A method for evaluating the running state of a medium-speed coal mill based on the size of stone coal particles
By establishing a stress model for stone and coal particles and analyzing their particle size distribution, the problem of insufficient grinding capacity of medium-speed coal mills for impurities was solved, enabling accurate assessment and improvement of the operating status of medium-speed coal mills.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- XIAN THERMAL POWER RES INST CO LTD
- Filing Date
- 2026-01-07
- Publication Date
- 2026-05-29
AI Technical Summary
In existing technologies, medium-speed coal mills have limited grinding capacity for impurities such as gangue and stones carried in raw coal during operation, resulting in the inability to effectively grind coke into coal powder. Existing evaluation methods also suffer from problems such as insufficient data representativeness and large measurement errors.
By establishing a mathematical model of the forces acting on stone and coal particles, calculating the particle Reynolds number and drag coefficient, determining the reasonable emission zone of stone and coal particles, fitting the standard particle size distribution curve, and comparing it with the actual particle size distribution curve, the operating status of the medium-speed coal mill is evaluated.
It enables accurate assessment of the operating status of medium-speed coal mills, improves assessment effectiveness, fills a gap in existing technology, and can promptly detect equipment wear and abnormal operating parameters.
Smart Images
Figure CN122108867A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of coal mill technology, and specifically to a method for evaluating the operating status of a medium-speed coal mill based on the particle size of gravel coal. Background Technology
[0002] Due to its advantages such as simple equipment, low power consumption, and flexible operation adjustment, the medium-speed coal mill direct-fired pulverizing system is currently the most widely used pulverizing system in coal-fired power plant boilers. However, during operation, the medium-speed coal mill has limited grinding capacity for impurities such as gangue and stones carried in the raw coal. These impurities cannot be effectively ground into coal powder but are separated and discharged through the slag discharge hole at the bottom of the mill, forming a certain amount of coke. Typically, the particle size of coke is less than or equal to 50mm, and the bulk density is usually in the range of 1300. ~1500 The temperature is around 150℃. According to the ash composition analysis results, the mass percentage of ash in the stone coal is very high. Among them, the content of silicon dioxide, ferric oxide, and aluminum oxide is the highest, which is the main reason why the stone coal has a high density and hardness.
[0003] Currently, the industry commonly evaluates coal mill performance by measuring the amount and calorific value of the coking stone. Specifically, the amount of coking stone is calculated by weighing the discharged coking stone over a period of time. If the amount exceeds 0.05% of the mill's rated output, a scaled-down sample of the coking stone is taken and analyzed to determine its calorific value. When the amount of coking stone is no greater than 0.05% of the rated output or the calorific value is no greater than 6.27 MJ / kg, the coal mill's performance is considered good. However, in practical applications, this method suffers from insufficient data representativeness and large measurement errors. To address the shortcomings of existing methods, this invention provides a method for evaluating the operating status of a medium-speed coal mill based on coking stone particle size. Summary of the Invention
[0004] The purpose of this invention is to provide a method for evaluating the operating status of a medium-speed coal mill based on the particle size of gravel and coal.
[0005] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for evaluating the operating status of a medium-speed coal mill based on the particle size of coke, comprising the following steps: S1: Establish a mathematical model of the forces acting on the stone and coal particles; S2: Calculate the particle Reynolds number; S3: Based on the particle Reynolds number calculated in step S2, the drag coefficient is obtained; S4: Calculate the reasonable discharge zone for stone coal particles based on the mathematical model established in step S1 and the drag coefficient in step S3. S5: Based on the reasonable emission zone of the stone coal particles calculated in step S4, the standard particle size distribution curve is obtained by fitting the experimental data. S6: Based on the actual discharge of stone coal from the medium-speed coal mill, obtain the actual particle size distribution curve; S7: Compare the actual particle size distribution curve from step S6 with the standard particle size distribution curve from step S5 to evaluate the operating status of the medium-speed coal mill.
