JPH1088248A - Method for controlling continuous heat treatment furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means for executing suitable and stable temp. control of a continuous heat treatment furnace. SOLUTION: In a heating zone 2 arranging direct firing type burner in the continuous heat treatment furnace, a relation between 'line speed' and 'fuel flow rate of the direct firing type burners dividedly arranged into plural zones' is beforehand obtd. Then, in the case the necessity extinguishing or igniting the direct firing burner 8 in a specific zone caused by variation of the line speed develops, the compensation of the fuel flowing rate is executed so as to satisfy the preset relation in the other zone to prevent the intermittent variation of the fuel flow rate, and the continuous variation of the fuel flow rate is secured. Further, in a soaking zone 3 arranging cup type burners 5, the combustion rate of the burner is controlled according to feedback control signal from a strip thermometer 7, and air/fuel ratio of the burner is controlled and thus, the operator deals with a low loaded operation of the heat treatment furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct-fired burner (a burner of a type heated by forced convection heat transfer of combustion gas) and a cup-type burner (heated by radiant heat transfer). Heating pattern (continuous annealing furnace for strip and wire, continuous annealing and pickling equipment for stainless steel plate) equipped with a type of burner), even if the line speed fluctuates, set heating pattern The present invention relates to a method for controlling a furnace for accurately maintaining (temperature).

[0002]

2. Description of the Related Art A continuous heat treatment furnace is used to continuously pass, for example, a stainless steel strip or the like hardened by hot rolling or cold rolling, and to heat the strip to a predetermined temperature. It is an essential facility for improving properties and other functions. In this continuous heat treatment furnace, a “heating method by radiant (radiation) heat transfer from the furnace wall” has been mainly employed in order to guarantee sufficiently uniform heating of the material to be treated.

[0003] However, in the continuous heat treatment furnace of this type, when a state in which the sheet passing speed has to be reduced occurs, an operation of lowering the furnace temperature is performed in order to suppress a rise in the temperature of the material to be processed. However, the thermal responsiveness at that time was slow, and there was a strong tendency for over-annealing (a phenomenon in which the temperature of the material to be processed rises above a target value) as the vehicle decelerated. For this reason, the continuous heat treatment furnace of the type that heats by radiant heat transfer has a problem that the allowable range of deceleration speed for obtaining a predetermined quality is narrow, and the product yield is likely to be reduced.

[0004] Therefore, the first half of the furnace following the entrance side of the furnace is referred to as a "heating zone having a direct fire burner (a burner of a type heated by forced convection heat transfer of combustion gas)" to provide a thermal response. A "cup-type burner (a burner of a type that heats by radiant heat transfer)" is provided to improve the temperature of the material to be heated only in a portion extending to the exit side of the furnace. Continuous heat treatment furnaces with "so-tropical" have been adopted. In such a furnace, the direct-fire burner arranged in the heating zone is divided into a plurality of zones so as to give a specific heating pattern to the material to be heated.

[0005] However, as described above, "" a heating zone having an open-fire burner for providing a predetermined heating pattern "and" a solitary tropical zone having a cup-type burner for ensuring a predetermined heating temperature of a steel sheet ". Also has the following problems. That is, in the above continuous heat treatment furnace, "means for lowering the fuel flow rate of the burner to lower the annealing temperature to the lower limit of the predetermined control range" is generally adopted as a method of controlling the temperature during low load operation such as deceleration. Can be However, the burner has a stable combustion range, and combustion outside the lower limit cannot be performed. For this reason, when low-load operation outside the lower limit range is required, the burner must be extinguished, and at this time the fuel flow to the burner is interrupted, and the fuel flow becomes Continuous points occur. Further, when the line speed is accelerated and the burned-out burner is ignited, the discontinued fuel flow is restarted, so that a discontinuous point of the fuel flow occurs at this time as well. When the discontinuous point of the fuel flow rate occurs as described above, the heating temperature of the material to be heated fluctuates at the discontinuous point of the fuel flow rate, resulting in a bad influence on the quality of the agent to be treated. .

