JPS61199013A - Method for controlling continuous heating furnace - Google Patents

Abstract

PURPOSE:To control the ejection temp. of each material with good accuracy and to reduce fuel consumption by determining the heating-up curve to minimize fuel flow rate with each material in accordance with the fuel flow rate by taking the future fluctuation of an in-furnace temp., furnace well temp. and material temp. into consideration. CONSTITUTION:A burner 105 for combustion and a furnace temp. detector 104 are disposed in a continuous heating furnace 101 divided to plural control zones and the flow rate is so controlled by a fuel flow rate controller 103 that the set temp. for each of the control zones determined by a function 106 to determine the furnace temp. is attained. A material information function 102 instructs the material information including the size, weight, ejection temp., etc., of the materials of the furnace to the function 106. The function 106 consists of a function 20 to calculate the present temp., a function 21 to determine the heating-up curve, a function 22 to calculate the future temp. and a function 23 to calculate the set furnace temp. and is periodically started. The function 20 calculates the present material temp. by a model 5 for calculating the furnace temp., a model 6 for calculating the furnace wall temp. and a model 7 for calculating the material temp. in accordance with the material information. The function 21 determines the heating-up curve of each material under the minimization of each fuel.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of controlling a continuous heating furnace having a plurality of control zones.

[Conventional technology]

Conventionally, as a method for determining the temperature rise curve online for temperature control of this type of heating furnace, for example, JP-A-56-
As shown in Publication No. 75533, nonlinear fuel minimization is performed using a double-valve linear model: a model that calculates material temperature from furnace temperature, and a model that calculates fuel flow rate from furnace temperature and material temperature. For this reason, we use a perturbation simulation method (a method in which linearization coefficients are determined by performing simulations in a standard state and a perturbed state) by changing the furnace temperature in steps.

[Problem that the invention seeks to solve]

・In the conventional continuous heating furnace control method as described above, the number of calculation zones for the furnace temperature is generally greater than the number of zones that can control the fuel flow rate. There was a problem in that the furnace temperature and temperature rise curve were not always in a realizable pattern.

In addition, when determining the linearization coefficient and temperature increase pattern, the simulation is performed by ignoring heat loss to the furnace wall, furnace wall temperature distribution, etc., and changing the furnace temperature in steps without considering the furnace response delay. As a result, there was a problem in that a temperature increase curve was determined that was far from the actual temperature increase trend of the material and the furnace condition.

Furthermore, even if some kind of temperature increase curve were determined, there was a problem in that it could not be determined with sufficient accuracy because the furnace temperature for baking with that temperature increase pattern was lower than the set temperature.

In other words, it is necessary to achieve the target material temperature.

The required amount of heat qA is: qA=C,G(θ,-θ,)Δt=α(T4-T')...(1)A
gA p However, Cp: Specific heat G: 1it material weight αA: Transfer coefficient θA: Target material temperature θ: Current material temperature TgA: Set furnace temperature (absolute temperature) T: Current material temperature (absolute temperature) In: Material surface area 418 hours The set furnace temperature can be determined by back-calculating θgA from the increments, but the heat transfer coefficient changes depending on the position in the furnace, temperature, combustion pattern, etc., and it is difficult to treat it as a constant, so it is difficult to determine the set furnace temperature with accuracy. There wasn't.

In addition, even if the set furnace temperature is determined for each material, the materials charged into the furnace are grouped based on combinations of size, physical properties, and heating steel type (extraction temperature upper and lower limits of billet, and soaking degree limits). Due to high-variety, low-volume production, there are sometimes dozens of material groups in the furnace, and it is difficult to bake each material in line with the temperature rise.

This invention was made to solve these problems, and it is possible to precisely control the extraction temperature of each material, and
The purpose of this invention is to obtain a control method for a continuous heating furnace that can reduce fuel consumption.

[Means for solving problems]

The control method for a continuous heating furnace according to the present invention takes into account future fluctuations in the furnace internal temperature, furnace wall temperature, and material temperature based on the fuel flow rate, and optimizes the heating rate to minimize the fuel flow rate for each material. Determine the temperature curve, determine the set furnace temperature for each material based on the optimum temperature rise curve obtained in this way, the current and future material temperatures, and each element of the future furnace temperature. In order to bake the materials on average or preferentially bake a certain material along each heating curve, set the furnace temperature of each control unit by multiplying the set furnace temperature of each material by the weighting coefficient for furnace temperature setting and use the weighted average value. It is set as a value.

