Electrolyte flow uniform distribution method and industrial-scale electrolytic bath

Abstract

The invention discloses an electrolyte flow uniform distribution method and an industrial-scale electrolytic bath, and the method comprises the steps: obtaining the local resistance of each small electrolysis chamber, and calculating the flow of each small electrolysis chamber according to a mass conservation equation and a Bernoulli equation; when the flow accords with uniform distribution, calculating the flow area ratio of the inlets of the electrolysis cells on the hydrogen side and the oxygen side of each electrolysis cell; and grouping the electrolysis cells on the hydrogen side and the oxygen side according to the total area of the inlet main pipeline, and distributing the inlet areas of the electrolysis cells on the hydrogen side and the oxygen side in each group according to an arithmetic progression. The internal structure of the electrolytic cell does not need to be additionally arranged, electrolyte enters the electrolytic cell from the inlet main pipeline and enters each small electrolysis chamber through the inlets of the small electrolysis chambers, alkali liquor is distributed more evenly on the hydrogen side and the oxygen side through the flow areas of the inlets of the different small electrolysis chambers, and energy consumption is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogen production by electrolyzing water, and particularly relates to a method for uniformly distributing the flow rate of an electrolyte and an industrial-scale electrolytic cell. Background Art

[0002] An industrial-scale alkaline electrolytic cell is composed of multiple electrolytic compartments. The electrolyte enters from one side of the electrolytic cell and flows through each electrolytic compartment in sequence. For an alkaline electrolytic cell, the amount of hydrogen gas generated at the cathode of the electrolytic cell is twice that of the oxygen gas generated at the anode. Affected by the gas holdup, the pressure drops on both sides of the cell and in each pipeline are unequal, resulting in uneven distribution of the alkali liquor flow rate on both sides of the electrolytic cell. If the amount of alkali liquor in the electrolytic compartment is too small, the gas holdup of the electrolyte will be too high, and an air cavity will easily form above the electrolytic compartment. Since the electrical conductivity of gas is weaker than that of the electrolyte, the existence of the air cavity will increase the resistance of each electrolytic compartment, increase the cell voltage, and thus increase the energy consumption of the equipment. At the same time, in severe cases, it will cause the diaphragm to decompose or be electrically broken down, resulting in hydrogen-oxygen intermixing and increasing the safety risk. If the amount of alkali liquor is too large, it will exceed the upper limit of the economic flow rate and also increase the cost. Therefore, it is very important to reasonably control the flow rate of the alkali liquor and evenly distribute the alkali liquor to each electrolytic compartment. In addition, due to the large number of electrolytic compartments, the labor and material costs required to install a flow control system for each electrolytic compartment are huge. Therefore, it is very important to improve the pipeline structure of the alkaline electrolytic cell to make the distribution of the alkali liquor flow rate uniform.

[0003] Currently, in an alkaline electrolytic cell, if there are n electrolytic compartments, there are n flow channels in parallel. Therefore, in addition to the gas holdup inside the electrolytic cell affecting the pressure drop difference, this external pipeline structure also makes the flow path and resistance of the alkali liquor flowing through each electrolytic compartment different, resulting in uneven distribution of the alkali liquor flow rate in the electrolytic compartment.

[0004] Especially when the number n of electrolytic compartments is large, the local resistance will directly determine the distribution of the alkali liquor flow rate. Therefore, for the flow rate distribution of each electrolytic compartment in an industrial-scale alkaline electrolytic cell, the pipeline structure at the inlet and outlet of the electrolytic compartment should be designed to control the local resistance.

[0005] In the patent document with the title "An electrolytic cell for uniformly distributing the flow rate of electrolyte" and the application number CN202310812077.8, the inlet flow channels and multiple groups of electrolysis units are connected through a commutating insulating tube to a distribution channel; this ensures that the total length of the flow path for each liquid stream is equal. However, just because the total length of each caustic liquid stream is equal does not mean the resistance is the same for all. For example, if there are n caustic liquid streams, the first chamber divides 1 stream from n streams, while the last chamber divides 1 stream from 1 stream, and the local resistances of these two are different. When the number of chambers n is large, the local resistance will directly determine the distribution of the caustic liquid flow rate; therefore, in this method, although the structure of the electrolytic cell is designed to be more complex with the same distribution channels, it cannot fundamentally and economically achieve the same electrolyte flow rate distribution for each electrolysis unit. Summary of the Invention

[0006] Therefore, the object of the present invention is to provide a method for uniformly distributing the electrolyte flow rate and an industrial-scale electrolytic cell, which can achieve uniform distribution of the electrolyte flow rate by changing the flow area of each pipeline.

