Fuel cell anode purging strategy making method based on hydrogen utilization rate

Abstract

The invention discloses a fuel cell anode purging strategy making method based on hydrogen utilization rate, and aims to solve the problem that hydrogen is wasted due to the fact that foreign gas needs to be blown out by a fuel cell in a purging mode, the relationship between the hydrogen utilization rate and the opening and closing time of a purging valve is established. Based on the actual measurement data of anode temperature, anode total pressure, purge valve outlet pressure, purge valve inlet and outlet pressure difference and anode humidity, and the given parameter current, the number of single cells and the hydrogen stoichiometric ratio in the stack design, the purge opening and closing time requirement meeting the hydrogen utilization rate can be quickly obtained; therefore, a specific purging strategy can be conveniently formulated, and the hydrogen utilization rate can be maximized or the purging efficiency can be optimized.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and particularly relates to a method for formulating an anode purge strategy of a fuel cell based on hydrogen utilization rate. Background Art

[0002] Existing hydrogen fuel cells are devices that directly convert chemical energy into electrical energy through electrochemical reactions using hydrogen and air as reactants. During the operation of a hydrogen fuel cell, the main component nitrogen in the air will diffuse through the proton exchange membrane to the anode side. If the nitrogen on the anode side is not discharged in time, it will accumulate continuously in the battery, causing the battery performance to decline and affecting the output power of the battery. Currently, the commonly used method is to use excess gas to purge the impurity gas out of the battery, but a large amount of hydrogen will be wasted during the purging process, or purging needs to be carried out after the fuel cell stops, which will reduce the working efficiency of the fuel cell. Therefore, it is necessary to formulate an anode purge strategy for fuel cells with high hydrogen utilization rate to overcome the above problems.

[0003] The prior art CN115692771A designs a hydrogen-air fuel cell system with high hydrogen utilization rate and its purging method. By setting a buffer device downstream of the fuel cell stack, the buffer device receives the impurity gas, and by presetting the safety voltage V m and the hydrogen supply duration t s , and resetting the pulse purge conduction time and the pulse purge interval t x to limit the purge frequency and extend the pulse purge interval, thereby reducing hydrogen waste. This strategy requires adding an additional buffer device and setting the corresponding pulse purge time and interval based on the buffer device, but no relevant measures are given on how to formulate the anode purge strategy for conventional fuel cells without a buffer device. Summary of the Invention

[0004] In view of the above technical problems, the present invention aims to provide a method for formulating an anode purge strategy of a fuel cell based on hydrogen utilization rate. By setting the target of hydrogen utilization rate, a relational expression between hydrogen utilization rate and the opening and closing time of the purge valve within a purge cycle is obtained. Through this relational expression, the distribution relationship between the opening time and closing time of the purge valve within a purge cycle can be quickly estimated, so as to help formulate the anode purge strategy of the fuel cell, thereby achieving the purpose of making the hydrogen utilization rate meet the target value.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for formulating an anode purge strategy of a fuel cell based on hydrogen utilization rate, comprising the following steps:

[0007] Step 1, according to the measured anode temperature T, obtain the absolute pressure of water vapor And according to the relationship between the total anode pressure and the absolute hydrogen pressure, the mass fraction of hydrogen in the mixed gas is obtained.

[0008] Step 2: According to the purge valve outlet pressure p va,out , the purge valve flow coefficient k v , the pressure difference Δp between the inlet and outlet of the purge valve, the hydrogen pressure and the water vapor pressure the total mass flow rate of the mixed gas passing through the purge valve is obtained.

[0009] Step 3: According to the mass fraction of hydrogen in the mixed gas and the total mass flow rate of the mixed gas passing through the purge valve the mass flow rate of hydrogen in the mixed gas discharged from the purge valve is obtained.

[0010] Step 4: The mass flow rate of consumed hydrogen is calculated according to the molar flow rate of consumed hydrogen.

[0011] Step 5: According to the hydrogen utilization rate during a purge cycle, and the mass flow rate of consumed hydrogen the mass flow rate of hydrogen discharged from the purge valve the purge valve opening time t on and the purge valve closing time t off the relationship between the hydrogen utilization rate and the anode temperature T, the total anode pressure p an , the purge valve outlet pressure p va,out , the pressure difference Δp between the inlet and outlet of the purge valve, the anode humidity (i.e., the humidity of the mixed gas in the anode) the current I, the number of single cells N in the stack design, the hydrogen stoichiometric ratio λ, the hydrogen pressure the water vapor pressure the relative molecular mass of water vapor the relative molecular mass of hydrogen the purge valve flow coefficient k v , the Faraday constant F, the purge valve opening time t on , the purge valve closing time t off is obtained.

