JPS61199022A - 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 optimum heating-up curve to minimize the fuel flow rate with each material by taking the future fluctuation of an in-furnace temp., furnace wall temp. and material temp. into consideration in accordance with the fuel flow rate. CONSTITUTION:A function 106 to set the furnace temp. is constituted 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. in a heating furnace 101 divided to plural separate control zones and is periodically started. The function 20 calculates the preset 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. The function 21 determines the heating-up curve of each material under the minimization of each fuel. The function 22 calculates the future material temp. and furnace temp. by the logic similar to the logic of the function 20. The function 23 compares the target heating-up temp. and present temp. of each material, calculates the furnace temp. of each control zone and instructs the set furnace temp. to a fuel flow rate controller 103.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to a method of controlling a continuous heating furnace having a plurality of control zones, and in particular, to determining a temperature increase pattern of a material that requires the least amount of fuel, and determining the temperature increase pattern. This relates to a method of determining the furnace temperature setting for the material so that the material is baked at

[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. 75555, there is a model that calculates the material temperature from the furnace temperature, and a model that calculates the fuel flow chamber from the furnace temperature and the material temperature. In order to perform nonlinear fuel minimization using a double-valve linear model as the model to be calculated, a perturbation simulation method is used in which the furnace temperature is changed in steps (simulations are performed in the standard state and perturbed state to determine the linearization coefficient). method) is used.

[Possible problem to be solved by the invention]

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 is a problem in that the temperature and temperature rise curve are not always in a realistic 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 that a temperature rise curve was determined that was far from the actual temperature rise trend of the material and the furnace condition.Also, even if a temperature rise curve of some kind was determined, There was a problem that the set furnace temperature for baking with that temperature increase pattern could not be determined with sufficient accuracy for the following reasons. In other words, the amount of heat qA required to reach the target material temperature is qA = OpG ( θ, -〇p)it = αA・(TgA'Tp') * *
*(1) However, Cp: Specific heat G: Material weight αA: Transfer coefficient θA Two target material temperature θp: Current material temperature r, A: Setting furnace @ (absolute temperature) Tp: Current material temperature (absolute temperature) From TgA However, the set furnace temperature can be determined by back-calculating σgA from θgA2 Setting furnace temperature A: material surface area Δ from the work time increments, but the heat transfer coefficient depends on the position in the furnace, temperature, combustion pattern, etc. It was difficult to determine the set furnace temperature with high accuracy because it was difficult to treat as a constant.

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

[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. The temperature curve is determined, and the set furnace temperature for each material is determined based on the optimal temperature rise curve thus determined, the current and future material temperatures, and each element of the future furnace temperature. [Operation] In this invention, a 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. As a result, a achievable optimal temperature rise curve can be obtained. In addition, the set furnace temperature for each material is determined based on the optimum temperature rise curve obtained in this way, the current and future material temperatures, and the future furnace temperature. Extraction temperature can be precisely controlled.

〔Example〕

The principle of this invention will be explained below.

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

T gi CΦ□ ... Temperature change in furnace temperature (it =: Ql ... Sensible heat of fuel and air + Hg
mW, life...Fuel calorific value rate Gi +
1°CI) gIITIIEi”1... Exhaust gas calorific value from upstream 4-C!-T... Exhaust gas heating lid i to downstream
Tag gl ... Radiation from furnace wall 1 Radiation to own material + 02 (Twl-Tgl) + 03 (T8.-Tg,)
... Convection to the reactor wall and materials - Qwi ... Skid cooling water loss fist ・
・(8) Here, H is the calorific value per unit flow rate of fuel, pg is the exhaust gas specific heat, 01 is the exhaust gas flow rate of each mesh, and K
, K and K are radiation exchange xlj
21k 31j The coefficients C, C2, 03 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, assuming that the fuel flow itW is given and the furnace wall temperature and slab temperature are known.

+ΣB1klITgk+C, (1=iaaan)...-
(4) This is a 0-dimensional simultaneous nonlinear differential equation, but i 5
By using the in-furnace temperature distribution before tep as a starting value, discretizing it with respect to time and converging it using Newton's method or the like, a new complete enumeration of the in-furnace temperature distribution can be easily obtained.

