JPH06271947A - Method for controlling heating in preheating furnace - Google Patents

Abstract

PURPOSE:To provide a heating control method of preheating furnace, by which a material to be heated is heated to a temp. higher than the aimed extraction temp. but lower than the max. permissible temp. and, in the case of continuously heating the material to be heated, the material having the low max. permissible temp. is attached more attention. CONSTITUTION:By using the relational equation based on the actual temp. and the aimed extraction temp. in the rotary hearth type preheating furnace arranged with a movable hearth 1, the effect of the variation in the furnace temp. at the first zone, second zone and third zone on the extraction temp. in billets A, B is examined. In the first zone and the second zone, by taking priority of selective the suitable furnace temp. for the billet B wherein the max. permissible temp. is low more than that for billet A, the setting furnace temp. is decided. In the third zone, by deciding the setting furnace temp. to the billet A, the heating control is executed so that the each extraction temp. of the billets A, B is higher than the aimed temp. but lower than the max. permissible temp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating control method for a multi-zone preheating furnace such as a rotary hearth type preheating furnace.

[0002]

2. Description of the Related Art FIG. 3 is a schematic diagram showing the structure of a heating furnace equipped with a rotary hearth type preheating furnace and a vertical induction heating furnace. In the figure, reference numeral 1 denotes a circular movable hearth of a rotary hearth type preheating furnace, which is rotatably arranged in a horizontal plane in the furnace. A charging port and an extraction port are provided on a furnace wall (not shown), a billet A as a material to be heated is charged from the charging port, is placed on the movable hearth 1 and moves with the rotation of the movable hearth 1, It is designed to be extracted outside the movable hearth from the extraction port. The rotary hearth-type preheating furnace has heating control divided into multiple areas.
A radial boundary line from the center of the movable hearth 1 is divided into, for example, three zones of 1 zone, 2 zones and 3 zones. Billets A, A charged in the rotary hearth type preheating furnace ...
Are sequentially moved to the zones of 1 zone, 2 zone and 3 zone and heated.

The extraction port of the rotary hearth type preheating furnace is connected to a vertical induction type heating furnace 3 via a conveying path 2. The billet A heated in the rotary hearth type preheating furnace is transferred to the vertical induction heating furnace 3 through the transfer path 2 and heated in the vertical induction heating furnace 3 to a temperature required for processing. .

As a method of controlling the heating of the material to be heated by using a heating furnace divided into a plurality of regions like the above-mentioned rotary hearth type preheating furnace, the expected extraction temperature of the material to be heated is calculated and The applicant of the present invention has proposed a method of adjusting the furnace temperature of the extraction port so that the target extraction temperature matches with the target extraction temperature (Japanese Patent Laid-Open No. 54-1144).
No. 05 bulletin). This method, in order to reduce the amount of fuel used per unit billet, the billet immediately after rolling or immediately after casting,
When charging directly into a heating furnace without cooling, it is a method of controlling the temperature inside the furnace according to the change in the charging temperature of the steel slab and setting the extraction temperature of the steel slab to the desired temperature. First, measure the charging temperature of the billet that is the material to be heated charged from the charging port,
Calculate the estimated in-reactor time from when the billet is charged to when it is extracted. Next, the predicted extraction temperature is calculated by assuming the furnace temperature of each region from the charging temperature and the predicted in-furnace time. Compare this expected extraction temperature with the target extraction temperature of the billet, and if the expected extraction temperature is below the target extraction temperature, raise the temperature on the extraction port side, and if it is above the extraction temperature, increase the temperature on the inlet side. Lower. Then, this operation is performed until the predicted extraction temperature matches the target extraction temperature. This method allows the expected extraction temperature of the billet to match the target extraction temperature.

As another method of heating control using a heating furnace divided into a plurality of regions, a heating control method using a linear programming method will be shown below. This is a method of controlling the temperature of the billet, which is the material to be heated, so that the temperature is higher than the target temperature and the temperature difference in the circumferential direction of the billet is lower than the target value. It is realized by calculating the ratio of the billet to the extraction temperature of the billet, obtaining the optimum set furnace temperature value in each region of the billet, and slightly changing the furnace temperature in each region. Here, the ratio of the furnace temperature change amount of each region to the billet extraction temperature is the coefficient of influence of the furnace temperature change of each region on the billet extraction temperature, and the coefficient of influence of the furnace temperature change of each region on the billet circumferential temperature difference. That is.

A constraint condition expression for obtaining the optimum set furnace temperature value in each region is shown below.

[0007]

[Equation 1]

Solving the above linear programming problem for the billet existing in each region of the heating furnace divided by a plurality of regions,
The solution becomes the optimum set furnace temperature in each region. In particular,
Under equations (1) and (2), find the set furnace temperature x _i that minimizes the objective function of equation (3). By this method, the billet moves in each region set to the optimum temperature and is heated to the target extraction temperature or higher. Such temperature control is also applied to the rotary hearth type preheating furnace shown in FIG.

