Simulation analysis method for oil-gas synergistic combustion based on subcritical boiler load working condition

Abstract

The application discloses a simulation analysis method for oil-gas collaborative combustion based on a subcritical boiler load working condition and relates to the technical field of data analysis.The application realizes the query and determination of the ignition delay time by establishing a three-dimensional model of the boiler and local grid segmentation, setting parameters and constructing a gas delay table and an oil delay table, simulates the interruption of natural gas supply, actively increases the oil pressure discrete value or reduces the oil particle discrete value according to the flame distance variation and the simulation switching time, ensures that the fuel oil flame timely replaces, finally calculates the radial deviation value of the center line of the coal powder track, optimizes the gas-coal mixing ratio by using the golden section method, and selects the candidate parameter combination with the largest volume of the high-temperature zone.The application realizes the identification and quantification of the mapping relationship between the axial deviation caused by the natural gas ignition delay and the radial deviation of the center line of the coal powder track, and finally maximizes the volume of the high-temperature zone under the premise that the deviation value is controllable by adaptively adjusting the key operation parameters and reconstructing the delay table.

Description

Technical Field

[0001] This invention relates to the field of data analysis technology, specifically to a simulation analysis method for oil-gas co-combustion based on subcritical boiler load conditions. Background Technology

[0002] Under extremely low load conditions in subcritical coal-fired units, the furnace temperature drops significantly. The high-temperature flame core formed by the premixed natural gas swirl and the centerline of the dense-phase pulverized coal trajectory generated by the pulverized coal separation device experience axial deviation due to the natural gas ignition delay, leading to the failure of staged ignition in oil-gas co-combustion. Existing technologies have the following drawbacks: First, current simulation methods cannot accurately quantify the impact of ignition delay times of natural gas and fuel oil on the flame core position under different parameter combinations. This results in the inability to adaptively compensate for flame core drift caused by ignition delay during simulation, and the spatial misalignment between the high-temperature flame core and the centerline of the dense-phase pulverized coal trajectory cannot be accurately identified and corrected, making it difficult to guarantee the temporal and spatial matching of staged ignition. Second, existing solutions cannot automatically determine whether the current oil pressure and oil droplet parameters meet the requirements for rapid response, relying solely on repeated manual trial and error adjustments. This not only fails to achieve efficient convergence but also easily misses the optimal solution due to the large parameter combination space, resulting in a persistently unsatisfactory ignition success rate for oil-gas co-combustion under extremely low load conditions.

[0003] A simulation analysis method for oil-gas co-combustion is needed to solve the above problems. This method involves constructing gas delay tables and oil delay tables to accurately predict ignition delay, automatically adjusting oil pressure and oil droplet parameters through natural gas interruption disturbance tests, modifying simulation parameters based on the deviation between pulverized coal trajectory and flame distance, and selecting the optimal parameter combination based on the principle of maximizing the volume of the high-temperature zone. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a simulation analysis method for oil-gas co-combustion based on subcritical boiler load conditions. This method solves the problem of staged ignition failure in oil-gas co-combustion caused by axial deviation between the high-temperature fire core position formed by the premixed natural gas swirl and the center line of the dense-phase pulverized coal trajectory generated by the pulverized coal concentration separation device under extremely low load conditions of subcritical coal-fired units due to the delayed ignition of natural gas.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution: a simulation analysis method for oil-gas co-combustion based on subcritical boiler load conditions, comprising the following steps: establishing a three-dimensional model of the boiler and performing local mesh division, generating a list of mesh cells and starting points of pulverized coal particles.

[0006] Simulation parameters were assigned, and discrete values ​​for gas velocity and air-fuel ratio were set at the natural gas chamber outlet, and discrete values ​​for oil pressure and oil droplets were set at the fuel nozzle outlet. At the same time, the pulverized coal trajectory was set.

[0007] A gas delay table is constructed based on the discrete values ​​of gas velocity and air-fuel ratio, and an oil delay table is constructed based on the discrete values ​​of oil pressure and oil droplets. Ignition determination and composition update are performed for each grid cell. At the same time, coal powder particles are released according to the starting point list. The process is repeated iteratively until the set conditions are met.

[0008] Simulate a natural gas supply interruption. If the change in flame distance before and after the interruption is greater than a set threshold, increase the oil pressure dispersion value and rebuild the oil delay table. If the simulation switching time is greater than a time threshold, decrease the oil droplet dispersion value and rebuild the oil delay table.

[0009] If the radial deviation of the coal powder trajectory centerline is greater than the deviation threshold, the simulation parameters are modified and the combustion simulation is repeated. Based on the deviation value, the optimal simulation parameters, oil pressure discrete value, and oil droplet discrete value are selected in combination with the volume of the high-temperature zone.

[0010] Compared with existing technologies, this invention has the following advantages: By establishing a three-dimensional boiler model and local mesh segmentation, this invention provides a high-resolution geometric basis for accurately capturing the ignition delay of natural gas and the trajectory of pulverized coal. Furthermore, by setting parameters and constructing gas delay tables and oil delay tables, it enables rapid querying and accurate determination of ignition delay time. Then, by simulating a natural gas supply interruption, it actively increases the oil pressure dispersion value or decreases the oil droplet dispersion value based on the flame distance change and the simulated switching time, ensuring that the fuel oil flame can take over in a timely manner. Finally, it calculates the radial deviation value of the pulverized coal trajectory centerline, optimizes the gas-coal blending ratio using the golden section method, and selects the candidate parameter combination with the largest high-temperature zone volume. This invention achieves the identification and quantification of the mapping relationship between the axial deviation caused by the natural gas ignition delay and the radial deviation of the pulverized coal trajectory centerline from the source. By adaptively adjusting key operating parameters and reconstructing the delay tables, it ultimately maximizes the high-temperature zone volume while ensuring the deviation value is controllable, thus completely solving the technical problem of staged ignition failure in oil-gas co-combustion under extremely low loads. Attached Figure Description

[0011] Figure 1 This is a flowchart of the simulation analysis method for oil-gas co-combustion based on subcritical boiler load conditions according to the present invention;

[0012] Figure 2 This is a flowchart of the process for constructing the gas delay table in the simulation analysis method for oil-gas co-combustion based on subcritical boiler load conditions in this invention.

[0013] Figure 3 This is a flowchart illustrating the calculation of radial deviation values ​​in the simulation analysis method for oil-gas co-combustion based on subcritical boiler load conditions, as described in this invention. Detailed Implementation

[0014] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. Please refer to the accompanying drawings. Figure 1The present invention provides a technical solution: a simulation analysis method for oil-gas co-combustion based on subcritical boiler load conditions, including the following steps: S1, establishing a three-dimensional model of the boiler and performing local mesh division to generate a list of mesh cells and starting points of pulverized coal particles.

[0015] Under extremely low load conditions in subcritical coal-fired units, there is an axial deviation between the high-temperature fire core formed by the premixed natural gas swirl and the centerline of the dense-phase pulverized coal trajectory generated by the pulverized coal concentration separator. This deviation stems from the strong local non-uniformity of the flow, mixing, and ignition processes in the burner region (especially near the natural gas nozzle, fuel oil nozzle outlet, and pulverized coal channel outlet). Using a uniform coarse mesh for the entire boiler would result in the loss of fine flow and temperature gradient information in the natural gas and fuel oil injection zones, leading to inaccurate ignition delay calculations. Furthermore, pulverized coal particles are not a continuous medium; their release location and initial velocity direction directly determine the centerline position of the pulverized coal trajectory. The outlet section of each pulverized coal channel behind the baffle of the pulverized coal concentration separator is precisely the starting interface for the actual entry of pulverized coal into the furnace. Setting the release point at this location accurately reflects the initial distribution state of the pulverized coal after concentration separation. Therefore, it is necessary to refine the local mesh in key areas and generate a list of pulverized coal particle starting points based on physical realities to provide the fundamental geometric and initial conditions for accurately capturing ignition delay and trajectory deviation.

