Method for calculating milling force of coal mill according to effective crushing intercept

Abstract

The invention relates to a method for calculating the milling output of a coal mill according to an effective crushing intercept, and belongs to the technical field of coal mills, the milling output can be accurately calculated by introducing the concept of the effective crushing intercept ECI and utilizing a proportionality coefficient k, the blank in the field of improvement and calculation of the output of the coal mill is filled, and the milling output can be accurately calculated. The calculation of the output improvement and transformation design is improved to a controllable stage, and reference can be provided for the output improvement and transformation design of the coal mill. In the calculation process, by making the grinding roller in the vertical state, calculating the average speed difference and simplifying calculation, the calculation amount can be greatly reduced, and the efficiency can be improved. When the average speed difference of the shearing area is calculated, the average speed difference is obtained by integrating the speed difference in the interval corresponding to the thickness of the grinding roller on the X axis and then dividing by the thickness of the grinding roller, and the average speed difference is well reflected. Through verification, the effective breaking intercept ECI can predict the milling output with extremely high precision, and the output transformation requirement of the coal mill can be met.

Description

Technical Field

[0001] This invention relates to the field of coal mill technology, and specifically to a method for calculating the grinding output of a ZGM type coal mill based on the effective crushing cutoff. Background Technology

[0002] Influenced by the global energy structure transformation, the high proportion of new energy connected to the grid, and the trend of flexible transformation of thermal power, the role of thermal power generation in the energy system is shifting from base load power to peak load power, which puts forward higher requirements for the efficiency, flexibility and intelligence of coal mills.

[0003] To meet peak-shaving demands, existing coal mill units urgently need a wider output range, necessitating upgrades to increase capacity. Taking the commonly used ZGM type coal mill as an example, the ZGM medium-speed roller mill, with its compact structure, high grinding efficiency, low power consumption, and convenient coal powder fineness adjustment, has become the mainstream pulverizing equipment in thermal power plants, resulting in a large existing stock and concentrated demand for upgrades. The ZGM type coal mill uses a grinding disc-roller grinding zone to achieve continuous pulverization of raw coal, combined with hot air drying, air-coal conveying, and dynamic / static separator classification. However, due to limitations in original design parameters, coal type adaptability, and equipment aging, existing ZGM coal mills generally suffer from insufficient rated output.

[0004] For the ZGM coal mill, the grinding of raw coal is accomplished by three grinding rollers mounted on a grinding disc. These three rollers are evenly distributed and fixed around their circumference. A loading cylinder drives a pull rod to apply downward pressure, causing the grinding disc to rotate. The roller sleeves and the grinding disc liner are in tangential contact, thus transmitting power. Due to the variation in the rotation radius of the rollers and liner outside the tangential position, the linear velocity of the rollers and liner at each grinding point is different, generating shear force to grind and crush the coal particles. Common modification methods for the ZGM coal mill include increasing the diameter of the grinding disc and widening the roller sleeves. For example, a power plant modified a ZGM95N coal mill (upgrading it to a ZGM95G model). By replacing the main grinding components such as the grinding disc and rollers, the output increased by more than 10.7% after the modification. However, this data is the result of post-test evaluation. Reliable predictive methods for pre-modification are lacking. The existing ZGM coal mill lacks an accurate grinding output prediction model after modification, resulting in blind setting of operating parameters and sluggish adjustment response, making it difficult to balance output improvement and equipment stability.

[0005] It is evident that the calculation of output for the modification of medium-speed roller mills is currently a blind spot. Most calculations are based on experience, which often results in actual output failing to meet customer requirements or having excessive redundancy due to a lack of rigor. Summary of the Invention

[0006] The present invention is proposed to alleviate or solve at least one aspect or point of the above-mentioned problems.

[0007] The present invention provides a method for calculating the grinding output of a coal mill based on the effective crushing intercept, comprising the following steps: Obtain the mill roller thickness B and pitch circle radius of the coal mill. Rated speed n, grinding roller radius Pitch circle radius Grinding roller radius ; Calculate the average velocity difference in the shear zone , ; Calculate the effective crushing distance of the coal mill: ; Obtain the proportionality coefficient k; Calculate the grinding output of the coal mill .

[0008] Preferably, the average velocity difference in the shear zone is calculated. It also includes the following steps: making the grinding roller vertical and calculating the average speed difference.

[0009] Preferably, the average velocity difference in the shear zone is calculated. It also includes the following steps: Establish a coordinate system with the center of the grinding disc as the origin, with the point of tangency between the grinding roller and the grinding disc located on the X-axis and the Y-axis in the vertical direction; The linear velocity of the grinding disc at the point where the grinding roller is tangent to the grinding disc By setting the linear velocity of the grinding roller to be the same as that of the grinding disc, the rotational speed of the grinding roller is calculated as: n g =n×R G / R m , where ng is the rotational speed of the grinding roller.

