JPH1088245A - Continuous heat treatment apparatus of metallic strip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the service life in high temp. of radiant tube in a heating zone and to reduce the cost by reducing the unit requirement of fuel in the heating zone. SOLUTION: Into three sets of storage type heat exchangers 1A-1C arranged in a preheating zone, combustion exhaust gas of burner devices from the radiant tubes in the heating zone are collectively fed and the sensible heat of this combustion exhaust gas is efficiently recovered into the sensible heat of the air. The air heated at the high temp. is directly blown to a strip in the preheating zone in order from each of the heat storage type heat exchangers 1A-1C to raise the temp. and temp. raising calory of the strip in the heating zone is reduced by this recovered calory and thus, the setting temp. of the radiant tube can be reduced. Further, to the heat storage type heat exchangers 1A-1C, small flow rate of purge valves 6A-6C are fitted, and at the time of changing over from the combustion exhaust gas supplying to the air supplying, the filling combustion exhaust gas is discharged with a part of the high temp. air supplied from the other heat storage type heat exchanger into the preheating zone to purge the gas in the storage type heat exchanger.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous heat treatment apparatus for a metal strip such as a continuous annealing furnace for annealing a continuously fed strip (steel strip). The present invention relates to a continuous heat treatment apparatus for a metal strip having a pre-tropical zone that preheats the metal strip to a certain extent at a tropical entrance side.

[0002]

BACKGROUND OF THE INVENTION continuous heat treatment apparatus for metal strip, such as a conventional continuous annealing furnace for continuous annealing a strip furnace called heating zone for heating a metal strip such as the strip temperature as high as more than A ₂ transformation structure And a number of heating devices called radiant tubes are arranged around the strip continuously fed into the heating zone. Especially when the metal strip to be delivered is a strip and the required heat treatment step is annealing in the finishing step, oxidation of the strip must be avoided as much as possible. Moreover, since the heating temperature is high as described above, the oxidation of the strip is promoted by the O component contained in CO ₂ and H ₂ O in the furnace atmosphere.
The continuous annealing atmosphere of this strip must be at least a non-oxidizing atmosphere or a reducing atmosphere, and
It is not possible to directly raise the temperature in the furnace, that is, the ambient temperature, with a burner device that generates combustion exhaust gas containing ₂ or H ₂ O. Therefore, the high-temperature combustion exhaust gas of the burner device or the gas heated by the high-temperature combustion exhaust gas is fed into the radiant tube, and the strip is heated by radiant heat from the outer wall of the radiant tube into the furnace. Therefore, by maintaining the atmosphere in the furnace in the non-oxidizing atmosphere or the reducing atmosphere, oxidation of the strip can be avoided,
In addition, the strip can be heated relatively efficiently.

[0003]

However, in the actual continuous annealing operation, there is a lower limit to the strip feeding speed (sheet passing speed) in order to improve the production efficiency. In response to the desire to keep the tropical size, ie the path length of the strip, as short as possible, the temperature in the furnace, ie in the radiant tube, must be set relatively higher than the desired strip achievement temperature. In other words, it is necessary to increase the temperature of the radiant tube to increase the temperature difference between the furnace temperature and the strip, so that the strip is quickly heated to a predetermined high temperature. However, if the temperature of the radiant tube is further increased in addition to the high heating temperature of the strip required as described above, a considerable heat load is applied to the radiant tube. The so-called high temperature life is shortened because the radiant tube itself is broken by creep. Setting the radiant tube at a higher temperature in this manner increases the unit fuel consumption (the amount of heat per unit weight of the heated product, etc.) calculated from the fuel gas to the burner device, which is the heat source. Therefore, there is a problem that the cost is increased accordingly.

[0004] The former of these problems, that is, the high-temperature life of the radiant tube is only about several years even if it is shortened, whereas the latter problem of the fuel consumption rate is directly related to the cost. To reflect this, the latter problem has been emphasized in the past. One of them is
It is to increase the combustion efficiency of the burner device for heating the radiant tube, and the sensible heat of the combustion exhaust gas that has finished heating the radiant tube is recovered to the sensible heat of the combustion air by the convection heat exchange device, that is, the burner device This is to raise the temperature of the supplied combustion air to improve the combustion efficiency in the burner device.

