Numerical simulation method for coke oven coking process under flue gas external circulation

Abstract

The application discloses a numerical simulation method of coke oven coking process under flue gas external circulation, and belongs to the technical field of computer numerical simulation. The application combines the change of coal physical parameters in the coke oven coking process, and on the basis of the existing mathematical model, couples a user-defined model, i.e. a reversing mode, an effective physical property formula, a flue gas external circulation model and a coking preservation mechanism, so that the numerical simulation of the coke oven coking process under flue gas external circulation is realized. It is verified that the change rule of the carbonization chamber temperature and other information obtained by the method is basically consistent with experimental data, the application can objectively and conveniently and efficiently reveal the coke oven coking behavior under flue gas external circulation, and provides strong theoretical basis and technical support for improvement of coking technology and NO emission reduction of coke ovens.

Description

Technical Field

[0001] The method of this invention belongs to the field of computer numerical simulation technology, and more specifically, relates to a numerical simulation method for the coking process of a coke oven under external flue gas circulation. Background Technology

[0002] In recent years, with the development of the steel industry, higher requirements have been placed on coke quality and its NO emissions. The coke oven is a crucial piece of equipment in coking. During operation, the inlet and outlet positions of the combustion chamber periodically interchange. Within the carbonization chamber, coal undergoes physicochemical processes such as moisture evaporation, volatile matter release, softening, melting, and bonding until solidification into semi-coke, and then shrinkage into coke. In particular, external flue gas recirculation is used to reduce NO emissions. Therefore, it is necessary to understand the coking behavior of coke ovens under external flue gas recirculation, clarify the gas combustion characteristics inside the combustion chamber, and the heat transfer process during the layering and coking of coke cake within the carbonization chamber.

[0003] Previously, existing technologies only used a single parameter, the nose brick temperature, to represent the combustion characteristics inside the combustion chamber, preventing operators from fully understanding the specific combustion state. Currently, with the help of numerical simulation analysis, the combustion characteristics of the coke oven combustion chamber are becoming increasingly clear to operators, allowing for the prediction of NO emission characteristics in the flue gas. As numerical simulation technology continues to be explored in the coke oven application field, the heat transfer model of the carbonization chamber is also constantly evolving. From a constant-property carbonization chamber heat transfer model to a variable-property carbonization chamber heat transfer model, and then to a coupled carbonization chamber-combustion chamber model, from single-chamber calculations to multi-chamber coupling, the model is becoming increasingly closer to the actual coking situation in coke ovens.

[0004] However, most researchers have overlooked the periodic reversal of the vertical flue in the coke oven combustion process, and there are few reports on the coking behavior of coke ovens under external flue gas circulation, thus failing to effectively demonstrate the actual coking process of current coke ovens. Summary of the Invention

[0005] 1. The problem to be solved

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies in capturing and reproducing coking behavior in coke ovens under external flue gas circulation, and to provide a new numerical simulation method for the coking process in coke ovens under external flue gas circulation based on FLUENT UDF and FLUENT Scheme. The technical solution provided by this invention can realistically, objectively, conveniently, and efficiently reveal the coking behavior in coke ovens under external flue gas circulation, thereby providing strong theoretical basis and technical support for the improvement of coking technology and the reduction of NO emissions from coke ovens.

[0007] 2. Technical Solution

[0008] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0009] This invention provides a numerical simulation method for the coking process in a coke oven under external flue gas circulation. Based on an existing basic model, it couples a custom model, namely, a reversing mode, an effective physical property formula for coal in the carbonization chamber, an external flue gas circulation model, and a coking preservation mechanism, to achieve numerical simulation of the coking process in a coke oven. The coupling relationship between the basic model and the custom model is as follows:

[0010] Based on the time step of the basic model iterative calculation, the switching mode determines the number of iterations based on the switching time to complete the current round of iterative calculation. The basic model periodically changes the inlet and outlet boundaries according to the switching mode.

[0011] The basic model provides the outlet flue gas parameters, and the flue gas external circulation model calculates the inlet air parameters based on these parameters, which are then used as the inlet air boundary conditions for the numerical solution of the coke oven.

