KR0118985B1 - Combustion control method of furnace - Google Patents

Abstract

The method is to control combustion of a heating furnace connected to a process computer and a spray control system and having the first and the second sensors and a burner. The method includes the steps of: receiving periodical temperature data from the first sensor for measuring the atmosphere temperature in the furnace and calculating a material temperature at the current time with respect to the entire material in the furnace; receiving temperature data from the second sensor for measuring the material temperature in the furnace and calculating a difference between the calculated temperature of the previous step and the measured temperature; comparing the temperature distributed in the entire material of the furnace and the calculated temperature according to an optical temperature rising pattern, to obtain a set temperature of the furnace; and sending the temperature of the furnace to the spray control system to control the amount of air and gas supplied to the burner.

Description

Combustion Control Method of Furnace

1 is a block diagram of a conventional furnace combustion control system.

2 is a configuration diagram of a furnace combustion control system to which the present invention is applied.

3 is the mesh partition of the material name for the temperature calculation.

* Explanation of symbols for main parts of the drawings

10: heating furnace 11: preheating table

12: heating zone 13: cracking zone

20 process computer 21,22 sensor

30: distributed control system

The present invention relates to combustion furnace heating control of a hot rolling process, and in particular, by automatically controlling the temperature in the furnace in order to supply the optimum material to the rolling process, which is a post-process, the amount of fuel to be injected while making the target temperature when the material is extracted. The present invention relates to an automatic combustion control method of a furnace using a mathematical model for minimization.

In order to perform precise combustion control in consideration of fluctuation of extraction temperature, fluctuation of extraction time of material, rest, etc., combustion control model is required.

Furnace combustion control model is a mathematical model used to set the temperature and the mathematical model used to make predictions by using the characteristics of the furnace and the information of the furnace and the material to set the furnace temperature to obtain the extraction target temperature. Speak throughout the model. The furnace combustion control system consists of a furnace consisting of a preheating zone, a heating zone, and a cracking zone, a combustion control equation model, and a distributed control system that controls the flow rate and idleness.

1 is a schematic configuration diagram of a conventional combustion control system, and includes a heating furnace device 10 including a preheating table 11, a heating table 12, and a cracking table 13, and a sensor for sensing an ambient temperature in a furnace ( 21 and a process computer 20 for processing a furnace temperature sensed by the heating burner 31 and the sensor 21 to calculate a furnace set value, and according to the furnace setting control signal of the process computer 20. The distribution control system 30 which controls the amount of air and the flow volume supplied to the burner 31 is included. Accordingly, the temperature of the material for all the materials existing in the furnace is calculated by receiving the atmosphere temperature in the furnace from each sensor 21. Next, a prediction time is calculated for the idle time of each material staying in the heating furnace, and an extraction temperature prediction calculation is performed for the material to predict the temperature of the scheduled extraction time at the present time. Once the predicted extraction temperature is obtained, the coefficient of influence, which is the change in temperature at the time of extraction for the change in the constant temperature at the present state, is obtained. Use to calculate the optimum solution and calculate the low temperature setting.

In this way, the low temperature set point obtained from the equation model is received by the distributed control system 30 to control the flow rate and the air amount so that the measured value is matched to adjust the intensity of the burner 31 in the furnace.

In the conventional mathematical model configuration, there is an error inevitably occurring in the time prediction calculation and the extraction temperature prediction calculation. As a result, the temperature setting value in the furnace may be inappropriate. In other words, in order to predict the extraction temperature of the material, it is necessary to know the ashing time of the material in each zone in the furnace.The estimation of the ashing time of the material is based on the current position of each material, rolling time of each material, and unexpected obstacles during rolling. In consideration of the pause due to the time is calculated in each day.

Here, the scheduled stop time should be input by the driver in consideration of the rolling roll replacement time and equipment inspection time, but since this time is flexible, it is not known exactly because the time is different from the actual pause time. The result of the phosphorus extraction temperature prediction calculation is also wrong.

In addition, in the extraction temperature prediction calculation, a calculation error occurs because it repeatedly calculates by dividing the minute time from the current point to the extraction scheduled time under the assumption that the current temperature is maintained from the current position to the extraction point. In addition, the calculation time is long, and the temperature setting calculation in the furnace cannot be completed within the calculation cycle.

The use of this low-precision mathematical model has a large deviation from the extraction target temperature, which adversely affects excessive fuel consumption and product quality.

