JPH06271946A - Method for controlling temperature rising in heating furnace - Google Patents

Abstract

PURPOSE:To enable the automation of temp. rising in a heating furnace, to prevent excess speed of the temp. raising in completing the temp. rising within a short time. CONSTITUTION:The temp. DT in the heating furnace is detected to examine whether the detected temp. is lower than the pre-fixed intermediate setting temp. T1, flow rate of fuel gas (COG flow rate and AIR flow rate) for supplying to burner is kept to be constant. When the detected temp. is higher than the intermediate setting temp. T1 and lower than the pre-fixed aimed setting temp. T2, according to the raising speed of the detected temp., the flow rate of fuel gas (COG flow rate and AIR flow rate) for supplying to the burner is automatically adjusted. By this method, always the suitable temp. rising speed is preserved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to combustion control of a heating furnace provided in, for example, a continuous steel strip processing facility having an annealing furnace, and more particularly to temperature rise control for restarting operation from a dormant state.

[0002]

2. Description of the Related Art For example, in a continuous steel strip processing facility having an annealing furnace, a heating furnace is provided, and during normal operation, for example, the furnace temperature of the heating furnace is maintained at 750 degrees C. The combustion state is controlled. When equipment failure or abnormality occurs, or when performing equipment maintenance, operation is suspended, but in that case the furnace temperature of the heating furnace falls to room temperature, so when restarting operation It is necessary to raise the furnace temperature of the heating furnace to a predetermined operating temperature.

In the case of raising the temperature of the heating furnace of this kind, the temperature raising control has been conventionally performed by a manual operation of an operator. That is, the opening of the control valve for adjusting the flow rate of the fuel gas supplied to the burner of the heating furnace can be remotely controlled by the operator, and the operator monitors the temperature detected by the temperature measuring device. Then, the opening degree of the flow rate control valve is sequentially adjusted so that the temperature rising curve matches a predetermined target temperature rising curve.

[0004]

Usually, it takes several hours to raise the temperature of the heating furnace from room temperature to the operating temperature. In the conventional method, a skilled operator must monitor the temperature and adjust the valve opening degree from the start to the completion of the temperature rise, so that the operator's burden is very large. . Moreover, since the adjustment is performed by human senses, there are cases where the individual temperature difference is large and an appropriate temperature raising operation is not performed.

That is, if the heating rate is too fast, heat buckles are likely to occur in the steel strip in the furnace, and if the heating rate is too slow, it is necessary to wait unnecessarily for a long time before restarting the operation. And the operating rate of the equipment will decrease.

However, it is extremely difficult to control the rate of temperature rise to be always constant. For example, immediately after the start of the temperature rise, the temperature rise rate greatly changes even with a slight adjustment, and there is a large time lag between the time when the adjustment is performed and the time when the effect actually appears in the furnace temperature. Therefore, it is difficult to automate the temperature rise control.

Therefore, it is an object of the present invention to make it possible to automate the temperature rise control, prevent the occurrence of a heat buckle due to the temperature rise, and complete the temperature rise in the shortest possible time.

[0008]

In order to solve the above problems, in the present invention, a predetermined fuel gas is supplied to a burner of a heating furnace through a flow rate control valve, and the heating furnace is heated by the burner. In a heating furnace temperature rising control method for raising the temperature from a temperature near room temperature to an operating temperature: The temperature of the heating furnace is detected, and when the detected temperature is lower than a predetermined intermediate set temperature, fuel supplied to the burner When the gas flow rate is maintained constant and the detected temperature is equal to or higher than the intermediate set temperature and lower than the predetermined target set temperature, the flow rate of the fuel gas supplied to the burner according to the rising rate of the detected temperature. Adjust automatically.

[0009]

When the temperature of the heating furnace is close to room temperature, for example, the temperature of the furnace is apt to rise very much, and even if a slight amount of combustion is adjusted, the temperature rising rate tends to change greatly. Further, when the temperature of the heating furnace is relatively low, the amount of combustion required to obtain a preferable temperature rising rate is very small and close to the lower limit of the combustion amount of the combustion equipment, but when the furnace temperature is close to the operating temperature, the combustion If the amount is not increased to some extent, the rate of temperature rise will be slow. Further, the adjusted flow rate of the fuel gas becomes fine near the lower limit combustion amount, but the fine adjustment of the flow rate near the lower limit combustion amount is extremely difficult due to the structure of the equipment.

