Multi-scale numerical simulation method for plasma catalytic synthesis ammonia reaction mechanism

Abstract

The invention discloses a multi-scale numerical simulation method for a plasma catalytic synthesis ammonia reaction mechanism, which comprises the following steps: constructing a two-dimensional geometric model of a plasma catalytic synthesis ammonia device, and constructing a plasma catalytic synthesis ammonia reaction system and a plasma discharge model, obtaining particle density space distribution generated by plasma single discharge through a plasma discharge model; constructing a plasma catalytic synthesis ammonia reaction kinetic model, and obtaining evolution characteristics and time-space distribution of active particles in two discharge gaps; taking the particle density as an initial condition, repeating a plurality of discharge cycles until the particle density tends to a cycle stable value, and obtaining the discharge characteristic of the plasma catalytic synthesis ammonia, the chemical reaction path and the spatio-temporal evolution characteristic of the particle density. According to the invention, discharge characteristics of plasma and catalyst action, chemical reaction paths and spatio-temporal evolution characteristics of particle density are analyzed from multiple time and space scales, and the problem that the reaction mechanism of ammonia synthesis catalyzed by plasma is unknown in the prior art is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of ammonia synthesis, and in particular relates to a multi-scale numerical simulation method for a plasma-catalyzed ammonia synthesis reaction mechanism. Background Art

[0002] Ammonia (NH3) is the world's second-largest industrially produced compound, commonly used to synthesize nitrogen fertilizers and other chemical raw materials. It is also a carbon-free hydrogen storage medium. Large-scale industrial ammonia synthesis primarily utilizes the Haber-Bosch (HB) process, but this method suffers from drawbacks such as high energy consumption, a significant greenhouse effect, and harsh operating conditions (high temperatures of 400-600°C and high pressures of 20-50 MPa).

[0003] Plasma-catalyzed ammonia synthesis has been widely researched and applied in existing technologies due to its ease of integration with renewable energy, the absence of high-pressure and high-temperature operating environments, and its ability to achieve zero CO2 emissions. However, current research in this field primarily relies on experimentally obtaining discharge images and macroscopic parameters of plasma-catalyzed ammonia synthesis, and analyzing the plasma-catalyzed ammonia synthesis reaction process using zero-dimensional reaction kinetic models. This lacks research on the evolutionary characteristics of plasma-catalyzed ammonia synthesis at multiple temporal and spatial scales, resulting in a lack of clarity regarding the reaction mechanism of plasma-catalyzed ammonia synthesis. This, in turn, limits the optimization and control of plasma-catalyzed ammonia synthesis and hinders the further development of plasma-catalyzed ammonia synthesis technology. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the above-mentioned existing technologies and provide a facial action unit recognition method based on multimodal fusion and text enhancement. This method can analyze the discharge characteristics, chemical reaction paths and spatiotemporal evolution characteristics of the particle density of the plasma-catalyst interaction from multiple time and space scales, so as to solve the problem of unclear mechanism of plasma-catalyzed ammonia synthesis reaction in the existing technology.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A multi-scale numerical simulation method for a plasma-catalyzed ammonia synthesis reaction mechanism comprises the following steps:

[0007] S1. Constructing a two-dimensional geometric model of a plasma catalytic ammonia synthesis device, wherein the two-dimensional geometric model includes a discharge electrode, an electrode blocking medium, a plasma region, and catalyst particles;

[0008] S2. Constructing a plasma-catalyzed ammonia synthesis reaction system and a plasma discharge model, wherein the plasma discharge model includes a mass conservation equation, an electron average energy control equation, and a Poisson equation;

[0009] S3. Obtain the spatial distribution of particle density generated by a single plasma discharge through simulation and calculation using a plasma discharge model;

[0010] S4. For the afterglow stage of plasma-catalytic ammonia synthesis, construct a reaction kinetics model for plasma-catalytic ammonia synthesis to obtain the evolution characteristics and spatio-temporal distribution of active particles during the interval between two discharges;

[0011] S5. Input the particle density obtained in step S4 into the plasma discharge model as the initial condition, and repeat steps S3 - S4 for simulation and calculation of multiple discharge cycles until the particle density obtained in step S4 tends to a periodic stable value. After processing the simulation and calculation results, obtain the discharge characteristics, chemical reaction path, and spatio-temporal evolution characteristics of particle density for plasma-catalytic ammonia synthesis.

