JP3364091B2 - Temperature control method for continuous annealing furnace - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a temperature control method for a continuous annealing furnace. More specifically, the present invention relates to a temperature control method for a continuous annealing furnace used when annealing a material to be heated such as a steel plate.

[0002]

2. Description of the Related Art In recent years, a heat storage type radiant tube burner has been used in a continuous annealing furnace from the viewpoint of improving thermal efficiency and reducing the amount of NO _x gas generated (JP-A-2-
254210, JP-A-7-103435, etc.).

According to the heat storage type radiant tube burner, as shown in FIG. 1, the air sent from the fan 5 is sent to the burner 1a via the air supply pipe 4a, and the air from the fuel pipe 5a is sent. Fuel gas is burned in the burner 1a. At this time, the burner 1a is heated, but in order to effectively utilize the generated heat, the generated heat is generated by the heat storage body 2a.
Stored in. The combustion gas of the burner 1a is fed into the air supply pipe 4b through the inside of the radiant tube 3 and the heat storage body 2b, and is exhausted from the exhaust pipe 6. Also at this time, the heat of the exhaust gas is stored in the heat storage body 2b, and the heat is effectively used. By switching this operation with the switching valve 7, combustion of the burners 1a and 1b is alternately performed. As described above, the heat storage type radiant tube burner alternately burns the two burners 1a and 1b, and since the radiant tube 3 can be rapidly heated by the exhaust gas, high combustion efficiency can be obtained.
Significant energy savings can be achieved.

On the other hand, however, the heat storage type radiant tube burner has a structure in which the heat is not released to the outside by the heat storage bodies 2a and 2b, so that it is very long for cooling the continuous annealing furnace after combustion. The drawback is that it takes time.

Further, when the type of the steel sheet is switched while the steel sheet is being passed through the continuous annealing furnace, it is necessary to change the setting to the furnace temperature according to the steel sheet after the switching. If the furnace temperature according to the steel plate after switching is significantly lower than the furnace temperature according to the previous steel plate (for example, 50 ° C. or more lower), it takes a long time to cool, so the cooling process is not performed during the cooling. The plated portion has a drawback that the quality is poor.

Therefore, a furnace temperature switching coil (hereinafter referred to as an adjustment coil) is required, and the longer the cooling time, the larger the number of adjustment coils required. Wasted,
It has the drawback of reducing production.

Further, for example, when lowering the furnace temperature at the time of repairing the furnace, the furnace temperature is divided into small pieces so as to ensure an optimum cooling rate in order to prevent damage to the bricks of the furnace wall by quenching. Although the setting is changed and the temperature is lowered, the cooling time is required to be more than twice as long as in the case where the conventional radiant tube burner is used, which also causes a decrease in productivity.

As described above, what can be commonly said when changing the setting of the furnace temperature and when decreasing the temperature is that the response at the time of cooling is poor with respect to the setting change of the furnace temperature little by little.

Therefore, a method generally considered as a method of improving the response during cooling is to stop combustion during cooling and blow a considerable amount of cooling air into the radiant tube at once.

However, if such a method of blowing cooling air is adopted, when the setting of the furnace temperature is changed, if the combustion is stopped and the setting of the furnace temperature is changed again,
There is a risk that the time and effort required for ignition will increase and controllability will deteriorate, and if a considerable amount of cooling air is blown in, the furnace temperature will drop too much and the furnace temperature will fluctuate, which may result in poor quality. If the cooling rate is too high during cooling, the brick wall may be damaged, and if the cooling time is extended, productivity may deteriorate.Therefore, it is necessary to secure the optimal cooling rate. But as mentioned above,
Just by stopping the combustion and blowing a considerable amount of cooling air,
There is a drawback that it is difficult to secure the optimum cooling rate.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above prior art, and when changing the setting of the furnace temperature of the continuous annealing furnace, it can be cooled in a desired cooling time. An object is to provide a temperature control method for a continuous annealing furnace.

