JPS61199014A - Method for setting temperature of heating furnace - Google Patents

Abstract

PURPOSE:To control the ejection temp. of the materials existing in a furnace with good accuracy by executing linearization to optimize the minimization of fuel flow rate by perturbation method simulation which changes stepwise the fuel flow rate by using three non-linear models including the model to determine a furnace wall temp. distribution. CONSTITUTION:A burner 105 for combustion and a furnace temp. detector 104 are disposed in a heating furnace 101 divided to plural control zone and the flow rate is controlled by a fuel flow rate controller 103 so that the set temp. for each of the control zones set 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 in the furface to the function 106. The function 106 consists of a function 20 to calculate the present temp., a function 21 to calculate the optimum furnace temp. of each material and a function 22 to calculate the set furnace temp. and is finally 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 determine the optimum furnace temp. of each material under the minimization of each fuel.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a furnace temperature setting method that minimizes fuel consumption in temperature control of a heating furnace in a hot rolling line.

[Conventional technology]

Conventionally, temperature control for this type of heating furnace has been carried out using a model that calculates the material temperature from the furnace temperature, and a model that calculates the fuel flow from the furnace temperature and the material temperature, as shown in Japanese Patent Application Laid-open No. 56-75533. In order to perform nonlinear fuel minimization using a double-valve linear model for calculating i, the furnace temperature is changed stepwise and the perturbation simulation method (simulation is performed in the standard state and perturbed state to determine the linearization coefficient). The method used is to perform linearization using the method of .

[Problem that the invention seeks to solve]

In the conventional furnace temperature setting method for a heating furnace as described above, the number of furnace temperature calculation zones is generally greater than the number of zones in which the fuel flow rate can be controlled. There has been a problem in that the temperature and temperature rise curves are not always achievable patterns.

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 rise curve was determined which was far from the actual temperature rise curve of the material and the state of the furnace.

This invention was made to solve these problems, and aims to provide a method for setting the furnace temperature of a heating furnace that not only allows accurate control of the extraction temperature of each material but also reduces fuel consumption. purpose.

[Means for solving problems]

The furnace temperature setting method for a heating furnace according to the present invention includes a model that calculates the furnace temperature using an unsteady heat balance formula based on the fuel flow, a model that calculates the furnace wall temperature distribution based on this furnace temperature,
Using three non-roaring models: 1 and 2, a model that calculates the material temperature based on the furnace temperature, and a perturbation method simulation in which the fuel flow rate is changed stepwise, V-linearization is performed to optimize the minimum fuel flow rate. , the furnace temperature setting value that satisfies the extraction temperature of the material existing in the furnace is determined without determining the temperature rise curve for each material.

[Effect]

In this invention, three nonlinear models including a model for determining the furnace wall temperature distribution are used, and linearization is performed using a perturbation method simulation that changes the fuel flow rate in steps to optimize the minimum fuel flow rate inside the furnace. Since the furnace temperature setting value that satisfies the extraction temperature of the materials present in the furnace temperature is determined, it is possible to determine a furnace temperature setting value that minimizes the fuel flow rate for each material and is also achievable.

〔Example〕

The principle of this invention will be explained below.

The furnace temperature calculation model is constructed as follows.

As shown in FIG. 1, 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.

dTg Engineering C・□ Fist 11e Temperature change in furnace temperature t -Q1 ... Heat decay of fuel and air + Hg
a W 1 ...Fuel calorific value + (
)1,1°Cpg"gi'1 ... Calorific value of exhaust gas from upstream - GC! @T i Pg gl ... Calorific value of exhaust gas to downstream + ΣK11j ((Tg, 1 + 273)' - (rg, +
27g') j = 1 ・Φ・ Radiation from other mesh furnace temperatures... Radiation from the furnace wall... Radiation to the material + C2 (Twi-Tgi) + C3 (Tel-Tgi)
・・Convection to the furnace wall and materials - QviL ・・Skid cooling water loss・
...(υ Here, H is the calorific value per unit flow rate of fuel, C7 is the exhaust gas specific heat, G1 is the exhaust gas flow rate of each mesh, and K work ij
, K2□1 (lK31J is the radiation exchange coefficient, C, C2, C3 are constants, n is the number of furnace length divisions, m is the number of slabs, For example, furnace wall temperature,
If the slab temperature is known, it can be transformed as follows.

