JPS639567B2 - - Google Patents

Description

[Detailed Description of the Invention] <Technical Field> The present invention relates to a method for controlling the temperature of a strip in a continuous annealing furnace equipped with a radiant tube. The present invention relates to a temperature control method in which the strip temperature at the furnace outlet is controlled by directly outputting a fuel flow rate set value.

<Prior Art> A conventional strip temperature control method in a radiant tube furnace is shown in FIG. In FIG. 1, the strip 1 is advanced through the furnace 4 by the hearth roll 2. At this time, the strip 1 is heated by the radiant tube 3, the inner wall of the furnace heated by the radiant tube 3, and the furnace atmosphere gas. I go outside. The traditional strip temperature control method is
By detecting the strip temperature from the temperature detector 5 and the furnace atmosphere temperature from the thermocouple 6,
The temperature controller 9, which has a furnace temperature model representing the relationship between the strip temperature and the furnace atmosphere temperature, outputs the furnace temperature set value to the furnace temperature controller 8, and maintains the strip temperature at the set value of the temperature setter 10. It is something to do. Furnace temperature controller 8 detects the furnace temperature using thermocouple 6, and outputs a fuel flow rate setting value to fuel flow rate controller 7 in order to control the furnace temperature. However, in the conventional method, it is difficult to measure the furnace temperature that contributes to the strip temperature, so there is a limit to the accuracy of the furnace temperature model, and the control accuracy is poor. Additionally, since the furnace is divided into multiple zones, it is difficult to allocate the furnace temperature settings to each zone.
The furnace temperature controller 8 may not be able to control the temperature to the set value, which also deteriorates control accuracy. On the other hand, in Japanese Patent Publication No. 55-22535, regarding a temperature control device that directly outputs the fuel flow rate set value, if the deviation between the strip temperature at the furnace outlet and the temperature set value is within a predetermined range, the detected strip temperature is A device has been devised to hold the fuel flow rate set value by holding the fuel flow rate, but since the response of radiant tube furnaces is slow, it is necessary to widen the deviation range for holding the fuel flow rate in order to achieve good stability. , there is a drawback that control accuracy deteriorates accordingly.

<Objective and Summary of the Invention> The present invention was developed with the aim of solving the above-mentioned problems, and it provides a strip temperature control model that expresses the dynamic relationship between strip temperature and fuel flow rate, and directly sets the fuel flow rate. This method attempts to control the strip temperature by separating the value into a steady fuel flow rate set value and a transient fuel flow rate set value and outputting the value, thereby improving the stability and responsiveness of strip temperature control and improving control. This can improve accuracy.

<Embodiments of the Present Invention> The details of the present invention will be described below with reference to the embodiment of FIG. 2. In FIG. 2, the strip 1 is advanced through the furnace 4 by the hearth roll 2, and at this time the strip 1 is heated by the radiant tube 3, the inner wall of the furnace heated by the radiant tube 3, and the furnace atmosphere gas. The fuel flow rate in each zone made up of a plurality of radiant tube groups is controlled by the fuel flow controller 7 for that zone. The set value of each fuel flow controller 7 is outputted by a fuel flow distributor 13. Fuel flow distributor 13
distributes the tall fuel flow rate set value to each zone according to the settings of the distribution pattern setter 11. The total fuel flow set value is output from the temperature controller 9 as the sum of the steady fuel flow set value and the transient fuel flow set value, but it is determined by the strip temperature detected by the temperature sensor 5 and the temperature setter 10. When the deviation from the set value is within a predetermined range, the transient fuel flow rate set value is not output. In this embodiment, the fuel flow rate distributor 13 and the temperature controller 9 are realized by separate controllers, but they can also be realized by combining them into one controller.

The strip temperature is detected by a temperature detector 5 at the outlet of the furnace 4, and the fuel flow rate in each zone is detected by a fuel flow detector 12 and input to a temperature controller 9. The strip temperature and fuel flow rate are input at regular time intervals, and a plurality of past measured values are stored in a storage device within the temperature controller 9. The temperature controller 9 has a temperature control model representing the dynamic relationship between the strip temperature and the fuel flow rate as shown in the first equation.

y^(k)=a^ ₀ (k-1)y(k-1)+a^ ₁ (k-1)
y(k-2) +...+a^n(k-1)y(k-n-1) +...+a^n(k-1)y(k-n-1) +b^ ₀ (k- 1) u(k-1)+b^ ₁ (k-1)u
(k-2) +...+a^n(k-1)y(k-n-1) +b^ ₀ (k-1)u(k-1)+b^ ₁ (k-1)u
(k-2) +...+b^m(k-1)u(k-m-1)...(
1) However, y^(k)=Cp(T^ ₀ (k))T^ ₀ (k)−Cp(T _I )T _I y(k)=Cp(T ₀ (k))T ₀ (k) −Cp (T _I ) T _I u(k)=B/ρhbVF _T (k) T^(k): Estimated strip temperature at the furnace outlet at time k T ₀ (k): Strip temperature at the furnace outlet at time k Measured value F _T (k): Sum of measured fuel flow values for each zone at time k Cp (T): Specific heat ρ of the strip at strip temperature T: Strip density h: Strip thickness b: Strip width V: Threading speed B : Calorific value per unit flow rate of fuel a^ ₀ (k), ..., a^n(k), b^ ₀ (k), ..., b^m(k): Estimation of unknown parameters at time k value, k time point means the current time, k−i (i=1,
) means a point in time i past the present. That is, the current strip temperature is equal to the past n
+1 strip temperatures and m+1 past fuel flows.

