JPS5858416B2 - How to operate a soaking furnace - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method of operating a soaking furnace.

In detail, this is an improved method of operating a soaking furnace that heats steel ingots with unsolidified parts, such as rimmed, killed, and semi-killed steel, and is an energy-saving method of operating a soaking furnace that minimizes fuel consumption. It is related to.

In general, the operational steps of a soaking furnace can be broadly classified into loading the steel ingot into the furnace, charging fuel into the furnace, and extracting the steel ingot from the furnace.

This article describes the conventional method of loading steel ingots into the furnace, fuel injection, and extraction.

(1) To prevent the occurrence of internal defects, the solidification rate must be 7.
The prevailing idea is that the solidification rate is important until it reaches 0 to 80%, and conventionally the solidification rate is 30 to 50% without bleeding.
% solidification rate, heat is dissipated into the atmosphere outside the mold to achieve a solidification rate of 70 to 80%, and as soon as this solidification rate is reached, the mold is charged into the furnace, and as soon as charging is completed. Fuel is being put into the furnace.

(n) Modern soaking furnaces use a fuel input system that controls the flow rate of fuel input into the furnace (continuous operation, intermittent operation, 0NOFF operation) until the furnace temperature reaches a set value. After the furnace temperature reaches the set value, the furnace temperature is controlled using the set value as the target value (continuous, intermittent, 0N
- a combustion control device that performs furnace temperature control (operated OFF);
Equipped with a furnace temperature detector to detect furnace temperature.

Conventionally, fuel injection is started at the same time as charging is completed, and various fuel injection flow rate curves shown in FIGS. 1 to 5 are employed, as is well known, for fuel injection until the furnace temperature reaches a target value.

Each curve is illustrated with the horizontal axis representing the elapsed time and the vertical axis representing the heat flow rate and furnace temperature. In the figure, the broken line 1 is the furnace temperature, and the solid line 2 is the fuel flow rate curve.

In addition, the thick solid line in the figure corresponds to the flow rate control area by the combustion control device of the soaking furnace during the heating period, and the solid line corresponds to the furnace temperature control area.

The curves shown in Figures 1 to 5 are (1) maximum flow rate constant curve, (2) flow rate gradient control curve, (3) flow rate multi-stage control curve, (4) two-stage flow rate heating curve, (5) It is called the temperature gradient control curve.

An outline of each of these curves will be explained below.

(1) Maximum flow rate constant curve The curve shown in Figure 1 indicates that the maximum amount of fuel is introduced from the beginning of the heating period to reach the final standard temperature in the furnace in the shortest possible time, and the maximum amount of fuel is introduced throughout the heating period. It lasts for a long time, and when the final reference temperature in the furnace is reached, the fuel flow rate is suppressed and the temperature is equalized.

In this method, the heating of the steel ingot is thought to be rate-limited by heat transfer, so it has the following drawbacks.

In other words, although the amount of heat obtained by the steel ingot at the initial stage of heating is large,
When the surface temperature rises and approaches the set temperature, only the amount of heat that diffuses from the surface of the steel ingot into the steel ingot enters the steel ingot, and the furnace temperature is kept high until the heat is sufficiently diffused inside the steel ingot. A soaking period is required.

As a result, most of the combustion heat is discharged outside the furnace as waste gas sensible heat, resulting in a very high fuel consumption rate.

To address these shortcomings, measures have been taken to slightly lower the maximum amount of fuel input (design value of burner capacity), but this reduction in the amount of input slows down the time it takes to reach the set temperature. The time will be extended, and in the end, it will not be possible to reduce the fuel consumption rate.

Most conventional ACC (automatic combustion device) controls have adopted this method.

However, with the introduction of program setters into the ACC components and the development of DDC computers, the development of various flow rate curves described below has progressed.

(2) Flow rate gradient control curve Figure 2 shows a constant flow rate gradient curve (straight line), a
``b'' minimizes the initial injection of fuel and raises the temperature at a constant slope, and ``b'' raises the temperature by changing the initial injection and the slope gradient.

The purpose of this is to measure energy saving with respect to the constant maximum flow rate curve (1).