[0012]

SUMMARY OF THE INVENTION The present invention is a continuous heat storage type radiant tube burner in which burners are provided at both ends of the burner, and a porous heat storage material having air permeability is provided around the burners. A method for controlling the temperature of a type annealing furnace, in which the furnace temperature is controlled by the burning operation of the burners for alternately burning the burners and annealing the material to be heated, when changing the set temperature of the furnace to a low temperature or When lowering the furnace temperature to stop the operation, while carrying out the combustion operation of the burner, forced cooling air is supplied from the air supply pipe connected to one burner, and the other burner is supplied through the inside of the radiant tube. Cooling supplement by ventilating the forced cooling air to the air supply pipe connected to
Compensation is made in advance for continuous cooling
Examine the temperature record of heating-cooling of the annealing furnace,
Based on actual results, the continuous annealing furnace was brought to the prescribed temperature in the prescribed time.
Determine the amount of forced cooling air required to cool the
Forced cooling to the air supply pipe based on the controlled cooling air volume
TECHNICAL FIELD The present invention relates to a temperature control method for a continuous annealing furnace, which is characterized by ventilating exhaust air . Forced cooling in the cooling compensation
(A) Estimate the quantity according to the actual temperature and the secondary delay transfer function.
It is preferable to determine from the deviation from the constant model output.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, the temperature control method for a continuous annealing furnace of the present invention is provided with burners at both ends thereof, and a porous heat storage material having air permeability is provided around the burners. A method for controlling the temperature of a continuous annealing furnace using a heat storage type radiant tube burner consisting of, wherein the furnace temperature is controlled by the burning operation of the burner for alternately burning the burners to anneal the material to be heated, When changing the set temperature of to a low temperature or when lowering the furnace temperature to stop the operation of the furnace, while performing the combustion operation of the burner, the forced cooling air is supplied from the air supply pipe connected to one burner. The cooling compensation is performed by supplying the forced cooling air to the air supply pipe connected to the other burner through the radiant tube.
In the cooling compensation, heating the continuous annealing furnace in advance ~
Examine the cooling temperature record and based on the temperature record
To cool the continuous annealing furnace to a specified temperature in a specified time.
Determine the amount of forced cooling air required and add
Vent the forced cooling air to the air supply pipe.
It is characterized by making it.

As described above, according to the temperature control method for the continuous annealing furnace of the present invention, the forced cooling air is supplied from the air supply pipe connected to one burner of the heat storage type radiant tube burner, and the inside of the radiant tube is supplied. The means for ventilating the forced cooling air to the air supply pipe connected to the other burner via the means is adopted, and by adjusting the forced cooling air amount, the cooling time can be reduced regardless of the temperature setting change amount. The desired cooling time can be adjusted.

Next, one embodiment of the temperature control method for a continuous annealing furnace of the present invention will be described with reference to the drawings.

FIG. 2 is a schematic explanatory view showing one embodiment of a continuous annealing furnace used in the temperature control method of the continuous annealing furnace of the present invention.

In FIG. 2, (a) is a schematic plan view of the continuous annealing furnace, and (b) is a schematic sectional view taken along line AA of FIG. 2 (a).

In FIG. 2, a sheet passing roll 12 is arranged in the sheet passing portion of the material to be heated in the continuous annealing furnace 11.
A material to be heated (not shown) such as a strip is threaded onto the threading roll 12. Radiant tubes 3 and 3 are provided in upper and lower two stages between the threading rolls 12 and 12,
The material to be heated passes between the upper and lower radiant tubes 3, 3.

When the material to be heated is passed through the sheet passing roll 12, heat is removed from the material to be heated, and the heat is removed and the radiant tube 3 heats the continuous annealing furnace 11.
Furnace temperature is controlled. The furnace temperature at which the material to be heated is annealed in the continuous annealing furnace 11 varies depending on the type of material to be heated and cannot be unconditionally determined. The furnace temperature at the time of annealing the material to be heated in the continuous annealing furnace 11 is adjusted by adjusting the supply amount of fuel and air supplied into the radiant tube 3 and the strip speed of the material to be heated.
It can be adjusted appropriately.

The radiant tube 3 has a burner 1a,
1b is connected, and the burners 1a and 1b are provided with a switching valve 7
It is connected to the. The switching valve 7 is connected to a combustion heating controller 14 including a combustion gas flow controller (FIC) and a combustion air flow controller.

The furnace temperature of the continuous annealing furnace 11 is detected by a temperature detector 13 such as a thermocouple, and the result is transmitted to a temperature performance measuring device.