[0012] Based on the effective physical property formula of coal in the carbonization chamber, the basic model obtains the coking temperature of the center surface of the carbonization chamber, and determines whether coking is completed based on the coking temperature. When coking is completed, a simulation end signal is sent and the software simulation is exited.

[0013] The coking preservation mechanism saves calculated data files based on the coking temperature at different times.

[0014] Furthermore, the specific steps include:

[0015] (1) Establish the geometric model of the coke oven;

[0016] (2) Divide the calculation areas for the fire channel, carbonization chamber and walls, and mesh the calculation areas;

[0017] (3) Determine the basic model of the coking process in a coke oven under external flue gas circulation;

[0018] (4) Set material properties, including fuel composition, wall physical property parameters and effective physical property formulas for coal in the carbonization chamber;

[0019] (5) Define the chemical reaction mechanism of fuel combustion;

[0020] (6) Specify boundary conditions;

[0021] (7) Define initial conditions: initial temperature of coal and initial temperature of furnace wall;

[0022] (8) Set monitoring variables: flue temperature, volume fraction of each component at the outlet, center temperature of carbonization chamber, and heat flux density;

[0023] (9) Discretize the control equations;

[0024] (10) Initialize the entire computational domain, set the time step and the number of iterations, and repeatedly iterate the algebraic equations in the computational domain until the center plane of the coking chamber meets the coking termination temperature and satisfies the conservation law, thus completing the numerical simulation of the coking process in the coke oven;

[0025] (11) According to the coking preservation mechanism, post-process the calculation results to obtain the temperature and component concentration distributions in the vertical flue at different coking times, as well as the variation law of the coal material temperature distribution in the coking chamber.

[0026] Furthermore, the basic model includes the basic conservation equations, the Realizable k-epsilon turbulence model, the P-1 radiation model, the eddy dissipation model, and the NO model.

[0027] Furthermore, the effective physical property formula of the coal in the coking chamber is as follows:

[0028] ① Thermal conductivity

[0029] When 300K ≤ T ≤ 902K:

[0030] λ = 22.4446 - 0.1801·T + 0.0005973·T 2 - 1.06075×10 -6 ·T 3 + 1.1193×10 -9 ·T 4 - 6.9732×10 -13 ·T 5 + 2.01172×10 -16 ·T 6

[0031] When 902K < T ≤ 2000K:

[0032] λ = -9.692 + 0.01151·T

[0033] ② Specific heat

[0034] When 300K ≤ T ≤ 850K:

[0035] C = 2738.274 - 17.4036·T + 0.06455·T 2 - 8.9606×10 -5 ·T 3 + 4.5013×10 -8 ·T 4

[0036] When 850K < T ≤ 1118K:

[0037] C = -0.5801 - 121.6123·T + 0.449·T 2 - 0.0005168·T 3 + 1.9048×10 -7 ·T 4

[0038] When 1118K < T ≤ 2000K:

[0039] C = -3914 + 3.9385·T

[0040] ③ Density

[0041] When 300K ≤ T ≤ 715K:

[0042] ρ = 544.5418 + 2.1303·T - 0.007764·T 2 + 1.1631×10 -5 ·T 3 - 0.6366×10 -8 ·T 4

[0043] When 715K < T ≤ 1194K:

[0044] ρ = 18877.328 - 73.982·T + 0.112103·T 2 - 7.54139×10 -5 ·T 3 + 1.89444×10 -8 ·T 4

[0045] When 1194K < T ≤ 2000K:

[0046] ρ = 622.757 - 0.11208·T

[0047] Furthermore, the inlet and outlet are cyclically reversed, and the reversal mode is as follows:

[0048] Ψ = f(in / out, bc, τ)

[0049] In the formula: Ψ is the reversal mode, in / out is the boundary type, bc is the boundary object, and τ is the reversal period.

[0050] Furthermore, the coking preservation mechanism is specifically as follows: according to different moments, that is, when the coking temperature meets the water evaporation stage of 403K, the volatile matter evolution stage of 728K, the semi-coke stage of 1048, and the coking end temperature of 1323K, the corresponding calculation data files are saved:

[0051] Ω = β i (τ)

[0052] Where: β i Let τ be the coking temperature at time i, τ be the coking time in the coke oven, and Ω be the preservation mechanism.