[0010] Let A be any point on the grinding roller with coordinates (x, y). Calculate the linear velocity of the grinding disc at point A as: v px =2πnx; Calculate the radius of rotation of the grinding roller at point A. , ; Calculate the linear velocity of the grinding roller at point A: v gx =2πn g × ; Calculate the difference in linear velocity at point A. Therefore, we get: = .

[0011] Preferably, the speed difference is within the range corresponding to the thickness of the grinding roller on the X-axis. The average speed difference can be obtained by integrating and dividing by the thickness of the grinding roller.

[0012] Preferably, the proportionality coefficient k is obtained as a preset value.

[0013] Preferably, obtaining the proportionality coefficient k includes: calculating the ECI of the coal mill before the modification, and obtaining the grinding output of the coal mill before the modification. .

[0014] Preferably, it is used for calculating the grinding output when modifying a coal mill.

[0015] Preferably, the grinding output of the coal mill is calculated. At that time, the ECI was calculated based on the parameters of the modified coal mill.

[0016] Preferably, if the working medium or operating conditions of the coal mill change, the coal mill output of the original coal mill is obtained based on the new working medium and operating conditions.

[0017] Preferably, the coal mill is a ZGM type coal mill.

[0018] This invention introduces the concept of Effective Crushing Interval (ECI) and utilizes the proportionality coefficient k to accurately calculate the grinding output. This fills a gap in the calculation field for improving the output of coal mills, elevating the calculation of output improvement design to a controllable stage and providing a reference for the design of coal mill output improvement projects.

[0019] In the calculation process, this invention simplifies the calculation by keeping the grinding roller in a vertical position and calculating the average speed difference, which can greatly reduce the amount of calculation and improve efficiency. When calculating the average speed difference in the shearing region, the average speed difference is obtained by integrating the speed difference in the X-axis interval corresponding to the thickness of the grinding roller and then dividing it by the thickness of the grinding roller, which better reflects the magnitude of the average speed difference.

[0020] Verification has confirmed that the parameters of this invention can predict the grinding output with extremely high accuracy, and can meet the output modification requirements of coal mills. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the fit between the grinding disc and grinding roller of the existing ZGM coal mill.

[0022] Figure 2 This is a schematic diagram illustrating the calculation of the average velocity difference in the shear region, as an exemplary embodiment of the present invention.

[0023] Figure 3 This is a schematic diagram illustrating the relationship between the effective crushing intercept (ECI) and the grinding output force, which is an exemplary embodiment of the present invention.

[0024] Figure 4This is a schematic diagram illustrating the relationship between the calculated force and the actual output force using the method of the present invention, as an exemplary embodiment of the present invention. Detailed Implementation

[0025] The following description of embodiments of the present invention with reference to the accompanying drawings is intended to explain the overall inventive concept of the invention and should not be construed as a limitation thereof. In this invention, the same reference numerals denote the same or similar parts.

[0026] The features described herein may be implemented in different forms and should not be construed as limited to the examples described herein. Rather, the examples described herein are provided only to illustrate some of the many feasible ways in which the methods, apparatuses, and / or systems described herein will become clear upon understanding the disclosure of the invention.

[0027] The terminology used herein is for the purpose of describing various examples only and is not intended to limit disclosure. Unless the context clearly indicates otherwise, the singular form is intended to include the plural form as well. The terms “comprising,” “including,” and “having” indicate the presence of the described features, quantities, operations, components, elements, and / or combinations thereof, but do not preclude the presence or addition of one or more other features, quantities, operations, components, elements, and / or combinations thereof.

[0028] To enable those skilled in the art to utilize the content of this invention, the following exemplary embodiments may be provided in conjunction with specific application scenarios, specific systems, device and component parameters, and specific connection methods. However, these embodiments are merely examples for those skilled in the art, and the general principles defined herein can be applied to other embodiments and application scenarios without departing from the spirit and scope of this invention.

[0029] According to an exemplary embodiment of the present invention: Figure 1 The diagram shown illustrates the fit (cross-sectional view) between the grinding rollers and the grinding disc of the ZGM coal mill. The main parameters include: D G —Grinding roller diameter, Rg—Grinding roller radius, Rm—Pitch circle radius, Dm—Pitch circle diameter, B—Grinding roller thickness, n—Grinding disc rotation speed. It is the angle between the centerline of the grinding roller and the horizontal plane.

