JPH0328488B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a temperature control device for a continuous heating furnace, particularly a continuous heating furnace for a hot strip mill.

[Technical background of the invention and its problems]

The continuous heating furnace of the hot strip mill is installed at the most upstream part of the mill line, and heats the material to be rolled, that is, the slab, to a temperature suitable for subsequent rolling steps while saving energy. FIG. 1 shows a mill line equipped with such a continuous heating furnace. The evaluation of the extraction temperature of the slabs 6 _i , 6 _i+1 , 6 _i+2 . The raw temperature is measured and controlled using a crude outlet side thermometer 5 installed on the outlet side of the tube. The material to be rolled passing through this area further passes through a finishing rolling mill group 3 and is wound up by a coiler 4.

The reason why the temperature of the slab heated in the continuous heating furnace 1 is measured at the exit side of the rough rolling mill group 2 rather than immediately after the continuous heating furnace 1 is because scale is attached to the slab immediately after the heating furnace. This is because the slab temperature cannot be measured accurately, and furthermore, it is difficult to accurately measure the slab temperature because it is affected by cooling water, scale, etc. between the rough rolling mills. Thus,
In the current operation of hot strip mills, the temperature of the slab at the time of extraction from the heating furnace is evaluated based on whether the slab temperature at the time of completion of rough rolling satisfies the target temperature on the roughing side.

Traditionally, in the operation of a heating furnace, operators have been able to determine the slab configuration inside the heating furnace based on their years of experience and intuition.
The method used was to determine the furnace temperature set value in consideration of the target temperature on the raw side, rolling conditions, etc., and then manually set it in the furnace temperature control device.

However, in recent years, arithmetic devices, especially computers, have developed, and they are now being introduced into heating furnace temperature control devices, allowing the furnace temperature setting to be automatically set according to the results of computer calculations. The method has come to be practiced. An example of this will be explained with reference to FIG.

In FIG. 2, it is assumed that slabs 6 _i , 6 _i+1 , 6 _{i+2 . .} . are located in the continuous heating furnace 1 in order from the extraction port side. The temperature θ _g inside the heating furnace 1 is detected by the furnace temperature detector 7 and input to the furnace temperature control means 8 . The furnace temperature control means 8 compares this furnace temperature θ _g with the furnace temperature set value θ _gref given from the set furnace temperature calculation means 11, and adjusts the temperature so that the two agree, that is, so that the deviation between the two becomes zero. The burner 9 of the heating furnace 1 is automatically controlled. In order to obtain the furnace temperature set value θ _gref , calculate the temperature of each slab from the time the slabs 6 _i , 6 _i+1 , 6 _i+2 ... are charged into the heating furnace 1 until they are extracted. Temperature calculation means 10 and crude output side target temperature θ _dref
An extraction target temperature calculation means 12 is provided for calculating an extraction target temperature θ _cref from the extraction target temperature θ cref, and a set furnace temperature calculation means 11 calculates the above-mentioned set furnace temperature θ _gref based on the results of both calculations.

The set furnace temperature calculating means 11 sequentially calculates the slab temperature at regular intervals after the slab is loaded into the furnace, or every time the slab is moved into the furnace. An example of this temperature trajectory is shown in FIG. Figure 3 shows the slab 6 _i , which has a temperature θ ai at the position t _a when _it is charged into the furnace, and a temperature θ _ai at the position t _b when it reaches the extraction port. It is _bi . Here, the control operation of the apparatus shown in FIG. 2 will be explained by considering the state when the slab 6 _i reaches the position t _b .

When the current slab temperature θ _bi of the slab 6 _i when the slab 6 _i reaches the extraction port is calculated by the in-furnace slab temperature calculation means 10, the set furnace temperature calculation means 11
calculates the furnace temperature setting value θ _gref based on the calculated current temperature θ _bi so that the extraction temperature θ _bi of the slab 6 _i becomes the extraction target temperature θ _crefi , and inputs it to the furnace temperature control means 8. . The furnace temperature control means 8 adjusts the burner 9 so that the furnace temperature θ _g becomes the furnace temperature set value θ _gref . As a result, the slab 6 _i is heated to the extraction target temperature θ _crefi . In this case, the extraction target temperature θ _crefi is calculated in advance from the raw extraction side target temperature θ _drefi .