(3) Flow rate multi-stage control curve Figure 3 shows the flow rate multi-stage control curve, where a is a type in which fuel is added in steps to raise the temperature, and b is called two-peak heating, in which fuel is increased or decreased. It raises the temperature.

Specifically, method a (Japanese Unexamined Patent Publication No. 52-120208) is a unit time obtained by calculating the heat input and output of the soaking furnace at consecutive instants during the heating period of the soaking furnace. Fuel is added so that the absorbed heat of the steel ingot remains constant, and the amount of heating fuel input is increased step by step, and the timing of fuel increase is determined so that the slope of the tangent to the furnace temperature rise curve is at the start of heating or This is done so that the slope becomes 1/2 to 1/3 of the slope when fuel increases.

Method b is a method of more effectively utilizing the internal sensible heat of a steel ingot whose center is unsolidified (Japanese Unexamined Patent Publication No. 52-39510). The fuel is supplied to the furnace at the maximum flow rate within a preset range for a short period of time at the beginning of heating, and then the fuel supply amount is reduced to the same amount as during soaking to gradually raise the temperature inside the furnace. At the time when the center of the steel ingot solidifies, the fuel supply amount is maximized again and the steel ingot is heated.

(4) Two-stage flow rate heating curve A in Figure 4 is a curve called impulse heating, and b is a curve called two-stage heating. A method that simplifies the flow rate control in Figure 3 and heats by repeating minimum and maximum fuel injection. It is.

It is well known that this method is used because the air-fuel ratio can be controlled with high precision and the control method is simple.

The impulse heating method is described in Japanese Unexamined Patent Publication No. 5, 1973 as a method for preventing uneven heat of steel ingots.
3-112212, in which fuel is injected at a constant flow rate until the temperature inside the ready furnace reaches the set value.
After the inside of the furnace reaches the set value, the combustion amount is minimized or completely stopped during low-load combustion, while the combustion amount is intermittently increased, and by repeating this operation, the temperature of the surrounding air inside the furnace is made almost uniform. It is.

The two-stage heating method b is presented in JP-A-52-142611, and is based on the effective use of the solidification heat generated until the unsolidified part of the steel ingot is completely solidified, and the heat dissipation from the high-temperature part inside the steel ingot. The steel ingot is heated by equalizing heat through heat diffusion and ensuring an optimal air-fuel ratio, thereby further improving the fuel consumption rate.The steel ingot, which has an unsolidified portion, is charged into a soaking furnace. death,
This steel ingot is heated until the solidification of the steel ingot is completed using a constant minimum fuel flow rate that can maintain the furnace temperature slightly higher than the cold point at the time of completion of solidification, and the steel ingot is heated from the time of completion of solidification to the maximum The steel ingot is heated and baked to a predetermined rolling temperature using a constant fuel flow rate of 60% or more of the input amount.

(5) Temperature gradient control curve As shown in Figure 5, the temperature is raised by controlling the temperature gradient.
Temperature control is a temperature increase curve that takes into account not only energy savings but also the impact on quality.

This control curve eliminates the excessive heat supply of the constant maximum flow rate line in (1) above, and for example,
It is presented in Publication No. 088.

The characteristics of conventional flow curves have been described above, but these methods are based on cold point 5, which is the temperature history of the steel ingot shown in Figure 6.
, hot point 3, and average temperature 4 are linked to the temperature distribution heat transfer calculation of the steel ingot, and it is possible to save energy for the constant maximum flow rate method in (1), and to improve the efficiency from the soaking furnace instrumentation and control side. Advantageous methods have been applied in consideration of control methods, relationships with NOx, etc.

However, as will be described later, none of these curves can be said to be a method that maximizes the energy saving effect (minimizes the amount of fuel used).

(III) Regarding the extraction method, the flow rate is controlled by continuous or intermittent operation of the fuel flow rate, and after the furnace temperature reaches the set value, the furnace temperature is maintained at the set value as shown in flow rate curve 2 in Figures 1 to 5. Similarly, continuous and intermittent flow rate operations are performed, and the soaking time for soaking the steel ingot is quite long, after which the steel ingot is extracted.

