as a "cold start." During a cold start, because the cell temperature is below the freezing point of water, residual water from the previous shutdown and water generated during the electrochemical reactions can potentially freeze. This freezing of water within the fuel cell stack poses four major risks: First, freezing hinders the transport of reactant gases and covers the active surfaces of the membrane electrode assembly (MEA), weakening or preventing reactant gases from reaching the reaction interface. Second, the ice deposits can damage the membrane structure, causing bulging, perforation, or rupture, ultimately leading to MEA leakage, gas shortage, and hydrogen deficiency, damaging the cell. Third, freezing reduces the reaction rate: low heat generation during cold starts further promotes the freezing of water generated after the electrochemical reactions, creating a vicious cycle that ultimately leads to cold start failure, significantly limiting the normal operation of the fuel cell stack and system in low-temperature environments. Fourth, the volume expansion after freezing will also generate stress in the battery stack, which will not only damage the catalyst interface and the matrix material of the porous electrode, but also affect the flow channels of the battery stack, as well as the corresponding pipes and sealing structures.

[0003] Therefore, under cold conditions, if the water stored on and inside the membrane electrode cannot be effectively drained, the water content will be too high, and freezing at low temperatures will affect the reaction area on the surface of the membrane electrode, which will easily lead to cold start failure. Moreover, after multiple start-ups and shutdowns, it will cause permanent damage to the battery stack and the membrane electrode.

[0004] However, if the water content on and inside the membrane electrode is too low, it will weaken the proton conduction characteristics of the proton membrane during the next startup, resulting in longer cold start time and deterioration of startup performance.

[0005] To ensure smooth and damage-free startup of battery stacks and fuel cell systems in low-temperature environments, purging must be carried out before cryogenic storage to control the water content in the porous electrodes to a reasonable range. The main method for controlling water content is to remove water from the carbon paper, catalyst layer, and membrane through shutdown purging procedures.

[0006] Previous methods for low-temperature non-destructive storage shutdown and purging include:

[0007] The invention patent application 202010586864.1 mentions that: the fuel cell controller controls the load current to 25% to 30% of the rated output current of the fuel cell stack, controls the heater and radiator to maintain the inlet cooling water temperature of the fuel cell stack at 60℃ to 65℃, controls the speed of the air compressor to ensure that the air flow rate is more than 10 times the air flow rate required under the output load current condition, and uses a single-cell voltage monitoring unit to detect the voltage of each cell in the fuel cell stack until the lowest voltage of each cell is less than 0.75V. While this scheme considers the purging air volume, it fails to consider the following: First, after purging, when the cooling water temperature drops below 60℃, water vapor in the fuel cell stack will continue to condense and produce water, re-wetting the membrane electrode assembly. Second, controlling the air compressor speed to ensure that the air flow rate is more than 10 times the air flow rate required under the output load current condition is too high. This not only increases the energy consumption of the air compressor but may also be insufficient due to the performance limitations of the air compressor, affecting the purging effect. Meanwhile, since the actual ambient temperature and humidity were not taken into account, an excessively high purge air volume may dry out the membrane electrode, affecting the membrane's start-up performance.

[0008] The invention patent application 202010779071.1 mentions the following solution: upon receiving a cryogenic shutdown command, the fuel cell stack current is reduced to I1, initiating the first stage of the purging process; when the total stack voltage is ≤ U1, or the purging duration reaches T5, or the individual cell voltage is ≤ U3, the second stage of the purging process begins; the fuel cell stack current and air compressor speed are set to 0, and the hydrogen pressure is set to P2. While this solution considers the characteristics of each stage of the shutdown purging process, it does not mention the calculation and control methods for the required purging gas volume.

[0009] In invention patent 202010240734.2, the proposed solution involves: purging the fuel cell with a first initial flow rate and a first purging descent rate; measuring the AC impedance value of the fuel cell and determining whether the AC impedance value reaches a first AC impedance value; if so, purging the fuel cell with a second initial flow rate and a second purging descent rate; measuring the AC impedance value of the fuel cell and determining whether the AC impedance value reaches a second AC impedance value; if so, purging the fuel cell with a third constant flow rate until the AC impedance value of the fuel cell reaches a target AC impedance. This solution does not consider ambient temperature and humidity as the basis for determining the purging gas volume, which may lead to an unsuitable, excessive, or insufficient purging gas volume, resulting in failure to achieve the required water content in the fuel cell stack, increased purging energy consumption, or prolonged purging time. Summary of the Invention

[0010] In order to solve the above-mentioned problems in the prior art, the purpose of this invention is to provide a method for low-temperature storage shutdown purging of a fuel cell system that takes into account ambient temperature and humidity to accurately control the purging gas volume.