The unknown parameter is the following value calculated from the current strip temperature T ₀ (k) detected by the temperature detector 5: y(k)=Cp(T ₀ (k))T ₀ (k)−Cp(T _I ) T _I and the current estimated value y^(k) of y(k) calculated from the first equation of the temperature control model, that is, the error of the temperature control model e(k) e(k) = y( k)−y^(k), for example, the modified gain α ₀ , ..., αn,
As β ₀ , ..., βm a^ ₀ (k)=a^ ₀ (k-1) + α ₀ e(k) 〓 a^n(k)=a^n(k-1)+αne(k) b ^ ₀ (k) = b^ ₀ (k-1) + β ₀ e(k) 〓 b^m(k) = b^m (k-1) + βme(k) It is automatically corrected as follows.

Next, the steady fuel flow rate set value F _T ^* for controlling the strip temperature at the outlet of the furnace 4 to the set value T ₀ ^* of the temperature setting device 10 is automatically corrected from the temperature control model equation 1. Parameter a^ ₀ (k),...
By using a^n(k), b^ ₀ (k), ...b^m(k) It is calculated as y ^* = Cp (T ₀ ^* ) T ₀ ^* − Cp (T _I ) T _I. These events occur during transient conditions, i.e., when the current and past strip temperatures do not match the setpoint T ₀ ^* , or when the current and past fuel flow rates do not match the steady-state fuel flow setpoint F _T ^* . Compensate for. In order to control the strip temperature to the set value T ₀ ^* under such transient conditions, the transient fuel flow set value ΔF _T ^* to be added to the steady fuel flow set value F _T ^* is It is calculated as follows. This transient fuel flow setpoint ΔF _T
^* is output when the deviation between the strip temperature and the set value exceeds the specified range, so the control gain
Using f ₀ , ..., fn, g ₁ , ..., gm, ΔF _T ^* = {f ₀ [y ^* -y(k)] + ... + f _o [y ^* -y(k-n
)]}ρhbV/B +g ₁ [F _T ^* −F _T (k−1)]+……+g _n [F _T ^* −F _T (k
-m)] It is also possible. In addition, changes in strip thickness and width, changes in strip threading speed, or changes in temperature set point change the steady fuel flow set point F _T , so transient fuel A flow rate set value ΔF _T can also be added.

The sum of the steady fuel flow rate set value and the transient fuel flow rate set value calculated as described above, that is, the total fuel flow rate set value, is output from the temperature controller 9 to the fuel flow rate distributor 13. The fuel flow rate distributor 13 outputs a total fuel flow rate setting value to the fuel flow rate controller 7 of each zone according to the distribution pattern of the distribution pattern setting device 11. Possible distribution patterns include, for example, a uniform load pattern that distributes the flow rate uniformly in all zones, or a high-load pattern for the latter zone that distributes the flow rate so that it becomes larger as it approaches the furnace outlet. It can also be used to distribute total fuel flow to each zone in a load pattern to prevent heat buckling in the strip.

<Effects of the Invention> As is clear from the above, the present invention has a temperature control model that dynamically expresses the relationship between strip temperature and fuel flow rate, and directly converts the fuel flow rate set value into a steady fuel flow rate set value. Since the output is separated into the and transient fuel flow rate set value, it is possible to obtain high control performance that satisfies the stability and high responsiveness of strip temperature control.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional strip temperature control method, Fig. 2 is a block diagram of an embodiment of a strip temperature control method to which the present invention is applied, and Fig. 3 shows how the fuel flow rate is adjusted to each zone using a rear zone high load pattern. This is a chart showing an example of distribution. 1: Strip, 2: Hearth roll, 3: Radiant tube, 4: Continuous annealing furnace, 5: Temperature detector, 6: Thermocouple, 7: Fuel flow controller, 8: Furnace temperature controller, 9: Temperature controller , 10: Temperature setting device, 1
1: Distribution pattern setter, 12: Fuel flow rate detector, 13: Fuel flow rate distributor.

Claims (1)

[Claims] 1. In a temperature control method for a continuous annealing furnace equipped with a radiant tube that continuously heats the strip, a temperature control model that dynamically expresses the relationship between the strip temperature at the furnace outlet and the fuel flow rate is provided, and the unknowns included in the model are The parameters are automatically corrected based on the measured values of strip temperature and fuel flow, and the fuel flow setpoint calculated from the model is separated into steady output and transient output, and the deviation between the strip temperature and temperature setpoint is When the deviation is within a predetermined range, only the steady fuel flow rate set value is output, and when the deviation is outside the predetermined range, a transient fuel flow rate set value is added to the steady fuel flow rate set value and output. A temperature control method for a continuous annealing furnace.