[0012] Step 6: According to the anode temperature T, the total anode pressure p an obtained from actual tests, the purge valve outlet pressure p va,out , the pressure difference Δp between the inlet and outlet of the purge valve, the anode humidity the number of single cells N in the stack design, the stack operating parameter current I and the hydrogen stoichiometric ratio λ, the hydrogen utilization rate and the purge valve opening time ton and the purge valve closing time t off ;

[0013] Step 7: Based on the relationships among the hydrogen utilization rate, the purge valve opening time, and the purge valve closing time obtained in Step 6, formulate the purge valve opening time and the purge valve closing time that conform to the relationships among the three.

[0014] Furthermore, the absolute pressure of hydrogen in Step 1 is where p an is the total anode pressure, is the absolute pressure of water vapor, which is calculated from the anode temperature and anode humidity. Specifically, p vs is the saturated partial pressure of water vapor at the corresponding anode temperature T, is the anode humidity,

[0015] Furthermore, the hydrogen mass fraction in the mixed gas in Step 1 is where

[0016] Furthermore, in Step 2, according to the ideal gas state equation pV = nRT, by transformation, pM = ρRT, then the density of the mixed gas According to the calculation formula of the purge valve flow coefficient k v the total volume flow rate Q of the mixed gas passing through the purge valve can be obtained , specifically N as According to formulas (3) and (4), the total mass flow rate of the mixed gas passing through the purge valve can be obtained Specifically:[[]] In formula (5), k v is the purge valve flow coefficient, p va,out is the outlet pressure of the purge valve, Δp is the pressure difference between the inlet and outlet of the purge valve, is the absolute pressure of water vapor, is the relative molecular mass of water, is the relative molecular mass of hydrogen, is the absolute pressure of hydrogen.

[0017] Furthermore, in Step 3, among the mixed gas discharged by the purge valve, the mass flow rate of hydrogen is where is the total mass flow rate of the mixed gas passing through the purge valve.

[0018] Furthermore, in step 4, the molar flow rate of hydrogen consumed The mass flow rate of hydrogen consumed is: where λ is the hydrogen stoichiometric ratio, I is the operating current of the stack, N is the number of single cells, F is the Faraday constant, and is the relative molecular mass of hydrogen.

[0019] Furthermore, in step 5, the hydrogen utilization rate and the mass flow rate of hydrogen consumed The mass flow rate of hydrogen discharged from the purge valve The opening time t of the purge valve on and the closing time t of the purge valve off are specifically related as follows: Then, based on the mass flow rate of hydrogen consumed obtained in steps 1 - 4 and the mass flow rate of hydrogen discharged from the purge valve the hydrogen utilization rate can be obtained in relation to the anode temperature T, the total anode pressure p an , the outlet pressure p of the purge valve va,out , the pressure difference Δp across the purge valve, the anode humidity the current I, the number of single cells N, the hydrogen stoichiometric ratio λ, the hydrogen pressure the water vapor pressure the relative molecular mass of water vapor the relative molecular mass of hydrogen the flow coefficient k of the purge valve v , the Faraday constant F, the opening time t of the purge valve on , the closing time t of the purge valve off . The relationship is specifically expressed as

[0020] In actual use, based on the measured data of the anode temperature T, the total anode pressure p an , the outlet pressure p of the purge valve va,out , the pressure difference Δp across the purge valve, the anode humidity the number of single cells N designed for the stack, the operating parameter current I of the stack and the hydrogen stoichiometric ratio λ, the calculated parameter hydrogen pressure the water vapor pressure constant value parameters k v , F, and then through step 5 Obtain with t on 、t off The specific relational formula (9), so as to set the purge valve opening time t according to the desired hydrogen utilization rate on and the purge valve closing time t off , and formulate a purge strategy that meets the hydrogen utilization rate.

