Analog simulation method based on NOx removal model

Abstract

The invention provides an analog simulation method based on a NOx removal model, and belongs to the technical field of gas separation, and the analog simulation method comprises the following steps: constructing a cyclone separator model, carrying out grid division on the constructed cyclone separator model, and carrying out urea injection parameter setting; constructing a drag force model, and simulating the movement behavior of the urea liquid drops in the airflow in the cyclone separator; constructing a chemical reaction rate model, and simulating evaporation of urea, generation of ammonia gas and a reduction reaction of the ammonia gas and NOx; acquiring actual working condition data of NOx removal, and setting boundary conditions of the cyclone separator model based on the actual working condition data; and determining input data of analog simulation, respectively inputting the input data into the models, and performing model optimization based on output results of all the models. According to the method, NOx removal can be accurately and efficiently simulated, the adaptability and prediction precision of the model are improved, the experiment cost is reduced, the efficiency of urea injection and NOx reduction is optimized, and more efficient industrial denitration analog simulation is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of gas separation, and in particular to a simulation method based on a NOx removal model. Background Art

[0002] Cyclone separators are often used for flue gas purification, but the coupled simulation of urea pyrolysis and NOx reduction reactions is not yet mature. Traditional models often ignore the motion and evaporation characteristics of urea droplets and lack a comprehensive description of complex airflow and chemical reaction dynamics, resulting in low simulation accuracy. Drag models, urea injection parameters, and chemical reaction rate models play a key role in these simulations, but the individual application of these models is difficult to accurately predict the overall denitrification effect, especially under complex industrial conditions.

[0003] Therefore, the present invention provides a simulation method based on the NOx removal model. Summary of the invention

[0004] The present invention provides a simulation method based on a NOx removal model. The separator model is constructed, the constructed cyclone separator model is gridded, urea injection parameters are set, a drag model and a chemical reaction rate model are constructed, the boundary conditions of the cyclone separator model are set according to actual operating data of NOx removal, the input data of the simulation is determined, and the data is input into the model respectively. The model is optimized based on the output results of all models. The NOx removal can be simulated accurately and efficiently, the adaptability and prediction accuracy of the model are improved, the experimental cost is reduced, the efficiency of urea injection and NOx reduction is optimized, and a more efficient industrial denitrification simulation is achieved.

[0005] The present invention provides a simulation method based on a NOx removal model, comprising: 101: Construct a cyclone separator model, mesh the constructed cyclone separator model, and set urea injection parameters; 102: Construct a drag model to simulate the motion behavior of urea droplets in the airflow in the cyclone separator; 103: Construct a chemical reaction rate model to simulate the evaporation of urea, the generation of ammonia, and the reduction reaction of ammonia and NOx; 104: Acquire actual operating data of NOx removal, and set boundary conditions of the cyclone separator model based on the actual operating data; 105: Determine input data for simulation, input the input data into the models respectively, and optimize the models based on the output results of all the models.

[0006] According to a simulation method based on a NOx removal model provided by the present invention, a cyclone separator model is constructed, grid division is performed on the constructed cyclone separator model, and urea injection parameters are set, including: Determining design parameters of the cyclone separator model, and constructing the cyclone separator model based on the design parameters of the cyclone separator model, wherein the design parameters of the cyclone separator model include all regions of the cyclone separator model; Determine a critical region based on all regions in the design parameters of the cyclone separator model, wherein the critical region includes a plurality of regions; Determine a refinement region of each region in the key region, set a first grid size of the refinement region of each region in the key region, and set a second grid size of all regions of each region in the key region except the refinement region; determining a third grid size in each of all regions of the cyclone separator except the critical region; Using the Cartesian grid generation technology built into the Barracuda software, meshing the corresponding areas in the key area based on the first grid size and the second grid size, and meshing the corresponding areas other than the key area based on the third grid size; Set urea injection parameters based on Barracuda software.

[0007] According to a simulation method based on a NOx removal model provided by the present invention, a drag model is constructed to simulate the movement behavior of urea droplets in the airflow in a cyclone separator, including: Determine urea droplet concentration, particle mass, particle volume fraction, fluid properties, and particle velocity based on the cyclone model sub-output results of the cyclone model; determining multiple fluids and fluid velocities based on fluid properties; a function for determining fluid and particle properties and flow conditions based on particle mass, particle volume fraction, fluid velocity, and particle velocity; in, is a function of the fluid f and particle p properties and flow conditions, represents the particle mass of particle p, represents the velocity of the fluid f, represents the particle velocity of particle p, D represents the drag function, represents the first sub-drag function, D2 represents the second sub-drag function, represents the particle volume fraction of the largest packed particles cp, represents the particle volume fraction of particle p, is the drag coefficient, represents the first Reynolds number, represents the fluid volume fraction of fluid f; A drag model is constructed based on the functions of fluid and particle properties and flow conditions to simulate the motion behavior of urea droplets in the airflow inside the cyclone separator.

[0008] According to a simulation method based on a NOx removal model provided by the present invention, constructing a chemical reaction rate model includes constructing a droplet evaporation model, constructing a urea thermal decomposition model, and constructing an SNCR reaction model.