[0016] Specifically, the process of generating the list of starting points for mesh elements and pulverized coal particles is as follows: S101. Import the 3D model of the boiler into the mesh generation software. The entire model is automatically meshed using tetrahedral meshes. During mesh generation, an upper limit for the global mesh size is set (e.g., a maximum side length of 50 mm), and the software is allowed to automatically refine areas with high curvature based on the model's curvature. After mesh generation, an initial mesh region is generated. At this point, the mesh element sizes in the initial mesh region are basically uniform, with only adaptive density variations at geometric boundaries. The quality of the initial mesh region is checked, including the skewness and aspect ratio of the mesh elements, to ensure there are no elements with excessive distortion.

[0017] S102. Locate the areas where the natural gas nozzle and fuel nozzle outlet are located. In the meshing software, select the spatial range of these two areas respectively (for example, a spherical area with a radius of 30 mm centered at the center of the natural gas nozzle, and a spherical area with a radius of 25 mm centered at the center of the fuel nozzle outlet). Perform meshing on these two selected areas using volume refinement, setting the target mesh cell size after meshing to one-quarter of the initial mesh size. After performing the meshing operation, the mesh cells in the areas where the natural gas nozzle and fuel nozzle outlet are located become denser than the surrounding areas, while other areas retain their original tetrahedral meshes. After meshing, check again whether the transition of mesh cells at the boundary between the meshed and unmeshed areas is smooth, avoiding excessively large abrupt changes in cell size. If the transition is not smooth, add a gradient mesh layer.

[0018] S103. Behind the baffle of the pulverized coal concentration separation device, move along the centerline of each pulverized coal channel until reaching the end of the channel, and locate the outlet section of each channel. For each outlet section, arrange multiple release points for pulverized coal particles at equal radial intervals and equal circumferential angles. An exemplary procedure is as follows: using the center of the section as the center, divide the radial direction into three equally spaced rings from the center to the edge. Each ring has eight points evenly distributed circumferentially, resulting in a total of 25 release points including the center point. Record the three-dimensional spatial coordinates of each release point. Simultaneously, determine the initial velocity direction of each pulverized coal particle (vector component is a unit vector) based on the axial direction of the outlet section, ensuring that the initial velocity direction of each release point is identical (all pointing towards the furnace interior along the pulverized coal channel axis). Finally, write the three-dimensional spatial coordinates of each release point and the corresponding initial velocity direction of the pulverized coal particles line by line into a text file to generate a list of starting points for the pulverized coal particles.

[0019] This embodiment significantly improves the mesh resolution of key ignition areas by locally meshing the regions where the natural gas nozzle and fuel oil nozzle exit are located. This allows for more accurate capture of temperature gradient changes during the ignition delay process of natural gas and fuel oil in subsequent simulations, avoiding the artificial smoothing of the high-temperature fire core formation location due to overly coarse meshes. Simultaneously, release points are arranged on the outlet section of each pulverized coal channel behind the baffle of the pulverized coal concentration separation device, and their three-dimensional spatial coordinates and initial velocity directions are recorded. The generated list of starting points can accurately reconstruct the initial trajectory line of dense-phase pulverized coal entering the furnace, thus ensuring that the pulverized coal trajectory centerline calculated subsequently is highly consistent with the actual physical process.

[0020] S2. Assign simulation parameters, and set discrete values ​​for gas velocity and air-fuel ratio at the natural gas chamber outlet, and discrete values ​​for oil pressure and oil droplets at the fuel nozzle outlet, while also setting the pulverized coal trajectory.

[0021] Considering that under extremely low load conditions in subcritical coal-fired units, natural gas and fuel oil, as auxiliary fuels, need to be co-combusted with pulverized coal, the ignition delay of natural gas and fuel oil is affected by various operating parameters in actual operation. Among them, the gas velocity and air-fuel ratio at the natural gas outlet directly affect the mixing degree of natural gas and air and the flame propagation speed, thus determining the formation location of the high-temperature flame core; the oil pressure at the fuel nozzle outlet determines the penetration distance and atomization effect of fuel injection, while the oil droplet dispersion value (i.e., oil droplet size distribution) directly affects the evaporation rate of fuel droplets and the ignition delay time.

[0022] Therefore, it is necessary to input the boiler load value, gas-coal blending ratio value, oil-coal blending ratio value and secondary air ratio value into the simulation software, and assign the corresponding variables to complete the simulation parameter assignment.

[0023] The process of setting the coal powder trajectory is as follows: the three-dimensional spatial coordinates of each release point are used as the initial spatial coordinates of the coal powder particles, the axial direction of the coal powder channel is used as the velocity direction vector, and the primary air velocity variable is used as the velocity magnitude of the coal powder particles, thereby obtaining the coal powder trajectory of each coal powder particle.

[0024] The boiler load value is the output power or steam production of the subcritical boiler under current operating conditions, reflecting the boiler's load level. During the design simulation, a specific value is set based on the typical range of extremely low load conditions (e.g., 20% to 40% of rated load), or it can be manually entered by the operator as an input variable in the simulation software.

[0025] The gas-coal blending ratio is the proportional relationship between natural gas and pulverized coal in terms of total input heat or mass flow rate. It is calculated by dividing the heat (or mass flow rate) provided by natural gas by the heat (or mass flow rate) provided by pulverized coal. The range is typically from 0 (pure pulverized coal) to a certain upper limit (e.g., 0.5, indicating that natural gas accounts for 50% of the pulverized coal's heat). A higher value indicates a higher proportion of natural gas relative to pulverized coal, resulting in more gaseous fuel in the furnace and making it easier for a high-temperature fire core to form, although its location may be shifted forward.

[0026] The oil-coal blending ratio is the proportion of fuel oil and pulverized coal in the total input heat, i.e., the heat provided by fuel oil divided by the heat provided by pulverized coal. A higher value indicates a greater contribution from fuel oil, resulting in a stronger fuel oil flame, which helps ignite natural gas and pulverized coal. However, an excessively high value can lead to localized high temperatures in the burner area.

[0027] The secondary air ratio is the proportion of secondary air (combustion air supplied from around the burner) to the total combustion air volume, typically between 0.6 and 0.8. A higher value indicates a larger volume of secondary air, resulting in sufficient oxygen in the rear section of the furnace, but may lower the flame temperature.

[0028] The gas velocity discrete value is a series of discrete values ​​representing the speed at which natural gas exits the gas chamber. It is typically 30%-120% of the gas velocity under rated load. The step size is designed to capture the gradient of nonlinear changes in ignition delay time, and several specific values ​​(e.g., 10, 20, 30, 40, 50) are uniformly distributed within this range. A larger value indicates a higher natural gas jet velocity, stronger penetration, and a higher position of the high-temperature fire core further from the nozzle, potentially increasing the axial deviation from the pulverized coal trajectory centerline.

[0029] The air-fuel ratio discrete value is a series of discrete values ​​representing the ratio of the actual amount of air to the theoretical amount of air during natural gas combustion. Based on the combustion characteristics of natural gas, several discrete values ​​(such as 0.7, 0.9, 1.1, 1.3) are taken within the range of lean to rich combustion (e.g., 0.7 to 1.3). A value less than 1 indicates insufficient air (rich combustion), resulting in a longer ignition delay time and the potential for incomplete combustion products; a value greater than 1 indicates excess air (lean combustion), resulting in a shorter ignition delay time but potentially a lower flame temperature.