[0030] Although Figure 1 The diagram illustrates the diameter D of the grinding roller. G To characterize the size of the grinding roller, R can obviously also be used. G —Characterized by the radius of the grinding roller, the radius of the grinding roller R G It is half the diameter of the grinding roller. Although Figure 1The size of the grinding disc is schematically represented by the pitch circle radius Rm, but it can also be represented by the pitch circle diameter Dm, which is twice the pitch circle radius. It should be noted that, in this invention, the pitch circle radius Rm and the grinding roller radius R are used in the calculation process as an example. G It is used to calculate the speed difference, but obviously, the pitch circle diameter Dm and the grinding roller diameter D can be used instead. G The above conversion method is obviously equivalent to the present invention and is within the protection scope of the present invention.

[0031] like Figure 1 As shown, in the ZGM coal mill, the grinding of raw coal is accomplished by three grinding rollers located on the grinding disc. The curved surface of the grinding roller sleeves forms tangential contact with the grinding disc liner, achieving power transmission. Because the rotation radius of the grinding rollers and liners in the corresponding grinding areas varies gradually outside the tangential contact point, there is a difference in the linear velocity of the grinding rollers and liners at each grinding point. The resulting shear force and compressive force work together to grind and crush the raw coal particles. Due to the variation in the rotation radius of the grinding rollers and liners outside the tangential contact point, the linear velocity of the grinding rollers and liners at each grinding point is different, thus generating shear force to complete the grinding and crushing of the coal powder particles.

[0032] Based on this principle, this paper introduces the concept of Effective Crushing Intercept (ECI), denoted by the symbol ECI. It refers to the shear zone where the grinding roller contacts the grinding disc after falling under normal operating conditions of the coal mill disc, and is used to characterize the actual amount of raw coal crushed during grinding. The formula for calculating ECI is as follows:

[0033] in, For the average velocity difference in the shear region, For the thickness of the grinding roller, The radius of the grinding disc is given, and ECI is the product of these three values. For example, the units for thickness and radius are meters (m), and the speed difference is in meters per second (m / s).

[0034] For example, the average speed difference in the shearing region is the average of all speed differences in the entire shearing region. Preferably, the average speed difference is obtained by integrating the speed difference along the arc of the grinding roller and then dividing by the thickness of the grinding roller.

[0035] According to an exemplary embodiment of the present invention: Figure 2As shown, to simplify calculations, this invention assumes the grinding roller is in a vertical position when calculating the average speed difference. Here, "grinding roller in a vertical position" means that during calculation, the angle α between the centerline of the grinding roller and the horizontal plane is 0 degrees. For example, a coordinate system is established with the center of the grinding disc as the origin, the point of tangency between the grinding roller and the grinding disc located on the X-axis, and the Y-axis as the vertical direction. The exemplary origin is located on the centerline of the grinding disc. On the horizontal plane, a perpendicular line is drawn from the point of tangency between the grinding roller and the grinding disc to the centerline of the grinding disc; the intersection of these two lines is the origin.

[0036] like Figure 2 As shown, the linear velocity of the grinding disc at the point where the grinding roller and the grinding disc are tangent is... We can assume that the linear velocity of the grinding roller is the same as that of the grinding disc. Therefore, the rotational speed of the grinding roller can be obtained: n g =n×R G / R m； Where n g This refers to the rotational speed of the grinding roller.

[0037] Let point A in the diagram be any point on the grinding roller, with coordinates (x, y). Calculate the linear velocity of the grinding disc at point A: v px =2πnx.

[0038] Calculate the radius of rotation of the grinding roller at point A. Calculate the linear velocity of the grinding roller at point A: v gx =2πn g × ;like Figure 2 As shown, For R G Subtract the length of line segment CD, and the length of CD ED is the result of subtracting the length of EC. The length of EC can be obtained from the relationship between right triangle AEC.

[0039] like Figure 2 As shown, calculate the difference in linear velocity at point A. = = = = ; Average velocity difference in the shear zone This is the average of all speed differences over the entire shearing region; therefore, the speed difference within the range corresponding to the roller thickness is... The average speed difference can be obtained by integrating and dividing by the thickness of the grinding roller: =

[0040] As can be seen from the above formula, the above... for The function, .

[0041] According to an exemplary embodiment of the present invention: calculating the K value. Obtaining the proportionality coefficient k includes: calculating the ECI of the coal mill before modification, and obtaining the grinding output of the coal mill before modification. .

[0042] Calculate the predicted output of the modified coal mill ECI is based on the thickness B of the grinding rollers and the pitch circle radius of the modified coal mill. Rated speed n, grinding roller radius Pitch circle radius Grinding roller radius Perform the calculation.

[0043] Experimental verification: Table 1

[0044] As shown in Table 1 and Figure 3 As shown in Table 1, ZGM80G, ZGM95N, ZGM113N, ZGM123N, and ZGM133N were selected for verification calculations of this scheme. The k parameter in Table 1 is set to 1.98, resulting in a very small error between the calculated output and the standard output. Therefore, a parameter of 1.98 can be used for calculating the basic output of almost all ZGM-type coal mills.

