PEM hydrogen production cathode water recovery system and method capable of keeping stable pressure difference between cathode and anode

Abstract

The PEM hydrogen production cathode water recovery system comprises a gas-liquid separation tank and a water storage tank, one side of the gas-liquid separation tank is provided with an input pipeline connected with an electrolytic bath cathode outlet, and the other side of the gas-liquid separation tank is provided with a hydrogen discharging pipeline. A separation tank middle liquid level sensor and a separation tank lower liquid level sensor are arranged on the gas-liquid separation tank, the lower end of the gas-liquid separation tank is connected with an inlet in the upper end of the water storage tank through a connecting pipeline, a separation tank water outlet control valve is arranged on the connecting pipeline, and a water storage tank inlet control valve is arranged at an inlet in the upper end of the water storage tank. A water storage tank upper liquid level sensor and a water storage tank lower liquid level sensor are arranged on the water storage tank, a water return pipeline is arranged at the lower end of the water storage tank and connected with the electrolytic bath water replenishing tank, and a water return control valve is arranged on the water return pipeline. In the cathode water discharging process, the cathode outlet pressure can be kept stable, meanwhile, the pressure difference between the cathode outlet pressure and the anode is always kept within the range meeting the requirement, and therefore the pressure difference balance between the cathode and the anode can be guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of PEM water electrolysis hydrogen production, in particular to a PEM hydrogen production cathode water recovery system and method for maintaining a stable anode-cathode pressure difference. Background Art

[0002] PEM water electrolysis is an emerging hydrogen production technology. Its working principle is that water molecules are first decomposed into oxygen and hydrogen ions (H+) under the catalytic action of the anode catalyst, and then H+ passes through the PEM membrane between the cathode and the cathode, and then generates hydrogen under the catalysis of the cathode catalyst. Since the hydrogen produced at the cathode and the oxygen produced at the anode are separated by the PEM membrane, PEM water electrolysis has the advantages of high hydrogen purity (>99.99%). At the same time, PEM water electrolysis has the advantages of high energy conversion efficiency, fast response speed, and small footprint.

[0003] However, when this technology is applied, the H+ at the anode also brings a small amount of water to the cathode when passing through the PEM membrane between the anode and the cathode and entering the cathode. Therefore, in addition to hydrogen, the cathode outlet product of the electrolyzer also contains deionized water and hydrogen discharged from the PEM electrolyzer together. This requires further separation of hydrogen and water, and the water produced in the cathode is first sent back to a normal pressure electrolyzer water replenishment tank for reuse. Although there is also water in the separated product of the anode, it is directly returned to the circulation system water pump to continue to participate in the electrolysis reaction.

[0004] With the development of PEM electrolyzer technology, the power and hydrogen production of electrolyzers are getting bigger and bigger, and the amount of water separated from the cathode and anode is also increasing. The water separated from the oxygen at the anode outlet directly enters the circulation system and does not need to be discharged, so the impact on the anode back pressure can be ignored. However, the water separated from the hydrogen at the cathode outlet needs to be discharged into the normal pressure water tank. This drainage process will affect the stability of the cathode pressure, which will lead to a larger pressure difference between the anode and cathode. The imbalance of the pressure difference between the anode and cathode will easily lead to the catalyst falling off during the operation of the hydrogen production system. Therefore, how to keep the pressure difference between the anode and cathode consistent during the steady-state operation of the high-pressure PEM electrolyzer and when the cathode is still continuously discharging the separated liquid water (that is, the cathode pressure remains stable when the excess liquid water is frequently discharged) is an urgent problem to be solved.

[0005] Patent CN114507870B discloses a pressure difference controller, a hydrogen production system, a control method and a device for a hydrogen production system. The hydrogen production system includes an electrolyzer, an oxygen separator, a first drive device, a hydrogen separator, a second drive device and a pressure difference controller. The system controls the drive device to drive the sealing piston to move according to the pressure difference signal feedback in the pressure difference controller, thereby making the pressure difference between the hydrogen separator and the oxygen separator within a preset range, thereby solving the problem of catalyst shedding during the operation of the PEM hydrogen production system. However, the device does not address the problem of increased pressure difference between the anode and cathode due to drainage at the cathode outlet.

