JPS6132377B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a strip temperature control method for a continuous annealing furnace, which controls the temperature of the strip by adjusting the flow rate of fuel gas flowing through a suction type radiant tube.

A continuous annealing furnace is one in which a strip formed by welding the rear end of a thin plate coil to the front end of another coil is continuously subjected to thermal cycles. As shown in Fig. 1, a conventional continuous annealing furnace has a suction-type radiant tube 2 disposed in a heating furnace 1, burns fuel gas in the tube 2 to heat the radiant tube 2, and uses its radiant heat. This heats the strip 3 that passes vertically between the two rows of radiant tubes.

The conventional strip temperature control method in this continuous annealing furnace is, for example, to divide the inside of the furnace into 6 groups and adjust the atmosphere temperature inside the furnace for each zone.
This adjustment indirectly controls the strip temperature.

More specifically, a furnace temperature detector 4 is provided in each zone, a target value of the furnace temperature is set in advance in the furnace temperature setting device 5, and the furnace temperature detected by the detector 4 is set in advance. The fuel flow rate controller 7 is controlled by the furnace temperature controller 6 so that the temperature becomes the target value of the furnace temperature setting device 5.

However, the above control method has the following drawbacks.

In other words, when we measure the response of the furnace temperature when the furnace temperature control system is turned off (closed loop) and the fuel flow rate is changed stepwise, we find that it takes 30 minutes for the furnace temperature to stabilize because the heat capacity of the continuous annealing furnace is extremely large. It takes a similar amount of time to respond to the strip temperature.

In this case, since the passage time of one coil is about 20 to 30 seconds, it is necessary to increase the control sensitivity of the furnace temperature controller to improve its responsiveness. However, if the control system is made unstable in this way, the furnace temperature will become unstable when annealing conditions change, such as changes in sheet dimensions, line speed, steel type, etc., and as a result, the strip temperature will become unstable and temporary However, it has the disadvantage of producing over-annealed and unannealed strips.

Therefore, conventionally, when operating a continuous annealing furnace, the furnace temperature setting value is set high to prevent the above-mentioned problems. However, as the annealing temperature increases, more thermal energy is required, leading to an increase in fuel flow rate.
Manufacturing costs increase.

For this reason, the inventor developed a method for controlling the fuel flow rate by directly detecting the strip temperature using a highly reliable strip temperature detector, thereby allowing operation without raising the annealing temperature unnecessarily. I thought about it. In this case, the strip temperature changes much faster than the furnace temperature when the load changes, such as the plate thickness or the stripping speed, so stricter controllability than the furnace temperature control is required. For this reason, conventional analog control of the fuel flow rate has poor responsiveness to the strip temperature, and it is not possible to control the strip temperature, which fluctuates significantly when the load changes.

The present invention has been made in consideration of the above-mentioned circumstances, and its purpose is to enable operation at a lower annealing temperature by performing control with excellent responsiveness, thereby saving resources and energy. The purpose of this invention is to provide a method for controlling the strip temperature of a continuous annealing furnace.

That is, the present invention provides a computer provided at the outlet of a continuous annealing furnace for controlling the strip temperature to a predetermined value, an in-furnace atmosphere detector, and a fuel flow rate to control the in-furnace atmosphere temperature to the target value of the in-furnace atmosphere temperature determined by the computer. In a method for controlling the strip temperature of a continuous annealing furnace, the strip temperature controller is equipped with a furnace atmosphere temperature controller that operates the Temporarily adjust the fuel flow rate during the start of optimal control operation calculated using the relational expression between the obtained annealing conditions, fuel flow rate, furnace atmosphere temperature, and strip temperature to avoid excessive or insufficient fuel flow rate calculated from the above relational expression. A strip temperature control method for a continuous annealing furnace is characterized in that:

In this case, the above relational expression is determined in advance from the annealing conditions, fuel flow rate, furnace temperature, and strip temperature using a theoretical heat balance mathematical model or arrangement of actual data, and the strip temperature fluctuation value is calculated from this relational expression. It is something to do.

Therefore, when the annealing conditions change and it is known in advance that the strip temperature will fluctuate, the static fluctuation of the strip temperature at that time is compensated for before the annealing conditions change (hereinafter this is referred to as the predictive control method). ).

Also, under normal operating conditions, if the deviation between the detected strip temperature value and the target value is extremely large due to plate thickness variations, strip speed variations, etc. This temporarily supplies the flow rate and increases the responsiveness of the strip temperature.

However, since this method rapidly changes the fuel flow rate, a control mechanism is required to keep the ratio of fuel flow rate to combustion air flow rate and the negative pressure inside the radiant tube constant so as not to adversely affect the combustion state inside the radiant tube. The premise is that it is applied to a continuous annealing furnace with

Furthermore, it goes without saying that there is no need to make the furnace temperature controller unstable to increase its responsiveness as in the conventional method.

The method of the present invention will be explained below based on illustrative examples.