+ΣB1 to 11Tgk+01 (1=1φ...n)...
(2) This is an 8-element simultaneous nonlinear differential equation, but 1et
Using the temperature distribution in the furnace before ep as a starting value, a time and material temperature model can be expressed as follows using a well-known two-dimensional heat conduction equation.

What is the boundary condition on the surface, where X is the thickness direction of the material and Y is the width direction of the material? Representation,
d and d2 are the thickness of the material and the coating inside the material, respectively. Also C8. λ8. γB is the specific heat, thermal conductivity, and specific gravity of the material, respectively, and q8 is the surface heat flux of the material, which can be expressed by the following equation.

q8= 3i i ((Tgl ” 275)
'-(T8□+273)''')1=1+03(T8,4.□)...(52 formula (3
1 can be solved by a normal differential method using the boundary condition of equation (4).

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 furnace inner surface is +02 (Tgl-Tw)...(7) The boundary condition on the furnace outer surface is where X is the furnace wall thickness direction, d, td is the furnace wall thickness, Cw,
Input w"w represents the specific heat, thermal conductivity, and ratio tt of the furnace wall, HOIJT represents the external heat transfer coefficient, and Ta1r represents the external temperature. ) can be solved using a normal difference equation.

By using the above five models in combination, if the fuel flow rate is given, the future values of the furnace temperature, material temperature, furnace wall temperature, and the six The temperature will be measured.

Next, a method for calculating the optimum furnace temperature for each material to minimize fuel consumption will be explained according to the flowchart shown in FIG. In the figure, (1)
is the first θtep of the heating curve determination, and (2) is the similar second θtep.
5top, (81 is the same 58th step, (5J 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 furnace temperature at the material passing position, (9) is the average temperature, calculation of the degree of uniform heating, and the symbol is the linearization gf
-,v, calculation (2) is a linear programming (LP) calculation.

First, as the first step (1), the time required until all materials are extracted with the current flow twK', the three models (
By repeating steps 5), (6), and (7), the average temperature iT8' and average mW Cj when extracting each material is
lei"8- jtit Im temperature) JT,'
, and the furnace temperature Tg□ at the valley position when the material passes through. can be calculated.

Next, as the 28th tθp(2), each fuel flow lid fffl
By using a skewer that changes the fuel flow rate in steps by ΔWK' every time, the average temperature at the time of each material extraction at each flow rate change is T 8K, soaked; ΔTK, and the furnace temperature rTg when the material passes through, "-
*It becomes possible to calculate θ.

Next, as the fifth atθp(3), the following linearization coefficient calculation (lO) is executed. By the procedure of the 28th tap (2J), the average temperature of each material at the time of extraction, the soaking degree, and the furnace temperature 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 PIK
IP2K and IP31K are linearization coefficients for each case where the flow rate is changed, and are given as follows.

'Also, each fuel flow rate can be expressed as w, = wK + ΔWK, where ΔWK is the amount of change in each control band.

Constraints in fuel optimization are due to metallurgical constraints on materials and constraints on reactor operation.

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

Furthermore, since the evaluation relationship for optimization is fuel minimization, the missing value is also k.

Minimization of Equation (16) under the constraint condition of Equation (15) can be obtained with a total cost of $ 1lll using the ordinary form planning method (4,p).

The flow of the upper part B is the strict flow of the material of the valley. At the same time, the optimum furnace temperature T0 of the valley material is calculated using equation α1).

The optimum furnace temperature for each valley meter zone for each valley material based on the above results has different meanings depending on the current position of each material even if it is a furnace temperature for the same calculation zone. In other words, the optimum furnace temperature for the fracture exit 9111 calculation zone for the material existing on the fracture exit side is the furnace temperature that must be set now, but the optimum furnace temperature for the fracture exit calculation zone for the material existing on the fracture entry side is The optimal furnace temperature is
It would be better to realize this when the material reaches the fracture exit position, but it is delayed in terms of time.

