Abnormal air volume assessment method for coal-fired unit boiler and hearth safety assessment method

Abstract

The invention provides a coal-fired unit boiler abnormal air volume evaluation method and a hearth safety evaluation method. The method comprises the steps that an analysis structure model is constructed with a combustion area of a coal-fired unit boiler as a computational domain; constructing a reaction model based on the analysis structure model so as to obtain an air volume analysis model; inputting normal induced air volume, operating the air volume analysis model, and obtaining a stable state by adopting a steady-state calculation method; inputting the to-be-evaluated induced air volume, taking a stable state as an initial condition, operating the air volume analysis model, and adopting a transient calculation method to obtain a transient hearth state to judge whether the to-be-evaluated induced air volume is an abnormal air volume or not; the transient hearth state comprises a transient high-temperature flame state of each time step length and transient hearth internal pressure of each time step length. According to the evaluation method, through a simulation means, an actual parameter adjustment test in a boiler system is not needed, the cost for evaluating whether the induced air volume to be evaluated is the abnormal air volume or not and evaluating the safety of the hearth can be greatly reduced, and the repeatability is high.

Description

Technical Field

[0001] The present invention relates to the technical field of energy conservation and safety control of coal-fired power plants, and in particular to a method for evaluating abnormal air volume of a coal-fired unit boiler and a method for evaluating furnace safety. Background Art

[0002] In power plant units, boiler equipment is relatively fragile, and the boiler furnace is one of the core components of the boiler. Its operating safety is related to the operating safety of the entire coal-fired boiler. Instability of boiler furnace combustion is one of the main forms of boiler accidents. Abnormal air volume is one of the key reasons for instability of boiler furnace combustion. Abnormal air volume will cause reduced combustion efficiency and furnace pressure fluctuations, which will affect the stable operation of the boiler. This long-term operating state may further increase the safety risks in the operation of the boiler, causing the boiler furnace to spray fire and smoke and damage, resulting in accidents and economic losses.

[0003] Since the temperature and pressure in the center of the boiler furnace are very high and cannot be directly measured by sensors, the main method of furnace status detection is to indirectly monitor the temperature, pressure and other parameters inside the furnace through a monitoring system installed on the periphery of the boiler furnace to determine its operating status. However, these methods generally have the problem of high working conditions or high costs. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides a method for evaluating abnormal air volume and furnace safety of a coal-fired unit boiler with strong repeatability, which can greatly reduce the cost of evaluating whether the induced draft volume is abnormal and the furnace safety by means of simulation and without the need to actually adjust parameter tests in the boiler system.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows: A method for evaluating abnormal air volume of a coal-fired unit boiler comprises the following steps: Taking the combustion area of ​​the coal-fired unit boiler as the calculation domain, constructing an analytical structural model of the coal-fired unit boiler; Constructing a reaction model based on the analytical structure model, wherein the reaction model includes a turbulent flow model, a radiation heat transfer model, a gas phase combustion reaction model and a solid phase combustion process model; Obtaining an air volume analysis model according to the analysis structure model and the reaction model; Obtain normal induced air volume, induced air volume to be evaluated, time step length and number of time steps; Inputting the normal induced air volume into the air volume analysis model to obtain a stable operating condition; Running the air volume analysis model under the stable working condition and obtaining a stable state by using a steady-state calculation method; In the air volume analysis model, the normal induced air volume is replaced by the induced air volume to be evaluated to obtain the working condition to be evaluated; Under the working condition to be evaluated, taking the stable state as the initial condition, running the air volume analysis model based on the time step and the number of time steps, and adopting a transient calculation method to obtain a transient furnace state; the transient furnace state includes a transient high-temperature flame state for each time step and a transient furnace pressure for each time step; Obtain abnormal air volume judgment criteria; In the same time step, when the transient high-temperature flame state and the transient furnace pressure both meet the abnormal air volume criterion, the induced air volume to be evaluated is judged to be abnormal air volume.

[0006] In some of the embodiments, the combustion area includes a combustion chamber and a burner; the combustion chamber includes a cold ash hopper area, a main combustion area, a burnout area and a horizontal flue area.

[0007] In some of the embodiments, when constructing the analytical structural model of the coal-fired unit boiler, the burner is meshed using an encrypted mesh, and the main combustion zone is meshed using a honeycomb polyhedron mesh.

