JPH04246130A - Method for controlling flow rate of combustion gas in continuous annealing furnace - Google Patents

Abstract

PURPOSE:To accurately control temp. of the following material having strip width different from that of the preceding material by using the prescribed heat transmission model equation and obtaining an overall coefficient of heat transfer from combustion gas flow rate and the strip width to obtain the set value of combustion gas flow rate for the following material. CONSTITUTION:To a strip prepared by joining the preceding material and the following material different in size, the target temp. and quality, the combustion gas flow rate of the following material is controlled by using the prescribed heat transmitting model equation. In this control method, the plural overall coefficients of heat transfer from the above model equation are calculated through the specific arithmetic equation for each of the calculation conditions different in strip widths and in the combustion gas flow rates. Successively, based on this calculated result, the overall coefficient of heat transfer is obtd. as functions of the combustion gas flow rate and the strip width. Successively, by using a flow rate arithmetic equation obtd. from these relations, the overall coefficient of heat transfer for the following material is obtd., and based on these, the set value of combustion gas flow rate of the following material is obtd. from the above flow rate arithmetic equation.

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for controlling the flow rate of combustion gas for controlling the temperature of a continuous annealing furnace. [0002] In a continuous annealing furnace, in order to continuously heat treat a steel plate (hereinafter referred to as a strip), the rear end of a strip (hereinafter referred to as a preceding material) being passed at the entrance side of the furnace,
The front end of the strip to be passed next (hereinafter referred to as the next strip) is joined by welding. When the preceding material and the subsequent material are joined and heat treated in this way, the temperature of the strip at the exit side of the furnace can be controlled to a predetermined target temperature by performing heat treatment according to the dimensions and material of each strip. Was. Conventional temperature control for such continuous annealing furnaces involves determining the combustion gas flow rate using a heat transfer model equation and setting the determined combustion gas flow rate as the set flow rate. For example, NKK Technical Report No. 126,
In P20 and 21, when the dimensions and materials of the preceding material and the succeeding material were different, the combustion gas flow rate was determined using the heat transfer model equation shown in equation (7) below, and the setting of the combustion gas flow rate was changed. . 60・V・ρ・h・(dQS/dx)=KS・
[UGS(u, TG)・{(TG +273)4
−
(TS +273)4 }+UWS(u
,TW )・{(TG
+273)4 -(
TS +273)4 }] …(7) 000
5] However, in the above equation (7), ρ is the density of the steel plate (
kg/cm2), h is the steel plate thickness (m), QS is the heat content of the steel plate (kcal/kg), KS is the model parameter, UGS is the heat transfer coefficient between the combustion gas and the steel plate (kc
al/m 2 ・h・℃), UWS is the heat transfer coefficient between the furnace wall and the steel plate (kcal/m 2 ・h・℃), u is the combustion gas flow rate (Nm 3 /h), and TG is the combustion gas temperature (°C), TW is the furnace wall temperature (°C), TS is the steel plate temperature (°C), V is the line speed (mpm), and x is the position of the steel plate in the furnace (m). [0006] However, when determining the combustion gas flow rate using the heat transfer model equation (7) as described above, radiation from the furnace wall and combustion gas are considered as heat transfer forms. Although it is practical because it takes into account radiation, the width of the strip is not taken into account in equation (7). Therefore, if the width of the preceding material differs from the width of the next material, there is a problem in that the strip temperature of the next material on the exit side of the furnace is not controlled to a predetermined target temperature. The present invention has been made in view of the above circumstances, and even when the width of the preceding material and the width of the next material are different, the strip temperature of the next material can reach a predetermined target temperature. An object of the present invention is to provide a method for controlling the flow rate of combustion gas in a continuous annealing furnace, which enables control with good accuracy. Means for Solving the Problems [0008] A combustion gas flow rate control method for a continuous annealing furnace according to the present invention provides a method for controlling the flow rate of combustion gas in a continuous annealing furnace. In order to control the temperature of the continuous annealing furnace, the set value of the combustion gas flow rate of the next material is determined using a predetermined heat transfer model equation, and the combustion gas flow rate of the next material is controlled to reach this set value. In the combustion gas flow rate control method, the overall heat transfer coefficient of the heat transfer model equation is calculated by a predetermined calculation formula for each calculation condition with different strip width and combustion gas flow rate, and the overall heat transfer coefficient is calculated based on the calculation results. A coefficient is determined as a function of the combustion gas flow rate and the width of the band material, and a flow rate calculation formula is determined from the function to calculate a set value of the combustion gas flow rate in relation to the width of the band material and the overall heat transfer coefficient. The overall heat transfer coefficient of the next row material is determined by the calculation formula, and the set value of the combustion gas flow rate of the next row material is determined using the flow rate calculation formula based on the width of the next row material and the determined overall heat transfer coefficient of the next row material. Characterized by seeking. [Operation] When the overall heat transfer coefficient, which collectively represents various heat transfer coefficients related to heat transfer to the strip material, is determined as a function of the combustion gas flow rate and the width of the strip material, this function determines the width of the strip material. If this changes, the overall heat transfer coefficient will change. From the above function, a flow rate calculation formula for calculating the set value of the combustion gas flow rate of the next row material in relation to the width of the next row material and the overall heat transfer coefficient can be obtained. The set value of the combustion gas flow rate in is a value obtained by taking into account the change in the overall heat transfer coefficient when the width of the strip material changes, so the combustion gas flow rate of the next material is controlled to achieve this set value. This compensates for the effect on the temperature control of the subsequent material due to the change in the width of the strip from the preceding material to the subsequent material. [0010] The present invention will be specifically explained below based on the drawings showing the embodiments. FIG. 1 is a schematic block diagram showing the configuration of a combustion gas flow rate control device for a continuous annealing furnace to which a combustion gas flow rate control method for a continuous annealing furnace according to the present invention is applied. 