A simulation method based on NOx removal model

Abstract

The present invention provides a simulation method based on a NOx removal model, which belongs to the field of gas separation technology, and includes: constructing a cyclone separator model, meshing the constructed cyclone separator model, and setting urea injection parameters; constructing a drag model to simulate the motion behavior of urea droplets in the airflow in the cyclone separator; constructing a chemical reaction rate model to simulate the evaporation of urea, the generation of ammonia, and the reduction reaction of ammonia and NOx; obtaining actual working condition data of NOx removal, and setting the boundary conditions of the cyclone separator model based on the actual working condition data; 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. It 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 realize more efficient industrial denitration simulation.

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 commonly used for flue gas purification, but coupled simulation of urea pyrolysis and NOx reduction reactions is still immature. Traditional models often overlook the motion and evaporation characteristics of urea droplets and lack a comprehensive description of the 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. However, the application of these models alone makes it 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 method comprises the following steps: 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 boundary conditions of the cyclone separator model according to actual operating data of NOx removal, determining input data for the simulation, and inputting the data into the model respectively. The method optimizes the model based on the output results of all the models. The method 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 realize more efficient industrial denitrification simulation.

[0005] The present invention provides a simulation method based on a NOx removal model, comprising:

[0006] 101: Construct a cyclone separator model, mesh the constructed cyclone separator model, and set urea injection parameters;

[0007] 102: Construct a drag model to simulate the motion behavior of urea droplets in the airflow inside a cyclone separator;

[0008] 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;

[0009] 104: Acquire actual operating data of NOx removal and set boundary conditions of the cyclone separator model based on the actual operating data;

[0010] 105: Determine the input data of the simulation, input the input data into the models respectively, and optimize the models based on the output results of all models.

[0011] According to a simulation method based on a NOx removal model provided by the present invention, a cyclone separator model is constructed, gridding is performed on the constructed cyclone separator model, and urea injection parameters are set, including:

[0012] 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;

[0013] determining 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;

[0014] Determining a refinement region for each region in the key region, setting a first grid size for the refinement region for each region in the key region, and setting a second grid size for all regions in each region in the key region except the refinement region;

[0015] determining a third grid size for each of all regions of the cyclone separator except for the critical region;

[0016] Using the Cartesian grid generation technology built into the Barracuda software, mesh the corresponding areas in the critical area based on the first grid size and the second grid size. At the same time, mesh the corresponding areas outside the critical area based on the third grid size.

[0017] Urea injection parameters were set based on Barracuda software.

[0018] According to a simulation method based on a NOx removal model provided by the present invention, a drag model is constructed to simulate the motion behavior of urea droplets in the airflow within a cyclone separator, including:

[0019] Based on the cyclone model sub-output results of the cyclone model, determine the urea droplet concentration, particle mass, particle volume fraction, fluid properties, and particle velocity;

[0020] Determine multiple fluids and fluid velocities based on fluid properties;

[0021] a function that determines fluid and particle properties and flow conditions based on particle mass, particle volume fraction, fluid velocity, and particle velocity;

[0022] in, is a function of the fluid f and particle p characteristics 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, represents the drag coefficient, represents the first Reynolds number, represents the fluid volume fraction of fluid f;

[0023] A drag model is constructed based on the functions of fluid and particle properties as well as flow conditions to simulate the motion behavior of urea droplets in the airflow inside the cyclone separator.

[0024] 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.

[0025] According to a simulation method based on a NOx removal model provided by the present invention, a droplet evaporation model is constructed, including:

[0026] 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:

[0027] Determine the heat balance equation for the droplet temperature based on the droplet mass, droplet temperature, and droplet surface area;

[0028] 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 radiation R;

[0029] 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;

[0030] When the droplets undergo evaporation and mass transfer, determine the diffusion rate of the droplets to the gas phase and the vapor concentration gradient between the urea solution droplets and the gas flow;

[0031] 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;

[0032] 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.

[0033] in, Indicates time The mass of droplet d is, represents the mass of droplet d at the current time t, represents the molar mass of substance i in the droplet;

[0034] When the droplet temperature 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;

[0035] in, represents the rate of change of droplet diameter over time, represents the droplet diameter of the droplet d, represents 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;

[0036] 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.

[0037] According to a simulation method based on a NOx removal model provided by the present invention, a urea pyrolysis model is constructed, including:

[0038] Determine the pyrolysis reaction equation and build a urea pyrolysis model based on the pyrolysis reaction equation to simulate the generation of ammonia;

[0039] 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.

