Method for calculating resistance loss of soft melting zone in blast furnace

Abstract

The invention discloses a method for calculating resistance loss of a soft melting zone in a blast furnace, which comprises the following steps of: acquiring furnace profile parameters, temperature distribution of cross temperature measurement and theoretical combustion temperature in front of a tuyere, and calculating a temperature distribution matrix in the furnace; the softening starting temperature and the dripping temperature of the ore are obtained, and the width of a soft melting zone is calculated; the average particle size of coke entering the furnace and tuyere coke sampling data are obtained, and the particle size distribution of coke in a soft melting zone coke window is calculated; calculating the flow rate of the coal gas passing through the soft melting coke window; calculating the resistance coefficient of the soft melting coke window; and calculating the pressure difference of the soft melting zone. The pressure difference of the soft melting zone can be calculated, a basis is provided for a blast furnace operator to control the overall pressure difference of the blast furnace and adjust an upper and lower system, and energy conservation and consumption reduction of the blast furnace are facilitated.

Description

Technical Field

[0001] The invention relates to a method for calculating the resistance loss of a soft melting zone inside a blast furnace, and belongs to the technical field of blast furnace operation control. Background Art

[0002] The gas temperature of a blast furnace gradually decreases from the tuyere to the throat, and can be divided into four areas: the combustion zone, the dripping zone, the soft melting zone, and the massive zone. The soft melting zone is composed of coke and molten ore. The coke and the molten ore are distributed in layers and are the area with the highest pressure difference in the blast furnace. Blast furnace operators have been committed to studying the shape, position and other parameters of the soft melting zone in order to improve the permeability of the soft melting zone and reduce the pressure difference in the soft melting zone, so as to create conditions for the blast furnace to further reduce the coke ratio and save energy. With the development of ironmaking technology, blast furnace operators pay more and more attention to the adjustment of soft melting zone parameters. Through experiments or blast furnace dissection, it is calculated that the pressure difference of the soft melting zone accounts for more than 50% of the overall pressure difference of the blast furnace, but there is a lack of a method to quantitatively calculate the pressure difference of the soft melting zone.

[0003] Therefore, a method for calculating the resistance loss of the soft melting zone inside the blast furnace is provided to solve the above problem. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for calculating the resistance loss of the soft melting zone inside a blast furnace, so as to better adjust the blast furnace operating parameters, improve the permeability of the soft melting zone, and provide a basis for blast furnace operators to optimize the blast furnace smelting system.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention specifically includes:

[0006] S1. Obtain furnace parameter information, cross temperature measurement information and theoretical combustion temperature information of the blast furnace, and calculate the furnace temperature distribution matrix according to the furnace parameter information, cross temperature measurement information and theoretical combustion temperature information of the blast furnace;

[0007] S2. Obtaining softening start temperature information and dripping temperature information of the ore, and calculating the width of the soft melting zone according to the softening start temperature information and dripping temperature information;

[0008] S3. Obtaining the average particle size information of the coke entering the furnace and the tuyere coke sampling data information, and calculating the particle size distribution of the coke in the soft melting zone coke window according to the average particle size information of the coke entering the furnace and the tuyere coke sampling data information;

[0009] S4. Calculate the gas flow rate through the soft melting zone coke window;

[0010] S5. Calculate the resistance coefficient of the soft melting zone focal window;

[0011] S6. Calculate the pressure difference of the soft melting zone.

[0012] Furthermore, the “obtaining furnace type parameter information, cross temperature measurement information and blast furnace theoretical combustion temperature information, and calculating the furnace temperature distribution matrix according to the furnace type parameter information, cross temperature measurement information and blast furnace theoretical combustion temperature information” includes:

[0013] Collect the temperature T at different radial positions of the cross temperature measurement within the set time r(j) , where j is the thermocouple number, j = 1, 2, ... k, where j = 1 represents the edge, and j = k represents the center; r(j) is the distance between thermocouple j and the furnace wall; T r(j) After dimensionless processing, we get in is the dimensionless position of the cross-type thermocouple, representing the dimensionless distance from the furnace wall. The calculation formula is as follows:

[0014]

[0015] In the formula, R L is the furnace throat radius;

