Simulation method for concentration diffusion of pollution gas in sludge composting workshop

Abstract

The invention provides a method for simulating concentration diffusion of polluted gas in a sludge composting workshop, belongs to the technical field of airflow diffusion simulation, and can solve the technical problem that the traditional CFD simulation method cannot simulate and calculate the concentration diffusion of the polluted gas in the sludge composting workshop. The simulation method comprises the steps of building a geometric model of the sludge composting workshop, performing grid division on the geometric model, setting a simulation solver, selecting a calculation model, setting boundary conditions, performing numerical simulation calculation and processing data. The device can be applied to simulation of the diffusion condition of the pollution gas in the sludge composting workshop with negative pressure suction, the boundary conditions of the pollution non-point source can be efficiently and accurately described by reasonably partitioning the pollution non-point source and combining field test data, and the concentration distribution of the pollution gas in each position of the sludge composting workshop can be controlled. Therefore, a deodorization and ventilation scheme is optimized, and the method has very important significance in improving the environment quality of a workshop.

Description

Technical Field

[0001] The present invention belongs to the technical field of air flow diffusion simulation, and particularly relates to a simulation method for the concentration diffusion of polluted gases in a sludge composting workshop. Background Art

[0002] As an important part of urban infrastructure, the operating efficiency of wastewater treatment plants and their impact on the environment have received extensive attention. Especially during the sludge composting fermentation process, a large amount of malodorous gases such as ammonia and hydrogen sulfide are generated on the surface of the sludge. These malodorous gases not only cause certain harm to the bodies of workshop staff, but also cause great pollution to the surrounding environment and have a certain impact on the surrounding air quality.

[0003] However, due to factors such as the large spatial scale and harsh local conditions in the sludge fermentation workshop, it is impossible to obtain the full concentration distribution of polluted gases in the workshop through on-site measurement, which restricts the staff's control over the concentration distribution of polluted gases in the workshop and the effect of the deodorization and ventilation plan. Moreover, since the rate of polluted gas generation from the fermentation heap is difficult to measure, and there is a negative pressure suction ventilation system under the sludge heap, which causes some of the polluted gases generated by sludge fermentation to be "short-circuited" and discharged from the workshop below, this limits the traditional CFD simulation method and makes it difficult to discretize the boundary conditions, thus unable to simulate and calculate similar polluted gas diffusion problems.

[0004] Therefore, the present invention proposes a simulation method for the concentration diffusion of polluted gases in a sludge composting workshop based on Fluent. Summary of the Invention

[0005] Aiming at the technical problem that the traditional CFD simulation method cannot simulate and calculate the concentration diffusion of polluted gases in a sludge composting workshop, the present invention proposes a simulation method for the concentration diffusion of polluted gases in a sludge composting workshop based on Fluent, which can simulate the diffusion of polluted gases in a sludge composting workshop with negative pressure suction. By reasonably partitioning the pollutant surface source and combining with on-site test data, the boundary conditions of the polluted surface source can be described efficiently and accurately, which is of great significance for controlling the concentration distribution of polluted gases in various parts of the sludge composting workshop, optimizing the deodorization and ventilation plan accordingly, and improving the environmental quality of the workshop.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: A simulation method for the concentration diffusion of polluted gas in a sludge composting workshop, including the steps of establishing a geometric model of the sludge composting workshop, meshing the geometric model, setting a simulation solver, selecting a calculation model, setting boundary conditions, numerical simulation calculation, and data processing steps; the step of setting boundary conditions includes: partitioning the sludge composting pollution area source, with both sides being outlets and multiple inlets being set in the middle partition. Preferably, the outlets include a first outlet and a second outlet, and the inlets include a first inlet, a second inlet, a third inlet, and a fourth inlet arranged in sequence. The present invention obtains the concentration distribution of polluted gas in the sludge composting workshop through simulation, evaluates whether the air flow organization in the workshop is reasonable, and is applicable to the simulation of the concentration diffusion of polluted gas in a sludge composting workshop with both a process ventilation system with downward exhaust and a deodorization ventilation system with upward exhaust. While simplifying the model, the accuracy of the simulation is improved.