[0006] Furthermore, the specific process of establishing the mathematical model in step S1 is as follows: Treating the cobblestone particles as equivalent to spherical particles, the cobblestone particles in the flowing air are subjected to the combined effects of drag, gravity, buoyancy, additional mass force, pressure gradient force, Basset force, and lift. The equation of motion for the cobblestone particles in the airflow is:
[0007] in, The mass of the coal particles; Let F be the velocity of the gravel and coal particles; F be the net force acting on the gravel and coal particles. For drag force; For gravity; For buoyancy; For added mass force; For pressure gradient force; Basset force; For lift; In the forces acting on the coal particles, drag, gravity, and buoyancy are the primary forces, while the additional mass force, pressure gradient force, Basset force, and lift are secondary forces. Neglecting the secondary forces, the equation of motion for the coal particles in the airflow simplifies to:
[0008] in, The mass of the coal particles; The velocity of the stone and coal particles; For drag force; The density of the airflow; This refers to the particle density of the cobblestone.
[0009] Furthermore, based on the mathematical model established in step S1, the movement of the stone and coal particles can be categorized into three cases: The gravel and coal particles are carried away by the airflow and cannot be discharged; The cobblestone particles are suspended in the nozzle ring, at the critical slag discharge point; The stone and coal particles cannot be carried away by the airflow and fall into the nozzle ring for discharge.
[0010] Furthermore, the formula for calculating the particle Reynolds number in step S2 is as follows: , in, The particle Reynolds number; The density of the gas; The particle size of the cobblestone; The gas dynamic viscosity; The airflow velocity; The velocity of the stone and coal particles.
[0011] Furthermore, the calculation process for the drag coefficient in step S3 is as follows: like (Stokes District), then , in, This is the drag coefficient; The particle Reynolds number; like (Transition zone), then , in, This is the drag coefficient; The particle Reynolds number; like (Turbulent region), then .
[0012] Furthermore, the specific process of step S4 is as follows: Based on the established mathematical model, taking the critical situation of stone and coal particle emission as an example, we have: , in, The velocity of the stone and coal particles; For drag force; The mass of the coal particles; The density of the airflow; Density of coke particles; It is the acceleration due to gravity; drag force Stone coal particle quality Volume of stone coal particles Substituting the formula, we can obtain the particle size of the stone coal. In critical cases, The critical emission diameter of cobblestone particles; Under a constant airflow velocity, when the equivalent diameter of the stone and coal particles is greater than the critical discharge diameter, the stone and coal particles will be discharged from the medium-speed coal mill; when the equivalent diameter of the stone and coal particles is less than the critical discharge diameter, the stone and coal particles cannot be discharged from the medium-speed coal mill. Plot the airflow velocity-equivalent diameter curve of the stone and coal particles. The area formed by the equivalent diameter of the stone and coal particles being greater than the critical discharge diameter is the reasonable discharge zone for the stone and coal particles.
[0013] Furthermore, the specific process of step S5 is as follows: S51: Select several medium-speed coal mills of the same model to conduct a stone and coal particle discharge test, and set the same test parameters for all medium-speed coal mills. S52: For the stone coal particles discharged from the medium-speed coal mill, weigh the same mass of stone coal particles discharged from each medium-speed coal mill, and sieve the same mass of stone coal particles symmetrically taken using sieves with different aperture sizes. S53: Statistically analyze the particle size distribution characteristics of the stone coal particles screened by each medium-speed coal mill, select the optimal medium-speed coal mill, in which the mass proportion of the stone coal particles near the critical discharge diameter of the stone coal particles at the corresponding airflow velocity calculated in step S4 is the largest. S54: Plot points based on the particle size distribution characteristics of the stone coal in this medium-speed coal mill; S55: Repeat steps S51 to S54 multiple times to fit the distribution curve spectrum of the particle size-particle size ratio of the cobblestone particles, and derive the standard particle size distribution curve from this curve spectrum.
[0014] Furthermore, the experimental parameters include the amount of stone and coal particles weighed, the size of the stone and coal particles, the airflow temperature, and the airflow velocity.
[0015] Furthermore, in step S7, if the actual particle size distribution curve matches the standard particle size distribution curve, the medium-speed coal mill is in a normal state; if the actual particle size distribution curve deviates from the standard particle size distribution curve, the medium-speed coal mill is in an abnormal state.
[0016] Furthermore, if the actual particle size distribution curve shifts to the left compared to the standard particle size distribution curve, then the proportion of small-diameter stone coal particles is high. Therefore, it is necessary to check and analyze the nozzle cross-sectional area of the medium-speed coal mill, the local wear of the medium-speed coal mill cylinder, and the air distribution of the medium-speed coal mill air chamber. If the actual particle size distribution curve shifts to the right compared to the standard particle size distribution curve, then the proportion of large-diameter stone and coal particles is high. Therefore, it is necessary to check and analyze the wear degree of the grinding rollers of the medium-speed coal mill, the rationality of the loading force, and the rationality of the ventilation volume.
