JPH05255762A - Method for controlling furnace temperature of continuous heating furnace - Google Patents

Abstract

PURPOSE:To restrain skid mark quantity within a prescribed value by controlling a target ejecting temp. and a target soaking degree at the time of ejecting a material in a furnace temp. control of a continuous heating furnace. CONSTITUTION:(i) The present temp. of a material to be heated is found. (S1) (ii) A predicted ejecting time and the remaining stay time in each combustion zone in the continuous heating furnace are found. (S2) (iii) Based on these, a predicted ejecting temp., a predicted temp. difference between inner and outer parts, a predicted temp. difference between front and back surfaces and a predicted skid mark quantity at the time of ejecting are found. (S3) (iv) A relation among the furnace temp. at each combustion zone, the predicted ejecting temp., the predicted temp. difference between the inner and outer parts, the predicted temp. difference between front and back surfaces and the predicted skid mark quantity at the time of ejecting is found from a linear equation and also, an evaluation function for minimizing the heat loss of the furnace body due to exhaust gas is set, and by a linear programming, the set furnace temp. of each combustion zone is found. (S4) (v) The target ejecting temp., the target ejecting temp. difference between the inner and outer parts, the target temp. difference between the front and back surfaces and the target skid mark quantity at the time of ejection designated at each material to be heated are achieved. (S5)

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a furnace temperature control method for a continuous heating furnace. More specifically, the present invention relates to a furnace temperature control method for a continuous heating furnace capable of controlling a target extraction temperature and a target soaking degree during extraction.

[0002]

2. Description of the Related Art Usually, a continuous heating furnace is composed of a pretropical zone, a heating zone and a soaking zone. The main purpose of this type of continuous heating furnace is to heat an object to be heated such as a slab to a predetermined temperature sufficient for rolling, and at the same time, so that the rolling ability can be sufficiently exhibited, that is, the rolling line. That is, the object to be heated is supplied to the rolling mill for operation without stopping.

In recent years, in order to reduce fuel consumption as much as possible in response to soaring fuel consumption, combustion control using a computer is performed in a large-scale continuous heating furnace. The target extraction temperature of each object to be heated in combustion control of a continuous heating furnace using a computer is determined in consideration of the pass schedule and heat transfer characteristics in rough rolling and finish rolling. The target soaking degree at the time of extraction is determined by the plate thickness tolerance of the product in consideration of the strength of the object to be heated, the size of the object to be heated, the ability of the rolling mill, and the like.

For example, in Japanese Unexamined Patent Publication No. 62-174325, the current average temperature of a material to be heated and a target average temperature after a lapse of a fixed time are calculated, and the target average temperature is calculated based on the average temperature and the target average temperature. Calculate the heat input required to bake, and calculate the upper furnace temperature standard and lower furnace temperature standard of the heating furnace based on the target upper and lower surface temperature difference of the material to be heated and the calculated heat input amount. A furnace temperature control method has been proposed in which the upper furnace temperature and the lower furnace temperature of the heating furnace are controlled so that the deviation between and becomes zero.

In Japanese Patent Laid-Open No. 63-149319, the average temperature of each material to be heated is secured at each control zone outlet target temperature, and the surface temperature of the upper and lower parts of each material to be heated is To keep below the upper and lower surface temperature limits of
Techniques for controlling the upper furnace temperature and the lower furnace temperature of a continuous heating furnace have been proposed.

Further, Japanese Patent Application Laid-Open No. 3-138319 discloses that the present heating material present in the heating furnace depends on the remaining furnace time of various materials to be continuously charged into the heating furnace and the present furnace temperature. Calculate the average temperature and the expected average extraction temperature during heating furnace extraction,
Based on these values, calculate the furnace temperature setting value for each heated material that achieves the target extraction temperature and minimizes heat loss when extracting the heated material for each heated material using linear programming. However, in the furnace temperature control method of the continuous heating furnace, these furnace temperature set values are smoothed and set in the heating furnace so that the sum of the deviations between the predicted extraction temperature of each heated material and the target extraction temperature becomes zero. Assuming that the smoothed furnace temperature set value is the current furnace temperature, the predicted extraction temperature of each heated material is calculated, and the predicted extraction temperature and the target extraction temperature are compared, and the predicted extraction temperature is the allowable lower limit of the target extraction temperature. There has been proposed a furnace temperature control method for a continuous heating furnace that corrects the furnace temperature set value so as to reach at least an allowable lower limit value when a material to be heated below the value is detected.