[0007] In some of the embodiments, the step of establishing a geometric model of the sludge composting workshop includes: using the modeling software SpaceClaim to establish a geometric model of the sludge composting workshop. When establishing the geometric model, a certain fixed point on the workshop floor is used as the origin to establish a three-dimensional rectangular coordinate system. The positive direction of the X-axis is defined as the first direction in the horizontal plane, the positive direction of the Y-axis is defined as the vertical direction perpendicular to the horizontal plane, and the positive direction of the Z-axis is defined as the second direction perpendicular to the X-axis in the horizontal plane. Preferably, a fixed point on the floor in the northeast corner of the workshop is used as the origin, the positive direction of the X-axis is defined as the south direction, the positive direction of the Y-axis is defined as the vertically upward direction, and the positive direction of the Z-axis is defined as the west direction; the geometric model only retains the fluid domain, inlets, and outlets, and the inlets and outlets are coupled with the fluid domain through shared topology processing. The geometric model established by the present invention includes workshop walls, sludge piles, door openings, and mechanical exhaust air vents, etc. By simplifying the geometric model, the geometric model only retains the fluid domain, inlets, and outlets. When setting the inlet and outlet planes on the fluid domain, the plane and the fluid domain are subjected to shared topology processing.

[0008] In some of the embodiments, the step of meshing the geometric model includes: importing the geometric model into the watertight workflow of FluentMeshing without adding local dimensions; using the size function of Curvature&Proximity to draw surface meshes and adjusting the maximum and minimum mesh sizes; updating the boundaries and regions after describing the geometric structure, and selecting the velocity inlet boundary condition for all inlet and outlet boundary conditions; adding a boundary layer in the fluid-wall contact area using the smooth-transition offset type, preferably with 3 boundary layers, and then filling the mesh with poly-hexcore, which is faster in calculation and has high accuracy. After the mesh drawing is completed, check whether the mesh quality meets the calculation requirements and save the mesh.

[0009] In some of these embodiments, the steps of setting up the simulation solver include: importing the drawn grid in Fluent Solution, adjusting the grid size ratio and setting the units, checking the grid quality report, selecting the pressure-based solver, absolute velocity, and steady-state time, and turning on the gravitational acceleration in the negative Y-axis direction. Among them, the basis for the sludge compost pollution area source is the geometric characteristics of the physical model, the flow field characteristics, the computing resources, and the accuracy requirements. The sludge compost workshop of the present invention belongs to the category of large spaces. Since its geometric changes are relatively gentle, the grid size can be relatively large when drawing the grid; in areas where the flow parameters change violently, such as near the boundary layer and the area source, smaller grid sizes should be used. In the present invention, 3 layers of boundary layers are added at each boundary during grid division to make the simulation more accurate; when a high computing accuracy is required, the grid size needs to be correspondingly reduced, but a smaller grid size will lead to a significant increase in the number of grids and higher requirements for computing resources. In the case of limited computing resources, the grid size can be appropriately increased to reduce the computing amount while ensuring that the basic physical phenomena can be simulated.

[0010] In some of these embodiments, the steps of selecting the calculation model include: turning on the energy equation; selecting the k-ε Standard model for the turbulence model and turning on the standard wall function; turning on the component transport model and checking the inlet diffusion and energy source terms.

[0011] In some of these embodiments, the energy equation includes the mass conservation equation (1), the momentum conservation equations (2)-(4), the energy conservation equation (5), and the component conservation equation (6).