[0011] The technical solution adopted in this invention is as follows:

[0012] A method for cryogenic storage shutdown purging of a fuel cell system includes the following steps:

[0013] S1: Calculate the water production W2 within the fuel cell stack based on the on-load purging current I during shutdown; calculate the target value λ for the water content of the membrane electrode under low temperature conditions. i Calculate the appropriate water volume W3 inside the fuel cell stack;

[0014] S2: Based on the total amount of air discharged from the reactor Q 出 , Exhaust air pressure P 出 RH of air discharged from the pile 出 and the temperature of the air exiting the reactor T 出 The water content W4 in the pile gas was calculated.

[0015] S3: Calculate the total water volume W1 required for the pile based on the water content mass conservation W1+W2=W3+W4;

[0016] S4: Then, based on the infeed air pressure P 入 RH of the air entering the pile 入 , Injection air temperature T 入 Calculate the total water volume W1 required for the fuel cell, and the purge gas volume Q required for the fuel cell. 入 ;

[0017] S5: The controller calculates the purge air volume Q. 入 The appropriate purging strategy is invoked to carry out purging.

[0018] According to Faraday's law, under a specific current, the mass flow rate of water produced is W2 = I / 2F*18, in g / s, where F is the Faraday constant: 96485 C / mol.

[0019] The program built into the controller in this invention: based on the target value λ of the water content of the membrane electrode at a lower temperature. i When calculating the reasonable water content W3 in the battery stack, the changes in water content caused by the continued condensation of water vapor in the battery stack after the cooling water temperature drops below 60°C in actual applications are fully considered. Therefore, it can avoid the membrane electrode becoming wet again after the purging is completed, which would lead to excessive water content and damage to the membrane electrode during low-temperature storage.

[0020] When calculating the water content W4 in the reactor gas, the exhaust air pressure P is taken into account. 出 RH of air discharged from the pile 出 and the temperature of the air exiting the reactor T 出 This allows for a more accurate calculation of the water content W4 in the reactor gas.

[0021] According to the purging requirements, the water content in the fuel cell stack after purging must satisfy the law of conservation of mass, i.e., the water content W4 in the effluent gas = the total water required for effluent input W1 + the water produced in the stack W2 - the appropriate water content in the stack W3. After accurately calculating the water content W3 in the stack and the water content W4 in the effluent gas, the precise total water required for effluent input W1 can be obtained, i.e., the water content in the effluent gas.

[0022] Then, the total water volume W1 required for reactor loading is accurately determined, taking into account the reactor loading air pressure P. 入 Humidity of the air entering the pile

[0023] RH 入 , Injection air temperature T 入 It can calculate the precise purge gas volume Q. 入 .

[0024] This is used to purge air volume Q 入 Purge can save energy and time spent on downtime purging, and prevent the water content in the membrane electrode from rising again after purging.

[0025] As a preferred embodiment of the present invention, the target value λ of water content in step S1 is... i W3 is obtained by the following method:

[0026] T1: The target water content λ required for low-temperature non-destructive storage of the membrane electrode at different low-temperature environments is preset in the controller. i ;

[0027] T2: The lowest temperature of the current year, month, or season is preset in the controller;

[0028] T3: During step S1, identify the real-time date, compare it with the preset date, month, or season in the controller, retrieve the corresponding minimum temperature, and determine the target value λ of the membrane electrode water content corresponding to this minimum temperature. i .

[0029] Determining the target value λ for water content in the membrane electrode i At that time, the target value λ of membrane electrode water content at the lowest temperature corresponding to the real-time date, month, or season is retrieved. i ,

[0030] Establishing the target value λ for water content in the membrane electrode i When determining the appropriate water storage volume W3 within the battery stack, it is necessary to fully consider, through experimental testing and theoretical calculations, the possibility that water vapor will continue to condense and generate water after purging, re-wetting the membrane electrode and leading to an increase in water storage volume. This provides a margin for the selection of W3, thereby establishing λ. i The relationship with W3.

