JPH0232330B2 - RENZOKUKANETSURONONENSHOSEIGYOHOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the heating and combustion of steel billets such as slabs, billets, and rough shaped steel billets in a continuous heating furnace.

In the past, various methods have been proposed for controlling continuous heating furnaces for steel billets, which are installed at the front stage of the hot rolling process. is becoming extremely difficult. In other words, hot charge or direct rolling has recently been implemented for the purpose of saving energy and processes, and cold, hot, and hot steel billets are charged into the heating furnace in an irregular order, resulting in different thermal histories. It has become difficult to efficiently control the heating of steel slabs to a target extraction temperature using conventional means.

Conventional control methods can be broadly divided into two types: temperature control and flow rate control. Temperature control directly measures the furnace atmosphere temperature and performs control according to the measured temperature, which has the advantage of good control accuracy when steel slabs with approximately the same thermal history continue, but on the other hand, the above-mentioned cooling and
When hot steel pieces are mixed, the amount of fuel input cannot follow the temperature of the steel pieces well, and the flow rate fluctuation becomes larger than necessary, making it difficult to obtain uniform heating and worsening the fuel consumption rate. It was hot. on the other hand,
The flow rate control method calculates the heat capacity of the steel billet by thermal calculation and predicts the firing temperature, but it has the advantage of suppressing unnecessary flow rate fluctuations because it directly controls the flow rate without requiring atmospheric temperature measurement. However, there was a problem that the temperature control accuracy was not sufficient.

The present invention makes use of the advantages of the conventional temperature control and flow rate control methods described above, and divides the combustion control zone in the length direction of the continuous heating furnace, controlling the flow rate in the front zone and controlling the furnace temperature in the rear zone. improve billet temperature prediction and baking temperature accuracy,
The purpose is to measure energy conservation. Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a schematic side view of a continuous heating furnace for carrying out the present invention, and the structure of the furnace body is a well-known six-zone continuous heating furnace. The heated steel billet 2 charged from the charging port 1 passes through three combustion zones: a preheating zone 3a, a heating zone 3b, and a soaking zone 3c on the skid conveying surface 30, where it is heated and heated.
It is heated uniformly and sent out from the extraction port 4 to the rolling line for the next process. Each zone is provided with a combustion burner 5 and a detector 6 for measuring the atmospheric temperature in the furnace, and a temperature detector 61 for measuring the temperature of the billet at the time of charging is provided near the charging port 1. It is provided. The arithmetic and control unit 7 calculates the required fuel flow rate or the required atmospheric temperature based on the input signals from each of the temperature detectors and the signals from the condition setter 8 that provides various setting conditions, and uses the results to calculate the required fuel flow rate or the required ambient temperature. The combustion burner 5 in each zone is controlled through the control section.

The present invention is different from the conventional method in that the preheating, heating, and soaking zones are controlled in two control zones. That is, the preheating zone 3a, the first control zone 10a, the heating zone 3b, and the soaking zone 3c are collectively divided into a second control zone 10b. In addition to the 6-zone continuous heating furnace of this embodiment, for example, in the case of a 5-zone type which is divided into three or more zones in the furnace length direction, at least one zone on the charging side is the first control zone, and two zones on the extraction side. The above is the second control zone, and the combination is 1:
There are three cases: 4, 2:3, and 3:2, but which one to choose depends on the required input heat amount for all zones, the input heat amount in the second control zone, and the charging of the heated steel billet, which will be explained later. It is determined by the relationship of temperature.