[0017] Compared with the prior art, the present invention has the following technical effects: The present invention provides a method for evaluating the operating status of a medium-speed coal mill based on the particle size of coke and stone. This method establishes a link between the particle size of coke and stone emitted by the medium-speed coal mill and the operating status of the mill. Through in-depth analysis of the emission characteristics of coke and stone, the operating status of the mill is evaluated and the operating characteristics of the mill are further improved. The evaluation results are accurate and fill the gap in this field. Attached Figure Description
[0018] Figure 1 This is a diagram illustrating the stone and coal discharge process of a medium-speed coal mill according to an embodiment of the present invention. Figure 2 The graph shows the calculation results of the particle Reynolds number in an embodiment of the present invention. Figure 3 This is a diagram showing the reasonable emission area of stone and coal particles from a typical medium-speed coal mill, calculated according to an embodiment of the present invention. Figure 4 This is a probability density distribution characteristic diagram of the particle size distribution of typical medium-speed coal mill stones obtained from calculations in an embodiment of the present invention. Detailed Implementation
[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present invention.
[0020] In this article, terms such as "left," "right," "up," "down," "front," and "back" are established based on the positional relationships shown in the attached drawings. Depending on the attached drawings, the corresponding positional relationships may also change. Therefore, they should not be interpreted as an absolute limitation on the scope of protection.
[0021] Figure 1 The diagram illustrates the process of discharging coking coal particles from a medium-speed coal mill. The mill nozzle ring rotates at speed N. Primary air enters the nozzle ring through the inlet, creating a high-speed airflow, which then exits through the nozzle ring into the mill body. The nozzle ring outlet section contains ground coal powder and coking coal particles. The high-speed airflow washes over these particles, generating an upward drag force, while the particles themselves are also subject to downward gravity. When the drag force is less than the gravity, the particles move downwards, entering the mill's air chamber through the nozzle ring gaps and then being discharged. When the drag force is greater than the gravity, the particles are lifted upwards, circulating within the mill or entering the separator at the top of the mill with the airflow.
[0022] Please see Figures 2 to 4This embodiment provides a method for evaluating the operating status of a medium-speed coal mill based on the particle size of coke stones, including the following steps: S1: Establish a mathematical model of the forces acting on the stone and coal particles.
[0023] Specifically, the process of establishing the mathematical model in step S1 is as follows: If we consider cobblestone particles as equivalent to spherical particles, the force situation of cobblestone particles in a flowing airflow is quite complex. Cobblestone particles in a flowing airflow are subjected to drag force, gravity, buoyancy, and other forces. The following are force models and mathematical descriptions of several forces: (1) Traction force
[0024] Direction: Opposite to the direction of the airflow velocity relative to the particles.
[0025] The formula is: , in, The drag coefficient (and particle Reynolds number) (Related) The density of the airflow; The windward area of the particles (for spherical particles) ); The airflow velocity; The velocity of the coal and stone particles; The particle size of the cobblestone is denoted as .
[0026] (2) Gravity With buoyancy
[0027] The formula is: , in: Density of coke particles; The volume of the cobblestone particles (spherical) is ); This is the acceleration due to gravity.
[0028] , in: The density of the airflow; The volume of the cobblestone particles (spherical) is ); This is the acceleration due to gravity.
[0029] (3) Other forces Other forces include the additional mass force. Pressure gradient force Basset force Lift (such as Saffman lift, Magnus force).
[0030] The equation of motion for gravel and coal particles in an airflow (Newton's second law) is:
[0031] in, The mass of the coal particles; Let F be the velocity of the gravel and coal particles; F be the net force acting on the gravel and coal particles. For drag force; For gravity; For buoyancy; For added mass force; For pressure gradient force; Basset force; For lift.