[0030] The fuel pressure discrete value is a series of discrete values ​​for the fuel pressure before the fuel injector. Several discrete values ​​(such as 5, 10, 15, 20, 25) are selected based on the actual fuel supply pressure range of the fuel injection system (e.g., 5 MPa to 25 MPa). A larger value results in a longer fuel injection penetration distance and a higher initial velocity of the atomized fuel droplets, which is beneficial for droplet breakup and evaporation, thus shortening the fuel ignition delay time. A value that is too small results in poor fuel atomization and a prolonged ignition delay.

[0031] The fuel droplet dispersion value is a series of discrete values ​​representing the droplet size (usually expressed as the Sauter mean diameter) formed after fuel atomization through a nozzle. Several discrete values ​​(such as 20, 50, 80, and 110) are selected based on the typical droplet size range (e.g., 20 micrometers to 120 micrometers) of the nozzle atomization characteristics as a function of fuel pressure. Smaller values ​​indicate finer droplets, faster evaporation rates, and shorter fuel ignition delay times; larger values ​​indicate coarser droplets, requiring longer evaporation times and extending ignition delay.

[0032] The pulverized coal trajectory is the spatial path of each pulverized coal particle as it moves through the furnace with the primary airflow, starting from its release point recorded in the starting point list. In the simulation software, aerodynamic drag and gravity are applied to each pulverized coal particle. Using the velocity direction vector, velocity magnitude, and initial spatial coordinates set in this step as initial conditions, the position update for each time step is calculated through numerical integration, resulting in a series of spatial coordinate points forming a trajectory. The shape of the pulverized coal trajectory reflects the degree of deflection of the pulverized coal carried by the airflow. The closer the trajectory is to the furnace centerline, the easier it is for it to encounter the natural gas or oil flame; excessive deviation from the trajectory leads to ignition failure.

[0033] The primary air velocity variable is the speed of the primary air stream carrying pulverized coal into the furnace, and it is a variable parameter in the simulation. An initial value (e.g., 15 meters per second) is set in the simulation software based on the boiler load and pulverized coal concentration, and is allowed to be varied in subsequent optimizations. A higher velocity results in a greater penetration depth of the pulverized coal jet, and the centerline of the pulverized coal trajectory penetrates deeper into the furnace; a lower velocity results in the pulverized coal trajectory falling earlier.

[0034] This embodiment sets discrete values ​​for gas velocity and air-fuel ratio at the natural gas chamber outlet, and discrete values ​​for oil pressure and oil droplet at the fuel nozzle outlet. This allows the subsequently constructed gas delay table and oil delay table to cover all combinations of these parameters within a reasonable range, thereby accurately identifying the variation patterns of natural gas ignition delay time under different gas velocities and air-fuel ratios, as well as the variation patterns of fuel ignition delay time under different oil pressures and oil droplets.

[0035] Furthermore, when axial deviations caused by ignition delay occur in actual simulations, the oil pressure or oil particle dispersion values ​​can be adjusted to shorten the fuel oil ignition delay, ensuring that the fuel oil flame can ignite the gap between the natural gas flame core and the pulverized coal trajectory in a timely manner. Simultaneously, the pulverized coal trajectory, set based on the primary air velocity variable and the three-dimensional spatial coordinates of the pulverized coal particles, can accurately reflect the movement path of dense-phase pulverized coal in the furnace, ensuring that the radial deviation value of the subsequently calculated pulverized coal trajectory centerline accurately reflects the degree of spatial misalignment caused by the natural gas ignition delay.

[0036] S3. Construct a gas delay table based on the discrete values ​​of gas velocity and air-fuel ratio, and construct an oil delay table based on the discrete values ​​of oil pressure and oil droplets. Perform ignition determination and component update for each grid cell, and release pulverized coal particles according to the starting point list. Repeat the iteration until the set conditions are met.

[0037] Under extremely low load conditions in subcritical coal-fired power units, the ignition of natural gas as auxiliary fuel injected into the furnace is not instantaneous, but involves a defined ignition delay time. The length of this delay time directly determines the spatial location of the high-temperature fire core; the longer the delay time, the farther the fire core is from the natural gas chamber outlet. The key operating parameters affecting the natural gas ignition delay time are the discrete values ​​of the gas velocity and air-fuel ratio at the natural gas chamber outlet.

[0038] Among these parameters, the gas velocity discrete value determines the turbulence intensity and mixing rate of the natural gas jet. The higher the gas velocity, the faster the natural gas mixes with the high-temperature flue gas, but it may also push the ignition core downstream due to excessive momentum. The air-fuel ratio discrete value determines the stoichiometric ratio of the mixture; the further it deviates from the stoichiometric ratio, the longer the ignition time. Since these two parameters change in actual operation, and the ignition delay time varies under different combinations, calculating the ignition delay on a case-by-case basis for each simulation would significantly increase the computational load and would not allow for quick lookup.

[0039] Therefore, it is necessary to pre-calculate all possible parameter combinations and organize the results into a table so that each grid cell can directly look up the table to obtain the accurate ignition delay time when making an ignition determination, without repeating the calculation. Specifically, for example... Figure 2 As shown, the process of constructing the gas delay table is as follows: S301, for each combination of gas velocity discrete value and air-fuel ratio discrete value, the temperature change is tracked from the initial moment at the natural gas chamber outlet. The calculation stops when the temperature rises to the ignition temperature, and the natural gas ignition delay time is obtained.

[0040] For example, for the first combination (e.g., gas velocity discrete value = 10 m / s, air-fuel ratio discrete value = 0.7), a representative grid cell is selected on the boundary of the natural gas chamber outlet (usually the grid cell at the center of the outlet cross-section). The initial temperature of this grid cell is set to the furnace ambient temperature. Starting from the initial time (t=0), the transient solver is started, and the temperature change of this grid cell is calculated at each time step (e.g., 0.001 seconds). The temperature change is determined by the heat released by natural gas combustion, convective heat transfer, and radiative heat transfer. At the end of each time step, the current temperature of this grid cell is compared with the preset ignition temperature. If the current temperature is less than the ignition temperature, the next time step continues; when the current temperature is greater than or equal to the ignition temperature for the first time, the calculation is stopped immediately, and the current cumulative physical time (i.e., the current step number multiplied by the single-step physical time step) is read. This time value is recorded as the natural gas ignition delay time.

[0041] S302. Store the discrete values ​​of gas velocity, air-fuel ratio, and corresponding natural gas ignition delay time as an entry. All entries are arranged in the order of the discrete values ​​of gas velocity and air-fuel ratio to form a gas delay table.

[0042] It should be noted that the gas delay table uses a two-dimensional array. The row index of the gas delay table is set to the discrete gas velocity value (sorted in ascending order, e.g., from 10 to 50), and the column index is set to the discrete air-fuel ratio value (sorted in ascending order, e.g., from 0.7 to 1.3). Each row and column index is traversed, and the corresponding combination is retrieved. For this combination, the natural gas ignition delay time calculated in S301 is found, and it is stored as the value at that position in the table. For example, the delay time corresponding to a discrete gas velocity value of 10 and a discrete air-fuel ratio value of 0.7 is stored in the first row and first column of the table. After all positions are filled, each entry is checked to ensure it is not empty; if any entry is missing, the process returns to S301 to recalculate the combination.

[0043] The initial moment refers to the instant when natural gas begins to be injected into the furnace, and the ignition temperature is the auto-ignition temperature of the natural gas components under the current pressure and air-fuel ratio conditions.