[0005] In order to solve the above-mentioned problems, a pre-tropical zone is provided in the operation line to pre-heat the strip. In this pre-tropical zone, the sensible heat of the combustion exhaust gas of the burner device is recovered as sensible heat of a predetermined gas by the same convective heat exchange device as described above, and the gas heated to a certain extent by this is heated to the heating zone. The temperature of the strip can be raised directly by spraying it directly on the entry side, i.e. in the pre-tropics.

However, in the above-mentioned convection heat exchanger, for example, a gas such as air or steam for combustion is passed through a tube, and the flue gas is flowed around the tube, and the sensible heat of the flue gas is passed through the tube. Therefore, a sufficient temperature difference and a large heat transfer area are required between the combustion exhaust gas and the gas to be recovered. Therefore, a large heat exchanger is required to perform sufficient heat recovery from the combustion exhaust gas, but the heat recovery rate is low due to the fact that sufficient installation space cannot be taken, and a sufficient heat transfer area could be secured. However, it is difficult to heat the gas in the tube to a sufficiently high temperature in a short time. Therefore, whether the combustion efficiency of the burner device is improved by using the convection type heat exchange device or the strip is preheated in the pre-tropical zone, the effect of improving the high-temperature life of the fuel consumption unit or the radiant tube is expected. It is not at present.

Therefore, as means for solving such problems, there is a continuous heat treatment apparatus such as a continuous annealing degree using a regenerative burner apparatus described in Japanese Patent Application Laid-Open No. 6-288519. This technology burns in one of the paired regenerative burners,
The sensible heat of the combustion exhaust gas is stored in the regenerator of the other regenerative burner device, and then, for example, the temperature of the regenerator of the other regenerative burner reaches the upper limit temperature, and the combustion-heat storage circulation up to that limit is reached. When reached, the combustion of the one burner device is stopped, and the combustion is performed by the other regenerative burner device.
For example, by passing the combustion air to the regenerative burner device through the regenerator for combustion, the sensible heat of the combustion exhaust gas can be recovered with high efficiency as the sensible heat of the combustion air. Therefore, since the heat recovery efficiency is improved by using the regenerative burner device as a burner device of a continuous heat treatment device such as the continuous annealing furnace, at least an effect of reducing the unit fuel consumption can be expected.

[0008] Even in the regenerative burner device, a heat storage element must be provided for each combustion burner device, and the unit itself becomes complicated and large-sized accordingly. However, in continuous heat treatment equipment such as a continuous annealing furnace used in actual operation, more than one hundred such burners or heating equipment,
Since a large one has hundreds of heaters, using a regenerative heater or regenerative burner for all of them will not only complicate and enlarge the structure, but also make the control very complicated. In addition, there is also a problem that maintenance and maintenance become difficult to that extent. In addition, in particular, remodeling the ordinary burner device to these regenerative heaters or regenerative burner devices with existing facilities is not only inferior in economical efficiency but also already provided in a limited space. There is also the fact that not all burners can be provided with heat storage.

The present invention has been developed in view of these problems. The sensible heat of the combustion exhaust gas from the burner device in the heating zone is collectively converted into the sensible heat of a predetermined gas by a large-scale regenerative heat exchanger. By collecting the gas with high efficiency and stably spraying the gas to the metal zone in the pre-tropical zone, the temperature of the metal zone sent to the heating zone is raised, and as a result, the metal zone required in the heating zone is By reducing the temperature rise, the set temperature required in the furnace, that is, the radiant tube, is lowered, thereby reducing the fuel consumption rate and improving the high-temperature life of the radiant tube. It is an object of the present invention to provide a continuous heat treatment apparatus for a metal strip, which stabilizes the blowing of gas to a metal strip and can efficiently use the combustion exhaust gas and the blowing gas.

[0010]

In order to solve the above problems, a continuous heat treatment apparatus for a metal strip according to claim 1 of the present invention comprises a radiant tube to which combustion exhaust gas from a plurality of burners is respectively supplied. A heating zone for heating a metal strip continuously fed by radiant heat from the radiant tube to a predetermined high temperature, and a sensible heat of combustion exhaust gas from a plurality of burner devices in the heating zone are collected and stored. A regenerative heat exchange device that stores heat in a body and recovers sensible heat to the gas by feeding a predetermined gas to the regenerator, and a gas from the regenerative heat exchange device on the inlet side of the heating zone And a pre-tropical zone that is preheated by spraying on a metal strip.