Accordingly, "a heating zone having an open flame burner which gives a predetermined heating pattern to the material to be heated" or "a cup type bar which secures and guarantees a predetermined heating temperature of the material to be heated."
In a continuous heat treatment furnace equipped with a "soaking zone having a knurl", development of means for performing appropriate and stable temperature control has been an important issue.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above problems and to enable appropriate and stable temperature control of a continuous heat treatment furnace. did it. (a) In a heating zone having an open-fire burner divided into a plurality of zones, the burner amount of the burner should be reduced so as not to cause over-annealing according to the reduction of the line speed. If it is necessary to adjust below the lower limit of the stable combustion range of the burner in the process of going, the burner in the entire heating zone may not be extinguished, without causing the fuel flow to be interrupted. The fire extinguishing of the corner is limited to the direct flame burner belonging to a certain zone corresponding to the combustion adjustment amount of the plurality of zones, and the direct fire burner belonging to another zone. In the case of-, if the combustion is performed in consideration of the extinguished direct fire burner, the fuel flow rate in the heating zone is secured while the calorific value adjustment according to the reduction of the line speed is achieved, and the fuel in the heating zone is secured. Intermittent changes in the flow rate can be prevented. In order to adjust the fuel flow rate using the burner of another zone, it is necessary to ignite the direct burner of the zone which has been extinguished because the line speed has been accelerated. This is also effective in the case where the temperature of the furnace can be controlled more accurately.

(B) In a solitary tropical zone equipped with a cup-type burner, when it is necessary to operate with a calorie lower than the combustion range of the burner due to a reduction in line speed or the like, the burner is also required. Even if the fire is not extinguished, the air-fuel ratio of the burner (the ratio of fuel to air supplied to the burner: air ratio) can be adjusted to enable low-load operation and intermittent fuel flow. Changes can be prevented.

The present invention has been made based on the above findings and the like, and provides a method for controlling a continuous heat treatment furnace described below. (1) In the continuous heat treatment furnace, "line speed" and "multiple zones" were determined in advance by the heat transfer model in the "heating zone in which the material to be heat treated was heated according to the heating pattern set by the direct fire burner". The fuel flow rate of the direct-fired burner divided and arranged in a separate zone, it is necessary to extinguish or ignite the direct-fired burner in a specific zone due to a change in line speed. In such a case, the fuel flow rate is compensated in another predetermined zone so as to satisfy the above-mentioned relationship, thereby preventing intermittent change in the fuel flow rate and ensuring continuous change in the fuel flow rate. A method for controlling a continuous heat treatment furnace.

(2) In the "uniform tropics in which the material to be heat-treated is heated by a cup-type burner" arranged on the outlet side of the continuous heat-treating furnace, the burner burning amount is measured by a plate thermometer. A method for controlling a continuous heat treatment furnace, wherein the method is controlled according to a feedback control signal and the air-fuel ratio of the burner is also controlled to cope with low-load operation of the heat treatment furnace.

(3) In a continuous heat treatment furnace, in a heating zone in which a material to be heat-treated is heated according to a set heating pattern with a direct-fired burner, the "line speed" and " It is necessary to extinguish or ignite the direct-fired burner of a specific zone by changing the line speed in advance by determining the relationship with the fuel flow rate of the direct-fired burner divided and arranged in the zone. In the event of occurrence of a fuel flow, the fuel flow rate is compensated in another predetermined zone to satisfy the above-mentioned relationship, intermittent changes in the fuel flow rate are prevented, and continuous changes in the fuel flow rate are ensured.
Further, in the solitary zone where the material to be heat-treated is heated by a cup-type burner disposed on the outlet side of the heat treatment furnace, the burner burning amount is controlled according to a feedback control signal from a sheet thermometer. A method for controlling a continuous heat treatment furnace, wherein the air-fuel ratio of the burner is also controlled to cope with low-load operation of the heat treatment furnace.

As described above, according to the present invention, when a metal strip or wire is heat-treated in a continuous heat treatment furnace, the cause of poor temperature control in the heating zone of the continuous heat treatment furnace when the line speed is reduced or accelerated. In order to eliminate the occurrence of the "discontinuous point of fuel flow to the heating zone", only one of the direct-fired burners divided into a plurality of zones is extinguished or ignited. At the same time, in accordance with the "rule determined by the required heating pattern", the "other zone" compensates for the fuel flow change at the time of fire extinguishing or ignition equivalently, so that the fuel flow according to the line speed can be continued. In the tropics, the measured air temperature is set to be larger than that in the steady state by setting the air-fuel ratio under deceleration according to the feedback signal from the thermometer. Set the temperature so that the target value is not exceeded. It has the feature in that control,
Hereinafter, the present invention will be described with reference to the drawings.