In this way, in conventional heating furnace control, the temperature of the slab inside the furnace is accurately calculated, and based on that calculated value, the furnace temperature required to heat the slab to the extraction target temperature is calculated and set. Eid-forward control is the basis. Therefore, it is important to accurately calculate the temperature of the slab in the furnace. If there is an error in the calculated slab temperature, the slab may not actually be heated even though it is predicted to have been heated to the extraction target temperature. This may result in the temperature not reaching the temperature suitable for rolling, which is a subsequent process in the furnace (insufficient heating), or conversely, overheating. For example, as shown in FIG. 3, even though it was predicted that the extraction temperature θ _ci of the slab 6 _i was heated to the extraction target temperature θ _crefi corresponding to the rough extraction side target temperature θ _drefi , the slab 6 i was actually heated. When _i is extracted from the heating furnace 1 and measured on the crude output side, it may show a value _di different from the crude output side target temperature θ _drefi . This is the temperature trajectory θ _ai −θ _bi − of slab 6 _i
This phenomenon can naturally occur if an error is included between θ _ci and the calculated value.

Here, the relationship between the extraction temperature of the slab and the raw temperature and the calculation error of the in-furnace slab temperature will be explained.

As already mentioned, the extraction temperature of the slab is currently controlled using the raw temperature. Therefore, the extraction target temperature θ _cref of the slab is determined from the raw extraction side target temperature θ _dref . Researchers in the field have already detailed the relationship between the slab extraction temperature and the roughing side temperature, that is, the crude temperature drop model calculation in which the slab extracted from the heating furnace is roughly rolled and the slab temperature gradually decreases. researched and revealed. That is, the relationship between the extraction temperature θ _c and the roughing side temperature θ _d depends on the rough rolling conditions, such as the rough rolling time t _rpll , the air cooling time t _air , the water cooling time t _w , the slab thickness h _j after each rough rolling pass, and the slab Functional formula θ _d = f (θ _c , t _rpll , t _air , t _w , h _j , H,…) with parameters such as thickness H… (
1) Calculated by Conversely, when calculating the extraction temperature from the raw temperature, it can be easily determined by convergence calculation using equation (1).

Next, we will discuss the furnace slab temperature calculation.

Normally, the temperature of a slab placed in a furnace is determined by the well-known Fourier one-dimensional heat conduction method ∂θ/∂t=a∂ ² θ/∂x ² ......(2) and its boundary condition K(∂ θ/∂X) _X=H/2 =q ......(3) Calculated from. In equations (2) and (3), θ is the temperature of the slab, t is time, X is the distance in the thickness direction of the slab, q is the heat input to the slab, and K and a are constants. X is zero at the center of the slab in the thickness direction, and X=
This corresponds to the slab surface position at H/2.

The heat input q into the slab in equation (3) is calculated using the Stefan-Boltzmann radiation equation q=σ・Φ _cg・{(θ _g +273) ⁴ −(σ _s +273) ⁴ }
......Calculated from (4). In equation (4), σ is the Stefan-Boltzmann constant, Φ _cg is the overall heat absorption rate, θ _g is the furnace temperature, and θ _s
is the slab surface temperature.

By calculating equations (2) to (4), the temperature of each slab in the furnace can be calculated from when each slab is charged into the furnace until it is extracted. The main reason for the error in calculating the slab temperature in the furnace is the calculation error of the heat input q to the slab in equation (4), and it is because it is difficult to grasp the true heat input to the slab. The reason why the true heat input to the slab cannot be grasped is the overall heat absorption rate Φ _cg
The problem is that it cannot be identified correctly, and that the detected value of the furnace temperature θ _g is not necessarily accurate. Therefore, many researchers are conducting research on heat transfer to the slab inside the furnace, but the reality is that the issue has not yet been fully elucidated.

For example, as shown in Figure 2, the furnace temperature θ _g is detected by the furnace temperature detector 7, but the temperature inside the furnace is not constant at any position, so The detected furnace temperature value differs depending on where it is located. Furthermore, it is affected by the flame caused by the combustion of fuel by the burner 9, making it difficult to grasp the furnace temperature that contributes to true heat input to the slab.