[0032] For the specific model of the forces acting on the coal particles at the nozzle ring outlet of the coal mill, among the various forces acting on the coal particles, only drag, gravity, and buoyancy are the main forces, playing a primary role. Additional mass force, pressure gradient force, Basset force, and lift are secondary forces, which are ignored. Therefore, the equation of motion of the coal particles in the airflow simplifies to:
[0033] in, For the mass of the coal particles, ; The velocity of the stone and coal particles; For drag force; The density of the airflow; This refers to the particle density of the cobblestone.
[0034] Specifically, based on the mathematical model established above, the movement of the stone and coal particles can be categorized into three cases: The gravel and coal particles are carried away by the airflow and cannot be discharged; The cobblestone particles are suspended in the nozzle ring, at the critical slag discharge point; The stone and coal particles cannot be carried away by the airflow and fall into the nozzle ring for discharge.
[0035] S2: Calculate the particle Reynolds number.
[0036] Specifically, the formula for calculating the particle Reynolds number in step S2 is as follows: , in, The particle Reynolds number; The density of the gas; The particle size of the cobblestone; The gas dynamic viscosity; The airflow velocity; The velocity of the stone and coal particles.
[0037] Specifically, for a medium-speed coal mill, the parameters in the model established in step S1 are assigned values. The hot air temperature at the nozzle ring outlet is typically around 240℃, and the theoretical flow velocity at the air outlet is approximately... When the stone and coal particles enter the nozzle ring, only the velocity of the particles along the diameter of the grinding disc is considered. That is, the vertical direction of the particles =0 The particle operation was analyzed based on the above parameters, and the particle Reynolds number for each stone coal particle size (i.e., equivalent particle diameter) at each airflow velocity was calculated. The calculation results are as follows Figure 2 As shown ( Figure 2 The image only shows an airflow velocity of 50. Wind speed and 70 (The situation under wind speed is given; other situations are not provided). According to the calculation results, the particle Reynolds number of stone coal particles in a typical medium-speed coal mill is all within the range of... Turbulent region >1000.
[0038] S3: Based on the particle Reynolds number calculated in step S2, the drag coefficient is obtained.
[0039] Specifically, the calculation process for the drag coefficient in step S3 is as follows: like (Stokes District), then , in, This is the drag coefficient; The particle Reynolds number; like (Transition zone), then , in, This is the drag coefficient; The particle Reynolds number; like (Turbulent region), then .
[0040] Specifically, according to the calculation results of step S1, the particle Reynolds number of the stone coal particles in the medium-speed coal mill is all within the range of... Turbulent regions >1000, therefore, .
[0041] S4: Calculate the reasonable discharge zone for stone and coal particles based on the mathematical model established in step S1 and the drag coefficient in step S3.
[0042] Specifically, the process of step S4 is as follows: Based on the established mathematical model, taking the critical situation of stone and coal particle emission as an example, we have: , in, The velocity of the stone and coal particles; For drag force; The mass of the coal particles; The density of the airflow; Density of coke particles; It is the acceleration due to gravity; drag force Stone coal particle quality Volume of stone coal particles Substituting the formula, we can obtain the particle size of the stone coal. In critical cases, This refers to the critical emission diameter of gravel and coal particles.
[0043] Under a constant airflow velocity (i.e., nozzle ring outlet velocity), when the equivalent diameter of the coking stones is greater than the critical discharge diameter, the coking stones will be discharged from the medium-speed coal mill; when the equivalent diameter is less than the critical discharge diameter, the coking stones cannot be discharged from the medium-speed coal mill. Based on the calculated critical discharge diameter of the coking stones, a nozzle ring outlet velocity-equivalent diameter curve is plotted. The area formed by the coking stone equivalent diameter being greater than the critical discharge diameter is the reasonable discharge zone for the coking stones. Figure 3 As shown in the figure, when the coal mill equipment and operating parameters are reasonable, the discharged stone coal particles should all fall within the reasonable discharge area shown in the figure, that is, the particle size distribution has obvious particle size range and probability density distribution characteristics.
[0044] S5: Based on the reasonable emission zone of stone and coal particles calculated in step S4, the standard particle size distribution curves for all airflow velocity values are obtained through experiment fitting.
[0045] Specifically, the process of step S5 is as follows: S51: Select several medium-speed coal mills of the same model to conduct a stone and coal particle discharge experiment. The experimental parameters of all medium-speed coal mills are set in the same way. The experimental parameters include the amount of stone and coal particles weighed, the size of the stone and coal particles, the airflow temperature and the airflow velocity.
