Abnormal air volume evaluation method for coal-fired unit boiler and furnace safety evaluation method

Abstract

The present application provides a kind of coal-fired unit boiler abnormal air volume evaluation method and furnace safety evaluation method, steps are: with the combustion region of coal-fired unit boiler as the calculation domain to construct analysis structure model;Based on analysis structure model, reaction model is constructed to obtain air volume analysis model;Input normal induced draft and run air volume analysis model, steady state is obtained using steady-state calculation method;Input to be evaluated induced draft, with steady state as initial condition, run air volume analysis model, transient furnace state is obtained using transient calculation method to judge whether to be evaluated induced draft is abnormal air volume;Transient furnace state includes transient high-temperature flame state of each time step and transient furnace internal pressure of each time step.The evaluation method can greatly reduce the cost of evaluation on whether to be evaluated induced draft is abnormal air volume and furnace safety evaluation through simulation means, without adjusting parameter test in boiler system, and has strong repeatability.

Description

Technical Field

[0001] This invention relates to the field of energy conservation and safety management technology for coal-fired power plants, specifically to a method for assessing abnormal airflow in a coal-fired boiler and a method for assessing furnace safety. Background Technology

[0002] In power plant units, boiler equipment is relatively vulnerable, and the boiler furnace is one of the core components, its operational safety directly impacting the overall safety of the coal-fired boiler. Furnace combustion instability is one of the main forms of boiler accidents, and abnormal airflow is a key cause of this instability. Abnormal airflow leads to reduced combustion efficiency and furnace pressure fluctuations, thus affecting the stable operation of the boiler. Prolonged operation in this state can further increase safety risks during boiler operation, leading to furnace flameouts, smoke eruptions, and damage, resulting in accidents and economic losses.

[0003] Because the temperature and pressure at the center of a boiler furnace are very high, they cannot be directly measured by sensors. Currently, the main method for detecting furnace condition is to indirectly monitor parameters such as temperature and pressure inside the furnace through monitoring systems installed on the periphery of the boiler furnace to determine its operating status. However, these methods generally have problems such as high operating conditions or excessively high costs. Summary of the Invention

[0004] This invention addresses the problems existing in the prior art by providing a method for assessing abnormal airflow in coal-fired boiler units and a method for assessing furnace safety. This method uses simulation and does not require actual parameter adjustment tests in the boiler system, which can greatly reduce the cost of assessing whether the induced draft volume is abnormal and assessing furnace safety. It is highly repeatable.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for assessing abnormal airflow in a coal-fired boiler unit, comprising the following steps:

[0006] An analytical structural model of the coal-fired boiler unit is constructed using the combustion zone of the boiler unit as the computational domain.

[0007] A reaction model is constructed based on the analytical structure model, which includes a turbulent flow model, a radiation heat transfer model, a gas-phase combustion reaction model, and a solid-phase combustion process model.

[0008] Based on the analytical structure model and the reaction model, an air volume analysis model is obtained;

[0009] Obtain the normal induced draft volume, the induced draft volume to be evaluated, the time step, and the number of time steps;

[0010] Input the normal induced draft volume into the air volume analysis model to obtain stable operating conditions;

[0011] The air volume analysis model is run under the stable operating conditions, and a steady-state calculation method is used to obtain the steady state.

[0012] In the air volume analysis model, the normal induced draft volume is replaced with the induced draft volume to be evaluated to obtain the operating condition to be evaluated;

[0013] Under the operating condition to be evaluated, with the steady state as the initial condition, the air volume analysis model is run based on the time step and the number of time steps, and the transient furnace state is obtained by using a transient calculation method; the transient furnace state includes the transient high-temperature flame state at each time step and the transient furnace pressure at each time step;

[0014] Criteria for determining abnormal airflow;

[0015] Within the same time step, when both the transient high-temperature flame state and the transient furnace pressure meet the abnormal air volume criterion, the induced draft volume to be evaluated is determined to be an abnormal air volume.