[0045] It should be noted that although the header of Table 1 indicates the units for each parameter, other units can obviously also be used; only the modified units are needed. During calculation, compared to before the modification The same parameters can be used.

[0046] At the same time, refer to Figure 3 As shown, ECI and milling output have a clear direct proportional relationship. By correcting with k, the calculated specific force is found to be very close to the standard output, which can be used for the design of mills.

[0047] Table 2

[0048] Table 2 and Figure 4 The table shows the calculation results of the Dujiangyan 95N mill renovation project using the method of this invention, and a comparison with the actual measurement results. As can be seen from Table 2, the k-coefficient is related to the specific circumstances of each project. Therefore, optionally, the k-coefficient of the old mill needs to be determined before each renovation, and then the renovation design is carried out. Multiplying the k-coefficient calculated from the old mill by the effective crushing intercept of the renovated coal mill yields the calculated output. Combined with... Figure 4 It can be seen that the calculated output and the actual output are very close, which can fully meet the requirements of the transformation.

[0049] Preferably, if the operating conditions change during application, the k-coefficient needs to be adjusted. Since the output of a coal mill is also related to the properties of the coal, the actual modification process is designed based on the same conditions, such as the modified coal mill using the same working fluid and operating conditions as the original coal mill. For example, if the working fluid or operating conditions change in this invention, a new working fluid and operating conditions are used to obtain the output of the original coal mill, and the k-value is recalculated, i.e., the k-value is readjusted.

[0050] This invention defines the effective crushing intercept, which achieves coal particle crushing through the shearing action generated by the difference between the linear velocity of the grinding roller and the liner at this point. Its advantage lies in the fact that the calculated results closely approximate the actual output B of the modified coal mill. M This changes the previous situation where power output was calculated based on selection.

[0051] This calculation method fills a gap in the field of calculation for improving the output of coal mills, elevates the calculation of output improvement design to a controllable stage, and can provide the best guidance for all coal mill output improvement design.

[0052] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that variations and combinations of elements may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for calculating the grinding output of a coal mill based on the effective crushing intercept, characterized in that: Includes the following steps: Obtain the mill roller thickness B and pitch circle radius of the coal mill. Rated speed n, grinding roller radius Pitch circle radius Grinding roller radius ; Calculate the average velocity difference in the shear zone , ; Calculate the effective crushing distance of the coal mill: ; Obtain the proportionality coefficient k; Calculate the grinding output of the coal mill .

2. The method according to claim 1, characterized in that: Calculate the average velocity difference in the shear zone It also includes the following steps: making the grinding roller vertical and calculating the average speed difference.

3. The method according to claim 2, characterized in that: Calculate the average velocity difference in the shear zone It also includes the following steps: Establish a coordinate system with the center of the grinding disc as the origin, with the point of tangency between the grinding roller and the grinding disc located on the X-axis and the Y-axis in the vertical direction; The linear velocity of the grinding disc at the point where the grinding roller is tangent to the grinding disc By setting the linear velocity of the grinding roller to be the same as that of the grinding disc, the rotational speed of the grinding roller is calculated as: n g =n×R G / R m , where ng is the rotational speed of the grinding roller; Let A be any point on the grinding roller with coordinates (x, y). Calculate the linear velocity of the grinding disc at point A as: v px =2πnx; Calculate the radius of rotation of the grinding roller at point A. , ; Calculate the linear velocity of the grinding roller at point A: v gx =2πn g × ; Calculate the difference in linear velocity at point A. Therefore, we get: = .

4. The method according to claim 3, characterized in that: The speed difference in the range corresponding to the thickness of the grinding roller on the X-axis The average speed difference can be obtained by integrating and dividing by the thickness of the grinding roller.

5. The method according to claim 1, characterized in that: Obtaining the scaling factor k involves setting k to a preset value.

6. The method according to claim 1, characterized in that: Obtaining the proportionality coefficient k includes: calculating the ECI of the coal mill before the modification, and obtaining the grinding output of the coal mill before the modification. .

7. The method according to claim 1, characterized in that: It is used for calculating the grinding output when modifying coal mills.

8. The method according to claim 1, characterized in that: Calculate the grinding output of the coal mill At that time, the ECI was calculated based on the parameters of the modified coal mill.

9. The method according to claim 1, characterized in that: If the working medium or operating conditions of the coal mill change, the original coal mill's grinding output can be obtained based on the new working medium and operating conditions.

10. The method according to claim 1, characterized in that: The coal mill is a ZGM type coal mill.

Images