FIG. 1 shows a continuous annealing equipment for a stainless steel strip.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic explanatory view according to an example, in which this equipment has a continuous annealing furnace composed of a pre-tropical zone 1, a heating zone 2, and a solitary zone 3. The heating zone 2 has a direct-fired burner-4 divided into a plurality of zones, and the soaking zone 3 has a cup-type burner 5, respectively. Plate thermometers 6 and 7 are installed on the exit side of tropical zone 3.

The stainless steel strip 8 to be treated is supported by the bridle roll 9, enters the continuous annealing furnace from the pre-tropical zone 1 side, and is cooled after leaving the soaking zone 3, but is cooled. A speed detector 10 is attached to 9 to detect the line speed. The line speed detected by the speed detector 10 is taken into the computer 12, and is used for setting a fuel flow rate and a target plate temperature.

When the control according to the present invention is carried out in such a continuous annealing equipment, first, information (such as material and thickness of the steel sheet, , Plate width, etc.) are received by the computer 12, which calculates the fuel flow rate and control rules of the direct-fired burner-4, and, if necessary, the target plate temperature of the solitary zone 3 at the same time. . That is, the computer 12 creates a heat transfer model of the heating zone 2 based on the information received from the production management system 11, and uses the heat transfer model in the computer 12 to determine “line speed V and V” as shown in FIG. The relation of the total fuel flow rate Q of the heating zone 2 "is calculated in advance. If necessary, a "relationship between the line speed V and the target plate temperature T" as shown in FIG.

A) Control of the heating zone 2 After the above preparation, the control of the heating zone 2 is performed as follows. The heating zone 2 is composed of a plurality of zones (here, it is described as 5 zones of 1Z to 5Z).
Emissions per flame-type Ba - Na - stable combustion range of the group is restricted by the maximum fuel flow rate q _max and a minimum fuel flow q _min allowed as indicated in the graph of (a) in FIG. 4. In addition,
Graph in FIG. 4 (b) is obtained by describing the relationship between the stability maximum of the fuel flow rate q in the flammable range heating zone 2 total fuel flow rate Q _max.

Here, the "relationship between the line speed and the total fuel flow rate in the heating zone" is related by the computer 12 as described above. Further, based on this, a direct fire type for securing a predetermined heating pattern is used. The burner fuel flow rate and control rules are calculated and set. The control Le - Le, for example the maximum speed ratio X (= line speed V and the ratio between the maximum line speed V _max: V / V _max) which zone the state of - zone down should control the fuel flow - of emissions Is set. FIG. 5 shows an example of this setting. The fire extinguishing command (ZER) is issued to each zone.
O), maximum fuel flow holding command (max), control target zone
The command (C) and the minimum fuel flow holding command (min) are determined according to the "necessary heating pattern of the steel sheet".
FIG. 6 is a schematic diagram of this.

The control process will be described with reference to FIGS. 5 and 6. When the maximum speed ratio X is "10", the control target zone command (C) is used to control the fuel in the zone 1Z according to the line speed. Flow control is performed (FIG. 6). The adjustment of the fuel flow rate is performed by the fuel flow rate controller 13 (see FIG. 1) and the fuel flow rate control valve 14 which have received instructions from the computer. When X decelerates to less than 9, 1
In Z, the minimum fuel flow holding state (q _min : in FIG. 6) is held, and instead, 2Z is the control target and the fuel flow compensation control is performed (in FIG. 6). X is 8
Is reached, the "q _min amount at 1Z = compensation amount at 2Z" is reached, and when X is reduced to less than 8, the fire is extinguished at 1Z by a fire extinguishing command (ZERO) (in FIG. 6).
At the same time, at 2Z, the fuel flow is increased by the compensated amount (in FIG. 6). By executing the above control in accordance with the rules shown in FIG. 5, it is possible to continuously control the total fuel flow rate until X becomes 1. At the time of heating (at the time of temperature rise), control may be performed so as to follow the reverse process of the above-described process, and thus, continuous total fuel flow control can be similarly performed.

