JPH10195545A - Preheating method for continuous annealing equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently heat a metallic strip by executing the change over of a heat reserve process and a heat radiating process to plural heat reservoirs in order in a regenerative heating device and controlling the pressure of hot blast blown to the metallic strip at the time of changing over. SOLUTION: Combustion exhaust gas in the heating furnace 1 for metallic strip 9 is introduced into the regenerative heating device 4 through a piping 3 to reserve the sensible heat of the exhaust gas. Atmosphere in a preheating furnace 5 is sucked with a circulating fan 6 and passed through the regenerative heating device 4 through a circulating gas piping 7, and the reserved sensible heat is received and introduced to the chamber 8 in the preheating furnace 5 and also, blown to the metallic strip 9 with the pressure of the circulating fan 6. In this constitution, plural heat reservoirs are provided as one set in the regenerative heating device 4 and the change over of the heat reserve process and the heat radiating process of each heat reservoir is executed in order by opening/closing the change over adjusting value. Further, at the time of changing over the heat reserve process and the heat radiating process of each heat reservoir, the variation of calory blown to the metallic strip 9 is compensated by controlling the blowing pressure of the circulating fan 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a preheating method for preheating a metal strip to be annealed by utilizing the sensible heat of exhaust gas from a continuous annealing facility, and more particularly, to a preheating furnace using a heat exchange facility having a heat storage device. The present invention relates to a preheating method for a continuous annealing facility that efficiently heats a passing metal strip, increases the temperature on the exit side of a preheating furnace, and uniformly heats the strip in the longitudinal direction.

[0002]

2. Description of the Related Art In continuous annealing equipment for metal strips, before the metal strip is introduced into the heating furnace for the purpose of lowering the load on the heating furnace, extending the life of the fuel consumption unit and the radiant tube, and improving the efficiency of the heating furnace equipment. Preheating is performed to increase the sheet temperature to some extent. For example, conventionally, waste heat contained in the combustion exhaust gas used for heating the heating furnace has been used, and the sensible heat of the exhaust gas has been exchanged by a heat exchanger into an atmosphere gas of a preheating furnace, which is a pre-process, and collected. There is generally known a method in which an atmospheric gas heated by a pressure is blown toward the surface of a metal strip plate in a preheating furnace under pressure. This method is also effective from the viewpoint of energy saving.

In such a method for preheating a metal strip, in order to make the atmosphere gas circulating in the preheating furnace efficiently receive the heat contained in the combustion exhaust gas of the heating furnace, first, the heat storage body of the heat exchanger is used. Heating the regenerator by passing the combustion exhaust gas, and when the regenerator is sufficiently heated, passing the atmosphere gas circulating in the preheating furnace into the regenerator to heat the atmosphere gas. A regenerative preheating method has been proposed.

[0004]

Further, in connection with this regenerative preheating method, three or more regenerators are set as one set, and in each set, the regenerators for heating the regenerating tropics of the respective regenerators are provided. The process and the heat release process of releasing the heat stored in the heat storage device to the circulating atmosphere gas are sequentially performed with the timing shifted by the operation of the switching valve, so that the flow of both the combustion exhaust gas and the circulating atmosphere gas is delayed. The inventors have previously developed a method that allows operation without any problems.

[0005] As described above, three or more of the heat storage elements are taken as a set, and in each set, the heat storage process of heating the heat storage area of each heat storage element and the heat stored in the heat storage device are released to the circulating atmosphere gas. According to a method in which the heat radiation process is sequentially performed at different times by the operation of the switching valve, the amount of heat blown to the metal strip can be averaged, which is advantageous. However, at the time of switching between the heat storage and heat dissipation processes or at the time of switching between the heat dissipation and heat storage processes, the flow rate and fluctuation of the circulating atmosphere gas occur, so that the amount of heat blown to the metal strip fluctuates. In some cases, there is room for improvement in this respect.