[0040] According to a simulation method based on a NOx removal model provided by the present invention, a SNCR reaction model is constructed, including:

[0041] The reduction reaction equation of ammonia and NOx reduction is determined, and an SNCR reaction model is constructed based on the reduction reaction equation to simulate the reduction reaction of ammonia and NOx.

[0042] 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;

[0043] The output results include the cyclone separator model sub-output results, the drag model sub-output results, the droplet evaporation model sub-output results, the urea pyrolysis model sub-output results, and the SNCR reaction model sub-output results;

[0044] Based on the sub-output results of each model, the corresponding model is optimized.

[0045] Compared with the prior art, the present invention has the following advantages:

[0046] 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, and the model is optimized based on the output results of all models. This 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 a more efficient industrial denitrification simulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the present invention or the prior art, a brief introduction is given below to 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 any creative work.

[0048] Figure 1It is a flow chart of a simulation method based on a NOx removal model provided by an embodiment of the present invention.

[0049] 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 by an embodiment of the present invention.

[0050] Figure 3 This is a urea injection point position diagram of a simulation method based on a NOx removal model provided by an embodiment of the present invention.

[0051] Figure 4 This is a parameter diagram of a simulation method based on a NOx removal model provided by an embodiment of the present invention.

[0052] Figure 5 The present invention provides a chemical reaction equation and reaction kinetics diagram in a urea pyrolysis model of a simulation method based on a NOx removal model.

[0053] Figure 6 It is a reaction kinetics diagram in an SNCR reaction model of a simulation method based on a NOx removal model provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0054] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0055] Example 1:

[0056] The embodiment of the present invention provides a simulation method based on a NOx removal model, such as Figure 1 As shown, including:

[0057] 101: Construct a cyclone separator model, mesh the constructed cyclone separator model, and set urea injection parameters;

[0058] 102: Construct a drag model to simulate the motion behavior of urea droplets in the airflow inside a cyclone separator;

[0059] 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;

[0060] 104: Acquire actual operating data of NOx removal and set boundary conditions of the cyclone separator model based on the actual operating data;

[0061] 105: Determine the input data of the simulation, input the input data into the models respectively, and optimize the models based on the output results of all models.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] In this embodiment, a preliminary design is performed for the base working condition based on the position and number of urea injection points, and then optimization is performed. For the base working condition, the injection point position is as follows: Figure 3 shown.

[0066] 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.

[0067] In this embodiment, constructing a chemical reaction rate model includes chemical reaction rate settings. 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.

[0068] In this example, Barracuda's built-in GPU parallel solver achieves speeds up to tens of times faster than traditional CPU parallel processing. Barracuda's built-in post-processing tool, tecplot, performs post-processing, including creating a cloud map of NO mass concentration (standard, dry, and 6% O2) in a cyclone separator simulation. This cloud map allows for intuitive analysis of NO distribution within the separator and extraction of inlet and outlet concentrations.

[0069] In this embodiment, after setting the boundary conditions, a numerical solution method is used for simulation calculation. During the numerical solution process, the flow field, temperature field, evaporation and thermal decomposition 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.

[0070] 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 identified, 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.

[0071] 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, 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, and 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.

[0072] Example 2:

[0073] The embodiment of the present invention provides a simulation method based on a NOx removal model, constructing a cyclone separator model, meshing the constructed cyclone separator model, and setting urea injection parameters, including:

[0074] 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;

[0075] determining 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;

[0076] Determining a refinement region for each region in the key region, setting a first grid size for the refinement region for each region in the key region, and setting a second grid size for all regions in each region in the key region except the refinement region;

[0077] determining a third grid size for each of all regions of the cyclone separator except for the critical region;

[0078] Using the Cartesian grid generation technology built into the Barracuda software, mesh the corresponding areas in the critical area based on the first grid size and the second grid size. At the same time, mesh the corresponding areas outside the critical area based on the third grid size.

[0079] Urea injection parameters were set based on Barracuda software.

[0080] 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 zones, etc.). Based on these parameters, a detailed three-dimensional model can be established to simulate the working state of the cyclone separator.

[0081] In this embodiment, the "critical areas" that have a greater impact on the simulation results are determined based on the functions of different areas in the cyclone separator model. These critical 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 mesh must be refined.

[0082] In this embodiment, the key areas are further divided into refined areas. These areas require a smaller grid size (first grid size) to ensure simulation accuracy. The remaining key areas can use a slightly larger grid size (second grid size) to balance computational efficiency and accuracy.