[0007] To achieve the above object, a method for uniformly distributing the electrolyte flow rate provided by the present invention includes arranging the electrolysis compartments of the electrolytic cell according to the following rules:

[0008] Obtain the local resistance of each electrolysis compartment, and calculate the flow rate of each electrolysis compartment according to the mass conservation equation and the Bernoulli equation;

[0009] When the flow rate meets the uniform distribution, calculate the ratio of the flow area at the inlet of the hydrogen side and the oxygen side of each electrolysis compartment;

[0010] Group the electrolysis compartments on the hydrogen side and the oxygen side according to the total area of the inlet main pipeline, and distribute the inlet areas of the electrolysis compartments on the hydrogen side and the oxygen side in each group according to an arithmetic progression.

[0011] Further preferably, when obtaining the local resistance of each electrolysis compartment, it includes modeling the electrolytic cell and using CFD simulation to calculate the local resistance coefficient of each electrolysis compartment, and the local resistance of each electrolysis compartment

[0012] where δ is the local resistance coefficient, ρ is the density of the fluid, and u is the velocity of the fluid.

[0013] Further preferably, calculate the flow rate of each electrolysis compartment according to the mass conservation equation and the Bernoulli equation;

[0014]

[0015] Q inletρliquid is the inlet mass flow rate of the alkaline electrolytic cell, is the liquid-phase mass flow rate at the outlet of each electrolysis cell compartment, is the gas-phase mass flow rate at the outlet of each electrolysis cell compartment; zρg is the gravitational potential energy term, and p is the static pressure term, is the dynamic pressure term, h f is the local resistance, C is a constant; n is the total number of electrolysis cell compartments, and i is the serial number of the current electrolysis cell compartment.

[0016] Further preferably, when the outlet is a gas-liquid mixture, the density is calculated according to the average density shown in the following formula:

[0017]

[0018] where ρ mix is the average density, is the gas-phase volume fraction, is the liquid-phase volume fraction.

[0019] Further preferably, when the flow rate conforms to uniform distribution, calculate the flow area ratio of the inlets of the hydrogen side and the oxygen side of each electrolysis cell compartment. It also includes determining the area ratio of the outlet main pipeline to the inlet main pipeline according to the area of the inlet main pipeline; determining the area of the outlet main pipeline;

[0020] Determine the inlet area ratio of the oxygen side and the hydrogen side according to the total area of the inlet main pipeline and the difference in gas production between the hydrogen side and the oxygen side.

[0021] The present invention also provides an industrial-scale electrolytic cell with uniform distribution of electrolyte flow rate, including: an anode end plate, a cathode end plate, and a number of electrolysis cell compartments are cooperatively installed between the anode end plate and the cathode end plate. The outlet of each electrolysis cell compartment is communicated with the outlet main pipeline of the electrolyte, and the inlet of the electrolysis cell compartment is communicated with the inlet main pipeline of the electrolyte; the electrolysis cell compartments of the electrolytic cell are arranged according to the above-mentioned method for uniform distribution of electrolyte flow rate.

[0022] Further preferably, a plurality of bipolar plates are also provided between the anode end plate and the cathode end plate, and the internal cavity of each bipolar plate is an alkali liquid flow channel.

[0023] Further preferably, two adjacent bipolar plates form an electrolysis cell compartment, and an intermediate diaphragm and an electrolysis electrode are provided in the middle of each electrolysis cell compartment.

[0024] The method for uniform distribution of electrolyte flow rate and the industrial-scale electrolytic cell disclosed in the present application have at least the following advantages compared with the prior art:

[0025] When the present application is in use, there is no need to add internal structures to the electrolytic cell. The electrolyte enters the electrolytic cell from the inlet main pipeline and enters each electrolysis cell compartment through the inlet of the electrolysis cell compartment. The flow areas of the inlets of different electrolysis cell compartments make the distribution of the alkali liquid on the hydrogen side and the oxygen side more uniform.