In this example, the main operations for implementing the present invention are performed by a computer (minicomputer, microcomputer, large computer, etc.).

In the figure, symbols a to l are input signals to the computer 11, and symbols m and n are output signals from the computer 11, and the contents of the symbols are as follows.

(1) Input a... Strip temperature detection signal b... Furnace temperature detection signal c... Furnace temperature controller output signal d... Fuel flow rate detection signal e... Strip speed detection Signal f…………Welding point entrance detection trigger signal g…………Plate thickness h…………Plate width i…………Coil weight j…………Steel type k…………Annealing speed (target value ) l...Annealing temperature (target value) In this case, g to k are input into the computer for each coil.

(2) Output m……Furnace temperature controller setting signal n……Additional fuel flow signal Also, static relational expression among annealing conditions, fuel flow rate, furnace temperature, and strip temperature (hereinafter referred to as relational expression A) is determined in advance, and the response time of the strip temperature to a step change in fuel flow rate when annealing is performed under various annealing conditions is determined in advance.

Here, as a strip temperature control method, when the magnitude and timing of the disturbance to the strip temperature are unknown, the normal strip temperature control method is used.
The method will be explained in two parts: (a) and a predictive control method for the known case, that is, the strip temperature fluctuation when the annealing conditions change (b).

The normal strip temperature control method (a) is based on the time required for predictive control (T minutes) and the welding point entrance time of the next coil where the annealing conditions will change, so that the current time is the same as the next welding point entrance time. Used when more than T minutes ago,
Also, the predictive control method (b) is used when the time is within T minutes ago.

Here, the time T required for predictive control can be obtained, for example, by the following method. However, the detailed structure will be explained later.

(1) Using relational formula A, determine the fuel flow rate q _fj of each zone from the plate thickness g, plate width h, steel type j, and annealing speed k of the strip to be annealed next.

Here, j is the next strip number.

(2) Find the excessive or insufficient fuel flow rate manipulated variable q _fpj using the following formula.

q _fpj = 2 × q _fj × Strip speed detection value (e) / Annealing speed
(k) (3) q When _fpj exceeds 100%, set it to 100%, and when it is below a predetermined minimum value, set it to the minimum value to find the time (T minutes) required to reach the predetermined strip temperature. The time T can be calculated, for example, from data on the response time of the strip temperature to a step change in the fuel flow rate when the strip is annealed under various annealing conditions previously obtained.
There is a method of interpolating response times corresponding to the following annealing conditions.

Further, the next welding point furnace time is determined using, for example, the following equation.

Here, T ₁ : Current welding point entry time T ₀ : Current time T ₂ : Next welding point entry time W _C : Coil weight T t _S : Plate thickness m W _S : Plate width m γ _S : Plate Specific weight of T/m ³ v _s(t) : Strip speed m/min v _STO : Current strip speed m/min (a) Normal strip temperature control Steady state, that is, strip temperature detection from the strip temperature detector 12 When the deviation between the value a and the target value l is within a predetermined value, the calculator 11 calculates the relational expression A and the plate thickness g, plate width h, steel type j, and annealing speed k that represent the current annealing conditions.
Furnace temperature Q _j-1 to set strip temperature target value l from
(Here, j is the next strip number.)
A furnace temperature set value signal m is sent to the furnace temperature controller 13, and the furnace temperature is controlled in the same manner as the conventional method shown in FIG. In this case, the fuel flow rate addition signal n is zero.

If the above deviation is greater than a predetermined value, calculate the excessive or insufficient additional fuel flow rate q _fsj-1 (n) from q _fpj-1 obtained by the method described above, and calculate (q _fsj-1 = q _{fpj -1} -q _ftj-1 , q _ftj-1 : Furnace temperature controller output) is output to the calculator 14, and at the same time calculates the furnace temperature setting value that compensates for the deviation of the strip temperature from the relational expression A, At the same time, the fuel flow rate q' _fj-1 at that time is memorized, and the calculated corrected furnace temperature set value signal m is sent to the furnace temperature controller 13.

When the above deviation falls within a predetermined value, the calculator 11 outputs q' _fsj-1 of the following equation to the arithmetic unit 14 (q' _fsj-1 =q' _fj-1 -q _ftj-1 ).

Furthermore, q' _fsj-1 (n) is slowly ramped up (for example, ±1Nm ³ /h/min) to approach 0, and q' _fj-1 = q _ftj
-1 . After that, the furnace temperature will be controlled normally.

The computing unit 14 adds the output signal c of the furnace temperature controller 13 and the fuel flow rate addition signal n from the computer 11, and provides a set value signal to the fuel flow rate controller 15.

The rest of the structure is the same as the conventional furnace temperature control system, so the explanation will be omitted.

(b) Predictive control of strip temperature when annealing conditions change This is to calculate the difference between the steady value of the strip temperature corresponding to the new annealing condition calculated from relational formula A and the original steady value for T minutes from the furnace entry time of the next welding point. This should be compensated in advance.