[0006] The patent CN116676639A discloses a method for controlling the pressure and pressure difference of the cathode and anode outlets of a water electrolysis hydrogen production system, which includes the following steps: setting the pressure standard value P and the pressure difference standard value ΔP of each parameter; obtaining the system cathode and anode outlet pressure Pi, and comparing the pressure standard value P with the measured value Pi; obtaining the system cathode and anode outlet pressure difference ΔPi, and comparing the pressure standard value ΔP with the measured value ΔPi; according to the comparison result, when the parameter is no longer within the predetermined range, the respective pressure control loop will automatically adjust the corresponding regulating valve to stabilize the pressure control at the target, wherein the method is mainly achieved by connecting the pressure regulating valve of the oxygen side separator in series with a booster pump, for example, when the outlet pressure of the oxygen side separator is small, the booster pump is used for boosting. This method is also not aimed at the problem of the anode and cathode pressure difference increasing due to drainage at the cathode outlet. Summary of the invention

[0007] The purpose of the present invention is to provide a PEM hydrogen production cathode water recovery system and method that maintains a stable anode-cathode pressure difference. During the cathode water discharge process, the cathode outlet pressure can be kept stable, and the pressure difference with the anode is always maintained within the required range, thereby ensuring the anode-cathode pressure difference balance.

[0008] The objective of the present invention is achieved through the following technical solutions:

[0009] A PEM hydrogen production cathode water recovery system for maintaining a stable anode-cathode pressure difference comprises a gas-liquid separation tank and a water storage tank, wherein an input pipeline is provided on one side of the gas-liquid separation tank to be connected to the cathode outlet of an electrolyzer, and a hydrogen exhaust pipeline is provided on the other side, a separation tank middle liquid level sensor and a separation tank lower liquid level sensor are provided on the gas-liquid separation tank, the lower end of the gas-liquid separation tank is connected to the upper inlet of the water storage tank through a connecting pipeline, and a separation tank water outlet control valve is provided on the connecting pipeline, a water storage tank inlet control valve is provided on the upper inlet of the water storage tank, an upper water storage tank liquid level sensor and a lower water storage tank liquid level sensor are provided on the water storage tank, a return water pipeline is provided at the lower end of the water storage tank to be connected to a water replenishment tank of the electrolyzer, and a return water control valve is provided on the return water pipeline.

[0010] The input pipeline is provided with an input temperature sensor, an input pressure sensor and a cooling heat exchange plate.

[0011] The hydrogen exhaust pipeline is provided with a cathode back pressure valve.

[0012] The gas-liquid separation tank is provided with an upper liquid level sensor of the separation tank, and the upper liquid level sensor of the separation tank, the middle liquid level sensor of the separation tank and the lower liquid level sensor of the separation tank are arranged in sequence from top to bottom.

[0013] The water storage tank is provided with a hydrogen discharge port.

[0014] The water tank is provided with a water tank temperature control valve and a water tank conductivity meter. A drainage pipeline is provided at the lower side of the water tank, and one end of the drainage pipeline is connected to the return pipeline, and the other end is connected to the cathode drainage port. A water tank drainage control valve is provided on the drainage pipeline.

[0015] When the conductivity detected by the conductivity meter of the water storage tank is higher than the recovery index, the water storage tank drainage control valve is opened and the return water control valve is closed; when the conductivity detected by the conductivity meter of the water storage tank is lower than the recovery index, the return water control valve is opened and the water storage tank drainage control valve is closed.

[0016] The return water pipeline is provided with a return water control valve, a return water pump, a return water check valve and a return water pressure sensor in sequence.