Next, the control means of the present invention will be explained in more detail based on the flowchart of FIG. In Fig. 2, 1 to M indicate all the slabs in the furnace, j is the zone number, 1 is the soaking zone, 2 is the heating zone, and 3 is the preheating zone. *The processing within the marked box is performed on the steel pieces in band j.
First, for all the billets charged in the heating furnace, calculate the temperature drop in the rolling process from the finish exit target temperature of the rolling process, which is set in advance at the time of charging the heating furnace, to calculate the target temperature T _AIM for extraction from the heating furnace. decide. Specific determination methods include a multiple regression model in which the target finishing exit temperature is the dependent variable and the finished product thickness, pre-rolling thickness, strip threading speed, required rolling power, strip width, etc. are independent variables, or the accumulation of conventional operational data. Any well-known calculation method such as tabulation by . Next, the charging temperature T ₀ is determined based on the actually measured billet temperature when charging the heating furnace.
Determine. In the case of a cold slab, for example, it may be assumed that the temperature is constant at 30°C, but in the case of a hot slab, the actual measured temperature is the surface temperature, so to find the temperature at the center of the slab, the temperature distribution in the thickness direction of the slab is calculated using a multidimensional curve. Alternatively, it can be approximated by a sine curve and the central temperature can be calculated from the amount of heat transfer due to the heat balance on the surface of the steel piece. It is assumed that most of the heat transfer from the inside of the heating furnace to the surface of the steel billet is due to radiation, and the amount of heat transfer is calculated using the well-known overall heat absorption rate method, and the internal temperature of the steel billet is calculated using the amount of heat transfer. The temperature T ₁ of the steel billet at the current position in the furnace of all the steel billets is determined at arbitrary control intervals, for example, at intervals of 2 minutes, using a well-known numerical method for heat conduction. Subsequently, when charging the billet, the required heat content H(i) for the billet i is determined from the extraction target temperature T _AIM and the charging temperature T ₀ using equations (1) and (2).

h=∫ ^TAIM _T0 CdT ……(1) H(i)=h×W ……(2) However, h: Heat content per weight (KCal/Kg) C: Specific heat (KCal/Kg・℃) T ₀ : Equipment Input temperature (℃) T _AIM : Extraction target temperature (℃) W: Billet weight (Kg) H(i): Required heat content for each piece (KCal) Next, the required heat content of i steel billet H(i) is converted into the required fuel input flow rate G(i) using equation (3).

G(i)=H(i)×1/q×1/η ……(3) However, G(i): Amount of fuel to be input (Nm ² ) q: Fuel calorific value (KCal/Nm ² ) η: Combustion Efficiency Also, the furnace time in each zone is determined from the extraction pitch and the width of the steel billet or the length of each zone in the heating furnace, which are planned in advance when charging the steel billet. The heating furnace in this example consists of three zones: preheating, heating, and soaking, so if the in-furnace time in each zone of the i-slab is determined, the required amount of fuel input for each zone is determined by the unit time for each zone. It can be determined by the product of the per unit flow rate and each of the above-mentioned furnace hours, and the sum of the products should be equal to the above-mentioned required fuel input flow rate G(i), so the relationship is (4).
It can be expressed by a formula.

G(i)=g _p(i) ×t _zp(i) +g _H(i) ×t _ZH(i) +g _s(i) ×t _ZS(i) ……(4) However, g _p(i) : Fuel flow rate per unit time in the preheating zone of the i slab (Nm ³ /hr) g _H(i) : Fuel flow rate per unit time in the heating zone of the i slab (Nm ³ /hr) g _s(i) : i slab Fuel flow rate per unit time in the soaking zone (Nm ² /hr) t _Zp(i) : Furnace time in the preheating zone of slab i (hr) t _ZH(i) : Furnace time in the heating zone of slab i ( hr) t _ZS(i) : I slab in-furnace time in the soaking zone (hr) Using equations (1) to (4) above, the required fuel input amount G( i), and the required fuel input amount Q for the total number n of steel slabs in the first control zone.
Find (i).