[0009]

By the way, the material to be heated has a maximum permissible temperature determined by its type, and in the preheating furnace of the previous step charged into the heating furnace, the temperature of the material to be heated does not exceed the maximum permissible temperature. It is required to heat to a temperature as high as possible above the target extraction temperature in the range, and after extraction from the preheating furnace, it is heated to a temperature necessary for processing in a vertical induction heating furnace. However, in the method of controlling the temperature in the furnace according to the change in the charging temperature of the material to be heated, the influence of the extraction temperature of the material to be heated in the temperature change in each region in the furnace is not considered, There is a problem that precise heating control over each area is not performed, and in the heating control method using the above-mentioned linear programming method, since the heating is performed above the target extraction temperature, the maximum heating material There is a problem that the allowable temperature may be exceeded.

When a plurality of types of materials to be heated are continuously preheated, different types of materials to be heated are heated in the same region within the range of switching the materials to be heated. In this case, in the above heating control method, since the average value of the optimum set furnace temperature of each heated material in each region is set as the set furnace temperature, the maximum allowable temperature placed in the billet switching range is low. There is a problem in that the material is heated far above the maximum allowable temperature. FIG. 4 is a graph showing changes in billet extraction temperature when two types of billets are preheated by a conventional temperature control method. The horizontal axis is the number of extraction billets,
The vertical axis represents the billet extraction temperature. As can be seen from the figure, when billets having different maximum allowable temperatures are mixed, the billet having a low maximum allowable temperature placed in the switching area is heated to exceed the maximum allowable temperature.

The present invention has been made in view of the above circumstances, and a heating control method for a preheating furnace in which a material to be heated is always heated to a temperature higher than a target extraction temperature and not exceeding a maximum allowable temperature in the preheating furnace, Further, even in the case of continuously heating a material to be heated having a greatly different maximum allowable temperature, it is an object to provide a heating control method of a preheating furnace that weights the optimum set furnace temperature for the material to be heated having a low maximum allowable temperature. To do.

[0012]

According to a first aspect of the present invention, there is provided a heating control method for a preheating furnace, wherein a measured temperature in the furnace and a measured temperature in the furnace are set so that an extraction temperature of a material to be heated extracted from the preheating furnace becomes higher than a target extraction temperature. Based on the set furnace temperature obtained by using the relational expression based on the target extraction temperature, in the heating control method of the preheating furnace for controlling the temperature in the furnace, the extraction temperature, from the maximum allowable temperature of the heated material In addition to the above relational expression, the set furnace temperature is obtained by using a relational expression based on the actually measured temperature in the furnace and the maximum allowable temperature so as to be lower.

A heating control method for a preheating furnace according to the second invention is
Based on the measured temperature in the furnace and the target extraction temperature so that the extraction temperature of the heated material extracted from the preheating furnace becomes higher than the target extraction temperature when there are multiple types of materials to be heated in the furnace. Based on the set furnace temperature obtained from the appropriate furnace temperature for each of a plurality of types of materials to be heated obtained from the relational expression, in the heating control method of the preheating furnace to control the temperature in the furnace, among the materials to be heated, the maximum It is characterized in that the set furnace temperature is obtained by weighting an appropriate furnace temperature for a material to be heated having a low allowable temperature.

[0014]

In the heating control method for the preheating furnace according to the first aspect of the present invention, the influence of the change in the furnace temperature on the extraction temperature of the material to be heated is obtained by using the relational expression based on the measured temperature in the furnace and the target extraction temperature. Since the set furnace temperature is set so that the extraction temperature of the material to be heated is higher than the target extraction temperature and lower than the maximum allowable temperature, heating control is always performed at the maximum allowable temperature.

In the heating control method for the preheating furnace according to the second aspect of the present invention, when a plurality of types of materials to be heated whose maximum allowable temperature is large exist in the furnace, it is suitable for each of the plurality of types of materials to be heated. Of the furnace temperatures, the set furnace temperature is calculated by emphasizing the optimum furnace temperature for the heated material with the lowest maximum allowable temperature, so the heated material with the lowest maximum allowable temperature is controlled without overheating. .

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. FIG. 1 is a schematic diagram showing the configuration of a heating furnace equipped with a rotary hearth type preheating furnace and a vertical induction heating furnace used for carrying out the present invention. In the figure, reference numeral 1 denotes a circular movable hearth of a rotary hearth type preheating furnace, which is rotatably arranged in a horizontal plane in the furnace. A furnace wall (not shown) is provided with a charging port and an extraction port, and billets A, A ..., Billets B, B ... and billets A, A. The movable hearth 1 is placed on the movable hearth 1 and moves with the rotation of the movable hearth 1, and is extracted from the extraction port to the outside of the movable hearth. Billet A has a maximum allowable temperature of 9
The maximum allowable temperature of billet b is 500 ° C.

