JP2980786B2 - Combustion control method in heating furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion control method in a heating furnace for optimally setting the temperature of a continuous heating furnace for heating a slab or the like.

[0002]

2. Description of the Related Art For example, Japanese Patent Publication No. 58-22523 discloses a temperature control method for a continuous heating furnace comprising a pre-tropical zone, a heating zone and a soaking zone. For each position in the thickness direction, the temperature of the slab at the current time is calculated from the calculation using a heat transfer model, and then, one or both of the upper atmosphere temperature in the furnace and the lower atmosphere temperature in the furnace after the current time are changed. Predicting and calculating the temperature at all (or at least one specific) position of each of the above-mentioned positions at the scheduled extraction time of the slab, the upper atmosphere temperature in the furnace where the difference between the predicted temperature and the target temperature is within a certain value, The temperature in the lower atmosphere in the furnace is determined, and the temperature in the furnace is controlled using this temperature as a set temperature.

Normally, when the set temperature of a certain band (n-th band) is determined, the set temperature of the n-th band is determined on the basis of a steel slab that becomes a neck during heating. The temperature is changing.

[0004]

However, in the above-mentioned prior art, since the inside of the furnace has a large thermal inertia, a very large and smoothly fluctuating dead time occurs.
This causes the slab to be delayed or overcooked. Conventionally, temperature control in consideration of the dead time has not been performed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a combustion control method in a heating furnace capable of eliminating the effects of dead time and reducing the delay of burning and the overheating of the material to be heated.

[0006]

In order to achieve the above object, the present invention obtains a mutual covariance representing a correlation from time-series data of an actual furnace temperature and a set furnace temperature, and obtains a maximum value based on the mutual covariance. Is estimated as a dead time, and the heating furnace is controlled based on the dead time.

[0007]

According to the above-mentioned means, a mutual spectrum is obtained based on the time series data of the actual furnace temperature and the time series data of the set furnace temperature, and a mutual covariance is obtained based on the mutual spectrum.
The dead time is estimated from the detection of the maximum value of the mutual covariance. Therefore, as a result of correcting the set furnace temperature history curve from the obtained dead time, it becomes possible to increase the degree of coincidence between the set furnace temperature and the actual furnace temperature, and reduce the occurrence of slab burning delay or overburning. .

[0008]

1 is a flow chart illustrating the method of the present invention. FIG. 2 is a block diagram showing a configuration of a control device for achieving the method of the present invention.

First, FIG. 2 will be described before the description of FIG.
The heating furnace 1 shown here comprises a pre-tropical zone 2, a heating zone 3 and a solitary zone 4, the pre-tropical zone 2 is an uncontrolled zone, and the heating zone 3 and a solitary zone 4 are a control zone. A thermocouple 5 for measuring the furnace temperature is attached to each zone. In addition, heating zone 3
A heating burner 7 controlled by an instrumentation controller 6 (the furnace temperature is adjusted by controlling the amount of combustion from the burner) is attached to each of the solitary tropics 4 and inserted into the belt. There is also provided a charging thermometer 8 for measuring the temperature. Each of the thermocouple 5, the instrument controller 6, and the charging thermometer 8 is connected to the arithmetic unit 9.

FIG. 3 is a characteristic diagram showing time-series data of the set furnace temperature and the actual furnace temperature. In the figure, the vertical axis indicates furnace temperature (° C.), and the horizontal axis indicates elapsed time (minutes). Further, the set furnace temperature x (t) is indicated by a solid line, and the actual furnace temperature y (t) is indicated by a dotted line. Here, the deviation in the abscissa direction between the set furnace temperature characteristic and the actual furnace temperature characteristic becomes a dead time (here, three minutes in the first half and five minutes in the second half). As is clear from FIG. 3, the inside of the heating furnace 1 has a large dead time after setting the furnace temperature, which is considered to be one of the factors that cause the slab to be delayed or overburned.

Therefore, in the present invention, slab burning delay and overburning are eliminated by two techniques.
That is, one is to obtain a set furnace temperature history characteristic that minimizes a difference between the set furnace temperature and the actual furnace temperature in order to eliminate slab burning delay and overheating caused by a difference from the actual furnace temperature. The other is to reflect the dead time in the setting history characteristic, so that the influence of the dead time can be completely eliminated. Hereinafter, the respective processes will be described. First, a method of obtaining the set furnace temperature history characteristic which is a premise of the present invention will be described with reference to FIG.

FIG. 4 is a flowchart showing a combustion control method. In the figure, "S" means a step.

First, based on the measurement results of the thermocouples 5 and the charging thermometer 8, the calculating device 9 calculates the billet temperature. Based on this result, the [n-1] band (= the preceding band, for example, if the heating zone 3 is the n band (= the band to be controlled), the pre-tropical zone 2 is the [n-1] band) A furnace temperature history curve is predicted and calculated (S401). This prediction calculation is [n
When the [-1] zone is a non-control zone, that is, in the pre-tropical zone 2, a pre-tropical furnace temperature history curve is obtained, and the [n-1] zone is a control zone (heating zone 3).
Alternatively, in the case of the solitary tropics 4), the furnace temperature history curve already obtained is used for the prediction calculation.