[0017] A control method for a PEM hydrogen production cathode water recovery system for maintaining a stable anode-cathode pressure difference comprises the following steps:

[0018] Step 1: Determine the fluctuation range of cathode outlet drainage pressure;

[0019] Step 2: Determine the drainage volume Va of the gas-liquid separation tank, and determine the installation positions of the liquid level sensor in the separation tank and the liquid level sensor under the separation tank accordingly, wherein the volume between the liquid level sensor in the separation tank and the liquid level sensor under the separation tank is Va;

[0020] Step 3: Determine the drainage times x of the gas-liquid separation tank, specifically:

[0021] According to the ideal gas equation, we can get the following formula (3):

[0022] P1V1=P2V2=nRT (3);

[0023] In the above formula (3), P1 and V1 are the pressure and gas volume before the change, P2 and V2 are the pressure and gas volume after the change, T is the temperature, n is the amount of gas, R is the molar gas constant, P1, P2, n, R, T are all known quantities, and V1 and V2 are obtained, and the difference between the two is the displacement V at each pressure discharge. B , then according to Va / V B Calculate the drainage times x;

[0024] Step 4: Determine the volume V of the water storage tank c and installation positions of the upper liquid level sensor of the water storage tank and the lower liquid level sensor of the water storage tank, wherein the volume between the upper liquid level sensor of the water storage tank and the lower liquid level sensor of the water storage tank is Va;

[0025] Step 5: Determine the maximum flow rate Q at each opening based on the shortest action time t1 of the separation tank outlet control valve and the return control valve MAX , specifically:

[0026]

[0027] Step 6: Determine the calculated flow rate Q of the separation tank outlet water control valve and return water control valve according to the PEM hydrogen production conditions:

[0028]

[0029] In the above formula (4), K V The flow coefficient, △P is the control valve inlet pressure minus the control valve outlet pressure, and ρ is the density of water;

[0030] Step 7: According to the drainage volume Va of the gas-liquid separation tank each time, the drainage times x of the gas-liquid separation tank and Q MAX And Q for drainage control, where the water tank inlet control valve according to Q MAX and Q control the opening amplitude. If Q≤Q MAX , the water tank inlet control valve is fully open and does not work. If Q>Q MAX , the opening range of the water tank inlet control valve becomes smaller to reduce the above K V .

[0031] In step 7, K V The value must be adjusted to meet the following requirements:

[0032]

[0033] The advantages and positive effects of the present invention are:

[0034] 1. In the process of cathode water discharge, the present invention can keep the cathode outlet pressure stable, and the pressure difference with the anode is always maintained within the required range, thereby ensuring the pressure difference balance between the anode and cathode, and preventing the problem of catalyst shedding during the operation of the hydrogen production system due to the increase in the pressure difference between the anode and cathode.

[0035] 2. The present invention only needs to add a water storage tank between the gas-liquid separation tank and the electrolyzer water supply tank to achieve stable anode-cathode pressure difference of the PEM hydrogen production system without affecting the normal drainage of the cathode. The structure is simple and convenient for technical transformation of existing equipment.

[0036] 3. The method of the present invention determines the drainage volume Va of the gas-liquid separation tank each time, the drainage times x of the gas-liquid separation tank, and the volume V of the water storage tank according to the fluctuation range of the drainage pressure. c , the maximum flow rate Q of the separation tank outlet control valve and the return water control valve MAX And calculate the flow rate Q and other parameters, among which the gas-liquid separation tank drainage volume Va, the gas-liquid separation tank drainage times x and other parameters can ensure the stability of the cathode outlet pressure, and the water tank inlet control valve on the water tank is adjusted according to Q MAX By controlling the opening amplitude with Q, it can be ensured that the amount of liquid discharged back to the electrolyte replenishment tank each time is not greater than the amount of liquid discharged to maintain pressure stability, that is, it will not affect the cathode outlet pressure stability, thereby enabling the present invention to ensure the pressure difference balance between the anode and cathode without affecting the normal drainage of the cathode. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a schematic diagram of the structure of the system of the present invention,

[0038] Figure 2 It is the principle diagram of anode system back pressure in the prior art.

[0039] Figure 3 It is the cathode system back pressure principle diagram in the prior art.

[0040] Figure 4 This is a schematic diagram of the effect of cathode drainage on cathode back pressure without intervention in the prior art.