However, in the present invention, when the furnace temperature is relatively low (below the intermediate set temperature), the flow rate of the fuel gas is kept constant, so it is not necessary to perform delicate flow rate adjustment, and combustion Since the influence of the change in the amount on the change in the furnace temperature is also irrelevant, the unstable control such as hunting can be prevented, and the temperature rising rate can be prevented from becoming excessive. Also, after the furnace temperature has risen to some extent (when it is at or above the intermediate set temperature), the flow rate of the fuel gas supplied to the burner is automatically adjusted according to the detected temperature rise rate, so an appropriate temperature rise is achieved. The speed can be obtained, and the heating can be completed in a short time. When the furnace temperature is relatively high, it is not necessary to finely adjust the flow rate, so there is no risk of unstable control results, and it is possible to maintain an appropriate heating rate at all times. Also, this type of control can be easily automated.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of the main part of the apparatus of one embodiment. The heating furnace 30 shown in FIG. 1 is installed in a continuous processing facility for steel strips having an annealing furnace, and the steel strip 34 is heated to a predetermined high temperature through the heating furnace 30. In this embodiment, a radiant tube 31 is provided as a burner for heating the heating furnace 30. That is, radiant tu
By supplying a predetermined fuel gas into the tube of the tube 31, and burning the fuel gas in the tube, the radiant tube 31
To heat the heating furnace indirectly. The pipe 10 is supplied with coke gas COG, and the pipe 20 is supplied with air AIR. The coke gas COG passes through the cutoff valve 11, the flow meter 12, and the flow rate control valve 13, and enters the inlet side of the radiant tube 31 from the pipe 15. Further, the air AIR passes through the flow meter 21 and the flow rate control valve 22 and enters the inlet side of the radiant tube 31. Although shown in FIG. 1 with a simple structure, a large number of radiant tubes 31 are actually installed in the heating furnace 30, and these radiant tubes are roughly divided into five sets of combustion zones. -Z1, Z2, Z3
It is divided into Z4 and Z5. Since these combustion zones have the same configuration except the size and shape, only the combustion zone Z1 will be described here. The coke gas COG and the air AIR are provided in the pipe 10 respectively.
20 and 20, a coke gas COG and air AIR are supplied to each radiant tube from each of the branched flow paths. A pilot burner 32 is installed on the inlet side of the radiant tube 31, and the pilot burner 32 ignites a fuel gas supplied thereto, that is, a mixture gas of coke gas COG and air AIR,
The ignited fuel gas enters the radiant tube 31. The exhaust gas after combustion goes through a pipe 33 to a predetermined exhaust gas passage.

The opening degree of the flow rate adjusting valve 13 is controlled by the flow rate adjusting meter 60, and the opening degree of the flow rate adjusting valve 22 is controlled by the flow rate adjusting meter 50. The flow rate controller 60 controls the flow rate of the coke gas COG passing through the pipe 10 to match the target value SV0. The flow rate controller 50 determines the target flow rate of the air AIR based on a predetermined function with the target flow rate value SV0 of coke gas as a parameter, and the pipe 2
The flow rate of the air AIR passing through 0 is controlled to match its target value. Each of the flow rate controllers 50 and 60 includes a coke gas flow rate FG detected by the flow meter 12 and a flow meter 21.
The air flow rate FA detected by is fed back.

In this embodiment, the relationship between the coke gas flow rate and the air flow rate is set as shown in FIG. That is, the ratio of the air AIR in the fuel gas is high when the combustion amount is small, and the air AIR in the fuel gas when the combustion amount is large.
Is low.

Coils applied to the flow controllers 50 and 60
The target flow rate SV0 of gas is generated by the furnace temperature controller 40. The furnace temperature controller 40 has five parameters,
That is, the detection furnace temperature DT, the intermediate temperature T1, the target flow rate SV, the target temperature T2, and the temperature increase rate RT are applied. Detection furnace temperature DT
Is the actual temperature of the zone Z1 in the heating furnace 30 detected by the furnace thermometer 35, and the intermediate temperature T1, the target flow rate SV, the target temperature T2, and the rate of temperature increase RT are predetermined. The intermediate temperature T1, the target flow rate SV and the target temperature T
2 can be set individually for each zone, and the rate of temperature rise RT can be set commonly for all zones, and each value can be adjusted by manual operation of the operator. In this embodiment, the values of the parameters in the initial state are that the intermediate temperature T1 is 400 degrees C, the target temperature T2 is 750 degrees C, and the temperature rising rate RT is 300.
It is C / hour.

The contents of the operation of the furnace temperature controller 40 are shown in FIG. The operation of the furnace temperature controller 40 will be described with reference to FIG.
In step 51, initialization is first executed, and further information of four parameters T1, SV, T2 and RT is read. In the next step 52, the latest furnace temperature DT detected by the furnace thermometer 35 is input. In the following step 53, the detection furnace temperature DT
And the intermediate temperature T1. When DT <T1, the process proceeds to step 54, and otherwise, step 55
Then, the detected furnace temperature DT is further compared with the target temperature T2. If DT is T1 or more and less than T2, the process proceeds to step 56, and if DT is T2 or more, the process proceeds to step 57.

That is, for example, when starting to raise the temperature of the heating furnace from room temperature, the process first proceeds to steps 53 to 54, then returns to step 52 to input a new furnace temperature DT, and repeatedly executes these processes. And the furnace temperature DT is the intermediate temperature T
Ascend to 1, go through steps 53 through 55 to 56
And then returns to step 52 to input a new furnace temperature DT and repeats these processes. And furnace temperature D
When T rises to the target temperature T2, steps 55 to 5
7, the process of step 57 is repeatedly executed.

In step 54, the value of the target flow rate SV input to the furnace temperature controller 40 is set as the target flow rate SV0, and the value is directly output to the flow rate controllers 50 and 60. That is,
When the furnace temperature DT is between room temperature and less than T1, the combustion amount is maintained constant as shown in FIG. Further, as can be seen from FIG. 3, the combustion amount at this time is very small and is close to the lower limit combustion amount of the equipment. Therefore, as can be seen from FIG. 4, the fuel gas at this time has a low mixing ratio of the coke gas COG and a high mixing ratio of the air AIR.

In step 56, first, the difference between the latest furnace temperature DT and the value of DT0 which holds the previous furnace temperature is registered in the register Δ.
Store at T. Next, register the latest furnace temperature DT with register D
Store in T0 and store ΔT in a predetermined memory. Then, an average value thereof is calculated from the latest n pieces of ΔT, further converted into a temperature increase amount per unit time, that is, a temperature rising rate, and the result is stored in the register DRT. Next, a predetermined function f () is calculated using the difference (temperature increase rate error) between the content of the register DRT and the set temperature increase rate RT as a parameter, and the result is stored in the register .DELTA.SV. The value of ΔSV corresponds to the adjustment amount of the combustion amount required to bring the temperature increase rate error close to zero. Therefore, next, a value obtained by adding ΔSV to the value of SV0 up to that point is set as a new SV0, and the value of SV0 is output to the flow rate controllers 50 and 60. That is, when the furnace temperature is between T1 and T2, as shown in FIG. 3, the combustion amount is automatically adjusted so that the temperature rising rate becomes constant (matches RT).

In step 57, the latest furnace temperature DT detected by the furnace thermometer 35 is input, and the difference (temperature error) between DT and the target temperature T2 is used as a parameter for a predetermined function (f (): step 56). Different) and store the result in register ΔSV. The value of ΔSV is equal to the temperature error
It corresponds to the amount of adjustment of the amount of combustion required to approach
Therefore, next, a value obtained by adding ΔSV to the value of SV0 up to that point is set as a new SV0, and the value of SV0 is output to the flow rate controllers 50 and 60. That is, the combustion amount is automatically adjusted so that the furnace temperature DT is maintained at the target temperature T2 after the furnace temperature has risen to the target temperature (see FIG. 3).

[0020]

As described above, according to the present invention, when the furnace temperature is relatively low (below the intermediate set temperature), the flow rate of the fuel gas is kept constant, so that a delicate flow rate adjustment is performed. It is not necessary to do so, and the effect of the time delay until the change in the combustion amount appears in the change in the furnace temperature becomes irrelevant, so unstable control such as hunting can be prevented, and the temperature rise rate becomes too high. Can be avoided. Also, after the furnace temperature has risen to some extent (when it is at or above the intermediate set temperature), the flow rate of the fuel gas supplied to the burner is automatically adjusted according to the detected temperature rise rate, so an appropriate temperature rise is achieved. The speed can be obtained, and the heating can be completed in a short time. When the furnace temperature is relatively high, it is not necessary to finely adjust the flow rate, so there is no risk of unstable control results, and it is possible to maintain an appropriate heating rate at all times. Also, this type of control can be easily automated.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of the configuration of an apparatus for implementing the present invention.

FIG. 2 is a flowchart showing the operation of the furnace temperature controller 40 of FIG.

FIG. 3 is a graph showing changes in the combustion amount and the furnace temperature in the example.

FIG. 4 is a graph showing the correlation between coke gas flow rate and air flow rate.

[Explanation of symbols]

10, 15, 20, 33: Piping 11: Shutoff valve 12, 21: Flow meter 13, 22: Flow control valve 30: Heating furnace 31: Radiant tube 32: Pilot burner 34: Steel strip 35: Furnace temperature Total 40: Furnace temperature controller 50, 60: Flow controller T1: Intermediate temperature T2: Target temperature SV: Target flow rate RT: Rate of temperature rise

Claims (1)

[Claims] 1. A heating furnace, in which a predetermined fuel gas is supplied to a burner of a heating furnace through a flow rate control valve to raise the heating furnace from a temperature near room temperature to an operating temperature. In the control method: the temperature of the heating furnace is detected, and when the detected temperature is lower than a predetermined intermediate set temperature, the flow rate of the fuel gas supplied to the burner is kept constant, and the detected temperature is the intermediate set temperature. When the temperature is lower than the predetermined target set temperature above, the flow rate of the fuel gas supplied to the burner is automatically adjusted according to the detected temperature rising rate. Control method.