In this way, the reality is that calculations of the furnace slab temperature inevitably involve errors. If there is an error in the furnace slab temperature calculation, as mentioned above, the slab will be extracted at a temperature different from the extraction target temperature using conventional feed forward control alone. In that case, if the slab is extracted at a temperature lower than the target extraction temperature, it will have a negative impact on the rolling process in the subsequent process and will impede quality.
If extraction is performed at a temperature higher than the extraction target temperature, energy loss will increase accordingly.

[Purpose of the invention]

An object of the present invention is to provide a temperature control device for a continuous heating furnace that can solve the problems of the conventional technology described above and improve the accuracy of slab extraction temperature, thereby achieving rolling stability, quality improvement, and energy saving. That is.

[Summary of the invention]

In order to achieve the above object, the temperature control device for a continuous heating furnace according to the present invention includes a furnace temperature detector that detects the temperature inside the continuous heating furnace into which a plurality of slabs are charged, and a temperature control device for heating the inside of the continuous heating furnace. a roughing side thermometer for detecting the roughing side slab temperature after being extracted from the continuous heating furnace and completing rough rolling;
a first calculating means for back-calculating an extraction target temperature of the slab when extracted from the continuous heating furnace from a roughing side target temperature after completion of rough rolling; a second calculating means for estimating and calculating the temperature of the slab when extracted from the continuous heating furnace from the detected value of the slab temperature on the outlet side; a third calculating means that sequentially performs predictive calculations until extracted from the extraction temperature; an estimated extraction temperature value calculated by the second calculating means; and a predicted extraction temperature value calculated by the third calculating means and a fourth calculation means for correcting the extraction target temperature calculated by the first calculation means according to the difference, and outputting the corrected extraction target temperature for the subsequent slab in the furnace. , based on the slab temperature determined by the third calculation means and the extraction target temperature determined by the fourth calculation means, the slab temperature at the time of heating furnace extraction is adjusted to the extraction target temperature. a fifth calculating means for calculating a furnace temperature set value necessary for the heating, and controlling the heating means so that the furnace temperature becomes the furnace temperature set value determined by the fifth calculating means. It is characterized by being equipped with a furnace temperature control means.

The present invention is based on the following two points.

(1) Since the slab temperature calculation in the furnace involves errors, it is not possible to avoid temperature fluctuations on the rough output side due to the errors using conventional feedforward control alone. Therefore, an already established crude temperature drop model is used to calculate and estimate the extraction temperature from the actual measured temperature on the crude output side, and this estimated value is used as feedback information. Specifically, the estimated extraction temperature value _c calculated from the actual measured value of the raw temperature is compared with the predicted extraction temperature value θ _c calculated by calculating the furnace slab temperature, and the signal of the deviation Δθ is used as feedback information. .

(2) Correct the extraction target temperature of the furnace slab according to the deviation Δθ calculated in item (1) above. After correcting the extraction target temperature, the furnace temperature is adjusted by a conventionally known technique, the extraction temperature is changed, and the rough extraction side target temperature is achieved.

[Embodiments of the invention]

FIG. 4 shows an embodiment of the present invention.
The device shown in FIG. 4 is based on the device shown in FIG. 2, and includes blocks surrounded by broken lines, that is, extraction temperature calculation means 13 and extraction target temperature correction means 14.
and adding means 15. The extraction temperature calculation means 13 is a means for estimating and calculating the extraction temperature based on the slab temperature _d detected by the roughing side thermometer 5, and performs extraction target temperature calculation except for using the actual information in rough rolling. Calculation is performed using the same crude temperature drop model equation (1) as in device 12. The extraction target temperature correction means 14 extracts the extraction temperature estimate _c estimated by the extraction temperature calculation means 13,
The extraction temperature prediction value θ _c calculated by the furnace slab temperature calculation means 10 is compared, and each extraction of the furnace slabs 6 _i+1 , 6 _i+2 , 6 _i+3 . . . is performed according to the deviation. A correction amount _Δθcref for correcting the target temperature is calculated. The extraction target temperature θ _cref calculated by the extraction target temperature calculation means 12 and the correction amount Δθ _cref calculated by the extraction target temperature correction means 14 are added by the addition means 15, and the sum (θ _cref +Δθ _cref ) is guided to the set furnace temperature calculation means 11. The configuration of other parts is the same as that in FIG. 2.