The present invention advantageously solves the above-mentioned problem, and minimizes fluctuations in the sheet temperature of a metal strip caused when a heat storage element is switched in a heat storage type preheating method, thereby maintaining high-efficiency heat exchange. Another object of the present invention is to propose a preheating method for continuous annealing equipment capable of obtaining a metal strip of stable quality.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a combustion exhaust gas generated from an annealing furnace in a continuous annealing facility is led to a regenerative heat exchange device to accumulate the sensible heat of the exhaust gas, and then a furnace atmosphere gas used in the furnace is used. Is introduced into the regenerative heat exchange device to raise the temperature, then led to a preheating furnace, and sprayed on the surface of the metal strip to be passed through the furnace to perform preheating, wherein the regenerative heat exchange device is A plurality of heat storage elements are set as a set, and the heat storage process and the heat radiation process of each heat storage material are sequentially switched, and at the time of switching between the heat storage process and the heat radiation process of each heat storage material, the fluctuation of the amount of heat blown to the metal strip is compensated. This is a method for preheating the continuous annealing equipment, characterized by performing spray pressure control. Here, the temperature and blowing pressure of the atmosphere gas in the furnace were measured, and when switching to the heat storage process and the heat radiation process of each heat storage body, the circulation fan of the circulation fan calculated from the temperature change amount of the furnace atmosphere gas and the blowing pressure was used. It is preferable to control the rotation speed to correct the blowing pressure, and the method of the present invention is effective when applied to preheating in a pre-tropical zone of an annealing furnace.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a method for preheating a continuous annealing equipment according to the present invention, a circulation fan for blowing atmospheric gas in a furnace is usually controlled by feedback control based on a sheet temperature of a metal strip at a preheating furnace exit side. While performing the control of the number of revolutions, the heat storage process of each heat storage body, when switching the heat dissipation process, heating through this heat storage body,
Immediately before spraying the pressurized circulating gas onto the steel strip being passed through the preheating furnace again, the pressure and temperature of the gas are measured so that the chamber is at a blowing pressure so as to compensate for fluctuations in the calorific value at the time of switching. By shifting the pressure, the fluctuation of the sheet temperature on the exit side of the preheating furnace is reduced.

Thus, according to the present invention, the chamber pressure is changed in consideration of the fluctuation of the flow rate and heat quantity of the circulating gas which fluctuates in the switching of the heat storage process by the heat exchanger utilizing the heat storage body, and the preheating furnace exit side is changed. By reducing the sheet temperature fluctuations in the heating furnace, the fluctuations in the entry temperature of the steel strip in the heating furnace and the fluctuations in the sheet temperature on the exit side of the heating furnace are also reduced, thereby producing a stable quality steel sheet while increasing the heat exchange efficiency of the preheating furnace. It becomes possible with that.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preheating method of the present invention will be described more specifically with reference to the drawings. FIG. 1 shows a schematic diagram of an example of a heat exchange system of a preheating furnace to which the method of the present invention is applied.
In the figure, reference numeral 1 denotes a heating furnace for a metal strip.
A plurality of radiant tube groups 2 as heating means for raising the temperature of the metal strip are arranged, and by burning the fuel in the radiant tube, the metal strip is radiated by the radiant heat without contaminating the inside of the heating furnace with the combustion exhaust gas. Heat. The combustion exhaust gas passing through the radiant tube 2 is collected in an exhaust gas pipe 3 and guided to a regenerative heat exchange device indicated by 4 in the figure to store sensible heat of the exhaust gas. A plurality of heat storage type heat exchange devices can be provided.
Then, the exhaust gas that has exited the heat exchange device 4 is sucked by an exhaust gas fan 10 and discharged to the atmosphere after appropriate treatment via an exhaust gas pipe 3 ′ and a chimney 11.