[0016] In some embodiments, the combustion zone includes a combustion chamber and a burner; the combustion chamber includes a cold ash hopper area, a main combustion zone, a burnout zone, and a horizontal flue area.

[0017] In some embodiments, when constructing the analytical structural model of the coal-fired boiler unit, the burner is meshed using a denser grid, and the main combustion zone is meshed using a honeycomb polyhedral grid.

[0018] In some embodiments, the horizontal flue region includes a rear screen superheater, a safe zone, and a non-safe zone, wherein the safe zone is located inside the rear screen superheater and the non-safe zone is located outside the rear screen superheater.

[0019] In some embodiments, the abnormal air volume criterion includes criterion one and criterion two;

[0020] The first criterion is that the transient high-temperature flame state is that the tail end of the high-temperature flame extends into the unsafe zone;

[0021] The second criterion is that the transient furnace pressure is higher than zero.

[0022] Within the same time step, when both criterion one and criterion two are met, the induced air volume to be evaluated is an abnormal air volume.

[0023] In some embodiments, the second criterion is that the transient furnace pressure range in the furnace located at the bottom of the burnout zone, the cold ash hopper area, and the main combustion zone is 200 Pa to 700 Pa.

[0024] In some embodiments, the turbulent flow model employs a swirl correction. Model.

[0025] In some embodiments, the radiative heat transfer model employs the P-1 model.

[0026] In some embodiments, the gas-phase combustion reaction model employs a non-premixed model, and the solid-phase combustion process model includes a precipitation process equation and a combustion equation.

[0027] A furnace safety assessment method includes the following steps:

[0028] An analytical structural model of the coal-fired boiler unit is constructed using the combustion zone of the boiler unit as the computational domain.

[0029] A reaction model is constructed based on the analytical structure model, which includes a turbulent flow model, a radiation heat transfer model, a gas-phase combustion reaction model, and a solid-phase combustion process model.

[0030] Based on the analytical structure model and the reaction model, an air volume analysis model is obtained;

[0031] Obtain the normal induced draft volume, the induced draft volume to be evaluated, the time step, and the number of time steps;

[0032] Input the normal induced draft volume into the air volume analysis model to obtain stable operating conditions;

[0033] The air volume analysis model is run under the stable operating conditions, and a steady-state calculation method is used to obtain the steady state.

[0034] In the air volume analysis model, the normal induced draft volume is replaced with the induced draft volume to be evaluated to obtain the operating condition to be evaluated;

[0035] Using the stable state as the initial condition, the operating condition to be evaluated is run under the operating condition to be evaluated.

[0036] Under the operating condition to be evaluated, with the steady state as the initial condition, the air volume analysis model is run based on the time step and the number of time steps, and the transient furnace state is obtained by using a transient calculation method; the transient furnace state includes the transient high-temperature flame state at each time step and the transient furnace pressure at each time step;

[0037] Criteria for determining abnormal airflow;

[0038] Within the same time step, when both the transient high-temperature flame state and the transient furnace pressure meet the abnormal air volume criterion, the induced draft volume to be evaluated is determined to be an abnormal air volume.

[0039] If the induced draft volume to be evaluated is an abnormal volume, then it is determined that the coal-fired boiler has a risk of combustion instability under the operating condition to be evaluated.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] This invention uses simulation to eliminate the need for actual parameter adjustments in the boiler system, which can greatly reduce the cost of assessing whether the induced draft volume is abnormal and the safety of the furnace, and it has strong repeatability.

[0042] This invention obtains induced draft volume assessment results and furnace safety assessment results by inputting actual adjustment parameters in the boiler unit into the air volume analysis model and using CFD calculation simulation. It has high repeatability and safety, obtains furnace safety assessment under different induced draft volumes, qualitatively analyzes the working state of the boiler under abnormal air volumes, and will not cause actual boiler equipment damage. The cost is relatively low. Attached Figure Description

[0043] Figure 1 This is a flowchart illustrating the abnormal airflow assessment method for coal-fired boiler units according to the present invention.