[0008] In some of the embodiments, the horizontal flue area includes a rear screen superheater, a safe zone and an unsafe zone, wherein the safe zone is located inside the rear screen superheater and the unsafe zone is located outside the rear screen superheater.

[0009] In some of the embodiments, the abnormal air volume criterion includes criterion one and criterion two; The first criterion is that the transient high-temperature flame state is that the tail end of the high-temperature flame extends to the unsafe zone; The second criterion is that the transient furnace pressure is higher than zero; In the same time step, when both the first criterion and the second criterion are satisfied, the induced air volume to be evaluated is an abnormal air volume.

[0010] In some of the embodiments, the second criterion is that the transient furnace pressure range of the furnace located at the bottom of the burnout zone, the cold ash hopper area and the main combustion zone is 200Pa~700Pa.

[0011] In some embodiments, the turbulent flow model uses a swirl correction Model.

[0012] In some of the embodiments, the radiation heat transfer model adopts the P-1 model.

[0013] In some of the embodiments, the gas phase combustion reaction model adopts a non-premixed model, and the solid phase combustion process model includes a precipitation process equation and a combustion equation.

[0014] A furnace safety assessment method comprises the following steps: Taking the combustion area of ​​the coal-fired unit boiler as the calculation domain, constructing an analytical structural model of the coal-fired unit boiler; Constructing a reaction model based on the analytical structure model, wherein the reaction model includes a turbulent flow model, a radiation heat transfer model, a gas phase combustion reaction model and a solid phase combustion process model; Obtaining an air volume analysis model according to the analysis structure model and the reaction model; Obtain normal induced air volume, induced air volume to be evaluated, time step length and number of time steps; Inputting the normal induced air volume into the air volume analysis model to obtain a stable operating condition; Running the air volume analysis model under the stable working condition and obtaining a stable state by using a steady-state calculation method; In the air volume analysis model, the normal induced air volume is replaced by the induced air volume to be evaluated to obtain the working condition to be evaluated; Taking the stable state as an initial condition, operating the working condition to be evaluated under the working condition to be evaluated; Under the working condition to be evaluated, taking the stable state as the initial condition, running the air volume analysis model based on the time step and the number of time steps, and adopting a transient calculation method to obtain a transient furnace state; the transient furnace state includes a transient high-temperature flame state for each time step and a transient furnace pressure for each time step; Obtain abnormal air volume judgment criteria; In the same time step, when the transient high-temperature flame state and the transient furnace pressure both meet the abnormal air volume criterion, the induced air volume to be evaluated is judged to be abnormal air volume; If the induced air volume to be evaluated is an abnormal air volume, it is determined that the coal-fired unit boiler has a risk of combustion instability under the operating condition to be evaluated.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses simulation means without the need to actually adjust parameter tests in the boiler system, which can greatly reduce the cost of determining whether the induced draft volume is abnormal and evaluating the safety of the furnace, and has strong repeatability.

[0016] The present invention inputs the actual adjustment parameters of the unit boiler into the air volume analysis model, and uses CFD calculation simulation to obtain the induced draft volume assessment results and the furnace safety assessment results. It has high repeatability and safety, and can obtain the furnace safety assessment under different induced draft volumes. It can qualitatively analyze the working state of the boiler under abnormal air volume, will not cause actual boiler equipment damage, and has relatively low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic flow chart of the abnormal air volume evaluation method of a coal-fired unit boiler of the present invention; FIG2 (a) is a schematic diagram of the analysis structure model in the present invention; Figure 2 (b) is a schematic diagram of the mesh division of the burner at position A in Figure 2 (a); Figure 3 Schematic diagram of parameter setting of a turbulent flow model in an embodiment of the present invention; Figure 4 Schematic diagram of parameter setting of the radiation heat transfer model in an embodiment of the present invention; Figure 5 Schematic diagram of parameter setting of a gas phase combustion reaction model in an embodiment of the present invention; Figure 6 It is a schematic diagram of the steady-state high-temperature flame state and the steady-state furnace temperature in Example 1 of the present invention; Figure 7 It is a schematic diagram of the steady-state furnace pressure in the steady state in Example 1 of the present invention; Figure 8 It is a schematic diagram of the transient high-temperature flame state and the transient furnace temperature when the running time is 0.4s in Example 1 of the present invention; Fig. 9 It is a schematic diagram of transient furnace pressure when the running time is 0.4s in Example 1 of the present invention; Fig.10 It is a structural schematic diagram of the horizontal flue area in the present invention.