[0012] Preferably, in step S1, the two-dimensional geometric model includes a high-voltage electrode, an upper electrode blocking medium, a plasma region, a lower electrode blocking medium, and a low-voltage electrode arranged in sequence from top to bottom. Catalyst particles are arranged between the upper electrode blocking medium and the lower electrode blocking medium.

[0013] Preferably, in step S2, the plasma-catalytic ammonia synthesis reaction system includes gas-phase chemical reactions and chemical reactions on the catalyst surface;

[0014] The gas-phase chemical reactions include electron impact ionization, electron impact excitation, electron impact dissociation, electron attachment, electron-ion recombination, ion-ion recombination, charge exchange, three-body reactions, and vibrational-translational relaxation reactions;

[0015] The chemical reactions on the catalyst surface include direct adsorption reactions, dissociative adsorption reactions, Eley-Rideal reactions, and Langmuir-Hinshelwood reactions.

[0016] Preferably, in step S2, the plasma discharge model includes a mass conservation equation, an electron average energy control equation, and a Poisson equation; the mass conservation equation includes an electron mass conservation equation, and ion and neutral particle mass conservation equations;

[0017] The electron mass conservation equation is:

[0018]

[0019] In the formula, n e is the electron density, t is the time, represents the divergence of a vector, and the electron flux Γ e is expressed as E is the electric field, μ e and D e respectively represent the electron mobility coefficient and diffusion coefficient, and the electron source term R e is expressed as x j is the mole fraction of the heavy particles participating in the reaction, k j is the reaction rate constant, N n is the total particle number density, and M is the total number of reactions;

[0020] The mass conservation equations for the ions and neutral particles are as follows:

[0021]

[0022] In the formula, ρ is the density of the mixed gas, R i is the particle source term, ω i is the mass fraction of particle i, M n is the average molar mass, q i is the charge number carried by the particle, μ i is the mobility, and the mixed mean diffusion coefficient D i,m The expression of D ij is the binary diffusion coefficient between particles i and j;

[0023] The electron average energy control equation is as follows:

[0024]

[0025] In the formula, n ε is the electron average energy density, and the electron energy flux density Γ ε The expression of The electron energy source term R ε The expression of where e is the elementary charge, ΔE j and R intel,j are the energy loss of the inelastic collision reaction and the corresponding reaction rate respectively, m e is the electron mass, M is the neutral particle mass, v en is the effective collision frequency between the electron and the neutral particle, T g is the gas temperature, k b is the Boltzmann constant, T e is the electron temperature;

[0026] The Poisson equation is as follows:

[0027]

[0028] In the formula, is the electric potential, ε r is the relative permittivity, ε0 is the vacuum permittivity, and ρ v is the space charge density.

[0029] Preferably, the specific process of step S3 is as follows:

[0030] S31. Set the solution domain and boundary conditions for the plasma discharge model. Among them, in the two-dimensional geometric model, set the electric potential of the high-voltage electrode to V, the electric potential of the low-voltage electrode to zero, and the boundary conditions at three positions, namely, the interface between the plasma region and the upper electrode blocking medium, the interface between the catalyst particles and the plasma region, and the interface between the plasma region and the lower electrode blocking medium, are the same;

[0031] S32. Set the grid parameters for different solution domains and boundary conditions;

[0032] S33. Configure the time unit, time step, and tolerance of the solver, and use the solver to solve for the spatial distribution of the particle density generated by a single plasma discharge.

[0033] Preferably, S31 specifically includes:

[0034] (1) Set the solution domain: The mass conservation equation and the electron average energy control equation are only solved in the plasma discharge region, and the Poisson equation is solved in the electrode region, the blocking medium region, the catalyst region, and the plasma discharge region;

[0035] (2) Set the boundary conditions:

[0036] The boundary condition of the electron mass conservation equation is:

[0037]

[0038] In the formula, n is the outward normal vector of the solid surface, Γ e is the electron flux, v e,th is the thermal velocity of the electron, n e is the electron density, μ e is the electron mobility coefficient, a total of Q particles, γ i is the secondary electron emission coefficient of particle i, Γ i is the flux of particle i on the solid surface;

[0039] The boundary condition of the electron average energy control equation is:

[0040]

[0041] In the formula, n ε is the average electron energy, Γ ε is the electron energy flux, μ ε is the electron energy mobility coefficient, ε i is the average initial energy of the secondary electrons emitted from the solid surface;