Here, calculator 11 calculates the additional fuel flow rate q _fsj
(q _fsj = q _fpj −q _ftj , q _fj : Furnace temperature controller output)
The signal n of is output to the arithmetic unit 14,
The output of the strip, that is, the set value of the fuel flow rate, is set to the above-mentioned q _fpj , and the strip temperature is stabilized to the predetermined value calculated above as quickly as possible. The signal n of q _fsj continues until the next welding point enters the furnace.

Further, the computer 11 switches to the above-mentioned normal strip temperature control method (a) at the same time as it receives the welding point entry detection trigger signal f which detects the next welding point entering the furnace.

Next, we will explain the control mechanism that maintains the ratio of fuel flow rate and combustion air flow rate and the negative pressure inside the radiant tube constant, and enables stable combustion even in the face of rapid changes in fuel flow rate, based on Figure 3. do.

(1) Control of the ratio of fuel flow rate and combustion air flow rate First, the fuel flow rate detector 21 detects the fuel flow rate, the combustion air flow rate detector 22 detects the combustion air flow rate, and these detection signals are used as the combustion air flow rate. Insert into controller 23. Combustion air flow rate controller 23
The combustion air flow rate is set at a predetermined ratio to the fuel flow rate, and the combustion air flow rate is adjusted by operating the control valve 24.

(2) Control of negative pressure inside the radiant tube First, the pressure detector 25 installed on the exhaust gas damper
The detection signal is input to the pressure regulator 26. This pressure regulator 26 operates the damper 27 so that the detected pressure becomes equal to the target value X.
It is connected to the damper 27 via the computing unit 28.

Separately, an arithmetic unit 29 adds the detected fuel flow rate from the fuel flow rate detector 21 and the combustion air flow rate from the combustion air flow rate detector 22, and inputs this to the valve opening controller 30. The valve opening controller 30 checks the rate of change in the output of the calculator 29, and if it is larger than the set rate of change (there is a set value of "+" when the fuel flow rate increases, and "-" when the fuel flow rate decreases), i.e. When the fuel flow rate increases rapidly, a signal is issued to forcibly open the valve opening of the exhaust gas damper 27 by a feed forward method, and this continues until the pressure detected from the pressure detector 25 exceeds the target value. When the detected pressure value exceeds the target value, the pressure control is switched to normal pressure control. In this case, the computing unit 29 adds the output of the valve opening degree regulator 30 and the output of the pressure regulator 26. However, normally the output from the valve opening controller 30 is zero.

In FIG. 3, the symbol Y is a comparison calculation start signal of the comparator 31 that compares the pressure target value signal X and the pressure detection signal from the pressure detector 25, and the symbol Z
is a valve opening regulator output stop signal (ie, a signal that sets the valve opening regulator output to 0).

As explained above, according to the present invention, when controlling the strip temperature, it is possible to control the strip temperature accurately and with excellent responsiveness, which makes it possible to operate at a lower annealing temperature and to reduce the amount of fuel required. This has remarkable effects such as saving resources and energy.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a conventional strip temperature control method for a continuous annealing furnace, and FIG. 2 is an explanatory diagram of a strip temperature control method showing an embodiment of the method of the present invention.
FIG. 3 is an explanatory diagram showing a control mechanism for controlling the air-fuel ratio and suction pressure of the continuous annealing furnace shown in FIG. 2. 1... Heating furnace, 2... Tube, 3... Strip, 4... Furnace temperature detector, 5... Furnace temperature setting device, 6
...Furnace temperature controller, 7...Fuel flow rate controller, 11...
...Calculator, 12...Strip temperature detector, 13
...Furnace temperature controller, 14...Calculator, 15...Fuel flow rate controller, 21...Fuel flow rate detector, 22...
Combustion air flow rate detector, 23... Combustion air flow rate controller, 24... Control valve, 25... Pressure detector, 26
...Pressure regulator, 27...Damper, 28...Arithmetic unit, 29...Arithmetic unit, 30...Valve opening degree regulator, 3
1... Comparator.

Claims (1)

[Claims] 1. A strip temperature detector installed at the outlet of the continuous annealing furnace, a computer that controls the detected strip temperature to a predetermined value, a furnace atmosphere temperature detector, and a furnace atmosphere temperature that adjusts the furnace atmosphere temperature to the furnace atmosphere temperature target value from the computer. In a method for controlling the strip temperature of a continuous annealing furnace, which is equipped with a furnace atmosphere temperature controller that operates the fuel flow rate to control the strip temperature, when the annealing conditions change or the deviation between the detected value of the strip temperature and the target value is less than a predetermined value. The annealing conditions obtained in advance, the fuel flow rate,
It is characterized by using a relational expression between the furnace atmosphere temperature and the strip temperature, and temporarily setting the fuel flow rate to an excessive or insufficient fuel flow rate calculated from the relational expression at the calculated optimum control operation start time. Strip temperature control method for continuous annealing furnace.