[0009] According to a simulation method based on a NOx removal model provided by the present invention, a droplet evaporation model is constructed, including: Based on the drag model sub-input data of the drag model, the droplet velocity, droplet temperature, droplet mass, droplet diameter, droplet surface area, and droplet density are determined: A heat balance equation for determining the temperature of the droplet based on the mass of the droplet, the temperature of the droplet, and the surface area of ​​the droplet; in, represents the droplet mass of droplet d, represents the constant-pressure specific heat capacity of droplet d, represents the continuous phase temperature, represents the droplet temperature of droplet d, represents the rate of change of droplet temperature with time, represents the convective heat transfer coefficient between the droplet and the continuous phase, A represents the effective surface area for convective heat transfer between the droplet and the continuous phase, represents the evaporation rate of droplet d, represents the latent heat of vaporization of the droplet, represents the droplet surface area of ​​the droplet d, represents the particle blackness of droplet d, represents the Stefan-Boltzmann constant, and , represents the radiation temperature of the radiation R; When the droplet temperature reaches the evaporation temperature, the droplet begins to evaporate and will not stop until the volatile components of the droplet are completely precipitated or the particle temperature reaches the boiling temperature of the droplet; When the droplets undergo evaporation and mass transfer, determine the diffusion rate of the droplets into the gas phase and the vapor concentration gradient between the urea solution droplets and the gas flow; in, represents the vapor molar flow rate of substance i in the droplet, represents the mass transfer coefficient of substance i in the droplet, represents the vapor concentration of the surface s of the substance i in the droplet, represents the gas phase region away from the substance i in the droplet The steam concentration of the air flow; Determine the mass transfer equation for droplet evaporation based on the molar flow rate of the vapor, the mass of the droplet, and the surface area of ​​the droplet; in, Indicates time The mass of the droplet d is, represents the droplet mass of droplet d at the current time t, represents the molar mass of substance i in the droplet; When the temperature of the droplet reaches the boiling temperature and the volatile matter of the droplet has not been completely precipitated, the droplet begins to boil. Considering the radiation heat transfer of the particles, the boiling evaporation rate equation is determined; in, represents the rate of change of droplet diameter over time, represents the droplet diameter of the droplet d, is the gas phase thermal conductivity, represents the droplet density of droplet d, It represents the second Reynolds number defined by the diameter of the droplet d as the qualitative size and the relative velocity between the droplet d and the fluid f; Based on the heat balance equation of droplet temperature, the mass transfer equation of droplet evaporation and the boiling evaporation rate equation, a droplet evaporation model was constructed to simulate the evaporation process of urea solution.

[0010] According to a simulation method based on a NOx removal model provided by the present invention, a urea pyrolysis model is constructed, comprising: Determine the pyrolysis reaction equation, and build a urea pyrolysis model based on the pyrolysis reaction equation to simulate the generation of ammonia; The urea pyrolysis process includes: the water in the urea solution gradually evaporates, the urea solution becomes solid urea, the solid urea begins to melt into liquid urea at 406K, the liquid urea changes from a molten state to gaseous urea at 413K, and the gaseous urea is completely decomposed into ammonia and isocyanic acid at 425K.

[0011] According to a simulation method based on a NOx removal model provided by the present invention, a SNCR reaction model is constructed, including: The reduction reaction equation of ammonia and NOx reduction is determined, and a SNCR reaction model is constructed based on the reduction reaction equation to simulate the reduction reaction of ammonia and NOx.

[0012] According to a simulation method based on a NOx removal model provided by the present invention, input data includes cyclone separator model sub-input data, drag model sub-input data, droplet evaporation model sub-input data, urea pyrolysis model sub-input data and SNCR reaction model sub-input data; The output results include cyclone separator model sub-output results, drag model sub-output results, droplet evaporation model sub-output results, urea pyrolysis model sub-output results and SNCR reaction model sub-output results; Based on the sub-output results of each model, the corresponding model is optimized.

[0013] Compared with the prior art, the present invention has the following beneficial effects: By constructing a separator model, meshing the constructed cyclone separator model, setting urea injection parameters, and constructing a drag model and a chemical reaction rate model, the boundary conditions of the cyclone separator model are set according to the actual operating data of NOx removal, the input data of the simulation is determined, and input into the model respectively. The model is optimized based on the output results of all models, which can accurately and efficiently simulate NOx removal, improve the adaptability and prediction accuracy of the model, reduce experimental costs, optimize the efficiency of urea injection and NOx reduction, and achieve more efficient industrial denitrification simulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0015] Figure 1 It is a flow chart of a simulation method based on a NOx removal model provided in an embodiment of the present invention.

[0016] Figure 2 It is a three-dimensional geometric diagram of a cyclone separator model based on a simulation method of a NOx removal model provided in an embodiment of the present invention.

[0017] Figure 3 It is a urea injection point position diagram of a simulation method based on a NOx removal model provided in an embodiment of the present invention.

[0018] Figure 4 It is a parameter diagram of a simulation method based on a NOx removal model provided in an embodiment of the present invention.

[0019] Figure 5 It is a chemical reaction equation and reaction kinetic diagram in a urea pyrolysis model of a simulation method based on a NOx removal model provided by an embodiment of the present invention.

[0020] Figure 6It is a reaction kinetics diagram in a SNCR reaction model of a simulation method based on a NOx removal model provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] Embodiment 1: The embodiment of the present invention provides a simulation method based on a NOx removal model, such as Figure 1 As shown, including: 101: Construct a cyclone separator model, mesh the constructed cyclone separator model, and set urea injection parameters; 102: Construct a drag model to simulate the motion behavior of urea droplets in the airflow in the cyclone separator; 103: Construct a chemical reaction rate model to simulate the evaporation of urea, the generation of ammonia, and the reduction reaction of ammonia and NOx; 104: Acquire actual operating data of NOx removal, and set boundary conditions of the cyclone separator model based on the actual operating data; 105: Determine input data for simulation, input the input data into the models respectively, and optimize the models based on the output results of all the models.