[0031] As a preferred embodiment of the present invention, in step S2, based on the discharge air pressure P...出 RH of air discharged from the pile 出 and the temperature of the air exiting the reactor T 出 The saturated water vapor pressure P was calculated using the IAPWS series of formulas developed by the International Association for the Study of Water and Water Vapor Properties. 出饱和 Then calculate the water content in the pile gas, W4 = P. 出饱和 / P 出 *Q 出 .

[0032] As a preferred embodiment of the present invention, in step S2, based on the discharge air pressure P... 出 RH of air discharged from the pile 出 and the temperature of the air exiting the reactor T 出 The saturated water vapor pressure P was calculated using the Antonie formula. 出饱和 Then calculate the water content in the pile gas, W4 = P. 出饱和 / P 出 *Q 出 .

[0033] As a preferred embodiment of the present invention, in step S2, based on the discharge air pressure P... 出 RH of air discharged from the pile 出 and the temperature of the air exiting the reactor T 出 Use the Gibbs formula to calculate the saturated water vapor pressure P. 出饱和 Then calculate the water content in the pile gas, W4 = P. 出饱和 / P 出 *Q 出 .

[0034] As a preferred embodiment of the present invention, in step S4, based on the infeed air pressure P... 入 RH of the air entering the pile 入 , Injection air temperature T 入 The saturated vapor pressure P of the injected air was calculated using the IAPWS series of formulas developed by the International Association for the Study of Water and Vapor Properties. 入饱和 Next, calculate the purge gas volume Q required for the fuel cell. 入 =W1*P 入 / P 入饱和 .

[0035] As a preferred embodiment of the present invention, in step S4, based on the infeed air pressure P... 入 RH of the air entering the pile 入 , Injection air temperature T 入 The saturated vapor pressure P of the injected air was calculated using the Antoni formula. 入饱和 Next, calculate the purge gas volume Q required for the fuel cell. 入 =W1*P 入 / P 入饱和 .

[0036] As a preferred embodiment of the present invention, in step S4, based on the infeed air pressure P... 入 RH of the air entering the pile 入 , Injection air temperature T 入 The saturated vapor pressure P of the injected air was calculated using the Gibbs formula. 入饱和 Next, calculate the purge gas volume Q required for the fuel cell. 入 =W1*P 入 / P 入饱和 .

[0037] The beneficial effects of this invention are as follows:

[0038] 1. The program built into the controller in this invention: based on the target value λ of the membrane electrode water content at a lower temperature. i When calculating the reasonable water content W3 in the battery stack, the changes in water content caused by the continued condensation of water vapor in the battery stack after the cooling water temperature drops below 60°C in actual applications are fully considered. Therefore, it can avoid the membrane electrode becoming wet again after the purging is completed, which would lead to excessive water content and damage to the membrane electrode during low-temperature storage.

[0039] 2. When calculating the water content W4 in the reactor gas, the exhaust air pressure P should be considered. 出 RH of air discharged from the pile 出 and the temperature of the air exiting the reactor T 出 This allows for a more accurate calculation of the water content W4 in the outflowing gas. Furthermore, based on the law of conservation of water mass and W2, W3, and W4, the total water volume W1 required for reactor injection can be accurately calculated, combined with the reactor injection air pressure P. 入 RH of the air entering the pile 入 , Injection air temperature T 入 It can accurately calculate the purging gas volume Q. 入 This is used to purge air volume Q. 入 Purge can save energy and time spent on downtime purging, and ensure that the water content of the membrane electrode can meet the requirements for low-temperature non-destructive storage after the purging is completed. Attached Figure Description

[0040] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0042] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the invention can be combined with each other.

[0043] like Figure 1 As shown, the cryogenic storage shutdown and purging method for a fuel cell system in this embodiment includes the following steps:

[0044] S1: Calculate the water production W2 within the fuel cell stack based on the on-load purging current I during shutdown; calculate the target value λ for the water content of the membrane electrode under low temperature conditions. i The appropriate water storage capacity W3 inside the fuel cell stack can be calculated accordingly.