[0042] The boundary conditions for the mass conservation equations of ions and neutral particles are as follows:

[0043] -Γ i ·n = M i R surf,i +M i c i μ i,m z i (n·E)((z i n·E)>0), Equation (7),

[0044] where Γ i is the flux of particle i, M i is the molar mass of particle i, R surf,i is the surface reaction rate, c i is the mole fraction of particle i, μ i,m is the mixed average mobility, z i is the charge number of particle i;

[0045] The boundary conditions for the Poisson equation are:

[0046] n·(D1 - D2) = ρ s , Equation (8),

[0047] where D1 and D2 represent the electric displacement fields above and below the boundary respectively, and ρ s is the charge density accumulated on the boundary surface, which is obtained from the following ordinary differential equation:

[0048]

[0049] where J e and J i are the electron and ion current densities on the boundary respectively.

[0050] Preferably, the grid parameters described in step S32 include grid shape, grid division method, maximum element size ratio adjustment coefficient, element growth rate, and grid curvature coefficient.

[0051] Preferably, the specific process of step S4 is as follows:

[0052] S41. For the afterglow stage of plasma-catalytic ammonia synthesis, construct a kinetic model for plasma-catalytic ammonia synthesis;

[0053] In step S4, the kinetic model for plasma-catalytic ammonia synthesis includes the Navier-Stokes equation, the continuity equation, and the convection-diffusion equation;

[0054] The Navier-Stokes equation is:

[0055]

[0056] The continuity equation is as follows:

[0057]

[0058] The convection-diffusion equation is as follows:

[0059]

[0060] In the formula, u is the fluid velocity, ρ is the density of the mixed gas, p is the pressure, η is the dynamic viscosity coefficient of the mixed gas, I is the unit vector matrix, F is the volume force vector, Di is the diffusion coefficient of the i-th particle in the mixed gas, and Mn is the average molar mass;

[0061] S42. Solve to obtain the evolution characteristics and spatio-temporal distribution of active particles in the discharge gap twice;

[0062] Solve the formulas (10), (11), and (12) corresponding to the Navier-Stokes equation, continuity equation, and convection-diffusion equation, and calculate to obtain the evolution characteristics and spatio-temporal distribution of active particles in the discharge gap twice.

[0063] Preferably, the specific process of step S5 is as follows:

[0064] Input the particle density corresponding to the particles generated by a single plasma discharge obtained at the first completion of step S3 into the plasma discharge model as the initial condition, repeat steps S3-S4 to simulate and calculate multiple discharge cycles until the particle density obtained in step S4 tends to the periodic stable value, process the obtained simulation results, obtain the particle density and reaction rate distribution diagrams generated by multiple discharges, generate the core reaction path of plasma-catalytic ammonia synthesis at different time scales, and obtain the discharge characteristics, chemical reaction path, and spatio-temporal evolution characteristics of particle density of plasma-catalytic ammonia synthesis.

[0065] Preferably, the discharge characteristics, chemical reaction path, and spatio-temporal evolution characteristics of particle density of plasma-catalytic ammonia synthesis include the particle density generated by multiple discharges, the reaction rate distribution diagram, and the core reaction path of plasma-catalytic ammonia synthesis generated at different time scales.

[0066] The present invention has the following advantages and beneficial effects compared with the prior art:

[0067] (1) The multi-scale numerical simulation method for the reaction mechanism of plasma-catalytic ammonia synthesis of the present invention facilitates the analysis of the discharge characteristics, chemical reaction paths, and spatio-temporal evolution characteristics of particle density in plasma-catalytic ammonia synthesis from multiple time and space scales, so as to explain the spatio-temporal evolution characteristics of electrons, anions, cations, neutral particles, and surface-adsorbed particles corresponding to the discharge stage and afterglow stage of plasma-catalytic ammonia synthesis at the microscopic level, and solve the problem that the reaction mechanism of plasma-catalytic ammonia synthesis in the prior art is unclear.

[0068] (2) The multi-scale numerical simulation method for the reaction mechanism of plasma-catalytic ammonia synthesis of the present invention can be used for the research of various plasma-catalytic ammonia synthesis reaction mechanisms. The plasma can be N2 / H2 plasma or N2 / H2O plasma, and the catalyst can be materials such as metal catalysts, ferroelectric materials, and molecular sieves. Without the need to conduct a large number of experiments, it can effectively guide the optimization and regulation of plasma-catalytic ammonia synthesis, and has broad application prospects in this field.