B) Control of level tropics 3 Control of level tropics 3 is performed as follows. As shown in FIG. 1, the leveling zone 3 has a cup-type burner 5, a plate thermometer 7, a plate temperature controller 15, an air-fuel ratio controller 16, a fuel flow rate disposed at the outlet of the continuous heat treatment furnace. It has a control valve 17 and an air flow control valve 18, and performs feedback control using a target temperature value from the computer 12 and a detected value of the sheet thermometer from the sheet thermometer 7. When the line speed is reduced, the sheet temperature feedback control is performed so that the material to be heated (steel sheet) maintains the target temperature, but the fuel flow rate below the lower limit of stable combustion of the burner is performed. When adjustment is required, as shown in FIG. 8 to be described later, combustion is performed by performing an "operation to increase the air-fuel ratio (increase the air ratio)" without extinguishing the burner. The temperature of the exhaust gas is lowered, thereby enabling low-load operation.

By performing the above control in the continuous heat treatment furnace, intermittent changes in the fuel flow rate can be prevented, and proper and stable temperature control can be achieved. Of course, the above-described furnace control may be carried out only in the heating zone or in the solitary tropics, depending on the situation. However, it is preferable to perform the control in both the heating zone and the soaking tropics because it leads to more accurate temperature control. .

Each zone of the heating zone is changed according to the line speed.
Concretely, the table for determining the state of the temperature and the solitary tropics is set in advance from the necessary heating pattern (the necessary heating rate of the heating zone, the heating temperature range, the necessary soaking time, etc.) It is possible to change the rule according to the coil information.

Next, the present invention will be described with reference to examples.

EXAMPLE In this example, a pre-tropical zone 1, a heating zone 2, and a level tropical zone 3 as shown in FIG.
The heating zone 2 is an annealing process for a stainless steel strip (SUS304, plate thickness: 0.7 mm) using a continuous annealing facility which is divided into 6 zones of 1Z to 6Z and provided with an open flame burner. Tried. In this annealing process, the line speed is gradually reduced from the maximum of 100 m / min, and at the same time, the following annealing furnace control is performed to change the sheet temperature (the temperature of the material to be processed). The situation was investigated.

In the annealing process, first, information necessary for heat treatment is received by a computer 12 from a higher-level production management system 11 shown in FIG. 1, and the computer 12 transmits the information and a previously prepared information. From the heat model, the fuel flow rate and the control rule of the direct-fired burner 4 in the heating zone 2 were calculated and set (that is, the "line speed" and "load speed" at which the target plate temperature was achieved). The relationship with the "total fuel flow rate of the direct-fired burners arranged in the tropics" is determined, and the "direct-fired burners are determined according to the reduction of the line speed" in the case of FIGS. And a control rule for compensating the fuel flow rate in accordance with the fire extinguishing in another zone so that the intermittent fuel particle quantity does not occur in the heating zone 2. Was calculated and set). At the same time, based on the information from the production management system 11 and the heat transfer model, the target plate temperature of the soaking zone 3 is also calculated, and based on this, the field temperature from the sheet thermometer 7 installed at the exit of the soaking zone 3 is calculated. Cup type burner-5 according to the feedback control signal
The control rules for adjusting the combustion amount and the air-fuel ratio of were also calculated and set.

FIG. 7 shows the "total fuel flow rate in the heating zone", the "sheet temperature at the heating zone outlet and the soot zone outlet" obtained when the continuous annealing of the stainless steel strip was performed under the above control, It shows the results of "feedback signal of leveling plate thermometer" and "air-fuel ratio signal to leveling cup-type burner".
The following can be confirmed from the results shown in FIG.

First, in the heating zone 2, when the maximum line speed is 100 m / min, the total fuel flow Q in the heating zone is 100
%, And as the line speed is reduced, the direct fire type burners are sequentially extinguished from zone 1Z, and
The line speed for extinguishing Z, 2Z, 3Z... 6Z was 85, 70, 55, 40, 25, and 14 m / min, respectively.
The other zone compensates for the change in fuel flow according to the rules according to the above, so that the total fuel flow in the heating zone changes continuously and no interruption occurs, and as a result, the heating zone outlet plate temperature is also continuous and smooth. It is a changing situation.