[0041] Figure 5 This is a schematic diagram of the pressure difference control between the cathode and the anode during cathode drainage according to the present invention.

[0042] Among them, 1 is the cathode outlet of the electrolytic cell, 101 is the input temperature sensor, 102 is the input pressure sensor, 103 is the cooling heat exchange plate, 2 is the gas-liquid separation tank, 201 is the hydrogen exhaust pipeline, 2011 is the cathode back pressure valve, 202 is the upper liquid level sensor of the separation tank, 203 is the liquid level sensor in the separation tank, 204 is the lower liquid level sensor of the separation tank, 205 is the water outlet control valve of the separation tank, 3 is the water storage tank, and 301 is the water storage tank inlet control valve , 302 is the water tank temperature sensor, 303 is the water tank conductivity meter, 304 is the water tank upper liquid level sensor, 305 is the water tank lower liquid level sensor, 306 is the hydrogen outlet, 4 is the return water pipeline, 401 is the return water control valve, 402 is the return water pump, 403 is the return water check valve, 404 is the return water pressure sensor, 5 is the electrolytic cell water supply tank, 6 is the drainage pipeline, 601 is the water tank drainage control valve, and 602 is the cathode drainage outlet. DETAILED DESCRIPTION

[0043] The present invention will be further described below in conjunction with the accompanying drawings.

[0044] like Figures 1 to 5 As shown, the system of the present invention comprises a gas-liquid separation tank 2 and a water storage tank 3, wherein an input pipeline is provided on one side of the gas-liquid separation tank 2 to be connected to the cathode outlet 1 of the electrolyzer, and a cooling heat exchange plate 103 is provided on the input pipeline, and a hydrogen exhaust pipeline 201 with a cathode back pressure valve 2011 is provided on the other side of the gas-liquid separation tank 2, and a separation tank upper liquid level sensor 202, a separation tank middle liquid level sensor 203 and a separation tank lower liquid level sensor 204 are provided on the gas-liquid separation tank 2 in descending order, and the lower end of the gas-liquid separation tank 2 is connected to the upper inlet of the water storage tank 3 through a connecting pipeline, In addition, a separation tank water outlet control valve 205 is provided on the connecting pipeline, a water tank inlet control valve 301 is provided at the upper inlet of the water tank 3, a water tank temperature control valve 302, a water tank conductivity meter 303, an upper liquid level sensor 304 and a lower liquid level sensor 305 are provided on the water tank 3, the lower outlet of the water tank 3 is connected to the return water pipeline 4, and a return water control valve 401 is provided on the return water pipeline 4, a drainage pipeline 6 is connected to the return water pipeline 4, and a water tank drainage control valve 601 is provided on the drainage pipeline 6.

[0045] like Figure 1 As shown, in this embodiment, an input temperature sensor 101 and an input pressure sensor 102 are provided on the input pipeline.

[0046] like Figure 1 As shown, in this embodiment, the water storage tank 3 is provided with a hydrogen outlet 306 .

[0047] like Figure 1 As shown, in this embodiment, the drainage pipeline 6 is connected to the cathode drainage port 602 .

[0048] like Figure 1 As shown, in this embodiment, the return water pipeline 4 is provided with a return water control valve 401, a return water pump 402, a return water check valve 403 and a return water pressure sensor 404 in sequence.

[0049] The temperature sensors, pressure sensors, control valves, cooling heat exchange plate 103 and water tank conductivity meter 303 of the present invention are all well-known technologies in the art and are commercially available products. In this embodiment, the separation tank outlet control valve 205 and the return water control valve 401 can adopt solenoid valves, and the water tank inlet control valve 301 can adopt an electric regulating needle valve, which can control the opening amplitude of the water tank 3 inlet. The cooling heat exchange plate 103 adjusts the temperature according to the feedback of each temperature sensor, and each pressure sensor detects the pressure of the corresponding pipeline or tank body in real time.