[0069] (3) The multi-scale numerical simulation method for the reaction mechanism of plasma-catalytic ammonia synthesis of the present invention can analyze the rapid chemical reactions in the plasma discharge stage and the slow chemical reactions in the afterglow stage, and can simultaneously calculate the gas-phase reactions and the heterogeneous reaction processes on the catalyst surface, greatly reducing the computational burden. Description of the Drawings

[0070] Figure 1 is a schematic flow chart of the multi-scale numerical simulation method for the reaction mechanism of plasma-catalytic ammonia synthesis provided by an embodiment of the present invention;

[0071] Figure 2 is a schematic working diagram between each model provided by an embodiment of the present invention;

[0072] Figure 3 is a schematic structural diagram of a two-dimensional geometric model of a plasma-catalytic ammonia synthesis device provided by an embodiment of the present invention.

[0073] In the figure, 1 is a high-voltage electrode, 2 is an upper electrode blocking medium, 3 is a reaction gas region, 4 is a catalyst particle, 5 is a lower electrode blocking medium, and 6 is a low-voltage electrode. Detailed Embodiments

[0074] The present invention will be further described below with reference to the drawings and embodiments.

[0075] In order to make the object, features, and advantages of the present invention more obvious and understandable, 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. Obviously, the embodiments described below are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0076] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and through specific embodiments.

[0077] A multi-scale numerical simulation method for the reaction mechanism of plasma-catalytic ammonia synthesis, the core of which is to create a plasma discharge model and a reaction kinetics model, and to repeatedly solve the plasma discharge model and the reaction kinetics model, so as to reveal the spatio-temporal evolution laws of various particles in the discharge stage and the afterglow stage of plasma-catalytic ammonia synthesis. The schematic diagram of the multi-scale numerical simulation method for the reaction mechanism of plasma-catalytic ammonia synthesis is as Figure 1 shown, where the plasma discharge model provides the densities of various particles generated by a single discharge for the reaction kinetics model, and the reaction kinetics model provides the densities of various particles generated in the afterglow stage for the discharge model.

[0078] Embodiment

[0079] As Figures 1 - 3 shown, a multi-scale numerical simulation method for the reaction mechanism of plasma-catalytic ammonia synthesis includes the following steps:

[0080] S1. Construct a two-dimensional geometric model of a plasma-catalytic ammonia synthesis device, and the two-dimensional geometric model includes a discharge electrode, an electrode barrier medium, a plasma region, and catalyst particles;

[0081] Specifically, as Figure 2 shown, the two-dimensional geometric model in step S1 includes a high-voltage electrode, an upper electrode barrier medium, a plasma region, a lower electrode barrier medium, and a low-voltage electrode arranged in sequence from top to bottom, and catalyst particles are arranged between the upper electrode barrier medium and the lower electrode barrier medium.

[0082] S2. Construct a plasma-catalytic ammonia synthesis reaction system and a plasma discharge model, and the plasma discharge model includes a mass conservation equation, an electron average energy control equation, and a Poisson equation;

[0083] In step S2, the plasma-catalytic ammonia synthesis reaction system includes gas-phase chemical reactions and chemical reactions on the catalyst surface;

[0084] The gas-phase chemical reactions include electron impact ionization, electron impact excitation, electron impact dissociation, electron attachment, electron-ion recombination, ion-ion recombination, charge exchange, three-body reactions, and vibrational-translational relaxation reactions;

[0085] The chemical reactions on the catalyst surface include direct adsorption reactions, dissociative adsorption reactions, Eley-Rideal reactions, and Langmuir-Hinshelwood reactions.

[0086] Specifically, the particles participating in the above reactions are divided into short-lived particles and long-lived particles. The short-lived particles only exist during plasma discharge, and the long-lived particles can also survive in the afterglow phase between two discharges. Therefore, only the chemical reactions involving long-lived particles need to be considered in the afterglow phase.

