KR20010010082A - Combustion control method for reheating furnace - Google Patents

Abstract

PURPOSE: A method for establishing an atmosphere temperature in a heating furnace is provided to obtain the extraction target temperature and cracking degree by improving methods for establishing the atmosphere temperature and calculating a temperature of a material and predicting the precise material extraction temperature and cracking degree. CONSTITUTION: A heating furnace is made up of preheating, plural heating and cracking zones. Herein, temperatures of all materials of each zone at the present point are calculated. A predictive value of an extraction temperature is calculated by using a mathematical equation combining a theoretical equation with a regression equation. The predictive value compensates a deviation generated upon comparing the extraction target temperature and cracking degree. Then, the atmosphere temperature of each zone is established.

Description

Combustion control method for reheating furnace

The present invention relates to a method for setting the atmosphere temperature in the furnace, in particular in the hot rolling process to set the atmosphere temperature in the furnace in order to control the temperature of the material to control the material temperature in the furnace atmosphere temperature setting method It is about.

In general, in the hot rolling process, in order to facilitate the rolling of the material, there is a heating furnace which heats the material to an appropriate temperature before rolling in consideration of the capacity of the rolling mill and the quality of the product. It is divided into preheating zone, heating zone, and cracking zone to heat the material by setting the atmosphere temperature of each zone.

Material temperature control calculates the condition of the furnace, that is, the furnace temperature, the location of the furnace, and the expected extraction time of the material, and sets the atmosphere temperature in the furnace in consideration of the calculated value. In the form of sending.

Conventional methods for controlling the atmosphere temperature in the furnace include a) the extraction target temperature and the target crack degree of the material in each of the preheating zone, the heating zone, and the cracking zone, the range that can be realized in the operation of the ambient temperature and the temperature difference between the zones; In consideration of minimizing energy, the ambient temperature of each unit is set, and the extraction temperature and the cracking degree of the material are obtained by solving the thermal conductivity equation by the difference method and by the equation made through the regression analysis. If you use the differential method, it is difficult to control fast cycles and control more material because it requires a lot of time to set up the calculation because there is a large amount of calculation for setting the atmosphere temperature. There is a problem that is incorrectly predicted. And b) a material temperature control method that follows the form of the atmosphere temperature in the furnace until the material is charged into the furnace and extracted, which is characterized by the characteristics of the furnace and the material and during the time the material stays in the furnace. There is a drawback to the type of atmosphere in the furnace being considered.

The present invention has been invented to solve various problems caused by the conventional method for setting the atmosphere temperature in the furnace in view of the above situation, by improving the method of setting the atmosphere temperature in the furnace and the method of calculating the material temperature in the calculation time The purpose of the present invention is to provide a method for setting the atmosphere temperature in a furnace that can obtain the extraction target temperature and the crack degree of the material by predicting the material extraction temperature and the crack degree more accurately.

1 is a schematic view showing a conventional heating furnace,

2 is a heating furnace according to the heating time when controlling the material temperature according to the conventional method

Graph showing the history of atmosphere temperature, material temperature and crack

3 is a heating furnace according to the heating time when controlling the temperature of the material in the method of the present invention

It is a graph showing the history of atmosphere temperature, material temperature, and crack degree.

In order to achieve the above object, the method for setting the atmosphere temperature in the furnace for controlling the material temperature according to the present invention is to control the material temperature in the hot rolling process. In this method, the difference equation is solved to calculate the temperature of all materials at each stage, and the prediction value of the extraction temperature is obtained by using the combination of the theoretical and regression equations. It is characterized by setting the atmospheric temperature for each target by compensating for the deviation caused when the deviation occurs compared to the target temperature and crack degree.

Hereinafter, a method of setting an atmosphere temperature in a furnace for controlling the temperature of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic view showing a conventional heating furnace, in order to set the atmosphere temperature in the heating furnace according to the method of the present invention, as shown in FIG. As a result, the material prediction temperature (Tm) is obtained. At this time, the current material prediction temperature (Tm) is obtained by calculating Fourier's heat transfer equation represented by Equation 1 below by implicit method (IMPLICIT) to calculate the temperature of the nodes (nodes) The average temperature of these grid points is obtained as the predicted material temperature (Tm).