[0050] The working principle of the present invention is:

[0051] like Figure 1 As shown, when the present invention is working, the liquid flowing out of the cathode outlet 1 of the electrolyzer first enters the gas-liquid separation tank 2 for separation, which is a well-known technology in the art, wherein the gas in the gas-liquid separation tank 2 is discharged through the hydrogen discharge pipeline 201, and the liquid enters the water storage tank 3 through the connecting pipeline, wherein the separation tank liquid level sensor 203 and the separation tank lower liquid level sensor 204 in the gas-liquid separation tank 2 control the volume of the single discharge, and the separation tank upper liquid level sensor 202 sends a signal to start the water level too high alarm program, and the separation tank water outlet control valve 205 opens When it is opened, the gas-liquid separation tank 2 discharges liquid into the water storage tank 3, and the water tank inlet control valve 301 at the upper end of the liquid storage tank 3 controls the opening amplitude of the liquid storage tank 3 inlet according to the flow conditions of the separation tank outlet control valve 205 and the return water control valve 401, thereby ensuring that the discharge amount is not greater than the discharge amount for maintaining pressure stability. The water tank upper liquid level sensor 304 and the water tank lower liquid level sensor 305 are used to control the discharge. When the water level of the water storage tank 3 is higher than the upper liquid level, the water is discharged from the lower end of the water storage tank 3. When the water level of the water storage tank 3 is lower than the lower liquid level, the discharge stops.

[0052] The water tank conductivity meter 303 on the water tank 3 is used to determine whether the water in the water tank 3 is used for recycling. When the conductivity is higher than the recycling index, the water tank drainage control valve 601 is opened and the return water control valve 401 is closed. At this time, the liquid is directly discharged out of the system through the cathode drainage port 602. When the conductivity is lower than the recycling index and meets the requirements, the return water control valve 401 and the return water pump 402 on the return water pipeline 4 are opened to input the liquid into the electrolytic cell water supply tank 5, and the water tank drainage control valve 601 is closed.

[0053] In addition, the present invention has been found through actual research. Figure 2As shown in FIG. 1 , in the prior art device, the water separated from the oxygen at the anode outlet directly enters the circulation system and does not need to be discharged, so the impact on the anode back pressure can be ignored. Figure 3 As shown, the water separated from the hydrogen at the cathode outlet needs to be discharged into the electrolyzer water supply tank 5 at normal pressure. Figure 4 As shown in Figure 2, this drainage process will affect the stability of the cathode pressure, which will lead to a larger pressure difference between the anode and cathode. Figure 4 In the figure, the left vertical axis unit is kPa, the right vertical axis unit is none. The horizontal axis unit is 100mS, where the cathode outlet water pressure refers to the left vertical axis, and the cathode drainage refers to the right vertical axis. 1 represents drainage, and 0 represents drainage stop.

[0054] The existing technology mostly uses the pulse discharge of the cathode outlet solenoid valve to maintain the pressure stable. However, when the gas production is low, the gas production of the electrolyzer cannot keep up with the pulse discharge of the solenoid valve under high pressure, which will cause the drainage pressure to continue to drop. Figure 4 As shown in the figure, the hydrogen production system uses solenoid valve pulse switching to drain water. It can be seen that the cathode is pulsed drained at a pressure of 3MPa, and the pressure continues to drop. When the drainage stops, the cathode outlet pressure has been reduced by 400kPa compared to the initial back pressure (that is, 3058.247 minus 2598.828 in the figure).

[0055] according to Figure 4 According to analysis, in order to maintain the pressure difference balance between the cathode and the cathode in the state of uninterrupted drainage during operation, the present invention forms a new control method, which includes the following steps:

[0056] Step 1: Determine the cathode outlet drainage pressure fluctuation range.

[0057] In this embodiment, in order to maintain the pressure difference between the anode and cathode at no more than 50 kPa during operation, it is necessary to ensure that the pressure drop of the cathode during drainage each time does not exceed 50 kPa. In addition, in order to leave room for pressure fluctuations caused by the fluctuations of the back pressure itself, the drainage pressure fluctuation range is set to 20 kPa in this embodiment.