Next, for example, when the set temperature of the continuous annealing furnace 11 is changed to a low temperature in order to switch the type of steel sheet, or when the furnace temperature is lowered to stop the operation of the furnace, the continuous type of the present invention is used. The temperature control method of the annealing furnace becomes effective.

An embodiment of the temperature control method for the continuous annealing furnace of the present invention will be described with reference to the block diagram shown in FIG.

In FIG. 3 , a portion surrounded by a frame line A is an existing furnace temperature control unit for controlling the furnace temperature when the continuous annealing furnace is in operation, and a frame frame B is a frame. The enclosed portion is a cooling compensator for supplying forced cooling air when cooling the continuous annealing furnace.

In the furnace temperature control unit, 21 is a furnace temperature set value (SV), 22 is a temperature controller (TIC), 23 is a temperature control manipulated variable (MV), and 24 is a combustion gas flow rate controller (F).
IC), 25 is a combustion gas flow rate control valve, 26 is a combustion air flow rate control device (FIC), and 27 is a combustion air flow rate control valve.

First, in the existing furnace temperature control unit, when the material to be heated is annealed in the continuous annealing furnace, a regenerative radiant tube burner is used and the burners at both ends are alternately burned. Is set to the furnace temperature set value 21, and the furnace temperature is controlled by the temperature control device 22 so that the furnace temperature set value 21 becomes the set value. The control is performed by a combustion gas flow rate control valve 25 and a combustion air flow rate control valve 27, respectively, via a combustion gas flow rate control device 24 and a combustion air flow rate control device 26 connected to the temperature control device 22.
By adjusting the combustion gas flow rate and the combustion air flow rate.

Next, as described above, for example, when changing the set temperature of the continuous annealing furnace 11 to a low temperature in order to switch the type of steel sheet or when lowering the furnace temperature to stop the operation of the furnace. The temperature control method of the continuous annealing furnace of the present invention is effective.

The temperature control method of the continuous annealing furnace of the present invention is as follows.
Specifically, while controlling the furnace temperature by the furnace temperature control unit, at the time of cooling, the cooling compensating unit is operated in parallel in order to help the existing furnace temperature control unit.

The reason for this is that the cooling time required for cooling is long only with the existing furnace temperature control section, and the desired cooling time cannot be obtained, and the furnace temperature is kept constant only with the cooling compensation section. However, the temperature of the furnace is too low and the temperature control of the furnace is greatly disturbed.

Therefore, in order to stably secure the furnace temperature with respect to an arbitrary temperature setting, it is necessary to operate the existing furnace temperature control section and the cooling compensation section at the same time.

Further, it is preferable to carry out the burner combustion operation within a range in which the torches of the burners at both ends of the heat storage type radiant tube burner do not extinguish the fire. The reason why the torch of the burner is not extinguished is that it takes a long time to ignite the torch when the continuous annealing furnace is started up if the torch is completely extinguished.

Further, in the cooling operation of the continuous annealing furnace in the cooling compensator, forced cooling air was supplied from the air supply pipe connected to one burner and connected to the other burner through the inside of the radiant tube. This is performed by ventilating the forced cooling air to the air supply pipe.

In the cooling compensator shown in FIG. 3, 28
Is a control model (G _{(s) p} ) for cooling compensation. As the control model, for example, cooling compensation can be performed with a second-order lag transfer function. The secondary delay transfer function G
_{(s) p} is the formula (I):

[0034]

[Equation 1]

It is represented by

In the formula (I), K is a gain constant, e
^{-TS is a} dead time estimation transfer function, T _p1 and T _p2 are furnace temperature estimation time constants, and s is a Laplace operator.

Next, the furnace temperature (actual temperature) is detected by the temperature detector, and the result is measured by the actual temperature measuring device (P
V) 29. Based on the temperature, according to the second-order lag transfer function G _{(s) p} , the PI controller (PI) 3
The forced cooling air amount is determined by 0, and the limiter (LM) 3
1, the required air amount is transmitted to the combustion air flow rate control device 26, and the combustion air flow rate control valve 27 adjusts the combustion air flow rate.