[0023] In this embodiment, the SNCR denitrification area of ​​the coal-fired boiler occurs in the cyclone separator. The flue gas of the coal-fired boiler enters the cyclone separator after leaving the furnace, and the reducing agent urea solution is sprayed at the inlet of the cyclone separator.

[0024] In this embodiment, the cyclone separator model includes an air flow inlet, an air flow outlet, a urea injection area, a reaction area, and the like.

[0025] In this embodiment, the Cartesian grid generation technology built into the Barracuda software is used for grid division. The grid generator can handle complex geometric structures, has good grid adaptation effect, and can quickly generate high-quality grids required for numerical simulation.

[0026] In this embodiment, according to the position and number of urea injection points, a preliminary design is performed for the benchmark working condition, and then an optimization is performed. For the benchmark working condition, the injection point position is as follows: Figure 3 shown.

[0027] In this embodiment, Barracuda has built-in pressure boundary conditions and velocity boundary conditions. The relevant parameters used in the simulation are as follows: Figure 4 shown.

[0028] In this embodiment, constructing a chemical reaction rate model includes setting the chemical reaction rate. The Barracuda software has built-in fully functional chemical reaction models, including the Euler volume average reaction model and the Lagrangian discrete reaction model. The former is mainly used for reactions between different components of a gas, and the latter is mainly used for chemical reactions of discrete particles.

[0029] In this embodiment, Barracuda has a built-in GPU parallel solver, which can achieve a speedup of dozens of times compared to traditional CPU parallel. Barracuda software has a built-in post-processing tool tecplot for post-processing, including a cyclone separator simulation of NO mass concentration (standard state, dry state, 6% O2) distribution cloud map. Based on the cloud map, the distribution state of NO in the separator can be intuitively obtained, and the mass concentration of the inlet and outlet can be extracted.

[0030] In this embodiment, after setting the boundary conditions, a numerical solution method is used to perform simulation calculations. During the numerical solution process, the flow field, temperature field, evaporation and pyrolysis of urea droplets, ammonia generation, and NOx reduction process are gradually simulated. This step is the core of the entire simulation process. Combined with the previous models and conditions, key parameters such as urea distribution, ammonia generation, and NOx concentration changes are calculated.

[0031] In this embodiment, the output results of all models (including flow field, temperature field, chemical reaction rate, NOx concentration distribution, etc.) provide detailed information on NOx reduction efficiency, urea evaporation and pyrolysis process. By analyzing these results, the influencing factors of temperature distribution, reaction rate and mixing effect can be found, and then the urea injection parameters, reactor temperature or flow field design can be adjusted according to the analysis results to further optimize the NOx reduction effect.

[0032] The beneficial effects of the above technical solution are as follows: by constructing a separator model, meshing the constructed cyclone separator model, setting urea injection parameters, constructing a drag model and a chemical reaction rate model, setting the boundary conditions of the cyclone separator model according to the actual operating data of NOx removal, determining the input data of the simulation, and inputting them into the model respectively, and optimizing the model based on the output results of all models, NOx removal can be simulated accurately and efficiently, the adaptability and prediction accuracy of the model can be improved, the experimental cost can be reduced, the efficiency of urea injection and NOx reduction can be optimized, and a more efficient industrial denitrification simulation can be achieved.

[0033] Embodiment 2: The embodiment of the present invention provides a simulation method based on a NOx removal model, constructs a cyclone separator model, meshes the constructed cyclone separator model, and sets urea injection parameters, including: Determining design parameters of the cyclone separator model, and constructing the cyclone separator model based on the design parameters of the cyclone separator model, wherein the design parameters of the cyclone separator model include all regions of the cyclone separator model; Determine a critical region based on all regions in the design parameters of the cyclone separator model, wherein the critical region includes a plurality of regions; Determine a refinement region of each region in the key region, set a first grid size of the refinement region of each region in the key region, and set a second grid size of all regions of each region in the key region except the refinement region; determining a third grid size in each of all regions of the cyclone separator except the critical region; Using the Cartesian grid generation technology built into the Barracuda software, meshing the corresponding areas in the key area based on the first grid size and the second grid size, and meshing the corresponding areas other than the key area based on the third grid size; Set urea injection parameters based on Barracuda software.

[0034] In this embodiment, the design parameters of the cyclone separator model are determined. These parameters define all geometric and operating characteristics of the device, including all internal areas (such as air flow channels, separation areas, etc.). Based on these parameters, a detailed three-dimensional model can be established to simulate the working state of the cyclone separator.

[0035] In this embodiment, the "key areas" that have a greater impact on the simulation results are determined based on the effects of different areas in the cyclone separator model. These key areas may include places where the airflow changes dramatically or areas where urea droplets evaporate and chemical reactions occur. These areas require higher simulation accuracy, so the grid must be refined during division.

[0036] In this embodiment, the key areas are further divided into refined areas, which require a smaller grid size (first grid size) to ensure simulation accuracy, and the remaining key areas can use a slightly larger grid size (second grid size) to balance computational efficiency and accuracy.

[0037] In this embodiment, a larger grid size (third grid size) is used for other areas in the cyclone separator model that are not divided into key areas, because these areas have little impact on the simulation results, and appropriately reducing the grid density can reduce the consumption of computing resources.