[0053] Furthermore, in step (2), the computational domain is divided into grids using a block unstructured grid. In step (9), the finite volume method is used to discretize the governing equations. The computation process uses a second-order upwind scheme and the SIMPLE velocity-pressure coupling algorithm. The pressure interpolation scheme uses the STANDARD scheme.

[0054] Furthermore, in the core modeling of step (4), the fuel is blast furnace gas, the wall is silica brick, and the coal is gas coal.

[0055] Furthermore, in step (6), both fuel and air inlets are mass inlets, the outlet is a free outflow boundary, the left and right center planes of the carbonization chamber are symmetrical boundaries, and the others are adiabatic boundaries.

[0056] Furthermore, step (6) determines the mixing inlet mass flow rate, temperature, and component volume fraction under different flue gas external circulation ratios based on the flue gas external circulation model.

[0057] Furthermore, the combustion chemical reaction formula in step (5) is:

[0058] 2CH4 + 3O2 → 2CO + 4H2O

[0059] 2H₂ + O₂ → 2H₂O

[0060] 2CO + O2 → 2CO2.

[0061] 3. Beneficial effects

[0062] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0063] This invention combines the changes in coal physical parameters during the coking process in coke ovens with a user-defined model on the basis of existing mathematical models, thereby enabling numerical simulation of the coking process in coke ovens under external flue gas circulation. Verification shows that the variation patterns of information such as the carbonization chamber temperature during the coking process obtained using the method of this invention are basically consistent with field experimental data. Compared with existing technologies, this invention enables convenient and efficient capture and reproduction of coking behavior in coke ovens under external flue gas circulation, providing an effective solution for the improvement and optimization design of coking technology, and has significant theoretical and practical value. Attached Figure Description

[0064] Figure 1 This is a flowchart illustrating the calculation process of a custom model for the coking process in a coke oven under external flue gas circulation, as described in this invention.

[0065] Figure 2 This is a FLUENT solution block diagram for the coking process in a coke oven under external flue gas circulation according to the present invention.

[0066] Figure 3 This is a calculation area diagram of the coke oven under external flue gas circulation according to the present invention;

[0067] Figure 4 This is a comparison chart of simulated and experimental values ​​of coke oven flue gas outlet parameters under external flue gas circulation according to the present invention;

[0068] Figure 5 The diagram shows the temperature variation of a single vertical flue in a coke oven under external flue gas circulation, obtained by simulation using the simulation method of this invention.

[0069] Figure 6 The diagram shows the temperature change at the center point of the coke oven carbonization chamber under external flue gas circulation, obtained by simulation using the simulation method of this invention.

[0070] Figure 7 This is a graph showing the volume fraction changes of each component at the outlet of the vertical flue gas under external circulation, obtained by simulation using the simulation method of this invention.

[0071] Figure 8 The diagram shows the change in heat flux density between coal and furnace wall under external flue gas circulation, simulated using the simulation method of this invention.

[0072] Figure 9 This is a graph showing the relationship between the NO concentration at the outlet and the flue gas external recirculation ratio, obtained using the simulation method of this invention. Detailed Implementation

[0073] Specifically, the application approach of this invention is explained in detail below:

[0074] The coking process in a coke oven under external flue gas circulation is highly complex, mainly involving gas-phase turbulent combustion in the vertical flue, coal coking in the carbonization chamber, and heat conduction through the partition walls. In general, the basic models include fundamental conservation equations (continuity equation, energy equation, composition equation, and momentum equation), a realizable k-epsilon turbulence model, a P-1 radiation model, a vortex dissipation model, and a NO model. These models, along with user-defined models, exchange heat and mass transfer information during the coking process by considering flue gas outlet composition and mass fraction, flue gas temperature, reversal period, and effective coal properties. They work together to achieve numerical simulation of the coking process under external flue gas circulation. Figure 1 As shown, the coupling relationship between the basic model and the user-defined model is as follows:

[0075] The basic model provides the composition, mass fraction, and temperature of the outlet flue gas. These outlet flue gas parameters are obtained, and the composition, mass fraction, and temperature of the inlet air are calculated. These parameters serve as the inlet air boundary conditions for the numerical solution of the coke oven. The time step is determined based on the iterative calculation of the basic model. Based on the commutation time, the number of iterations is determined, and the calculation for this round of iterations is completed. The basic model is based on... Periodically change import and export boundaries, and according to Determine the boundary values. Based on the coal in the carbonization chamber. The basic model obtains the coking temperature of the center surface of the carbonization chamber. When the coking temperature reaches 1323K, coking is completed, a simulation end signal is sent, and FLUENT is exited. Based on the coking temperature at different times, the calculation data file is saved, namely the moisture evaporation stage at 403K, the volatile matter precipitation stage at 728K, the semi-coke stage at 1048K, and the coking end temperature at 1323K. It also includes the temperature of the vertical flue, the volume fraction of each component at the outlet, the center temperature of the carbonization chamber, and the heat flux density.

[0076] Figure 2 The following is a flowchart of the FLUENT solution for the coking process in a coke oven under external flue gas circulation, as described in this invention.

[0077] 1) The init_func function completes the parameter setting for the coking process of the coke oven under external flue gas circulation, namely the initial coal temperature, initial coal density, and initial furnace wall temperature.

[0078] 2) coal_density, coal_thermal_conductivity, and coal_specific_heat determine the effective physical properties of coal, namely density, thermal conductivity, and specific heat.

[0079] 3) The `coking_proc` procedure and the `coking_func` function exchange information such as the composition, mass fraction, temperature, and switching time of the outlet flue gas. The simulation results are saved based on the coking changes at different times. The calculation process of the `coking_func` function is as follows: Figure 1 As shown. According to Determine the import and export boundaries, and then based on The composition, mass fraction, and temperature of the outlet flue gas, as well as the mixing inlet mass flow rate, air mass flow rate, flue gas external recirculation mass, and flue gas external recirculation ratio, are determined. The mixing inlet composition and mass fraction are calculated, followed by the mixing inlet temperature, and then the boundary conditions for the numerical calculations are determined. Simultaneously, the coal... Based on the different times, when the coking temperature meets the following conditions: 403K for the moisture evaporation stage, 728K for the volatile matter precipitation stage, 1048K for the semi-coke stage, and 1323K for the coking end temperature, the corresponding calculation data file is saved. When the temperature of the center surface of the carbonization chamber reaches 1323K, the coking of the coke oven ends under external flue gas circulation.

[0080] To better understand the technical solution of the present invention, the following detailed description is provided in conjunction with the accompanying drawings and specific embodiments.

[0081] Example

[0082] This embodiment presents a numerical simulation method for the coking process in a coke oven under external flue gas recirculation. Based on FLUENT UDF and FLUENT Scheme, and building upon the existing software's basic model, it considers the characteristics of coking in a coke oven under external flue gas recirculation by coupling a user-defined model, namely... Therefore, the computational fluid dynamics software FLUENT was used to numerically simulate the coking process in a coke oven under external flue gas circulation, specifically including the following steps:

[0083] (1) Select a single vertical flue of the coke oven, as well as the left and right partition walls and half of the carbonization chambers on the left and right sides, with cross-passing holes and exhaust gas circulation holes inside, and establish a geometric model of the coke oven.

[0084] Specifically, such as Figure 3 As shown in the figure, the JN43-58-Ⅱ type coke oven is used as an example in this embodiment. The single vertical flue, the cross-pass hole and the exhaust gas circulation hole of the coke oven are defined as the gas phase zone, and the wall (including the partition wall) and the carbonization chamber are defined as the solid phase zone. The main dimensions of the JN43-58-Ⅱ type coke oven are shown in Table 1.

[0085] Table 1 Main Dimensions of JN43-58-Ⅱ Type Coke Oven

[0086]

[0087] (2) Divide the calculation area of ​​the fire channel, carbonization chamber and walls (including partition walls), and use block unstructured mesh to divide the geometric model into meshes;

[0088] (3) Use FLUENT to establish basic physical models for the grid: continuity equation, momentum equation, energy equation, composition equation, Realizable k-epsilon turbulence model, P-1 radiation model, vortex dissipation model and NO model;

[0089] (4) Set material properties, including fuel composition, wall physical properties, and coal in the carbonization chamber. in:

[0090] 1) The fuel is blast furnace gas, the composition of which is shown in Table 2 below:

[0091] Table 2 Composition of Blast Furnace Gas

[0092]

[0093] 2) The wall is made of silica bricks, and its physical properties are as follows:

[0094] Density:

[0095] ρ w = 1900 kg / m 3

[0096] Specific heat:

[0097] C w = 837.2 + 0.2512·T

[0098] Thermal conductivity:

[0099] λ w = 0.8 + 0.93×10 -3 ·T

[0100] In the formula, T is the temperature of the silica bricks.