As detailed above, the conventional method of operating a soaking furnace is as follows: (1) Cutting the mold at a solidification rate of 30 to 50%, solidifying outside the furnace or mold until the solidification rate reaches 70 to 80%, and Since it is charged into the furnace at the same time as it solidifies to ~80%, the sensible heat during the solidification process of ~70 to 80% is not effectively utilized.

(2) Fuel injection is started at the same time as charging, and the flow rate is controlled until the set furnace temperature is reached, but the injection flow rate curve at this time is not the minimum curve for the amount of fuel used.

(3) After reaching the set furnace temperature, a fairly long soaking period is required before extraction, and according to the knowledge of the present inventors, this soaking period can be eliminated, so the conventional method reduces the amount of fuel used. It is very difficult to find an energy-saving reactor operation method that minimizes the

In view of the above circumstances, from the perspective of minimizing fuel consumption, (1) the timing of extraction of steel ingots from the soaking furnace (especially regarding the necessity of the soaking period);

) (2) Timing of charging the steel ingot to the soaking furnace (30-50
Regarding the necessity of % die cutting and 70-80% charging method) (3)
We investigated the fuel input curve from charging to extraction that minimizes the amount of fuel used.

Based on the results of this study, the method of operating a soaking furnace with minimal fuel consumption according to the present invention has been developed, and the gist of the present invention is as follows.

Until the furnace temperature reaches the set value, the input fuel flow rate is controlled. After reaching the set value, the furnace temperature is controlled using the set value as the target value. In a soaking furnace for steel ingots equipped with a detector, 70~
A steel ingot with a solidification rate of 80% or less is charged into the furnace and the solidification rate is 70-80%.
Under the prerequisites that fuel is not added until the predetermined solidification rate is reached, and fuel injection is started when the predetermined solidification rate is reached, the unsolidified rate is such that internal cracks do not occur during blooming. The minimum in-furnace time necessary to obtain a soaked steel ingot at a temperature equal to or higher than the minimum temperature during rolling that does not cause surface cracks during rolling is determined, and the time is the addition of the shortest in-furnace time to the charging time,
If the horizontal axis is the time at which the input flow rate reaches a predetermined flow rate that is less than the maximum flow rate, and the time at which the furnace temperature reaches a predetermined set value from the minimum temperature during rolling, and the vertical axis is the flow rate, then the input start time is With respect to the straight line connecting the above flow rate at the time of charging time plus the shortest in-furnace time, the flow rate curve that curves downward at the minimum usable flow rate is calculated based on the thermal condition of the steel ingot and the soaking time. The steel ingot is charged at the charging solidification rate determined by a formula using a regression coefficient depending on the furnace condition, and when the charging solidification rate is reached, fuel injection is started, and thereafter the flow rate is controlled along the flow rate curve. This is a method of operating a soaking furnace in which a steel ingot is extracted immediately when the furnace temperature reaches the set value.

In other words, in the conventional steel ingot heating method, the input flow rate curve becomes linear over time until the set furnace temperature is reached, whereas under the temperature increasing conditions of the present invention, Sensible heat is used as a heat source in the initial stage of temperature rise, so
The furnace temperature can be raised according to a curve curving downward.

The method of the present invention will be explained in detail below.

First, we will discuss the results of a study on the timing of extracting steel ingots from a soaking furnace.

Figure 7 shows the relationship between the minimum temperature of the steel ingot during blooming rolling and the occurrence of surface cracks during blooming rolling, as well as the unsolidified rate during blooming rolling,
The results of investigating the relationship with the occurrence of internal cracks during blooming rolling are shown. Surface cracks occur when the temperature is 850° C. or lower, while internal cracks occur when the unsolidified rate is 20% or higher.

That is, the minimum temperature of the steel ingot during blooming rolling is set to 850°C or higher,
Furthermore, if the solidification rate is set to 20% or less, a specified steel billet with good quality and properties can be obtained by rolling without forming cracks inside the surface during blooming rolling.