[0016] Collect the theoretical combustion temperature before the tuyere, assume that the gas temperature from the tuyere to the cross temperature measurement position is linearly distributed, and obtain the gas temperature distribution function along the height direction of the blast furnace Where x is the material line depth;

[0017] Obtain the internal dimensions of the blast furnace and obtain the blast furnace radius function R(x) at different material line positions, where x is the material line depth;

[0018] Get the tuyere position material line h T , operating material line h C , divide the tuyere to the operating material line into n parts along the height direction, with a step length of Δh, Δh = (h T -h C ) / n, the radial gas temperature distribution at position i·Δh below the operating material line is: The temperature distribution matrix A in the furnace can be obtained n×k , k is the number of temperature measuring points in the radius direction of the furnace throat;

[0019] Furthermore, the “obtaining softening start temperature information and dripping temperature information of the ore, and calculating the width of the soft melting zone according to the softening start temperature information and the dripping temperature information” includes:

[0020] Get the softening start temperature t of the ore s And the dripping temperature t d , if in the temperature distribution matrix A n×k In the g-th row, A is found g,i ≤t d ≤A g,i+1 , where A g,m Dot and Ag,m+1 The distance between the point and the furnace wall can be calculated by the blast furnace radius function R(x), and the linear interpolation method is used to calculate the ore on the material line h C The softening start position at +g·Δh is at a distance from the furnace wall:

[0021]

[0022] If A is not found g,i ≤t d ≤A g,i+1 , it means that the area is not a soft melting zone;

[0023] Query A g,i ≤t d ≤A g,i+1 After that, continue to query A g,m ≤t s ≤A g,m+1 , calculate the ore in the material line h C The distance L between the dripping position at +g·Δh and the furnace wall g,s ; If A is not found g,m ≤t s ≤A g,m+1 , then L g,s =0;

[0024] Get Satisfaction A g,m ≤t d ≤A g,m+1 The position is the area where the soft melting zone starts. The number of soft melting zone layers in this area is calculated using the volume method. The width of the soft melting zone is:

[0025] W i =L g,d -L g,s

[0026] In the formula, h R,i is the material line position of the i-th soft melting zone.

[0027] Furthermore, the “obtaining the average particle size information of the coke entering the furnace and the sampling data information of the tuyere coke, and calculating the particle size distribution of the coke in the coke window of the soft melting zone according to the average particle size information of the coke entering the furnace and the sampling data information of the tuyere coke” includes:

[0028] Get the average particle size d of the coke entering the furnace coke And tuyere sampling coke d tuyere , then the average particle size of coke in the focal window of the i-th soft melting zone is:

[0029]

[0030] In the formula, h R,1It is the position of the focus window material line of the first layer of soft melting zone, that is, the top of the soft melting zone.

[0031] Furthermore, the “calculating the gas flow rate through the coke window of the soft melting zone” includes:

[0032] Obtain the number of soft melting zone layers, coke window thickness and bosh gas volume, and the gas flow rate through the coke window of the soft melting zone is:

[0033]

[0034] In the formula, Q 煤气 is the amount of furnace gas, which can be calculated based on the nitrogen balance of the gas; R(h R,i ) is the inner radius of the blast furnace at the position of the i-th soft melting zone; B i is the focal window thickness of the i-th soft melting zone; S 中心 is the area of ​​the central coke column.

[0035] Furthermore, the “calculating the resistance coefficient of the soft melting zone focal window” includes:

[0036] The resistance coefficient of each focal window is calculated using the Ergen formula, and the resistance coefficient of the entire soft melting zone is the harmonic mean of the resistance coefficients of each focal window.

[0037]

[0038] Where, ξ is the resistance coefficient of the soft melting zone; i is the resistance coefficient of the focal window of the i-th soft melting zone;

[0039]

[0040] Where, ε is the coke porosity; d i is the average particle size of coke in the i-th soft melting zone coke window; W i is the width of the i-th soft melting zone.

[0041] Furthermore, the “calculating the pressure difference of the soft melting zone” includes:

[0042]

[0043] In the formula, ρ g is the gas density, v g is the gas flow velocity, ξ is the resistance coefficient.