[0007]

The target soaking degree in the technology proposed by Japanese Patent Laid-Open No. 62-174325 or the technology proposed by Japanese Patent Laid-Open No. 63-149319 is expressed as a difference between front and back temperatures or a difference between inside and outside temperatures. Defined, the furnace temperature control predicts the temperature of the heated material at the time of extraction from the remaining furnace time of each heated material so that these two indicators are satisfied for all heated materials in the furnace. The furnace temperature set value of the zone is determined. Therefore, in these technologies, since the temperature deviation in the longitudinal direction of the steel slab cannot be reduced, skid marks are generated, which is a main factor causing variations in strip thickness and strip width during finish rolling, which causes operational problems. Become.

In the technique proposed in Japanese Patent Laid-Open No. 3-138319, the inside / outside temperature difference or the skid mark amount is used as the soaking degree, but it is not considered to control these at the same time. Since it is not possible to control the rolling, it is easy to cause operational troubles due to the defective shape of the material to be rolled during the finishing of the rolled material.

The present invention has been made in order to solve such a problem, and the temperature deviations in the plate thickness direction and the longitudinal direction of the material to be heated are both the soaking degree (evaluation index), and It is an object of the present invention to provide a furnace temperature control method for a continuous heating furnace capable of suppressing both temperature deviations in the longitudinal direction.

[0010]

The gist of the present invention is to provide a furnace temperature control method for a continuous heating furnace in which a material to be heated is continuously charged into a heating furnace and heated to a target temperature. Therefore, (i) the current temperature of the material to be heated is obtained, (ii) the estimated extraction time and the remaining zone time in each combustion zone of the continuous heating furnace are obtained, and (iii) the estimated extraction based on these Calculate the temperature, the predicted inside and outside temperature difference, the predicted front and back temperature difference, and the predicted skid mark during extraction, and (iv) the furnace temperature of each combustion zone, and the predicted extraction temperature, the predicted inside and outside temperature difference, the predicted front and back temperature difference, and the predicted skid during extraction. The relationship with the mark amount is obtained in a linear form, and an evaluation function that minimizes the furnace heat loss due to exhaust gas is set,
Obtain the set furnace temperature of each combustion zone by linear programming, and (v)
A furnace temperature control method for a continuous heating furnace, wherein a target extraction temperature, a target inside / outside temperature difference, a target front / back temperature difference, and a target skid mark amount at the time of extraction are achieved for each material to be heated.

[0011]

The present invention will be described in detail below with reference to the accompanying drawings together with its function and effect. FIG. 1 is a control flowchart of a furnace temperature control method for a continuous heating furnace according to the present invention. Hereinafter, the present invention will be described by dividing it into steps S1 to S5.

[Step S1] The present temperature of the material to be heated is determined. For the current temperature of the material to be heated, the charging temperature at the time of charging the heating furnace is used as the initial value. For example, a two-dimensional unsteady heat conduction equation is calculated online by the difference method at regular intervals of about 3 minutes, 2 minutes or 1.5 minutes. Calculated by For example, the two-dimensional unsteady heat conduction equation

[0013]

[Equation 1]

However, ρ: density λ: thermal conductivity C: specific heat θ: temperature x: space coordinate in the longitudinal direction y: space coordinate in the thickness direction t: difference calculation based on time

[0015]

[Equation 2]

It can be illustrated by way of example (see FIG. 2).
The boundary condition is obtained by dividing the longitudinal direction of the material to be heated into (m-1) and the thickness direction into (n-1), and applying a heat flux as follows. Here, heat flux qu (i) (upper surface), ql (i) (lower surface), and qs (j) (side surface) are given as follows, respectively.