[0101] 3) The coal charge is gas coal, and its is as follows:

[0102] ① Thermal conductivity

[0103] When 300K ≤ T ≤ 902K:

[0104] λ = 22.4446 - 0.1801·T + 0.0005973·T 2 - 1.06075×10 -6 ·T 3 + 1.1193×10 -9 ·T 4 - 6.9732×10 -13 ·T 5 + 2.01172×10 -16 ·T 6

[0105] When 902K < T ≤ 2000K:

[0106] λ = - 9.692 + 0.01151·T

[0107] ② Specific heat

[0108] When 300K ≤ T ≤ 850K:

[0109] C = 2738.274 - 17.4036·T + 0.06455·T 2 - 8.9606×10-5 ·T 3 +4.5013×10 -8 ·T 4

[0110] When 850K < T ≤ 1118K:

[0111] C = -0.5801 - 121.6123·T + 0.449·T 2 -0.0005168·T 3 +1.9048×10 -7 ·T 4

[0112] When 1118K < T ≤ 2000K:

[0113] C = -3914 + 3.9385·T

[0114] ③ Density

[0115] When 300K ≤ T ≤ 715K:

[0116] ρ = 544.5418 + 2.1303·T - 0.007764·T 2 +1.1631×10 -5 T 3 -0.6366×10 -8 ·T 4

[0117] When 715K < T ≤ 1194K:

[0118] ρ = 18877.328 - 73.982·T + 0.112103·T 2 -7.54139×10 -5 ·T 3 +1.89444×10 -8 ·T 4

[0119] When 1194K < T ≤ 2000K:

[0120] ρ = 622.757 - 0.11208·T

[0121] (5) Define the chemical reaction mechanism of fuel combustion, specifically including chemical reaction equations, stoichiometric coefficients. The combustion chemical reactions are:

[0122] 2CH4 + 3O2 → 2CO + 4H2O

[0123] 2H2 + O2 → 2H2O

[0124] 2CO + O2 → 2CO2

[0125] (6) Specify boundary conditions: Both fuel and air inlets are mass inlets, the outlet is a free outflow boundary, the left and right center planes of the carbonization chamber are symmetrical boundaries, and the others are adiabatic boundaries, i.e.:

[0126] ①Carbonization chamber

[0127] top:

[0128]

[0129] bottom:

[0130]

[0131] Symmetry plane:

[0132]

[0133] ② Combustion chamber

[0134] Blast furnace gas inlet:

[0135] V bfg =q mbfg =0.0273kg / s, T bfg =1373K

[0136] Air inlet:

[0137] V air =q mair =0.0195kg / s, T bfg =1373K

[0138] The import and export directions are periodically reversed. The implementation details are as follows:

[0139] Ψ = f(in / out, bc, τ)

[0140] In the formula: Ψ represents the commutation mode, in / out represents the boundary type, bc represents the boundary object, and τ represents the commutation period.

[0141] In step (6), the mixing inlet mass flow rate, temperature, and component mass fraction are determined under different flue gas external recirculation ratios. The implementation details are as follows:

[0142] ①Inlet mass flow rate

[0143] m air =m in -m rec

[0144]

[0145] In the formula, m in The mass flow rate of the air-to-circulating flue gas mixture; m rec For circulating flue gas mass flow rate; m air R represents the air mass flow rate; R represents the flue gas recirculation ratio.

[0146] ②Inlet component mass fraction

[0147]

[0148] In the formula, This represents the mass fraction of each component at the mixing inlet; This represents the mass fraction of each component in the air. This represents the mass fraction of each component at the flue gas outlet.