[0012]

[0013]

[0014] In the above formulas, t is the time, used to describe the change of physical quantities over time; x, y, and z are the three coordinate directions of the spatial rectangular coordinate system, used to describe the distribution of physical quantities in space; ρ is the density of the mixed gas of ammonia and air; u, v, and w are the velocity components of the mixed gas in the x, y, and z directions respectively; p is the pressure of the mixed gas; τ xx 、τ xy 、τ xz 、τ yy 、τ yx 、τ yz 、τ zz 、τ zx 、τ zy are the respective components of the viscous stress tensor, describing the stress generated inside the mixed gas due to viscosity; F x 、F y 、F zare the external force components in the x, y, and z directions acting on the mixed gas; T is the temperature of the mixed gas; k is the thermal conductivity of the mixed gas; c p is the specific heat capacity at constant pressure of the mixed gas; S r is the source term in the energy equation, representing the generation or consumption of energy per unit volume per unit time; c s is the mass fraction of ammonia; D s is the diffusion coefficient of ammonia, a physical quantity describing the diffusion ability of components; S s is the source term in the component conservation equation, representing the generation or consumption of ammonia per unit volume per unit time.

[0015] In some of these embodiments, the step of setting boundary conditions includes: adding air and polluted gas to the fluid material, mixing the air and the polluted gas and designating air as the last component; keeping the fluid domain conditions default; setting the velocities at both outlets to the field measurement values, setting the initial pollutant concentrations at both outlets to zero; setting the velocity at the inlet to the estimated value, and setting the initial pollutant concentration at the inlet to the field measurement value.

[0016] In the step of setting boundary conditions, the workshop door opening and the upper outlet are set as velocity inlet boundary conditions, and the velocity is set to a negative value; since the on-site measured value of natural makeup air is not accurate enough, the inlet data of the workshop door opening is given as an estimated value based on the measured data, and the outlet value is the value calculated from the on-site measurement, and the initial pollutant concentration is set to zero. Since the sludge composting pile of aerobic fermentation is equipped with a process fan, there are both upward and downward wind speeds on the surface of the pile. Considering the sinking of fresh air and the diffusion of polluted gas, and the emission rates of polluted gas in different fermentation stages are also very different, the zoning setting of the pollution surface source of the sludge composting in the present invention can meet the accuracy of the emission of pollution sources in each fermentation stage.

[0017] In some of these embodiments, the numerical simulation calculation steps include: selecting appropriate solution methods and control methods, initializing the fluid domain of the workshop and then starting iterative calculations. Among them, the pressure-velocity coupling scheme selects Coupled; in the spatial discretization method, the gradient selects Least Squares Cell Based, the pressure selects Second Order, the turbulent kinetic energy and the turbulent dissipation rate both select First Order Upwind, and other energy and momentum equations all select Second Order Upwind; initialize the fluid domain of the geometric model, select standard initialization, the calculation reference domain selects the entire fluid domain, and set the initial concentration of the polluted gas to zero; select Automatic as the time-step iteration method, and start iterative calculations after setting the number of iteration steps. The present invention selects Automatic as the time-step iteration method for calculation, which can automatically adjust the time step according to the change rate of physical quantities during the calculation process. In the stage where the flow field changes violently, such as when vortices are generated, broken, or shock waves appear in transient flows, it will automatically reduce the time step, so as to more precisely capture these rapidly changing processes, which helps to improve the accuracy of simulating these key phenomena, maintain the stability of the calculation, reduce the waste of computing resources caused by setting the time step too small, and avoid numerical instabilities such as calculation divergence caused by too large a time step, enabling the simulation to proceed smoothly to the desired state, thereby obtaining relatively complete and reasonable results, and indirectly ensuring the physical rationality and accuracy of the simulation results.

[0018] In some of these embodiments, the data processing steps include: processing the calculation results according to research requirements, verifying the calculation results by combining the measured data of the concentration distribution of the polluted gas in the workshop, adjusting the boundary conditions according to the verification results, and performing iterative calculations again until the calculation results pass the verification of the measured data.