The conventional mathematical model manages only the target temperature at the time of extraction and ignores the temperature raising process according to the heating pattern of the material. Therefore, this model can be used only for general steel such as carbon steel, and for special steel such as spring steel, which requires a special heating pattern (rapid heating).

For precise combustion control, it is necessary to set the optimum temperature with little calculation error within a reasonable time. However, the conventional calculation method is a calculator that calculates the time error for the prediction of the working time and the calculation error and the excessive calculation time in the extraction temperature prediction. Is difficult to solve.

The purpose of the present invention is to install a sensor that can measure the material temperature for each unit in order to eliminate the error in the prediction calculation, to correct the error between the calculated temperature and the measured temperature, as well as to control the extraction target temperature by applying the optimum heating pattern In addition, it is possible to control according to the heating pattern to provide a new type of combustion control method that enables the operation, such as by the rapid heating pattern that has a great impact on the product quality of special steel.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated based on an accompanying drawing.

2 is a schematic diagram of a combustion control system for explaining the present invention, the configuration of which is generally similar to the conventional system shown in FIG. The peculiarity here is that in addition to the first sensor 21 for detecting the atmosphere in the furnace 10, a second sensor 22 is further provided to sense the temperature of each material.

In the furnace temperature control process of the present invention using such a system, first, the temperature is received every cycle from the first sensor 21 that measures the atmospheric temperature of each unit in the furnace, and the material temperature at the present time is measured for all materials in the furnace. Calculating; Receiving a temperature value from the second sensor 22 measuring the temperature of the material in the furnace to calculate a difference between the calculated temperature and the measured temperature and correcting it; Calculating a set temperature by comparing the temperature distribution of all the materials in the furnace with the calculated temperature of the optimum heating pattern at the current time point obtained as described above and applying an influence coefficient for each unit; And controlling the flow rate supplied to the burner by transmitting the obtained on-set value to the distributed control system every cycle.

In particular, the present invention is to compare the difference between the temperature distribution and the optimum temperature rise pattern temperature for the entire material in the furnace that compensated the difference between the material calculation temperature and the actual temperature without going through the process of predictive calculation used in the existing mathematical model By compensating control, it is possible to control the heating pattern according to each steel type as well as the extraction target temperature.

First, in the step of calculating the material temperature (a) receives the temperature every cycle from the first sensor 21 for measuring the atmosphere temperature of each unit in the furnace to calculate the material temperature at the present time for all the materials in the furnace.

The material in the furnace changes in temperature due to radiant heat from the furnace walls, heat transfer from the atmosphere gas (heat exchange by convection), and heat transfer by conduction inside the material. As a prerequisite for calculating the temperature of the material, the temperature profile is divided into 10 points as shown in Fig. 3 by ignoring the temperature difference in the longitudinal direction of the material and considering the thickness direction and the width direction. Only one half of is calculated using the two-dimensional thermal conductivity equation.

The thermal conductivity governing equations and initial and boundary conditions in steel are as follows.

(Domination equation)

(Initial condition)

(Boundary condition)

here, : Specific heat, density, temperature, time, thermal conductivity

Stefan-Boltzman constant, heat absorption rate, shape factor

: Steel atmosphere temperature, Steel surface temperature, Tropical flow temperature

: Heat flux by radiation and convection

The thermal conductivity equation (2-1) was differentially calculated to calculate the temperature of the steel.

The differential expression is

Here, Ti: temperature of mesh i

: Mesh width and thickness direction length

: Heat flux of X, Y plane of mesh

The difference is expressed as

For the above equation to converge, the following conditional expression must be satisfied.

therefore Must be selected so that the following condition is satisfied.

On the other hand, when the material temperature calculation is completed, the process computer 20 measures the temperature measured value b of the material from the second sensor 22 installed in each unit 11, 12, 13 to measure the material temperature in the heating furnace. The difference between the calculated temperature and the calculated material is calculated (c), and the difference between the calculated temperature and the measured temperature is compensated for each unit (d).

This is expressed as follows.

Tip-Tcp = Ap

Tih-Tch = Ah

Tis-Tcs = As

Here, Tip, Ti, Tis: sensor measurement temperature of the preheating zone 11, heating zone 12, crack zone 13 material

Tcp, Tch, Tcs: Calculated temperature of preheating zone, heating zone, crack zone material

Ap, Ah, As: Difference between measured and calculated temperature in preheating zone, heating zone, and cracking zone

Only when the temperature difference of each unit obtained above is positive (Ap, Ah, As0) or all negative (Ap, Ah, As0), the value is compensated for each unit as follows.