[0149] ③Enthalpy at the entrance

[0150] H in =H air +H rec

[0151]

[0152]

[0153] In the formula, H in H represents the total enthalpy of the mixture at the inlet. air H represents the enthalpy of the air at the inlet. rec The enthalpy of the circulating flue gas at the inlet; The specific heat (T) of each component in air at a specific temperature air =1373K); It represents the specific heat of each component in the flue gas at a specific temperature.

[0154] ④ Temperature at the entrance

[0155]

[0156]

[0157] In the formula, T in The inlet temperature of the mixture; The mass-average specific heat of the mixture.

[0158] (7) Set initial conditions: initial temperature of coal and initial temperature of furnace wall, where:

[0159] ① Initial temperature of coal

[0160] T| coal，t＝0 =300K

[0161] ② Initial density of coal

[0162] ρ| coal，t＝0 =750kg / m 3

[0163] ③ Initial temperature of furnace wall

[0164] T| brick，t＝0 =1400K

[0165] (8) Determine the monitoring variables: temperature of the flue, volume fraction of each component at the outlet, temperature of the carbonization chamber center, heat flux density, etc.

[0166] (9) The above control equations are discretized using the finite volume method. The calculation process uses the second-order upwind scheme and the SIMPLE velocity-pressure coupling algorithm. The pressure interpolation scheme uses the STANDARD scheme.

[0167] (10) Initialize the entire computational domain, set the time step and number of iterations, and iterate the algebraic equations within the computational domain repeatedly until the coking termination temperature of the center surface of the carbonization chamber is met and the conservation law is satisfied, thus completing the numerical simulation of the coking process in the coke oven. Specifically, in this embodiment, the time step is 5 minutes and the reversal cycle is 25 minutes.

[0168] (11) Based on The calculation results are post-processed to obtain the temperature and component concentration distribution in the vertical flue at different coking times, as well as the variation patterns of coal temperature distribution in the carbonization chamber. Specifically, the... The implementation details are as follows:

[0169] To process the numerical simulation results of the coking process in the coking oven, data files are automatically saved according to specific coking temperatures. When the center temperature on both sides of the carbonization chamber reaches 1323K, coking is completed. The results of each stage are saved according to the coking temperature and FLUENT is exited, namely the moisture evaporation stage at 403K, the volatile matter precipitation stage at 728K, the semi-coke stage at 1048K, and the coking end temperature at 1323K.

[0170] Ω=β i (τ)

[0171] Where: β i Let τ be the coking temperature at time i, τ be the coking time in the coke oven, and Ω be the preservation mechanism.

[0172] The simulation method and model for the coke oven were validated and compared with the basic data provided by heat balance calculations, as shown in Table 3 below. Figure 4As shown, a comparison with data from the model without the commutation and experimental data reveals that, after introducing periodic commutation and external flue gas recirculation, the error of the simulated values ​​at the outlet is within a relatively reasonable range, proving the rationality of the numerical model and calculation method.

[0173] Table 3 Comparison of numerical simulation results and experimental results

[0174]

[0175] like Figure 5 As shown, frontcomb represents the rising vertical combustion chamber in the initial state, and backcomb represents the falling vertical combustion chamber in the initial state. With periodic reversals, the rising and falling vertical combustion chambers continuously interchange. Since the combustion process occurs on one side of the rising combustion chamber, its average temperature is consistently higher than that of the falling combustion chamber. However, within the same cycle, the average temperature of both the rising and falling combustion chambers increases slowly, and as the coking process progresses, the average temperature within the combustion chambers shows an upward trend, gradually decreasing the temperature difference between the rising and falling combustion chambers.

[0176] like Figure 6 As shown, the temperature at the center of the coal continuously increases during the coking process, and the rate of increase suddenly accelerates when the temperature reaches around 800K. This is because the thermal conductivity of coal suddenly increases at around 800K, causing heat to transfer more rapidly from the edges of the coal to its center. As the coking process continues, the temperature difference between the furnace wall and the temperature inside the flue gradually decreases due to the gradual increase in furnace wall temperature, thus causing the rate of increase in coal temperature to gradually decrease.

[0177] like Figure 7 As shown, the drastic changes in composition within the coke oven only occur for a short period immediately after the reversal, during which intense combustion reactions take place. For the rest of the time, the component contents remain in relative equilibrium. The volume fractions of CO and O2 at the outlet continuously decrease, while the volume fraction of CO2 continuously increases. Due to the combustion of blast furnace gas, the gas volume at the outlet is smaller than that at the inlet, resulting in a slight increase in N2 content relative to the inlet. In the next adjacent cycle, the combustion chamber outlet becomes the inlet again, and the volume fractions of each component at the inlet remain constant.

