JPS5941489B2 - How to set the furnace temperature correction amount for a multi-zone continuous heating furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for setting a furnace temperature correction amount when controlling the temperature of a multi-zone continuous heating furnace.

A multi-zone continuous heating furnace usually consists of a preheating zone, a heating zone, and a soaking zone, and the main purpose of the heating furnace is to heat a slab or other piece of steel (object to be heated) to a predetermined temperature sufficient for rolling it. At the same time, it is important to operate the rolling mill so that the rolling capacity is fully utilized, that is, the rolling line can be supplied with billets to the rolling mill without stopping.

However, in actual operation, the steel pieces (objects to be heated) charged into the heating furnace are of various sizes, and each has a predetermined required temperature, so it is necessary to control the temperature of each piece individually. It is difficult to do so, and if the billet is extracted according to the rolling pitch, heating may be excessive or insufficient depending on the size of the billet.

In actual furnace temperature control, although the furnace temperature is set so that the furnace temperature in the charging side zone (preparation zone) is low and the furnace temperature in the extraction side zone (soaking zone) is high, overheating is not allowed. In order to prevent insufficient heating, the furnace temperature is controlled by targeting the steel slabs that are least likely to be heated in each phase, which causes the problem that the fuel consumption rate cannot be significantly reduced.

In recent years, various proposals have been made regarding continuous heating furnace control.

For example, in Japanese Patent Publication No. 49-29403, the average temperature of each piece of steel in the furnace is determined, the deviation between this temperature and the set temperature is weighted according to its position in the furnace, and these are combined to determine the performance index. A method is known in which the heating means is controlled according to the magnitude of the figure of merit, but in this method, the weight is changed depending on the position in the furnace, regardless of the size of the temperature deviation, that is, the weight is changed depending on the position in the furnace. Although a method is used to give greater weight to the temperature deviation of the steel slab, when controlling the temperature of the slab in the heating furnace, the time constant is large, so control based only on the current deviation is not so desirable, and predictive control is preferable.

Furthermore, in Japanese Patent Publication No. 51-30526, the required furnace temperature is determined for each slab in each band, and one furnace temperature is selected for each zone from the required furnace temperature group to determine the representative furnace temperature. More specifically, the method is to determine the temperature that will not damage the heating furnace, the temperature that will not melt the surface of the steel billet, and the temperature that is determined by the quality of the steel billet, and also the required furnace temperature. When the group temperature is below the limit temperature, there is a known method of selecting the highest temperature as the representative temperature, but this method takes into account the relationship with the rolling operation, and there is no problem of reduced productivity, but This control method in a zone with a large load has large changes in furnace temperature and fuel, and has problems due to actual operational errors and combustion stability.Moreover, it is suitable for those that are least likely to be heated under the above temperature limits. Since the temperature is controlled using the same method, it is not possible to reduce the fuel consumption rate.

Although conventional heating furnace control has improved to some extent in terms of productivity stability and quality stability, as mentioned above, the problem of fuel cost related to temperature control, that is, the problem of reducing fuel consumption, remains unsolved. The current situation is that this has not been done.

In view of the above-mentioned problems, the present invention provides a method for determining the amount of furnace temperature correction for performing temperature control to reduce fuel consumption rate, stabilize productivity, and stabilize quality.
Its characteristics are that the temperature of each heated object located in each zone of a multi-zone continuous heating furnace can be calculated based on the atmospheric temperature within that zone, the furnace characteristics, the thermal characteristics of the heated object, and the thermal history. In addition, the remaining residence time of each heated object in each zone is determined from the position of the heated object, the position of the heated object in front of the heated object in the extraction direction, and the extraction pitch. For each phase, the furnace temperature correction amount ΔTli of each phase is determined from the outlet target temperature of the heated body in that zone, the heated body temperature, the remaining residence time, and the atmospheric temperature in that zone,
In the method of determining the amount of furnace temperature correction △Tl in each phase, a weighting coefficient Wli is determined for each zone furnace temperature correction amount △Tli for each heated object (where n is The furnace temperature correction amount ΔTl in each phase is determined by the number of objects), and the weighting coefficient W11 is determined for each zone furnace temperature correction amount ΔTli for each heated object by its weight gradient α(- d'Mi/d
ΔTli ) is set to be small in the charging side zone and large in the extraction side zone (where n is the number of objects to be heated in the l zone), and the amount of furnace temperature correction ΔTl in each phase is determined.