[0019] In some of these embodiments, in the data processing steps, post-processing analysis is performed on the data in the main personnel activity areas and the areas close to the inlet and outlet, and visual results are output or chart analysis is performed. Among them, the data processing steps are performed after the iterative calculations are completed. The visual results include at least one of the polluted gas velocity trace diagram, vector diagram, or concentration cloud diagram; during data verification, if the calculation results are consistent with the measured data, the simulation is completed; if the calculation results are not consistent with the measured data, the boundary conditions are adjusted and iterative calculations are performed again until the simulation calculation results pass the verification of the measured data. Because during the on-site measurement process, the wind speed and the concentration of the polluted gas are all instantaneous values, especially the wind speed changes greatly, so during the simulation, parameters are adjusted within the wind speed range, and the influence of the estimated values on the airflow organization in the simulation is found by repeatedly simulating and comparing with the on-site measured results through adjusting the parameters to find the most suitable parameters.

[0020] Compared with the prior art, the advantages and positive effects of the present invention are as follows: The present invention uses ANSYS Fluent to simulate the air flow organization of the polluted gas diffusion in the sludge composting workshop. By setting up the polluted surface source area of the sludge composting, according to the characteristics of the fermentation process in the workshop and combining the actual measurement and simulation values, the sludge in the entire fermentation cycle is divided into multiple parts horizontally to estimate the emission amount of the pollution source, and the inlet area and the outlet area are divided vertically, which can greatly simplify the model under the condition of accurately simulating the air flow organization in the workshop, and verify its accuracy in the subsequent simulation process, which is of great significance for controlling the concentration distribution of the polluted gas in the workshop. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a flowchart of the simulation method for the concentration diffusion of the polluted gas in the sludge composting workshop provided by the embodiment of the present invention;

[0022] Figure 2 It is a workshop model diagram established by the embodiment of the present invention;

[0023] Figure 3 It is a simplified workshop model diagram of the embodiment of the present invention;

[0024] Figure 4 It is a fluid domain model diagram of the embodiment of the present invention;

[0025] Figure 5 It is a grid sectional view of the embodiment of the present invention;

[0026] Figure 6 It is a diagram of the polluted surface source area setting of the sludge compost body of the embodiment of the present invention;

[0027] Figure 7 It is Figure 2 The ammonia concentration distribution diagram of the aisle section at one end of the geometric model along the X-axis direction at α in ;

[0028] Figure 8 It is Figure 2 The ammonia concentration distribution diagram of the aisle section at the other end of the geometric model along the X-axis direction at β in ;

[0029] Figure 9 It is Figure 2 The ammonia concentration distribution diagram of the surface height section of the compost body at γ in ;

[0030] Figure 10 It is Figure 2 The ammonia concentration distribution diagram of the 1.75m height section of the compost body at δ in ;

[0031] Figure 11 It is the mainstream wind speed trace diagram in the workshop of the embodiment of the present invention;

[0032] Figure 12Comparison diagram of the measured and simulated ammonia concentrations at a height of 1.75 m in the heap body of the embodiment of the present invention;

[0033] In the attached drawings, 1. Heap body, 2. Feeding port, 3. Return material port, 4. Process air inlet, 5. Deodorization air inlet; α. Aisle section at one end of the geometric model along the X-axis direction, β. Aisle section at the other end of the geometric model along the X-axis direction, γ. Heap surface height section, δ. 1.75 m height section. Detailed implementation manners

[0034] In order to understand the features and technical content of the embodiments of the present invention in more detail, the technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the embodiments described next are only a part of the embodiments of the present invention, rather than all the embodiments of the present invention. In the following technical description, for the sake of explanation, multiple details are provided to provide a full understanding of the disclosed embodiments. However, one or more embodiments can still be implemented without these details. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection claimed by the present invention.