On the other hand, in the figure, reference numeral 5 denotes a preheating furnace provided upstream of the heating furnace 1 in the line. The atmosphere in the furnace in the preheating furnace 5 is sucked by a circulation fan 6 and passed through a circulation gas pipe 7. Through the regenerative heat exchanger 4. The circulating gas that has received the sensible heat of the exhaust gas thus accumulated in the heat exchanger 4 is guided to the chamber 8 in the preheating furnace 5 and blown onto the metal strip 9 passing through the preheating furnace 5 by being pressurized by the circulating fan 6. Put on.

Such a system for raising the temperature of the metal strip in the preheating furnace utilizing the sensible heat of the exhaust gas is the same as the conventional one, and the metal strip on the exit side of the heating furnace is rapidly raised by convective heat transfer by a high-temperature atmosphere gas. The radiant tube can be heated, and as a result, the set temperature required in the heating furnace can be reduced, and the high-temperature life of the radiant tube can be improved. In such a preheating method, three or more heat storage bodies are provided for one set of heat exchange systems, and the heat storage stage for the heat storage body and the heat release stage for the circulation atmosphere gas are sequentially shifted in each of the heat storage bodies. Attempts have been made to average the temperature of the atmosphere gas blown to the metal strip in the preheating furnace in the direction of feeding the metal strip.

That is, FIG. 2 shows a main part of a piping system of a regenerative heat exchanger when three heat storage bodies are used.
At least one of the three regenerators is heated (heat storage state) by the sensible heat of the combustion exhaust gas from the heating furnace, and at least one of the other regenerators is circulated through the preheated furnace to the retained regenerator. The gas is supplied, and the circulating gas having enjoyed the heat of the heat storage body is blown into the preheating furnace (radiation state). Then, while maintaining that state, the process is performed while circulating a process in which another unit is switched from the heat radiation state to the heat storage state or from the heat storage state to the heat radiation state.

In the piping system shown in FIG. 2, these controls are performed by opening and closing a switching adjustment valve. That is, the control of the heat storage / radiation cycle will be described by typifying the heat storage body of the A system in the figure. First, in order to store heat in the heat storage body, the exhaust gas intake valve 13a and the exhaust gas discharge valve 14a are opened, and the circulation gas intake valve is opened. 15a and the circulation gas discharge valve 16a are closed. Thus, the exhaust gas fan 10 is operated and sucked to supply the high-temperature exhaust gas from the heating furnace to the heat storage unit 12a to collect and store heat in the exhaust gas. Next, when switching from the heat storage process to the heat release process, the exhaust gas suction valve 13a is closed, the circulating gas suction valve 15a is opened, and the circulating gas of the preheating furnace 5 is temporarily led to the heat storage body 12a. Drive out. Next, the exhaust gas discharge valve 14
Then, the circulating gas suction valve 16a is opened and the circulating gas in the preheating furnace is guided to the regenerator 12a by the circulating fan 6 to recover the heat of the regenerator 12a and supplied to the chamber 8 in the preheating furnace 5. . Further, when switching from the heat radiation state to the heat storage state, the circulation gas intake valve 15a and the circulation gas discharge valve 16a are closed, and the exhaust gas intake valve 13a and the exhaust gas discharge valve 14a are opened. By repeating the opening and closing operation of the switching control valve as described above, the heat storage-radiation cycle control in each heat storage body is performed. The same applies to the heat storage-radiation cycle control of other heat storage bodies.

The switching timings of the switching adjustment valves in the heat storage units A, B and C are shifted so that they do not coincide with each other. Thereby, the temperature applied to the metal strip is averaged, and it is possible to suppress the temperature variation of the metal strip. However, when the state of the heat release and the state of heat storage are switched, the flow rate and the amount of heat of the circulating gas fluctuate remarkably. Therefore, in this method, the temperature of the metal strip varies at the time of spraying corresponding to the switching.

Therefore, according to the present invention, when switching between the heat storage process and the heat radiation process of each heat storage body, the blowing pressure control for compensating the fluctuation of the amount of heat blown to the metal strip is performed to change the sheet temperature on the exit side of the preheating furnace. Is to make it smaller.