Next, the operation of the apparatus shown in FIG. 4 will be explained with reference to FIG. 5, focusing on a particular slab 6 _i .

First, let us consider the case where the slab 6 _i is in the continuous heating furnace 1 . In this case, the in-furnace slab temperature calculation means 10
The temperature of the slab is calculated sequentially using equations (2) to (4) at regular intervals or as the slab is moved, from when the slab 6 _i is loaded into the furnace until it is extracted. Based on this slab temperature calculation result,
The furnace temperature setting calculation means 11 calculates the furnace temperature setting value θ _gref so that the extraction temperature of the slab 6 _i becomes θ _crefi , and outputs the calculation result to the furnace temperature control device 8 . The furnace temperature control device 8 forms a furnace temperature control minor loop, and adjusts the burner 9 so that the furnace temperature measured by the furnace temperature detector 7 becomes the furnace temperature set value θ _gref . As a result, it is predicted that the extraction temperature θ _ci of the slab 6 _i calculated by the in-furnace slab temperature calculation means 10 has been heated to the extraction target temperature θ _crefi . The temperature trajectory so far is the fifth
Corresponds to part A in the figure. Note that the extraction target temperature θ _crefi is calculated in advance by the extraction target temperature calculation means 12 from the crude extraction side target temperature θ _drefi when or before the slab 6 _i is charged into the continuous heating furnace 1. Ru.

Next, this slab 6 _i is extracted from the heating furnace 1,
Let us consider the time t _d when the rough rolling is completed and the rough rolling passes directly under the roughing side thermometer 5. At this time, the temperature _di of the slab 6 _i detected by the roughing side thermometer 5 is the roughing side target temperature because the slab 6 _i is heated to the extraction target temperature θ _crefi corresponding to the roughing side target temperature θ _dref . It should match the temperature θ _drefi , but as mentioned above, it does not necessarily match because the calculation of the furnace temperature slab temperature includes an error.

Here, for example, as shown in FIG. 5, it is assumed that the detected slab temperature value _di is lower than the target temperature θ _drefi . In this way, when slab 6 _i does not satisfy the target temperature on the roughing side, due to the characteristics of a continuous heating furnace, slabs 6 _i+1 , 6 _{i +2} , 6 _i+3 in the furnace following slab 6 i
... similarly causes a state of insufficient temperature. This is because a plurality of slabs are continuously charged in a continuous heating furnace, and the slabs following slab 6 _i are heated under almost the same furnace atmosphere conditions as slab 6 _i .
This tendency is more pronounced in slabs closer to slab 6 _i .

The present invention is characterized in that it takes into consideration the characteristics of such a continuous heating furnace and adds a feedback control function to the conventional control function. Therefore, first, the temperature _di of the slab 6 _i detected by the raw-output side thermometer 5 is input to the extraction temperature calculation means 13, where the estimated extraction temperature value _ci of the slab 6 _i is calculated. In this case, the estimated value _ci is obtained from the rough output side detected temperature _di using the rough temperature drop model of equation (1).

The extraction target temperature correction means 14 first compares the extraction temperature _ci calculated by the extraction temperature calculation means 13 with the extraction temperature predicted value θ _ci calculated by the furnace slab temperature calculation means 10, and calculates the difference Δθ _i is calculated according to the formula Δθ _i =θ _ci − _ci (5).

Next, depending on this difference Δθ _i, the furnace slabs 6 _i+1 and 6 _i
+2 , 6 _i+3 ... Calculate the extraction target temperature correction amount according to the formula below.

Δθ _crefi+1 = C _i+1・Δθ _i Δθ _crefi+2 = C _i+2・Δθ _i Δθ _crefi+3 = C _i+3・Δθ _i 〓 ……(6) Here, C _i+1 , C _i+2 , C _i+3 ... are constants.