(3 Ap + 2 Ah + As) / 6: Error compensation value of preheating zone 11

(2 Ah + As) / 3: Error compensation value of heating table 12

As: error compensation value of crack zone 13

Here, the position of the material in the current furnace is not too calibrated. For example, in the case of current heating element, only the temperature deviation of the heating zone and the temperature deviation of the cracking zone are considered, and the temperature deviation already passed is ignored.

In addition, the method of compensating the temperature deviation is only compensated if the deviation between the calculated temperature and the measured temperature is higher than a certain value in consideration of the temperature difference of the material surface when measuring the material temperature. Apply separately for each unit.

In this way, when the temperature calculation for all materials in the furnace is completed, the optimum temperature rise pattern (e) is derived for each steel type, and the temperature difference between the calculated temperature and the optimum temperature rise pattern temperature according to the position of all materials existing in the furnace for each unit. Calculate

The reason why the temperature rise pattern should be applied differently for each steel type is that special steels such as spring steel have extremely low temperature in the preheating zone, and then control the combustion of the rapid heating method that heats rapidly in the heating zone. When the temperature is high enough to crack the product, the load on the rolling mill is less and the product quality is improved. As such, the temperature rising pattern for each steel type is an important part in determining the product quality in producing special steel. In the existing mathematical model, only the target temperature during extraction is managed and the temperature raising process of the material is ignored. Therefore, it cannot be used for the control of special steel such as spring steel or stainless steel.

Once the temperature difference of each material is found, the sum of the temperature difference according to the location of the material's heating furnace is calculated. At this time, weight coefficient is calculated by applying the influence coefficient (f) and the importance of each steel grade. For example, when the material in the heating table is mixed with special steel such as spring steel and general steel such as mild steel, it is a method to control by placing more weight on special steel.

If this is expressed by formula (Roon setting calculation: g), it is as follows.

Here, Tpa, Tha, Tsa: each temperature (preheating zone, heating zone, cracking zone) set temperature

Tp, Th, Ts: each atmosphere temperature

Np, Nh, Ns: the number of materials present in each unit

Tsi, Tsj, Tsk: Temperature rising pattern temperature by steel grade

Tci, Tcj, Tck: Calculation temperature of material for each location

Wi, Wj, Wk: Importance factor by steel type

Cp, Ca, Cs: Influence coefficient for each unit

In the above formula, the importance factor for each steel type means that the temperature is set by giving more weight to steel types that have a greater influence on temperature when several steel types are mixed in the heating furnace. The temperature difference varies depending on the location, so the closer the material is to the extraction side, the smaller the change in temperature. When controlled in this way, by setting the temperature in the direction closest to the temperature increase pattern, not only the final extraction target temperature can be managed but also the special temperature increase pattern is possible according to each steel type.

After calculating the low temperature set point (g) by the above method, the temperature is transferred to the distributed control system 30 every cycle and the flow rate supplied to the burner 31 in the furnace is controlled to optimally control the material temperature in the furnace. Done.

As described above, the present invention, unlike the conventional mathematical model, by controlling the temperature rise pattern is not only possible to control the special steel grades, such as stainless steel or spring steel that is difficult to control in the existing model, but also the structure of the heating furnace is different (for example, heating table, It can be easily applied to a special type of furnace, and by controlling the extraction target temperature by the optimum pattern, it is possible to obtain stable operation of the furnace and fuel cost reduction (about 5% or more).

Claims (1)

Receiving the temperature inspection data every cycle from the first sensor for measuring the atmosphere temperature of each unit in the furnace, calculating the material temperature at the present time for all the materials in the furnace, and from the second sensor for measuring the material temperature in the furnace. Receiving the temperature data and calculating the difference between the calculated temperature and the measured temperature in the previous step, and correcting it, and comparing the temperature distribution of all materials in the furnace obtained at the previous step with the calculated temperature of the optimum heating pattern, Comprising the step of calculating the on-set device, and the step of controlling the amount of air and gas supplied to the burner by transmitting the set-on temperature to the injection control system every cycle, and is coupled to the process computer and distributed control system A combustion control method of a heating furnace having first and second sensors and a burner.