[0044] The ignition temperature is not a fixed constant and is obtained by the following method: for the local pressure and air-fuel ratio of the current grid cell, a homogeneous adiabatic compression ignition simulation of the natural gas / air mixture is performed using chemical kinetic software (such as Cantera or CHEMKIN), and the relationship curve between its ignition delay time and initial temperature is calculated. The initial temperature corresponding to the sharp inflection point of the curve is defined as the ignition temperature of the grid cell.

[0045] This embodiment constructs a gas delay table, enabling subsequent simulations to quickly retrieve the corresponding natural gas ignition delay time directly from the table whenever ignition determination is needed for the grid cell corresponding to the natural gas chamber outlet. This allows for precise judgment of when natural gas ignition will occur in that grid cell. In this way, the gas delay table compresses the complex chemical kinetics and physical mixing process into a single lookup table, ensuring the real-time nature and accuracy of ignition determination.

[0046] Under extremely low load conditions in subcritical coal-fired power units, fuel oil, as an auxiliary fuel, is injected into the furnace in droplet form. Its ignition process differs fundamentally from that of gaseous fuels. Specifically, fuel oil must first undergo heating, evaporation, and gas-phase mixing before ignition. Therefore, the ignition delay time of fuel oil depends not only on the time required for the gas phase temperature to rise to the ignition temperature but also on the time required for the droplets to completely evaporate. Only when the droplet diameter decreases to a preset evaporation threshold and the gas phase temperature simultaneously reaches the ignition temperature can the fuel oil truly ignite.

[0047] It is important to note that the two key operating parameters affecting fuel ignition delay are fuel pressure discrete value and fuel droplet discrete value. The fuel pressure discrete value determines the initial velocity and atomization energy of the fuel injection; higher fuel pressure generally results in a smaller initial droplet diameter. The fuel droplet discrete value directly indicates the initial droplet size distribution; larger droplets require a longer time for complete evaporation. Since these two parameters are adjustable in actual operation, and the ignition delay time varies significantly under different combinations, performing ad-hoc calculations for each simulation would be extremely time-consuming. Therefore, it is necessary to pre-calculate the combined droplet evaporation and vapor phase temperature rise for all combinations of fuel pressure and fuel droplet discrete values ​​to obtain the fuel ignition delay time for each combination. This time, the calculations are then organized into a fuel delay table according to the parameter order, allowing for rapid lookup when determining the ignition of the corresponding mesh element at the fuel nozzle outlet.

[0048] Specifically, the process of constructing the oil delay table is as follows: S303, for each combination of oil pressure discrete value and oil droplet discrete value, the droplet diameter change and gas phase temperature change are tracked from the start of fuel injection at the fuel nozzle outlet. The calculation stops when the droplet diameter decreases to the preset evaporation threshold and the gas phase temperature rises to the ignition temperature, thus obtaining the fuel ignition delay time.

[0049] For example, for the first combination (e.g., oil pressure discrete value = 5 MPa, oil droplet discrete value = 20 μm), a particle representing a droplet is created at the fuel nozzle outlet. Starting from the fuel injection initiation time (t=0), the transient solver is started, and the single-step physical time step is set to 0.0001 seconds. Within each time step, the evaporation rate is first calculated based on the current droplet diameter, droplet temperature, and vapor phase temperature, and the droplet diameter is updated. Simultaneously, the change in vapor phase temperature (affected by combustion heat release and heat transfer) is calculated. At the end of each time step, two conditions are checked sequentially: first, whether the current droplet diameter is less than or equal to zero; second, whether the current vapor phase temperature is greater than or equal to the ignition temperature. The calculation stops only when both conditions are true. If only one condition is met and the other is not, the calculation continues to the next time step. The cumulative physical time at the time of stopping (step number multiplied by the single-step physical time step) is recorded, and this time value is recorded as the fuel ignition delay time.

[0050] S304. Store the oil pressure discrete value, oil droplet discrete value and the corresponding fuel ignition delay time as an entry. All entries are arranged in the order of oil pressure discrete value and oil droplet discrete value to form an oil delay table.

[0051] It should be noted that the oil delay table also uses a two-dimensional array format. For example, the delay times corresponding to oil pressure discrete value = 5 and oil droplet discrete value = 20 are stored in the first row and first column of the table. After all positions are filled, each item is checked for abnormal entries with a delay time of zero or negative value. If an abnormality is found, the process returns to S303 to recalculate the combination. After confirming that the table is complete and error-free, it is stored in the simulation software's memory, and a fast indexing mechanism is established.

[0052] The preset evaporation threshold refers to the critical diameter at which the droplet is considered to have completely evaporated and no longer participates in subsequent liquid phase reactions. It is usually taken as 0.1%-1% of the initial Sotter average diameter, with an example value of 0.3%.

[0053] This embodiment stores the oil pressure discrete value, oil droplet discrete value, and corresponding fuel ignition delay time as a single entry, forming an oil delay table in sequence. This allows for quick lookup of the table to determine the fuel ignition delay time based on the current oil pressure and oil droplet discrete values ​​when ignition determination is needed for the mesh element corresponding to the fuel nozzle outlet in subsequent simulations. Accurately knowing the fuel ignition delay time allows for assessment of whether the fuel flame can ignite in time within the gap between the natural gas flame core and the pulverized coal trajectory. This enables evaluation of whether the oil pressure or oil droplet discrete values ​​need to be adjusted to shorten the fuel ignition delay and compensate for the axial deviation caused by the natural gas ignition delay.

[0054] It should be noted that the ignition of natural gas depends on the ignition delay time in the gas delay table, the ignition of fuel oil depends on the oil delay table, and the volatilization of pulverized coal particles is driven by the difference between the local gas phase temperature and the surface temperature of the pulverized coal particles within the grid cell. These three processes must proceed synchronously on the same time axis; otherwise, the true physical process of co-combustion of oil and gas cannot be simulated. However, directly solving all the combustion reaction kinetic equations would be computationally intensive. Therefore, an ignition determination method is adopted. By pre-constructing gas and oil delay tables, the ignition timing can be determined in the simulation simply by checking whether the accumulated physical time has reached the delay time in the tables, avoiding real-time solution of chemical kinetics.

[0055] Specifically, the process of determining ignition and updating the composition for each grid cell, and releasing coal powder particles according to the starting point list, repeating the iteration until the set conditions are met is as follows: S305, store the temperature value, pressure value and composition mass fraction value of each grid cell into memory. The initial composition mass fraction value includes nitrogen mass fraction, oxygen mass fraction, water vapor mass fraction and carbon dioxide mass fraction.

[0056] S306. For the grid cell corresponding to the natural gas chamber outlet, read the gas velocity discrete value at the location of the natural gas chamber outlet grid cell, find the natural gas ignition delay time that matches the gas velocity discrete value and air-fuel ratio discrete value in the gas delay table, and multiply the current calculation step number by the single-step physical time step to obtain the cumulative physical time starting from the reaction start time. When the cumulative physical time is greater than or equal to the natural gas ignition delay time, it is determined that the natural gas chamber outlet grid cell has ignited, and the nitrogen mass fraction, oxygen mass fraction, water vapor mass fraction and carbon dioxide mass fraction of the natural gas chamber outlet grid cell are replaced with the corresponding mass fractions of natural gas combustion products.