[0044] Compared with the prior art, the present invention has the following advantages and effects: the present invention can calculate the gas temperature distribution inside the blast furnace through parameters such as furnace body parameters, cross-temperature measurement temperature distribution, coke particle size entering the furnace, theoretical combustion temperature before the tuyere, etc., and determine the soft melting zone width at different material line positions of the blast furnace in combination with the ore soft melting temperature range, and then calculate the soft melting zone pressure difference, which can provide a basis for the blast furnace operator to adjust the gas distribution, thereby improving the permeability of the soft melting zone area, which is conducive to achieving high-efficiency and low-consumption smelting in the blast furnace. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a flow chart of the calculation of the pressure difference of the soft melting zone of the present invention.

[0046] Figure 2 It is a schematic diagram of the parameters of the soft melting zone of the present invention. DETAILED DESCRIPTION

[0047] In order to elaborate on the technical scheme adopted by the present invention to achieve the predetermined technical purpose, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only partial embodiments of the present invention, rather than all embodiments, and the technical means or technical features in the embodiments of the present invention can be replaced without paying creative work. The present invention will be described in detail below with reference to the drawings and in conjunction with the embodiments.

[0048] Example

[0049] like Figure 1-2 As shown, this embodiment provides a method for calculating the resistance loss of the soft melting zone inside a blast furnace, comprising the following steps:

[0050] S1. Obtain furnace parameter information, cross temperature measurement information and theoretical combustion temperature information of the blast furnace, and calculate the furnace temperature distribution matrix according to the furnace parameter information, cross temperature measurement information and theoretical combustion temperature information of the blast furnace;

[0051] S2. Obtaining softening start temperature information and dripping temperature information of the ore, and calculating the width of the soft melting zone according to the softening start temperature information and dripping temperature information;

[0052] S3. Obtaining the average particle size information of the coke entering the furnace and the tuyere coke sampling data information, and calculating the particle size distribution of the coke in the soft melting zone coke window according to the average particle size information of the coke entering the furnace and the tuyere coke sampling data information;

[0053] S4. Calculate the gas flow rate through the soft melting zone coke window;

[0054] S5. Calculate the resistance coefficient of the soft melting zone focal window;

[0055] S6. Calculate the pressure difference of the soft melting zone.

[0056] The “obtaining furnace type parameter information, cross temperature measurement information and blast furnace theoretical combustion temperature information, and calculating the furnace temperature distribution matrix according to the furnace type parameter information, cross temperature measurement information and blast furnace theoretical combustion temperature information” includes:

[0057] Collect the temperature T at different radial positions of the cross temperature measurement within the set time r(j) , where j is the thermocouple number, j = 1, 2, ... k, where j = 1 represents the edge, and j = k represents the center; r(j) is the distance between thermocouple j and the furnace wall; T r(j) After dimensionless processing, we get in is the dimensionless position of the cross-type thermocouple, representing the dimensionless distance from the furnace wall. The calculation formula is as follows:

[0058]

[0059] In the formula, R L is the furnace throat radius;

[0060] Collect the theoretical combustion temperature before the tuyere, assume that the gas temperature from the tuyere to the cross temperature measurement position is linearly distributed, and obtain the gas temperature distribution function along the height direction of the blast furnace Where x is the material line depth;

[0061] The internal dimensions of the blast furnace are obtained to obtain the blast furnace radius function R(x) at different material line positions, where x is the material line depth; the specific steps for obtaining the blast furnace radius function mentioned in this embodiment are to divide the blast furnace into sections, model the blast furnace in each section, and obtain the blast furnace radius function.

[0062] Get the tuyere position material line h T , operating material line h C , divide the tuyere to the operating material line into n parts along the height direction, with a step length of Δh, Δh = (h T -h C ) / n, the radial gas temperature distribution at position i·Δh below the operating material line is: The temperature distribution matrix A in the furnace can be obtained n×k , k is the number of temperature measuring points in the radius direction of the furnace throat. The temperature measuring points are thermocouples, so the last number k of the thermocouple is the number of temperature measuring points;

[0063] The “obtaining softening start temperature information and dripping temperature information of the ore, and calculating the width of the soft melting zone according to the softening start temperature information and the dripping temperature information” includes:

[0064] Get the softening start temperature t of the ore s And the dripping temperature t d , if in the temperature distribution matrix An×k In the g-th row, A is found g,i ≤t d ≤A g,i+1 , where A g,m Dot and A g,m+1 The distance between the point and the furnace wall can be calculated by the blast furnace radius function R(x), and the linear interpolation method is used to calculate the ore on the material line h C The softening start position at +g·Δh is at a distance from the furnace wall:

[0065]

[0066] If A is not found g,i ≤t d ≤A g,i+1 , it means that the area is not a soft melting zone;

[0067] Query A g,i ≤t d ≤A g,i+1 After that, continue to query A g,m ≤t s ≤A g,m+1 , calculate the ore in the material line h C The distance L between the dripping position at +g·Δh and the furnace wall g,s ; If A is not found g,m ≤t s ≤A g,m+1 , then L g,s =0;

[0068] Get Satisfaction A g,m ≤t d ≤A g,m+1 The position is the area where the soft melting zone starts. The number of soft melting zone layers in this area is calculated using the volume method. The width of the soft melting zone is:

[0069] W i =L g,d -L g,s

[0070] In the formula, h R,i is the material line position of the i-th soft melting zone.

[0071] The “obtaining the average particle size information of the coke entering the furnace and the sampling data information of the tuyere coke, and calculating the particle size distribution of the coke in the coke window of the soft melting zone according to the average particle size information of the coke entering the furnace and the sampling data information of the tuyere coke” includes:

[0072] Get the average particle size d of the coke entering the furnace coke And tuyere sampling coke d tuyere , then the average particle size of coke in the focal window of the i-th soft melting zone is:

[0073]

[0074] In the formula, h R,1 It is the position of the focus window material line of the first layer of soft melting zone, that is, the top of the soft melting zone.

[0075] The “calculation of the gas flow rate through the coke window of the soft melting zone” includes:

[0076] Obtain the number of soft melting zone layers, coke window thickness and bosh gas volume, and the gas flow rate through the coke window of the soft melting zone is:

[0077]

[0078] In the formula, Q 煤气 is the amount of furnace gas, which can be calculated based on the nitrogen balance of the gas; R(h R,i ) is the inner radius of the blast furnace at the position of the i-th soft melting zone; B i is the focal window thickness of the i-th soft melting zone; S 中心 is the area of ​​the central coke column.

[0079] The “calculation of the resistance coefficient of the soft melting zone focal window” includes:

[0080] The resistance coefficient of each focal window is calculated using the Ergen formula, and the resistance coefficient of the entire soft melting zone is the harmonic mean of the resistance coefficients of each focal window.

[0081]

[0082] Where, ξ is the resistance coefficient of the soft melting zone; i is the resistance coefficient of the focal window of the i-th soft melting zone;

[0083]

[0084] Where, ε is the coke porosity; d i is the average particle size of coke in the i-th soft melting zone coke window; W i is the width of the i-th soft melting zone.

[0085] The “calculation of the pressure difference of the soft melting zone” includes:

[0086]

[0087] In the formula, ρ g is the gas density, v g is the gas flow velocity, ξ is the resistance coefficient.

[0088] Example

[0089] like Figure 1-2 As shown, this embodiment provides a method for calculating the resistance loss of the soft melting zone inside a blast furnace, comprising the following steps:

[0090] S1. Obtain the hourly average temperature of the radial direction of the cross temperature measurement, where T r(1) =90℃, T r(2) =80℃, T r(3) =85℃, T r(4) =100℃, T r(5) =230℃, T r(6) =900℃, r(1)=0.3m, r(2)=1.06m, r(3)=1.82m, r(4)=2.58m, r(5)=3.34m, r(6)=4.1m, the furnace throat radius is 4.1m, calculate The theoretical combustion temperature before the tuyere is 2350℃, the material line at the tuyere is 23.5m, and the operating material line is 1.5m. Calculate the temperature distribution function along the height direction of the blast furnace

[0091]

[0092] Where x is the position of the material line, is the radial position.