[0083] In this embodiment, a larger grid size (third grid size) is used for other areas of the cyclone separator model that are not divided into critical areas, because these areas have little impact on the simulation results. Appropriately reducing the grid density can reduce the consumption of computing resources.

[0084] In this example, the Cartesian mesh generation technology built into the Barracuda software is used. This technology can effectively generate meshes, especially for complex geometric structures. Barracuda accurately meshes different areas of the model based on the different mesh sizes defined previously (first, second, and third mesh sizes), ensuring a balance between computational efficiency and simulation accuracy.

[0085] 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 can ensure the accuracy of key areas while reducing computing resource consumption in other areas. Combined with the urea injection parameter setting, efficient and accurate NOx removal simulation can be achieved.

[0086] Example 3:

[0087] The embodiment of the present invention provides a simulation method based on a NOx removal model, constructing a drag model to simulate the motion behavior of urea droplets in the airflow within a cyclone separator, including:

[0088] Based on the cyclone model sub-output results of the cyclone model, determine the urea droplet concentration, particle mass, particle volume fraction, fluid properties, and particle velocity;

[0089] Determine multiple fluids and fluid velocities based on fluid properties;

[0090] a function that determines fluid and particle properties and flow conditions based on particle mass, particle volume fraction, fluid velocity, and particle velocity;

[0091] in, is a function of the fluid f and particle p characteristics 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, represents the drag coefficient, represents the first Reynolds number, represents the fluid volume fraction of fluid f;

[0092] A drag model is constructed based on the functions of fluid and particle properties as well as flow conditions to simulate the motion behavior of urea droplets in the airflow inside the cyclone separator.

[0093] In this embodiment, Barracuda includes a rich set of built-in drag models, enabling calculations for both dilute and dense phase flows. Typical drag models include the Wen-Yu drag model, the Ergun drag model, and the WenYu-Ergun model. The Wen-Yu drag model is more appropriate when simulating pneumatic conveying with relatively few particles; the Ergun drag model is suitable for simulating dense particle accumulation; and the WenYu-Ergun drag model is more appropriate when simulating both sparse and dense particle density.

[0094] In this embodiment, for the urea injection model, the particle volume fraction is generally below 10%, indicating dilute phase flow. However, the possible localized particle aggregation can be calculated using the Ergun model. Therefore, in this invention, the WenYu-Ergun model is the most appropriate particle drag model, as it describes the particle motion process more closely resembling reality.

[0095] 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.

[0096] In this embodiment, the urea droplet concentration refers to the number or mass of urea droplets per unit volume.

[0097] In this embodiment, the first Reynolds number reflects the influence of the fluid flow state on the drag coefficient.

[0098] 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.

[0099] In this embodiment, the fluid velocity refers to the velocity of the airflow in the cyclone separator, which determines the force exerted on the particles in the airflow.

[0100] In this embodiment, particle velocity refers to the velocity of the particles relative to the airflow, which is usually different from the airflow velocity because the particles have inertia and are subject to different forces.

[0101] In this embodiment, the fluid properties include gas density, viscosity, etc., which determine the gas flow mode and the impact on particles.

[0102] In this embodiment, the particle characteristics such as particle diameter, density, shape, etc. determine the drag force on the particle in the airflow.

[0103] In this embodiment, the flow conditions include air flow velocity, the difference in particle velocity, turbulence intensity in the air flow, etc. The function is used to simulate the interaction between fluid and particles.

[0104] In this example, a drag model was constructed based on the aforementioned fluid and particle characteristics, as well as a function of flow conditions. The drag model primarily describes the resistance exerted by the airflow on urea droplets or particles, which affects the particle's trajectory. The magnitude of the drag depends on factors such as the particle's velocity, the velocity difference between the particle and the gas, and the gas's viscosity. The drag model can be used to predict the trajectory of urea droplets within the cyclone separator, thereby understanding how they evaporate, release ammonia, and react with NOx.

[0105] In this embodiment, in the cyclone separator, the fluid usually contains a mixture of gas and solid particles, which is a multiphase flow. The characteristics 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 characteristics of the fluid.

[0106] In this embodiment, the interaction between fluid and particles: The interaction between gas and particles (such as drag force, collision, viscous force, 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.

[0107] In this embodiment, localized property variations occur: The flow field within a cyclone separator is complex, and fluid properties (such as velocity, pressure, and turbulence intensity) vary across different regions. Furthermore, due to the uneven distribution of particles, localized fluid properties can also vary. The fluid may exhibit different flow patterns (such as laminar flow and turbulent flow) in different regions of the separator, resulting in variations in its properties across different locations.