[0018] Among them, the accompanying drawings are marked as: 1. horizontal flue area; 11. rear screen superheater; 12. safe area; 13. unsafe area; 2. burnout area; 3. main combustion area; 4. cold ash hopper area; 5. burner. DETAILED DESCRIPTION

[0019] In order to clearly illustrate the technical features of this solution, the following will be combined with the accompanying drawings and examples to describe in detail the implementation methods of this application, so that the application can fully understand how to use technical means to solve technical problems and achieve the corresponding technical effects and implement them accordingly. The embodiments of this application and the various features in the embodiments can be combined with each other without conflict, and the technical solutions formed are all within the scope of protection of this application.

[0020] In daily production, it is common for the induced draft volume of coal-fired boilers to be abnormal. Therefore, it is necessary to evaluate whether the induced draft volume of the boiler furnace is abnormal and the safety of the boiler furnace under abnormal induced draft volume. However, in reality, abnormal induced draft volume in the boiler furnace will cause economic losses and even casualties. Therefore, simulation is a safe analysis method that can simulate the working state of the boiler furnace when the induced draft volume is abnormal, and then evaluate whether the induced draft volume of the boiler furnace is abnormal and the safety of the boiler furnace under abnormal induced draft volume. Figure 1 The embodiment of the present invention provides a method for evaluating abnormal air volume of a coal-fired boiler, comprising the following steps: The analytical structural model of the coal-fired boiler is constructed with the combustion area of ​​the coal-fired boiler as the calculation domain; see Figure 2 (a), the combustion area includes the combustion chamber and the burner 5; the combustion chamber includes the cold ash hopper area 4, the main combustion area 3, the burnout area 2 and the horizontal flue area 1; Fluent is used to construct the analytical structural model and reaction model, and the combustion area as the calculation domain is meshed to make the mesh quality and quantity fit the computer performance and calculation accuracy requirements; the combustion chamber and the burner 5 are meshed as a whole, so that the mesh nodes overlap and the calculation accuracy is high. In addition, pseudo-diffusion can be avoided during numerical calculation or analysis. When constructing the analytical structural model of the coal-fired boiler, the burner 5 is meshed with an encrypted mesh, see the enlarged view of the mesh division of the burner part in Figure 2 (b), and the main combustion area 3 is meshed with a honeycomb polyhedron mesh. Compared with the tetrahedron mesh, the use of a honeycomb polyhedron mesh can greatly reduce the number of meshes and improve the mesh quality.

[0021] Based on the analytical structural model, the reaction model is constructed. The reaction model includes turbulent flow model, radiation heat transfer model, gas phase combustion reaction model and solid phase combustion process model. In the process of constructing the reaction model, the selection of a suitable model can improve the accuracy and performance of the simulation and has a vital impact on the simulation results. The turbulent flow model uses a swirl correction Model; In the selection of turbulent flow model, it is necessary to comprehensively consider the flow characteristics of the calculation object and the applicability of the optional turbulent flow model. This embodiment selects the k-Ɛ model with swirl correction, namely Realizable Model, the turbulent flow model uses the following two sets of equations to expand the calculation: The k equation describes the transfer of turbulent kinetic energy. The k equation is: ; In the formula, is the fluid density, is the Reynolds stress tensor, For time, is the average velocity component, is the spatial coordinate, are the components of the spatial coordinates, is the dynamic viscosity coefficient, is the turbulent viscosity, is the Prandtl number of turbulent kinetic energy, is the generation term of turbulent kinetic energy, is the buoyancy generation term, is the turbulent kinetic energy dissipation rate, is the vibration term caused by turbulent kinetic energy; The equation describes the transfer of turbulent dissipation rate, The equation is: ; In the formula, is the Prandtl number for the turbulent kinetic energy dissipation rate, is a constant that is part of the turbulent kinetic energy generation term, usually taken as 1.44. is the strain rate, is the constant of the turbulent kinetic energy dissipation term, usually taken as 1.9, is the kinematic viscosity, is the constant used to calculate the dissipation rate term, usually taken as 1.44. is the turbulent kinetic energy dissipation rate, is a constant for the buoyancy generation term, whose value may be adjusted according to the magnitude of the buoyancy effect. is the turbulent kinetic energy; The radiation heat transfer model adopts the P-1 model; in the selection of the radiation heat transfer model, the P-1 model has the advantages of small calculation amount and considering the scattering effect of radiation, so this embodiment selects the P-1 model as the radiation heat transfer model for calculation and solution. The radiation heat transfer model is: ; In the formula, is the radiation heat flux, the subscript "r" is usually used to indicate quantities related to radiation. Represents the absorption coefficient, which is calculated using the built-in gray body weighted average model (WSGGM) in Fluent. is the particle equivalent absorption coefficient, is the particle equivalent scattering coefficient, is the incident radiation.