[0038] In this embodiment, the Cartesian grid generation technology built into the Barracuda software is used. This technology can effectively generate grids, especially for complex geometric structures. Barracuda accurately divides different areas in the model based on the different grid sizes (first, second, and third grid sizes) defined previously, ensuring a balance between computational efficiency and simulation accuracy.

[0039] The beneficial effects of the above technical solution are as follows: constructing a cyclone separator model, meshing the constructed cyclone separator model, and setting urea injection parameters, which can ensure the accuracy of key areas while reducing the consumption of computing resources in other areas. Combined with the urea injection parameter setting, efficient and accurate NOx removal simulation can be achieved.

[0040] Embodiment 3: The embodiment of the present invention provides a simulation method based on a NOx removal model, constructs a drag model, and simulates the motion behavior of urea droplets in the airflow in a cyclone separator, including: Determine urea droplet concentration, particle mass, particle volume fraction, fluid properties, and particle velocity based on the cyclone model sub-output results of the cyclone model; determining multiple fluids and fluid velocities based on fluid properties; a function for determining fluid and particle properties and flow conditions based on particle mass, particle volume fraction, fluid velocity, and particle velocity; in, is a function of the fluid f and particle p properties and flow conditions, represents the particle mass of particle p, represents the velocity of the fluid f, represents the particle velocity of particle p, D represents the drag function, represents the first sub-drag function, D2 represents the second sub-drag function, represents the particle volume fraction of the largest packed particles cp, represents the particle volume fraction of particle p, is the drag coefficient, represents the first Reynolds number, represents the fluid volume fraction of fluid f; A drag model is constructed based on the functions of fluid and particle properties and flow conditions to simulate the motion behavior of urea droplets in the airflow inside the cyclone separator.

[0041] In this embodiment, Barracuda has built-in a variety of drag models, which can realize the calculation of dilute phase flow and dense phase flow at the same time. Typical drag models include Wen-Yu drag model, Ergun drag model, and WenYu-Ergun model. When simulating pneumatic conveying with fewer particles, the Wen-Yu drag model is more appropriate; when simulating the phenomenon of dense accumulation of particles, the Ergun drag model should be used; when simulating the situation where sparse and dense particles exist at the same time, the WenYu-Ergun drag model is more appropriate.

[0042] In this embodiment, for the urea injection model, the volume fraction of particles is almost below 10%, which belongs to the dilute phase flow. The particle aggregation that may exist locally can be calculated using the Ergun model. Therefore, in the present invention, the WenYu-Ergun model is the most suitable drag model for particles, and the particle movement process described by the model is closer to the actual situation.

[0043] In this embodiment, the drag model is used to simulate the movement of urea droplets in the airflow. After being sprayed, the urea droplets will be affected by the airflow, and the drag model is used to calculate the drag effect of the airflow on the droplets to ensure that the droplets can be reasonably distributed and reach the appropriate reaction area.

[0044] In this embodiment, the urea droplet concentration refers to the number or mass of urea droplets per unit volume.

[0045] In this embodiment, the first Reynolds number reflects the influence of the fluid flow state on the drag coefficient.

[0046] In this embodiment, the particle volume fraction represents the volume ratio occupied by the particles in the airflow, reflecting the distribution density of the particles in the airflow.

[0047] In this embodiment, the fluid velocity refers to the velocity of the airflow in the cyclone separator, which determines the force applied to the particles in the airflow.

[0048] In this embodiment, the particle velocity refers to the velocity of the particle relative to the airflow, which is usually different from the airflow velocity because the particle has inertia and is subject to different forces.

[0049] In this embodiment, the fluid properties include the density and viscosity of the gas, which determine the flow mode of the gas and the impact on the particles.

[0050] In this embodiment, the particle characteristics such as particle diameter, density, shape, etc., determine the drag force on the particle in the airflow.

[0051] In this embodiment, the flow conditions include the difference in air flow velocity, particle velocity, turbulence intensity in the air flow, etc. The function is used to simulate the interaction between the fluid and the particles.

[0052] In this embodiment, a model for simulating drag is constructed based on the above-mentioned characteristics of the fluid and particles, as well as a function of the flow conditions. The drag model is mainly used to describe the resistance exerted by the airflow on urea droplets or particles, which affects the movement trajectory of the particles. The magnitude of the drag depends on factors such as the speed of the particles, the speed difference between the particles and the gas, and the viscosity of the gas. Through the drag model, the movement trajectory of urea droplets in the cyclone separator can be predicted, so as to understand how they evaporate, release ammonia and react with NOx.

[0053] In this embodiment, in the cyclone separator, the fluid usually contains a mixture of gas and solid particles, which belongs to multiphase flow. The properties of the fluid not only depend on the gas phase (such as the velocity, pressure, and temperature of the flue gas), but are also affected by the presence of solid particles, such as the mass, volume fraction, and velocity of the particles, which will change the overall properties of the fluid.

[0054] In this embodiment, the interaction between fluid and particles: The interaction between gas and particles (such as drag force, collision, viscosity, etc.) will affect the movement and characteristics of the fluid. For example, when the particle concentration is high, the flow resistance of the gas will increase, and the viscosity, density and other properties of the fluid will also change accordingly.