[0026] On the oxygen side or the hydrogen side, the flow channel area at the inlet of the electrolysis cell changes in an arithmetic progression, so that the average relative deviation of the electrolyte flow rate distribution of each electrolysis unit is less than 2%, reducing the energy consumption. Brief Description of the Drawings

[0027] Figure 1 It is a cross-sectional view of an electrolytic cell with uniform distribution of electrolyte flow rate according to the present invention.

[0028] Figure 2 It is the influence of the ratio of the outlet main pipeline to the inlet area on the average flow deviation.

[0029] Figure 3 It is the influence of the ratio of the inlet areas of the electrolysis cells on both sides on the flow rate distribution on both sides.

[0030] Figure 4 It is the flow rate distribution curve before the improvement of the inlet of the electrolysis cell on the oxygen side.

[0031] Figure 5 It is the flow rate distribution curve after the improvement of the inlet of the electrolysis cell on the oxygen side.

[0032] Figure 6 It is the flow chart of uniform distribution of electrolyte flow rate provided by the present invention.

[0033] In the figure:

[0034] 1. Anode end plate; 2. Bipolar plate; 3. Cathode end plate; 4. Outlet main pipeline; 5. Electrolysis cell outlet; 6. Alkali liquid flow channel; 7. Electrolysis cell inlet; 8. Inlet main pipeline; 9. Electrolysis cell; 10. Electrolysis electrode; 11. Diaphragm. Detailed Embodiments

[0035] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0036] As Figure 6 shown, an embodiment of the present invention provides a method for uniform distribution of electrolyte flow rate, including setting the electrolysis cells of the electrolytic cell according to the following rules:

[0037] Obtain the local resistance of each electrolysis cell, and calculate the flow rate of each electrolysis cell according to the mass conservation equation and the Bernoulli equation; further preferably, when obtaining the local resistance of each electrolysis cell, it includes modeling the electrolytic cell and using CFD to simulate and calculate the local resistance coefficient of each electrolysis cell, and the local resistance of each electrolysis cell

[0038] wherein, δ is the local resistance coefficient, ρ is the density of the fluid, and u is the velocity of the fluid.

[0039] Further preferably, the flow rate of each electrolysis cell is calculated according to the mass conservation equation and the Bernoulli equation;

[0040]

[0041] Q inletρliquid is the inlet mass flow rate of the alkaline electrolyzer, is the liquid-phase mass flow rate at the outlet of each electrolysis cell, is the gas-phase mass flow rate at the outlet of each electrolysis cell; zρg is the gravitational potential energy term, and p is the static pressure term, is the dynamic pressure term, and h f is the local resistance, C is a constant; n is the total number of electrolysis cells, and i is the serial number of the current electrolysis cell.

[0042] Further preferably, when the outlet is a gas-liquid mixture, the density is calculated according to the average density shown in the following formula:

[0043]

[0044] where ρ mix is the average density, is the gas-phase volume fraction, is the liquid-phase volume fraction.

[0045] When the flow rate conforms to uniform distribution, calculate the ratio of the flow areas at the inlets of the hydrogen side and the oxygen side of each electrolysis cell;

[0046] According to the area of the inlet main pipeline, determine the ratio of the area of the outlet main pipeline to the area of the inlet main pipeline; determine the area of the outlet main pipeline;

[0047] According to the total area of the inlet main pipeline and the difference in the gas production amounts on the oxygen side and the hydrogen side, determine the ratio of the inlet areas on the oxygen side and the hydrogen side.

[0048] According to the total area of the inlet main pipeline, group the electrolysis cells on the hydrogen side and the oxygen side, and distribute the inlet areas of the electrolysis cells on the hydrogen side and the oxygen side in each group according to an arithmetic progression.

[0049] The present invention also provides an industrial-scale electrolyzer with uniform distribution of electrolyte flow rate, including: an anode end plate, a cathode end plate, and a plurality of electrolysis cells are cooperatively installed between the anode end plate and the cathode end plate. The outlet of each electrolysis cell is communicated with the outlet main pipeline of the electrolyte, and the inlet of the electrolysis cell is communicated with the inlet main pipeline of the electrolyte; the electrolysis cells of the electrolyzer are arranged according to the above-mentioned method for uniform distribution of electrolyte flow rate.