[0093] The blast furnace radius function R(x) is a piecewise function and can be obtained according to the internal dimensions of the blast furnace. The softening temperature of the ore is 1100°C, the dripping temperature is 1450°C, the step length Δh=0.1m, n=220, and the temperature distribution matrix in the furnace is:

[0094] S2. From the temperature matrix A ij Query A g,i ≤t d ≤A g,i+1 The area is the soft melting zone area, and then query A g,m ≤t s ≤A g,m+1 According to the example data, the starting material line position of the soft melting zone is calculated to be 14.7m, the top material line position is 9.9m, and the number of layers and width of the soft melting zone are calculated, such as Figure 2 shown.

[0095] Table 1 Soft melting zone parameters

[0096]

[0097]

[0098] S3. The average particle size of the coke entering the furnace is 50 mm, and the average particle size of the tuyere coke sampling is 30 mm. The particle size begins to degrade from the top of the soft melting zone, and the particle size distribution of the coke in the soft melting zone is obtained.

[0099] S4. The gas flow rate through the coke window of the soft melting zone is the empty tube flow rate, S 中心 From the cloth equation, we can get S 中心 =1.57m 2 The area of ​​the focal window 1-9 is 7.95m 2 The standard state of the furnace gas volume is 100m 3 / s, the average gas temperature in the soft melting zone is 1770℃, the pressure is 360kPa, and the average gas flow rate through the focal window is 21.85m / s.

[0100] S5. The resistance coefficient of each focal window is calculated using the Ergen formula. The resistance coefficient of the entire soft melting zone is the harmonic mean of the resistance coefficients of each focal window. The resistance coefficient of the entire soft melting zone is 328.92.

[0101] Table 2 Resistance coefficient of soft melting zone

[0102] Number of layers 1 2 3 4 5 6 7 8 Coke particle size / mm 50.0 48.9 47.9 47.0 46.1 45.2 44.4 43.7 Porosity 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Drag coefficient 819.8 1501.4 5205.5 5262.1 5299.6 5312.9 5300.8 4839.3

[0103] S6. Substituting the resistance coefficient and the gas flow rate into the resistance loss calculation formula, the pressure difference in the soft melting zone is obtained to be 102.1 kPa, accounting for 66.7% of the total pressure difference.

[0104] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent replacement and improvement made to the above embodiments without departing from the content of the technical solution of the present invention, based on the technical essence of the present invention, within the spirit and principles of the present invention, still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for calculating the resistance loss of the soft melting zone inside a blast furnace, characterized in that: The following steps are involved: S1. Obtain furnace parameter information, cross temperature measurement information and theoretical combustion temperature information of the blast furnace, and calculate the furnace temperature distribution matrix according to the furnace parameter information, cross temperature measurement information and theoretical combustion temperature information of the blast furnace; S2. Obtaining softening start temperature information and dripping temperature information of the ore, and calculating the width of the soft melting zone according to the softening start temperature information and dripping temperature information; S3. Obtaining the average particle size information of the coke entering the furnace and the tuyere coke sampling data information, and calculating the particle size distribution of the coke in the soft melting zone coke window according to the average particle size information of the coke entering the furnace and the tuyere coke sampling data information; S4. Calculate the gas flow rate through the soft melting zone coke window; S5. Calculate the resistance coefficient of the soft melting zone focal window; S6. Calculate the pressure difference of the soft melting zone.