[0022] The gas phase combustion reaction model adopts a non-premixed model; the non-premixed model is more efficient in solving the transport equations of the mixture components. In this gas phase combustion reaction model, the fuel and oxidant enter the reaction system through different channels. When the non-premixed model is used for modeling, it is assumed that the instantaneous thermochemical state of the fluid is related to the mass fraction of the mixture. When the non-premixed model is used to model the gas phase combustion reaction model, the mass fraction of the mixture is a conserved scalar, which can be expressed by the atomic mass fraction. The mass fraction of the mixture is: ; In the formula, is the mass fraction of the fluid mixture, express Element mass fraction; represents the value of the oxidant flow at the inlet; represents the value of the fuel flow at the inlet; The solid phase combustion process model includes the precipitation process equation and the combustion equation. In the selection of the solid phase combustion process model, since the process of volatile precipitation is very complicated, two equation models are selected to connect for calculation, including the precipitation process equation and the combustion equation of volatiles. The two-equation model divides the precipitation process of volatiles into two parts according to the temperature. Under low temperature environment, the precipitation process equation of volatiles plays a major controlling role, and under high temperature environment, the combustion equation plays a major controlling role. Specifically: ; In the formula, Indicates that in a low temperature environment, the primary slow reaction generation rate factor is 0.3; It indicates the secondary fast reaction generation rate factor under high temperature environment, and its value is 1; and are the reaction rates, Represents coal, represents the volatile matter, Represents coke, Indicates solid state, Indicates gaseous state.

[0023] Obtain the air volume analysis model based on the analysis structure model and reaction model; set reasonable fuel properties and boundary conditions according to the unit operation status, see Figure 3-5 ; Get the normal induced draft volume, the induced draft volume to be evaluated, the time step and the number of time steps; usually, the time step is 0.001 s~0.1s, and the number of time steps is not less than 50 steps. The value of the time step depends on how long the boiler state needs to be obtained under the operating condition to be evaluated. For example, when the time step is 0.01s and the number of time steps is 100 steps, all the operating condition changes that occur every 0.01 seconds within 1 second can be obtained through the transient calculation method; The time step setting refers to Formula 1, which is: ; In the formula, is the time step, is the Courant number, Usually 1~10, is the grid size, is the fluid velocity; Still see Figure 1 , input the normal induced air volume into the air volume analysis model to obtain a stable operating condition; The air volume analysis model is run under stable conditions, and the steady state calculation method is used to obtain the stable state, that is, the boiler operating condition after stabilization under stable conditions; In the air volume analysis model, the normal induced air volume is replaced with the induced air volume to be evaluated to obtain the working condition to be evaluated; Under the working condition to be evaluated, the air volume analysis model is run based on the time step and the number of time steps with the stable state as the initial condition, and the transient furnace state is obtained by the transient calculation method; the transient furnace state includes the transient high-temperature flame state of each time step and the transient furnace pressure of each time step; Obtain abnormal air volume judgment criteria; In the same time step, when both the transient high-temperature flame state and the transient furnace pressure meet the abnormal air volume criterion, it is determined whether the induced air volume to be evaluated is abnormal air volume.

[0024] The present disclosure adopts a method that combines a steady-state calculation method and a transient calculation method for calculation. The steady-state calculation method can only obtain boiler field data after the residuals of each equation converge, that is, the boiler operating condition after stabilization. The abnormal boiler operating condition caused by the abnormal air volume (abnormal induced draft volume) involved in this evaluation method is itself an unstable operating condition. Only using the steady-state method for calculation cannot reflect the detailed process. For example, the highest pressure in the furnace after the abnormal air volume appears may not appear after the residuals of each equation converge, but in the process of convergence of the residuals of each equation. By means of simulation, there is no need to actually adjust the parameters in the boiler system for testing, which can greatly reduce the cost of evaluating whether the induced draft volume is abnormal air volume and the safety of the furnace, and the repeatability is strong.