[0017]

[Equation 3]

[Step S2] The expected extraction time of the material to be heated and the remaining zone time in each combustion zone are obtained. That is, the expected extraction time of the material to be heated is obtained from the extraction pitch given for each material to be heated in the heating furnace, and when the material to be heated is operated at the expected extraction pitch, each combustion zone of the heating furnace is The remaining zone time in each combustion zone is calculated from the estimated time of passage.

[Step S3] An expected extraction temperature at the time of extraction, an expected inside / outside temperature difference, an expected front / back temperature difference, and an expected skid mark amount at the time of extraction are obtained. That is, assuming that the current temperature of the material to be heated is the initial value, the furnace temperature in each combustion zone is assumed to remain at the current temperature, and the remaining zone time in each combustion zone is given to determine the time of extraction of the material to be heated. Predict the internal temperature distribution. From this, the predicted extraction temperature, the predicted inside / outside temperature difference, the predicted front / back temperature difference, and the predicted skid mark amount during extraction are obtained.

Here, the predicted internal / external temperature difference means the difference between the upper surface of the material to be heated and the temperature in the central portion in the thickness direction, and the internal temperature distribution means the temperature distribution in the temperature calculation target region. The temperature distribution is as shown in 3. In addition, the predicted inside and outside temperature difference, the predicted front and back temperature difference, and the predicted skid mark amount during extraction are

[0021]

[Equation 4]

[0022]

[Equation 5]

[0023]

[Equation 6]

It can be expressed as [S4 step] The relationship between the furnace temperature of each combustion zone, the expected extraction temperature, the predicted internal and external temperature difference, the predicted front and back temperature difference, and the predicted skid mark amount during extraction is determined in a linear form, and the furnace heat loss due to exhaust gas is minimized. Set an evaluation function for and set the furnace temperature for each combustion zone by linear programming. For each line format, for example

[0025]

[Equation 7]

[0026]

[Equation 8]

[0027]

[Equation 9]

Can be exemplified. That is, in this process,
The influence coefficient of each combustion zone is calculated, and the set furnace temperature of the combustion zone is calculated by linear programming so that the heat loss due to exhaust gas is minimized. Specifically, the furnace temperature of each combustion zone is changed from the present furnace temperature by a small amount, and the various amounts obtained in the step S3 are recalculated. From this, the coefficient of influence of the furnace temperature in each combustion zone is calculated as (variation of various amounts) / (reactor temperature variation). The inequality that shows the constraint expression of each variable is

[0029]

[Equation 10]

It is FIG. 4 is a graph showing an example of the relationship between the furnace temperature and time. The influence coefficient at this time is

[0031]

[Equation 11]

Is given by Further, as an evaluation function, a linear expression of the furnace temperature change amount of each combustion zone, for example,

[0033]

[Equation 12]

Variable

[0035]

[Equation 13]

Then, the optimum set furnace temperature for the material to be heated is determined.

[0037]

[Equation 14]

Is calculated as In order to minimize the heat loss due to exhaust gas, the weight on the bottom side of the furnace is maximized. At this time, the furnace temperature change amount is obtained as a solution of the following linear programming problem.

AX ≦ b J = CX → Minimization, where X: vector representing the amount of change in furnace temperature A: matrix of each zone temperature influence coefficient b: vector determined by constraints of various amounts C: amount of change in furnace temperature Is a vector representing the effect given by on the evaluation function J.

If only the amount of skid marks is considered, it is sufficient to heat the material to be heated from the front stage of the heating furnace.
It is disadvantageous in terms of fuel consumption. This is because if the furnace temperature in the first stage of the heating furnace is set high, the exhaust gas temperature rises, the heat loss in the furnace body increases, and the fuel consumption rate deteriorates. Therefore, in the present invention, the evaluation function is used to obtain the furnace temperature set value that can reduce the heat loss of the furnace body due to the exhaust gas.

[S5] The optimum furnace temperature found for each steel piece in the furnace is weighted for each steel piece and smoothed to obtain the final set furnace temperature. As the smoothing process, for example, a weighted average may be taken.