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

The boundary conditions on the surface are as follows: X represents the material thickness direction, Y represents the width direction of the material, and d and d2 represent the material thickness and the inside of the material, respectively. Also C8. λ6. γS is the specific heat, thermal conductivity, and
It is the specific gravity, and q8 is the surface heat flux of the material, which can be expressed by the following formula.

qll= ΣK" 1g ((Tg i+ 2 gates)'-
(T8□+273)') 1=1 +03(T, , -Tg□) 1・(7
) Equation (5) can be solved by a normal differential method by using the boundary condition of Equation (6).

As shown in FIG. 1, the furnace wall temperature model can be expressed as follows using a one-dimensional heat conduction knife equation in the thickness direction only within the mesh for each division in the longitudinal direction of the furnace.

The boundary condition on the inner surface of the furnace is + C2 (Tg□-Tw)...
(9) The boundary conditions on the outer surface of the furnace are as follows: X is the thickness direction of the furnace wall, d3 is the thickness of the furnace wall, and Cw
, X W l 7 pr represent the specific heat, thermal conductivity, and specific gravity of the furnace wall, HOUT represents the external heat transfer ratio, and Ta□ represents the external temperature. Formula (8) also formula (9), formula α0)
By using the boundary conditions, it becomes possible to solve with a normal difference equation.

By using the above three models in combination, if the amount of fuel R 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 three can be calculated.

Next, a method for determining a temperature increase curve for a material that minimizes fuel consumption will be explained according to the flowchart shown in FIG. In the figure, (1)
is the jth 5tsp of temperature rise curve determination, (2) is the similar 25th top, (81 is the similar 55th top, (
4) is the same 45th step, (5) is the furnace temperature calculation model, (6) is the furnace wall temperature calculation model, (γ) 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 uniformity, and the expression is the calculation of the linearization coefficient, C1
1) is linear programming (Lp) calculation.

First, as the first stop (1), the time until all the materials are extracted with the current flow rate W, is calculated using the six models (
5) l (6) T (By repeatedly using γ-n, the average temperature T, Q, soaking degree (maximum temperature - minimum temperature) ΔTs at the time of extraction of each material, and the temperature at each position when the material passes through. The furnace temperature T glo can be calculated.

As a second stop (2), by changing the fuel flow rate by ΔWK'' in 5 steps in each fuel flow rate control zone, as in the first stop (1), when each material is extracted at each flow rate change. It becomes possible to calculate the average temperature 〒-1, the soaking degree ΔT, K, and the furnace temperature Tg□' when the material passes through.

Next, the third stop (as 81, the following linearization coefficient calculation αO) is executed. By the procedure of the 26th step (2J), the average temperature of each material at the time of extraction, the soaking degree, and the temperature inside the furnace in each calculation zone when each material passes, which are solutions of the nonlinear equation, can be linearized as follows.

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

P2, I, and P31 are linearization coefficients when the flow rate is changed, and are given as follows.

ΔWK.

Further, each fuel flow rate can be expressed as W section = WK + ΔWK, where ΔW 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 MIN and MAX indicate the respective lower and upper limits.

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

Minimization of formula (to) under the constraint condition of formula α7) can be obtained by ordinary linear programming (bp) calculations (with one stroke).

The flow rate of the above solution is the optimal flow rate JjkWKop of each material, and the optimal flow rate of each material until extraction is determined by the above six models (5), (6), and (7) based on this fLit as the fourth θtap (4). It becomes possible to calculate the temperature curve.

The amount of heat required to burn the material after Δ time along the temperature rise curve obtained in this way is determined by equation (1), and the heat required to reach the temperature θ after Δ time is ft qy is q , = Cp@G・(θF−θp)Δt=α(T g
, 4-T p4 ) , ・('1
g) However, θF: Future material temperature TgF: Future furnace temperature (absolute temperature). In the above formula (1), 2〇〇), if α-'-α, the set furnace temperature θgA for the material becomes 0. Fuel '#' to achieve the set furnace temperature determined in this way.
By controlling the L-shape, the temperature of the steel billet can be precisely fired to the target temperature. FIG. 6 shows this state.