FIG. 3 is a schematic diagram showing an example of the configuration of an instrumentation flow for performing such control. In the drawing, a regenerative heat exchange device 4, a preheating furnace 5, a circulation fan 6, a circulation gas pipe 7, a chamber 8, and a metal strip 9 are the same as those in FIG.
In such an instrumentation flow, the surface temperature of the metal strip 9 drawn out of the preheating furnace by a plurality of rolls including 21 is sequentially measured by a sheet thermometer 22 provided on the exit side of the preheating furnace. On the other hand, the pressure of the circulating gas pushed into the chamber 8 in the preheating furnace 5 by the circulating fan 6 is measured by a pressure gauge 23 provided in the chamber, and the circulating gas heated via the regenerative heat exchanger 4 is heated. Gas temperature in chamber 8
The temperature is measured by a thermometer 24 disposed immediately before the air is blown into the air. Metal strip surface temperature at the exit of these preheating furnaces,
Based on chamber pressure and circulating gas temperature data, calculate the chamber pressure value to cancel the change in the amount of heat due to fluctuations in the circulating gas temperature when switching between the heat storage process and the heat radiation process of each heat storage unit, and calculate the circulation fan speed. Control.

The advantageous effects obtained by applying the method of the present invention will be clarified by comparing the state of fluctuation of the surface temperature of the metal strip on the exit side of the preheating furnace with the conventional method. FIG. 4 shows a time chart of the sheet temperature on the exit side of the preheating furnace in a case where the control of only the normal sheet temperature control is continued, together with a time chart of the circulation gas temperature and the circulation fan rotation speed. In the same figure, for example, at the moment when the A-system heat storage unit shown in FIG. 2 is switched from the heat storage state to the heat release state, the circulating gas flow rate and the amount of heat are abundant. Therefore, in the feedback control usually performed from the preheating furnace exit side sheet temperature,
Once the plate temperature has risen rapidly, the number of revolutions of the circulating fan is reduced to try to match the plate temperature to the target. Next, at the moment when another system (system C) switches from the heat radiation state to the heat storage state, the flow rate and heat amount of the circulating gas decrease slightly, and the sheet temperature on the exit side of the preheating furnace decreases. These sheet temperature fluctuations at the time of switching could not be sufficiently followed by the feedback control. In addition, in the period (X) between the time when the heat storage body of the A system switches from the heat storage state to the heat dissipation state and the time when the system C switches from the heat dissipation state to the heat storage state, the heat amount of the heat storage body is gradually lost. The rotation speed of the circulation fan increases, but during this time, the sheet temperature feedback can be followed.

Therefore, in the present invention, at the moment of the switching process from heat storage to heat dissipation and from heat dissipation to heat storage, the sheet temperature feedback control is stopped and the chamber pressure is corrected as follows to reduce the sheet temperature on the exit side of the preheating furnace. Compensate.

A model of heat transfer by a gas jet is generally expressed by the following equation.

(Equation 1)

[0021] Thus, in the present invention, thermal storage of the heat storage body - is recorded and the circulation gas pressure P ₁ measured by the pressure gauge 23 and thermometer 24 immediately before switching to the heat storage circulation gas temperature Tg ₁ - heat radiation or heat block . Next, at the time of switching between the heat storage process and the heat release process of the heat storage body, the switching control valve is opened and closed by the switching signal of the heat storage type heat exchange device, and at the same time, the rotation speed control of the circulation fan by the plate temperature feedback control is stopped.

The temperature of the circulating gas is changed from Tg ₁ to Tg ₂ (Tg ₂
= Tg ₁ + ΔTg). From the above equation (1), we want to change the heat transfer coefficient so that Ti and To become the same before and after the temperature of the circulating gas changes.

(Equation 2) It will lead to a ₂ of only becomes.

On the other hand, the chamber pressure P is generally expressed by P = ka ^1/2 (3) (where k is a proportional constant).
From the equation (3), the following relationship is obtained: P ₂ = P ₁ (a ₂ / a ₁ ) ^1/2 = P ₁ Q ^1/2 .