The rotary hearth type preheating furnace is divided into a plurality of areas, and the heating control as described below is performed. For example, in the radial boundary line from the center of the movable hearth 1, one zone,
It is divided into three areas, two zones and three zones.
The billets A, A ..., Billets B, B ... and billets A, A ... charged into the rotary hearth type preheating furnace are sequentially moved to the zones of 1 zone, 2 zone and 3 zone so that they are heated. It has become.

The extraction port of the rotary hearth type preheating furnace is connected to the vertical induction type heating furnace 3 via the conveying path 2. The billet A heated and extracted in the rotary hearth type preheating furnace is transferred to the vertical induction heating furnace 3 through the transfer path 2 and heated in the vertical induction heating furnace 3 to a temperature required for processing. To be done.

The heating control method of the rotary hearth type preheating furnace will be described below. First, the appropriate furnace temperature of each region for each of billets A and B is calculated according to the following formula.

[0020]

[Equation 2]

As described above, the constraint condition expression (1) that the billet extraction temperature is equal to or higher than the target extraction temperature, the constraint condition expression (2) that the billet circumferential temperature difference is equal to or less than a predetermined value, and the billet Under the constraint equation (4) that the extraction temperature does not exceed the maximum allowable temperature and equation (4), the solution of the objective function (3), i-th zone set furnace temperature x _i, is obtained. By setting the temperature of each region to this temperature, the billets A and B are heated to the target extraction temperature or higher, and are heated to temperatures not exceeding their respective maximum allowable temperatures.

Further, the set furnace temperature T _si of the region where billet A and billet B are mixed (zones 1 and 2 in FIG. 1) is determined by the following equation (5).

[0023]

[Equation 3]

In the equation (5), G _j is set to a value larger than 1 for the billet having the lowest maximum allowable temperature in the region, for example, 3 and smaller than 1 for other billets. Set a value, for example 0.3. As a result, in a region where different types of billets are mixed, the optimum furnace temperature for the billet having a low maximum allowable temperature, that is, the optimum set furnace temperature is emphasized. In this way, the set furnace temperature in the region in which different types of billets are mixed can be obtained by emphasizing the billet solution having the lowest maximum allowable temperature.

FIG. 2 is a graph showing the transition of the billet extraction temperature when the heating control is performed as described above. The horizontal axis represents the number of extracted billets, and the vertical axis represents the extraction temperature of billets. As can be seen from the figure, the temperatures of the extracted billets A and B are within the maximum allowable temperature range from the target extraction temperature. Further, it can be seen that the billet b, which has a low maximum allowable temperature and is placed in the switching area between the billet A and the billet B, is also heated without exceeding the maximum allowable temperature.

[0026]

As described above, in the present invention, since the set furnace temperature of each region that satisfies the constraint condition equation such that heating is performed in the range from the target extraction temperature to the maximum allowable temperature is obtained, The material to be heated can be heated above the target extraction temperature without exceeding the maximum allowable temperature. Further, in a region where different types of materials to be heated are mixed, the set furnace temperature is calculated by emphasizing the optimum furnace temperature for the materials to be heated having a low maximum allowable temperature, so the materials to be heated having a low maximum allowable temperature are overheated. The present invention has excellent effects such as the above.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a heating furnace equipped with a rotary hearth type preheating furnace and a vertical induction heating furnace used for carrying out the present invention.

FIG. 2 is a graph showing a transition of a billet extraction temperature according to the implementation of the present embodiment.

FIG. 3 is a schematic diagram showing a configuration of a heating furnace including a rotary hearth type preheating furnace and a vertical induction heating furnace.

FIG. 4 is a graph showing changes in billet extraction temperature due to heating control by a conventional method.

[Explanation of symbols]

 1 Movable hearth 2 Transfer furnace 3 Vertical induction heating furnace A, B billet

Claims (2)

[Claims] 1. A set furnace obtained by using a relational expression based on an actually measured temperature in the furnace and the target extraction temperature so that the extraction temperature of the material to be heated extracted from the preheating furnace becomes higher than the target extraction temperature. Based on the temperature, in the heating control method of the preheating furnace for controlling the temperature in the furnace, the extraction temperature is lower than the maximum allowable temperature of the material to be heated, in addition to the relational expression, the actual measurement in the furnace A heating control method for a preheating furnace, characterized in that a set furnace temperature is obtained using a relational expression based on a temperature and the maximum allowable temperature. 2. The measured temperature in the furnace and the target so that the extraction temperature of the material to be heated extracted from the preheating furnace becomes higher than the target extraction temperature when a plurality of types of material to be heated are present in the furnace. In a heating control method of a preheating furnace for controlling the temperature inside the furnace, based on the set furnace temperature obtained from the respective suitable furnace temperatures for a plurality of types of materials to be heated obtained from a relational expression based on the extraction temperature, A heating control method for a preheating furnace, characterized in that a set furnace temperature is obtained by weighting an appropriate furnace temperature for a material to be heated having a low maximum allowable temperature among the materials.