[0057] S307. For the grid cell corresponding to the fuel nozzle outlet, read the oil pressure discrete value at the location of the fuel nozzle outlet grid cell, find the fuel ignition delay time that matches the oil pressure discrete value and the oil droplet discrete value in the oil delay table, and start from the fuel injection start time. Multiply the current calculation step number by the single-step physical time step to obtain the cumulative physical time. When the cumulative physical time is greater than or equal to the fuel ignition delay time, it is determined that the fuel nozzle outlet grid cell has ignited, and the nitrogen mass fraction, oxygen mass fraction, water vapor mass fraction and carbon dioxide mass fraction of the fuel nozzle outlet grid cell are replaced with the corresponding mass fractions of fuel combustion products.

[0058] S308. In each calculation step, release coal powder particles one by one according to the coordinate order in the starting point list. After each coal powder particle is released, obtain the local gas phase temperature of the grid cell where the coal powder particle is located and the surface temperature of the coal powder particle. Subtract the surface temperature of the coal powder particle from the local gas phase temperature to obtain the temperature difference. Multiply the temperature difference by the preset volatile matter extraction coefficient, and then multiply it by the mass of the coal powder particle to obtain the volatile matter extraction rate. Multiply the volatile matter extraction rate by the single-step physical time step to obtain the volatile matter extraction mass of the current calculation step. Add the volatile matter extraction mass to the volatile matter mass fraction of the grid cell where the coal powder particle is located.

[0059] S309. Update the temperature, pressure, and component mass fraction values ​​of all grid cells. The temperature update method is as follows: obtain the heat release rate of the grid cell in the current calculation step, multiply the heat release rate by the single-step physical time step, divide by the heat capacity of the grid cell to obtain the temperature increment, and then add the temperature increment to the temperature value of the previous calculation step to obtain the temperature value of the current calculation step. Calculate the temperature change rate of each grid cell between the current and previous calculation steps. The temperature change rate is calculated as follows: subtract the temperature value of the previous calculation step from the temperature value of the current calculation step to obtain the temperature difference, and divide the temperature difference by the single-step physical time step to obtain the temperature change rate. Stop the iteration when the temperature change rate of all grid cells is lower than the change rate threshold, and complete the repeated iteration process. The change rate threshold is set according to the simulation accuracy requirements, and the value range is 1×10⁻⁶. -5 K / s to 1×10 -3 K / s.

[0060] The component mass fraction is the dimensionless ratio of the mass of a certain chemical component (such as nitrogen, oxygen, water vapor, carbon dioxide, volatile matter, etc.) within a grid cell to the total gas mass of that cell. Initially, it is set according to the air composition, then replaced by combustion products after ignition, and the volatile matter mass fraction is increased as it is released. The sum of the mass fractions of all components is 1. A high oxygen mass fraction indicates sufficient oxidant, and a high volatile matter mass fraction indicates available fuel.

[0061] The natural gas ignition delay time is the time required from the emission of natural gas to ignition, measured in seconds, and can be found in the gas delay table. The longer the delay time, the later the ignition occurs, and the further the high-temperature fire core is from the natural gas cavity outlet.

[0062] The fuel ignition delay time is the time required from the start of fuel injection until the fuel droplets have completely evaporated and the vapor temperature reaches the ignition temperature, measured in seconds. It can be found in the fuel delay table. A longer delay time means the fuel flame forms later, potentially preventing timely ignition of the gap between the natural gas and pulverized coal.

[0063] Natural gas combustion products are the gaseous components and their mass fractions produced after the complete combustion of natural gas. They mainly include carbon dioxide and water vapor, as well as the remaining nitrogen and oxygen. The mass fraction of each component in the products is calculated based on the stoichiometric reaction equations for natural gas.

[0064] The local gas phase temperature is the gas temperature value of the grid cell where the pulverized coal particle is currently located. In each calculation step, the grid cell containing the pulverized coal particle is located based on its three-dimensional spatial coordinates, and the temperature value of that cell is read. The higher the local gas phase temperature, the greater the temperature difference between the gas phase temperature and the surface temperature of the pulverized coal particle, and the faster the volatile matter is released.

[0065] The volatile matter release coefficient (VLCC) is a rate proportionality factor for the volatilization of pulverized coal particles under a unit temperature difference. It is preset as a constant in simulation software. A larger coefficient indicates greater sensitivity to temperature differences, resulting in faster volatilization at the same temperature difference. This value varies depending on the type of coal. The VLCC is determined based on the coal type, using the following method: Take a sample of pulverized coal to be tested and heat it in a laboratory to a temperature similar to that of the boiler furnace. Measure the mass of volatiles released per unit mass of pulverized coal per unit time for every 1 Kelvin difference between the surface temperature of the pulverized coal particles and the surrounding gas temperature. This measured value is taken as the VLCC. If experimental measurement is not possible, empirical values ​​can be used directly: For bituminous coal, the VLCC is 0.00005 kg of volatiles released per Kelvin per second per kilogram of pulverized coal; for anthracite, it is 0.00001; and for lignite, it is 0.0001. These empirical values ​​can be further adjusted based on actual boiler operating data.

[0066] The volatile matter release rate is the mass of volatile matter released by pulverized coal particles per unit time, measured in kilograms per second. A higher rate means that the grid cell containing the pulverized coal particles receives more volatile matter per unit time.

[0067] The volatile matter content is the total mass of volatiles released by a single coal particle within the time step of the current calculation step.

[0068] The volatile matter mass fraction is the proportion of the mass of volatile matter (combustible gas released from the pyrolysis of pulverized coal) within a grid cell to the total gas mass. It is initially set to 0 and updated at each calculation step by accumulating the volatile matter mass and dividing it by the total gas mass within the grid cell. A higher volatile matter mass fraction indicates a greater amount of combustible gas within the grid cell, and a higher probability of subsequent ignition.

[0069] Heat release rate is the amount of heat released per unit time due to combustion reaction within a grid cell, measured in watts. A higher heat release rate indicates a greater temperature increase and more intense combustion.

[0070] The heat capacity of a grid cell is the amount of heat required to raise the temperature of the gas within that cell by one unit, measured in joules per Kelvin. A higher heat capacity results in a slower temperature increase for the same heat release rate.

[0071] The temperature increment is the increase in grid cell temperature within the current calculation step's time step, measured in Kelvin. The current temperature is obtained by adding the temperature increment to the temperature value from the previous calculation step. A larger increment indicates a faster temperature rise.

[0072] This embodiment determines the precise timing of ignition in each grid cell by independently determining ignition time and comparing the accumulated physical time with the ignition delay time in the gas or oil delay table. This allows for accurate simulation of the formation of the high-temperature fire core. Simultaneously, in each calculation step, pulverized coal particles are released sequentially from the starting point list. The volatile matter emission rate is calculated based on the temperature difference between the local gas phase temperature and the surface temperature of the pulverized coal particles. The volatile matter mass is added to the volatile matter mass fraction of the corresponding grid cell, coupling the ignition preparation process of pulverized coal with the ignition process of natural gas and fuel oil on the same time axis. Then, the temperature, pressure, and component mass fraction values ​​of all grid cells are updated, and the temperature change rate is calculated. Iteration stops when the temperature change rate of all grid cells is below the threshold. This allows the simulation to accurately determine whether combustion has reached a quasi-steady state, thus obtaining the axial deviation between the high-temperature fire core position and the pulverized coal trajectory after natural gas ignition under stable operating conditions. Only the deviation value calculated after the iteration has fully converged is reliable and can be used to determine whether the oil pressure discrete value or oil droplet discrete value needs to be adjusted.

[0073] S4. Simulate natural gas supply interruption. If the change in flame distance before and after the interruption is greater than the set threshold, increase the oil pressure dispersion value and rebuild the oil delay table. If the simulation switching time is greater than the time threshold, decrease the oil droplet dispersion value and rebuild the oil delay table.