[0055] In this embodiment, local characteristics change: the flow field in the cyclone separator is complex, and the fluid characteristics (such as velocity, pressure, turbulence intensity, etc.) in different regions will change with position. At the same time, due to the uneven distribution of particles, the local fluid characteristics will also be different. The fluid may show different flow patterns (such as laminar flow, turbulent flow, etc.) in different regions of the separator, so its characteristics will also change with position.

[0056] In this embodiment, the fluid at different positions in the separator may present different velocity distributions, pressure gradients and turbulence intensities, resulting in significant differences in local fluid properties. Fluid properties (such as density, viscosity, etc.) may be affected by factors such as temperature, pressure, and chemical composition. In actual working conditions, the temperature, pressure and other parameters of the fluid in different areas may be different, resulting in changes in the local properties of the fluid.

[0057] The beneficial effects of the above technical solution are as follows: by constructing a drag model to simulate the movement behavior of urea droplets in the airflow in the cyclone separator, the model's accuracy in capturing the interaction between fluid and particles can be improved, making the simulation closer to actual working conditions, which helps to optimize the urea injection strategy and improve the NOx removal efficiency.

[0058] Embodiment 4: The embodiment of the present invention provides a simulation method based on a NOx removal model. Constructing a chemical reaction rate model includes constructing a droplet evaporation model, constructing a urea thermal decomposition model, and constructing an SNCR reaction model.

[0059] In this embodiment, after the drag model determines the motion behavior of the droplets, the next step is to simulate the evaporation process of the droplets. The droplets will gradually evaporate due to heat in the high-temperature airflow. The evaporation model is responsible for calculating the evaporation rate of the droplets and the heat required. The motion position of the droplets (determined by the drag model) and the airflow temperature (defined in the geometric model and mesh) jointly determine the evaporation rate.

[0060] In this embodiment, after the droplets evaporate, the gaseous urea begins to pyrolyze and decompose into ammonia (NH3) and ammonium cyanate (HNCO). The pyrolysis model calculates the chemical decomposition rate and conditions based on the amount of urea gas provided by the evaporation process, and ensures that ammonia is released in time within the appropriate temperature window for the NOx reduction reaction.

[0061] In this embodiment, ammonia generated by urea thermal decomposition is the key reducing agent of the SNCR reaction. The ammonia generated by thermal decomposition reacts with NOx in the reaction area of ​​the cyclone separator model. The SNCR reaction model is used to simulate the reaction process of ammonia and NOx. The reaction rate depends on the concentration of ammonia (provided by urea thermal decomposition), the concentration of NOx and the local temperature. The three together determine the efficiency of NOx reduction.

[0062] In this embodiment, after the SNCR reaction model is constructed, it is necessary to set the boundary conditions of the simulation. These boundary conditions include the velocity, temperature, NOx concentration at the air flow inlet, and the urea injection rate and temperature. The setting of the boundary conditions ensures that the simulation environment is consistent with the actual operating conditions, so as to more accurately simulate the NOx reduction process in actual operation.

[0063] The beneficial effects of the above technical solution are as follows: by determining the chemical reaction rate model, the denitrification efficiency can be optimized and a more efficient and accurate NOx removal simulation can be achieved.

[0064] Embodiment 5: The embodiment of the present invention provides a simulation method based on a NOx removal model to construct a droplet evaporation model, including: Based on the drag model sub-input data of the drag model, the droplet velocity, droplet temperature, droplet mass, droplet diameter, droplet surface area, and droplet density are determined: A heat balance equation for determining the temperature of the droplet based on the mass of the droplet, the temperature of the droplet, and the surface area of ​​the droplet; in, represents the droplet mass of droplet d, represents the constant-pressure specific heat capacity of droplet d, represents the continuous phase temperature, represents the droplet temperature of droplet d, represents the rate of change of droplet temperature with time, represents the convective heat transfer coefficient between the droplet and the continuous phase, A represents the effective surface area for convective heat transfer between the droplet and the continuous phase, represents the evaporation rate of droplet d, represents the latent heat of vaporization of the droplet, represents the droplet surface area of ​​the droplet d, represents the particle blackness of droplet d, represents the Stefan-Boltzmann constant, and , represents the radiation temperature of the radiation R; When the droplet temperature reaches the evaporation temperature, the droplet begins to evaporate and will not stop until the volatile components of the droplet are completely precipitated or the particle temperature reaches the boiling temperature of the droplet; When the droplets undergo evaporation and mass transfer, determine the diffusion rate of the droplets into the gas phase and the vapor concentration gradient between the urea solution droplets and the gas flow; in, represents the vapor molar flow rate of substance i in the droplet, represents the mass transfer coefficient of substance i in the droplet, represents the vapor concentration of the surface s of the substance i in the droplet, represents the gas phase region away from the substance i in the droplet The steam concentration of the air flow; Determine the mass transfer equation for droplet evaporation based on the molar flow rate of the vapor, the mass of the droplet, and the surface area of ​​the droplet; in, Indicates time The mass of the droplet d is, represents the droplet mass of droplet d at the current time t, represents the molar mass of substance i in the droplet; When the temperature of the droplet reaches the boiling temperature and the volatile matter of the droplet has not been completely precipitated, the droplet begins to boil. Considering the radiation heat transfer of the particles, the boiling evaporation rate equation is determined; in, represents the rate of change of droplet diameter over time, represents the droplet diameter of the droplet d, is the gas phase thermal conductivity, represents the droplet density of droplet d, It represents the second Reynolds number defined by the diameter of the droplet d as the qualitative size and the relative velocity between the droplet d and the fluid f; Based on the heat balance equation of droplet temperature, the mass transfer equation of droplet evaporation and the boiling evaporation rate equation, a droplet evaporation model was constructed to simulate the evaporation process of urea solution.