Q ₀ = _o 〓 ⁱ⁼¹ [g _p(i) ×t _ZP(i) ] + _o 〓 ⁱ⁼¹ [g _H(i) ×t _ZH(i) ] + _o 〓 ⁱ⁼¹ [g _{S( i)} ×t _ZS(i) ] ...(5) By the way, since the first control zone contains cold, warm, and hot steel pieces, it is not appropriate to control the furnace temperature by detecting the ambient temperature. In the invention, if flow rate control is applied to the first control zone and the temperature of each steel slab is heated almost uniformly in this zone, the furnace temperature is controlled in the subsequent zone, that is, the second control zone. We focused on the ability to perform highly accurate control. In other words, in the first control zone, the difference in temperature level of each piece of steel is kept within a certain tolerance range, rather than the strictness of control accuracy.
It is sufficient to leave a margin for control in the control zone. Therefore, the required fuel input amount _o 〓 ⁱ⁼¹ [g _p(i) ×t _Zp(i) ] in the first control zone in equation (5) can be determined with rough accuracy, and Q ₀ and each zone Furnace time t _Zp(i) ,
Since t _ZH(i) and t _ZS(i) are known, the fuel flow rates g _H and g _S per unit time in the heating zone and soaking zone are assumed by the following equation (5'). In addition, the in-furnace time t _Zp(i) of each zone,
For _tZH(i) and tZS _(i) , it is necessary to calculate one representative value for each zone, so the average value of the furnace time of each slab is used, or the longest or shortest value of the slabs in the zone is used. It is sufficient to use the time in the furnace. Therefore, the above equation (5) becomes (5')
It can be easily expressed as the formula.

Q ₀ = _o 〓 ⁱ⁼¹ g _p(i) ×t _Zp +g _H ×t _ZH +g _S ×t _ZS ……(5′) However, g _H : Maximum equipment capacity flow rate per unit time of heating zone × α _H ( Nm ³ /hr) g _S : Maximum equipment capacity flow rate per unit time of the soaking element x α _S (Nm ³ /hr) α _H and α _S are the flow rates that are as close to the equipment capacity MAX as possible when the furnace is in use for a long time. If the furnace time is short, the flow rate is restricted to leave a control margin, and the coefficient is determined to improve the fuel consumption rate as much as possible under high load conditions in the later stages. Bye. Rearranging equation (5') gives equation (6).

Q ₀ = Q ₁ + Q ₂ ...(6) However, Q ₁ : _o 〓 ⁱ⁼¹ g _p(i) ×t _Zp → Required amount of fuel input in the first control zone (Nm ³ ) Q ₂ : g _H × t _ZH + g _S × t _ZS → Standard fuel injection flow rate in the second control zone (Nm ³ ) g _p in equation (6) = _o 〓 ⁱ⁼¹ g _p(i) is the set flow rate in the first control zone (Nm ³ /hr). Next, calculate the predicted remaining furnace time L until extraction determined by the extraction scheduled pitch of the steel billet in each zone in the second control zone, and at the same time calculate the remaining furnace time required for firing until the extraction target temperature can be secured. It is calculated assuming that L' is set to the maximum allowable ambient temperature for each zone. Figure 3 shows the relationship between the predicted remaining furnace time L and the required remaining furnace time.
The difference ΔL in L' is determined as an index for determining the resistance to burning of the steel slab, and this ΔL is calculated for all the steel slabs in each band,
By setting the steel piece with the smallest difference between L and L' as the steel piece to be controlled in the zone, the other steel pieces in the same zone can achieve the extraction target temperature without any problem. Note that the code P _n
shows the temperature increase pattern when each zone is brought to the maximum allowable ambient temperature.

