JPS61199018A - Method for controlling heating of heating furnace - Google Patents

Abstract

PURPOSE:To control ejection temp. with good accuracy by setting the set value of the furnace temp. and the mixing ratio in each control zone in accordance with the required furnace temp. at which the fuel flow rate for each material is minimized by taking the future fluctuation of an in-furnace temp., furnace wall temp. and material temp. into consideration on the basis of 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 optimum furnace temp. of each material and a function 22 to calculate fuel mixing ratio and set furnace temp. and is periodically started in a heating furnace 101 divided to plural control zones 101a. 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 optimum furnace temp. of each material under the minimization of each fuel. The function 22 calculates the furnace temp. of each control zone by using the required furnace temp. and position of each material and instructs the same to a fuel flow rate controller 103. As a result the control of the ejection temp. with good accuracy is made possible even in the case in which high-load materials and low-load materials exist mixedly in the furnace.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for setting a furnace temperature set value and a co-firing ratio of multiple fuels to minimize the amount of fuel used in temperature control of a heating furnace in a hot heating line. It is something.

[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 rate from the furnace temperature and the material temperature, as shown in Japanese Patent Laid-Open No. 56-75533. Using the bivalve linear model of the model to calculate,
In order to perform nonlinear fuel minimization, linearization is performed by changing the furnace temperature in steps and using the perturbation simulation method (a method in which the linearization coefficient is determined by performing simulations in the standard state and perturbed state). A method is adopted in which the temperature rise curve of the material is determined, and the furnace temperature is determined by comparing this temperature rise curve with the current temperature of the material0 [Problems to be solved by the invention] In conventional heating control methods for heating furnaces, as shown in Figure 5, the number of calculation zones for furnace temperature is generally greater than the number of zones in which fuel flow rate can be controlled. There has been a problem in that the optimum furnace temperature and temperature rise curve are not always achievable patterns.

In addition, when determining the linearization coefficient and temperature increase pattern, the heat loss to the furnace wall, the temperature distribution of the furnace wall, etc. are ignored, and the furnace temperature is changed in steps without considering the response delay of the furnace. 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.

In addition, in the conventional method, as shown in Figure @6, the furnace temperature detector (104) that obtains the feedback signal is
01a), there is one location, and therefore the furnace temperature at this one location is controlled.

By the way, in a normal heating furnace, the temperature of the material increases as it approaches the extraction end, so the burner design is such that the temperature on the burner side increases as shown in FIG. For this reason, as shown in FIG. 6, when a low-load material at the front and a high-load material at the rear exist within the control zone (101a), the furnace temperature is controlled according to the required furnace temperature of the high-load material.
Therefore, there is a problem in that the furnace temperature setting value must always be set high, resulting in a large loss in terms of fuel consumption.This invention was made to solve this problem, and the loss in fuel consumption is It is an object of the present invention to provide a heating control method for a heating furnace that can reduce the temperature distribution in the control zone and appropriately control the temperature distribution in the control zone.

Means for Solving Problem C] The heating control method for a heating furnace according to the present invention uses a model that calculates the furnace temperature using an unsteady heat balance formula based on the fuel flow rate;
Using three nonlinear models: 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, linearization is performed using a perturbation method simulation that changes the flow rate in steps. Optimize the minimum flow rate to determine the optimal furnace temperature for each material, and divide the total calorific value of each fuel by the total calorific value of all fuels to obtain the mixed combustion ratio of multiple fuels and the furnace temperature setting value. The temperature is calculated and set using the optimum furnace temperature for each material.

[Effect]

In this invention, there are three models: a model that calculates the furnace temperature using an unsteady heat balance formula based on the fuel flow rate, 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. Three nonlinear models are used to determine the optimal furnace temperature for each material, and this optimal furnace temperature for each material is used to calculate and set the co-firing ratio of multiple fuels and the furnace temperature setpoint, so the temperature inside the furnace is Even when high-load materials and low-load materials are mixed, it is possible to obtain a furnace temperature setting that satisfies the required furnace temperature for each material and minimizes the fuel flow rate, making it possible to control the extraction temperature with precision. becomes.

〔Example〕

The principle of this invention will be explained below.

Figure 1 is a flowchart showing the method for determining the optimum furnace temperature for each material, and (1) in the figure shows the first step of calculating the optimum furnace temperature for each material;
(2) and (8) are the same second and third 5te
p, (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 furnace temperature at the material passing position, (9) is the average temperature, Calculation of fever,
αO1 is the calculation of the linearization coefficient, (6) is the linear programming (LP)
) is the calculation of 0 Next, each model (5), (6),
(γ) will be explained.

The furnace temperature calculation model 1 is configured as follows.