[0058] Step 2: Determine the drainage volume Va of the gas-liquid separation tank 2, and accordingly determine the installation positions of the upper liquid level sensor 202, the middle liquid level sensor 203 and the lower liquid level sensor 204 of the separation tank, wherein the volume between the middle liquid level sensor 203 and the lower liquid level sensor 204 is the drainage volume Va of the gas-liquid separation tank 2 each time.

[0059] Assume that the volume of the cathode gas-liquid separation tank 2 is V m 3, the drainage volume is from the middle liquid level of the gas-liquid separation tank 2 to the lower liquid level. The gas needs to be drained from the top of the gas-liquid separation tank 2, so the upper liquid level of the gas-liquid separation tank 2 is mostly set at a position slightly above the middle. In this embodiment, the distance from the middle liquid level to the lower liquid level is 1 / 8 of the volume of the entire tank, that is, the volume to be discharged each time the gas-liquid separation tank 2 is drained is 1 / 8×V.

[0060] Step 3: Determine the drainage times x of the gas-liquid separation tank 2.

[0061] According to the settings of step 1 and step 2 above, at the moment of each pressure discharge of the gas-liquid separation tank 2, the gas pressure in the gas-liquid separation tank 2 should drop from 3MPa to 2.98MPa (the drop range is 20kPa in step 1).

[0062] According to the ideal gas equation:

[0063] PV = nRT (1);

[0064]

[0065] Where: P is pressure, V is gas volume, T is temperature, n is the amount of gas, R is the molar gas constant, P1, P2, V1, V2, T1, T2 are the pressure, gas volume and temperature before and after the change. In the present invention, under ideal conditions, the volume and temperature of the gas-liquid separation tank 2 are fixed, and only the gas pressure changes. At this time, the change in gas volume is the change in displacement. According to the above formulas (1) and (2), it can be obtained that:

[0066] P1V1=P2V2=nRT (3);

[0067] According to the above formula (3), in this embodiment, P1 = 3MPa, P2 = 2.98MPa, and n, R, and T are all known quantities. In this way, the volume V1 and V2 before and after the gas change can be obtained, and the difference between the two is the displacement V at each pressure discharge. B , and then through Va / V B The drainage times x are obtained. In this embodiment, the drainage volume V at each pressure discharge can be obtained through the above calculations. B It is approximately equal to 0.0065V, so the drainage times x is 1 / 8×V÷0.0065V, which is approximately equal to 20 times, among which 1 / 8×V is Va.

[0068] like Figure 5 As shown, the present invention can ensure that the cathode outlet pressure fluctuates stably and does not exceed the set range through the above steps 2 and 3.

[0069] Step 4: Determine the volume V of water tank 3 cAnd the installation positions of the upper liquid level sensor 304 and the lower liquid level sensor 305 of the water tank, wherein the volume between the upper liquid level sensor 304 and the lower liquid level sensor 305 of the water tank is Va.

[0070] like Figure 1 As shown, during the drainage process, the water outlet control valve 205 and the return water control valve 401 of the separation tank above and below the water storage tank 3 are not opened at the same time, so the water storage tank 3 should at least be able to store the volume of the gas-liquid separation tank 2 for one drainage (in this embodiment, 1 / 8×V). In addition, a hydrogen outlet 306 is provided above the water storage tank 3 to discharge a small amount of hydrogen carried in the water discharged from the gas-liquid separation tank 2. Therefore, the volume of the gas-liquid separation tank 2 needs to be further increased. In this embodiment, the volume V of the water storage tank 3 is c It is set to 1 / 4×V, wherein the volume between the upper liquid level sensor 304 of the water storage tank and the lower liquid level sensor 305 of the water storage tank is 1 / 8×V.

[0071] Step 5: Determine the maximum flow rate Q when the separation tank outlet control valve 205 is opened each time according to the shortest action time t1 of the separation tank outlet control valve 205 and the return water control valve 401 MAX , specifically:

[0072]

[0073] In this embodiment, V B is 0.0065V, and the shortest action time of the commonly used solenoid valve is about t1 = 0.1s, so the minimum opening and closing time should be 0.2s. Based on this calculation, Q MAX That is 0.0325V.