2. The method for calculating the resistance loss of the soft melting zone inside the blast furnace according to claim 1, characterized in that: The "obtaining furnace type parameter information, cross temperature measurement information and blast furnace theoretical combustion temperature information, and calculating the furnace temperature distribution matrix according to the furnace type parameter information, cross temperature measurement information and blast furnace theoretical combustion temperature information" includes: Collect the temperature T at different radial positions of the cross temperature measurement within the set time r(j) , where j is the thermocouple number, j = 1, 2, ... k, where j = 1 represents the edge, and j = k represents the center; r(j) is the distance between thermocouple j and the furnace wall; T r(j) After dimensionless processing, we get T r(j) ,in is the dimensionless position of the cross-type thermocouple, representing the dimensionless distance from the furnace wall. The calculation formula is as follows: In the formula, R L is the furnace throat radius; Collect the theoretical combustion temperature before the tuyere, assume that the gas temperature from the tuyere to the cross temperature measurement position is linearly distributed, and obtain the gas temperature distribution function along the height direction of the blast furnace Where x is the material line depth; Obtain the internal dimensions of the blast furnace and obtain the blast furnace radius function R(x) at different material line positions, where x is the material line depth; Get the tuyere position material line h T , operating material line h C , divide the tuyere to the operating material line into n parts along the height direction, with a step length of Δh, Δh = (h T -h C ) / n, the radial gas temperature distribution at position i·Δh below the operating material line is: The temperature distribution matrix A in the furnace can be obtained n×k , k is the number of temperature measuring points in the radius direction of the furnace throat; 3. The method for calculating the resistance loss of the soft melting zone inside the blast furnace according to claim 1, characterized in that: The "obtaining softening start temperature information and dripping temperature information of the ore, and calculating the width of the soft melting zone according to the softening start temperature information and the dripping temperature information" includes: Get the softening start temperature t of the ore s And the dripping temperature t d , if in the temperature distribution matrix A n×k In the g-th row, A is found g,i ≤t d ≤A g,i+1 , where A g,m Dot and A g,m+1 The distance between the point and the furnace wall can be calculated by the blast furnace radius function R(x), and the linear interpolation method is used to calculate the ore on the material line h C The softening start position at +g·Δh is at a distance from the furnace wall: If A is not found g,i ≤t d ≤A g,i+1 , it means that the area is not a soft melting zone; Query A g,i ≤t d ≤A g,i+1 After that, continue to query A g,m ≤t s ≤A g,m+1 , calculate the ore in the material line h C The distance L between the dripping position at +g·Δh and the furnace wall g,s ; If A is not found g,m ≤t s ≤A g,m+1 , then L g,s =0; Get Satisfaction A g,m ≤t d ≤A g,m+1 The position is the area where the soft melting zone starts. The number of soft melting zone layers in this area is calculated using the volume method. The width of the soft melting zone is: W i =L g,d -L g,s In the formula, h R,i is the material line position of the i-th soft melting zone.

4. The method for calculating the resistance loss of the soft melting zone inside the blast furnace according to claim 1, characterized in that: The "obtaining the average particle size information of the coke entering the furnace and the sampling data information of the tuyere coke, and calculating the particle size distribution of the coke in the coke window of the soft melting zone according to the average particle size information of the coke entering the furnace and the sampling data information of the tuyere coke" includes: Get the average particle size d of the coke entering the furnace coke And tuyere sampling coke d tuyere , then the average particle size of coke in the focal window of the i-th soft melting zone is: In the formula, h R,1 It is the position of the focus window material line of the first layer of soft melting zone, that is, the top of the soft melting zone.

5. The method for calculating the resistance loss of the soft melting zone inside the blast furnace according to claim 1, characterized in that: The "calculation of the gas flow rate through the coke window of the soft melting zone" includes: Obtain the number of soft melting zone layers, coke window thickness and bosh gas volume, and the gas flow rate through the coke window of the soft melting zone is: In the formula, Q 煤气 is the amount of furnace gas, which can be calculated based on the nitrogen balance of the gas; R(h R,i ) is the inner radius of the blast furnace at the position of the i-th soft melting zone; B i is the focal window thickness of the i-th soft melting zone; S 中心 is the area of ​​the central coke column.

6. The method for calculating the resistance loss of the soft melting zone inside the blast furnace according to claim 1, characterized in that: The "calculation of the resistance coefficient of the soft melting zone focal window" includes: The resistance coefficient of each focal window is calculated using the Ergen formula, and the resistance coefficient of the entire soft melting zone is the harmonic mean of the resistance coefficients of each focal window. Where, ξ is the resistance coefficient of the soft melting zone; i is the resistance coefficient of the focal window of the i-th soft melting zone; Where, ε is the coke porosity; d i is the average particle size of coke in the i-th soft melting zone coke window; W i is the width of the i-th soft melting zone.

7. The method for calculating the resistance loss of the soft melting zone inside the blast furnace according to claim 1, characterized in that: The "calculation of the pressure difference of the soft melting zone" includes: In the formula, ρ g is the gas density, v g is the gas flow velocity, ξ is the resistance coefficient.

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