In the present invention, the determination of the second-order lag transfer function G _{(s) p} represented by the formula (I) is previously shown in the actual temperature of heating to cooling of the continuous annealing furnace, for example, shown in FIG. This is done by examining the temperature performance (PV) with the waveform. Regarding the response of G _{(s) p,} the furnace temperature estimated time constants T _p1 and T _p2 are set so that the existing heating time is almost matched and the cooling time becomes the desired cooling time T (time between B and C).
To set. When you do not need control accuracy,
T _p1 and T _p2 may have the same numerical value, and when control accuracy is required, T _p should be adjusted to match the response waveform of the existing furnace.
The distribution of _p1 and T _p2 may be changed. The dead time estimation transfer function e ^−TS is also determined based on the ^acquired actual waveform.

In FIG. 4, the temperature rising curve is from the origin 0 to the time A, the steady state is from the time A to the time B, and the cooling curve is from the time B to the time D.

Next, when the heating of the continuous annealing furnace is finished at time B and the temperature is cooled to a predetermined temperature at time C, the second-order lag transfer function G _(s) represented by the formula (I) is given. _A temperature estimation curve SV1 is drawn according to _p .

Therefore, in order to be cooled to a predetermined temperature at time C after the end of heating, the amount of cooling air required to remove the energy represented by the shaded area in FIG. 4 ( The amount of forced cooling air) may be determined by the PI controller 30, the amount of forced cooling air may be adjusted by the combustion air flow rate control valve 27, and forced cooling air may be ventilated into the air supply pipe. However, the limiter 31 is the PI control device 30.
Output only positive values (not negative values)
To make adjustments. By adjusting in this way, even if the furnace temperature set value 21 changes to an arbitrary value, the desired cooling time T can always be secured during cooling.

In the second-order lag transfer function G _{(s) p} represented by the formula (I), the gain constant K is preferably set so as to satisfy K> 1. When the gain constant K is set in this way, during heating to steady state,
It is possible to control the output of the forced cooling air from the limiter 31.

[0043]

EXAMPLES Next, the temperature control method of the continuous annealing furnace of the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

Example 1 A heat storage type radiant tube burner as shown in FIG. 1 (tube outer diameter 178 mm, width 1000 mm from upper end of first straight pipe to lower end of second straight pipe, length 2000 m)
m) was used.

First, fuel gas (coke oven gas) was supplied from the fuel pipe 5a and air was supplied from the air supply pipe 4a to the burner 1a at an air ratio of 2.4, and after 30 seconds had passed, the same operation was performed. The operation of performing 30 seconds from the fuel pipe 5b and the air supply pipe 4b is repeated as one cycle, and while the steel sheet (temperature 400 ° C) is passed at a speed of 2 m / sec, the burners 1a and 1b are annealed to 600 ° C. A burning operation was performed.

After finishing the annealing of the steel sheet,
While performing the burning operation of the burner, by the second-order lag transfer function G _{(s) p} represented by the formula (I), cooling is completed in 1000 seconds (cooling temperature: 200 ° C. or less), P
The I control unit determines the forced cooling air amount, the limiter transmits the required air amount to the combustion air flow rate control unit, the combustion air flow rate control valve adjusts the combustion air flow rate, and the forced cooling air is supplied from one air supply pipe. It was supplied and the continuous annealing furnace was cooled. The result is shown by curve A of a to b in FIG.

Then, again, the steel plate
The burners 1a and 1b were annealed to anneal to 00 ° C.

After finishing the annealing of the steel sheet,
While performing the burning operation of the burner, the PI controller so that the cooling is completed again in 1000 seconds (cooling temperature: 400 ° C. or less) by the second-order lag transfer function G _{(s) p} represented by the formula (I). The amount of forced cooling air was determined by, and the flow rate of combustion air was adjusted by a limiter, and forced cooling air was supplied from one air supply pipe to cool the continuous annealing furnace. The result is shown by a curve B of cd in FIG.

Next, for comparison, the burners 1a and 1b for annealing the steel sheet to 900 ° C. are again carried out in the same manner as described above.
Burning operation was performed.

When the annealing is finished after passing the steel plate,
While performing the burning operation of the burner, it was allowed to cool to a cooling temperature of 400 ° C. or lower without supplying forced cooling air. The result is shown by a curve C of e to f in FIG.