[0035] The embodiment of the present invention provides a method for simulating the concentration diffusion of polluted gases in a sludge composting workshop. The specific process flow is shown in the attached Figure 1 drawings. For a negative-pressure suction type sludge fermentation workshop, the suction below the sludge causes the gas in the workshop to be discharged from below the sludge. However, due to the fermentation process, the pollution source item is also the sludge itself, resulting in the emission of polluted gases from above the sludge. Conventional CFD simulations are not suitable for negative-pressure suction sludge fermentation workshops. The present invention proposes a reasonable method for setting the pollution source surface source partition based on the measured wind speed at the inlet and outlet of the workshop, the concentration of polluted gases at the outlet, and the concentration of polluted gases on the surface of the sludge heap body, and conducts an air flow organization simulation of the polluted gases to obtain the concentration distribution of polluted gases at various locations in the workshop. While simplifying the model, the accuracy of the simulation is improved, which is of great significance for controlling the concentration distribution in the workshop and is applicable to the simulation of the concentration diffusion of polluted gases in a sludge composting workshop with both a process ventilation system with downward air extraction and a deodorization ventilation system with upward air extraction.

[0036] In the embodiment of the present invention, the method for simulating the concentration diffusion of polluted gases in a sludge composting workshop includes the following steps:

[0037] S1. Establish a geometric model of the sludge composting workshop

[0038] S11. As shown in the attached Figure 2As shown in the figure, taking the ground in the northeast corner of the workshop as the origin, the positive direction of the X-axis faces south, the positive direction of the Y-axis is vertically upward, and the positive direction of the Z-axis faces west. The sludge composting workshop is modeled at a scale of 1:1 using the modeling software SpaceClaim. The established geometric model mainly includes the workshop wall, sludge heap 1, feed inlet 2, return material inlet 3, process air inlet 4, deodorization air inlet 5, door opening, and mechanical exhaust air inlet, as shown in Appendix Figure 3 and Appendix Figure 4 As shown, by simplifying the geometric model, only the fluid domain, inlet, and outlet are retained. Before drawing the mesh, group naming and shared topology processing are performed on the inlet and outlet. Among them, the involved inlets and outlets are the upper deodorization air inlet, feed and return material inlet, pollution source on the surface of the heap, and process air inlet below the heap;

[0039] S2. Mesh generation for the geometric model

[0040] S21. As shown in Appendix Figure 5 As shown, import the geometric model in the watertight workflow of Fluent Meshing, without adding local dimensions. Use the Curvature&Proximity size function to draw the surface mesh. The maximum size of the surface mesh is 3225, and the minimum size is 125.9;

[0041] S22. Update the boundaries and regions after describing the geometric structure, and set all inlets and outlets as velocity inlet boundary conditions;

[0042] S23. Add 3 layers of boundary layers in the fluid-wall contact area using the smooth-transition offset type;

[0043] S24. Use the poly-hexcore filling mesh, which is faster in calculation and has high accuracy. The total number of meshes is 2,755,972, and the minimum orthogonal quality of the mesh is 0.08;

[0044] S3. Set the simulation solver

[0045] Import the mesh obtained in step S24 into Fluent Solution to check the mesh, adjust the mesh size ratio and set the unit, check the mesh quality report. The solver selects the pressure-based, absolute velocity, and steady-state time, and turns on the gravitational acceleration in the negative y-axis direction;

[0046] S4. Select the calculation model

[0047] Open the energy equation. The viscous model selects the k-ε Standard model, the standard wall function, turn on the component transport model, and check the inlet diffusion and energy source term;

[0048] S5. Set the boundary conditions

[0049] S51. Set the material. Add air and polluted gas to the fluid material, mix the air and the polluted gas and specify the air as the last component;

[0050] S52. Keep the fluid domain conditions default;

[0051] S53. Set the boundary conditions

[0052] The inlet and return material ports are set as the velocity inlet boundary conditions, the velocity magnitude is 6.788 m / s, the turbulence intensity is set to 5%, the turbulence viscosity ratio is 10, and the mass fraction of ammonia is 0; the upper mechanical outlet is set as the velocity inlet boundary condition and the velocity in the opposite direction is given, the velocity magnitude is -1.667 m / s, the turbulence intensity is set to 5%, the turbulence viscosity ratio is 10, and the initial mass fraction of ammonia is 0;