[0021] Compared with the prior art, the beneficial effects of the present invention are: (1) By establishing the relationship between the hydrogen utilization rate and the opening and closing time of the purge valve, according to the actual measurement data of the anode temperature, the total anode pressure, the purge valve outlet pressure, the purge valve inlet and outlet pressure difference, the anode humidity, and the given parameters in the fuel cell design, such as current, the number of single cells, and the hydrogen stoichiometry, the time requirements for the opening and closing of the purge to meet the hydrogen utilization rate can be quickly obtained, so as to facilitate the formulation of a specific purge strategy. This method is simple to calculate and operate, and the required parameters can be directly measured or set according to the usage requirements of the fuel cell during the design stage. Not only can the hydrogen utilization rate be ensured without adding additional equipment and structures, but also the purge can be implemented without shutting down the fuel cell, obtaining a good hydrogen utilization rate. (2) When the design parameters of the fuel cell are fixed, through the obtained relationship between the hydrogen utilization rate and the opening and closing time of the purge valve, corresponding purge strategies can be formulated and adjusted to obtain the maximum hydrogen utilization rate of the system when the purge cycle is fixed, or the purge cycle can be changed through the existing situation of the self-purge equipment to maximize the purge efficiency when the hydrogen utilization rate is set as expected. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Referring to the accompanying drawings, the disclosure of the present invention will become more understandable. It is easy for those skilled in the art to understand that these drawings are only used to illustrate the technical solutions of the present invention and are not intended to limit the protection scope of the present invention.

[0023] Figure 1 is a flowchart for formulating a fuel cell anode purge strategy based on hydrogen utilization rate according to an embodiment of the present invention.

[0024] Figure 2 is a relationship diagram between the purge opening time and the hydrogen utilization rate within a purge cycle according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0026] An anode purge strategy formulation method based on hydrogen utilization rate is proposed in an embodiment of the present invention, as Figure 1 shown, which includes the following steps:

[0027] Step 1, according to the measured anode temperature T, obtain the absolute pressure of water vapor and, according to the relationship between the total anode pressure and the absolute hydrogen pressure, obtain the mass fraction of hydrogen in the mixed gas

[0028] Step 2, according to the purge valve outlet pressure p va,out the purge valve flow coefficient k v the pressure difference Δp between the inlet and outlet of the purge valve, the hydrogen pressure and the water vapor pressure obtain the total mass flow rate of the mixed gas passing through the purge valve

[0029] Step 3, according to the mass fraction of hydrogen in the mixed gas and the total mass flow rate of the mixed gas passing through the purge valve obtain the mass flow rate of hydrogen in the mixed gas discharged by the purge valve

[0030] Step 4, calculate and obtain the mass flow rate of consumed hydrogen according to the molar flow rate of consumed hydrogen

[0031] Step 5, according to the hydrogen utilization rate within a purge cycle, the relationship with the mass flow rate of consumed hydrogen the mass flow rate of hydrogen discharged from the purge valve the purge valve opening time t on and the purge valve closing time t off obtain the relationship between the hydrogen utilization rate and the anode temperature T, the total anode pressure p an the purge valve outlet pressure p va,out the pressure difference Δp between the inlet and outlet of the purge valve, the anode humidity the current I, the number of single cells N, the hydrogen stoichiometric ratio λ, the hydrogen pressure the water vapor pressure the relative molecular mass of water vapor Relative molecular mass of hydrogen Flow coefficient k of the purge valve v , Faraday constant F, purge valve opening time t on , purge valve closing time t off Relationships

[0032] Step 6: Based on the anode temperature T and total anode pressure p obtained from actual tests an , purge valve outlet pressure p va,out , purge valve inlet-outlet pressure difference Δp, anode humidity and the design requirement value current I, number of single cells N, hydrogen stoichiometry λ, obtain the hydrogen utilization rate and the purge valve opening time t on , purge valve closing time t off Relationships;

[0033] Step 7: Based on the relationships between the hydrogen utilization rate, purge valve opening time, and purge valve closing time obtained in Step 6, formulate the purge valve opening time and purge valve closing time that conform to the relationships among the three.

[0034] In the said Step 1, ignoring the nitrogen pressure of the anode, the absolute pressure of hydrogen is where p an is the total anode pressure, is the absolute pressure of water vapor, which is calculated from the anode temperature and anode humidity, specifically p vs is the saturated partial pressure of water vapor at the corresponding anode temperature T, is the anode humidity,

[0035] In the said Step 1, according to the ideal gas state equation pV = nRT, it is transformed to pMV = mRT, from which it can be known that According to the absolute pressure relationship between hydrogen and water vapor in the mixed gas, the hydrogen mass fraction of the mixed gas can be obtained where

[0036] In the said Step 2, according to the ideal gas state equation pV = nRT, it is transformed to pM = ρRT, then the density of the mixed gas According to the calculation formula of the purge valve flow coefficient k v the total volume flow rate Q of the mixed gas passing through the purge valve can be obtained , specifically N as The total mass flow rate of the mixed gas passing through the purge valve can be obtained according to Formulas (3) and (4). Specifically In Formula (5), k v is the flow coefficient of the purge valve, p va,out is the outlet pressure of the purge valve, and Δp is the pressure difference between the inlet and outlet of the purge valve. is the absolute pressure of water vapor, is the relative molecular mass of water, is the relative molecular mass of hydrogen, is the absolute pressure of hydrogen.