[0074] Under extremely low load conditions in subcritical coal-fired units, when the natural gas supply is suddenly interrupted, the high-temperature flame core provided by the natural gas flame will weaken or disappear. At this time, the fuel oil flame needs to quickly take over to maintain the ignition capability of the pulverized coal. However, if the flame distance (i.e., the distance between the high-temperature flame core and the reference point) changes too much before and after the natural gas interruption, it indicates that the fuel oil flame has failed to replenish heat in time, causing the flame core position to drift drastically. This directly reflects the insufficient ignition capability of the fuel oil.

[0075] The root cause of excessive flame distance variation is likely an excessively long fuel ignition delay. This ignition delay is significantly affected by the fuel pressure dispersion value; higher fuel pressure results in better atomization and faster ignition. On the other hand, during co-combustion of oil and gas, when the system needs to switch from natural gas to fuel oil as the primary combustion mode, if the simulated switching time (i.e., the time from the issuance of the natural gas interruption command to the stable establishment of the fuel flame) exceeds the time threshold, it indicates that the fuel ignition response is too slow. This is mainly affected by the fuel droplet dispersion value; smaller droplet diameters lead to faster evaporation and a faster ignition response. Therefore, targeted adjustment strategies need to be adopted based on these two different fault phenomena. Specifically, increasing the fuel pressure dispersion value and decreasing the fuel droplet dispersion value are as follows: When increasing the fuel pressure dispersion value, select the next position after the current fuel pressure dispersion value from all preset fuel pressure dispersion values ​​in ascending order as the increased fuel pressure dispersion value.

[0076] When reducing the oil droplet discrete value, all preset oil droplet discrete values ​​are sorted in descending order, and an oil droplet discrete value is selected from the next position after the current oil droplet discrete value as the reduced oil droplet discrete value.

[0077] The simulation switching time is defined as the cumulative physical time from the start of the calculation step when the simulated natural gas supply interruption command is issued until the grid cell corresponding to the fuel nozzle outlet first meets the ignition condition (i.e., the cumulative physical time is greater than or equal to the fuel ignition delay time in the current fuel delay table).

[0078] This embodiment simulates the extreme condition of natural gas supply interruption to test the backup ignition capability of the oil-gas co-combustion system under natural gas shortage. When the change in flame distance before and after the interruption exceeds a set threshold, it indicates that the fuel flame cannot maintain a stable flame core position after the natural gas flame core disappears. In this case, increasing the fuel pressure dispersion value increases the fuel injection pressure, resulting in finer fuel atomization and a longer penetration distance, thereby shortening the fuel ignition delay and allowing the fuel flame to quickly fill the space left by the natural gas flame core, reducing axial deviation. When the interruption simulation switching time exceeds a time threshold, it indicates that the response speed of fuel from injection to complete ignition is insufficient. In this case, decreasing the fuel droplet dispersion value uses a finer droplet size, accelerating droplet evaporation and gas-phase mixing, thereby shortening the fuel ignition delay time. After increasing the fuel pressure dispersion value and decreasing the fuel droplet dispersion value, the fuel delay table is rebuilt to ensure that all subsequent ignition determinations are based on the new parameter combination. In this way, by simulating the extreme disturbance of natural gas interruption, it is possible to proactively identify whether the current oil pressure and oil droplet parameters meet the requirements for rapid response and automatically adjust them to better values, thereby fundamentally solving the problem of staged ignition failure caused by excessively long fuel ignition delay.

[0079] S5. If the radial deviation of the coal powder trajectory centerline is greater than the deviation threshold, the simulation parameters are modified and the combustion simulation is repeated. Based on the deviation value, the optimal simulation parameters, oil pressure discrete value and oil droplet discrete value are selected in combination with the volume of the high temperature zone.

[0080] The delayed ignition of natural gas causes an axial deviation between the high-temperature flame core and the centerline of the pulverized coal trajectory, leading to the failure of staged ignition. To quantify the radial deviation between the pulverized coal trajectory centerline and the flame, a cylindrical coordinate system needs to be established with the reference point as the origin and the furnace centerline as the axis. The spatial curve is then projected onto a plane perpendicular to the axis. The maximum radial distance from the axis on the projected line directly reflects the maximum offset of the pulverized coal trajectory centerline relative to the axis (i.e., the ideal center direction).

[0081] Specifically, such as Figure 3 As shown, the calculation process for the radial deviation value of the coal powder trajectory centerline is as follows: S501, take the common geometric center of the area where the natural gas nozzle is located and the area where the fuel oil nozzle outlet is located as the reference point.

[0082] S502. From the temperature values ​​of all grid cells after the iteration, determine the grid cell with the maximum temperature, obtain the position coordinates of the grid cell, and take the spatial straight-line distance from the reference point to the position coordinates as the flame distance.

[0083] S503. Based on the spatial position coordinates of each coal powder particle in the coal powder trajectory at each calculation step, calculate the arithmetic mean of the spatial position coordinates of all coal powder particles at the same calculation step to obtain the coordinates of the center point of the coal powder trajectory. Connect the center points of each coal powder trajectory in the order of calculation steps to form the center line of the coal powder trajectory.

[0084] S504. Establish a cylindrical coordinate system with the reference point as the origin and the center line of the furnace as the axis. Project the center line of the pulverized coal trajectory onto a plane perpendicular to the axis. Take the radial distance value of the maximum distance from the axis on the projection line as the radial deviation value of the center line of the pulverized coal trajectory.

[0085] Among them, the coal dust trajectory centerline describes the center of the coal dust cloud's trajectory over time and is a characteristic line for measuring the overall direction of the coal dust flow.

[0086] A cylindrical coordinate system is a three-dimensional coordinate system established with a reference point as the origin and the furnace centerline as the axis. The coordinate quantities are radial distance, azimuth, and axial height. The coordinates of points in three-dimensional space are transformed into a new coordinate system with the reference point as the origin and the furnace centerline direction as the z-axis. The cylindrical coordinate system allows the radial distance to be directly read from the transformed radial coordinate values.

[0087] The common geometric center is calculated as follows: extract the spatial coordinates of all grid nodes in the area where the natural gas nozzle is located and the spatial coordinates of all grid nodes in the area where the fuel nozzle outlet is located, calculate the geometric center point of the two areas (i.e., the arithmetic mean of the coordinates of all nodes in each area), and then take the midpoint of the line connecting the two geometric center points as the common geometric center.

[0088] This embodiment establishes a unified reference origin by extracting the common geometric center of the natural gas nozzle area and the fuel oil nozzle outlet area as a reference point, enabling the flame distance and pulverized coal trajectory position to be measured relative to the same reference. Then, from the temperature values ​​of all grid cells after iteration, the grid cell with the maximum temperature is determined, and the position coordinates of that grid cell are obtained. The spatial straight-line distance from the reference point to that position coordinate is taken as the flame distance, avoiding the ambiguity caused by using the center of the entire flame volume.

[0089] Simultaneously, the coordinates of the center point of the pulverized coal trajectory are obtained by calculating the arithmetic mean of the spatial position coordinates of each pulverized coal particle in each calculation step, and then connected in the order of calculation steps to form the center line of the pulverized coal trajectory, transforming the movement of a large number of discrete pulverized coal particles into a continuous center trajectory line. Finally, a cylindrical coordinate system is established with the reference point as the origin and the furnace center line as the axis. The center line of the pulverized coal trajectory is projected onto a plane perpendicular to the axis, and the radial distance from the axis to the maximum value on the projected line is taken as the deviation value, directly quantifying the maximum radial offset of the center line of the pulverized coal trajectory relative to the axis. The axial deviation is a direct manifestation of the failure of staged ignition caused by the delayed ignition of natural gas.