[0045] S2: Based on the exhaust air pressure P 出 RH of air discharged from the pile 出 and the temperature of the air exiting the reactor T 出 The saturated water vapor pressure P is calculated using the IAPWS series of formulas developed by the International Association for the Properties of Water and Water Vapor or other calculation formulas such as the Antoni and Gilli formulas. 出饱和 Then calculate the water content in the pile gas, W4 = P. 出饱和 / P 出 *Q 出 ;

[0046] S3: Calculate the total water volume W1 required for the pile based on the water content mass conservation W1+W2=W3+W4;

[0047] S4: Based on the infeed air pressure P 入 RH of the air entering the pile 入 , Injection air temperature T 入 The saturated vapor pressure P of the infeed air is calculated using the IAPWS series of formulas developed by the International Association for the Properties of Water and Steam or other calculation formulas such as the Antoni and Gilli formulas. 入饱和 Then calculate the amount of air to be fed into the fuel cell stack or the required amount of purge air Q. 入 =W1*P 入 / P 入饱和 .

[0048] S5: The controller calculates the purge air volume Q. 入 The appropriate purging strategy is invoked to carry out purging.

[0049] The program built into the controller in this invention: based on the target value λ of the water content of the membrane electrode at a lower temperature.i When calculating the reasonable water content W3 in the battery stack, the changes in water content caused by the continued condensation of water vapor in the battery stack after the cooling water temperature drops below 60°C in actual applications are fully considered. Therefore, it can avoid the membrane electrode becoming wet again after the purging is completed, which would lead to excessive water content and damage to the membrane electrode during low-temperature storage.

[0050] When calculating the water content W4 in the reactor gas, the exhaust air pressure P is taken into account. 出 RH of air discharged from the pile 出 and the temperature of the air exiting the reactor T 出 This allows for a more accurate calculation of the water content W4 in the reactor gas.

[0051] According to the purging requirements, the water content in the fuel cell stack after purging must satisfy the law of conservation of mass, i.e., the water content W4 in the effluent gas = the total water required for effluent input W1 + the water produced in the stack W2 - the appropriate water content in the stack W3. After accurately calculating the water content W3 in the stack and the water content W4 in the effluent gas, the precise total water required for effluent input W1 can be obtained, i.e., the water content in the effluent gas.

[0052] Then, the total water volume W1 required for reactor loading is accurately determined, taking into account the reactor loading air pressure P. 入 RH of the air entering the pile 入 , Injection air temperature T 入 It can calculate the precise purge gas volume Q. 入 .

[0053] This is used to purge air volume Q 入 Performing purging can save energy and time spent on downtime purging, and also prevent the membrane electrode from becoming wet again after purging.

[0054] Among them, the target value of water content λ in step S1 i Obtained by the following method:

[0055] T1: The target water content λ required for low-temperature non-destructive storage of the membrane electrode at different low-temperature environments is preset in the controller. i ;

[0056] T2: The lowest temperature of the current year, month, or season is preset in the controller;

[0057] T3: During step S1, identify the real-time date, compare it with the preset date, month, or season in the controller, retrieve the corresponding minimum temperature, and determine the target value λ of the membrane electrode water content corresponding to this minimum temperature. i .

[0058] Establishing the target value λ for water content in the membrane electrode iWhen determining the appropriate water storage volume W3 within the battery stack, it is necessary to fully consider, through experimental testing and theoretical calculations, the possibility that water vapor will continue to condense and generate water after purging, re-wetting the membrane electrode and leading to an increase in water storage volume. This provides a margin for the selection of W3, thereby establishing λ. i The relationship with W3.

[0059] Example:

[0060] 1. The controller is pre-set with target values ​​λ for membrane electrode water content corresponding to different low-temperature environments and a conversion formula for water storage W3;

[0061] 2. The controller is preset with the lowest temperature of the current year, month, or season in previous years;

[0062] 3. When the machine is stopped and purged, the real-time date is identified and compared with the date, month or season preset in the controller. The corresponding minimum temperature-corresponding membrane electrode water content target value λ is called: for example, the minimum temperature is 5℃ from March to September, which corresponds to λ1, and the minimum temperature is -25℃ from October to February, which corresponds to λ2.

[0063] 4. The system obtains the infeed air pressure P of the fuel cell system during shutdown. 入 RH of the air entering the pile 入 , Injection air temperature T 入 Transmitted to the controller;

[0064] 5. Using the data collected above, combined with the water production W2 in the fuel cell stack corresponding to the current purging load current I, and the target water content λ of the fuel cell stack, i This allows for the calculation of the purging gas volume.

[0065] 6. The controller calls the corresponding purging strategy based on the calculated purging air volume and carries out purging.