[0025] Furthermore, the steps of the evaluation method also include: When the induced draft volume to be evaluated is abnormal, the instability time is obtained according to the transient furnace state, and the instability time is the time corresponding to the maximum pressure in the furnace under the working condition to be evaluated.

[0026] In some of these embodiments, see Fig.10The horizontal flue area 1 includes a rear screen superheater 11, a safe area 12 and an unsafe area 13. The safe area 12 is located on the inner side of the rear screen superheater 11, and the unsafe area 13 is located on the outer side of the rear screen superheater 11.

[0027] The abnormal air volume criterion includes criterion one and criterion two; The first criterion is that the transient high temperature flame state is that the tail end of the high temperature flame extends to the unsafe zone 13; The second criterion is that the transient furnace pressure is higher than zero; In the same time step, when both criterion 1 and criterion 2 are established, the induced air volume to be evaluated is abnormal air volume.

[0028] In some of the embodiments, the second criterion is that the transient furnace pressure range at the bottom of the burnout zone 2, the cold ash hopper area 4 and the main combustion zone 3 in the furnace is 200Pa~700Pa.

[0029] By consulting the national standard DL / T 435-2018 explosion-proof regulations for power plant boiler furnaces, the standard value of the transient pressure bearing capacity of the furnace structure is ±8.7 kPa. It can be concluded that by judging whether the induced draft volume to be evaluated is abnormal, the safety of the furnace can be further judged or the safety assessment result of the furnace can be obtained. When the induced draft volume of the induced draft fan is abnormal, that is, the induced draft volume to be evaluated makes both criterion one and criterion two valid, the boiler will spray flames and smoke, and the furnace pressure will rise at the same time. Even when the transient pressure range in the furnace reaches 200Pa~700Pa, it does not reach the pressure limit of the furnace structure, so it will not cause damage to the main structure of the boiler furnace and will not affect the repeated application of the air volume analysis model.

[0030] See also Figure 1 The embodiment of the present invention also provides a furnace safety assessment method, comprising the following steps: The analytical structural model of the coal-fired boiler is constructed with the combustion area of ​​the coal-fired boiler as the calculation domain; Building a reaction model based on the analytical structure model, the reaction model includes a turbulent flow model, a radiation heat transfer model, a gas phase combustion reaction model and a solid phase combustion process model; Obtaining an air volume analysis model based on the analysis structure model and the reaction model; Obtain normal induced air volume, induced air volume to be evaluated, time step length and number of time steps; Input the normal induced air volume into the air volume analysis model to obtain a stable operating condition; The air volume analysis model was run under stable conditions, and the steady state calculation method was used to obtain the stable state; In the air volume analysis model, the normal induced air volume is replaced with the induced air volume to be evaluated to obtain the working condition to be evaluated; Under the working condition to be evaluated, the air volume analysis model is run based on the time step and the number of time steps with the stable state as the initial condition, and the transient furnace state is obtained by the transient calculation method; the transient furnace state includes the transient high-temperature flame state of each time step and the transient furnace pressure of each time step; Obtain abnormal air volume judgment criteria; In the same time step, when both the transient high-temperature flame state and the transient furnace pressure meet the abnormal air volume criterion, it is determined whether the induced air volume to be evaluated is abnormal air volume; If the induced draft volume to be evaluated is abnormal, it is judged that the boiler of the coal-fired unit has a risk of combustion instability under the operating conditions to be evaluated.

[0031] Calculation example 1 The analytical structural model of the coal-fired unit boiler is constructed with the combustion area of ​​the coal-fired unit boiler as the calculation domain; the combustion area includes the combustion chamber and the burner 5; the combustion chamber includes the cold ash hopper area 4, the main combustion area 3, the burnout area 2 and the horizontal flue area 1; when constructing the analytical structural model of the coal-fired unit boiler, the burner 5 is meshed using an encrypted grid, and the main combustion area 3 is meshed using a honeycomb polyhedron grid.