That is, the present invention first determines the temperature of each billet in each zone, and determines the remaining residence time of each billet in each zone, and from the billet temperature and remaining residence time, each billet is The degree to which the furnace temperature needs to be corrected in order to reach a predetermined temperature at the zone exit is determined, weight is added depending on the magnitude of the correction amount, and the weighted average is used as the furnace temperature correction amount for each phase. The idea is to change the way weights are applied to each phase (depending on which zone it is located in from the charging side to the extraction side of the heating furnace).

The present invention will be explained in detail below.

First, an example of calculating the temperature of each billet in each zone will be described. The temperature Ui of each billet in the furnace is determined by numerical analysis using the well-known one-dimensional forward difference method, and inside the billet can be expressed by the following equation.

However, θ is the numerical solution of the temperature at the internal position of the steel billet at ΔX2 time JΔt, and the sum of θ is 1/(Δx)2. a is the temperature conductivity, Δt is a minute interval of time, and ΔX is a minute interval of the internal position of the steel billet.

Further, if the heat flux at the boundary of the steel slab is q(t), the boundary condition of the steel slab can be expressed by the following equation.

Here, A=ΔX/λ, λ is thermal conductivity.

Furthermore, the heat flux q(t) at the boundary of the steel billet is expressed by formula 7%. However, φcG is the overall heat absorption rate, which can be determined from temperature measurement experiments etc. depending on the heating furnace shape and operating conditions.
Further, Tg is the temperature of the atmosphere inside the furnace, and is detected by a temperature detector such as a thermocouple installed inside the furnace.

The temperature θli of each billet in each band is determined by equations 1) to (3), and this calculation is performed every predetermined time, or each time a billet is charged, or This is done every time a piece is extracted.

Next, the remaining residence time of each steel slab in each band is determined.

The steel pieces in the furnace are taken from the extraction side as Sl, S2. S3.・・・・・・
Assuming that the i-th steel billet Si is currently located within the 4th zone, the remaining residence time T in that 1th zone is Sk...
Ai is determined as follows.

If m holds true, even if m pieces of steel are extracted, the piece of steel S
i still exists within the l band.

Here, Xi: position of steel piece Si XF'#: 1. Band exit position SBk: Width Gk of steel billet: Distance between steel billet Sk and steel billet Sk+t, determined by in-furnace tracking of the steel billet and in-furnace instructor.

Therefore, the residence time τei can be expressed by the following equation.

However, C: loss time due to mill suspension due to rolling roll replacement, etc., which is zero in normal operation.

Pk: Extraction pitch, which is the time from when the (k-1)th steel piece is extracted until when the (k-1)th steel piece is extracted.

Next, from the billet temperature θAi, remaining residence time τei, etc. determined by the above calculation formula, what is the furnace temperature correction amount ΔTh required for each billet to reach the target temperature at each zone outlet? Find i.

This furnace temperature correction amount ΔTII is expressed by the following equation, for example.

However, all: Temperature of the steel billet Si in the l band θlim: L1 target temperature T' of the steel billet S1 in the l band
li: The steel billet Si in the l band has a target temperature θ11 at the exit of the l band
Required furnace temperature Tl: Actual furnace temperature in l band τei Remaining residence time of steel billet Si in l zone in near zone Shi: Thickness of steel billet Si alo, all, a12: Heat transfer characteristics for each phase , can be determined by experiment, taking into consideration the billet dimensions and billet temperature during calculation.