From the results shown by the curves B and C in FIG. 5, the following can be understood. That is, when the annealing is finished after passing the steel sheet as in the conventional case, if the continuous annealing furnace is cooled to a cooling temperature of 400 ° C. or less when left to stand without supplying forced cooling air. Cooling time required 350
While it is 0 seconds or more (curve C in FIG. 5), when the annealing of the steel sheet is finished, forced cooling air is passed through the air supply pipe to force the continuous annealing furnace to be cooled. ,
Since the cooling time required to cool the continuous annealing furnace to a cooling temperature of 400 ° C. or less is about 1000 seconds (curve B in FIG. 4), the temperature control method of the present invention enables rapid continuous annealing. It can be seen that the furnace can be cooled and the cooling time can be controlled almost in accordance with the desired cooling time even for an arbitrary set value of the furnace temperature.

Further, from the results of the curves A and B of FIG. 5, the following can be understood. That is, in the cooling method of the present invention, the amount of forced cooling air required to cool the continuous annealing furnace to a predetermined temperature is determined in advance, and the forced cooling air is vented to the air supply pipe based on the amount of forced cooling air. When the cooling is set to be completed within a predetermined time, the cooling of the continuous annealing furnace can be completed when the predetermined time is reached. Therefore, if the switching temperature difference of the furnace temperature is large, the adjusting coil is required, and if the cooling time is long, the number of adjusting coils is increased and the productivity of the product is reduced, but as described above, If it is possible to cool the continuous annealing furnace within a predetermined time, the number of adjusting coils can be reduced,
There is an advantage that productivity can be improved.

[0053]

As described above, according to the temperature control method of the continuous annealing furnace of the present invention, when the annealing of the material to be heated is finished, the air supply pipe is used while the burner is being burnt. Then, since the means of forcing forced cooling air into the radiant tube is adopted, there is an effect that the time required for cooling can be greatly shortened.

Further, in the temperature control method for the continuous annealing furnace of the present invention, the actual temperature of heating to cooling of the continuous annealing furnace is checked in advance, and the continuous annealing furnace is cooled to a predetermined temperature based on the actual temperature. The amount of forced cooling air required to do so is determined, and when the forced cooling air is ventilated to the air supply pipe based on the amount of forced cooling air, cooling of the continuous annealing furnace can be completed in a predetermined time. The effect of being able to be played is exhibited.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing an embodiment of a heat storage type radiant tube burner used in a conventional temperature control method for a continuous annealing furnace.

FIG. 2 is a schematic explanatory view showing an embodiment of a continuous annealing furnace used in the temperature control method for the continuous annealing furnace of the present invention.

FIG. 3 is a block diagram showing an embodiment of a temperature control method for a continuous annealing furnace of the present invention.

FIG. 4 is a schematic explanatory diagram of heating-cooling curves in the temperature control method for the continuous annealing furnace of the present invention.

FIG. 5 is a heating-cooling curve in an example of the temperature control method for the continuous annealing furnace of the present invention.

[Explanation of symbols]

1a burner 1b burner 2a Heat storage 2b Heat storage 3 radiant tubes 4a Air supply pipe 4b Air supply pipe 11 Continuous annealing furnace

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) F23N 5/02 350 F23D 14/12 F23D 14/66 F23L 15/02

Claims (2)

(57) [Claims] 1. Burners are provided at both ends of the burner, respectively.
A method for controlling the temperature of a continuous annealing furnace using a heat storage radiant tube burner in which a porous heat storage material having air permeability is provided around the burner, and the burners are alternately burned to be heated. While controlling the furnace temperature by the burner burning operation to anneal the material, when changing the set temperature of the furnace to a low temperature or when lowering the furnace temperature to stop the operation of the furnace, while performing the burning operation of the burner , Forcibly cooling air is supplied from an air supply pipe connected to one of the burners, and cooling compensation is performed by ventilating the forced cooling air to the air supply pipe connected to the other burner through the inside of the radiant tube , The cooling supplement
In advance, the temperature from heating to cooling of the continuous annealing furnace
The actual temperature is checked, and at a specified time based on the actual temperature.
The strength required to cool the continuous annealing furnace to the specified temperature during
Determine the controlled cooling air amount and based on the forced cooling air amount
A forced cooling air is ventilated through the air supply pipe . 2. A forced cooling air amount in the cooling compensation.
Is an estimated model according to the actual temperature and the second-order lag transfer function.
The temperature control method for a continuous annealing furnace according to claim 1, wherein the temperature is determined from a deviation from the Dell output .