[0087] Specifically, the plasma discharge model in step S2 includes a mass conservation equation, an electron average energy control equation, and a Poisson equation; the mass conservation equation includes an electron mass conservation equation, an ion and neutral particle mass conservation equation;

[0088] The electron mass conservation equation is:

[0089]

[0090] where n e is the electron density, t is time, represents the divergence of a vector, and the electron flux Γ e is expressed as E is the electric field, μ e and D e represent the electron mobility and diffusion coefficient respectively, and the electron source term R e is expressed as x j is the mole fraction of the heavy particles participating in the reaction, k j is the reaction rate constant, N n is the total particle number density, and M is the total number of reactions;

[0091] The ion and neutral particle mass conservation equation is:

[0092]

[0093] where ρ is the density of the mixed gas, R i is the particle source term, ω i is the mass fraction of particle i, M n is the average molar mass, q i is the charge number carried by the particle, μ i is the mobility, and the mixed average diffusion coefficient D i,m is expressed as Dij is the binary diffusion coefficient between particles i and j;

[0094] The electron average energy control equation is as follows:

[0095]

[0096] In the formula, n ε is the electron average energy density, and the electron energy flux density Γ ε has the expression of The electron energy source term R ε has the expression of where e is the elementary charge, ΔE j and R intel,j are respectively the energy loss and the corresponding reaction rate of the inelastic collision reaction, m e is the electron mass, M is the neutral particle mass, v en is the effective collision frequency between electrons and neutral particles, T g is the gas temperature, k b is the Boltzmann constant, T e is the electron temperature;

[0097] The Poisson equation is as follows:

[0098]

[0099] In the formula, is the electric potential, ε r is the relative permittivity, ε0 is the vacuum permittivity, and ρ v is the space charge density.

[0100] S3. Obtain the spatial distribution of the particle density generated by a single plasma discharge through plasma discharge model simulation and calculation; the specific process is as follows:

[0101] S31. Set the solution domain and boundary conditions for the plasma discharge model. Among them, in the two-dimensional geometric model, set the electric potential of the high-voltage electrode to V, the electric potential of the low-voltage electrode to zero, and the boundary conditions at the three positions of the interface between the plasma region and the upper electrode blocking medium, the interface between the catalyst particles and the plasma region, and the interface between the plasma region and the lower electrode blocking medium are the same;

[0102] Specifically, S31 specifically includes:

[0103] (1) Set the solution domain: The mass conservation equation and the electron average energy control equation are only solved in the plasma discharge region, and the Poisson equation is solved in the electrode region, the blocking medium region, the catalyst region, and the plasma discharge region;

[0104] (2) Set boundary conditions:

[0105] The boundary conditions for the electron mass conservation equation are:

[0106]

[0107] where n is the outward normal vector of the solid surface, Γ e is the electron flux, v e,th is the thermal velocity of the electrons, n e is the electron density, μ e is the electron mobility coefficient, a total of Q particles, γ i is the secondary electron emission coefficient of particle i, Γ i is the flux of particle i on the solid surface;

[0108] The boundary conditions for the electron average energy control equation are:

[0109]

[0110] where n ε is the average electron energy, Γ ε is the electron energy flux, μ ε is the electron energy mobility coefficient, ε i is the average initial energy of the secondary electrons emitted from the solid surface;

[0111] The boundary conditions for the ion and neutral particle mass conservation equations are as follows:

[0112] -Γ i ·n = M i R surf,i +M i c i μ i,m z i (n·E)((z i n·E)>0), Equation (7),

[0113] where Γ i is the flux of particle i, M i is the molar mass of particle i, R surf,i is the surface reaction rate, c i is the mole fraction of particle i, μ i,m is the mixed average mobility, z i is the charge number of particle i;

[0114] The boundary conditions for the Poisson equation are:

[0115] n·(D1 - D2) = ρ s , Equation (8),

[0116] Wherein, D1 and D2 respectively represent the electric displacement fields above and below the boundary, and ρ s is the charge density accumulated on the boundary surface, which is obtained from the following ordinary differential equation:

[0117]

[0118] Wherein, J e and J i are respectively the electron and ion current densities on the boundary.

[0119] S32. Set grid parameters for different solution domains and boundary conditions;

[0120] Specifically, the grid parameters described in step S32 include grid shape, grid division method, maximum element size ratio adjustment coefficient, element growth rate, and grid curvature coefficient.

[0121] S33. Configure the time unit, time step, and tolerance of the solver, and use the solver to solve for the spatial distribution of particle density generated by a single plasma discharge.

