Direct fire heating section strip steel temperature forecasting method

Abstract

The invention discloses a direct fire heating section strip steel temperature forecasting method. The method comprises the steps of constructing transverse division of strip steel under a single pair of furnace rollers, collecting process parameters of a field production direct fire heating section, calculating the forced convective heat transfer capacity of a direct fire burner, calculating the radiation heat transfer of flue gas to the strip steel, calculating the radiation heat transfer of a furnace wall to the strip steel, and calculating the temperature of a direct fire heating outlet. According to the method, infinitesimal calculation is carried out on the single pair of furnace rollers in the direct fire heating section, the outlet temperature of the strip steel in the direct fire heating stage is obtained, and the temperature condition of the strip steel can be effectively forecasted. By applying the method, the temperature of the strip steel can be effectively and accurately forecasted, the temperature condition of the strip steel can be forecasted in advance before production, the temperature fluctuation of the strip steel is prevented from being too large, and the performance fluctuation of the strip steel is reduced; and the repair condition caused by strip steel temperature fluctuation is reduced, and the production efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the field of direct fire heating, and in particular relates to a method for predicting the temperature of a strip steel in a direct fire heating section. Background Art

[0002] In the continuous annealing process, a preheating section and a radiant tube heating section are usually used to heat the strip to the process temperature. The high-temperature and high-speed flame in the direct-fire heating furnace of the continuous annealing unit directly impacts the surface of the strip to heat the strip. Whether the transverse temperature distribution of the strip is uniform will directly determine its stability in the furnace. Different steel grades have different surface radiation coefficients, which causes large fluctuations in the temperature measurement of the direct-fire strip, and then causes disorder in the direct-fire load regulation. The strip temperature fluctuates greatly, affecting the performance of the final product. Therefore, it is very important to develop a set of strip temperature prediction technology based on the existing equipment and combined with the equipment and process characteristics of the continuous annealing unit. This can not only improve the stability of the heating temperature of ultra-high-strength steel, but also reduce the impact of temperature fluctuations on the performance stability of ultra-high-strength steel products, thereby bringing greater economic benefits to the unit. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for predicting the temperature of the strip in the direct fire heating section, which can accurately and effectively predict the temperature of the strip, and can predict the temperature of the strip in advance before production, thereby avoiding excessive temperature fluctuations of the strip and reducing fluctuations in strip performance.

[0004] In order to achieve the above technical objectives, the present invention adopts the following technical solution: a method for predicting the temperature of a strip steel in a direct-fire heating section, characterized in that it comprises the following steps: (A) Collect direct fire heating parameters, including strip inlet temperature, furnace temperature of each section, direct fire burner temperature, flue gas temperature, burner diameter ; (B) Divide the strip steel in the direct fire heating section into 7 sections horizontally, and divide each heating area into n small strips for unitization, with the section marked as k; (C) Calculate the forced convection heat transfer of the direct-fire burner in unit k of section i ; , in: is the convective heat transfer coefficient; is the furnace temperature; is the strip temperature; The contact area between the direct fire burner and the strip steel; is the Nusselt number; is the heat transfer coefficient of flue gas; is the strip thickness; is the Reynolds number; is the Prandtl number of the furnace gas; is a constant, determined according to the fluid type, impact angle and geometric parameters, and obtained by fitting the historical data of actual temperature changes on site; (D) Calculate the radiation heat transfer of flue gas to the strip at time k in segment i ; , in: is the emissivity of the strip; is the Boltzmann constant; is the flue gas temperature; (E) Calculate the radiation heat transfer of the furnace wall to the strip at time k in the i-th segment ; , in: is the angle coefficient of the strip to the furnace wall, is the emissivity of the strip steel, is the emissivity of the furnace wall; (F) Calculate the temperature at time k+1 in segment i ; , in: is the temperature of the strip at time k+1 and time k, is the time step, is the specific heat capacity, is the density of the strip, is the strip thickness; (G) Determine whether k > n. If yes, get the outlet temperature of the i-th segment and proceed to the next step. If not, return to (C). (H) Determine whether i > 7. If so, obtain the direct fire heating outlet temperature and end. If not, use the outlet temperature of segment i as the initial temperature of segment i+1 and return to (C). (i) Output the direct fire heating outlet temperature and the calculation ends.

[0005] The beneficial effects of the present invention are: compared with the existing technology, the method of the present invention can effectively and accurately predict the temperature of the strip steel, and can predict the temperature conditions of the strip steel in advance before production, avoid excessive fluctuations in the strip steel temperature, and reduce fluctuations in strip steel performance.