[0090] Under extremely low load conditions in subcritical coal-fired power units, the gas-coal blending ratio is a key adjustable parameter affecting the axial deviation between the high-temperature fire core position and the centerline of the pulverized coal trajectory. However, the optimal gas-coal blending ratio is not known in advance and needs to be found within a reasonable range through a search to minimize the deviation. The boiler load, oil-coal blending ratio, and secondary air ratio are usually fixed by the operating procedures under extremely low load conditions and should not be arbitrarily changed. Therefore, these should be kept unchanged, with only the gas-coal blending ratio used as the optimization variable. To efficiently find the optimal value, an exhaustive search of all possible values ​​or random attempts are not feasible. The golden section method (0.618 method) is a one-dimensional search method for optimizing a single-peaked function, which can significantly reduce the number of simulations while ensuring the optimal solution is found.

[0091] Therefore, the process of modifying the simulation parameters is as follows: S505, keep the boiler load value, oil-coal blending ratio value and secondary air ratio value in the simulation parameters unchanged, and set the variable range of the gas-coal blending ratio value in the simulation parameters from the minimum value to the maximum value.

[0092] S506. Within the current variable range, take the golden section point as the first test point. The value of the first test point is the lower limit of the variable range plus 0.618 times the width of the variable range. Take the supplementary point of the variable range as the second test point. The value of the second test point is the lower limit of the variable range plus 0.382 times the width of the variable range.

[0093] S507. Replace the original gas-coal blending ratio with the gas-coal blending ratio values ​​of the first and second test points respectively. Perform the following process once: construct a gas delay table based on the discrete values ​​of gas velocity and air-fuel ratio; perform ignition determination and component update for each grid cell; release coal powder particles according to the starting point list; and repeat the iteration until the set conditions are met. Obtain the radial deviation value of the corresponding coal powder trajectory centerline and record it as the first deviation value and the second deviation value.

[0094] S508. If the first deviation value is less than the second deviation value, then the upper limit of the variable range is updated to the value of the second trial point; otherwise, the lower limit of the variable range is updated to the value of the first trial point.

[0095] S509. Repeat the process of updating the variable range until the width of the variable range is less than the preset convergence width. Take the gas-coal blending ratio value at any point in the variable range at this time as the corrected gas-coal blending ratio value.

[0096] In the golden section method, the complementary point is the point that is symmetrical about the center of the interval with respect to the first trial point.

[0097] The convergence width is a pre-defined allowable value for the variable range width. Iteration stops when the range width is less than this value. It is set according to engineering accuracy requirements, such as 0.01 (dimensionless). A smaller convergence width results in higher accuracy of the final gas-coal blending ratio, but requires more iterations.

[0098] This embodiment keeps the boiler load, oil-coal blending ratio, and secondary air ratio constant, treating only the gas-coal blending ratio as a variable parameter. This eliminates interference from other operating factors, ensuring that any deviation is entirely attributable to adjustments in the gas-coal blending ratio. Using the golden ratio method, a first and second trial point are selected within the current variable range. These two values ​​replace the original gas-coal blending ratio, and the entire process from constructing the gas delay table to iterative iterations is performed for each, yielding the corresponding first and second deviation values. Based on the relationship between the first and second deviation values, the upper or lower limit of the variable range is dynamically updated, rapidly narrowing the search interval. Thus, only a few simulations (usually within a few dozen) are needed to find the gas-coal blending ratio that minimizes the radial deviation of the pulverized coal trajectory centerline. This allows for precise adjustment of the natural gas blending ratio in oil-gas co-combustion, ensuring the high-temperature flame core position coincides as closely as possible with the pulverized coal trajectory centerline, fundamentally solving the problem of staged ignition failure caused by improper gas-coal blending.

[0099] Considering that under extremely low load conditions, in addition to requiring the deviation value to be less than the deviation threshold (i.e., the axial deviation is acceptable), sufficient high-temperature zone volume is also required to ensure that the pulverized coal can be fully ignited and burned stably. An insufficient high-temperature zone volume means insufficient combustion intensity, and even if the deviation value meets the standard, staged ignition may fail. Therefore, the optimal parameters cannot be determined solely by minimizing the deviation value; instead, the set of parameters with the largest high-temperature zone volume should be selected from all candidate operating conditions that satisfy the deviation value not exceeding the deviation threshold.

[0100] Specifically, the process of selecting the optimal simulation parameters, oil pressure discrete value, and oil droplet discrete value based on the deviation value and the high temperature zone volume is as follows: S510. After each modification of the simulation parameters and re-run of the combustion simulation, if the deviation value is not greater than the deviation threshold, record the currently used simulation parameters, oil pressure discrete value, oil droplet discrete value, as well as the currently calculated deviation value and high temperature zone volume, and store them as a candidate item in the candidate set.

[0101] S511. After all simulation conditions have been executed, traverse each candidate item in the candidate set and find the candidate item with the largest high-temperature zone volume as the optimal simulation parameter, as well as the oil pressure discrete value and oil droplet discrete value.

[0102] The calculation process for the volume of the high-temperature zone is as follows: a high-temperature threshold temperature is preset, which is input by the user in the simulation parameter setting interface according to the boiler load; all grid cells are traversed, and grid cells with temperature values ​​greater than the high-temperature threshold temperature are filtered out; the geometric volumes of all filtered grid cells are accumulated, and the sum is taken as the volume of the high-temperature zone.

[0103] This embodiment records the operating conditions that meet the acceptable axial deviation as candidate items after each modification of simulation parameters and re-run of combustion simulation. From these, the candidate item with the largest high-temperature zone volume is selected as the optimal simulation parameter, along with the oil pressure and oil droplet discrete values. This selection mechanism ensures that the final selected parameter combination not only solves the axial deviation problem but also further optimizes the combustion effect. The largest high-temperature zone volume means that the pulverized coal receives the most sufficient thermal environment in the furnace, resulting in the highest success rate of staged ignition. Simultaneously, because the candidate items include oil pressure and oil droplet discrete values, the final optimal combination can simultaneously meet the requirements for rapid response after natural gas interruption and ignition delay.

[0104] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, in the form of a computer program product.

[0105] Those skilled in the art will recognize that the modules and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0106] In addition, the functional modules in the various embodiments of this application can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module.

[0107] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0108] Finally, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A simulation analysis method for oil-gas co-combustion based on subcritical boiler load conditions, characterized in that, Includes the following steps: Establish a 3D model of the boiler and perform local meshing to generate a list of mesh elements and the starting points of pulverized coal particles; Simulation parameters were assigned, and discrete values ​​for gas velocity and air-fuel ratio were set at the natural gas chamber outlet, discrete values ​​for oil pressure and oil droplets were set at the fuel nozzle outlet, while the coal powder trajectory was also set. A gas delay table is constructed based on the discrete values ​​of gas velocity and air-fuel ratio, and an oil delay table is constructed based on the discrete values ​​of oil pressure and oil droplets. Ignition determination and composition update are performed for each grid cell. At the same time, coal powder particles are released according to the starting point list. The process is repeated iteratively until the set conditions are met. Simulate a natural gas supply interruption. If the change in flame distance before and after the interruption is greater than a set threshold, increase the oil pressure dispersion value and rebuild the oil delay table. If the simulation switching time is greater than a time threshold, decrease the oil droplet dispersion value and rebuild the oil delay table. If the radial deviation of the coal powder trajectory centerline is greater than the deviation threshold, the simulation parameters are modified and the combustion simulation is repeated. Based on the deviation value, the optimal simulation parameters, oil pressure discrete value, and oil droplet discrete value are selected in combination with the volume of the high-temperature zone.