[0050] Several bipolar plates 2 are installed between the positive end plate 1 and the negative end plate 3. An alkali solution flow channel 6 is provided inside the bipolar plate 2. An outlet main pipeline 4 and an inlet main pipeline 8 are also provided inside the bipolar plate 2. One end of the alkali solution flow channel 6 is communicated with the outlet main pipeline 4 through the electrolysis cell outlet 5, and the other end of the alkali solution flow channel 6 is communicated with the inlet main pipeline 8 through the electrolysis cell inlet 7. A diaphragm 11 and an electrolysis electrode 10 are sandwiched between two bipolar plates 2. The middle diaphragm 11, the electrolysis electrodes 10 on both the hydrogen and oxygen sides, and the alkali solution flow channel 6 form an electrolysis cell 9.

[0051] The structural layouts on the hydrogen side and the oxygen side are similar. The key to the uniform distribution of the electrolyte flow rate lies in adjusting the flow areas of each pipeline.

[0052] Calculation method for the flow rate of each electrolysis cell in an alkaline electrolyzer:

[0053] The fluid in the alkaline electrolyzer can be described by the mass conservation equation and the Bernoulli equation. The inlet of the alkaline electrolyzer is liquid, and the outlet is a gas-liquid mixture. The inlet mass flow rate Q of the alkaline electrolyzer inletρliquid is equal to the sum of the liquid-phase mass flow rate and the gas-phase mass flow rate at the outlet of each electrolysis cell. The fluid everywhere in the alkaline electrolyzer satisfies the Bernoulli equation. In the equation, zρg is the gravitational potential energy term, p is the static pressure term, is the dynamic pressure term, h f is the local resistance, and C is a constant.

[0054]

[0055]

[0056] The key in the equation is the local resistance h f . Since all the alkali solution flowing through different electrolysis cells has the same inlet and outlet, the pressure drops are all equal. For any electrolysis cell, the resistance h f consists of five parts, namely the pipeline resistance of the inlet main pipeline, the local resistance at the electrolysis cell inlet, the internal resistance of the electrolysis cell, the local resistance at the electrolysis cell outlet, and the pipeline resistance of the outlet main pipeline. For the local resistance h f at any place, the following formula is satisfied, ρ is the density of the fluid, δ is the local resistance coefficient, and u is the velocity of the fluid.

[0057]

[0058] For the gas-liquid mixture, the density is calculated according to the average density. In the above formula, ρ mix is the average density, is the gas-phase volume fraction, is the liquid volume fraction. The key to affecting the flow rate distribution of each electrolysis cell is the local resistance coefficient δ at each location. The local resistance coefficient δ is related to the pipeline structure, flow rate, and flow rate ratio. The local resistance coefficient δ at each location can be obtained through CFD simulation calculation. Thus, the flow rate distribution of each electrolysis cell in the alkaline electrolyzer can be calculated by solving the above equation.

[0059] The area ratio of the outlet main pipeline 4 to the inlet main pipeline 8:

[0060] Existing electrolyzers usually adopt the same inlet and outlet pipelines. However, the gas generated by electrolysis increases the flow velocity in the outlet pipeline, which leads to uneven flow rate distribution in the electrolysis cell. To make the flow rate distribution in the electrolysis cell more uniform, it is necessary to increase the area of the outlet main pipeline 4. As Figure 2 shown, as the area of the outlet main pipeline 4 increases, the average flow rate deviation decreases rapidly, and then increases with the increase of the area ratio. The range of the area ratio of the outlet main pipeline 4 to the inlet main pipeline 8 is 1.5 - 2.

[0061] The area ratio of the inlet of the oxygen-side electrolysis cell to the hydrogen-side area:

[0062] For the electrolyzer, the flow rate distribution of the electrolyte on the hydrogen side and the oxygen side is very important. Due to the different gas production amounts on both sides, the pressure drop under the same flow rate is different, resulting in uneven flow rate distribution on both sides. The flow rate entering both sides can be adjusted by adjusting the area ratio of the inlets of the electrolysis cells on both sides. As Figure 3 shown, the optimal area ratio range of the oxygen side to the hydrogen side is 2.5 - 3.