[0046] S52: For the stone coal particles discharged from the medium-speed coal mill, weigh the same mass of stone coal particles discharged from each medium-speed coal mill, and sieve the same mass of stone coal particles symmetrically taken using sieves of different aperture sizes.
[0047] S53: Statistically analyze the particle size distribution characteristics of the stone coal particles screened by each medium-speed coal mill, and select the optimal medium-speed coal mill. Among the stone coal particles of this medium-speed coal mill, the mass proportion of the stone coal particles near the critical discharge diameter of the stone coal particles at the corresponding airflow velocity calculated in step S4 (which needs to be determined according to the actual situation) is the largest.
[0048] S54: Plot points based on the particle size distribution characteristics of the stone coal particles in this medium-speed coal mill.
[0049] S55: Repeat steps S51-S54 multiple times, setting the experimental parameters consistently for all experiments. Based on the data from multiple experiments, fit a distribution curve spectrum of stone coal particle size versus particle size percentage. From this spectrum, derive the curve with the largest critical discharge diameter mass percentage, and use this as the standard particle size distribution curve. This curve is the distribution curve of stone coal particle size versus particle size percentage, which is also the distribution curve of stone coal sieve aperture diameter versus the proportion of stone coal sample on the sieve.
[0050] Specifically, the emission characteristics of stone coal under reasonable operating conditions of the coal mill were analyzed, and the theoretical distribution characteristics of the stone coal particle size distribution, i.e., the standard particle size distribution curve, were obtained, such as... Figure 4 As shown. Figure 4 The high-output operating condition shown in the image corresponds to the rated output operating condition of the coal mill (i.e., 70). Wind speed), medium output condition corresponds to 75% of rated output condition (i.e., 60). Wind speed), low output condition corresponds to 50% rated load condition (i.e., 50) (Wind speed), the points with the largest stone and coal particle size distribution under all operating conditions are located near the theoretically calculated critical emission diameter of stone and coal particles. The standard particle size distribution curves for other wind speeds are not found in... Figure 4 The information is provided in the text.
[0051] S6: Based on the actual discharge of stone coal from the medium-speed coal mill, the actual particle size distribution curve is obtained.
[0052] Specifically, the process of step S6 is as follows: Weigh the same mass of stone coal particles actually discharged from the medium-speed coal mill, symmetrically take the same mass of stone coal particles using screens of different apertures for screening, statistically analyze the particle size distribution characteristics of the stone coal particles screened by the medium-speed coal mill, and then plot the points and draw lines to obtain the actual particle size distribution curve.
[0053] S7: Compare the actual particle size distribution curve from step S6 with the standard particle size distribution curve from step S5 to evaluate the operating status of the medium-speed coal mill.
[0054] Specifically, in step S7, if the actual particle size distribution curve matches the standard particle size distribution curve, the medium-speed coal mill is in normal condition; if the actual particle size distribution curve deviates from the standard particle size distribution curve, the medium-speed coal mill or its operating parameters are in abnormal condition. That is, if the actual particle size distribution curve shifts to the left compared to the standard particle size distribution curve, the proportion of small-diameter stone and coal particles is high, and the nozzle circumferential area, local wear of the medium-speed coal mill cylinder, and air distribution in the medium-speed coal mill's air chamber should be checked and analyzed; if the actual particle size distribution curve shifts to the right compared to the standard particle size distribution curve, the proportion of large-diameter stone and coal particles is high, and the wear degree of the medium-speed coal mill's grinding rollers, the rationality of the loading force, and the rationality of the ventilation volume should be checked and analyzed.
[0055] Specifically, the prerequisite for the falling of small-diameter coal pebbles is a low outlet velocity at the nozzle ring. Therefore, when the proportion of small-diameter coal pebbles in the discharged coal pebbles increases, there will inevitably be nozzle rings with excessively low local velocities. This could be due to uneven flow fields with low-velocity regions, severe wear of the nozzle ring leading to increased cross-sectional area and lower velocity, or abnormal mill operating parameters and insufficient ventilation. Therefore, when the amount of small-diameter coal pebbles at the mill discharge port is too low, the cross-sectional area of the mill nozzle ring, local wear of the mill cylinder, and air distribution in the mill's air chamber should be inspected and analyzed.