Now, as is well known, in order to minimize the fuel consumption rate, the set atmospheric temperature for the zone is determined based on the basic idea of heating the steel billets as soon as possible just before extraction. explain.
That is, as shown in Fig. 4, the predicted remaining furnace time L of the steel billet to be controlled is divided into the first half furnace time _l1 and the second half furnace time _l2 , and first the second half furnace time _l2 is set to the maximum allowable furnace time. Assuming that the ambient temperature is T _n , and assuming that the first furnace life time l ₁ is once the same as the current ambient temperature T _p , estimate the temperature T ₂ at the time of extraction from the current temperature T ₁ of the control target steel slab. . This estimated temperature T ₂ at the time of extraction is compared with the pre-calculated extraction target temperature T _AIM , and if the two almost match, the atmospheric temperature assumed during the first half of the furnace life is set as the set temperature for the zone. . In this case, there is no problem as long as the allowable temperature difference is within about ±5° C. in practice. On the other hand, the estimated temperature
If T ₂ is lower than the allowable temperature difference compared to the extraction target temperature T _AIM , the atmospheric temperature during the first half of the furnace life is assumed to be higher, and if it is higher, the atmospheric temperature is re-assumed to be lower.
The temperature at the time of extraction of the steel slab to be controlled is recalculated, and the atmospheric temperature during the first half of the furnace life is adjusted so that it falls within the allowable temperature difference, and this is set as the set temperature for the zone. The set flow rates or set temperatures in the first control zone and the second control zone determined by the above procedure are recalculated at regular intervals, each time a billet is charged, or each time a billet is extracted, and output to the combustion control device. The symbol T _p indicates the current ambient temperature, the symbol P ₁ indicates the ambient temperature pattern 1, and the symbol P ₂ indicates the ambient temperature pattern 2. C ₁ is a steel billet temperature increase curve in atmospheric temperature pattern 1, and C ₂ is a steel billet temperature increase curve in pattern 2.

When determining the material to be controlled, for example, if the rolling line is equipped with a means to arbitrarily control the temperature of the steel material, such as having an intermediate heating device, it is not necessary to select the steel piece that is least likely to burn as the material to be controlled. Of course, it is also possible to change the material to be controlled or the set temperature in consideration of the temperature compensation ability.
In addition, for example, a heating furnace other than the three zones of preheating, heating, and soaking in the furnace length direction of this embodiment
In the case of 6 zones, the effects of the present invention can be fully exerted by setting the control zones so that the sum of the reference flow rates of the second control zone (temperature control zone) is 50% or more of the required fuel input flow rate of all zones. can.

As detailed above, according to the present invention, even if cold, hot, and hot steel billets with different thermal histories are charged in an irregular order, unnecessary flow rate fluctuations in the first control zone can be suppressed and energy can be saved. This is an industrially useful combustion control method, as it is possible to achieve this, and also to take advantage of the temperature control in the second control zone, enabling highly accurate control.

[Brief explanation of drawings]

Fig. 1 is a schematic explanatory diagram of a continuous heating furnace in which the present invention is implemented, Fig. 2 is a diagram showing the flow of the control method of the present invention,
FIG. 3 is an explanatory diagram showing the relationship between the furnace use time, and FIG. 4 is an explanatory diagram showing the atmospheric temperature pattern. 1: Charging port, 2: Steel billet, 30: Skid conveyance surface, 3a: Pre-preparation zone, 3b: Heating zone, 3c: Soaking zone, 4: Extraction port, 5: Combustion burner, 6, 61: Temperature detector, 7 : Arithmetic control device, 8: Condition setting device,
9: Combustion control device, 10a: First control zone, 1
0b: second control zone.

Claims (1)

[Claims] 1. When heating slabs or other steel pieces in a continuous heating furnace where the combustion zone is divided into three or more zones in the furnace length direction,
One or more zones on the charging side of the combustion zone are divided in advance into a first control zone, and at least two zones on the remaining extraction side are divided into a second control zone. The required fuel input flow rate Q ₀ for the entire zone is determined from T ₀ and the extraction target temperature T _AIM , and then the standard fuel input flow rate for the zone is determined from the reactor occupancy time in the second control zone and the maximum equipment capacity flow rate per unit time. After determining Q ₂ , the flow rate in the first control zone is controlled using the remaining flow rate Q ₁ obtained by subtracting the reference fuel input flow rate Q ₂ from the required fuel input amount Q ₀ in all zones, and then the flow rate in the second control zone is controlled. Assuming the atmospheric temperature pattern during the remaining furnace time at
Obtain the billet temperature T ₂ at the time of extraction from the atmospheric temperature pattern, the current billet temperature T ₁ and the remaining furnace time, and
Compare the billet temperature T ₂ and the extraction target temperature T _AIM with T ₂ .
A combustion control method for a continuous heating furnace, characterized in that the atmospheric temperature pattern is changed so that T _AIM substantially coincides with each other, and the temperature of the second control zone is controlled based on the atmospheric temperature pattern.