[0122] S4. For the afterglow stage of plasma-catalytic ammonia synthesis, construct a reaction kinetic model of plasma-catalytic ammonia synthesis, and obtain the evolution characteristics and spatio-temporal distribution of active particles during the gap between two discharges;

[0123] S5. Input the particle density obtained in step S4 into the plasma discharge model as the initial condition, repeat steps S3 - S4 to simulate multiple discharge cycles until the particle density obtained in step S4 tends to a periodic stable value, and process the simulation results to obtain the discharge characteristics, chemical reaction path, and spatio-temporal evolution characteristics of particle density of plasma-catalytic ammonia synthesis.

[0124] Preferably, the specific process of step S4 is as follows:

[0125] S41. For the afterglow stage of plasma-catalytic ammonia synthesis, construct a reaction kinetic model of plasma-catalytic ammonia synthesis;

[0126] In step S4, the reaction kinetic model of plasma-catalytic ammonia synthesis includes the Navier - Stokes equation, continuity equation, and convection - diffusion equation;

[0127] The Navier - Stokes equation is:

[0128]

[0129] The continuity equation is:

[0130]

[0131] The convection - diffusion equation is:

[0132]

[0133] wherein, u is the fluid velocity, ρ is the density of the mixed gas, p is the pressure, η is the dynamic viscosity coefficient of the mixed gas, I is the unit vector matrix, F is the volume force vector, Di is the diffusion coefficient of the i-th kind of particle in the mixed gas, and Mn is the average molar mass;

[0134] S42. Solve to obtain the evolution characteristics and spatio-temporal distribution of active particles in the discharge gap for two times;

[0135] Solve the corresponding formulas (10), (11) and (12) of the Navier-Stokes equation, the continuity equation and the convective diffusion equation, and calculate the evolution characteristics and spatio-temporal distribution of active particles in the discharge gap for two times.

[0136] The specific process of step S5 is as follows:

[0137] Input the particle density corresponding to the particles generated by a single plasma discharge obtained when step S3 is initially completed into the plasma discharge model as the initial condition, repeat steps S3-S4 to simulate and calculate multiple discharge cycles until the particle density obtained in step S4 tends to a periodic stable value, process the obtained simulation results, obtain the particle density and reaction rate distribution diagrams generated by multiple discharges, generate the core reaction path of plasma catalytic ammonia synthesis at different time scales, and obtain the discharge characteristics, chemical reaction path and spatio-temporal evolution characteristics of particle density of plasma catalytic ammonia synthesis.

[0138] Specifically, the discharge characteristics, chemical reaction path and spatio-temporal evolution characteristics of particle density of the plasma catalytic ammonia synthesis include the particle density generated by multiple discharges, the reaction rate distribution diagram and the generation of the core reaction path of plasma catalytic ammonia synthesis at different time scales.

[0139] In summary, the multi-scale numerical simulation method for the reaction mechanism of plasma catalytic ammonia synthesis of the present invention is convenient for analyzing the discharge characteristics, chemical reaction path and spatio-temporal evolution characteristics of particle density of plasma catalytic ammonia synthesis from multiple time and space scales, so as to be able to explain the spatio-temporal evolution characteristics of electrons, anions, cations, neutral particles and surface adsorbed particles corresponding to the discharge stage and the afterglow stage of plasma catalytic ammonia synthesis at the microscopic level, and solve the problem that the reaction mechanism of plasma catalytic ammonia synthesis in the prior art is unclear. In addition, the multi-scale numerical simulation method for the reaction mechanism of plasma catalytic ammonia synthesis of the present invention can be used for the research of various plasma catalytic ammonia synthesis reaction mechanisms, without the need to carry out a large number of experiments, and can effectively guide the optimization and regulation of plasma catalytic ammonia synthesis, and has a wide application prospect in this field.

[0140] The above specific implementation manners are the preferred embodiments of the present invention and cannot limit the present invention. Any other changes or other equivalent replacement manners made without departing from the technical solutions of the present invention are included within the protection scope of the present invention.