[Effect]

In this invention, the temperature rise curve that minimizes the fuel flow rate for each material is determined based on the fuel flow rate, taking into account future fluctuations in the furnace temperature, furnace wall temperature, and material temperature. A possible optimal heating curve is obtained. In addition, we determine the set furnace temperature for each material based on the optimum temperature rise curve obtained in this way, the current and future material temperatures, and the future furnace temperature, and also calculate the temperature of the various materials in the furnace. In order to make it possible to bake on average or preferentially a certain material along each temperature increase curve, the set furnace temperature is corrected, so the extraction temperature of each material can be controlled with high precision.

〔Example〕

The principle of this invention will be explained below.

The furnace temperature calculation model is constructed as follows. As shown in Figure 1, the heating furnace is divided into n pieces in the furnace length direction,
The following heat balance equation is established for each divided mesh.

Tgi C・□ ・・Temperature change in furnace temperature (It = Qi ・・sensible heat of fuel, air + Hg・W
□ ...Fuel heat generation quantum G1 + □・Gpg-Tgi+1 ... Exhaust gas calorific value from upstream - G-C・T ... Exhaust gas calorific value i I
) g gl -・Other mesh furnace heating radiation skewer・・Radiation from the furnace wall +Σ K3□, ((T8t+273')'-CTg□+
273'l't=1 ・Radiation to buildings/materials" C2 (Ty+, -Tgi) 10c3 (Tsi-T
gj)...Convection to the furnace wall and materials-Qwi...Skid cooling water loss・Fist・
(3) Here, Hg is the calorific value per unit flow rate of fuel, cpg is the specific heat of the exhaust gas, and the exhaust gas flow rate of each mesh in G1. C2, C3 are constants. Further, n is the number of furnace length divisions, and m is the number of slabs.

The above equation (8) can be transformed as follows if the fuel flow t- is given and the furnace wall temperature and slab temperature are known.

+ΣB @T +c, (1=1. 1l
llllrl) klk gk l...(4) This is a nonlinear differential equation with n elements, but the 1st
By using the in-furnace temperature distribution before ep as a starting value, discretizing it with respect to time and converging it using Newton's method, etc., a new in-furnace temperature distribution can be easily calculated.

Furthermore, the material warm model can be expressed using the well-known two-dimensional heat conduction equation as follows.

The boundary conditions at the surface are: Here, xtd represents the material thickness direction, Y represents the width direction of the material, and d and G2 represent the material thickness and the inside of the material, respectively.

Also, cs, λ8. γ8 is the specific heat, thermal conductivity, and specific gravity of the material, respectively, and qs is the surface heat flux of the material, which can be expressed by the following equation.

Equation (5) can be solved (1!) using the boundary condition of Equation (6) using a normal difference method.

As shown in the first factor, the furnace wall temperature model can be expressed as follows using a one-dimensional heat conduction equation in the thickness direction only within the mesh for each division in the furnace length direction.

The boundary condition on the inner surface of the furnace is -(T +273)'+c2(Tg, -Tw)
・ ・ (91 The boundary conditions on the outer surface of the furnace are: where X is the thickness direction of the furnace wall, G3 is the thickness of the furnace wall, C, λ
, yl 1. ,)d represents the specific heat, thermal conductivity, and specific gravity of the furnace wall, HoUT represents the external sound 3 thermal conductivity, and T1□1 represents the external temperature. Equation (8) can also be solved by a normal difference equation by using the boundary condition of Equation (9).

By using the above three models in combination, if the fuel flow rate is given, the current values of the furnace temperature, material temperature, and furnace wall temperature are used as initial values, and the future temperatures of the furnace temperature, material temperature, furnace wall temperature, and the can be calculated.

Next, the second method for determining the temperature rise curve of the material that minimizes the amount of fuel is explained.
The explanation will be given according to the flowchart shown in the figure. In the figure, (1) is the first step of determining the temperature rise curve (2) is the same 'il
c 25top, (81ij: similar third step,
(4) is the same fourth stop, (5) is the furnace temperature calculation model, (6) is the furnace wall temperature calculation model, (7) is the material temperature calculation model, (8) is the calculation of the material passing position furnace temperature, ( 9) is the calculation of the average temperature and degree of thermal uniformity, ``The ``Circle'' is the calculation of the linearization coefficient, and ``CI ring'' is the calculation of the linear programming (LP).