[0056] Specifically, for large-diameter particles to be discharged from the coal mill, they must be able to pass through the gap between the grinding rollers and the grinding disc and be squeezed to the nozzle ring outlet. Therefore, when the proportion of large-diameter particles in the discharged coal increases, the gap between the grinding rollers and the grinding disc will inevitably be larger, indicating either severe roller wear, insufficient loading force, or a larger gap reserved during installation. Thus, when a high proportion of large-diameter particles is detected in the coal, parameters such as the degree of roller wear and the appropriateness of the loading force can be assessed. It should be noted that as roller wear intensifies, the proportion of large-diameter particles in the coal should gradually increase.
[0057] Specifically, this method can also be used in conjunction with the appearance evaluation of coking coal. After the evaluation is completed using this method, the appearance of the coking coal particles can be evaluated again. If the grinding marks of the discharged coking coal are insufficient, it indicates that the coking coal was not "bitten" by the grinding roller in time and was not effectively blocked by the grinding disc, resulting in it being discharged without being ground. This is likely due to a problem with the fit between the grinding roller and the grinding disc, which leads to abnormal operation of the coal mill. Therefore, the structure of the coal mill should be inspected in a timely manner.
[0058] Specifically, the present invention provides a method for evaluating the operating status of a medium-speed coal mill based on the particle size of coke and stone. This method establishes a link between the particle size of coke and stone emitted by the medium-speed coal mill and the operating status of the mill. Through in-depth analysis of the emission characteristics of coke and stone particle size, the operating status of the mill is evaluated and the operating characteristics of the mill are further improved. The evaluation results are accurate and fill a gap in this field.
[0059] The above embodiments merely illustrate the basic principles and characteristics of the present invention, but are not limited to the above implementation schemes. It should be understood that those skilled in the art can make various changes and modifications to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined freely by the appended claims and their equivalents.
Claims
1. A method for evaluating the operating status of a medium-speed coal mill based on the particle size of coke stones, characterized in that, Includes the following steps: S1: Establish a mathematical model of the forces acting on the stone and coal particles; S2: Calculate the particle Reynolds number; S3: Based on the particle Reynolds number calculated in step S2, the drag coefficient is obtained; S4: Calculate the reasonable discharge zone for stone coal particles based on the mathematical model established in step S1 and the drag coefficient in step S3. S5: Based on the reasonable emission zone of the stone coal particles calculated in step S4, the standard particle size distribution curve is obtained by fitting the experimental data. S6: Based on the actual discharge of stone coal from the medium-speed coal mill, obtain the actual particle size distribution curve; S7: Compare the actual particle size distribution curve from step S6 with the standard particle size distribution curve from step S5 to evaluate the operating status of the medium-speed coal mill.
2. The method for evaluating the operating status of a medium-speed coal mill based on the particle size of gravel coal as described in claim 1, characterized in that, The specific process of establishing the mathematical model in step S1 is as follows: Treating the cobblestone particles as equivalent to spherical particles, the cobblestone particles in the flowing air are subjected to the combined effects of drag, gravity, buoyancy, additional mass force, pressure gradient force, Basset force, and lift. The equation of motion for the cobblestone particles in the airflow is: in, The mass of the coal particles; Let F be the velocity of the gravel and coal particles; F be the net force acting on the gravel and coal particles. For drag force; For gravity; For buoyancy; For added mass force; For pressure gradient force; Basset force; For lift; In the forces acting on the coal particles, drag, gravity, and buoyancy are the primary forces, while the additional mass force, pressure gradient force, Basset force, and lift are secondary forces. Neglecting the secondary forces, the equation of motion for the coal particles in the airflow simplifies to: in, The mass of the coal particles; The velocity of the stone and coal particles; For drag force; The density of the airflow; This refers to the particle density of the cobblestone.
3. The method for evaluating the operating status of a medium-speed coal mill based on the particle size of gravel coal as described in claim 2, characterized in that, Based on the mathematical model established in step S1, the movement of the stone and coal particles can be categorized into three cases: The gravel and coal particles are carried away by the airflow and cannot be discharged; The cobblestone particles are suspended in the nozzle ring, at the critical slag discharge point; The stone and coal particles cannot be carried away by the airflow and fall into the nozzle ring for discharge.