Next, [n−
1] Based on the zone furnace temperature history curve, the outlet temperature of the [n-1] zone of all the slabs existing in the [n-1] zone is predicted and calculated (S402). Thereafter, the required minimum furnace temperature that satisfies the target temperature on the outlet side of each n-band of all the slabs existing in the n-band is calculated by the arithmetic unit 9 (S403). Furthermore, [n-
1] The minimum required furnace temperature that satisfies the target temperature on the outlet side of each n-band of all the slabs existing in the zone is calculated by the arithmetic unit 9 (S404). Next, a smooth n-zone furnace temperature history curve is created in consideration of the furnace time constant so as not to fall below the required minimum furnace temperature of all the slabs existing in the [n-1] band and the n band (S405).

The n-zone furnace temperature hysteresis curve obtained in this way is shown in FIG. 5, and a gentle curve is drawn. As is clear from the figure, since the change width can be reduced, the actual furnace temperature follows even in a heating furnace having a large thermal inertia, and optimal control can be performed. As a result, delay in burning can be reduced. However, even if the furnace temperature control is performed using the ideal furnace temperature hysteresis curve obtained in this way, it is possible to eliminate the slab burning delay and overburning because the dead time described in FIG. 3 exists. Can not.

Therefore, in the present invention, as shown in FIG. 1, time-series data of the actual temperature is fetched (S101), the data is differentiated (S102), and a Fourier transform is performed to convert from the time axis to the frequency axis. (S103). Similarly,
The time series data of the set temperature is fetched (S104), the data is differentiated (S105), and a Fourier transform is performed (S106). The result of each Fourier transform is multiplied to obtain a cross spectrum indicating a correlation in the frequency domain (S107). A process for removing high-frequency components is performed on the obtained mutual spectrum (S10).
8). This is to remove noise mixed under the influence of the temperature of the slab or the belt. Next, a process of performing an inverse Fourier transform and returning to the time axis again is performed (S109). Thereafter, as shown in FIG. 5, the mutual covariance Rxy (u) is obtained (S110), and u when the maximum value is obtained within 6 minutes of Rxy (u) is set as a dead time (S111, S112). The calculation time can be shortened by finding the mutual covariance from the mutual spectrum without solving it as defined.

Next, the furnace temperature after the dead time is determined from the above-mentioned furnace temperature history curve so that the actual furnace temperature matches the furnace temperature history curve, and the furnace temperature after the dead time is set to the set furnace temperature. . Using the set furnace temperature history curve for each furnace, each zone 1 minute,
The set furnace temperature of each zone is obtained by line interpolation. For example, 2
The set furnace temperature after 12 minutes is 1225 ° C, and the set furnace temperature after 3 minutes is 12
Assuming that the temperature is 50 ° C. and the dead time is 2 minutes and 18 seconds, the set furnace temperature is as shown in the following equation.

Set furnace temperature = 1225 + ｛(1250-12)
25) {60} × 18 = 1232.5 (° C.) As a result, the influence of the dead time can be eliminated, the set furnace temperature can be matched with the actual furnace temperature, and slab burning delay and excessive burning are eliminated. Becomes possible.

[0019]

As described above, according to the present invention, the mutual covariance representing the correlation is obtained from the time series data of the actual furnace temperature and the set furnace temperature, and the time when the maximum value is obtained is determined based on this. Since the heating furnace is controlled based on the estimated dead time, the set furnace temperature history curve can be modified from the obtained dead time, and the degree of coincidence between the set furnace temperature and the actual furnace temperature is determined. It is possible to reduce the occurrence of slab burning delay or overburning.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a combustion control method according to the present invention.

FIG. 2 is a block diagram illustrating a configuration of a control device that achieves the present invention.

FIG. 3 is a characteristic diagram showing a relationship between a set furnace temperature and an actual furnace temperature and a dead time.

FIG. 4 is a flowchart showing a combustion control method.

FIG. 5 is a characteristic diagram showing an n-band furnace temperature history curve obtained by the process of FIG. 4;

FIG. 6 is a characteristic diagram showing a furnace temperature history curve in consideration of a dead time.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Pretropical zone 3 Heating zone 4 Uniform tropical zone 5 Thermocouple 6 Instrumentation controller 7 Heating burner 8 Charge thermometer 9 Arithmetic unit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C21D 1/52 C21D 9/00 101 C21D 11/00 101

Claims (1)

(57) [Claims] 1. A mutual covariance representing a correlation is obtained from time-series data of an actual furnace temperature and a set furnace temperature, and a time when a maximum value is obtained is estimated as a dead time based on the calculated covariance. A method for controlling combustion in a heating furnace, comprising controlling the heating furnace by heating.