First, as the first stop (1), the current flow rate wK
Therefore, by repeatedly using the three models (5), (6), and (γ) until all materials are extracted, the average temperature at the time of each material extraction is T5+, of which 1 degree (maximum temperature - minimum temperature) ΔT0, and furnace temperature Tg□ at each position when the material passes. can be calculated.

Next, as a second step (2), by changing the fuel flow t by ΔvrK11 in a tap shape for each fuel flow rate control band, each material at each flow rate change is changed as in the fifteenth step (1). Average temperature during extraction 〒3, soaking degree ΔTK
1 and the furnace temperature Tg11- when the material passes through.

Next, m 35iep (as 11, the following linearization coefficient calculation α0) is executed. By the second stop (2), the average temperature of each material at the time of extraction, which is the solution of the nonlinear equation,
The furnace temperature in each calculation zone when each material passes through the soaking process can be linearized as follows.

Here, KMAX is the number of fuel flow control bands, and PlX
.

P2K''3iK is a linearization coefficient when each flow rate is changed, and is given by the following.

Further, each fuel flow it can be expressed as WK = WK + ΔWK, where ΔWx is the amount of change in each control band.

The constraints in determining the temperature rise curve are as follows due to metallurgical constraints of the material and constraints on furnace operation.

Here, the subscripts M, N and MAX indicate the respective lower and upper limits.

Furthermore, the evaluation relationship for optimization is as follows since it is fuel minimization.

Minimization of equation (18) under the constraint condition of equation qη can be obtained by ordinary linear programming (LP) calculations.

The mud tank of the above solution is the optimal flow iw of each material, and as Opt 4th stop (4), each material is extracted by the above three models (6) + (6), (7) based on this flow filt It becomes possible to calculate the optimal temperature rise curve for

The amount of heat required to bake the material after Δ time along the temperature rise curve obtained in this way is determined by equation (1), and the heat jjk q, required to reach the temperature θ2 after Δ time, is q, = Cp@G・(θ2−θp)Δt=α(Tg,
4-Tp4) ■-・α9) However, θ2: future material temperature T g ,: future furnace temperature (absolute temperature). If αF: α□ in the above equations α force and α equation, then the set furnace temperature θgA for the material will be. By controlling the fuel flow rate so as to reach the set furnace temperature determined in this manner, the steel billet temperature can be fired with high precision to the target temperature. FIG. 3 shows this state.

For example, according to the formula (sha), the target temperature θ□ is the current temperature θ
If a case occurs where the future temperature θ7 is higher than the current temperature θ and lower than the current temperature θ, the temperature increase will be lower than the target temperature increase pattern if the current fuel flow rate is maintained in the future.
It will act to increase the current fuel flow rate.

Also, in the case opposite to the above, that is, θ□<θ9. θa〉θ
If the case of , occurs, if the current fuel flow rate remains unchanged, the temperature will become higher than the temperature increase pattern, so the current fuel flow rate will be lowered.

Generally, in a heating furnace, there are more calculation zones for furnace temperature than controllable zones, and in order to obtain the temperature at the set position, the set value at that position can only be secured by converting it back to the control temperature. So T'” Tgh
” (Tg(j)-Tg(x)) ・
・ ・ @1) In A), since the furnace temperature distribution is known above, it corresponds to the correction term for the set furnace temperature, and by doing this, the necessary furnace temperature for a certain material can be obtained reliably.

However, T': Set furnace temperature A Tg (j): Furnace temperature Tg (K) of furnace temperature setting zone:
In this way, the set furnace temperature for each material was determined.Based on this set value, the furnace temperature set value for each control zone was determined as follows. Obtained by the formula.

Here, C(1) is the setting room coefficient for each material, and if all C(1) are the same, baking will be averaged along each temperature increase pattern, and depending on the operation, If you want to bake preferentially, this can be achieved by increasing the weight of C(1) regarding the material. FIG. 4 shows this state.

Next, heating and furnace control based on an embodiment of the present invention will be explained with reference to FIG.

In Fig. 5, a heating furnace (1
01) includes a combustion burner (105) and a furnace temperature detector (10).
4) is arranged, and the flow rate is controlled by the fuel flow rate controller (103) K so that the temperature is set by the furnace temperature setting function (106) or set for each control zone.

A material information function (102) instructs the furnace temperature setting function (106) to provide material information such as the dimensions and weight of the material in the furnace, extraction temperature, and furnace conveyance information.