Therefore, in the soaking furnace, it is only necessary to obtain a steel ingot with a temperature of 850° C. or higher and an unsolidified rate of 20% or less during the above-mentioned blooming rolling.

In other words, considering the handling time from extraction of the steel ingot from the soaking furnace to rolling, the temperature should be at least 850°C during blooming.
As mentioned above, if the timing is such that the steel ingot has an unsolidified rate of 20% or less, the quality is good even if the steel ingot is extracted from the soaking furnace without the soaking period.

Next, we will discuss the timing of charging the steel ingot into the soaking furnace.

Conventionally, as shown in Figure 8, the coagulation rate is (30~50)%~(70~
A solidification rate rate of up to 80% is important for preventing the occurrence of internal defects, and this rate can be obtained in the atmosphere outside the mold and outside the furnace. 80
)%, solidify outside the mold and outside the furnace to (70-80)%
As mentioned above, the fuel is charged into the furnace as soon as the fuel reaches a predetermined value, and the fuel is charged into the furnace as soon as the charging is completed.

Regarding this point, various studies were conducted from the viewpoint of energy saving, and as shown in Fig. 9, even if the mold is cut at a solidification rate of 30 to 50% and then charged into the furnace, the fuel will be removed immediately after charging is completed. If the fuel is not charged, that is, if the fuel is stopped, the solidification rate is almost the same as that outside the mold or outside the furnace, and the solidification rate is 70 to 80% of that of conventional charging or fuel injection. It has been found that it is possible to reach a solidification rate, and that during this solidification process, the amount of heat that was conventionally dissipated into the atmosphere can be retained in the steel ingot.

That is, Figures 8 and 9 above show the transition of the coagulation rate.
In FIG. 8, 6 is a solidification curve inside the mold, 7 is a curve outside the mold and outside the furnace, and 8 is a curve inside the fuel charging furnace.

9 in Figure 9 is the curve inside the mold and outside the furnace, 10 is the fuel injection stop,
The curve 11 in the furnace is the curve in the fuel-injected furnace.

In this way, the start of fuel injection is the same as before, with a solidification rate of 70~
80%, but from (30-50)% to (70-80%)
)% differs from the conventional method in that it solidifies in the furnace with fuel input stopped to obtain an energy-saving effect.

The reason why the charging is started at the same timing as in the conventional method is to achieve a solidification rate of 70 to 80% or more at almost the same speed as in the conventional method.

Next, we will discuss the fuel input curve from charging to extraction, which requires the minimum amount of fuel used.

That is, as mentioned above, a steel ingot with a solidification rate of 70 to 80% or less is charged into a furnace, and fuel is not input until the solidification rate reaches a predetermined solidification rate of 70 to 80%. Under the prerequisites for starting the charging, the above-mentioned unsolidified rate is maintained so that internal cracks do not occur during blooming, and the temperature is soaked at a temperature higher than the minimum temperature during blooming and rolling that does not cause surface cracks. The shortest in-furnace time required to obtain a steel ingot is determined, and at the time when the shortest in-furnace time is added to the charging time, the input fuel amount reaches a predetermined flow rate that is less than the maximum flow rate, and the furnace temperature is at the same time as the rolling time. When a predetermined set value is reached from the minimum temperature of With respect to the flow rate straight line that connects the flow rate with the above flow rate, a flow rate curve that curves downward and becomes the minimum usable flow rate is determined by an equation using regression coefficients depending on the thermal conditions of the steel ingot and the furnace conditions of the soaking furnace.

The shortest in-furnace time is the in-furnace time at which a soaked steel ingot with no internal or external defects can be obtained during blooming rolling, no matter what fuel injection pattern is adopted.

This time is set as 2.5 to 3 hours, for example, depending on the steel ingot size, steel type, or product type (for example, the direction of thick plates, hot coils, cold coils, etc. is on the front side).

Therefore, in the charging, charging, and extraction of the furnace operation method of the present invention, as shown in FIG. )
The flow rate is controlled according to the above, and when the furnace temperature reaches the set value, extraction of the steel ingot starts immediately without taking the conventional soaking period.

Note that the furnace temperature is controlled until the extraction is complete.

In the drawings, 29 indicates a furnace temperature curve, and 30 indicates a surface temperature curve of the steel ingot.

Next, a specific example of the method for determining the flow rate curve will be described.

In Fig. 11, T1 is the charging completion time, T2 is the fuel injection start time, 'rs is the shortest in-reactor time, and T3 (-T1+Ts).
is the extraction start time, T4 is the extraction completion time, T (Foff)
= T2- T is the fuel injection/stop time, and T (Fon) is the fuel injection time plus the flow rate control time.

Qo is the amount of naturally flowing fuel when fuel injection is stopped, and is zero (uncontrollable) or a very small value close to zero.

Ql is equal to or slightly smaller than the maximum input fuel flow rate Qmax which is fixed by the combustion system of the soaking furnace.

The above time T1. T2. T3 and time T8゜T(Fo
ff) and T(Fon) are determined as follows.

The time T1 is the time when charging of a steel ingot with a solidification rate of 80% or less at the time of charging is completed, and then the shortest in-furnace time Ts is determined from, for example, the steel ingot size, steel type side or type table, and the extraction start time is determined. T3 (=T1+Ts) is determined.

Next, based on the solidification rate at the time of charging (calculated value) and the actual (or assumed) furnace temperature, fuel injection is stopped at the time of charging based on steel ingot heat transfer calculations, and a solidification rate of 80% is reached in the furnace. Time T (Foff) is determined, time T2 (= T1 + T (Foff)), time T (F
on)=Ts-T(Foff).

In the same figure, 12 is (elapsed time X1 flow rate y) = ('
r2. QO) and (x, y)=(T3.Ql).

Reference numeral 13 indicates a flow rate curve that curves downward with respect to the flow rate straight line and is the minimum usable flow rate, which is adopted by the present invention.

Now, assuming that the flow rate curve 13 is controlled by five stages of gradient time as shown in Fig. 12, (1) Conditions at time T1; (setting conditions) ■ Solidification rate at the time of charging 80% or less ■ Steel ingot brought in Heat Xkm/T (2) At time T2 (turn-off time T
=) Conditions at ) = (setting conditions) ■ Up to 80% solidification rate in the furnace (3) Conditions at time T3; (conditions to be ensured) ■
The flow rate Q1 satisfies the relationship Qmax≧Q1.

(2) Furnace temperature θ is the final set furnace temperature θB.

The furnace temperature θS is determined to be 100 to 150° C. or lower than the solidification temperature of the steel ingot, taking into account the minimum temperature of 850° C. during blooming.

(2) Unsolidified rate during extraction O ~ 20% or less This is determined from the occurrence of internal cracking during blooming and the unsolidified rate mentioned above.

Based on the conditions (1) and (2) above, consider the 5-step slope and time that satisfy the condition (3) above, and if the sensible heat brought in of the steel ingot at time T1 is X = 170 For example, with the following calculation formula, the 5-step slope in Fig. 12,
I was able to decide on the time.

The relationship between the symbols in FIG. 12 and FIG. 11 is EGAS=
QoITiME=T(Foff).

An apparatus for implementing the method of the present invention, its operation, and implementation results will be described below.

FIG. 13 shows an example of the block configuration of the device.

15 is a soaking furnace, and 16 and 17 are connected to the burner boat of the furnace 15 through combustion gas and air piping, respectively.

Reference numeral 18.19 indicates a flow rate control valve of a flow rate adjustment operating section provided in piping 16.17, and reference numeral 20.21 indicates a flow rate detector provided upstream of valve 18.19.

22 is a furnace thermometer.

23 is a host computer into which information such as the steel ingot history and steel ingot specifications is input; 24 is the calculation formula for the sensible heat of the steel ingot, the solidification rate, and the above-mentioned item (1) for determining the flow rate curve.

(2), (3) equations for calculating the initial flow rate, flow time, flow rate gradient, calculation formulas for the final set furnace temperature (set value), etc., and the shortest furnace time table, etc. are set (program).
The running process computer (pro-computer) 25 is a device control computer.