4. The method for evaluating the operating status of a medium-speed coal mill based on the particle size of gravel coal as described in claim 3, characterized in that, The formula for calculating the particle Reynolds number in step S2 is as follows: ， in, The particle Reynolds number; The density of the gas; The particle size of the cobblestone; The gas dynamic viscosity; The airflow velocity; The velocity of the stone and coal particles.
5. The method for evaluating the operating status of a medium-speed coal mill based on the particle size of gravel coal according to claim 4, characterized in that, The calculation process for the drag coefficient in step S3 is as follows: like (Stokes District), then ， in, This is the drag coefficient; The particle Reynolds number; like (Transition zone), then ， in, This is the drag coefficient; The particle Reynolds number; like (Turbulent region), then .
6. The method for evaluating the operating status of a medium-speed coal mill based on the particle size of gravel coal as described in claim 5, characterized in that, The specific process of step S4 is as follows: Based on the established mathematical model, taking the critical situation of stone and coal particle emission as an example, we have: ， in, The velocity of the stone and coal particles; For drag force; The mass of the coal particles; The density of the airflow; Density of coke particles; It is the acceleration due to gravity; drag force Stone coal particle quality Volume of stone coal particles Substituting the formula, we can obtain the particle size of the stone coal. In critical cases, The critical emission diameter of cobblestone particles; Under a constant airflow velocity, when the equivalent diameter of the stone and coal particles is greater than the critical discharge diameter, the stone and coal particles will be discharged from the medium-speed coal mill; when the equivalent diameter of the stone and coal particles is less than the critical discharge diameter, the stone and coal particles cannot be discharged from the medium-speed coal mill. Plot the airflow velocity-equivalent diameter curve of the stone and coal particles. The area formed by the equivalent diameter of the stone and coal particles being greater than the critical discharge diameter is the reasonable discharge zone for the stone and coal particles.
7. The method for evaluating the operating status of a medium-speed coal mill based on the particle size of gravel coal as described in claim 6, characterized in that, The specific process of step S5 is as follows: S51: Select several medium-speed coal mills of the same model to conduct a stone and coal particle discharge test, and set the same test parameters for all medium-speed coal mills. S52: For the stone coal particles discharged from the medium-speed coal mill, weigh the same mass of stone coal particles discharged from each medium-speed coal mill, and sieve the same mass of stone coal particles symmetrically taken using sieves with different aperture sizes. S53: Statistically analyze the particle size distribution characteristics of the stone coal particles screened by each medium-speed coal mill, select the optimal medium-speed coal mill, in which the mass proportion of the stone coal particles near the critical discharge diameter of the stone coal particles at the corresponding airflow velocity calculated in step S4 is the largest. S54: Plot points based on the particle size distribution characteristics of the stone coal in this medium-speed coal mill; S55: Repeat steps S51 to S54 multiple times to fit the distribution curve spectrum of the particle size-particle size ratio of the cobblestone particles, and derive the standard particle size distribution curve from this curve spectrum.
8. The method for evaluating the operating status of a medium-speed coal mill based on the particle size of gravel coal as described in claim 7, characterized in that, The experimental parameters include the amount of gravel and coal particles weighed, the size of the gravel and coal particles, the airflow temperature, and the airflow velocity.
9. The method for evaluating the operating status of a medium-speed coal mill based on the particle size of gravel coal as described in claim 8, characterized in that, In step S7, if the actual particle size distribution curve matches the standard particle size distribution curve, the medium-speed coal mill is in normal condition; if the actual particle size distribution curve deviates from the standard particle size distribution curve, the medium-speed coal mill is in abnormal condition.
10. The method for evaluating the operating status of a medium-speed coal mill based on the particle size of gravel coal according to claim 9, characterized in that, If the actual particle size distribution curve shifts to the left compared to the standard particle size distribution curve, then the proportion of small-sized stone and coal particles is high. Therefore, it is necessary to check and analyze the nozzle cross-sectional area of the medium-speed coal mill, the local wear of the cylinder of the medium-speed coal mill, and the air distribution of the air chamber of the medium-speed coal mill. If the actual particle size distribution curve shifts to the right compared to the standard particle size distribution curve, then the proportion of large-diameter stone and coal particles is high. Therefore, it is necessary to check and analyze the wear degree of the grinding rollers of the medium-speed coal mill, the rationality of the loading force, and the rationality of the ventilation volume.