[0065] In this embodiment, the droplet velocity refers to the moving speed of the droplet relative to the airflow.

[0066] In this embodiment, the droplet temperature is an important variable in the droplet heat transfer process, which directly affects the evaporation rate.

[0067] In this embodiment, the convection heat transfer coefficient represents the amount of heat transferred through a unit area per unit time under a unit temperature difference during the convection heat transfer process, and reflects the speed of the convection heat transfer.

[0068] In this embodiment, the latent heat of vaporization refers to the heat absorbed by a unit mass of a substance when it changes from liquid to gas at a certain temperature.

[0069] In this embodiment, the droplet mass refers to the mass of the droplet, which gradually decreases as it evaporates.

[0070] In this embodiment, the droplet diameter refers to the size of the droplet, which generally decreases as it evaporates.

[0071] In this embodiment, the droplet surface area refers to the surface area of ​​the droplet in contact with the airflow, which determines the evaporation rate. The droplet surface area is closely related to the droplet diameter.

[0072] In this embodiment, the droplet density means that the density of the droplet is affected by temperature, and the density may change when the temperature of the droplet increases.

[0073] In this embodiment, a heat balance equation is constructed based on the mass, temperature and surface area of ​​the droplets. The equation describes the heat transfer process between the droplets and the surrounding airflow, involving the absorption or release of heat by the droplets. The temperature change of the droplets can be calculated through the heat balance equation to determine when the droplets reach the critical temperature of evaporation or boiling.

[0074] In this embodiment, when the temperature of the droplet reaches its evaporation temperature, the droplet begins to evaporate. During the evaporation process, the droplet continues to lose mass until the volatile components are completely evaporated or the temperature of the droplet reaches the boiling temperature, and then the droplet stops evaporating.

[0075] In this embodiment, during evaporation, urea or other volatile components in the droplets diffuse into the airflow, and the diffusion rate is affected by the vapor concentration gradient between the droplet surface and the airflow. The larger the concentration gradient, the faster the diffusion rate, which can describe the diffusion process of the substance in the droplet from liquid to gas.

[0076] In this embodiment, a mass transfer equation is established based on the molar flow rate of the vapor (indicating the flow rate of the vapor during the evaporation of the droplets), the mass of the droplets, and the surface area of ​​the droplets. The equation describes the mass loss rate of the droplets during the evaporation process, that is, how the mass of the droplets decreases over time.

[0077] In this embodiment, when the temperature of the droplets reaches their boiling temperature and the volatile components in the droplets are not completely precipitated, the droplets will enter a boiling state. During the boiling process, the radiation heat transfer effect of the particles needs to be considered, which affects the heat transfer and boiling rate of the droplets to determine the evaporation rate of the droplets during boiling.

[0078] In this embodiment, a complete droplet evaporation model is constructed based on the previously constructed heat balance equation, mass transfer equation and boiling evaporation rate equation. The model is used to simulate the evaporation and boiling process of urea solution droplets in the cyclone separator airflow, and predict how the droplets gradually evaporate and release volatile substances as the temperature rises until they are completely evaporated or boiled.

[0079] The beneficial effects of the above technical solution are as follows: a droplet evaporation model is constructed to simulate the evaporation process of urea solution, which can accurately simulate the evaporation and boiling process of urea droplets at different temperatures, enhance the simulation accuracy of urea thermal decomposition and evaporation behavior, optimize the denitrification efficiency and enhance the industrial application value of the simulation.

[0080] Embodiment 6: The embodiment of the present invention provides a simulation method based on a NOx removal model to construct a urea pyrolysis model, including: Determine the pyrolysis reaction equation, and build a urea pyrolysis model based on the pyrolysis reaction equation to simulate the generation of ammonia; The urea pyrolysis process includes: the water in the urea solution gradually evaporates, the urea solution becomes solid urea, the solid urea begins to melt into liquid urea at 406K, the liquid urea changes from a molten state to gaseous urea at 413K, and the gaseous urea is completely decomposed into ammonia and isocyanic acid at 425K.

[0081] In this embodiment, gaseous isocyanic acid then reacts with gaseous water to produce ammonia and carbon dioxide. The urea thermal decomposition rate is lower than the evaporation rate of water in the solution. The thermal decomposition reaction rate of urea is limited by kinetic parameters. The chemical reaction equation and reaction kinetic parameters are as follows: Figure 5 shown.

[0082] In this embodiment, based on the pyrolysis reaction equation and the state changes of urea at different temperatures, a urea pyrolysis model can be constructed. This model can simulate the generation process of ammonia and predict how urea decomposes to generate ammonia and isocyanic acid at different temperatures and conditions. The beneficial effects of the above technical solution are as follows: a urea pyrolysis model is constructed to simulate the generation of ammonia, which can efficiently predict the generation of ammonia, improve the accuracy and control ability of the denitrification process, and enhance the effect of industrial application.

[0083] Embodiment 7: The embodiment of the present invention provides a simulation method based on a NOx removal model to construct a SNCR reaction model, including: The reduction reaction equation of ammonia and NOx reduction is determined, and a SNCR reaction model is constructed based on the reduction reaction equation to simulate the reduction reaction of ammonia and NOx.

[0084] In this embodiment, the mainstream urea denitrification model adopts a 7-step total package reaction. Thanh et al. modified the model in 2008. The reaction kinetics are as follows: Figure 6 shown.