(Where T is the material temperature, t is the time, y is the coordinate representing the length in the material thickness direction, and α represents the thermal diffusion coefficient, respectively.)

Where T _i is the temperature of lattice point _i of the material, T _{i + 1} is the temperature of lattice point _{i + 1} of the material, Ti-1 is the temperature of lattice point i-1 of the material, Δt is the time Increment, α _i is the thermal diffusion coefficient of lattice point i, Δy is the lattice point spacing, S _i is the generation term for lattice point i.) In general, in consideration of the computer performance and calculation time Constraints on time increment (Δt) are followed because the urban method (EXPLICIT) is used rather than the implicit method for differentiation. However, in the present invention, using the implicit method, the time increment (Δt) is stable without limitation. (stable) Temperature prediction is possible. Equation 2 is obtained by solving a Tri-Diagonal Matrix Algorithm (TDMA) method.

With the material average temperature obtained in Equation 2, the material predicts the passage temperature and the extraction temperature for each unit. In this case, a differential or simple regression method is usually used. However, when the differential method is used, the second differential equation must be solved. Therefore, the calculation time is greatly increased. Very far away. In the present invention, in order to increase the degree of extraction temperature prediction, the optimum regression form based on the theoretical formula was derived and the form is as shown in Equation 3 below.

(Where T _out is the predicted extraction temperature of the material, T _g is the ambient atmosphere temperature, T _m is the current material average temperature, t is the residual residing time, D is the material thickness, and β is the heat transfer rate.)

The heat transfer rate β is calculated by the following equation (4).

C ₁ , C ₂ -------, C ₈ shown in Equations 3 and 4 denote coefficient values for the regression equation. When using a regression formula combining the theoretical and regression equations as described above, the reliability is 99% when compared with the result of using the differential equation. The accuracy of the extraction temperature prediction is the most important in the process of setting the appropriate atmospheric temperature for each.

When the extraction temperature prediction value of the material obtained by using Equation 3 is different from the extraction target temperature of the material, or the equation for calculating the appropriate atmospheric temperature for matching the extraction allowable cracking degree, Equation 5 and 6 Obtain

(Where ΔT _g1 , ΔT _g2 , -------------, ΔT _gn is the temperature change of each unit, T _out ^* is the target temperature of extraction of the material, T _g1 , T _g2, ---- T _gn is the ambient temperature, T _out is the extraction prediction temperature of the material, T _sout ^* is the extraction target crack of the material, and T _sout is the extraction prediction crack of the material. The derivative term can be obtained by simply differentiating the above Equation 3.) In the end, it means that the amount of change in the temperature of each unit is calculated so that the extraction prediction temperature of the material becomes the extraction target temperature. Since there are n unknown numbers for Equations 5 and 6, Equations 5 and 6 can be solved simply by using an operating range that can be realized in the operation of the ambient temperature and the temperature difference between the units. As described above, the atmosphere temperature values of the final titration zones are set according to the following Equation 7 with the values obtained by obtaining the atmosphere temperatures of the respective units to match the extraction target temperature and the extraction crack degree for each material.

Where T ^* _g1 , T ^* _g2 , ------------------ T ^* _gn is the appropriate ambient temperature, ω _ij is the weight, a ₁ , a ₂ ,- ---------------, _n is a number of classified material, T ⁱ _Σ represents a classified proper atmosphere temperature calculated for the material present in the i-th stand.)

In Equation 7, the weight is preferably the largest weight for the atmosphere temperature obtained for the materials present in the band.

As described above, by predicting the material temperature in an implicit manner with respect to the heating furnace in which n units exist, stable temperature prediction is possible without restriction in time increment Δt. In addition, the calculation time is shortened compared to using the differential equation by estimating the extraction temperature for the material in the furnace by deriving the formula of the combination of theory and regression as a method for predicting the extraction temperature. Compared to using the form, the extraction temperature prediction accuracy is improved.