Claims

1. A multi-scale numerical simulation method for the reaction mechanism of plasma-catalytic ammonia synthesis, characterized in that It includes the following steps: S1. Construct a two-dimensional geometric model of a plasma catalytic ammonia synthesis device, where the two-dimensional geometric model includes a discharge electrode, an electrode barrier medium, a plasma region, and catalyst particles; S2. Construct a plasma catalytic ammonia synthesis reaction system and a plasma discharge model, where the plasma discharge model includes a mass conservation equation, an electron average energy control equation, and a Poisson equation; S3. Obtain the spatial distribution of particle density generated by a single plasma discharge through simulation calculation using the plasma discharge model; S4. For the afterglow stage of plasma catalytic ammonia synthesis, construct a plasma catalytic ammonia synthesis reaction kinetic model to obtain the evolution characteristics and spatio-temporal distribution of active particles during the gap between two discharges; S5. Input the particle density obtained in step S4 into the plasma discharge model as the initial condition, and repeat steps S3 - S4 for simulation calculation of multiple discharge cycles until the particle density obtained in step S4 tends to a periodic stable value. After processing the simulation calculation results, obtain the discharge characteristics, chemical reaction path, and spatio-temporal evolution characteristics of particle density of plasma catalytic ammonia synthesis.

2. The multi-scale numerical simulation method for the plasma-catalytic ammonia synthesis reaction mechanism according to claim 1, wherein In step S1, the two-dimensional geometric model includes a high-voltage electrode, an upper electrode barrier medium, a plasma region, a lower electrode barrier medium, and a low-voltage electrode arranged in sequence from top to bottom. Catalyst particles are arranged between the upper electrode barrier medium and the lower electrode barrier medium.

3. The multi-scale numerical simulation method for the plasma-catalytic ammonia synthesis reaction mechanism according to claim 1, wherein In step S2, the plasma catalytic ammonia synthesis reaction system includes gas-phase chemical reactions and chemical reactions on the catalyst surface; The gas-phase chemical reactions include electron impact ionization, electron impact excitation, electron impact dissociation, electron attachment, electron-ion recombination, ion-ion recombination, charge exchange, three-body reactions, and vibrational-translational relaxation reactions; The chemical reactions on the catalyst surface include direct adsorption reactions, dissociative adsorption reactions, Elery Dill reaction, and Langmuir-Hinshelwood reactions.

4. The multi-scale numerical simulation method for the plasma-catalytic ammonia synthesis reaction mechanism according to claim 1, characterized in that, In step S2, the plasma discharge model includes a mass conservation equation, an electron average energy control equation, and a Poisson equation; the mass conservation equation includes an electron mass conservation equation, an ion and neutral particle mass conservation equation; The electron mass conservation equation is: where n e is the electron density, t is the time, denotes the divergence of a vector, and the electron flux Γ e is expressed as E is the electric field, μ e and D e represent the electron mobility coefficient and the diffusion coefficient respectively, and the electron source term R e is expressed as x j is the mole fraction of the heavy particles participating in the reaction, k j is the reaction rate constant, N n is the total particle number density, and M is the total number of reactions; The ion and neutral particle mass conservation equation is: where ρ is the density of the mixed gas, R i is the particle source term, ω i is the mass fraction of particle i, M n is the average molar mass, q i is the charge number carried by the particle, μ i is the mobility, and the expression for the mixture-averaged diffusion coefficient D i,m is D ij is the binary diffusion coefficient between particles i and j; The electron average energy control equation is: Where n ε is the average energy density of electrons, and the electron energy flux density Γ ε is expressed as Γ ε = The electron energy source term R ε is expressed as where e is the elementary charge, ΔE j and R intel,j are the energy loss and the corresponding reaction rate of inelastic collision reactions respectively, m e is the electron mass, M is the neutral particle mass, v en is the effective collision frequency between electrons and neutral particles, T g is the gas temperature, k b is the Boltzmann constant, and T e is the electron temperature; The Poisson equation is: In the formula, is the electric potential, ε r is the relative permittivity, ε0 is the vacuum permittivity, and ρ v is the space charge density.

5. The multi-scale numerical simulation method for the plasma-catalytic ammonia synthesis reaction mechanism according to claim 1, wherein, The specific process of step S3 is as follows: S31. Set the solution domain and boundary conditions for the plasma discharge model. Among them, in the two-dimensional geometric model, set the electric potential of the high-voltage electrode to V, the electric potential of the low-voltage electrode to zero, and the boundary conditions at the interfaces of the plasma region and the upper electrode barrier medium, the interfaces of the catalyst particles and the plasma region, and the interfaces of the plasma region and the lower electrode barrier medium are the same; S32. Set grid parameters for different solution domains and boundary conditions; S33. Configure the time unit, time step, and tolerance of the solver, and use the solver to solve to obtain the spatial distribution of particle density generated by a single plasma discharge.