[0037] In Step 3, among the mixed gas discharged by the purge valve, the mass flow rate of hydrogen is: Substituting Formula (2) can obtain where

[0038] In Step 4, the molar flow rate of hydrogen consumed Then the mass flow rate of hydrogen consumed is: where λ is the hydrogen stoichiometric ratio, I is the operating current of the fuel cell stack, N is the number of single cells, F is the Faraday constant, is the relative molecular mass of hydrogen.

[0039] In Step 5, within one purge cycle, the hydrogen utilization rate is related to the mass flow rate of hydrogen consumed and the mass flow rate of hydrogen discharged from the purge valve the opening time y of the purge valve on and the closing time t of the purge valve off specifically as: Then, according to the mass flow rate of hydrogen consumed obtained in Steps 1 - 4 and the mass flow rate of hydrogen discharged from the purge valve the hydrogen utilization rate can be obtained in relation to the anode temperature T, the total anode pressure p an , the outlet pressure p of the purge valve va,out , the pressure difference Δp between the inlet and outlet of the purge valve, the anode humidity the current I, the number of single cells N, the hydrogen stoichiometric ratio λ, the hydrogen pressure the water vapor pressure the relative molecular mass of water vapor Relative molecular mass of hydrogen Flow coefficient k of the purge valve v , Faraday constant F, purge valve opening time t on , purge valve closing time t off The relationship, which is specifically manifested as

[0040] The parameters of the fuel cell stack designed in this embodiment are specifically: current I = 550 A, number of single cells N = 440, hydrogen stoichiometric ratio θ = 1.4. The anode temperature T = 315 K and the total anode pressure p an = 226.3 KPaA, purge valve outlet pressure p va,out = 1 bar, pressure difference Δp between the inlet and outlet of the purge valve = 0.1 bar, anode humidity (i.e., the humidity of the mixed gas in the anode) Substituting the above parameters into formula (9) gives

[0041] In this embodiment, if the hydrogen utilization rate is set Then the purge valve opening time t on and the purge valve closing time t off The relationship is t off ≥1.7t on . Accordingly, according to the usage requirements of the purge equipment in the system, the purge cycle can be changed while ensuring that the hydrogen utilization rate meets the target value, so as to maximize the purge efficiency.

[0042] In this embodiment, when the purge cycle is set to 10 s, that is, t on +t off = 10, from which we can get Accordingly, a relationship diagram of the hydrogen utilization rate and the purge valve opening time within a purge cycle as shown in Figure 2 can be obtained. Based on this relationship diagram, the maximum purge valve opening time under different hydrogen utilization rates can be obtained, and then the corresponding purge strategy can be formulated according to the system's own design conditions to maximize the hydrogen utilization rate.

[0043] The above content is a further detailed description of the present invention in combination with specific / optimal implementation manners. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, several alternatives or modifications can be made to these described embodiments, and these alternative or modified manners should all be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for formulating a fuel cell anode purge strategy based on hydrogen utilization rate, characterized in that, Including the following steps: Step 1: Obtain the absolute pressure of water vapor based on the measured anode temperature T And obtain the mass fraction of hydrogen in the mixed gas based on the relationship between the total anode pressure and the absolute pressure of hydrogen Step 2, according to the outlet pressure p of the purge valve va，out , the flow coefficient k of the purge valve v , the pressure difference Δp between the inlet and outlet of the purge valve, the hydrogen pressure and the steam pressure obtain the total mass flow rate of the mixed gas passing through the purge valve Step 3, according to the hydrogen mass fraction in the mixed gas and the total mass flow rate of the mixed gas passing through the purge valve obtain the mass flow rate of hydrogen in the mixed gas discharged from the purge valve Step 4, calculate the mass flow rate of hydrogen consumed based on the molar flow rate of hydrogen consumed Step 5, according to the hydrogen utilization rate within a purge cycle and the mass flow rate of the consumed hydrogen the mass flow rate of hydrogen the purge valve opening time t on and the purge valve closing time t off to obtain the relationship between the hydrogen utilization rate and the anode temperature T, the total anode pressure p an , the purge valve outlet pressure p va，out , the pressure difference Δp between the inlet and outlet of the purge valve, the anode humidity the current I, the number of single cells N, the hydrogen stoichiometric ratio λ, the hydrogen pressure the water vapor pressure the relative molecular mass of water vapor the relative molecular mass of hydrogen the flow coefficient k of the purge valve v , the Faraday constant F, the purge valve opening time t on and the purge valve closing time t off ; Step 6: According to the anode temperature T, the total anode pressure p obtained from actual tests an , the pressure p at the outlet of the purge valve va，out , the pressure difference Δp between the inlet and outlet of the purge valve, the anode humidity and the designed required value of current I, the number of single cells N, the hydrogen stoichiometric ratio λ, obtain the hydrogen utilization rate and the relationship with the opening time t of the purge valve on , the closing time t of the purge valve off ; Step 7: According to the relationship between the hydrogen utilization rate and the purge valve opening time and the purge valve closing time obtained in Step 6, formulate the purge valve opening time and the purge valve closing time that conform to the relationship among the three.