The furnace temperature setting function (106) consists of a current temperature calculation function (company), a temperature increase curve determination function (21), a future temperature calculation function (4), and a set furnace temperature calculation function (conversion). is activated. The current temperature calculation function □□□ uses the furnace temperature calculation model (5) and furnace wall temperature calculation model (6) based on material information.
), the current material temperature is calculated using the material temperature calculation model (γ). As described in the explanation of this invention, the temperature rise curve determination function 1) determines the temperature rise curve for each material according to the flowchart shown in FIG. 2 while minimizing the amount of fuel. 4) calculates the future material temperature and furnace temperature using the same logic as the current thermometer X function (goods).

Setting furnace temperature calculation function + 23) Fi, calculates the furnace temperature for each control zone by comparing the target temperature rise curve for each material and the current temperature,
Instruct the fuel flow rate controller (103) to set the furnace temperature. Therefore, based on the fuel flow rate, the fuel flow rate for each material is determined by taking into account future fluctuations in the furnace internal temperature, furnace wall temperature, and material temperature. Since the minimum realizable temperature increase curve is determined, not only can the extraction temperature of each material be controlled with high accuracy, but the effect of reducing the fuel flow rate is also very large.

〔Effect of the invention〕

As explained above, this invention takes into consideration future fluctuations in the furnace temperature, furnace wall temperature, and material temperature based on the fuel flow rate.
Since the optimum temperature rise curve for each material with the minimum fuel flow rate is determined, a achievable optimum temperature rise curve can be obtained.

In addition, the furnace setting B for each material is determined based on the optimum temperature rise curve determined in this way, the current and future material temperatures, and the future furnace temperature. In order to preferentially bake materials that have an average temperature along each heating curve, the set furnace temperature of each material is multiplied by the weight for setting the furnace temperature, and the weighted average value is calculated as the furnace temperature of each control zone. Since the extraction temperature fr of each material is set to a set value, it is possible to precisely control the extraction temperature fr, and there are effects such as being able to reduce fuel consumption.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing the furnace temperature calculation zone division of a heating furnace, Figure 2 is a flowchart for determining the optimum temperature rise curve, Figure 3 is a conceptual diagram of determining the furnace temperature set value, and Figure 4 is a diagram of the furnace temperature set value. Conceptual diagram of correction value determination,
FIG. 5 is an overall configuration diagram showing one embodiment of the present invention. (5) Furnace temperature calculation model (6) Furnace wall temperature calculation model (7) Material temperature calculation model 120) Current temperature calculation function (21) Temperature rise curve calculation function... Future Temperature calculation function -) Setting furnace temperature calculation function (101) Warm heating furnace (103) Fuel flow control (104) Furnace temperature detector (105)
Combustion burner (106): Furnace temperature setting function In the drawings, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] In the furnace control of a continuous heating furnace that has multiple control zones, the first function calculates the time change in the furnace temperature using an unsteady heat balance formula based on the fuel flow rate, and calculates the time change in the furnace wall internal temperature from the furnace temperature. A second function to calculate the temporal change in material internal temperature from the furnace temperature, a third function to calculate the average temperature at the time of material extraction at the current fuel flow rate in each control zone using each of the first, second, and third functions. A fourth function that calculates the soaking degree and each furnace temperature when the material passes through, and when the fuel flow rate in each control zone is changed by a certain value from the current flow rate using the first, second, and third functions described above. The fifth function calculates the average temperature during material extraction, the degree of soaking, and each furnace temperature when the material passes through, and calculates the linearization coefficient around the current fuel flow rate based on the results of the fourth and fifth functions above. and a sixth function that uses this to calculate the optimal fuel flow rate that minimizes the heating charge under constraint conditions, and the first function described above.
, a seventh function for determining a temperature increase curve from the current position of the material to extraction using the second and third functions, and inputting the optimal fuel flow rate obtained in the sixth function to the seventh function. Find the optimal temperature rise curve, determine the set furnace temperature of the material at the furnace temperature setting position based on the current material temperature, future material temperature, future furnace temperature, and each element of the above optimal temperature rise curve, and then In order to bake the required materials on average or preferentially along the temperature rise curve of each material, set the furnace temperature of each control zone by multiplying the set furnace temperature of each material by the weighting coefficient for furnace temperature setting and use the weighted average value. 1. A method for controlling a continuous heating furnace, characterized in that: