Alkaline electrolytic hydrogen production system mixed spatial scale dynamic response modeling method

Abstract

The invention discloses a mixed spatial scale dynamic response modeling method for an alkaline electrolytic hydrogen production system, and belongs to the technical field of new energy. According to the method disclosed by the invention, a mixed spatial scale framework comprising a one-dimensional alkaline electrolytic cell model and a zero-dimensional separation cycle model is constructed. The method comprises the following steps: firstly, establishing a one-dimensional alkaline electrolytic cell model for representing internal cross permeation of the alkaline electrolytic cell, a substance transfer process and dynamic response characteristics of voltage and current; secondly, establishing a zero-dimensional separation circulation model for representing dynamic response characteristics of alkali liquor circulation and hydrogen-oxygen two-side gas-liquid separation; and then discretizing the obtained data by adopting a finite volume method, solving the one-dimensional alkaline electrolytic cell model by adopting a pressure-velocity coupling algorithm, and solving the zero-dimensional separation cycle model by adopting a finite difference method. The method disclosed by the invention has a remarkable effect on improving the modeling precision of the dynamic response characteristic of the alkaline electrolytic hydrogen production, realizes one-dimensional substance transmission observability in the alkaline electrolytic cell, and provides an effective tool for system simulation and control design.

Description

Technical Field

[0001] The present invention belongs to the field of new energy technology, and in particular relates to a mixed spatial scale dynamic response modeling method for an alkaline electrolysis hydrogen production system. Background Art

[0002] Alkaline water electrolysis has the advantages of mature technology and low cost, and will have great development potential in the large-scale consumption of renewable energy in the future. However, in the alkaline electrolysis hydrogen production system, the internal state of the electrolyzer is difficult to observe in real time, which limits the development of its safe operation control and the analysis of its dynamic response characteristics. The technical difficulty lies in the coupling effect of multiple state quantities such as electrochemical reactions and two-phase flows inside the alkaline electrolyzer, which affect each other. Secondly, when the electrolysis power changes, the electrical characteristics of the system show significant nonlinear characteristics. In model construction, it is necessary to solve the problem that the current zero-dimensional model of the alkaline electrolysis hydrogen production system is difficult to observe its internal state change process, and ignore the influence of the separation and circulation system on the electrical characteristics of the alkaline electrolysis hydrogen production system, resulting in the model's inadequacy in reflecting the dynamic performance of the system.

[0003] Therefore, a new technical solution is urgently needed in the prior art to solve this problem. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a mixed spatial scale dynamic response modeling method for an alkaline electrolysis hydrogen production system, which is used to solve the problem that the zero-dimensional model of the alkaline electrolysis hydrogen production system in the prior art is difficult to observe the internal state change process, and ignores the influence of the separation and circulation system on the electrical characteristics of the alkaline electrolysis hydrogen production system, resulting in the model being insufficient in reflecting the dynamic performance of the system.

[0005] The technical solution adopted by the present invention is to provide a mixed spatial scale dynamic response modeling method for an alkaline electrolysis hydrogen production system, comprising the following steps:

[0006] S1: Establish a one-dimensional alkaline electrolytic cell model based on the cross-permeation, material transport process and voltage and current dynamic response characteristics inside the alkaline electrolytic cell;

[0007] S2: Establish a zero-dimensional separation cycle model based on the dynamic response characteristics of alkali liquid circulation and gas-liquid separation on both sides of hydrogen and oxygen;

[0008] S3: The obtained data are discretized using the finite volume method;

[0009] S4: The one-dimensional alkaline electrolyzer model is solved using the pressure-velocity coupling algorithm, and the zero-dimensional separated cycle model is solved using the finite difference method.

[0010] The cross permeation inside the alkaline electrolytic cell in step S1 uses Fick and Darcy's laws to characterize the permeation of oxygen generated at the anode through the diaphragm to the cathode and the permeation of hydrogen generated at the cathode through the diaphragm to the anode.

[0011] The material transfer process in step S1 uses the law of conservation of mass to characterize the convective mass transfer of hydrogen, oxygen and alkali solution in the one-dimensional flow channel, and uses the law of conservation of momentum to characterize the pressure and velocity changes of hydrogen, oxygen and alkali solution in the one-dimensional flow channel.

[0012] The voltage-current dynamic response characteristics in step S1 are characterized by reversible voltage, activation overvoltage, and ohmic overvoltage on the voltage-current characteristics of the electrolytic chamber in the alkaline electrolytic cell.

[0013] The dynamic response of the alkali liquid circulation and the gas-liquid separation on both sides of hydrogen and oxygen in step S2 is characterized by the hydrogen, oxygen and alkali liquid material flows, and the material flows are divided into the gas after gas-liquid phase separation, the hydrogen and oxygen discharged from the gas-liquid separator, and the alkali liquid circulating on both sides of hydrogen and oxygen.

[0014] The dynamic behavior of the pressure change in the hydrogen and oxygen separators in the zero-dimensional separation cycle model in step S2 is characterized by applying the ideal gas law.

[0015] Through the above design scheme, the present invention can bring the following beneficial effects: This method can realize the observation of material transfer in the alkaline electrolyzer and the accurate characterization of the dynamic response of the gas-liquid material flow in the separation circulation subsystem by constructing a one-dimensional mass transfer model of the alkaline electrolyzer. It has a significant effect on improving the accuracy of modeling the dynamic response characteristics of alkaline electrolysis hydrogen production, and realizes the observable one-dimensional transfer of hydrogen, oxygen and other materials in the alkaline electrolyzer, providing an effective tool for system dynamic simulation analysis and control design. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of material flow of an alkaline electrolysis hydrogen production system according to a mixed spatial scale dynamic response modeling method of an alkaline electrolysis hydrogen production system of the present invention;

[0017] Figure 2 A schematic diagram of an alkaline electrolytic cell voltage of a mixed spatial scale dynamic response modeling method for an alkaline electrolysis hydrogen production system according to the present invention;

[0018] Figure 3 A schematic diagram of oxygen concentration at the anode of an alkaline electrolytic cell in a mixed spatial scale dynamic response modeling method for an alkaline electrolysis hydrogen production system according to the present invention;

[0019] Figure 4 A schematic diagram of the hydrogen concentration at the cathode of an alkaline electrolyzer in a mixed spatial scale dynamic response modeling method for an alkaline electrolysis hydrogen production system of the present invention;

[0020] Figure 5A schematic diagram of the hydrogen-oxygen separator pressure of a mixed spatial scale dynamic response modeling method for an alkaline electrolysis hydrogen production system according to the present invention. DETAILED DESCRIPTION

[0021] The present invention is further described below with reference to the accompanying drawings and specific embodiments:

[0022] The mixed spatial scale dynamic response modeling method of the alkaline electrolysis hydrogen production system includes the following steps:

[0023] (1) One-dimensional alkaline electrolyzer model

[0024] The molar rate of hydrogen generation in an alkaline electrolyzer is expressed as follows:

[0025]

[0026] Where: is the cathode hydrogen generation rate; η EL is the Faraday efficiency, i is the current; F is the Faraday constant.

[0027] Through the stoichiometric coefficient of the chemical reaction, the molar rate of oxygen and water generation at the anode and the molar rate of water consumption at the cathode can be calculated according to the molar rate of hydrogen generation, which is expressed as follows:

[0028]

[0029] Where: is the anode oxygen generation rate; is the anode water generation rate, is the cathode water consumption rate.

[0030] In alkaline electrolyzers, the concentration and pressure gradients at the anode and cathode cause cross-permeation of hydrogen and oxygen through the diaphragm, which can be expressed by Fick's law and Darcy's law, respectively, as follows:

[0031]

[0032] Where: is the hydrogen permeation rate; is the Darcy coefficient of hydrogen, is the Fick coefficient of hydrogen; is the cathode hydrogen partial pressure; is the anode hydrogen partial pressure; is the cathode hydrogen concentration; is the anode hydrogen concentration; δ m is the thickness of the diaphragm; is the oxygen permeation rate; is the Darcy coefficient of oxygen; is the oxygen Fick coefficient; is the anode oxygen partial pressure; is the cathode oxygen partial pressure; is the anode oxygen concentration; is the cathode oxygen concentration.

[0033] The transport process of each substance in the electrolytic chamber of the alkaline electrolytic cell can be expressed by the mass conservation equation of fluid mechanics. Since the model is established as a one-dimensional model along the flow channel, the diffusion effect is much smaller than the convection in this dimension. Therefore, the diffusion effect is ignored in the model. The mass conservation equation of each substance is expressed as:

[0034]

[0035] Where: C w,a is the anode water concentration; C w,c is the cathode water concentration; u a is the anode flow rate; γ ch is the flow channel width; u c is the cathode flow velocity; z is the spatial position; t is the time.

[0036] The velocity change of the substance in the electrolytic chamber of the alkaline electrolytic cell can be described by the momentum equation. In the modeling assumption, each substance has the same flow rate. For this reason, the gas-liquid mixed density is used in the construction of the momentum equation. At the same time, the viscosity of the fluid and other external forces such as gravity are ignored, because the inertial force in the electrolytic chamber is significantly greater than the viscosity force, and the external force is not the main influencing factor. It is specifically expressed as:

[0037]

[0038] Where: is the average density of gas-liquid mixture in the alkaline electrolytic cell; P EL,a is the anode cell pressure; P EL,c is the cathode cell pressure.

[0039] The voltage of the electrolytic cell of the alkaline electrolytic cell is expressed as:

[0040] U cell =U oc +U ac +U ohm (14)

[0041] Where: U cell is the voltage of the electrolytic cell of the alkaline electrolytic cell; U oc is the reversible voltage of the electrolytic cell of the alkaline electrolytic cell; U ac The overvoltage for activating the electrolytic chamber of the alkaline electrolytic cell; U ohm Ohmic overvoltage of the electrolytic chamber of the alkaline electrolyzer.

[0042] The reversible voltage represents the minimum voltage that triggers the electrolysis reaction in an alkaline electrolytic cell and is expressed as follows:

[0043]

[0044] Where: U oc,ref is the reference reversible voltage of the electrolytic cell of the alkaline electrolytic cell; R is the gas constant; T is the temperature; λ w For the activity of water.

[0045] The activation overvoltage expression is:

[0046]

[0047] Where: α a is the number of electrons transferred to the anode; α c is the number of cathode transferred electrons; i 0,a is the anode exchange current density; i 0,c is the cathode exchange current density.

[0048] The ohmic overvoltage is expressed as follows:

[0049] U ohm =i*A m *(r bp,a +r bp,c +r ele +r m ) (17)

[0050] Where: r bp,a is the anode plate resistance; r bp,c is the cathode plate resistance; r ele is the electrolyte resistance; r m is the diaphragm resistance.

[0051] The voltage of the alkaline electrolyzer is expressed as the total voltage of all electrolytic cells, expressed as:

[0052] U EL =K cell U cell (18)

[0053] Where: K cell is the total number of electrolytic chambers; U EL is the voltage of the alkaline electrolyzer.

[0054] (2) Separation and circulation model

[0055] Based on the one-dimensional model of the alkaline electrolyzer, the separation and circulation process of the alkaline electrolysis hydrogen production system is dynamically modeled using material flow. In order to clearly illustrate this part of the modeling process, the separation and circulation material flow transfer process is numerically annotated, such as Figure 1 shown.

[0056] The flow rates of streams 1 and 5 and the concentrations of their components can be calculated using the one-dimensional model of an alkaline electrolyzer as follows:

[0057]

[0058]

[0059] Where: u1 is the flow rate of material flow 1; u5 is the flow rate of material flow 5; C is the concentration; subscripts w, H2, O2 are water, hydrogen, and oxygen respectively; subscripts 1, 5 are material flow 1 and material flow 5 respectively.

[0060] To facilitate modeling of the material flows, the concentrations of the different species in the alkaline electrolyzer were converted to molar flow rates as follows:

[0061]

[0062] Where: A EL,out is the cross-sectional area of ​​the outlet pipe of the alkaline electrolyzer.

[0063] By using the molar flow rates of the various substances, the molar flow rates of substance streams 1 and 5 can be calculated and expressed as follows:

[0064]

[0065] Where: is the molar flow rate of substance flow j.

[0066] The volume flow rates of material flows 1 and 5 are expressed as the sum of the volume flow rates of their respective materials as follows:

[0067]

[0068] Where: is the volume flow rate of potassium hydroxide aqueous solution of material flow j; is the hydrogen volume flow rate of material flow j; is the oxygen volume flow rate of material flow j; is the volume flow rate of material flow j.

[0069] Material streams 2 and 6 represent the gas after gas-liquid phase separation. Considering that the process of gas and liquid separation in the separator takes time, a time constant is introduced to describe the dynamic process of gas release, as follows:

[0070]

[0071] Where: τ SEP is the separation time constant; is the molar flow rate of hydrogen bubbles in material flow j; is the molar flow rate of oxygen bubbles in material flow j.

[0072] The volume flow rates of material flows 2 and 6 are expressed as:

[0073]

[0074] Where: P SEP,j is the pressure of material flow j.

[0075] For material flows 4 and 8, at a fixed caustic soda circulation flow rate, the distribution of the molar flow rate can be approximately calculated based on the pressure of the hydrogen and oxygen separators, as follows:

[0076]

[0077] Where: κ is the unit conversion coefficient; Q lye is the alkali solution circulation flow rate; ρ KOH,aq is the density of potassium hydroxide solution; M4 is the average mass fraction of material flow 4; M8 is the average mass fraction of material flow 8.

[0078] The volume flow rates of material flows 4 and 8 can be calculated as follows:

[0079]

[0080] The molar flow rates of material flows 3 and 7 can be expressed as follows:

[0081]

[0082] Where: H valve is the valve coefficient; is the valve opening on the oxygen side; is the valve opening on the hydrogen side; P atm is the external pressure at the separator outlet; ρ IV is the average density of container IV; ρ II is the average density of container II.

[0083] Based on the molar flow model, the mass changes in the hydrogen and oxygen separators can be calculated using the mass conservation law as follows:

[0084]

[0085] Where: is the mass change of container 1; is the mass change of container III; is the mass change of container II; This is the change in the amount of substance in container IV.

[0086] The dynamics of the liquid level in the separator are determined by the volume flow rates of the various species present in the liquid portion of the separator as follows:

[0087]

[0088] Where: is the liquid level change of container 1; A is the liquid level change in container III; SEP is the cross-sectional area of ​​the separator.

[0089] The dynamic behavior of the pressure changes within the hydrogen and oxygen separator can be explained by applying the ideal gas law as follows:

[0090]

[0091] Where: is the oxygen separator pressure; is the hydrogen separator pressure; L SEP is the separator height.

[0092] In order to verify the accuracy of the dynamic model of the present invention, the model results are compared with the experimental data under dynamic conditions for analysis and accuracy verification. Figure 2 The dynamic change of the voltage of the alkaline electrolyzer is shown when the input current of the alkaline electrolysis hydrogen production system changes from 73A to 78A. Figure 2 As shown in the figure, the total voltage of the electrolytic cell exhibits a dynamic response in multiple time stages under dynamic response, and the model can accurately reflect the change process of its voltage under dynamic conditions. Figure 3 and Figure 4 The dynamic changes of oxygen and hydrogen concentrations at five positions in the one-dimensional space of the electrolytic cell (2.442 cm, 4.844 cm, 7.362 cm, 9.768 cm, and 12.21 cm along the flow direction of the anode and cathode channels of the electrolytic cell, with a total length of 24.4 cm in the flow channel diameter) are displayed. Figure 5 The dynamic changes of hydrogen and oxygen pressures in the alkaline electrolysis hydrogen production system are shown. According to the experimental data and the model results, the average relative error of voltage is 0.39%, and the average relative error of oxygen pressure is 0.98%, indicating that the model has a high accuracy in describing the dynamic behavior of the alkaline water electrolysis hydrogen production system.

[0093] The implementation methods of the present invention are not limited to the above-mentioned embodiments, and any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A mixed spatial scale dynamic response modeling method for an alkaline electrolysis hydrogen production system, characterized by: The following steps are involved: S1: Establish a one-dimensional alkaline electrolytic cell model based on the cross-permeation, material transport process and voltage and current dynamic response characteristics inside the alkaline electrolytic cell; S2: Establish a zero-dimensional separation cycle model based on the dynamic response characteristics of alkali liquid circulation and gas-liquid separation on both sides of hydrogen and oxygen; S3: The obtained data are discretized using the finite volume method; S4: The one-dimensional alkaline electrolyzer model is solved using the pressure-velocity coupling algorithm, and the zero-dimensional separated cycle model is solved using the finite difference method.

2. The method for modeling a mixed spatial scale dynamic response of an alkaline electrolysis hydrogen production system according to claim 1, characterized in that: The cross permeation inside the alkaline electrolytic cell in step S1 uses Fick and Darcy's laws to characterize the permeation of oxygen generated at the anode through the diaphragm to the cathode and the permeation of hydrogen generated at the cathode through the diaphragm to the anode.

3. The method for modeling a mixed spatial scale dynamic response of an alkaline electrolysis hydrogen production system according to claim 1, characterized in that: The material transfer process in step S1 uses the law of conservation of mass to characterize the convective mass transfer of hydrogen, oxygen and alkali solution in the one-dimensional flow channel, and uses the law of conservation of momentum to characterize the pressure and velocity changes of hydrogen, oxygen and alkali solution in the one-dimensional flow channel.

4. The method for modeling a mixed spatial scale dynamic response of an alkaline electrolysis hydrogen production system according to claim 1, characterized in that: The voltage-current dynamic response characteristics in step S1 are characterized by reversible voltage, activation overvoltage, and ohmic overvoltage on the voltage-current characteristics of the electrolytic chamber in the alkaline electrolytic cell.

5. The method for modeling a mixed spatial scale dynamic response of an alkaline electrolysis hydrogen production system according to claim 1, characterized in that: The dynamic response of the alkali liquid circulation and the gas-liquid separation on both sides of hydrogen and oxygen in step S2 is characterized by the hydrogen, oxygen and alkali liquid material flows, and the material flows are divided into the gas after gas-liquid phase separation, the hydrogen and oxygen discharged from the gas-liquid separator, and the alkali liquid circulating on both sides of hydrogen and oxygen.

6. The method for modeling a mixed spatial scale dynamic response of an alkaline electrolysis hydrogen production system according to claim 1, characterized in that: The dynamic behavior of the pressure change in the hydrogen and oxygen separators in the zero-dimensional separation cycle model in step S2 is characterized by applying the ideal gas law.

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