[0085] In this embodiment, the SNCR system flue gas denitrification process includes the following four process steps: receiving and storing reducing agent; metering output of reducing agent, mixing and diluting with water or air; spraying the diluted reducing agent at a suitable position in the furnace; mixing the reducing agent with flue gas to carry out denitrification reaction.

[0086] In this embodiment, the phenomenon that ammonia that does not participate in the reaction in the flue gas is discharged into the flue gas through the reactor during the denitration reaction is called ammonia escape. Ammonia escape may cause the following problems: it is easy to cause ash accumulation and blockage of downstream devices such as air preheaters, resulting in increased pressure loss and low-temperature corrosion; it affects the quality of fly ash, causing ash accumulation on the poles of the electrostatic precipitator or sticking of the bag filter; it forms a visible smoke column, increasing PM2.5 emissions; and it has a negative impact on human health when released into the atmosphere.

[0087] The beneficial effects of the above technical solution are as follows: constructing an SNCR reaction model to simulate the reduction reaction of ammonia and NOx can optimize the reaction control of the denitrification process, improve the NOx removal efficiency, and enhance the accuracy and performance of the industrial denitrification system.

[0088] Embodiment 8: The embodiment of the present invention provides a simulation method based on a NOx removal model, wherein input data includes cyclone separator model sub-input data, drag model sub-input data, droplet evaporation model sub-input data, urea pyrolysis model sub-input data, and SNCR reaction model sub-input data; The output results include cyclone separator model sub-output results, drag model sub-output results, droplet evaporation model sub-output results, urea pyrolysis model sub-output results and SNCR reaction model sub-output results; Based on the sub-output results of each model, the corresponding model is optimized.

[0089] In this embodiment, the cyclone separator model input data may include gas flow rate, solid particle diameter, density, temperature, etc.

[0090] In this embodiment, the drag model input data may include velocity, size, density, fluid viscosity, etc. of droplets or particles.

[0091] In this embodiment, the sub-input data of the droplet evaporation model may include the initial temperature of the droplet, the mass of the droplet, the diameter of the droplet, the air flow temperature, the relative humidity, etc.

[0092] In this embodiment, the urea pyrolysis model sub-input data may include the initial temperature, mass, activation energy and reaction rate constant of the decomposition reaction of the urea particles, etc.

[0093] In this embodiment, the SNCR reaction model sub-input data may include the concentrations of ammonia and NOx, reaction temperature, gas flow velocity and other chemical reaction parameters.

[0094] In this embodiment, the cyclone separator model optimization can optimize the separation efficiency and reduce the particle content entering the subsequent reaction process.

[0095] In this embodiment, the drag model optimization can optimize the motion trajectory of the droplets or particles, ensuring that the droplets can remain in the reaction zone long enough to complete evaporation or reaction.

[0096] In this embodiment, the droplet evaporation model optimization can optimize the evaporation rate of the droplets, ensuring that the urea droplets can fully evaporate and generate ammonia.

[0097] In this embodiment, the urea pyrolysis model optimization can optimize the generation rates of ammonia and isocyanic acid by adjusting the reaction parameters of urea pyrolysis, thereby ensuring that the reaction process is carried out within a suitable temperature range.

[0098] In this embodiment, the SNCR reaction model optimization can optimize the reaction efficiency of ammonia and NOx, reduce NOx emissions, and improve the denitrification efficiency by adjusting the reaction temperature or the molar ratio of ammonia / NOx.

[0099] The beneficial effects of the above technical solution are as follows: determining the input data of the simulation, inputting the input data into the model respectively, and optimizing the model based on the output results of all models, which can accurately and efficiently simulate NOx removal, improve the adaptability and prediction accuracy of the model, reduce experimental costs, optimize the efficiency of urea injection and NOx reduction, and achieve more efficient industrial denitrification simulation.

[0100] The device embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative labor.

[0101] Through the description of the above implementation methods, those skilled in the art can clearly understand that each implementation method can be implemented by means of software plus a necessary general hardware platform, and of course, can also be implemented by hardware. Based on this understanding, the above technical solution is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a disk, an optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A simulation method based on a NOx removal model, characterized in that: include: 101: Construct a cyclone separator model, mesh the constructed cyclone separator model, and set urea injection parameters; 102: Construct a drag model to simulate the motion behavior of urea droplets in the airflow in the cyclone separator; 103: Construct a chemical reaction rate model to simulate the evaporation of urea, the generation of ammonia, and the reduction reaction of ammonia and NOx; 104: Acquire actual operating data of NOx removal, and set boundary conditions of the cyclone separator model based on the actual operating data; 105: Determine input data for simulation, input the input data into the models respectively, and optimize the models based on the output results of all the models.

2. A simulation method based on a NOx removal model according to claim 1, characterized in that: Construct a cyclone separator model, mesh the constructed cyclone separator model, and set urea injection parameters, including: Determining design parameters of the cyclone separator model, and constructing the cyclone separator model based on the design parameters of the cyclone separator model, wherein the design parameters of the cyclone separator model include all regions of the cyclone separator model; Determine a critical region based on all regions in the design parameters of the cyclone separator model, wherein the critical region includes a plurality of regions; Determine a refinement region of each region in the key region, set a first grid size of the refinement region of each region in the key region, and set a second grid size of all regions of each region in the key region except the refinement region; determining a third grid size in each of all regions of the cyclone separator except the critical region; Using the Cartesian grid generation technology built into the Barracuda software, meshing the corresponding areas in the key area based on the first grid size and the second grid size, and meshing the corresponding areas other than the key area based on the third grid size; Set urea injection parameters based on Barracuda software.