EXAMPLE

It is said that stainless steel (thickness 200mm) is loaded into a heating furnace consisting of preheating table (11,500mm), 1 heating table (10,500mm), 2 heating table (10,500mm) and cracking table (9,000mm), and is heated and extracted while being transported at a constant speed When the extraction target temperature is 1,180 ° C and the target crack degree is 1 ° C, the material temperature is controlled by using the present invention and the conventional method (when setting the ambient temperature by regression). Then, the extraction temperature of the material and the degree of cracking of the material were examined and the results are shown in FIG. 2 in the case of the conventional method and in FIG. 3 in the case of the present invention, respectively.

At this time, the average value of the ambient temperature setpoint in the furnace was calculated by the conventional method and the present invention is shown in Table 1.

division Preheat 1 heating zone 2 heating stand Crack Extraction temperature Crack road Conventional method 1000 ℃ 1192 ℃ 1258 ℃ 1201 ℃ 1192.4 ℃ 5 ℃ The present invention 990 ℃ 1186 ℃ 1250 ℃ 1191 ℃ 1182.4 ℃ 1 ℃

As can be clearly seen from Table 1, when the atmosphere temperature is set by the conventional method (material temperature control), the ambient temperature of each unit is controlled so that the extraction temperature deviates by about 10 ° C. or more higher than the target temperature. The set point is set higher than the optimum set point. At the time of setting the atmosphere temperature according to the present invention, it was controlled to extract about 2 ° C. higher than the extraction target temperature. At this time, the average value of the ambient temperature set value for each unit was also controlled at about 10 ° C. lower than the conventional method. Compared to the method, energy consumption was reduced.

That is, compared to the conventional method in the combustion control according to the present invention it can be controlled to extract close to the extraction target temperature, extraction target cracking degree when extracting the material, and it was possible to reduce the energy consumption through the optimal control.

As described above, according to the method for setting the atmosphere temperature in the furnace for controlling the material temperature of the present invention, regardless of the calculation time for calculating the material temperature, the extraction temperature and the crack degree of the material can be determined by more accurate material extraction temperature and crack degree prediction. There is an advantage that can be obtained.

Claims (4)

In order to control the material temperature in the hot rolling process, a method of setting the atmosphere temperature in the furnace consisting of n preheating zones, multiple heating zones, and cracking zones is solved. The differential equation is solved, and the temperature of all materials at each stage is calculated. After calculating the extraction temperature by using the combination of the formula and the regression equation, the prediction value compensates the deviation occurred when the deviation occurs compared to the extraction target temperature and cracking degree for the material and sets the atmospheric temperature for each. Method for setting the ambient temperature in the furnace for controlling the temperature of the material. The material temperature control according to claim 1, wherein the differential equation is represented by Equation 2 below, and the following Equation 2 is solved by a tri-diagonal matrix algorithm (TDMA) to calculate all material temperatures at each point in time. How to set the ambient temperature in the furnace for. [Equation 2] Where T _i is the temperature of lattice point _i of the material, T _{i + 1} is the temperature of lattice point _{i + 1} of the material, Ti-1 is the temperature of lattice point i-1 of the material, Δt is the time Increment, α _i is the thermal diffusion coefficient of grid point i, Δy is the grid point spacing, S _i is the generation term for grid point i.) The method of claim 1, wherein the combination of the formula and the regression formula is the following equations (3) and (4). [Equation 3] [Equation 4] Where T _out is the predicted extraction temperature of the material, T _g is the ambient atmosphere temperature, T _m is the current material average temperature, t is the residual ash time, D is the material thickness, β is the heat transfer rate, and C ₁ , C ₂ --- ----, C ₈ represents the coefficient value for the regression equation.) The method according to claim 1, wherein each atmospheric temperature for compensating for the deviation is calculated by the following equations (5) and (6). [Equation 5] [Equation 6] (Where ΔT _g1 , ΔT _g2 , -------------, ΔT _gn is the temperature change of each unit, T _out ^* is the target temperature of extraction of the material, T _g1 , T _g2, ---- T _gn is the ambient atmosphere temperature, T _out is the extraction prediction temperature of the material, T _sout ^* is the extraction target crack of the material, and T _sout is the extraction prediction crack of the material. )