[0053] As shown in the Figure 6 attachment, the polluted surface source is set in zones, including the outlet zones on both sides, and multiple inlet zones are set in the middle zone, including the first inlet zone, the second inlet zone, the third inlet zone, and the fourth inlet zone arranged in sequence. Among them, the velocities of the first inlet zone, the second inlet zone, the third inlet zone, and the fourth inlet zone are 0.0135 m / s, 0.00814 m / s, 0.00543 m / s, and 0.00271 m / s respectively, and the ammonia concentrations are 307.22 mg / m 3 、281.62 mg / m 3 、179.21 mg / m 3 and 128.01 mg / m 3 respectively;

[0054] The pipes, tanks, and walls in the workshop are all set as adiabatic no-slip wall boundary conditions. Among them, the wind speed calculation of each air outlet and the calculation of the average wind speed and the average ammonia emission component concentration of the polluted surface source are as follows: The wind speed of the deodorizing air outlet and the process air outlet (the velocity outlet on the surface of the stack) is directly calculated by dividing the deodorizing air volume and the process air volume by the air outlet area; The air volume emitted from the pollution source on the surface of the stack is first estimated as 1.3 times the process air volume, then the average wind speed of the entire pollution source can be directly obtained by dividing the air volume by the air outlet area; The air volume and wind speed of the inlet and return material ports can be obtained according to the air volume conservation; According to the measured ammonia concentrations in the main pipes of the deodorizing air duct and the process air duct, the ammonia emission amount of the entire workshop can be calculated by mass conservation, and the average ammonia emission concentration can be obtained by dividing the ammonia emission amount by the average wind speed of the pollution source; Adjust the pollution source emission amounts and velocities of different zones according to the measured and calculated data;

[0055] S6. Numerical simulation calculation

[0056] In S61, select Coupled for the pressure-velocity coupling scheme in the solution method, LeastSquares Cell Based for the gradient in the spatial discretization method, Second Order for the pressure, Second Order Upwind for the momentum, First Order Upwind for the turbulent kinetic energy, First Order Upwind for the turbulent dissipation rate, and Second Order Upwind for the energy;

[0057] In S62, set the pseudo-transient explicit relaxation factors in the control method to 0.5 for the pressure and momentum, 0.25 for the density, 1 for the body force and turbulent viscosity, and 0.75 for the turbulent kinetic energy, turbulent dissipation rate, and energy;

[0058] In S63, initialize the fluid domain of the geometric model, select standard initialization, choose the entire fluid region as the calculation reference domain, and ensure that the initial concentration of the polluted gas is 0; select the adaptive time step, set the convergence residual to 1e-07, set the number of iterations to 2000 steps, and start the calculation;

[0059] S7. Data processing

[0060] After the calculation converges, as shown in the appendix Figure 7 - Appendix Figure 10 Create the ammonia concentration distribution contour maps of the main personnel activity area, the areas near the inlet and outlet, and the cross-sections at each height in the workshop; as shown in the appendix Figure 11 Create the velocity vector and streamline diagrams;

[0061] As shown in the appendix Figure 12 The simulation results obtained by post-processing are consistent with the measured results in the workshop, and the simulation is completed.

[0062] Finally, it should be noted that: The present invention is not limited to the above-listed embodiments. The above are only the preferred and feasible embodiments of the present invention. The above embodiments are only used to illustrate the technical solutions of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations, modifications, evolutions, and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A simulation method for the concentration diffusion of polluted gas in a sludge composting workshop, characterized in that, It includes the steps of establishing a geometric model of the sludge composting workshop, meshing the geometric model, setting the simulation solver, selecting the calculation model, setting the boundary conditions, numerically simulating and calculating, and data processing steps; The step of setting the boundary conditions includes: partitioning the sludge composting pollution area source, with both sides being outlets and multiple inlets being set in the middle partition.

2. The simulation method for the concentration diffusion of polluted gas in a sludge composting workshop according to claim 1, characterized in that The step of establishing the geometric model of the sludge composting workshop includes: using the modeling software SpaceClaim to establish the geometric model of the sludge composting workshop, only retaining the fluid domain, inlets and outlets in the geometric model, and making the inlets, outlets and fluid domain coupled through shared topology processing.