[0108] In this embodiment, the fluid at different locations within the separator may exhibit different velocity distributions, pressure gradients, and turbulence intensities, resulting in significant differences in local fluid properties. Fluid properties (such as density and viscosity) may be affected by factors such as temperature, pressure, and chemical composition. In actual operating conditions, fluid parameters such as temperature and pressure may vary in different areas, leading to changes in local fluid properties.

[0109] 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 within the cyclone separator, the model's accuracy in capturing the interaction between fluid and particles can be improved, making the simulation closer to actual operating conditions, helping to optimize the urea injection strategy and improve NOx removal efficiency.

[0110] Example 4:

[0111] An 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.

[0112] In this embodiment, after the drag model determines the motion behavior of the droplet, the next step is to simulate the droplet evaporation process. The droplet will gradually evaporate due to heat in the high-temperature airflow. The evaporation model is responsible for calculating the droplet evaporation rate and the heat required. The droplet's motion position (determined by the drag model) and the airflow temperature (defined in the geometric model and mesh) jointly determine the evaporation rate.

[0113] In this embodiment, after the droplets evaporate, the gaseous urea begins to pyrolyze, decomposing 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 a timely manner within the appropriate temperature window for the NOx reduction reaction.

[0114] In this embodiment, ammonia generated by urea thermal decomposition is the key reducing agent in 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.

[0115] 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 of 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, thereby being able to more accurately simulate the NOx reduction process in actual operation.

[0116] The beneficial effects of the above technical solution are: 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.

[0117] Example 5:

[0118] The embodiment of the present invention provides a simulation method based on a NOx removal model to construct a droplet evaporation model, including:

[0119] 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:

[0120] Determine the heat balance equation for the droplet temperature based on the droplet mass, droplet temperature, and droplet surface area;

[0121] 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 radiation R;

[0122] 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;

[0123] When the droplets undergo evaporation and mass transfer, determine the diffusion rate of the droplets to the gas phase and the vapor concentration gradient between the urea solution droplets and the gas flow;

[0124] 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;

[0125] 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.

[0126] in, Indicates time The mass of droplet d is, represents the mass of droplet d at the current time t, represents the molar mass of substance i in the droplet;

[0127] When the droplet temperature 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;

[0128] in, represents the rate of change of droplet diameter over time, represents the droplet diameter of the droplet d, represents 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;

[0129] 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.

[0130] In this embodiment, the droplet velocity refers to the velocity of the droplets relative to the airflow.

[0131] In this embodiment, the droplet temperature is an important variable in the droplet heat transfer process, which directly affects the evaporation rate.

[0132] In this embodiment, the convective heat transfer coefficient represents the amount of heat transferred through a unit area per unit time under a unit temperature difference during the convective heat transfer process, and reflects the speed of the convective heat transfer.

[0133] 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.

[0134] In this embodiment, the droplet mass refers to the mass of the droplet, which gradually decreases as it evaporates.

[0135] In this embodiment, the droplet diameter refers to the size of the droplet, which generally decreases gradually as it evaporates.

[0136] 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.

[0137] In this embodiment, the droplet density indicates that the density of the droplet is affected by temperature, and the density may change when the temperature of the droplet increases.

[0138] In this embodiment, a heat balance equation is constructed based on the mass, temperature, and surface area of ​​the droplets. This equation describes the heat transfer process between the droplets and the surrounding airflow, including the absorption or release of heat by the droplets. The heat balance equation can be used to calculate the temperature change of the droplets and determine when the droplets reach the critical temperature for evaporation or boiling.

[0139] In this embodiment, when the temperature of the droplet reaches its evaporation temperature, the droplet begins to evaporate. During the evaporation process, the droplet will continue to lose mass until the volatile components are completely evaporated or the temperature of the droplet reaches the boiling temperature, at which point the droplet will stop evaporating.

[0140] In this embodiment, during evaporation, urea or other volatile components in the droplets diffuse into the airflow. 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.

[0141] 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. This equation describes the mass loss rate of the droplets during the evaporation process, that is, how the mass of the droplets decreases over time.

[0142] In this embodiment, when the temperature of the droplet reaches its boiling temperature and the volatile components in the droplet have not been completely precipitated, the droplet 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 droplet to determine the evaporation rate of the droplet during boiling.

[0143] 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. This 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.

[0144] The beneficial effects of the above technical solution are: constructing a droplet evaporation model 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 denitrification efficiency and enhance the industrial application value of the simulation.