As described above, according to the present invention, in the process of formulation of the linear programming problem, the constraints relating to various values such as the average temperature at the time of extracting the heating furnace, the inside / outside temperature difference, the front / back temperature difference, and the skid mark amount at the time of extraction are expressed by the vector b. Since it is included in the above, the set furnace temperature obtained for each material to be heated satisfies the given constraint conditions regarding these various quantities, and is optimal from the viewpoint of fuel consumption rate. In comparison with a known furnace temperature control method that considers only two indices, the target temperature and the target soaking degree, it is possible to suppress the plate thickness and the temperature deviation in the longitudinal direction to a given value or less. It has features such as improvement of fuel consumption rate. Further, the present invention will be described with reference to other examples, but this is an example of the present invention and the present invention is not limited thereto.

[0043]

[Embodiment] In the above description of the present invention, the temperature calculation model of the material to be heated in the furnace is two-dimensional, but in this embodiment, the temperature calculation model is three-dimensional and the temperature control during extraction is performed. The index was expanded three-dimensionally. FIG. 5 and FIG. 7 are both schematic explanatory views showing the generation state of the skid mark amount by the conventional control method. In this conventional control method, the slab average temperature ≧ the target extraction temperature slab inside / outside temperature difference ≦ the target inside / outside temperature Only the difference is satisfied. Therefore, this method cannot control the front-back temperature difference and the skid mark amount during extraction.

FIG. 6 and FIG. 8 are both schematic explanatory views showing the generation state of the skid mark amount by the furnace temperature control system according to the present invention. According to the present invention, slab average temperature ≧ target extraction temperature slab inside / outside Temperature difference ≦ Target inside / outside temperature difference Slab front / back temperature difference ≦ Target front / back temperature difference Slab Skid mark amount ≦ Target skid mark amount are all satisfied. Note that, in the present invention, it is also conceivable to incorporate the temperature difference in the width direction of the material to be heated during extraction, for example.

[0045]

As described in detail above, according to the present invention,
While the material to be heated is in the furnace, there is an effect that the average temperature can be secured above the target temperature and the inside and outside temperature difference, the front and back temperature difference, and the skid mark amount can be maintained below a predetermined value. The significance of the present invention having such effects is extremely remarkable.

[Brief description of drawings]

FIG. 1 is a control flowchart of a furnace temperature control method for a continuous heating furnace according to the present invention.

FIG. 2 is an explanatory diagram showing a coordinate system in a slab.

FIG. 3 is an explanatory diagram showing an example of an internal temperature distribution.

FIG. 4 is a graph showing an example of the relationship between furnace temperature and time.

FIG. 5 is a schematic explanatory view showing a situation of generation of skid marks by a conventional control method.

FIG. 6 is a schematic explanatory view showing a situation of generation of skid marks by the furnace temperature control system according to the present invention.

FIG. 7 is a schematic explanatory view showing a situation of generation of skid marks by a conventional control method.

FIG. 8 is a schematic explanatory view showing a situation of generation of skid marks by the furnace temperature control method according to the present invention.

Claims (1)

[Claims] 1. A furnace temperature control method for a continuous heating furnace in which a material to be heated is continuously charged into a heating furnace to heat it to a target temperature, comprising: (i) determining a current temperature of the material to be heated; ii) Obtain the estimated extraction time and the remaining zone time in each combustion zone of the continuous heating furnace, and (iii) based on these, the estimated extraction temperature, the estimated internal and external temperature difference, the estimated front and back temperature difference, and the estimated extraction skid. The mark amount is calculated, and (iv) the relationship between the furnace temperature in each combustion zone and the predicted extraction temperature, the predicted internal / external temperature difference, the predicted front / back temperature difference, and the predicted skid mark amount during extraction is calculated in a linear format, and the furnace body caused by the exhaust gas Set the evaluation function that minimizes heat loss,
Obtain the set furnace temperature of each combustion zone by linear programming, and (v)
A furnace temperature control method for a continuous heating furnace, wherein a target extraction temperature, a target inside / outside temperature difference, a target front / back temperature difference, and a target skid mark amount during extraction are achieved for each material to be heated.