[0032] Building a reaction model based on the analytical structure model, the reaction model includes a turbulent flow model, a radiation heat transfer model, a gas phase combustion reaction model and a solid phase combustion process model; Obtain the air volume analysis model based on the analysis structure model and reaction model; set reasonable fuel properties and boundary conditions according to the unit operation status, see Figure 3-5 ; Get the normal induced air volume, the induced air volume to be evaluated, the time step, and the number of time steps; in this example, the normal induced air volume is 294.4 kg / s, the induced air volume to be evaluated is 30 kg / s, the time step is 0.004 s, and the number of time steps is 750 steps; In the air volume analysis model, input the normal induced air volume of 294.4 kg / s to obtain a stable working condition; Run the air flow analysis model under stable conditions and use the steady-state calculation method to obtain the stable state. Figure 6 , Figure 7 ,from Figure 6 It can be seen from the figure that under the normal induced draft, the steady-state high-temperature flame state is that the tail end of the high-temperature flame mainly stays in the safe zone 12, and a very small part extends to the rear screen superheater 11 but does not exceed the rear screen superheater 11; Figure 7 It can be seen that under this normal induced draft, the steady-state furnace pressure is -42.5Pa below zero; In the air volume analysis model, the normal induced air volume is replaced with the induced air volume to be evaluated 30kg / s to obtain the working condition to be evaluated; Under the working condition to be evaluated, the air volume analysis model is run based on the time step and the number of time steps with the stable state as the initial condition. The transient furnace state is obtained by the transient calculation method. The transient furnace state when the running time is 0.4s is shown in Figure 8 , Fig. 9 ; The transient furnace state includes the transient high temperature flame state at each time step and the transient furnace pressure at each time step; Determine whether the induced draft volume to be evaluated is abnormal based on the transient furnace state.

[0033] from Figure 8 It can be seen from the figure that under the induced draft to be evaluated, the transient high-temperature flame state is that the tail end of the high-temperature flame exceeds the rear screen superheater 11 and extends to the unsafe area 13; Fig. 9 It can be seen that under the induced draft volume to be evaluated, the transient furnace pressure is 572.5Pa, which is higher than zero. According to the criterion for judging whether the induced draft volume is abnormal, it can be seen that the induced draft volume to be evaluated is 30kg / s, which is an abnormal induced draft volume. Under this induced draft volume, the coal-fired unit boiler has the risk of combustion instability.

[0034] contrast Figure 6 The steady high temperature flame state of horizontal flue area 1 is Figure 8 It can be seen from the transient high-temperature flame state of the horizontal flue area 1 that the high-temperature flame and high-temperature flue gas in the furnace will stretch to the unsafe area 13 or even to the tail outlet of the unsafe area 13 when the induced draft fan air volume is abnormal, and even have been ejected outside the unsafe area 13. This situation is consistent with the boiler flame and smoke ejection accident conditions in various accident cases with abnormal air volume. For example, a coal-fired unit has a faulty air and smoke damper, which causes the induced draft fan outlet smoke pressure to rise, and the induced draft fan air volume is abnormal, resulting in a large amount of smoke ejected from the boiler room. This can ensure the approximate accuracy of this simulation.

[0035] contrast Figure 7 The steady-state furnace pressure in the red circle is Fig. 9 It can be seen from the transient furnace pressure in the red circle that the pressure in the furnace will rise sharply when the induced draft fan air volume is abnormal. From the steady state to the transient furnace state at 0.4s, the pressure in the furnace at the bottom of the burnout zone 2, the cold ash hopper area 4 and the main combustion zone 3 in this example rises from -42.5Pa to 572.5Pa. This situation is consistent with the accident conditions in various accident cases where the furnace pressure rises sharply when the induced draft fan volume is abnormal. For example, the induced draft fan of a unit trips due to low oil pressure, and the furnace pressure rises from -42.5Pa to 600Pa. This can further ensure the approximate accuracy of this simulation.