The processor 24 receives information from the computer 23 and calculates the shortest in-furnace time, fuel injection/stopping time, set furnace temperature, time, slope, etc. of the flow rate curve.

The processor 24 gives the calculation result to the computer 25 as a command value.

The calculator 25 gives the flow rate command value directly to the operating part (valve), and also receives the flow rate value and furnace temperature as feedback from the devices 18, 19, and 22. When the furnace temperature reaches the set furnace temperature, the computer 25 immediately changes the control mode to the furnace temperature from the flow rate control. It switches to control and directly gives a flow rate command to the operating unit to eliminate the furnace temperature deviation.

In the figure, 26 is a changeover switch, and 27 is a switch 26, which is a backup device for the computer 25 that is connected to the detection unit and operation unit to be controlled when the computer 25 goes down, and has the same function as the computer 25. .

Next, the operation will be explained.

(4) Steel ingot charging completion timing■ The computer 23 provides information such as the history and specifications of the charged steel ingot to the pro-controller 24.

(2) The processor 24 calculates the shortest in-furnace time of the steel ingot, solidification rate at the time of charging, and sensible heat from the above information and the actual furnace temperature obtained through the calculator 25.

Based on this calculation result, the fuel injection stop time is calculated.

Also, determine the final furnace temperature (set value).

(B) Fuel supply stop time elapsed timing■ The processor 24 calculates the time and slope of the flow rate curve for the minimum usage amount.

■ Send this calculation result to the device control computer 25.

(Timing for reaching the set value of 0 furnace temperature■ When the calculator 25 reaches the set value of the furnace temperature, it notifies the program controller 24 that it has reached the set value, and at the same time calculates the flow rate using the flow rate curve defined by the slope for the past time as the target value. Switch the mode from the control mode to the furnace temperature control mode in which the set furnace temperature is the target value.

(2) The processor 24 sends a steel ingot extraction start command to an external display device, etc., and also sends various data related to the steel ingot to the host computer 23.

(D) Transition period between (B) → C) (see Figure 12)
Time: I TiME-→Gradient I until 2TiME
At 5 LOP, time: 2 TiME → 3 TiME: slope 25L
In the OP, time: 3 TiME→4TiME has a slope of 3 SI
, OP, time; gradient 45LO from 4 TiME to 5TiME
P controls the input flow rate, and at (T1+5 TiME) time,
Based on the actual measurement data, the slope of the 5th stage (
5SLOP), for example, if it is predicted that 68LOP with gradient=O as shown by the broken line in FIG. 12 will occur, the control is corrected to 58LOP shown by the solid line in FIG. 12.

In addition, 55LOP and 65LOP indicated by solid lines in FIG.
is, the flow rate Q is Qmax between 5TiME → 6TiME
, and the furnace temperature has not yet reached the set furnace temperature at this point and the maximum flow rate retention time occurs.

FIG. 14 shows an actual measurement time chart of the fuel injection flow rate curve Q and the furnace temperature θ when the method of the present invention is carried out using the apparatus shown in FIG. 13. T3. T4 is the steel ingot charging completion time, fuel injection (flow rate control) start time, extraction start time, and completion time, respectively.

The specifications in this chart are as follows.

Unit weight of steel ingot・・・・・・・・・・・・・・・ 21
Solidification rate when charging T・・・・・・・・・・・・65.69
Sensible heat brought into the steel ingot during charging...179.29X 10k
$T Shortest in-reactor time・・・・・・・・・・・・2.
5Hr initial fuel stop time・・・・・・・・・1.5
Solidification rate at the start of Hr fuel injection...80% Solidification rate at the time of extraction...100% Furnace time...... ...2.8
Hr (Charging completed - Extraction completed) As a result, the minimum temperature during rolling...1000.0°C Rolling finish...1066.4°C Fuel consumption...・・・・・・・・・ 23.3 X
It was $T for 103.

Table 1 shows the fuel consumption rate according to the present invention in comparison with that of conventional methods (specifically, a method using a constant maximum flow rate line as a flow rate curve and a method using a flow rate gradient control curve).

It is clear from Table 1 how the method of the present invention is an energy-saving method for operating a soaking furnace.

As explained above, the method of the present invention (1) makes the charging solidification rate smaller than conventional charging, solidifies in the furnace without charging fuel until it reaches the solidification rate at the start of charging and fuel injection, and in this process By effectively utilizing the amount of heat that was conventionally dissipated into the atmosphere, (2) during the heating period, the steel ingot is heated according to the flow rate curve that curves downward with respect to the flow rate straight line, which is the minimum fuel flow rate used, and (3) next, When the furnace temperature reaches the final set temperature near the maximum flow rate of the flow rate curve, the steel ingot is extracted without taking a soaking period as in conventional methods, so the amount of fuel used is minimized and the maximum energy saving effect can be obtained. It is extremely effective in soaking furnace operation.

[Brief explanation of drawings]

Figures 1 to 6 are explanatory diagrams of the conventional method of operating a soaking furnace, particularly the input fuel flow rate curve, and Figures 7 to 9 are explanatory diagrams of new findings by the present inventor, which are prerequisites for the method of the present invention. FIG. 10 is an explanatory diagram of the present invention, FIGS. 11 and 12 are explanatory diagrams of a method for determining a flow rate curve according to the present invention, and FIG. 13 is a block diagram showing an example of an apparatus configuration for implementing the present invention method. FIG. 14 is an actual measurement time chart of the operational results of the apparatus shown in FIG. 13, ie, flow rate and furnace temperature. 1... Furnace temperature line, 2... Fuel flow line, 3... Hot point, 4... Average temperature, 5... Cold point, 6...
・Solidification curve (inside the mold), 7... Solidification curve (inside the furnace outside the mold), 8... Solidification curve (inside the fuel charging furnace), 9.
...Coagulation curve, 10...Coagulation curve, 11
... Solidification curve, 12 ... Flow rate straight line, 1
3...Flow rate curve, 14...5 stage flow rate line, 15...Soaking furnace, 16...Gas piping, 1γ... Air piping, 18...Flow rate control valve, 19...Flow rate control valve, 20...
・Flow rate detector, 21...Flow rate detector, 22...
... Furnace thermometer, 23 ... Upper computer, 2
4...Processing computer, 25...Device control computer, 26...Selector switch, 27...
...Backup device, 28...Flow rate curve, 2
9... Furnace temperature curve, 30... Steel ingot surface temperature curve.

Claims (1)

[Claims] 1. Input fuel flow control is performed to control the flow rate of fuel input into the furnace until the furnace temperature reaches the set value, and after the furnace temperature reaches the set value, furnace temperature control is performed to control the furnace temperature using the set value as the target value. In a steel ingot soaking furnace equipped with a combustion control device and a furnace temperature detector, a steel ingot with a solidification rate of 70 to 80% or less is charged into the furnace until a predetermined solidification rate of 70 to 80% is reached. Under the prerequisites of starting fuel injection when the predetermined solidification rate is reached without inputting the charge, the unsolidified rate is such that no internal cracks occur during blooming, and no surface cracks occur during blooming. The shortest in-furnace time required to obtain a soaked steel ingot at a temperature equal to or higher than the minimum temperature during rolling is determined, and the input flow rate reaches a predetermined flow rate below the maximum flow rate at the time when the shortest in-furnace time is added to the charging time. If the horizontal axis is the time when the furnace temperature reaches the set temperature and the vertical axis is the charging flow rate, then the flow rate at the charging start time and the above flow rate at the time when the shortest furnace time is added to the charging time is With respect to the connecting flow rate straight line, a flow rate curve that curves downward to provide the minimum usable flow rate is determined, and the steel ingot is charged with a solidification rate of 70 to 80% or less, and the solidification rate is reached to the specified solidification rate in the fuel injection and shutdown furnace. A method for operating a soaking furnace, characterized in that when the furnace temperature reaches the set value, fuel injection is started, and thereafter the flow rate is controlled along the flow rate curve, and then when the furnace temperature reaches the set value, the ready steel ingot is extracted.