Based on the equation (4), the pressure required for control
Value P_TwoAnd input the control signal to the adjustment end of the circulation fan
To change the number of revolutions and increase the chamber pressure to P for a certain period.₁Or
R _TwoPressure control to shift to. In this way heat storage
Actual heat to compare with chamber pressure just before body switch
The transmission rate does not need to be calculated, and no learning coefficient is required. Constant
After the period is over, control the sheet temperature by feedback control again.
Execute.

Including such a pressure control process of the present invention,
FIG. 5 shows a time chart of the circulation fan rotation speed control together with the changes over time of the preheating furnace outlet plate temperature and the circulation gas temperature.
It is apparent from the figure that the preheating method according to the present invention effectively suppresses the sheet temperature fluctuation on the exit side of the preheating furnace as compared with the case of only the sheet temperature feedback control shown in FIG. As described above, the present invention has been described based on the drawings. However, the method for preheating the continuous annealing equipment of the present invention is not limited to the illustrated example. For example, the present invention can be applied to a soaking zone in a continuous annealing furnace. The means for switching between the heat storage process and the heat release process is not limited to a valve, and may be, for example, a rotary switching device.

[0026]

According to the present invention, as a heat exchange device utilizing sensible heat of exhaust gas, a plurality of heat accumulators are provided as a single unit, so that the flow of heat is prevented without obstructing any flow of the exhaust gas and the circulating gas. In preheating furnace equipment that uses a regenerative heat exchange device that can switch heat radiation, metal strips passing through the preheating furnace due to changes in the amount of heat and flow of circulating gas generated when switching the switching valve Can be minimized by forcibly correcting the rotation speed of the circulation fan.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an example of a heat exchange system of a preheating furnace to which the method of the present invention is applied.

FIG. 2 is a diagram showing an example of a piping system of a regenerative heat exchange device.

FIG. 3 is a diagram showing an example of an instrumentation flow configuration for applying the method of the present invention.

FIG. 4 is a diagram showing a change in sheet temperature on the exit side of a preheating furnace when control of only sheet temperature control is continued.

FIG. 5 is a diagram showing a change in sheet temperature on the exit side of a preheating furnace when the method of the present invention is applied.

[Explanation of symbols]

 Reference Signs List 1 heating furnace 2 radiant tube group 3 exhaust gas pipe 4 regenerative heating device 5 preheating furnace 6 circulation fan 7 circulation gas pipe 8 chamber 9 metal strip 10 exhaust gas fan

Claims (3)

[Claims] 1. An exhaust gas generated from an annealing furnace in a continuous annealing facility is guided to a regenerative heat exchange device to accumulate the sensible heat of the exhaust gas, and then an atmosphere gas in the furnace used in the furnace is supplied to the regenerative heat exchange device. It is a method of preheating by conducting to the annealing furnace after guiding and raising the temperature and spraying the surface of the metal strip through which the inside of the furnace is pre-heated, wherein the heat storage type heat exchange device includes a plurality of heat storage bodies as one set. The switching of the heat storage process and the heat radiation process of each heat storage element is performed sequentially, and the blowing pressure control for compensating the fluctuation of the amount of heat blown to the metal strip is performed at the time of the switching of the heat storage process and the heat radiation process of each heat storage element. Characteristic preheating method for continuous annealing equipment. 2. The temperature and the blowing pressure of the atmosphere gas in the furnace are measured, and when switching between the heat storage process and the heat radiation process of each heat storage element, a circulation calculated from the temperature change amount of the furnace atmosphere gas and the blowing pressure. 2. The preheating method for continuous annealing equipment according to claim 1, wherein the blowing pressure is corrected by controlling the rotation speed of the fan. 3. The method for preheating a continuous annealing facility according to claim 1, wherein the method is applied to preheating in a pre-tropical zone of an annealing furnace.