As shown in FIG. 5, 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 = Qe ... Sensible heat of fuel and air + H*W
...fuel calorific value"GlloCpg'Tgi11 ...exhaust gas calorific value from upstream i pg gi ...exhaust gas calorific value to downstream...
Radiation from other mesh furnace temperature... Radiation from the furnace wall... Radiation to e material + 02 (TWl-T,) +03 (Ta□-Tg,)
・Cloudy・Convection to the furnace wall and materials-Q, □ ...Skid cooling water top loss・1 (1
) Here, H is the calorific value of the unit flow rate of fuel, C is the specific heat of the exhaust gas, G1 is the exhaust gas flow rate g of each mesh, K us K2 □k'''3it is the radiation intersection coefficient, and C knee 02 , 03 are constants, n is the number of furnace length divisions, and m is the number of slabs.

The above equation (1) can be transformed as follows if the fuel flow ft1w is given and the furnace wall temperature and slab temperature are known.

+Σ 81keTgk 10, (1=1.5on)
...(2) This is a nonlinear differential equation with n elements, but i 5
VjA in the furnace before tep! If we use the distribution as a starting value, discretize it with respect to time, and converge it using Newton's method etc., we get
A new furnace warm distribution can be calculated for the quantity rate.

Further, the material temperature model (7) can be expressed as follows using the well-known two-dimensional heat conduction equation.

(8) The boundary conditions on the surface are as follows: X represents the material thickness direction, Y represents the material width direction, and d and d2 represent the material thickness and the inside of the material, respectively. Also, Ca, λ8. γ8 is the specific heat, thermal conductivity, and specific gravity of the material, respectively, and q is the surface heat flux of the material, which can be expressed by the following equation.

G8: □ Protein, 31t ((1g1+273)'-(T
st+276)') Equation (8) can be solved by the ordinary difference method using the boundary condition of Equation (4).

Further, the furnace wall temperature model (6) can be expressed as follows using a one-dimensional heat conduction knife equation only in the thickness direction within the mesh for each division in the furnace length direction, as shown in FIG.

The boundary condition on the inner surface of the furnace is -(T, +273)'J+C2('rg1-'rw)・
・(7) 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, Cw,
λyl represents the specific heat, thermal conductivity, and specific gravity of the 1"Ji furnace wall, H is the external heat transfer coefficient, and Ta1r is the external temperature. Equation (6) is also expressed by Equation (7) and Equation (8). ) can be solved using a normal difference equation.

Using a combination of the above three models (5), (6), and (a), if the fuel flow is given, the furnace temperature, material temperature, and Temperature, furnace wall temperature, and future temperatures of the three components can be calculated.Next, a method for determining the optimum furnace temperature for each material will be explained with reference to FIG.

First, as the first step (1), at the current flow rate WKO, the time until all the materials are extracted with the three models +
5) By repeatedly using , (6'l, (7)), the average temperature T at the time of extraction of each material, the soaking degree (maximum temperature - minimum temperature) ΔT, and the temperature above the furnace at each position when the material passes through. By changing the fuel flow rate by #1 in 5 steps, the average temperature T at the time of each material extraction at each flow rate change, the soaking degree ΔT, and the furnace temperature at the time of material passage can be changed as in the i-th step (1). It becomes possible to calculate vT.

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

Here, KMAX is the number of fuel flow noise control bands, and PIK
"2K" 3□ is a linearization coefficient when the flow rate is changed and fc is given as follows.

Also, if each fuel flow t is #Kft the amount of change in each control band, WK=WK +ΔW It can be expressed as

Constraints in fuel optimization are as follows due to metallurgical constraints of materials and constraints on furnace operation.

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

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

Minimization of equation α6) under the constraint condition of equation (15) can be obtained by ordinary linear programming (LP) calculation C11).

The flow rate of the above solution is the optimum flow rate W for each material, and at the same time, the optimum furnace temperature of each material per gram is calculated using equation (9).

Next, a method of calculating the set furnace temperature and co-firing ratio for each control zone will be explained using the optimum furnace temperature for each material.

Since the optimum furnace temperature of each material at all positions in the furnace has been calculated, the optimum furnace temperature of the calculation zone corresponding to the position of each material after an arbitrary time from the current time is set as the required furnace temperature of each material. However, for materials that exist on the extraction side and are extracted after an arbitrary time, the temperature is taken as the temperature in the calculation zone on the fracture exit side. The position of each material at this time is xj, and the required furnace temperature is Tgj*. Furthermore, J indicates the material number.