[0145] Example 6:

[0146] The embodiment of the present invention provides a simulation method based on a NOx removal model to construct a urea pyrolysis model, including:

[0147] Determine the pyrolysis reaction equation and build a urea pyrolysis model based on the pyrolysis reaction equation to simulate the generation of ammonia;

[0148] 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.

[0149] In this embodiment, gaseous isocyanate 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.

[0150] In this embodiment, a urea pyrolysis model can be constructed based on the pyrolysis reaction equation and the state changes of urea at different temperatures. This model can simulate the generation process of ammonia and predict how urea decomposes to produce ammonia and isocyanic acid under different temperatures and conditions.

[0151] The beneficial effects of the above technical solution are: constructing a urea pyrolysis model 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 industrial application effect.

[0152] Example 7:

[0153] The embodiment of the present invention provides a simulation method based on a NOx removal model to construct an SNCR reaction model, including:

[0154] The reduction reaction equation of ammonia and NOx reduction is determined, and an SNCR reaction model is constructed based on the reduction reaction equation to simulate the reduction reaction of ammonia and NOx.

[0155] In this embodiment, the mainstream urea denitrification model adopts a 7-step total reaction. Thanh et al. modified the model in 2008. The reaction kinetics are as follows: Figure 6 shown.

[0156] In this embodiment, the SNCR system flue gas denitrification process includes the following four process steps: receiving and storing the reducing agent; metering the reducing agent and diluting it with water or air; injecting the diluted reducing agent into the appropriate position of the furnace; and mixing the reducing agent with the flue gas to perform a denitrification reaction.

[0157] In this embodiment, ammonia slip occurs when unreacted ammonia in the flue gas is released into the flue gas through the reactor during the denitration process. This phenomenon can lead to several problems: it can easily cause ash accumulation and blockage in downstream equipment such as air preheaters, resulting in increased pressure drop and low-temperature corrosion; it can also affect fly ash quality, leading to dust accumulation on the electrostatic precipitator (ESP) electrodes or sticking of bag filters; it can also create a visible smoke column, increasing PM2.5 emissions; and its release into the atmosphere can negatively impact human health.

[0158] The beneficial effects of the above technical solution are: constructing an SNCR reaction model to simulate the reduction reaction of ammonia and NOx, which 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.

[0159] Example 8:

[0160] An 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;

[0161] The output results include the cyclone separator model sub-output results, the drag model sub-output results, the droplet evaporation model sub-output results, the urea pyrolysis model sub-output results, and the SNCR reaction model sub-output results;

[0162] Based on the sub-output results of each model, the corresponding model is optimized.

[0163] In this embodiment, the cyclone separator model sub-input data may include gas flow rate, solid particle diameter, density, temperature, etc.

[0164] In this embodiment, the drag model sub-input data may include velocity, size, density, fluid viscosity, etc. of the droplet or particle.

[0165] 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.

[0166] In this embodiment, the sub-input data of the urea pyrolysis model may include the initial temperature and mass of the urea particles, the activation energy and reaction rate constant of the decomposition reaction, etc.

[0167] In this embodiment, the SNCR reaction model sub-input data may include the concentrations of ammonia and NOx, reaction temperature, air flow velocity, and other chemical reaction parameters.

[0168] In this embodiment, the cyclone separator model optimization can optimize the separation efficiency and reduce the content of particles entering the subsequent reaction process.

[0169] 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.

[0170] 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 gas.

[0171] 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.

[0172] 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 to NOx.

[0173] The beneficial effects of the above technical solution are: 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.

[0174] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, i.e., they may be located in one location or distributed across multiple network units. Some or all of the modules may be selected based on actual needs to achieve the objectives of the present embodiment. Persons of ordinary skill in the art will be able to understand and implement the present invention without inventive effort.

[0175] Through the above description of the embodiments, those skilled in the art will clearly understand that each embodiment can be implemented using software plus a necessary general-purpose hardware platform, or of course, hardware. Based on this understanding, the essence of the above technical solution, or the portion that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a magnetic disk, or an optical disk, and includes a number of instructions for causing a computer device (such as a personal computer, server, or network device) to execute the methods described in each embodiment or certain portions of the embodiments.

[0176] 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 various 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; Among them, a drag model is constructed to simulate the movement 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 in the cyclone separator. Among them, building a chemical reaction rate model includes building a droplet evaporation model, building a urea thermal decomposition model, and building a SNCR reaction model; Among them, the 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.

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: 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.

4. The simulation method based on the NOx removal model according to claim 1 is characterized in that: Construct 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.

5. The simulation method based on the NOx removal model according to claim 1 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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