[0063] The inlet area of the oxygen-side electrolysis cell:

[0064] Although the flow rate of the lye entering the hydrogen side and the oxygen side is almost equal, the flow rate distribution in a single oxygen-side electrolysis cell is still not uniform enough, as Figure 4 shown. When the number of electrolysis cells n is 200, the flow rate of the first two hundred electrolysis cells on the oxygen side is small, and the flow rate of the last two hundred electrolysis cells is large. For the convenience of processing and installation, taking 50 electrolysis cells as a unit, the inlet area S 1 、S 2 、S 3 、S 4 , while ensuring that the total area remains unchanged, decreases in an arithmetic progression. S 1 : S 2 : S 3 : S 4 = 12:10:8:6. As Figure 5 shown, the average flow rate deviation is 1.22%, and the maximum flow rate deviation is 4%. This electrolyzer structure can make the lye flow rate distribution uniform.

[0065] Obviously, the above embodiments are only examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation manners here. And the obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. A method for uniformly distributing electrolyte flow, characterized in that: The electrolytic chamber of the electrolytic cell is set up according to the following rules: Obtain the local resistance of each electrolytic chamber, and calculate the flow rate of each electrolytic chamber according to the mass conservation equation and the Bernoulli equation; When the flow rate meets the uniform distribution, the flow area ratio of the electrolysis chamber inlet on the hydrogen side and the oxygen side of each electrolysis chamber is calculated; The electrolysis chambers on the hydrogen side and the oxygen side are grouped according to the total area of ​​the inlet main pipeline, and the inlet areas of the electrolysis chambers on the hydrogen side and the oxygen side in each group are allocated according to an arithmetic progression.

2. The method for uniformly distributing electrolyte flow according to claim 1, characterized in that: The acquisition of the local resistance of each electrolytic chamber includes modeling the electrolytic cell and using CFD simulation to calculate the local resistance coefficient of each electrolytic chamber. Among them, δ is the local resistance coefficient, ρ is the density of the fluid, and u is the velocity of the fluid.

3. The method for uniformly distributing electrolyte flow according to claim 1, characterized in that: Calculate the flow rate of each electrolytic chamber according to the mass conservation equation and Bernoulli equation; Q inlet ρ liquid is the inlet mass flow rate of the alkaline electrolyzer, is the mass flow rate of liquid at the outlet of each electrolytic chamber, is the gas mass flow rate at the outlet of each electrolysis chamber; zρg is the gravitational potential energy term, p is the static pressure term, is the dynamic pressure term, h f is the local resistance, C is a constant; n is the total number of electrolytic chambers, and i is the serial number of the current electrolytic chamber.

4. The method for uniformly distributing electrolyte flow according to claim 3, characterized in that: When the outlet is a gas-liquid mixture, the density is calculated according to the average density shown in the following formula: Among them, ρ mix is the average density, is the gas phase volume fraction, is the liquid volume fraction.

5. The method for uniformly distributing electrolyte flow according to claim 1, characterized in that: When the flow rate meets the uniform distribution, the flow area ratio of the electrolysis chamber inlet on the hydrogen side and the oxygen side of each electrolysis chamber is calculated, and the ratio of the area of ​​the outlet main line to the inlet main line is determined according to the area of ​​the inlet main line; Determine the area of ​​the main exit road; The inlet area ratio of the oxygen side and the hydrogen side is determined based on the total area of ​​the inlet main pipeline and the difference in gas production on the hydrogen side and the oxygen side.

6. An industrial-scale electrolytic cell with uniform electrolyte flow distribution, characterized in that: include: The anode end plate, the cathode end plate and a plurality of electrolysis chambers are installed in cooperation between the anode end plate and the cathode end plate, the outlet of each electrolysis chamber is connected to the outlet main line of the electrolyte, and the inlet of the electrolysis chamber is connected to the inlet main line of the electrolyte; the electrolysis chamber of the electrolytic cell is arranged according to the method for uniformly distributing the electrolyte flow rate described in any one of claims 1 to 4 above.

7. The industrial-scale electrolytic cell with uniform electrolyte flow distribution according to claim 5, characterized in that: A plurality of bipolar plates are arranged between the anode end plate and the cathode end plate, and the inner cavity of each bipolar plate is an alkaline solution flow channel.

8. The industrial-scale electrolytic cell with uniform electrolyte flow distribution according to claim 5, characterized in that: Two adjacent bipolar plates form an electrolysis chamber, and a middle diaphragm and an electrolysis electrode are arranged in the middle of each electrolysis chamber.

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