2. The method for formulating a fuel cell anode purge strategy based on hydrogen utilization rate according to claim 1, wherein The relationship between the total anode pressure and the absolute hydrogen pressure in Step 1 is where is the absolute hydrogen pressure, p an is the total anode pressure, is the absolute pressure of water vapor; is calculated from the anode temperature and anode humidity, specifically where p vs is the saturated partial pressure of water vapor at the corresponding anode temperature T, is the anode humidity, p vs is specifically expressed as 3. A method for formulating a fuel cell anode purge strategy based on hydrogen utilization rate according to claim 1, characterized in that, In Step 1, the hydrogen mass fraction of the mixed gas wherein 4. A method for formulating a fuel cell anode purge strategy based on hydrogen utilization rate according to claim 1, characterized in that, In Step 2, the purge valve flow coefficient k v is calculated by the formula The total volumetric flow rate of the mixed gas passing through the purge valve The density of the mixed gas The total mass flow rate of the mixed gas passing through the purge valve is: where k v is the purge valve flow coefficient, p va，out is the outlet pressure of the purge valve, Δp is the pressure difference between the inlet and outlet of the purge valve, is the absolute pressure of water vapor, is the relative molecular mass of water, is the relative molecular mass of hydrogen, is the absolute pressure of hydrogen.

5. The method for formulating a fuel cell anode purge strategy based on hydrogen utilization rate according to claim 1, wherein In Step 3, the mass flow rate of hydrogen in the mixed gas discharged by the purge valve wherein is the total mass flow rate of the mixed gas passing through the purge valve.

6. A method for formulating a fuel cell anode purge strategy based on hydrogen utilization rate according to claim 1, characterized in that In step 4, the molar flow rate of hydrogen consumed The mass flow rate of hydrogen consumed is: where λ is the hydrogen stoichiometric ratio, I is the operating current of the stack, N is the number of single cells, F is the Faraday constant, and is the relative molecular mass of hydrogen.

7. A method for formulating a fuel cell anode purge strategy based on hydrogen utilization rate according to claim 1, characterized in that, In step 5, the hydrogen utilization rate and the mass flow rate of the consumed hydrogen the mass flow rate of the hydrogen discharged from the purge valve the purge valve opening time t on and the purge valve closing time t off are specifically related as follows:

8. A method for formulating a fuel cell anode purging strategy based on hydrogen utilization rate according to claim 7, characterized in that, According to the mass flow rate of the consumed hydrogen obtained in the above steps 1-4 and the mass flow rate of the hydrogen discharged from the purge valve the hydrogen utilization rate can be obtained relating to the anode temperature T, the total anode pressure p an , the purge valve outlet pressure p va，out , the pressure difference Δp between the inlet and outlet of the purge valve, the anode humidity the current I, the number of single cells N, the hydrogen stoichiometric ratio λ, the hydrogen pressure the water vapor pressure the relative molecular mass of water vapor the relative molecular mass of hydrogen the flow coefficient k of the purge valve v , the Faraday constant F, the purge valve opening time t on , the purge valve closing time t off The relationship of, the hydrogen utilization rate can be obtained relating to the purge valve opening time t on , the purge valve closing time t off is specifically as follows:

9. The method for formulating a fuel cell anode purge strategy based on hydrogen utilization rate according to claim 8, wherein After setting the fixed purge cycle, according to the hydrogen utilization rate and the purge valve opening time t on , the purge valve closing time t off , formulate a purge strategy to obtain the maximum value of hydrogen utilization rate.

10. A method for formulating a fuel cell anode purge strategy based on hydrogen utilization rate according to claim 8, characterized in that, According to the minimum required value of the hydrogen utilization rate, based on the hydrogen utilization rate and the purge valve opening time t on , the purge valve closing time t off relationship, obtain the relationship between the purge valve opening time t on and the purge valve closing time t off in the purge strategy.

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