[0036] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A method for evaluating abnormal air volume of a coal-fired boiler, characterized in that: The following steps are involved: Taking the combustion area of ​​the coal-fired unit boiler as the calculation domain, constructing an analytical structural model of the coal-fired unit boiler; Constructing a reaction model based on the analytical structure model, wherein the reaction model includes a turbulent flow model, a radiation heat transfer model, a gas phase combustion reaction model and a solid phase combustion process model; Obtaining an air volume analysis model according to the analysis structure model and the reaction model; Obtain normal induced air volume, induced air volume to be evaluated, time step length and number of time steps; Inputting the normal induced air volume into the air volume analysis model to obtain a stable operating condition; Running the air volume analysis model under the stable working condition and obtaining a stable state by using a steady-state calculation method; In the air volume analysis model, the normal induced air volume is replaced by the induced air volume to be evaluated to obtain the working condition to be evaluated; Under the working condition to be evaluated, taking the stable state as the initial condition, running the air volume analysis model based on the time step and the number of time steps, and adopting a transient calculation method to obtain a transient furnace state; the transient furnace state includes a transient high-temperature flame state for each time step and a transient furnace pressure for each time step; Obtain abnormal air volume judgment criteria; In the same time step, when the transient high-temperature flame state and the transient furnace pressure both meet the abnormal air volume criterion, the induced air volume to be evaluated is judged to be abnormal air volume.

2. The method for evaluating abnormal air volume of a coal-fired boiler according to claim 1, characterized in that: The combustion area includes a combustion chamber and a burner; the combustion chamber includes a cold ash hopper area, a main combustion area, a burnout area and a horizontal flue area.

3. The method for evaluating abnormal air volume of a coal-fired boiler according to claim 2, characterized in that: When constructing the analytical structural model of the coal-fired unit boiler, the burner is meshed using an encrypted mesh, and the main combustion zone is meshed using a honeycomb polyhedron mesh.

4. The method for evaluating abnormal air volume of a coal-fired boiler according to claim 2, characterized in that: The horizontal flue area includes a rear-panel superheater, a safe area and an unsafe area. The safe area is located inside the rear-panel superheater, and the unsafe area is located outside the rear-panel superheater.

5. The method for evaluating abnormal air volume of a coal-fired boiler according to claim 4, characterized in that: The abnormal air volume criterion includes criterion one and criterion two; The first criterion is that the transient high-temperature flame state is that the tail end of the high-temperature flame extends to the unsafe zone; The second criterion is that the transient furnace pressure is higher than zero; In the same time step, when both the first criterion and the second criterion are satisfied, the induced air volume to be evaluated is an abnormal air volume.

6. The method for evaluating abnormal air volume of a coal-fired boiler according to claim 5, characterized in that: The second criterion is that the transient furnace pressure range in the furnace at the bottom of the burnout zone, the cold ash hopper area and the main combustion zone is 200Pa~700Pa.

7. The method for evaluating abnormal air volume of a coal-fired boiler according to claim 1, characterized in that: The turbulent flow model adopts a swirl correction Model.

8. The method for evaluating abnormal air volume of a coal-fired boiler according to claim 1, characterized in that: The radiation heat transfer model adopts the P-1 model.

9. The method for evaluating abnormal air volume of a coal-fired boiler according to claim 1, characterized in that: The gas phase combustion reaction model adopts a non-premixed model, and the solid phase combustion process model includes a precipitation process equation and a combustion equation.

10. A furnace safety assessment method, characterized in that: The following steps are involved: Taking the combustion area of ​​the coal-fired unit boiler as the calculation domain, constructing an analytical structural model of the coal-fired unit boiler; Constructing a reaction model based on the analytical structure model, wherein the reaction model includes a turbulent flow model, a radiation heat transfer model, a gas phase combustion reaction model and a solid phase combustion process model; Obtaining an air volume analysis model according to the analysis structure model and the reaction model; Obtain normal induced air volume, induced air volume to be evaluated, time step length and number of time steps; Inputting the normal induced air volume into the air volume analysis model to obtain a stable operating condition; Running the air volume analysis model under the stable working condition and obtaining a stable state by using a steady-state calculation method; In the air volume analysis model, the normal induced air volume is replaced by the induced air volume to be evaluated to obtain the working condition to be evaluated; Under the working condition to be evaluated, taking the stable state as the initial condition, running the air volume analysis model based on the time step and the number of time steps, and adopting a transient calculation method to obtain a transient furnace state; the transient furnace state includes a transient high-temperature flame state for each time step and a transient furnace pressure for each time step; Obtain abnormal air volume judgment criteria; In the same time step, when the transient high-temperature flame state and the transient furnace pressure both meet the abnormal air volume criterion, the induced air volume to be evaluated is judged to be abnormal air volume; If the induced air volume to be evaluated is an abnormal air volume, it is determined that the coal-fired unit boiler has a risk of combustion instability under the operating condition to be evaluated.

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