For example, according to equation (support)), if the target temperature θ□ is higher than the current temperature θ and the future temperature θ is lower than the current temperature 0p, then if the current fuel flow rate is to be maintained in the future, the target temperature Since the temperature rise is lower than the temperature rise pattern, the current amount of fuel #L will be increased. Also, in the opposite case to the above, that is, θ 〈θ9. θ2〉
If the case θ occurs, the temperature will be higher than the temperature increase pattern if the current fuel flow rate remains, so the current fuel flow noise will be lowered.

Next, heating furnace control based on an embodiment of the present invention will be explained with reference to FIG. 4.

In Figure 4, a heating furnace (
101) includes a combustion burner (105) and a furnace temperature detector (105).
04) is arranged, and the current flow is controlled by the fuel flow rate controller (103) so as to reach the set temperature for each control zone set by the furnace temperature setting function (106). (
Reference numeral 102) is a material information function, which instructs the furnace temperature setting function (106) to provide material information such as the dimensions, weight, extraction temperature, and conveyance information of the material in the furnace.

The furnace temperature setting function (106) is the current temperature calculation function (20)
and temperature rise curve determination function (21) and future temperature calculation function (2)
) and a set furnace temperature calculation function -), which are activated periodically. The current temperature calculation function (2Q) uses the furnace temperature calculation model (5) and furnace wall temperature calculation model (5) based on material information.
6), the material temperature calculation model (7) calculates the current material temperature.The temperature rise curve determination function (211) calculates the temperature rise for each material according to the flowchart shown in FIG. Each temperature curve is determined under fuel minimization.

The future temperature calculation function (b)) is the current temperature calculation function (20
) to calculate the future material temperature and furnace temperature using the same logic.

An example of the set furnace temperature calculation function compares the target temperature increase curve for each material with the current temperature, calculates the furnace temperature for each control zone, and instructs the fuel flow rate controller (103) to set the entire furnace temperature.

Therefore, based on the fuel flow rate, we also take into account future fluctuations in the furnace temperature, furnace wall temperature, and material temperature, and determine a feasible temperature rise curve that minimizes the fuel flow rate for each material. Not only can the extraction temperature of each material be controlled with high accuracy, but also the effect of reducing the fuel flow rate is extremely 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 that minimizes the fuel flow rate is determined for each material, the optimum temperature rise curve that can be achieved can be obtained. Since the set furnace temperature for each material is calculated based on the future material temperature and each element of the future furnace temperature, the extraction temperature of each material can be precisely controlled and fuel consumption can be reduced. There are effects such as being able to.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing the zone division of furnace temperature calculation of a heating furnace, Fig. 2 is a flowchart of determining the optimum temperature rise curve, Fig. 3 is a conceptual diagram of determining the furnace temperature set value, and Fig. 4 is an embodiment of the present invention. FIG. 2 is an overall configuration diagram showing an aspect. (5)+1・Furnace temperature calculation model (6)・Furnace wall temperature calculation model (7)・・Material temperature calculation model (company)・Current temperature calculation function @ll・Fist temperature rise curve calculation function diagram・・Future Temperature calculation function (sniff) Setting furnace temperature calculation function (101) Heating furnace (103) Fuel flow controller (104) Furnace temperature detector (105) Combustion burner (106) Furnace temperature setting function

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 fuel under constraint conditions, and the first function described above.
, a seventh function that determines the temperature increase curve from the current position of the material to extraction using the second and third functions, and the optimal fuel flow rate obtained in the sixth function is input to the seventh function. Determine the optimal temperature rise curve, and use this optimal temperature rise curve, current material temperature,
A control method for a continuous heating furnace, characterized in that a set furnace temperature of a material at a furnace temperature setting position is determined based on a future material temperature and each element of the future furnace temperature.