[0044] Figure 2(a) is a schematic diagram of the analytical structure model in this invention;

[0045] Figure 2(b) is a schematic diagram of the grid division of the burner at point A in Figure 2(a);

[0046] Figure 3 This is a schematic diagram of the parameter settings for the turbulent flow model in an embodiment of the present invention;

[0047] Figure 4 This is a schematic diagram of the parameter settings for the radiation heat transfer model in an embodiment of the present invention;

[0048] Figure 5 This is a schematic diagram of the parameter settings for the gas-phase combustion reaction model in an embodiment of the present invention;

[0049] Figure 6 This is a schematic diagram of the steady-state high-temperature flame state and steady-state furnace temperature under steady-state conditions in Example 1 of this invention;

[0050] Figure 7 This is a schematic diagram of the steady-state furnace pressure under steady-state conditions in Example 1 of this invention;

[0051] Figure 8 This is a schematic diagram of the transient high-temperature flame state and transient furnace temperature when the running time is 0.4s in Example 1 of this invention;

[0052] Figure 9 This is a schematic diagram of the transient furnace pressure when the running time is 0.4s in Example 1 of this invention;

[0053] Figure 10 This is a schematic diagram of the structure of the horizontal flue region in this invention.

[0054] The attached diagram is labeled as follows: 1. Horizontal flue area; 11. Rear screen superheater; 12. Safe zone; 13. Unsafe zone; 2. Combustion zone; 3. Main combustion zone; 4. Cold ash hopper area; 5. Burner. Detailed Implementation

[0055] To clearly illustrate the technical features of this solution, the implementation methods of this application will be described in detail below with reference to the accompanying drawings and embodiments. This will allow for a full understanding and implementation of how this application uses technical means to solve technical problems and achieve corresponding technical effects. The embodiments of this application and the various features within them can be combined with each other without conflict, and the resulting technical solutions are all within the protection scope of this application.

[0056] Abnormal induced draft rates are common in coal-fired boiler units during daily production. Therefore, it is necessary to determine whether the induced draft rate in the boiler furnace is abnormal and to conduct a safety assessment under abnormal conditions. However, in reality, abnormal induced draft rates in the boiler furnace can cause economic losses and even casualties. Therefore, simulation is a safe analytical method that can simulate the working state of the boiler furnace under abnormal induced draft rates, thereby assessing whether the induced draft rate is abnormal and the safety of the boiler furnace under such conditions. (See also...) Figure 1 This invention provides a method for assessing abnormal airflow in a coal-fired boiler, comprising the following steps:

[0057] An analytical structural model of a coal-fired boiler unit was constructed using the combustion zone of the boiler as the computational domain. Referring to Figure 2(a), the combustion zone includes the combustion chamber and burner 5. The combustion chamber comprises the cold ash hopper region 4, the main combustion zone 3, the burnout zone 2, and the horizontal flue region 1. Fluent was used to construct the analytical structural model and reaction model. The combustion zone, serving as the computational domain, was meshed to ensure that the mesh quality and quantity met the performance and accuracy requirements of the computer. Meshing the combustion chamber and burner 5 as a whole allows for overlapping mesh nodes, resulting in high computational accuracy. Furthermore, it avoids pseudo-diffusion phenomena during numerical calculations or analysis. When constructing the analytical structural model of the coal-fired boiler unit, the burner 5 was meshed using a denser mesh (see the enlarged view of the burner mesh in Figure 2(b)). The main combustion zone 3 was meshed using a honeycomb polyhedral mesh. Compared to tetrahedral meshes, using a honeycomb polyhedral mesh significantly reduces the number of meshes and improves mesh quality.

[0058] Reaction models are constructed based on analytical structural models, including turbulent flow models, radiation heat transfer models, gas-phase combustion reaction models, and solid-phase combustion process models. In the process of constructing reaction models, selecting appropriate models can improve the accuracy and performance of simulations and has a crucial impact on the simulation results.

[0059] The turbulent flow model uses a swirl correction. Model; In selecting a turbulent flow model, it is necessary to comprehensively consider the flow characteristics of the computational object and the applicability of the available turbulent flow models. In this embodiment, the k-α model with swirl correction, i.e., Realizable, is selected. The model, a turbulent flow model, is calculated using the following two sets of equations:

[0060] The k-equation describes the transfer of turbulent kinetic energy. The k-equation is:

[0061] ;

[0062] In the formula, For fluid density, Let Reynolds stress tensor be the stress tensor. For time, For the average velocity component, For spatial coordinates, These are the components of the spatial coordinates. The dynamic viscosity coefficient is... For turbulent viscosity, The Prandtl number is the turbulent kinetic energy. For the generation of turbulent kinetic energy, For buoyancy generation, The turbulent kinetic energy dissipation rate, The vibration term is caused by turbulent kinetic energy;

[0063] The equation describes the transfer of turbulent dissipation rate. The equation is:

[0064] ;

[0065] In the formula, The Prandtl number is the rate of turbulent kinetic energy dissipation. This is a constant that forms part of the turbulent kinetic energy generation term, and is typically taken as 1.44. For strain rate, This is a constant for the turbulent kinetic energy dissipation term, typically taken as 1.9. Kinematic viscosity, The constant used to calculate the dissipation rate term is typically taken as 1.44. The turbulent kinetic energy dissipation rate, This is a constant for the buoyancy generation term, and its value may be adjusted according to the magnitude of the buoyancy effect. It is turbulent kinetic energy;

[0066] The P-1 model is used for radiation heat transfer. Among the various radiation heat transfer models, the P-1 model has advantages such as low computational cost and consideration of radiation scattering. Therefore, this embodiment selects the P-1 model for calculation and solution. The radiation heat transfer model is as follows:

[0067] ;

[0068] In the formula, For radiative heat flux, the subscript "r" is typically used to indicate quantities related to radiation. The absorption coefficient is represented by the gray body weighted average (WSGGM) model built into Fluent. The particle equivalent absorption coefficient, The equivalent scattering coefficient of the particles, This is incident radiation.

[0069] The gas-phase combustion reaction model employs a non-premixed model. The non-premixed model offers higher efficiency in solving the transport equations for the mixture components. In this model, fuel and oxidizer enter the reaction system through separate channels. When using the non-premixed model, it is assumed that the instantaneous thermochemical state of the fluid is related to the mass fraction of the mixture. In this non-premixed model, the mass fraction of the mixture is a conserved scalar, which can be expressed as atomic mass fraction. The mass fraction of the mixture is:

[0070] ;

[0071] In the formula, The mass fraction of the fluid mixture. express Element mass fraction; This indicates the value of the oxidant flow at the inlet; This represents the value of the fuel flow at the inlet;

[0072] The solid-phase combustion process model includes a precipitation process equation and a combustion equation. Due to the complexity of the volatile matter precipitation process, a two-equation model is used for calculation. Specifically, it includes the volatile matter precipitation process equation and the combustion equation. The two-equation model divides the volatile matter precipitation process into two parts according to temperature. At low temperatures, the volatile matter precipitation process equation plays a major controlling role; at high temperatures, the combustion equation plays a major controlling role. Specifically:

[0073] ;

[0074] In the formula, This indicates the rate of formation of a slow reaction under low-temperature conditions, with a value of 0.3. This indicates the secondary fast reaction formation rate factor under high temperature conditions, with a value of 1. and All represent reaction rates. It represents coal. Indicates volatile matter, It refers to coke. Indicates solid state. It indicates a gaseous state.

[0075] An airflow analysis model was obtained based on the structural and reaction models; reasonable fuel properties and boundary conditions were set according to the unit's operating status, see [reference needed]. Figure 3-5 ;

[0076] Obtain the normal induced draft volume, the induced draft volume to be evaluated, the time step, and the number of time steps. Typically, the time step is 0.001 s to 0.1 s, and the number of time steps is not less than 50. The value of the number of time steps depends on how long the boiler state under the operating condition to be evaluated needs to be obtained. For example, when the time step is 0.01 s and the number of time steps is 100, all changes in the boiler's operating condition that occur every 0.01 seconds within 1 second can be obtained through transient calculation methods.

[0077] The time step setting refers to Formula 1, which is:

[0078] ;

[0079] In the formula, For time step, Let be the Courant number. Usually, the value is 1 to 10. For grid size, For fluid velocity;

[0080] See also Figure 1 By inputting the normal induced draft volume into the air volume analysis model, a stable operating condition can be obtained.

[0081] The air volume analysis model is operated under stable conditions, and the steady-state calculation method is used to obtain the steady state, that is, the boiler operating condition after stabilization under stable conditions.

[0082] In the air volume analysis model, the normal induced air volume is replaced with the induced air volume to be evaluated to obtain the operating condition to be evaluated.

[0083] Under the operating condition to be evaluated, with a steady state as the initial condition, the air volume analysis model is run based on the time step and the number of time steps. The transient furnace state is obtained by using the transient calculation method. The transient furnace state includes the transient high-temperature flame state at each time step and the transient furnace pressure at each time step.

[0084] Criteria for determining abnormal airflow;

[0085] Within the same time step, when both the transient high-temperature flame state and the transient furnace pressure meet the abnormal air volume criteria, it is determined whether the induced draft volume to be evaluated is an abnormal air volume.

[0086] This disclosure employs a combination of steady-state and transient calculation methods. Steady-state calculations only yield boiler field data after the residuals of the equations have converged, representing the stable boiler operating condition. The abnormal boiler operating condition caused by abnormal airflow (abnormal induced draft) involved in this evaluation method is itself an unstable condition. Steady-state calculations alone cannot capture the detailed process; for example, the highest furnace pressure after the abnormal airflow occurs may not appear after the residuals of the equations have converged, but rather during the convergence process. Simulation eliminates the need for actual parameter adjustments in the boiler system, significantly reducing the cost of assessing whether the induced draft is abnormal and evaluating furnace safety, while also ensuring high repeatability.

[0087] Furthermore, the evaluation method also includes the following steps:

[0088] When the induced draft volume to be evaluated is an abnormal flow rate, the instability time is obtained based on the transient furnace state. The instability time is the time corresponding to the maximum pressure in the furnace under the operating condition to be evaluated.

[0089] In some of these embodiments, see Figure 10 The horizontal flue region 1 includes a rear screen superheater 11, a safe zone 12, and an unsafe zone 13. The safe zone 12 is located inside the rear screen superheater 11, and the unsafe zone 13 is located outside the rear screen superheater 11.

[0090] Abnormal air volume criteria include criterion one and criterion two;

[0091] Criterion 1 is that the transient high-temperature flame state is that the tail end of the high-temperature flame extends into the unsafe zone 13;

[0092] Criterion 2 is that the transient pressure inside the furnace is higher than zero;

[0093] Within the same time step, when both criterion one and criterion two are met, the induced draft volume to be evaluated is an abnormal air volume.

[0094] In some embodiments, the second criterion is that the transient furnace pressure range in the bottom of the burnout zone 2, the cold ash hopper area 4, and the main combustion zone 3 is 200 Pa to 700 Pa.

[0095] By consulting the national standard DL / T 435-2018, "Explosion-proof Code for Boiler Furnaces in Power Plants," the standard value for the transient pressure-bearing capacity of the furnace structure is ±8.7 kPa. Therefore, it can be concluded that the safety of the furnace or the results of a furnace safety assessment can be obtained by judging whether the induced draft volume to be evaluated is abnormal. When the induced draft volume of the induced draft fan is abnormal, i.e., when the induced draft volume to be evaluated makes both criteria one and two true, it will cause the boiler to emit flames and smoke, and simultaneously increase the furnace pressure. Even when the transient furnace pressure ranges from 200 Pa to 700 Pa, it does not reach the pressure-bearing 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.

[0096] See Figure 1 This invention also provides a furnace safety assessment method, comprising the following steps:

[0097] An analytical structural model of a coal-fired boiler unit is constructed using the combustion zone of the boiler unit as the computational domain.

[0098] The reaction model is constructed based on the analysis of the structural 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.

[0099] The air volume analysis model is obtained based on the structural model and the reaction model.

[0100] Obtain the normal induced draft volume, the induced draft volume to be evaluated, the time step, and the number of time steps;

[0101] Input the normal induced draft volume into the air volume analysis model to obtain stable operating conditions;

[0102] The air volume analysis model is operated under stable conditions, and the steady-state calculation method is used to obtain the steady state.

[0103] In the air volume analysis model, the normal induced air volume is replaced with the induced air volume to be evaluated to obtain the operating condition to be evaluated.

[0104] Under the operating condition to be evaluated, with a steady state as the initial condition, the air volume analysis model is run based on the time step and the number of time steps. The transient furnace state is obtained by using the transient calculation method. The transient furnace state includes the transient high-temperature flame state at each time step and the transient furnace pressure at each time step.

[0105] Criteria for determining abnormal airflow;

[0106] Within the same time step, when both the transient high-temperature flame state and the transient furnace pressure meet the abnormal air volume criteria, it is determined whether the induced draft volume to be evaluated is an abnormal air volume.

[0107] If the induced draft volume to be evaluated is abnormal, it is determined that the coal-fired boiler has a risk of combustion instability under the operating conditions to be evaluated.

[0108] Calculation example 1

[0109] An analytical structural model of a coal-fired boiler unit is constructed using the combustion zone of the boiler unit as the computational domain. The combustion zone includes the combustion chamber and burner 5. The combustion chamber includes the cold ash hopper region 4, the main combustion zone 3, the burnout zone 2, and the horizontal flue region 1. When constructing the analytical structural model of the coal-fired boiler unit, the burner 5 is meshed using a dense mesh, and the main combustion zone 3 is meshed using a honeycomb polyhedral mesh.

[0110] The reaction model is constructed based on the analysis of the structural 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.

[0111] An airflow analysis model was obtained based on the structural and reaction models; reasonable fuel properties and boundary conditions were set according to the unit's operating status, see [reference needed]. Figure 3-5 ;

[0112] Obtain the normal induced draft volume, the induced draft volume to be evaluated, the time step, and the number of time steps; in this example, the normal induced draft volume is 294.4 kg / s, the induced draft volume to be evaluated is 30 kg / s, the time step is 0.004 s, and the number of time steps is 750.

[0113] A stable operating condition was obtained by inputting a normal induced draft volume of 294.4 kg / s into the air volume analysis model;

[0114] The air volume analysis model operates under stable conditions, and the steady-state calculation method is used to obtain the steady state. (See [link / reference]). Figure 6 , Figure 7 ,from Figure 6 As can be seen from this, under this normal induced draft volume, the steady-state high-temperature flame state is that the tail end of the high-temperature flame mainly remains in the safe zone 12, with a very small portion extending to the rear superheater 11 but not exceeding it; from Figure 7 As can be seen from this, under this normal induced draft volume, the steady-state pressure inside the furnace is -42.5 Pa, which is below zero.

[0115] In the air volume analysis model, the normal induced air volume is replaced with the induced air volume to be evaluated, 30 kg / s, to obtain the working condition to be evaluated.

[0116] Under the operating condition to be evaluated, with a steady state as the initial condition, and based on the time step and the number of time steps, the air volume analysis model is run. The transient furnace state is obtained using a transient calculation method. The transient furnace state at a running time of 0.4s is shown in [reference]. Figure 8 , Figure 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.

[0117] Determine whether the induced draft volume to be evaluated is abnormal based on the transient furnace status.

[0118] from Figure 8 As can be seen from this, under the induced draft volume to be evaluated, the transient high-temperature flame state is that the tail end of the high-temperature flame extends beyond the rear superheater 11 and into the unsafe zone 13; from Figure 9 As can be seen from the data, under the induced draft volume to be evaluated, the transient furnace pressure is 572.5 Pa, which is higher than zero. According to the criteria for judging whether the induced draft volume is abnormal, the induced draft volume to be evaluated is 30 kg / s, which is an abnormal induced draft volume. Under this induced draft volume, the coal-fired boiler has the risk of combustion instability.

[0119] contrast Figure 6 Steady-state high-temperature flame state in horizontal flue region 1 and Figure 8 The transient high-temperature flame state in horizontal flue region 1 shows that, under abnormal induced draft fan flow conditions, the high-temperature flame and flue gas in the furnace will be stretched towards unsafe zone 13 and even towards the tail outlet of unsafe zone 13, and may even have been ejected outside unsafe zone 13. This situation is consistent with the boiler flame and smoke ejection accidents caused by abnormal airflow in various accident cases. For example, a malfunction of the flue gas damper in a coal-fired unit caused the flue gas pressure at the induced draft fan outlet to rise, resulting in abnormal induced draft fan flow and a large amount of flue gas being ejected from the boiler room. This ensures the approximate accuracy of this simulation.

[0120] contrast Figure 7 The steady-state furnace pressure within the red circle and Figure 9 The transient furnace pressure within the red circle shows that the furnace pressure rises significantly under abnormal induced draft fan conditions. From the steady-state state to the transient furnace state at 0.4 s, in this example, the pressure in the furnace located at the bottom of burnout zone 2, cold ash hopper area 4, and main combustion zone 3 rises from -42.5 Pa to 572.5 Pa. This situation is consistent with the accident conditions of significant furnace pressure rise when induced draft fan volume is abnormal in various accident cases. For example, in a certain unit, the induced draft fan oil pressure was low and tripped, causing the furnace pressure to rise from -42.5 Pa to 600 Pa. This further ensures the approximate accuracy of this simulation.

[0121] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for assessing abnormal airflow in a coal-fired boiler unit, characterized in that: Includes the following steps: An analytical structural model of the coal-fired boiler unit is constructed using the combustion zone of the boiler unit as the computational domain. A reaction model is constructed based on the analytical structure model, which includes a turbulent flow model, a radiation heat transfer model, a gas-phase combustion reaction model, and a solid-phase combustion process model. Based on the analytical structure model and the reaction model, an air volume analysis model is obtained; Obtain the normal induced draft volume, the induced draft volume to be evaluated, the time step, and the number of time steps; The time step is set to 0.001s ~ 0.1s; Input the normal induced draft volume into the air volume analysis model to obtain stable operating conditions; The air volume analysis model is run under the stable operating conditions, and a steady-state calculation method is used to obtain the steady state. In the air volume analysis model, the normal induced draft volume is replaced with the induced draft volume to be evaluated to obtain the operating condition to be evaluated; Under the operating condition to be evaluated, with the steady state as the initial condition, the air volume analysis model is run based on the time step and the number of time steps, and the transient furnace state is obtained by using a transient calculation method; the transient furnace state includes the transient high-temperature flame state at each time step and the transient furnace pressure at each time step; Criteria for determining abnormal airflow; Within the same time step, when both the transient high-temperature flame state and the transient furnace pressure meet the abnormal air volume criterion, the induced draft volume to be evaluated is determined to be an abnormal air volume. The combustion zone includes a combustion chamber; the combustion chamber includes a horizontal flue area; The horizontal flue area includes a rear screen superheater and a non-safe zone, with the non-safe zone located outside the rear screen superheater. The abnormal air volume criteria include 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 into the unsafe zone; The second criterion is that the transient furnace pressure is higher than zero. Within the same time step, when both criterion one and criterion two are met, the induced draft volume to be evaluated is an abnormal air volume. When the induced draft volume to be evaluated is the abnormal air volume, 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 operating condition to be evaluated.