1 in the figure is a vertical direct-fired heating furnace, and inside the heating furnace 1, a strip S is arranged in the direction from the furnace entry side to the furnace exit side, as indicated by the white arrow in the figure. A plurality of hearth rolls 2, 2 are provided for transferring to. The interior of the heating furnace 1 is divided into three regions from the upstream side to the downstream side of the strip S. Each of these areas is provided with a burner 3, 3, 3 that emits a flame, respectively, and the burner 3, 3, 3 of each area receives a corresponding flow rate from a fuel supply source (not shown). Combustion gas is supplied through the control valves 4, 4, 4, and the burners 3, 3, 3 heat the strip S directly by flame. The strip S is transferred while being heated in each of the above-mentioned areas. The flow rate control valves 4, 4, 4 are individually controlled by corresponding combustion gas flow rate controllers 40, 40, 40, respectively. On the outlet side of the flow control valves 4, 4, 4, there are flow rate detectors 41, 41, which detect the flow rate of combustion gas.
41 are provided respectively, and the flow rate detectors 41, 41,
The detection data of 41 is the combustion gas flow rate controller 40, 40, 4.
0 respectively. Furthermore, combustion temperature detectors 7, 7, 7 for detecting the combustion temperature TG of each region are provided in each of the aforementioned regions, and the detection data of these combustion temperature detectors 7, 7, 7 is is provided to a first arithmetic unit 81 and a second arithmetic unit 82, which will be described later. An inlet temperature detector 51 is provided on the inlet side of the heating furnace 1 to detect the inlet temperature Ti of the strip S, while an inlet temperature detector 51 is provided on the outlet side of the heating furnace 1 to detect the outlet temperature To of the strip S. An outlet temperature detector 52 for detecting the temperature and a transfer speed detector 6 for detecting the transfer speed V of the strip S are provided. The detection data of the inlet temperature detector 51 and the transfer speed detector 6 are given to the first arithmetic unit 81 and the second arithmetic unit 82, and the detection data of the outlet temperature detector 52 is given to the first arithmetic unit 81 and the second arithmetic unit 82. The signal is supplied to the arithmetic unit 81. In addition to the above-mentioned detection data, the first computing unit 81 receives data on the thickness h and specific heat c of the preceding material of the strip S from a data input device (not shown). The first calculator 81 calculates a linear equation representing the overall heat transfer coefficient HC (Q, W) based on each data given as described above and by a calculation method described later, and calculates the coefficients of the obtained linear equation. The table is made into a table and stored in the memory 9. In addition to the above-mentioned detection data and the overall heat transfer coefficient HC stored in the memory 9, the second computing unit 82 stores the target plate temperature Tm and plate thickness h1 of the next row material of the strip S.
and specific heat c1 are given from a data input device (not shown). The second computing unit 82 calculates a target overall heat transfer coefficient HC1 based on each data given in this manner using a calculation method described later, and calculates the heating furnace by using a calculation method described later based on the obtained target overall heat transfer coefficient HC1. Find the total combustion gas flow rate Q1 of 1,
The obtained data of the total combustion gas flow rate Q1 is provided to the combustion gas flow rate distribution setting device 400. The combustion gas flow rate distribution setter 400 determines the set value of the combustion gas flow rate for each region of the heating furnace 1 based on a predetermined distribution ratio, and uses the data of the determined combustion gas flow rate set value as the combustion gas flow rate. It is given to the flow rate controllers 40, 40, 40, respectively. The combustion gas flow rate controllers 40, 40, 40 control the combustion gas flow rate in each region to match a given set value. Next, the effect on temperature control of the strip when the widths of the preceding material and the succeeding material are different will be explained. For example, in a direct-fired heating furnace of a horizontal continuous hot-dip galvanizing line, a preceding material and a succeeding material differ only in sheet width.
Actual heating is performed with the combustion gas flow rate and transfer speed constant,
FIG. 2 shows the results of detecting the furnace exit temperatures of the preceding material and the subsequent material. Figure 2 is a time chart showing the results of strip temperature changes when a preceding material and a succeeding material differing only in sheet width are heated under the same conditions. , B is the furnace wall temperature of the direct-fired heating furnace, and C is the strip temperature on the outlet side of the direct-fired heating furnace. Note that the line speed in this control was 96 mpm, and the thickness of the strip was 0.6 mm. When the width of the strip increases by 200 mm at the joint between the preceding material and the succeeding material as shown in A of FIG. 2, the furnace wall temperature decreases by 25° C. as shown in B, and The strip temperature was reduced by 30°C. In this way, it can be seen that the strip temperature is affected when the widths of the preceding material and the succeeding material are different. From the results shown in FIG. 2, the heat transfer form of the direct-fired heating furnace can be modeled by the heat transfer equation shown in equation (1) below. 60・V・c・ρ・h・(dTS/dx)=2H
(Q)・(TG −TS )+2Fse(W)・σ・[
{(TW +273)/100}4 - {(TS +2
73)/100}4 ]...(1) [0020] However, in the above equation (1), c is the specific heat of the strip (
kcal/kg °C), ρ is the density of the strip (kg
/cm2), h is the strip thickness (m), W is the strip width (m), and Q is the combustion gas flow rate (Nm).
3/h), H(Q) is the heat transfer coefficient between the combustion gas and the strip (kcal/m 2 ・h・℃), Fse (
W) is the view factor between the furnace wall and the strip, TG is the combustion gas temperature (℃), TW is the furnace wall temperature (℃), TS