[0178] like Figure 8As shown, the initial furnace wall temperature is 1400K and the coal temperature is 300K, resulting in a relatively high heat flux density between the coal and the furnace wall initially. In the early stages of coking, the coal-side temperature increases rapidly while the furnace wall-side temperature decreases rapidly, leading to a rapid decrease in heat flux density. As the coal-side temperature rises slowly, the furnace wall-side temperature increases slowly, causing the heat flux density to increase rapidly again. Simultaneously, due to periodic reversing combustion and the changes in the density, specific heat, and thermal conductivity of coal and the furnace wall with temperature, the temperature difference between the two sides exhibits an alternating periodic decrease. Furthermore, as the coking process progresses, the temperature difference between the two sides gradually decreases and tends to stabilize, and the heat flux also gradually stabilizes.

[0179] like Figure 9 As shown, with the increase of the flue gas external recirculation ratio, the highest temperature inside the vertical flue gradually decreased, from 2086 K without flue gas external recirculation to 1932 K with an external recirculation ratio of 0.2, a decrease of 154 K. The average NO concentration at the outlet also decreased from 1150 mg / m³. 3 Reduced to 130 mg / m 3 The reduction was approximately 89%. With an external recirculation ratio of approximately 0.12, the NO concentration at the outlet was approximately 350 mg / m³. 3 Meanwhile, by considering factors such as the coking time of coal in the carbonization chamber, the flue gas recirculation ratio can be effectively controlled to meet NO emission concentration requirements without affecting coking efficiency. Furthermore, the effects of parameters such as air consumption coefficient, initial coal temperature, reversal time, multi-point heating, and the thermal conductivity of silica bricks on coking behavior in the coke oven can be investigated.

Claims

1. A numerical simulation method for the coking process in a coke oven under external flue gas recirculation, characterized in that, Based on the existing basic model, a custom model is coupled, namely the commutation mode, the effective physical property formula of the coal in the carbonization chamber, the flue gas external circulation model, and the coking preservation mechanism, to achieve the numerical simulation of the coking process of the coke oven. The coupling relationship between the basic model and the custom model is as follows: According to the time step calculated iteratively by the basic model, the commutation mode determines the number of iterations based on the commutation time, completes the current round of iterative calculation, and the basic model replaces the periodic inlet and outlet boundaries according to the commutation mode; The basic model provides the flue gas parameters at the outlet, and the flue gas external circulation model calculates the inlet air parameters based on this and uses them as the inlet air boundary conditions for the numerical solution of the coke oven; According to the effective physical property formula of the coal in the carbonization chamber, the basic model obtains the coking temperature of the center plane of the carbonization chamber, and judges whether coking is completed according to the coking temperature. When coking is completed, a simulation end signal is sent to exit the software simulation; The coking preservation mechanism saves the calculation data files according to the coking temperature at different times.

2. The numerical simulation method for the coking process in a coke oven under external flue gas circulation as described in claim 1, characterized in that, Specifically, it includes the following steps: (1) Establish the geometric model of the coke oven; (2) Divide the calculation areas of the flue, the carbonization chamber, and the wall, and perform mesh division on the calculation areas; (3) Determine the basic model of the coking process of the coke oven under the external circulation of flue gas; (4) Set the material properties, including fuel composition, wall physical property parameters, and the effective physical property formula of the coal in the carbonization chamber; (5) Define the chemical reaction mechanism of fuel combustion; (6) Specify the boundary conditions; (7) Define the initial conditions: the initial temperature of the coal charge and the initial temperature of the furnace wall; (8) Set the monitoring variables: the temperature of the flue, the volume fraction of each component at the outlet, the center temperature of the carbonization chamber, and the heat flux density; (9) Discretize the control equations; (10) Initialize the entire calculation area, set the time step and the number of iterations, and repeatedly iterate the algebraic equations in the calculation area until the center plane of the carbonization chamber meets the coking termination temperature and satisfies the conservation law, completing the numerical simulation of the coking process of the coke oven; (11) According to the coking preservation mechanism, post-process the calculation results to obtain the temperature and component concentration distribution in the flue and the change law of the coal charge temperature distribution in the carbonization chamber at different coking times.