Therefore, the furnace temperature setting calculation for 6 fireflies is determined as follows.

Predict the position of all materials in the furnace after an arbitrary time from the visual time, and calculate the optimum furnace temperature at the position of the furnace temperature detector for the valley control zone of all the materials that will remain in each control zone after an arbitrary time. Use to determine.

However, T: Control zone setting furnace temperature s IT n: Material book that will exist in the future in the control zone number Cj: Weight per material T0: Furnace temperature detection g’+J for each control zone of material j Optimal furnace temperature at the vessel position It is.

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

In Fig. 5, a combustion burner (105) and a furnace temperature detector (104) are arranged in the heating furnace (IOI) divided into a plurality of flI:I two emperors, and a furnace temperature setting function (106).
) #L''Ji is controlled by the fuel flow controller (103) so that the temperature is set for each control system. (102) is a material information function, and the material size in the furnace , the material information such as weight, extraction weight, and furnace conveyance information to the furnace temperature setting function (106).

The furnace temperature setting function (106) is the current temperature calculation function (a))
It consists of an optimum furnace temperature calculation function for each material (21: and a setting furnace temperature calculation function (2)), which are activated periodically. Current temperature calculation function) J uses the material information to calculate the current material temperature using the furnace temperature calculation model (6), furnace wall temperature calculation model (6), and material temperature calculation model (7). The optimum furnace temperature calculation function for each material (21) is described in the description of this invention. The furnace temperature is calculated and the set furnace temperature is instructed to the fermentation material flow rate controller (103).

Therefore, based on the fuel R171t: tt, the furnace temperature setting value that minimizes the fuel flow rate for each material is determined, taking into account the furnace temperature, furnace temperature requirement, and material * + temperature valley factor. Therefore, a furnace temperature setting value that is both achievable and realistic can be set.

〔Effect of the invention〕

As explained above, this invention
Six nonlinear models are used: a model that calculates the furnace temperature using an unsteady heat balance equation based on K, a model that calculates the furnace wall temperature distribution based on the furnace temperature, and a model that calculates the material temperature based on the furnace temperature. However, based on the fuel consumption, I+k fa, the furnace temperature setting value that minimizes the fuel flow rate for each material is determined, taking into account the furnace temperature, furnace wall temperature, and the material's 1M degree valley element. It becomes possible to determine a furnace temperature setting value that is realizable and satisfies the extraction temperature of the material present in the furnace without determining a temperature rise curve for each material. Therefore, not only can the extraction temperature of each material be controlled with high accuracy, but also the amount of S consumption can be significantly reduced.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram showing the zone division of the furnace temperature calculation, FIG. 2 is a flowchart for determining the continuous furnace temperature set value, and FIG. 6 is an overall configuration diagram showing one implementation mode of the present invention. (51-・Furnace temperature calculation model (6)・Furnace wall temperature calculation model (7)・・Material temperature calculation model threshold”)・・Current temperature calculation function (211・・IVT appropriate furnace temperature calculation function for each material) ... Setting furnace temperature needle n function (101) ... Heating furnace (103) ... Fuel flow rate controller (104) ... Furnace temperature detector (105) ... Combustion burner (106) ... Furnace temperature setting Function: In the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] In the furnace control of continuous heating furnaces that have multiple control zones, a function that calculates the time change in furnace temperature using an unsteady heat balance formula based on the fuel flow rate, and a function that calculates the time change in the furnace wall internal temperature from the furnace temperature. , and a function to calculate the temporal change in material internal temperature from the furnace temperature, and use the above three functions to calculate the average temperature at the time of material extraction, soaking degree,
In addition to calculating each furnace temperature when the material passes through,
Using the function, the average temperature at the time of material extraction, the soaking degree, and each furnace temperature at the time of material passage are calculated when the fuel flow rate in each control zone is changed by a certain value from the current flow rate, and the current state is calculated based on the above calculation results. A furnace temperature setting method for a heating furnace characterized by calculating a linearization coefficient around a flow rate and using this to determine an optimal furnace temperature that minimizes fuel under constraint conditions.