When the furnace temperature correction amount ΔTli for all the steel slabs in each zone is determined by the above equation (6), the furnace temperature correction amount ΔTl for each phase is determined.

The furnace temperature correction amount △Tli differs depending on each piece of steel, but the furnace temperature correction amount △Tli is ranked in advance according to the size of the furnace temperature correction amount △Tli.
Weighting coefficient Wl whose value is determined according to the size of i
The furnace temperature correction amount ΔTl is determined by weighted averaging of I using the following formula.

However, n is the number of steel slabs in the l band, and the weighting coefficient W11 is a value that varies linearly according to the magnitude of the furnace temperature correction amount ΔTll of each steel slab, as shown in Fig. 1. may be determined in advance, but VWi may be changed in a curved or stepwise manner depending on the size of △Tli.
The O value may be determined, and in short, the slope or rate of change is adjusted according to the characteristics of the furnace, the material to be heated, and the heating conditions so that the larger the furnace temperature correction amount ΔT11, the larger the value of the weighting coefficient W11. Just select it.

In other words, the weighting coefficient ', VWi, is determined by the necessary furnace temperature correction amount ΔTl for each slab, taking into account the burner capacity in each zone, the heat transfer characteristics in the furnace, the slab configuration in the furnace, and the production pitch.
It is determined by the size of i.

According to the present invention, in determining the furnace temperature correction amount ΔT7 for each phase, the furnace temperature correction amount ΔTli is determined for each of the objects to be heated in each phase, and the furnace temperature correction amount for each heated pot is determined. From △Tli and the weighting coefficient Wll determined according to the size of △Tli, the furnace temperature correction amount △Tl in each phase is calculated as follows:
The amount of furnace temperature correction determined for each object to be heated is determined by the above-mentioned (method). Since weighting coefficients Wli of different values are weighted and averaged depending on the size of △TlI, when heating various objects of different sizes continuously, it is necessary to heat all the objects with a smaller amount of heat. It can be heated to a high temperature, and the fuel consumption rate is dramatically reduced.

Next, a case will be described in which the furnace temperature correction amount ΔTl is determined by changing the settings of the weighting coefficient ' and Wl i for each phase.

Conventionally, in order to reduce fuel consumption, furnace temperatures have been set in heating furnaces such that the charging side zone furnace temperature is low and the extraction side zone furnace temperature is high.

The present invention further promotes this. First, when the temperature inside the furnace is changed in each phase, that is, when a large amount of fuel is input in each phase, when the steel billets in each band are extracted, In other words, the extent to which changes in each zone furnace temperature affect the billet extraction temperature was investigated.

Figure 2 shows the temperature change of a steel billet when the furnace temperature of each phase is raised in a continuous four-zone heating furnace consisting of a preheating zone, a first heating zone, a second heating zone, and a soaking zone. Curve A shows the basic pattern of steel billet temperature rise, and curves B, C, D, and E
The furnace temperature in each of the preheating zone, first heating zone, second heating zone, and soaking zone is 50℃.

It shows the temperature increase pattern of the steel piece when the temperature was increased by 50°C, 240°C, and 250°C.

Furthermore, Table 1 shows the degree of influence of each average zone furnace temperature on the extraction temperature with respect to the general set temperature when the slab thickness is 160 mm to 250 mm and the furnace time is 8000 Sec to 15000 sec. .

As is clear from Fig. 2 and Table 1, the temperature change in the billet caused by the change in the charging side zone furnace temperature is alleviated during the process of the billet moving to the extraction side, and the influence on the billet extraction temperature is is small, and the temperature change in the extraction side zone has a large effect on the extraction temperature.

Therefore, it is not necessary to set the furnace temperature in the zone near the charging side to correspond to the steel billet that is least heated in the other zone, and to adopt a more average furnace temperature setting, and in the extraction side zone, The furnace temperature can be set by placing more weight on the steel pieces that are less likely to be heated.

