JPH04285130A - Controlling method for flow rate of combustion gas in heating furnace of continuous annealing equipment - Google Patents

Abstract

PURPOSE:To control the flow rate of combustion gas in a heating furnace in a continuous annealing equipment so that the surface temp. of a radiant tube is uniformed between the respective zones. CONSTITUTION:The inside of a heating furnace is partitioned into a plurality of zones along the advancing direction of a strip. Moreover, necessary quantity of heat at every zone is calculated on the basis of a temp. rise curve wherein the temp. rise speed of this strip is predicted as the strip is passed through every zone. The flow rate of combustion gas supplied to the burners of respective radiant tubes is controlled in accordance with this quantity of heat. The durable period of the radiant tube is uniformed. The controlling precision of the temp. of the strip is enhanced. The consumption unit of fuel is improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the flow rate of combustion gas in a heating furnace of continuous annealing equipment.

0002

[Prior Art] As a heating furnace for continuous strip annealing equipment, a large number of radiant tubes are arranged in parallel so as to face the advancing strip surface, combustion gas is combusted within the radiant tubes, and is radiated from the radiant tube surface. A type of heating device in which the strip is heated by radiant heat is known. On the other hand, methods for controlling the amount of combustion gas supplied to the burners provided in each radiant tube include a method of distributing the amount of gas supplied equally to all burners, and a method of controlling the amount of combustion gas supplied to the burner on the inlet side to the maximum. Generally, a method is adopted in which the gas supply amount is increased at a constant rate toward the outlet side.

0003

[Problems to be Solved by the Invention] Among the above methods, according to the former method, the surface temperature of the radiant tube is relatively low because the plate temperature is low on the inlet side and the amount of heat absorbed by the strip is large; Conversely, the surface temperature of the radiant tube tends to become excessively high. As a result, the degree of wear is not uniform for each radiant tube,
This is undesirable in terms of equipment maintenance because of the difference in service life.

On the other hand, in the latter case, although such inconveniences can be corrected to some extent, since the rate of change in the gas supply amount is generally fixed, it is not possible to perform appropriate control according to the target plate temperature, actual furnace temperature, etc. There is a drawback that there is no

[0005] The present invention was devised in order to eliminate such inconveniences of the prior art, and its main purpose is to make the surface temperature of the radiant tube uniform between each zone in consideration of equipment maintenance. An object of the present invention is to provide a combustion gas flow rate control method in a heating furnace of continuous annealing equipment.

[0006]

[Means for Solving the Problems] According to the present invention, such an object is to control the flow rate of combustion gas in a heating furnace of a continuous strip annealing facility equipped with a plurality of radiant tubes arranged in parallel along the course of the strip. The method involves dividing the inside of the heating furnace into multiple zones along the direction in which the strip travels, and calculating the amount of heat required for each zone based on a temperature increase curve that predicts the rate of increase in strip temperature as the strip passes through each zone. This is achieved by calculating the amount of heat and controlling the flow rate of combustion gas supplied to the burner of each radiant tube in accordance with the amount of heat.

[0007]

[Operation] According to such a configuration, the amount of heat supplied can be controlled so that the surface temperature of each radiant tube becomes uniform by setting the rise curve of the strip temperature. Moreover, since the combustion gas flow rate is controlled according to the required amount of heat calculated for each zone, it is possible to immediately respond to changes in strip specifications.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the present invention will be described in detail below based on specific embodiments shown in the accompanying drawings.

FIG. 1 shows a schematic configuration of a strip heating furnace 1 to which the present invention is applied, in which a large number of hearth rolls 2 are arranged in parallel at equal intervals in the upper and lower positions of the furnace body. . The strip 3 is folded in multiple strips and stretched between the upper and lower rolls 2, and is given an appropriate tension and speed by driving the hearth rolls 2, and is fed from the inlet 4 to the outlet 5 inside the furnace. The steps are to proceed sequentially.

A radiant tube type heater 6 is installed so as to face the surface of the strip 3 stretched between the rolls 2.
Many are arranged side by side. This radiant tube type heater 6 is of a known type that burns combustible gas within its tube, and the amount of heat is controlled by adjusting the flow rate of combustion gas supplied to a burner (not shown). has been done.