Now, in each control zone, we use fuel A (e.g., heavy oil) that can achieve a normal temperature distribution in the furnace where the burner side becomes higher, and fuel B (e.g., converter gas), which is a slow combustion type that suppresses combustion on the burner side as much as possible. Consider the case where there are two types of fuel that have different combustion temperature characteristics.

The co-firing ratio is defined as follows.

...07) By changing the above-mentioned co-firing ratio, it is possible to change the temperature distribution in the furnace as shown in FIG. 2 at the same total calorific value in each control zone.

The co-firing ratio and the set furnace temperature are determined by the following formula based on the position X of each material and the required furnace temperature.

...(g) N is the number of materials in the control zone XT is the temperature of the furnace temperature sensor. However, as shown in Figure 3, it also applies when high-load materials and low-load materials coexist in the furnace. , not only can the extraction temperature be controlled with precision, but also each fuel A.

A heating furnace control based on an embodiment of the present invention of zero-order heating, which makes it possible to minimize the loss of B, will be described with reference to FIG.

! In Figure 4, a heating furnace (101) divided into a plurality of control zones (101a) is equipped with a combustion burner (105), a furnace temperature detector (1o4), and a furnace temperature setting function (1o4).
The fuel flow rate is controlled by a fuel flow rate controller (103) so as to reach the set temperature for each control zone set by the fuel flow rate controller (106). (1o2) 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) consists of the current temperature calculation function (goods), the optimum furnace temperature calculation function for each material (@l), and the co-firing ratio and set furnace temperature calculation function (2), which are activated periodically. be done. The current temperature calculation function calculates the current material temperature using the furnace temperature calculation model (6), furnace wall temperature calculation model (6), and material temperature calculation model (γ) based on the material information. The optimal furnace temperature calculation function for each material (21) determines the optimal furnace temperature for each material while minimizing fuel according to the flowchart in Figure WJ1 as described in the explanation of this invention. The temperature calculation function (□□□) calculates the furnace temperature of each control zone according to formulas (g) and (o) using the required furnace temperature and temperature for each material, and sends it to the fuel flow rate controller (103). Give instructions.

〔Effect of the invention〕

As explained above, this invention considers future fluctuations in the furnace temperature, furnace wall temperature, and material temperature based on the fuel flow rate, and calculates the necessary furnace temperature that is possible while minimizing the fuel flow rate for each material. Since the furnace temperature setting value and co-firing ratio for each control zone are set based on this, accuracy can be maintained even when high-load materials and low-load materials are mixed in the furnace. Not only can the extraction temperature be well controlled, but the fuel flow rate can be greatly reduced.

[Brief explanation of drawings]

Figure 1 is a flowchart showing the method for determining the optimum furnace temperature for each material, Figure 2 is a diagram showing the relationship between co-firing ratio and furnace temperature, Figure 3 is an explanatory diagram showing the effects of this invention, and Figure 4 is a diagram showing the effect of this invention. FIG. 5 is a schematic diagram showing a furnace temperature calculation zone division of a heating furnace, and FIG. 6 is an explanatory diagram showing a conventional heating control method for a heating furnace. (6) - Furnace temperature calculation model (6) - Φ Furnace wall temperature calculation model (γ) - Material temperature calculation model - - Current temperature calculation function (21 + - Optimal furnace temperature calculation function for each material) - Mixed firing Ratio, setting furnace temperature calculation function (101), Φ heating furnace (103), fuel flow controller (104), furnace temperature detector (105), combustion burner (106), furnace temperature setting function. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] In a heating furnace that has multiple heating control zones and can burn multiple fuels with different combustion temperature characteristics in the same heating control zone, time changes in furnace temperature are calculated using an unsteady heat balance formula based on the fuel flow rate. A first function that calculates the time change in the internal temperature of the furnace wall from the furnace temperature, a third function that calculates the time change in the material internal temperature from the furnace temperature, and the first and second functions described above.
, a fourth function that uses the third functions to calculate the average temperature at the time of material extraction, the degree of soaking, and each furnace temperature at the time of material passage at the current fuel flow rate in each control zone; a fifth function that calculates the average temperature at the time of material extraction, the degree of uniformity, and each furnace temperature at the time of material passage when the fuel flow rate in each control zone is changed by a certain value from the current flow rate using each function of 3; A sixth function calculates the linearization coefficient around the current fuel flow rate based on the results of the fourth and fifth functions above, and uses this to determine the optimal furnace temperature for each material that minimizes fuel under constraint conditions. The mixed combustion ratio of multiple fuels and the furnace temperature set value obtained by dividing the total calorific value of each fuel by the total calorific value of all fuels are calculated using the optimal furnace temperature for each material obtained in the sixth function above. A heating control method for a heating furnace characterized by calculating and setting each.