However, in this case, consideration must be given so that the extraction temperature of each billet falls within a certain allowable range for rolling.

That is, at the time when the furnace temperature correction amount ΔTli for each steel billet is determined, as shown in FIG.
Even though there is a large difference in Tli, the weighting gradient α is made small without making much of a difference in the weighting coefficient Wli, and the furnace temperature correction amount ΔTd for that zone is determined more averagely using the above formula (7). , in the extraction side band, the weighting coefficient wll is made different based on the difference in ΔTli to increase the weighting gradient α, and the furnace temperature correction amount ΔT7 for that band is determined by the above equation (7).

Incidentally, once the furnace temperature correction amount ΔTl is determined for each phase, the temperature is controlled by a conventionally known heating means based on the furnace temperature correction amount ΔT.

The present invention is as described above, and according to the present invention, the furnace temperature correction amount ΔTli is determined for each steel slab in each band, and the weighting coefficient VWi is determined based on the value of this correction amount, and the weighted average is calculated. Since the furnace temperature correction amount △Tl for each phase is determined, the fuel consumption rate can be significantly reduced compared to conventional control methods, and although weighted averaging is performed in the charging side zone, the weight gradient can be reduced. and set it to a more average setting, and in the extraction sideband,
Since weighted averaging is performed by increasing the weight gradient in consideration of the target temperature of each steel billet, fuel consumption can be further reduced.

Also, as a matter of course, since the subsequent process of rolling and the target temperature of each piece of steel are taken into account, there is no concern that productivity or product quality will deteriorate.

[Brief explanation of the drawing]

Fig. 1 shows an example of the weighting coefficient in the present invention, Fig. 2 shows the situation of steel billet temperature rise due to furnace temperature changes in each phase of a four-zone continuous heating furnace, and Fig. 3 shows an example of the steel billet temperature in each phase. It is a graph showing an example of weighting coefficients.

Claims (1)

[Claims] 1. The temperature of each object to be heated located in each zone of a multi-zone continuous heating furnace can be determined based on the ambient temperature within that zone, the furnace characteristics, the thermal characteristics and thermal history of the object to be heated. In addition, the remaining residence time of each heated object in each zone is determined from the position of the heated object, the position of the heated object in front of the heated object in the extraction direction, and the extraction pitch. For each phase, the furnace temperature correction amount ΔTli of each phase is determined from the outlet target temperature of the heated body in that zone, the heated body temperature, the remaining residence time, and the atmospheric temperature in that zone, In the method of determining the furnace temperature correction amount △Tl in each phase, a weighting coefficient Wli is determined for each zone furnace temperature correction amount △Tli for each heated object (where n is the heated object in the l zone). A method for setting a furnace temperature correction amount for a multi-zone continuous heating furnace, characterized in that the furnace temperature correction amount ΔTl in each phase is determined based on the number of furnace temperature correction amounts ΔTl in each phase. 2. Determine the temperature of each heated object located in each zone of the multi-zone continuous heating furnace from the ambient temperature in that zone, the furnace characteristics, the thermal characteristics and thermal history of the heated object, and The remaining residence time of the heated object in each zone is determined from the position of the heated object, the position of the heated object in front of the heated object in the extraction direction, and the extraction pitch force, and each phase is determined for each heated object. The furnace temperature correction amount ΔTri in each phase is calculated from the outlet target temperature of the heated body in that zone, the heated body temperature, the remaining residence time, and the ambient temperature in the zone. In the method of determining the temperature correction amount △Tl, a weighting coefficient Wli and a sono weight gradient α (-dwli / d△T#i) are inserted for each zone furnace temperature correction amount △Tli for each heated object. Multi-zone continuous heating characterized by determining the furnace temperature correction amount △Tl in each phase to be small in the side zone and large in the extraction side zone (where n is the number of objects to be heated in the 1 zone). How to set the furnace temperature correction amount.