is the strip temperature (°C), σ is the Stefan Boltzmann constant, V is the line speed (mpm), and x is the position of the strip in the furnace (m). The heat transfer model equation (1) above differs from the conventional heat transfer model equation in that it uses the view factor Fse(W) between the furnace wall and the strip as a function of the strip width W.
Further, the above equation (1) can be equivalently expressed as the following equation (2). ##EQU1## In the above equation (2), the overall heat transfer coefficient HC (Q , W ) is expressed as a function of the combustion gas flow rate Q and the width W of the strip. Next, a calculation method in the first calculation unit 81 and the second calculation unit 82 of the combustion gas flow rate control device configured as described above will be explained. The first computing unit 81 calculates the overall heat transfer coefficient HC (Q, W
). HC (Q,W)=[(60・c・ρ・h・
V) /(2・L)]・ln[(TG −
Ti)/(TG-T
o )] … (3) 0026] However, the above (
3) where L is the effective heating length of the strip S. Overall heat transfer coefficient HC obtained in this way (
Q, W) are obtained under a number of conditions in which the width of the strip S and the combustion gas flow rate are different, and based on these results, a multiple regression calculation method is used to calculate the overall heat transfer coefficient HC.
(Q, W) is obtained as a linear equation as shown in equation (4) below, and its coefficients A0, A1, and A2 are obtained. [0027]HC(Q,W)=A0+A1
・Q+A2 ・W...(4) 0028] And the coefficients A0, A1, A
2 is stored in the memory 9 as table data. The coefficients A0, A1, A2 are determined for each material of the strip S, and the coefficients A0, A2 for each material are stored in the memory 9.
A1 and A2 are stored as table data of a layered table according to the material of the strip S. In the second computing unit 82, when the next material whose material is different from the preceding material reaches the entrance side of the heating furnace 1, the furnace entry side temperature Ti detected by the entrance side temperature detector 51 and the transfer speed are detected. The transfer speed V detected by the detector 6, the combustion temperature detector 7,
Combustion temperature TG detected in step 7 and target plate temperature T of the next material
Based on m, plate thickness h1, specific heat c1, the following (5)
The target overall heat transfer coefficient HC1 of the next material is determined using the formula. HC1=[(60・c1・ρ・h1・V)/
(2・L)]・ln[(TG-Ti)/
(TG - Tm) ...(5) 0
[031] When the target overall heat transfer coefficient HC1 is determined, the data of the coefficients A0, A1, and A2 corresponding to the material of the next material are read out from the memory 9, and this and the target overall heat transfer coefficient HC1 and the data of the next material are read out from the memory 9. Based on the plate width W1, the total combustion gas flow rate Q1 is determined using the following equation (6). Q1 = (1/A1)・(HC1−A0−A2・
W1) ...(6) [0033] Since the total combustion gas flow rate Q1 determined in this way is a value determined including the condition of the plate width W of the strip S, the following material and the preceding material are combined to form a strip. Even when only the plate width W of S differs, temperature control can be performed with high accuracy. Next, the results of actual temperature control using the method for controlling the flow rate of combustion gas in a continuous annealing furnace as described above will be explained. FIG. 3 is a time chart showing the results of temperature control of the preceding material and the succeeding material, which have different sheet widths and target sheet temperatures, using the combustion gas flow rate control method of the present invention, and A in the figure indicates the input temperature of the direct-fired heating furnace. B is the total combustion gas flow rate of the direct-fired heating furnace, and C is the strip temperature on the outlet side of the direct-fired heating furnace. However, the broken line in B above is the set value of the total combustion gas flow rate, and the solid line is the actual value.
Moreover, the broken line in C is the target plate temperature, and the solid line is the actual value. Note that the line speed in this control is 60 mpm.
The thickness of the strip was 2.3 mm. Even if the width of the strip is increased by 150 mm at the joint between the preceding material and the succeeding material as shown in FIG. 3A, the total combustion gas flow rate is increased by 500 Nm as shown in FIG.
It can be seen that by increasing the strip temperature by 3/h, the strip temperature on the exit side of the furnace is controlled to the target plate temperature as shown in C. [0036] In this embodiment, a case has been described in which combustion gas flow rate control is performed in a continuous annealing line using a vertical direct-fired heating furnace, but the present invention is not limited to this. It can also be applied to a continuous hot-dip galvanizing line having a direct-fired heating furnace and a continuous hot-dip galvanizing line having a horizontal direct-fired heating furnace. Effects of the Invention As detailed above, in the combustion gas flow rate control method for a continuous annealing furnace according to the present invention, an overall heat transfer coefficient that collectively represents various heat transfer coefficients related to heat transfer to the strip material is calculated. When calculated as a function of the combustion gas flow rate and the width of the strip material, if the width of the strip material changes, the overall heat transfer coefficient will change according to this function, and the combustion gas flow rate of the next material obtained from the above function. The set value of the combustion gas flow rate of the next material, which is calculated using the calculation formula in relation to the width of the next material and the overall heat transfer coefficient, is the overall heat transfer coefficient when the width of the strip material changes. This value is obtained by taking into account the change in the coefficient, so if the combustion gas flow rate of the next material is controlled to achieve this set value, the effect on the temperature control of the next material due to the change in the width of the strip material will be reduced. Even if the width of the preceding material and the width of the succeeding material are different,
The present invention has excellent effects such as being able to control the temperature of the next material on the exit side of the furnace to a predetermined target temperature.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing the configuration of a combustion gas flow rate control device for a continuous annealing furnace to which a combustion gas flow rate control method for a continuous annealing furnace according to the present invention is applied.