[0066] This invention is not limited to the above-described optional embodiments. Anyone can derive other various forms of products under the guidance of this invention. However, regardless of any changes made in their shape or structure, any technical solution that falls within the scope of the claims of this invention shall be protected by this invention.

Claims

1. A method for cryogenic storage shutdown purging of a fuel cell system, characterized in that: Includes the following steps: S1: Calculate the water production W2 within the fuel cell stack based on the on-load purging current I during shutdown; calculate the target value λ for the water content of the membrane electrode under low temperature conditions. i The appropriate water storage volume W3 within the fuel cell stack is determined accordingly. S2: Based on the total amount of air discharged from the reactor Q 出 , Exhaust air pressure P 出 RH of air discharged from the pile 出 and the temperature of the air exiting the reactor T 出 The water content W4 in the pile gas was calculated. S3: Calculate the total water volume W1 required for the pile based on the water content mass conservation W1+W2=W3+W4; S4: Then, based on the infeed air pressure P 入 RH of the air entering the pile 入 , Injection air temperature T 入 Calculate the total water volume W1 required for the fuel cell, and the purge gas volume Q required for the fuel cell. 入 ; S5: The controller calculates the purge air volume Q. 入 The appropriate purging strategy is invoked to carry out shutdown purging; The target water content value λ in step S1 i Obtained by the following method: T1: The target water content λ required for low-temperature non-destructive storage of the membrane electrode at different low-temperature ambient temperatures is preset in the controller. i ; T2: The lowest temperature of the current year, month, or season is preset in the controller; T3: During step S1, identify the real-time date, compare it with the preset date, month, or season in the controller, retrieve the corresponding minimum temperature, and determine the target value λ of the membrane electrode water content corresponding to this minimum temperature. i .

2. The method for cryogenic storage shutdown and purging of a fuel cell system according to claim 1, characterized in that: In step S2, based on the outflow air pressure P 出 RH of air discharged from the pile 出 and the temperature of the air exiting the reactor T 出 The saturated water vapor pressure P was calculated using the IAPWS series of formulas developed by the International Association for the Study of Water and Water Vapor Properties. 出饱和 Then calculate the water content in the pile gas, W4=P 出饱和 / P 出 *Q 出 .

3. The method for cryogenic storage shutdown and purging of a fuel cell system according to claim 1, characterized in that: In step S2, based on the outflow air pressure P 出 RH of air discharged from the pile 出 and the temperature of the air exiting the reactor T 出 The saturated water vapor pressure P was calculated using the Antonie formula. 出饱和 Then calculate the water content in the pile gas, W4=P 出饱和 / P 出 *Q 出 .

4. The method for cryogenic storage shutdown and purging of a fuel cell system according to claim 1, characterized in that: In step S2, based on the outflow air pressure P 出 RH of air discharged from the pile 出 and the temperature of the air exiting the reactor T 出 Use the Gibbs formula to calculate the saturated water vapor pressure P. 出饱和 Then calculate the water content in the pile gas, W4=P 出饱和 / P 出 *Q 出 .

5. The method for cryogenic storage shutdown and purging of a fuel cell system according to claim 1, characterized in that: In step S4, based on the infeed air pressure P 入 RH of the air entering the pile 入 , Injection air temperature T 入 The saturated vapor pressure P of the injected air was calculated using the IAPWS series of formulas developed by the International Association for the Study of Water and Vapor Properties. 入饱和 Next, calculate the purge gas volume Q required for the fuel cell. 入 = W1 *P 入 / P 入饱和 .

6. The method for cryogenic storage shutdown and purging of a fuel cell system according to claim 1, characterized in that: In step S4, based on the infeed air pressure P 入 RH of the air entering the pile 入 , Injection air temperature T 入 The saturated vapor pressure P of the injected air was calculated using the Antoni formula. 入饱和 Next, calculate the purge gas volume Q required for the fuel cell. 入 = W1 *P 入 / P 入饱和 .

7. The method for cryogenic storage shutdown and purging of a fuel cell system according to claim 1, characterized in that: In step S4, based on the infeed air pressure P 入 RH of the air entering the pile 入 , Injection air temperature T 入 The saturated vapor pressure P of the injected air was calculated using the Gibbs formula. 入饱和 Next, calculate the purge gas volume Q required for the fuel cell. 入 = W1 *P 入 / P 入饱和 .

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