6. The multi-scale numerical simulation method for the plasma-catalytic ammonia synthesis reaction mechanism according to claim 5, wherein S31 specifically includes: (1) Set the solution domain: The mass conservation equation and the electron average energy control equation are solved only in the plasma discharge region, and the Poisson equation is solved in the electrode region, the barrier medium region, the catalyst region, and the plasma discharge region; (2) Set the boundary conditions: The boundary condition of the electron mass conservation equation is: where n is the outward normal vector of the solid surface, Γ e is the electron flux, v e,th is the thermal velocity of the electrons, n e is the electron density, μ e is the electron mobility coefficient, a total of Q particles, γ i is the secondary electron emission coefficient of particle i, Γ i is the flux of particle i on the solid surface; The boundary condition of the electron average energy control equation is: where n ε is the average electron energy, Γ ε is the electron energy flux, μ ε is the electron energy transfer coefficient, ε i is the average initial energy of the secondary electrons emitted from the solid surface; The boundary conditions of the ion and neutral particle mass conservation equations are as follows: -Γ i ·n = M i R surf,i +M i c i μ i,m z i (n·E)((z i n·E)>0), Equation (7), where Γ i is the flux of particle i, M i is the molar mass of particle i, R surf,i is the surface reaction rate, c i is the mole fraction of particle i, μ i,m is the mixed average mobility, z i is the charge number of particle i; The boundary condition of the Poisson equation is: n·(D1 - D2) = ρ s , Equation (8), where D1 and D2 represent the electric displacement fields above and below the boundary, respectively, and ρ s is the charge density accumulated on the boundary surface, which is obtained from the following ordinary differential equation: where J e and J i are the electron and ion current densities at the boundary, respectively.

7. The multi-scale numerical simulation method for the plasma-catalytic ammonia synthesis reaction mechanism according to claim 5, characterized in that The grid parameters in step S32 include the grid shape, the grid division method, the maximum element size ratio adjustment coefficient, the element growth rate, and the grid curvature coefficient.

8. The multi-scale numerical simulation method for the plasma-catalytic ammonia synthesis reaction mechanism according to claim 1, characterized in that, The specific process of step S4 is as follows: S41. For the afterglow stage of plasma-catalytic ammonia synthesis, construct a reaction kinetic model for plasma-catalytic ammonia synthesis; In step S4, the reaction kinetic model for plasma-catalytic ammonia synthesis includes the Navier-Stokes equation, the continuity equation, and the convection-diffusion equation; The Navier-Stokes equation is: The continuity equation is: The convection-diffusion equation is: In the formula, u is the fluid velocity, ρ is the density of the mixed gas, p is the pressure, η is the dynamic viscosity coefficient of the mixed gas, I is the unit vector matrix, F is the volume force vector, Di is the diffusion coefficient of the i-th particle in the mixed gas, and Mn is the average molar mass; S42. Solve to obtain the evolution characteristics and spatio-temporal distribution of active particles in the discharge gap for two times; Solve the formulas (10), (11), and (12) corresponding to the Navier-Stokes equation, the continuity equation, and the convection-diffusion equation, and calculate the evolution characteristics and spatio-temporal distribution of active particles in the discharge gap for two times.

9. The multi-scale numerical simulation method for the plasma-catalytic ammonia synthesis reaction mechanism according to claim 1, characterized in that, The specific process of step S5 is as follows: Input the particle density corresponding to the particles generated by a single plasma discharge obtained in the initial completion of step S3 into the plasma discharge model as the initial condition, repeat steps S3 - S4 to simulate and calculate multiple discharge cycles until the particle density obtained in step S4 tends to a periodic stable value, process the obtained simulation results to obtain the particle density and reaction rate distribution maps generated by multiple discharges, generate the core reaction path of plasma-catalytic ammonia synthesis at different time scales, and obtain the discharge characteristics, chemical reaction path, and spatio-temporal evolution characteristics of particle density of plasma-catalytic ammonia synthesis.

10. The multi-scale numerical simulation method for the plasma-catalytic ammonia synthesis reaction mechanism according to claim 9, characterized in that, The discharge characteristics, chemical reaction path, and spatio-temporal evolution characteristics of particle density of plasma-catalytic ammonia synthesis include the particle density generated by multiple discharges, the reaction rate distribution map, and the generation of the core reaction path of plasma-catalytic ammonia synthesis at different time scales.

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