FIG. 2 is a time chart showing the results of temperature changes in a strip when a preceding material and a succeeding material differing only in sheet width are heated under the same conditions.

FIG. 3 is a time chart showing the results of temperature control of a preceding material and a succeeding material having different sheet widths and target sheet temperatures using the combustion gas flow rate control method of the present invention.

[Explanation of symbols]

81 First computing unit 82 Second computing unit S strip

Claims (1)

[Claims] [Claim 1] At least one of dimensions, target temperature, and material.
In order to control the temperature of a strip material made by joining a preceding material and a succeeding material with different values, a predetermined heat transfer model equation is used to determine the set value of the combustion gas flow rate of the succeeding material, and it is necessary to achieve this set value. In a combustion gas flow rate control method for a continuous annealing furnace that controls the combustion gas flow rate of a subsequent material, the overall heat transfer coefficient of the heat transfer model formula is calculated using a predetermined calculation formula for each calculation condition where the width of the strip material and the combustion gas flow rate are different. Based on the calculation results, the overall heat transfer coefficient is determined as a function of the combustion gas flow rate and the width of the strip material, and from this function, the combustion gas flow rate is set in relation to the width of the strip material and the overall heat transfer coefficient. A flow rate calculation formula for calculating the value is determined, the overall heat transfer coefficient of the next row material is determined using the predetermined calculation formula, and the flow rate is calculated based on the width of the next row material and the determined overall heat transfer coefficient of the next row material. A combustion gas flow rate control method for a continuous annealing furnace, characterized in that the set value of the combustion gas flow rate of the next material is determined by the formula.