The meanings of equations (5) and (6) are as follows.
If Δθ _i is positive in equation (5), the in-furnace slab temperature calculation by the in-furnace slab temperature calculating means 10 is estimated to be higher than the true slab temperature by Δθ _i . That is, it means that the true extraction temperature of slab 6 _i did not reach the temperature θ _ci predicted by the furnace slab temperature calculation means 10, and the prediction error corresponds to Δθ _i in equation (5). . Therefore, due to the characteristics of the continuous heating furnace, the subsequent slabs will also be underheated, so the extraction target temperature of the subsequent slabs is increased by an amount corresponding to Δθ _i . The amount of correction is the value determined by equation (6). As a result, the set furnace temperature calculation means 11 calculates a new extraction target temperature _cref by adding the correction amount of equation (6) to the preset extraction target temperature, that is, _crefi+1 =θ _crefi+1 +Δθ _{crefi+1 crefi +2} = θ _crefi+2 +Δθ _{crefi+2 crefi+3} =θ _crefi+3 +Δθ _crefi+3 〓 ...Based on (7), the furnace temperature set value is calculated by the addition means 15, and it is It is output to the furnace temperature control means 8.

The furnace temperature control means 8 adjusts and controls the burner 9 so that the furnace temperature becomes the furnace temperature set value, just as in the case of FIG. In this case, the extraction target temperature of the slab in the furnace becomes higher, so the furnace temperature is raised compared to the case where there is no target value correction amount by equation (6), and the rough extraction side temperature of the subsequent slab matches the new target temperature. It will be controlled to do so.

By performing the above operation every time the slab passes directly under the rough output side thermometer 5, it is possible to improve the precision of the rough output side slab temperature.

In equation (6), the constants C _i+1 , C _i+2 , C _i+3 . . . are weighting coefficients, and the closer the slab is to the extraction port, the closer the characteristics to the slab detected by the raw-output side thermometer 5 are. As shown, the relationship is C _i+1 ＞C _i+2 ＞C _i+3 ＞...

Each component mentioned above 8, 10, 11, 12,
Each operation by 13 and 14 can be executed by a common computer, for example a microcomputer. However, each functional unit may be configured as a digital or analog type device.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to improve the precision of the roughing side slab temperature, and as a result, it is possible to improve rolling quality, stabilize rolling, and save energy.

[Brief explanation of the drawing]

Fig. 1 is a side layout diagram of a hot strip mill line, Fig. 2 is a block diagram of a conventional heating furnace control device, Fig. 3 is a characteristic diagram showing an example of the slab temperature trajectory by the control device, and Fig. 4 The figure is a block diagram showing one embodiment of the present invention, and FIG. 5 is a characteristic diagram showing an example of a slab temperature trajectory for explaining the control mode by the same device. 1... Continuous heating furnace, 2... Rough rolling mill group, 5...
Rough output side thermometer, 6... Slab, 7... Furnace temperature detector, 8... Furnace temperature control means, 9... Burner, 10...
...Furnace slab temperature calculation means, 11...Setting furnace temperature calculation means, 12...Extraction target temperature calculation means, 13...
... Extraction temperature calculation means, 14 ... Extraction target temperature correction means, 15 ... Addition means.

Claims (1)

[Claims] 1. A furnace temperature detector for detecting the temperature inside the continuous heating furnace into which a plurality of slabs are charged; a heating means for heating the inside of the continuous heating furnace; and a heating means for heating the inside of the continuous heating furnace; a roughing side thermometer for detecting the roughing side slab temperature after completing rough rolling; and a roughing side thermometer for detecting the roughing side slab temperature after rough rolling is completed; a first calculation means that performs a back calculation; and a second calculation means that estimates the temperature of the slab when it is extracted from the continuous heating furnace, based on the temperature detection value of the roughing side slab detected by the roughing side thermometer. a calculation means; a third calculation means that sequentially predicts and calculates the temperature of the slab in the continuous heating furnace from when the slab is charged into the furnace until it is extracted; The extracted extraction temperature estimated value calculated by the third calculation means is compared with the extracted extraction temperature predicted value calculated by the third calculation means, and according to the difference,
a fourth calculation means for correcting the extraction target temperature calculated by the first calculation means and outputting the corrected extraction target temperature as a new extraction target temperature for the subsequent slab in the furnace; Based on the obtained slab temperature and the extraction target temperature obtained by the fourth calculation means, calculate a furnace temperature set value necessary to bring the slab temperature during heating furnace extraction to the extraction target temperature. and a furnace temperature control means that controls the heating means so that the furnace temperature becomes the furnace temperature set value determined by the fifth calculation means. Temperature control device.