In this continuous annealing furnace, the lower limit of stable combustion of the cup-type burner installed in the soaking zone 3 is 30% as shown in FIG. 8, and the line speed is reduced to 38 m / min. When the feedback signal of the sheet thermometer 7 reaches 30% at this time, when the deceleration further proceeds, the air-fuel ratio (air ratio) according to the degree of the deceleration as set by the computer 12 as shown in FIG. Was raised. As a result, the temperature could be continuously reduced without extinguishing the burner, and the plate temperature at the soaking zone outlet could be smoothly reduced in accordance with the target value.

[0027]

As described above, according to the present invention, it is possible to properly avoid a heat treatment failure (for example, over-annealing due to a decrease in line speed) in a continuous heat treatment furnace, which tends to be caused by a change in line speed. Thus, industrially useful effects such as an increase in the operation range of the continuous heat treatment furnace and an improvement in product yield can be achieved.

[Brief description of the drawings]

FIG. 1 is an example of an apparatus configuration of a continuous heat treatment facility applied in the present invention.

FIG. 2 is a relationship diagram between a line speed and a total fuel flow rate in a heating zone.

FIG. 3 is a graph showing a relationship between a line speed and a target temperature of a solitary tropical zone.

[4] 1 zone - per emission direct-fired bar - Na - relationship between the maximum total fuel flow rate Q _max of the fuel flow rate q and the heating zone of stable combustion range of the graph (a) Toko showing the stable combustion range of the group Is a graph (b) explaining the above.

FIG. 5 is a heating zone zone control rule showing the maximum speed ratio of the line and the combustion state of each zone.

FIG. 6 is a graph showing the control rules of the heating zone shown in FIG. 5;

FIG. 7 is a graph showing a control example of the continuous annealing furnace in the embodiment.

FIG. 8 is a diagram showing a relationship between a plate thermometer feedback signal and an air-fuel ratio.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pre-tropical zone 2 Heating zone 3 Uniform tropical zone 4 Direct-fired burner 5 Cup-type burner 6 Sheet thermometer 7 Sheet thermometer 8 Stainless steel strip 9 Bridle roll 10 Speed detector 11 Production control system 12 Computer 13 Fuel flow controller 14 Fuel flow control valve 15 Plate temperature controller 16 Air-fuel ratio controller 17 Fuel flow control valve 18 Air flow control valve

Claims (3)

[Claims] In a continuous heat treatment furnace, "line speed" and "plurality" are determined in advance by a heat transfer model in a "heating zone in which a material to be heat treated is heated according to a set heating pattern by a direct-fired burner". It is necessary to extinguish or ignite the direct-fired burner of a specific zone by changing the line speed in advance by determining the relationship with the fuel flow rate of the direct-fired burner divided and arranged in the zone. In the case of occurrence of fuel flow, the fuel flow rate is compensated in another predetermined zone so as to satisfy the above-mentioned relationship, thereby preventing intermittent changes in the fuel flow rate and ensuring continuous changes in the fuel flow rate. A method for controlling a continuous heat treatment furnace. 2. In the "uniform tropics in which the material to be heat-treated is heated by a cup-type burner" disposed on the outlet side of the continuous heat-treating furnace, the burner burn-up amount is measured from a sheet thermometer. A method for controlling a continuous heat treatment furnace, characterized by controlling according to a feedback control signal and also controlling an air-fuel ratio of a burner to cope with a low load operation of the heat treatment furnace. 3. In a continuous heat treatment furnace, in a heating zone in which a material to be heat-treated is heated according to a set heating pattern by a direct-fired burner, "line speed" is determined in advance by a heat transfer model.
And "the fuel flow rate of the direct-fired burner divided and arranged in a plurality of zones", and the direct-fired burner of a specific zone is extinguished or When it becomes necessary to ignite, the fuel flow rate is compensated by another predetermined zone so as to satisfy the above-mentioned relationship, and the intermittent change in the fuel flow rate is prevented to ensure a continuous fuel flow rate change. Further, in a soaking zone where the material to be heat-treated is heated by a cup-type burner arranged on the outlet side of the heat treatment furnace, the burner burn amount is controlled according to a feedback control signal from a sheet thermometer. Along with
A method for controlling a continuous heat treatment furnace, characterized in that the air-fuel ratio of a burner is also controlled to cope with low-load operation of the heat treatment furnace.