3. The simulation method for the concentration diffusion of polluted gas in the sludge composting workshop according to claim 1, characterized in that, The step of meshing the geometric model includes: importing the geometric model in the watertight workflow of Fluent Meshing, drawing surface meshes using the size function of Curvature&Proximity, adding boundary layers in the fluid-wall contact area using the smooth-transition offset type, and then filling the meshes with poly-hexcore.

4. The simulation method for the concentration diffusion of polluted gas in a sludge composting workshop according to claim 3, characterized in that The step of setting the simulation solver includes: importing the drawn meshes in Fluent Solution, adjusting the mesh size ratio and setting the unit, selecting the pressure-based, absolute velocity and steady-state time for the solver, and turning on the gravitational acceleration.

5. The simulation method for the concentration diffusion of polluted gas in a sludge composting workshop according to claim 1, characterized in that, The step of selecting the calculation model includes turning on the energy equation; selecting the k-ε Standard model for the turbulence model and turning on the standard wall function; turning on the component transport model and checking the inlet diffusion and energy source terms.

6. The simulation method for the concentration diffusion of polluted gas in the sludge composting workshop according to claim 5, characterized in that, The energy equation includes the mass conservation equation (1), the momentum conservation equations (2)-(4), the energy conservation equation (5) and the component conservation equation (6), In the above formula, t is time; x, y, and z are the three coordinate directions of the rectangular coordinate system of the geometric model space; ρ is the fluid density; u, v, and w are the velocity components of the fluid in the x, y, and z directions respectively; p is the fluid pressure; τ xx , τ xy , τ xz , τ yy , τ yx , τ yz , τ zz , τ zx , τ zy are the respective components of the viscous stress tensor; F x , F y , F z are the external force components acting on the fluid in the x, y, and z directions respectively; T is the temperature; k is the thermal conductivity; c p is the specific heat capacity at constant pressure; S r is the source term in the energy equation; c s is the mass fraction of a certain component; D s is the diffusion coefficient of a certain component; S s is the source term in the component conservation equation.

7. The simulation method for the concentration diffusion of polluted gas in the sludge composting workshop according to claim 2, characterized in that, The step of setting the boundary conditions includes: adding air and polluted gas in the fluid material, mixing the air and polluted gas and designating air as the last component; keeping the fluid domain conditions default; setting the velocities of both side outlets as the on-site measured values and setting the initial pollutant concentrations of both side outlets as zero; setting the velocity of the inlets as the estimated value and setting the initial pollutant concentration of the inlets as the on-site measured value.

8. The simulation method for the concentration diffusion of polluted gas in the sludge composting workshop according to claim 2, characterized in that, The step of numerically simulating and calculating includes: selecting appropriate solution methods and control methods, initializing the fluid domain of the workshop and then starting iterative calculations, where the pressure-velocity coupling scheme selects Coupled; in the spatial discretization method, the gradient selects LeastSquares Cell Based, the pressure selects Second Order, and both the turbulent kinetic energy and the turbulent dissipation rate select First Order Upwind; initializing the fluid domain of the geometric model, selecting standard initialization, choosing the entire fluid domain as the calculation reference domain, and setting the initial polluted gas concentration as zero; selecting Automatic as the time step iterative method, and starting iterative calculations after setting the number of iterative steps.

9. The simulation method for the concentration diffusion of polluted gas in a sludge composting workshop according to claim 8, characterized in that, The data processing steps include: processing the calculation results according to research requirements, verifying the calculation results by combining the measured data of the concentration distribution of workshop pollution gases, adjusting the boundary conditions according to the verification results, and performing iterative calculations again until the calculation results are verified by the measured data.

10. The simulation method for the concentration diffusion of polluted gas in a sludge composting workshop according to claim 9, characterized in that, In the data processing steps, post-processing analysis is performed on the data in the main personnel activity areas and the areas near the inlet and outlet, and visual results are output or chart analysis is performed.

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