3. A numerical simulation method for the coking process in a coke oven under external flue gas circulation as described in claim 1 or 2, characterized in that, The basic model includes the basic conservation equations, the Realizable k-epsilon turbulence model, the P-1 radiation model, the eddy dissipation model, and the NO model.

4. A numerical simulation method for the coking process of a coke oven under external flue gas circulation as described in claim 1 or 2, characterized in that, The effective physical property formula of the coal in the carbonization chamber is as follows: ① Thermal conductivity When 300K ≤ T ≤ 902K: λ=22.4446-0.1801·T+0.0005973·T 2 -1.06075×10 -6 ·T 3 +1.1193×10 -9 ·T 4 -6.9732×10 -13 ·T 5 +2.01172×10 -16 ·T 6 When 902K < T ≤ 2000K: λ = -9.692 + 0.01151·T ② Specific heat When 300K ≤ T ≤ 850K: C=2738.274-17.4036·T+0.06455·T 2 -8.9606×10 -5 ·T 3 +4.5013×10 -8 ·T 4 When 850K < T ≤ 1118K: C=-0.5801-121.6123·T+0.449·T 2 -0.0005168·T 3 +1.9048×10 -7 ·T 4 When 1118K < T ≤ 2000K: C = -3914 + 3.9385·T ③ Density When 300K ≤ T ≤ 715K: ρ=544.5418+2.1303·T-0.007764·T 2 +1.1631×10 -5 ·T 3 -0.6366×10 -8 ·T 4 When 715K < T ≤ 1194K: ρ=18877.328-73.982·T+0.112103·T 2 -7.54139×10 -5 ·T 3 +1.89444×10 -8 ·T 4 When 1194K < T ≤ 2000K: ρ = 622.757 - 0.11208·T.

5. A numerical simulation method for the coking process in a coke oven under external flue gas circulation as described in claim 1 or 2, characterized in that, Perform periodic commutation on the inlet and outlet, and the commutation mode is as follows: Ψ = f(in / out, bc, τ) In the formula: Ψ represents the commutation mode, in / out represents the boundary type, bc represents the boundary object, and τ represents the commutation period.

6. A numerical simulation method for the coking process in a coke oven under external flue gas circulation according to claim 1 or 2, characterized in that, The coking preservation mechanism is as follows: Based on the different time points when the coking temperature meets the following criteria: 403K for the moisture evaporation stage, 728K for the volatile matter precipitation stage, 1048K for the semi-coking stage, and 1323K for the coking end temperature, the corresponding calculated data file is saved. Ω=β i (t) Where: β i Let τ be the coking temperature at time i, τ be the coking time in the coke oven, and Ω be the preservation mechanism.

7. The numerical simulation method for the coking process of a coke oven under external flue gas circulation as described in claim 2, characterized in that, In step (2), the computational domain is divided into grids using a block unstructured grid. In step (9), the finite volume method is used to discretize the governing equations. The calculation process uses a second-order upwind scheme and the SIMPLE velocity-pressure coupling algorithm. The pressure interpolation scheme uses the STANDARD scheme.

8. The numerical simulation method for the coking process of a coke oven under external flue gas circulation as described in claim 2, characterized in that, In step (4) core modeling, the fuel is blast furnace gas, the wall is silica brick, and the coal is gas coal.

9. The numerical simulation method for the coking process in a coke oven under external flue gas circulation as described in claim 2, characterized in that, In step (6), both fuel and air inlets are mass inlets, the outlet is a free outflow boundary, the left and right center planes of the carbonization chamber are symmetrical boundaries, and the others are adiabatic boundaries; based on the flue gas external circulation model, the mixing inlet mass flow rate, temperature and component volume fraction under different flue gas external circulation ratios are determined.

10. The numerical simulation method according to claim 2, characterized in that, The combustion chemical reaction formula in step (5) is: 2CH4 + 3O2 → 2CO + 4H2O 2H₂ + O₂ → 2H₂O 2CO + O2 → 2CO2.

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