3. The simulation method based on the NOx removal model according to claim 1 is characterized in that: A drag model is constructed to simulate the motion behavior of urea droplets in the airflow in the cyclone separator, including: Determine urea droplet concentration, particle mass, particle volume fraction, fluid properties, and particle velocity based on the cyclone model sub-output results of the cyclone model; determining multiple fluids and fluid velocities based on fluid properties; a function for determining fluid and particle properties and flow conditions based on particle mass, particle volume fraction, fluid velocity, and particle velocity; in, is a function of the fluid f and particle p properties and flow conditions, represents the particle mass of particle p, represents the velocity of the fluid f, represents the particle velocity of particle p, D represents the drag function, represents the first sub-drag function, D2 represents the second sub-drag function, represents the particle volume fraction of the largest packed particles cp, represents the particle volume fraction of particle p, is the drag coefficient, represents the first Reynolds number, represents the fluid volume fraction of fluid f; A drag model is constructed based on the functions of fluid and particle properties and flow conditions to simulate the motion behavior of urea droplets in the airflow inside the cyclone separator.

4. The simulation method based on the NOx removal model according to claim 1 is characterized in that: Constructing a chemical reaction rate model includes constructing a droplet evaporation model, constructing a urea thermal decomposition model, and constructing a SNCR reaction model.

5. A simulation method based on a NOx removal model according to claim 4, characterized in that: Build a droplet evaporation model, including: Based on the drag model sub-input data of the drag model, the droplet velocity, droplet temperature, droplet mass, droplet diameter, droplet surface area, and droplet density are determined: A heat balance equation for determining the temperature of the droplet based on the mass of the droplet, the temperature of the droplet, and the surface area of ​​the droplet; in, represents the droplet mass of droplet d, represents the constant-pressure specific heat capacity of droplet d, represents the continuous phase temperature, represents the droplet temperature of droplet d, represents the rate of change of droplet temperature with time, represents the convective heat transfer coefficient between the droplet and the continuous phase, A represents the effective surface area for convective heat transfer between the droplet and the continuous phase, represents the evaporation rate of droplet d, represents the latent heat of vaporization of the droplet, represents the droplet surface area of ​​the droplet d, represents the particle blackness of droplet d, represents the Stefan-Boltzmann constant, and , represents the radiation temperature of the radiation R; When the droplet temperature reaches the evaporation temperature, the droplet begins to evaporate and will not stop until the volatile components of the droplet are completely precipitated or the particle temperature reaches the boiling temperature of the droplet; When the droplets undergo evaporation and mass transfer, determine the diffusion rate of the droplets into the gas phase and the vapor concentration gradient between the urea solution droplets and the gas flow; in, represents the vapor molar flow rate of substance i in the droplet, represents the mass transfer coefficient of substance i in the droplet, represents the vapor concentration of the surface s of the substance i in the droplet, represents the gas phase region away from the substance i in the droplet The steam concentration of the air flow; Determine the mass transfer equation for droplet evaporation based on the molar flow rate of the vapor, the mass of the droplet, and the surface area of ​​the droplet; in, Indicates time The mass of the droplet d is, represents the droplet mass of droplet d at the current time t, represents the molar mass of substance i in the droplet; When the temperature of the droplet reaches the boiling temperature and the volatile matter of the droplet has not been completely precipitated, the droplet begins to boil. Considering the radiation heat transfer of the particles, the boiling evaporation rate equation is determined; in, represents the rate of change of droplet diameter over time, represents the droplet diameter of the droplet d, is the gas phase thermal conductivity, represents the droplet density of droplet d, It represents the second Reynolds number defined by the diameter of the droplet d as the qualitative size and the relative velocity between the droplet d and the fluid f; Based on the heat balance equation of droplet temperature, the mass transfer equation of droplet evaporation and the boiling evaporation rate equation, a droplet evaporation model was constructed to simulate the evaporation process of urea solution.

6. A simulation method based on a NOx removal model according to claim 4, characterized in that: Construct a urea pyrolysis model, including: Determine the pyrolysis reaction equation, and build a urea pyrolysis model based on the pyrolysis reaction equation to simulate the generation of ammonia; The urea pyrolysis process includes: the water in the urea solution gradually evaporates, the urea solution becomes solid urea, the solid urea begins to melt into liquid urea at 406K, the liquid urea changes from a molten state to gaseous urea at 413K, and the gaseous urea is completely decomposed into ammonia and isocyanic acid at 425K.

7. A simulation method based on a NOx removal model according to claim 4, characterized in that: Construct the SNCR reaction model, including: The reduction reaction equation of ammonia and NOx reduction is determined, and a SNCR reaction model is constructed based on the reduction reaction equation to simulate the reduction reaction of ammonia and NOx.

8. The simulation method based on the NOx removal model according to claim 4 is characterized in that: The input data includes cyclone separator model sub-input data, drag model sub-input data, droplet evaporation model sub-input data, urea pyrolysis model sub-input data and SNCR reaction model sub-input data; The output results include cyclone separator model sub-output results, drag model sub-output results, droplet evaporation model sub-output results, urea pyrolysis model sub-output results and SNCR reaction model sub-output results; Based on the sub-output results of each model, the corresponding model is optimized.

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