2. The simulation analysis method for oil-gas co-combustion based on subcritical boiler load conditions according to claim 1, characterized in that, The process of generating the list of starting points for grid cells and pulverized coal particles is as follows: Import the 3D model of the boiler into the mesh generation software, and automatically generate the initial mesh region by using tetrahedral meshes on the entire model. The initial grid region where the natural gas nozzle and fuel oil nozzle outlet are located is divided into grid cells. Multiple release points for pulverized coal particles are arranged on the outlet section of each pulverized coal channel behind the baffle of the pulverized coal concentration-degradation device. The three-dimensional spatial coordinates of each release point and the corresponding initial velocity direction of the pulverized coal particles are recorded to generate a list of starting points for pulverized coal particles.

3. The simulation analysis method for oil-gas co-combustion based on subcritical boiler load conditions according to claim 2, characterized in that, The process of setting the pulverized coal trajectory is as follows: The three-dimensional spatial coordinates of each release point are used as the initial spatial coordinates of the pulverized coal particles. The axial direction of the pulverized coal channel is used as the velocity direction vector, and the primary air velocity variable is used as the velocity magnitude of the pulverized coal particles. In this way, the pulverized coal trajectory of each pulverized coal particle is obtained.

4. The simulation analysis method for oil-gas co-combustion based on subcritical boiler load conditions according to claim 1, characterized in that, The process of constructing the gas delay table is as follows: For each combination of gas velocity discrete value and air-fuel ratio discrete value, the temperature change at the natural gas outlet is tracked from the initial moment. The calculation stops when the temperature rises to the ignition temperature, and the natural gas ignition delay time is obtained. The discrete values ​​of gas velocity, air-fuel ratio, and corresponding natural gas ignition delay time are stored as one entry. All entries are arranged in the order of the discrete values ​​of gas velocity and air-fuel ratio to form a gas delay table.

5. The simulation analysis method for oil-gas co-combustion based on subcritical boiler load conditions according to claim 1, characterized in that, The process of constructing the oil delay table is as follows: For each combination of oil pressure discrete value and oil droplet discrete value, the change in droplet diameter and gas phase temperature is tracked from the moment of fuel injection at the fuel nozzle outlet. The calculation stops when the droplet diameter decreases to the preset evaporation threshold and the gas phase temperature rises to the ignition temperature, thus obtaining the fuel ignition delay time. The oil pressure discrete value, oil droplet discrete value, and corresponding fuel ignition delay time are stored as one entry. All entries are arranged in the order of oil pressure discrete value and oil droplet discrete value to form an oil delay table.

6. The simulation analysis method for oil-gas co-combustion based on subcritical boiler load conditions according to claim 1, characterized in that, The process of determining ignition and updating composition for each grid cell, while releasing pulverized coal particles according to the starting point list, and repeating this iteration until the set conditions are met is as follows: For the grid cell corresponding to the natural gas chamber outlet, the matching natural gas ignition delay time is found in the gas delay table based on the gas velocity discrete value and the air-fuel ratio discrete value. When the cumulative physical time is greater than or equal to the natural gas ignition delay time, the component mass fraction value of the grid cell is replaced with the component mass fraction value of the natural gas combustion products. For the grid cell corresponding to the fuel nozzle outlet, the matching fuel ignition delay time is found in the fuel delay table based on the fuel pressure discrete value and the fuel droplet discrete value. When the cumulative physical time is greater than or equal to the fuel ignition delay time, the component mass fraction value of the grid cell is replaced with the component mass fraction value of the fuel combustion products. In each calculation step, coal powder particles are released one by one according to the coordinates in the starting point list. After each coal powder particle is released, the volatile matter release rate is calculated based on the local gas phase temperature of the grid cell around the particle and the particle surface temperature. The volatile matter release mass is added to the component mass fraction value of the grid cell. Update the temperature, pressure, and component mass fraction values ​​of all grid cells, and repeat the iteration until the set conditions are met. The set conditions are: the temperature change rate of each grid cell between the current calculation step and the previous calculation step is lower than the change rate threshold.

7. The simulation analysis method for oil-gas co-combustion based on subcritical boiler load conditions according to claim 1, characterized in that, The processes of increasing the oil pressure dispersion value and decreasing the oil droplet dispersion value are as follows: When increasing the oil pressure discrete value, select an oil pressure discrete value from the next position after the current oil pressure discrete value in ascending order from all preset oil pressure discrete values ​​as the increased oil pressure discrete value. When reducing the oil droplet discrete value, all preset oil droplet discrete values ​​are sorted in descending order, and an oil droplet discrete value is selected from the next position after the current oil droplet discrete value as the reduced oil droplet discrete value.

8. The simulation analysis method for oil-gas co-combustion based on subcritical boiler load conditions according to claim 1, characterized in that, The calculation process for the radial deviation value of the coal powder trajectory centerline is as follows: The common geometric center of the area where the natural gas nozzle is located and the area where the fuel oil nozzle outlet is located is taken as the reference point; From the temperature values ​​of all grid cells after the iteration, determine the grid cell with the maximum temperature, obtain the position coordinates of the grid cell, and take the spatial straight-line distance from the reference point to the position coordinates as the flame distance; The center line of the coal powder trajectory is formed based on the spatial position coordinates of each coal powder particle in the coal powder trajectory at each calculation step. A cylindrical coordinate system is established with the centerline of the furnace as the axis. The centerline of the pulverized coal trajectory is projected onto a plane perpendicular to the axis, and the radial distance from the axis to the maximum value on the projection line is taken as the deviation value.

9. The simulation analysis method for oil-gas co-combustion based on subcritical boiler load conditions according to claim 1, characterized in that, The process of modifying simulation parameters is as follows: Keep the boiler load, oil-coal blending ratio, and secondary air ratio values ​​in the simulation parameters unchanged, and set the variable range of the gas-coal blending ratio value in the simulation parameters to be from the minimum value to the maximum value. Within the current variable range, the golden section point is taken as the first trial point, and the second trial point is taken as the supplementary point of the variable range; The original gas-coal blending ratio values ​​were replaced with the gas-coal blending ratio values ​​of the first and second test points, respectively. The process of repeated iteration was performed until the set conditions were met. The radial deviation values ​​of the corresponding coal powder trajectory center lines were obtained and recorded as the first deviation value and the second deviation value. If the first deviation value is less than the second deviation value, the upper limit of the variable range is updated to the value of the second trial point; otherwise, the lower limit of the variable range is updated to the value of the first trial point. Repeat the process of updating the variable range until the width of the variable range is less than the preset convergence width. Then, take the gas-coal blending ratio value at any point in the variable range at this time as the corrected gas-coal blending ratio value.

10. The simulation analysis method for oil-gas co-combustion based on subcritical boiler load conditions according to claim 1, characterized in that, The process of selecting the optimal simulation parameters, oil pressure discrete value, and oil droplet discrete value based on the deviation value and the high-temperature zone volume is as follows: After each modification of simulation parameters and re-run of combustion simulation, if the deviation value is not greater than the deviation threshold, record the currently used simulation parameters, oil pressure discrete value and oil droplet discrete value, as well as the currently calculated deviation value and high temperature zone volume, and store them as a candidate entry in the candidate set. After all simulation conditions have been executed, each candidate item in the candidate set is traversed, and the candidate item with the largest high-temperature zone volume is selected as the optimal simulation parameter, as well as the oil pressure discrete value and oil droplet discrete value.

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