[0074] Step 6: Determine the calculated flow rate Q of the separation tank outlet water control valve 205 and the return water control valve 401 according to the PEM hydrogen production conditions:

[0075]

[0076] In the above formula (4), K V Flow coefficient; △P is the control valve inlet pressure minus the control valve outlet pressure, which can be obtained by detecting the pressure sensors before and after the control valve; ρ is the density of water.

[0077] Step 7: According to the drainage volume Va of the gas-liquid separation tank 2 each time, the drainage times x of the gas-liquid separation tank 2 and Q MAX and Q for drainage control, where the water tank inlet control valve 301 is based on Q MAX and Q control the opening amplitude. If Q≤Q MAX , then the water tank inlet control valve 301 can be fully opened without action. If Q>Q MAX, the opening range of the water storage tank inlet control valve 301 needs to be reduced to reduce the above K V , thereby ensuring that the amount of liquid discharged each time is not greater than the amount of liquid discharged to maintain stable pressure, that is, it will not affect the stability of the cathode outlet pressure.

[0078] In addition, if Q is much smaller than Q MAX , which will lead to longer drainage time and more drainage times, so generally speaking, Q MAX The closer to Q, the better. In this embodiment, K V The value should be adjusted to meet the following requirements:

[0079]

[0080] The present invention can ensure that the amount of liquid discharged back to the electrolytic cell water replenishment tank each time will not affect the cathode outlet pressure stability, and further will not affect the anode and cathode pressure stability through the design of the above steps four to seven.

[0081] like Figure 5 As shown, this embodiment can stabilize the anode and cathode back pressure at 3MPa, wherein during the cathode drainage process, the anode and cathode pressure difference is always maintained at 30k. Figure 5 The unit of the left vertical axis is kPa, and the unit of the right vertical axis is kPa. The unit of the horizontal axis is seconds. The anode water outlet pressure (blue in the legend) and the cathode water outlet pressure (red in the legend) refer to the left vertical axis, the anode and cathode pressure difference (gray in the legend) refer to the right vertical axis, and the cathode drainage (yellow in the legend) refers to the right vertical axis. 1 represents drainage, and 0 represents drainage stop.

Claims

1. A PEM hydrogen production cathode water recovery system that maintains a stable anode-cathode pressure difference, characterized in that: The invention comprises a gas-liquid separation tank (2) and a water storage tank (3), wherein one side of the gas-liquid separation tank (2) is provided with an input pipeline connected to the cathode outlet (1) of the electrolyzer, and the other side is provided with a hydrogen exhaust pipeline (201), the gas-liquid separation tank (2) is provided with a separation tank middle liquid level sensor (203) and a separation tank lower liquid level sensor (204), the lower end of the gas-liquid separation tank (2) is connected to the upper inlet of the water storage tank (3) through a connecting pipeline, and the connecting pipeline is provided with a separation tank water outlet control valve (205), the upper inlet of the water storage tank (3) is provided with a water storage tank inlet control valve (301), the water storage tank (3) is provided with an upper water storage tank liquid level sensor (304) and a lower water storage tank liquid level sensor (305), the lower end of the water storage tank (3) is provided with a return water pipeline (4) connected to the electrolyzer water replenishment tank (5), and the return water pipeline (4) is provided with a return water control valve (401).

2. The PEM hydrogen production cathode water recovery system for maintaining a stable anode-cathode pressure difference according to claim 1, characterized in that: The input pipeline is provided with an input temperature sensor (101), an input pressure sensor (102) and a cooling heat exchange plate (103).

3. The PEM hydrogen production cathode water recovery system for maintaining a stable anode-cathode pressure difference according to claim 1, characterized in that: The hydrogen exhaust pipeline (201) is provided with a cathode back pressure valve (2011).

4. The PEM hydrogen production cathode water recovery system for maintaining a stable anode-cathode pressure difference according to claim 1, characterized in that: The gas-liquid separation tank (2) is provided with a separation tank upper liquid level sensor (202), and the separation tank upper liquid level sensor (202), the separation tank middle liquid level sensor (203) and the separation tank lower liquid level sensor (204) are arranged in sequence from top to bottom.