Now, from the viewpoint of equipment protection, the most preferable heat amount control of the radiant tubes is to make the surface temperature of each radiant tube uniform. Assuming that as a certain portion of the continuously passed strip passes through the furnace, its temperature increases in the pattern shown in Figure 2, the surface temperature of each radiant tube is made uniform. In order to achieve this, it is sufficient to balance the burner calorific value of each zone where the furnace is divided appropriately with the strip heat absorption amount on the temperature rise curve, so the heat amount given to the strip is determined by the hatched area in the diagram. It will be expressed. Therefore, it is understood that the flow rate of combustion gas of the burner in each zone may be adjusted according to this area ratio.

That is, as shown in the control flow of FIG. 3, first, based on the coil information (material specifications, manufacturing specifications) from the computer 11, a speed pattern is set in consideration of the furnace capacity and threadability. Set by the operation support AI section 12. At the same time, an optimal target plate temperature schedule is set based on this speed pattern, including transient conditions before and after the welding point.

Next, in the predictive control type optimal control section 13,
Future changes in plate temperature are predicted based on the target plate temperature schedule, and the combustion gas flow rate is calculated to minimize plate temperature deviation and flow rate fluctuation. Then, in the zone-specific distribution unit 14, this flow rate is distributed to each zone so that it becomes an appropriate flow rate, and an air ratio corresponding to this is calculated, and based on this, the flow rate of the combustion gas to be supplied to the furnace burner 15 is determined. Control. The combustion gas flow rate as this control end is set based on the model equation shown below.

[0014]

[Formula 1]

[0015] However, Ts: exit side plate temperature
a1 ・bi ・ci: model parameters
d: wasted time n
: Time to consider the influence of combustion gas flow rate on plate temperature t
: Time u
: Combustion gas flow rate vi
:Function of center speed, plate thickness, plate width, etc.

0016
] The above model formula calculates the current temperature using the past plate temperature Ts (t-d), the combustion gas flow rate u for the time that can affect the current plate temperature, and the function vi of the central velocity, plate thickness, plate width, etc. This is a regression equation that determines the plate temperature Ts (t). By rewriting this formula into the future tense, it is possible to predict the plate temperature during speed changes and transient conditions before and after the welding point, and it is possible to obtain a manipulated variable (gas flow rate) with less plate temperature deviation.

[0017] The manipulated variable is as shown in the following model formula:
It is determined by an evaluation function to minimize the deviation from the plate temperature target value and the fluctuation in the combustion gas flow rate. Here, the deviation from the plate temperature target value is a factor related to control accuracy, and the minimization of flow rate fluctuation is a factor related to realizing stable operation, but which factor is prioritized is weighted by w. Furthermore, according to this model formula, the manipulated variable is the combustion gas flow rate, so high responsiveness can be obtained.

[0018]

[Formula 2]

[0019] However, Ts: Expected plate temperature at exit side T
sr: Target outlet plate temperature N2
: Time to consider plate temperature deviation NU : Time to consider flow rate fluctuation w : Weight of plate temperature deviation and flow rate fluctuation

On the other hand, in the adaptive control section 16, each coefficient or control parameter is adaptively corrected and sequentially identified based on control results such as the actual plate temperature and the actual gas flow rate fed back from the heating furnace 1.

Next, the combustion gas flow rate setting routine for each zone will be explained below with reference to FIG. First, the current flow rate results for each zone flpvi and the air ratio mi for each zone
The data is imported in step 1. Then, the flow rate flpvci for each zone corresponding to the standard air ratio and the actual flow rate flp
vi is converted in step 2, and the total flow rate FLpvc corresponding to the standard air ratio is calculated in step 3. Next, in step 4, an evaluation function (
The fuel flow rate increment ΔFLopt(t
) to determine the total flow rate set value FLsv.