[0006] The specific prediction steps include: establishing a horizontal strip partition beneath a single pair of furnace rollers, collecting process parameters from the direct-fire heating section during on-site production, calculating the forced convection heat transfer from the direct-fire burners, calculating the radiative heat transfer from the flue gas to the strip, calculating the radiative heat transfer from the furnace wall to the strip, and calculating the direct-fire heating outlet temperature to predict the strip temperature in the heating section. The application of this method in continuous annealing equipment has improved the quality of finished strip, bringing economic benefits to the enterprise and possessing great promotional value. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 This is a flow chart of the method for predicting the temperature of strip steel in the direct-fire heating section of the present invention; Figure 2 This is the microelement division diagram of the direct fire heating area of the present invention; Figure 3 This is a diagram of forced convection heat transfer of a direct-fire burner in Example 1; Figure 4 This is a diagram of radiation heat transfer of flue gas to steel strip in Example 1; Figure 5 This is a diagram of radiation heat transfer from the furnace wall to the strip steel in Example 1; Figure 6 is the temperature distribution of the steel strip in Example 1; Figure 7 This is a diagram of forced convection heat transfer of a direct-fire burner in Example 2; Figure 8 This is a diagram of the radiation heat transfer of flue gas to the steel strip in Example 2; Figure 9 This is a diagram of radiation heat transfer from the furnace wall to the strip steel in Example 2; Figure 10 is the temperature distribution of the steel strip in Example 2; DETAILED DESCRIPTION

[0008] In order to further illustrate the application process of the technology of the present invention, the production performance of a continuous annealing production line is taken as an example to illustrate in detail the application of the method in the field. Example 1

[0009] like Figure 1 As shown, the present invention provides a method for predicting the necking amount of strip steel during the continuous annealing process, and the implementation steps are as follows.

[0010] (1) In step (A), collect the direct fire heating field parameters, strip inlet temperature ℃, each furnace temperature ℃, strip width mm, burner diameter mm. Strip speed =120m / min.

[0011] (2) In step (B), the strip steel in the direct fire heating section is divided into 7 sections, each section is 3 m long, and each heating area is divided into 100 small strips for unitization, and the section is recorded as k. Each small unit is 0.03 m long.

[0012] (3) In step (C), calculate the forced convection heat transfer of the direct-fire burner of unit k in section i. ,in: =1.268*0.03*2=0.07608; =0.45W / (m*K); =33333; =0.7; .

[0013] , The calculation results are as follows Figure 3 shown.

[0014] (4) In step (D), calculate the radiation heat transfer of flue gas to the strip at time k in the i-th segment :Where: =0.3; ; , The calculation results are as follows Figure 4 shown.

[0015] (5) In step (E), calculate the radiation heat transfer of the furnace wall to the strip at time k in the i-th segment : .

[0016] , The calculation results are as follows Figure 5 shown.

[0017] (6) In step (F), calculate the temperature at time k+1 in the i-th segment : , The calculation results are as follows Figure 6 shown.

[0018] (7) Calculated direct fire heating outlet temperature ℃.

[0019] (1) In step (A), collect the direct fire heating field parameters, strip inlet temperature ℃, each furnace temperature ℃, strip width mm, burner diameter mm. Strip speed =115m / min.

[0020] (2) In step (B), the strip steel in the direct fire heating section is divided into i = 7 segments, each 3 m long, and each heating area is divided into 100 small strips for unitization, with the segment being denoted as k. Each small unit is 0.03 m long.

[0021] (3) In step (C), calculate the forced convection heat transfer of the direct-fire burner of unit k in section i. ,in: =1.2*0.03*2=0.072; =0.45W / (m*K); =33333; =0.7; .

[0022] , The calculation results are as follows Figure 7 shown.

[0023] (4) In step (D), calculate the radiation heat transfer of flue gas to the strip at time k in the i-th segment :Where: =0.3; ; , The calculation results are as follows Figure 8 shown.

[0024] (5) In step (E), calculate the radiation heat transfer of the furnace wall to the strip at time k in the i-th segment : .

[0025] , The calculation results are as follows Figure 9 shown.

[0026] (6) In step (F), calculate the temperature at time k+1 in the i-th segment : , The calculation results are as follows Figure 10 shown.

[0027] (7) Calculated direct fire heating outlet temperature ℃.

[0028] The above content is only used to illustrate the technical solution of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention made by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A method for predicting the temperature of strip steel in a direct-fire heating section, characterized in that: The steps include: (A) Collect direct fire heating parameters, including strip inlet temperature, furnace temperature of each section, direct fire burner temperature, flue gas temperature, burner diameter ; (B) Divide the strip steel in the direct fire heating section into 7 sections horizontally, and divide each heating area into n small strips for unitization, with the section marked as k; (C) Calculate the forced convection heat transfer of the direct-fire burner in unit k of section i ; 2. Among them: is the convective heat transfer coefficient; is the furnace temperature; is the strip temperature; The contact area between the direct fire burner and the strip steel; is the Nusselt number; is the heat transfer coefficient of flue gas; is the strip thickness; is the Reynolds number; is the Prandtl number of the furnace gas; is a constant; (D) Calculate the radiation heat transfer of flue gas to the strip at time k in segment i ; 3. Among them: is the emissivity of the strip; is the Boltzmann constant; is the flue gas temperature; (E) Calculate the radiation heat transfer of the furnace wall to the strip at time k in the i-th segment ; 4. Among them: is the angle coefficient of the strip to the furnace wall, is the emissivity of the strip steel, is the emissivity of the furnace wall; (F) Calculate the temperature at time k+1 in segment i ; 5. Among them: is the temperature of the strip at time k+1 and time k, is the time step, is the specific heat capacity, is the density of the strip, is the strip thickness; (G) Determine whether k > n. If yes, get the outlet temperature of the i-th segment and proceed to the next step. If not, return to (C). (H) Determine whether i > 7. If so, obtain the direct fire heating outlet temperature and end. If not, use the outlet temperature of segment i as the initial temperature of segment i+1 and return to (C). (i) Output the direct fire heating outlet temperature and the calculation ends.

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