5. The PEM hydrogen production cathode water recovery system for maintaining a stable anode-cathode pressure difference according to claim 1, characterized in that: The water storage tank (3) is provided with a hydrogen discharge outlet (306).

6. The PEM hydrogen production cathode water recovery system for maintaining a stable anode-cathode pressure difference according to claim 1, characterized in that: The water tank (3) is provided with a water tank temperature control valve (302) and a water tank conductivity meter (303); a drainage pipeline (6) is provided at the lower side of the water tank (3); one end of the drainage pipeline (6) is connected to the return pipeline (4), and the other end is connected to the cathode drainage port (602); and a water tank drainage control valve (601) is provided on the drainage pipeline (6).

7. The PEM hydrogen production cathode water recovery system for maintaining a stable anode-cathode pressure difference according to claim 6, characterized in that: When the conductivity detected by the water storage tank conductivity meter (303) is higher than the recovery index, the water storage tank drainage control valve (601) is opened and the return water control valve (401) is closed; when the conductivity detected by the water storage tank conductivity meter (303) is lower than the recovery index, the return water control valve (401) is opened and the water storage tank drainage control valve (601) is closed.

8. The PEM hydrogen production cathode water recovery system for maintaining a stable anode-cathode pressure difference according to claim 1, characterized in that: The return water pipeline (4) is provided with a return water control valve (401), a return water pump (402), a return water check valve (403) and a return water pressure sensor (404) in sequence.

9. A control method for a PEM hydrogen production cathode water recovery system for maintaining a stable anode-cathode pressure difference according to claim 1, characterized in that: The steps include: Step 1: Determine the fluctuation range of cathode outlet drainage pressure; Step 2: Determine the drainage volume Va of the gas-liquid separation tank (2), and determine the installation positions of the liquid level sensor (203) in the separation tank and the liquid level sensor (204) below the separation tank accordingly, wherein the volume between the liquid level sensor (203) in the separation tank and the liquid level sensor (204) below the separation tank is Va; Step 3: Determine the drainage times x of the gas-liquid separation tank (2), specifically: According to the ideal gas equation, we can get the following formula (3): P1V1=P2V2=nRT (3); In the above formula (3), P1 and V1 are the pressure and gas volume before the change, P2 and V2 are the pressure and gas volume after the change, T is the temperature, n is the amount of gas, R is the molar gas constant, P1, P2, n, R, T are all known quantities, and V1 and V2 are obtained, and the difference between the two is the displacement V at each pressure discharge. B , then according to V a / V B Calculate the drainage times x; Step 4: Determine the volume V of the water storage tank (3) c and installation positions of an upper liquid level sensor (304) and a lower liquid level sensor (305) of the water storage tank, wherein the volume between the upper liquid level sensor (304) and the lower liquid level sensor (305) of the water storage tank is Va; Step 5: Determine the maximum flow rate Q at each opening according to the shortest action time t1 of the separation tank outlet control valve (205) and the return water control valve (401) MAX , specifically: Step 6: Determine the calculated flow rate Q of the separation tank outlet water control valve (205) and the return water control valve (401) according to the PEM hydrogen production conditions: In the above formula (4), K V The flow coefficient, △P is the control valve inlet pressure minus the control valve outlet pressure, and ρ is the density of water; Step 7: According to the drainage volume Va of the gas-liquid separation tank (2) each time, the drainage times x of the gas-liquid separation tank (2) and Q MAX and Q for drainage control, wherein the water storage tank inlet control valve (301) is adjusted according to Q MAX and Q control the opening amplitude. If Q≤Q MAX , the water tank inlet control valve (301) is fully open and does not work. If Q>Q MAX , the opening range of the water storage tank inlet control valve (301) becomes smaller to reduce the above K V .

10. The control method of the cathode water recovery system for PEM hydrogen production for maintaining a stable anode-cathode pressure difference according to claim 9, characterized in that: In step 7, K V The value must be adjusted to meet the following requirements:

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