For zones that are not in use, the flow rate flsvk is uniformly output as 0 (step 5), and C
Flow rate flsvj of zones operating in modes other than PU mode
, the actual flow rate flpvi is output (step 6
), flow rate flsv of the zone operating in CPU mode
Regarding i, the value obtained by subtracting the total actual flow rate value Σflsvj of zones operating in a mode other than the CPU mode from the total flow rate set value FLsv obtained in step 4, and dividing it by the predetermined inter-zone distribution ratio wfi/Σwfi (Step 7).

Furthermore, it is determined in step 8 whether or not the set value flsvi for the CPU mode zone obtained in step 7 is equal to or higher than the controllable lower limit flow rate, and if it is equal to or higher than the lower limit flow rate, the flow rate data is outputted, If the lower limit flow rate is not reached, the flow rate data is output through a low-load combustion processing routine to be described later.

[0024] When the range of change in the thickness and width of the strip to be processed is large and low-load combustion is required where the set value of the combustion gas flow rate is below the controllable limit, the method shown in FIG.
The combustion gas flow rate is set by the low-load combustion processing routine shown in .

If there is a zone that does not meet the control lower limit flow rate, first compare the control lower limit flow rate x number of zones and the total flow rate in step 11, and if the total flow rate exceeds the control lower limit flow rate x the number of zones. In step 12, zones that are below the control lower limit flow rate are set to the control lower limit flow rate, and in step 13, the flow rates in other zones are reduced so that the calculated flow rate and the corrected total flow rate are equal.

Next, the combustion gas flow rate of all zones and the control lower limit flow rate are compared in step 14, and if the flow rate of all zones is less than the control lower limit flow rate, the process returns to step 11 and the above program is repeated.

On the other hand, if it is determined in step 11 that the total flow rate is less than the control lower limit flow rate times the number of zones,
In step 15, the flow rate of all zones is set to the control lower limit flow rate, and the air ratio is set so that the value obtained by subtracting the exhaust gas loss heat from the calorific value at the control lower limit flow rate becomes the amount of heat originally required to heat the strip. 16, and output these values.

On the other hand, if it is determined in step 14 that the flow rate in all zones is equal to or higher than the control lower limit flow rate, step 12
Additionally, the values of the flow rate and standard air ratio determined in step 13 are output.

FIG. 6 shows the concept of combustion gas flow rate control according to the above.
Shown below.

[0030]

As described above, according to the present invention, the heat generation amount of the burner is controlled by the combustion gas flow rate so that the surface temperature of the radiant tube becomes uniform according to the amount of heat absorbed by the strip. It becomes possible to extend the lifespan. Furthermore, since the distribution of combustion gas for each zone is calculated and optimally controlled, fine-grained furnace temperature control can be performed according to the furnace conditions, increasing plate temperature control accuracy and reducing walk width fluctuations. be done. In addition, load distribution between zones is optimized, improving fuel consumption.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a heating furnace to which the present invention is applied.

FIG. 2 is a strip temperature rise diagram showing the amount of heat received by the strip in each zone.

FIG. 3 is a control configuration diagram according to the present invention.

FIG. 4 is a control flow diagram showing a zone-by-zone combustion gas flow rate setting routine.

FIG. 5 is a control flow diagram showing a combustion gas flow rate setting routine during low-load combustion.

FIG. 6 is a combustion gas flow rate setting diagram for each zone.

[Explanation of symbols]

1 Strip heating furnace 2 Hearth roll 3 Strip 4 Entrance 5 Exit 6 Radiant tube heater 11 Computer 12 Furnace operation support AI 13 Predictive control type optimal control unit 14 Zonal distribution department 15　Furnace burner 16 Adaptive control section

Claims (1)

[Claims] 1. A combustion gas flow rate control method in a heating furnace of continuous strip annealing equipment equipped with a plurality of radiant tubes arranged in parallel along the course of a strip, the method comprising: A temperature rise curve is set that predicts the rate of rise in strip temperature as the strip passes through each zone, and the burner of each radiant tube is set according to the required heat amount for each zone calculated based on the curve. A method for controlling the flow rate of combustion gas in a heating furnace of continuous annealing equipment, the method comprising: controlling the flow rate of combustion gas supplied to the heating furnace of continuous annealing equipment.