2. The method for assessing abnormal airflow in a coal-fired boiler unit according to claim 1, characterized in that: The combustion zone also includes a burner, and the combustion chamber also includes a cold ash hopper area, a main combustion zone, and a burnout zone.

3. The method for assessing abnormal airflow in a coal-fired boiler unit according to claim 2, characterized in that: When constructing the analytical structural model of the coal-fired boiler unit, the burner is meshed using a denser mesh, and the main combustion zone is meshed using a honeycomb polyhedral mesh.

4. The method for assessing abnormal airflow in a coal-fired boiler unit according to claim 2, characterized in that: The horizontal flue area also includes a safety zone, which is located inside the rear screen superheater.

5. The method for assessing abnormal airflow in a coal-fired boiler unit according to claim 2, characterized in that: The second criterion is that the transient furnace pressure range in the furnace located at the bottom of the burnout zone, the cold ash hopper area, and the main combustion zone is 200Pa~700Pa.

6. The method for assessing abnormal airflow in a coal-fired boiler unit according to claim 1, characterized in that: The turbulent flow model uses a swirl correction. Model.

7. The method for assessing abnormal airflow in a coal-fired boiler unit according to claim 1, characterized in that: The radiation heat transfer model adopted is the P-1 model.

8. The method for assessing abnormal airflow in a coal-fired boiler unit 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.

9. A method for assessing furnace safety, characterized in that: Includes the following steps: An analytical structural model of the coal-fired boiler unit is constructed using the combustion zone of the boiler unit as the computational domain. A reaction model is constructed based on the analytical structure model, which includes a turbulent flow model, a radiation heat transfer model, a gas-phase combustion reaction model, and a solid-phase combustion process model. Based on the analytical structure model and the reaction model, an air volume analysis model is obtained; Obtain the normal induced draft volume, the induced draft volume to be evaluated, the time step, and the number of time steps; Input the normal induced draft volume into the air volume analysis model to obtain stable operating conditions; The air volume analysis model is run under the stable operating conditions, and a steady-state calculation method is used to obtain the steady state. In the air volume analysis model, the normal induced draft volume is replaced with the induced draft volume to be evaluated to obtain the operating condition to be evaluated; Under the operating condition to be evaluated, with the steady state as the initial condition, the air volume analysis model is run based on the time step and the number of time steps, and the transient furnace state is obtained by using a transient calculation method; the transient furnace state includes the transient high-temperature flame state at each time step and the transient furnace pressure at each time step; Criteria for determining abnormal airflow; Within the same time step, when both the transient high-temperature flame state and the transient furnace pressure meet the abnormal air volume criterion, the induced draft volume to be evaluated is determined to be an abnormal air volume. If the induced draft volume to be evaluated is an abnormal air volume, then it is determined that the coal-fired boiler has a risk of combustion instability under the operating condition to be evaluated. The combustion zone includes a combustion chamber; the combustion chamber includes a horizontal flue area; The horizontal flue area includes a rear screen superheater and a non-safe zone, with the non-safe zone located outside the rear screen superheater. The abnormal air volume criteria include 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 into the unsafe zone; The second criterion is that the transient furnace pressure is higher than zero. Within the same time step, when both criterion one and criterion two are met, the induced draft volume to be evaluated is an abnormal air volume. When the induced draft volume to be evaluated is the abnormal air volume, 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 operating condition to be evaluated.

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