According to the present invention, the sensible heat of the combustion exhaust gas supplied to and discharged from the plurality of burner devices to the radiant tube in the heating zone is collectively stored in the heat storage body of the large-scale regenerative heat exchanger, and the heat storage is performed. By sending a predetermined gas such as air to the body, the sensible heat of the flue gas is collected and collected into the sensible heat of the predetermined gas, and this gas is sprayed on a metal band such as a strip in the pre-tropical zone. This preheats the metal strip. The heat storage type heat exchange device is different from the convection type heat exchange device described above, because the heat recovery efficiency is extremely excellent, so that the sensible heat of the predetermined gas becomes large, that is, becomes high temperature by passing through the heat storage body, Therefore, by directly blowing the high-temperature gas onto the metal strip, the temperature of the metal strip becomes significantly higher than in the past. Therefore, the temperature rise of the metal zone required in the subsequent heating zone becomes smaller, and the furnace temperature, that is, the temperature required for the radiant tube may be lower by that amount. By the way, since the rupture life of the radiant tube in the high temperature region as described above is given by an exponential function of the reciprocal of the temperature, it is known that the rupture life is double to several times at only tens of degrees C to tens of degrees C This greatly improves the high-temperature life of the radiant tube,
It is possible to reduce the unit fuel consumption of fuel gas and the like supplied to the burner device.

According to a second aspect of the present invention, there is provided the continuous heat treatment apparatus for a metal strip, wherein the regenerative heat exchange device switches between the combustion exhaust gas and a predetermined gas to supply the gas to the regenerator. It is configured to include at least three or more regenerative heat exchangers equipped with valves, and at least one of these regenerative heat exchangers converts a predetermined gas obtained by collecting sensible heat stored in the heat storage body into a metal band. Control means for sequentially opening and closing the valves of each of the heat storage heat exchangers so that the sensible heat of the combustion exhaust gas is stored in the heat storage body by spraying and the remaining heat storage heat exchanger. It is.

In the present invention, three or more regenerative heat exchangers are used, and at least one of them recovers the sensible heat of the combustion exhaust gas stored in the heat storage body as the sensible heat of the predetermined gas. The control valve is sequentially opened and closed so that the sensible heat of the combustion exhaust gas is stored in the regenerator of the regenerative heat exchanger in the pre-tropical zone. Actually, there are only two regenerative heat exchangers, and one of the regenerative heat exchangers heats a predetermined gas and sprays it on the metal strip, while the other regenerative heat exchanger burns. From the state in which the sensible heat of the exhaust gas is stored in the regenerator, the regenerative heat exchanger that is spraying the gas is switched to the regenerator heat storage, and at the same time, the regenerator heat storage is performed. It is impossible to switch the exchanger to spraying the predetermined gas because of the response of the valves that supply and discharge the respective gases. There will be times when the band is not sprayed. Of these, spraying the combustion exhaust gas onto the metal strip should be absolutely avoided from the viewpoint of the working environment, and no gas is sprayed on the metal strip, that is, a predetermined gas heated to a high temperature. The time during which the metal strip is not sprayed on the metal strip means that a temperature variation occurs in the feeding direction of the metal strip, and this must also be avoided. Therefore, at least three regenerative heat exchangers are indispensable in order to maintain a state in which a predetermined gas having a high temperature is always blown onto the metal strip, and these control valves are appropriately switched and controlled by control means. This makes it possible to continuously blow a high-temperature predetermined gas from at least one regenerative heat exchanger to the metal strip, and at the same time, efficiently transfers the sensible heat of the combustion exhaust gas to the regenerator in the remaining regenerative heat exchanger. It is possible to store heat.

Further, in the continuous heat treatment apparatus for a metal strip according to claim 3 of the present invention, each of the regenerative heat exchangers comprises:
A valve for sending the combustion exhaust gas to a heat storage element and a valve for sending the predetermined gas to the heat storage element; and a valve for discharging the combustion exhaust gas from the heat storage element to the outside of the pre-tropical zone. A valve for sending gas from the heat storage unit into the pre-tropical zone, and a valve for branching from a system for sending the predetermined gas from the heat storage unit into the pre-tropical zone and purging the heat exchanger. Provided, the control means, after a valve for sending combustion exhaust gas to the heat storage of each regenerative heat exchanger is closed, then open a valve for purging the heat exchanger with the predetermined gas,
While opening the valve for purging the heat exchanger with the predetermined gas, open the valve for discharging the combustion exhaust gas and close the valve for supplying the predetermined gas, After closing a valve for purging the heat exchanger with the predetermined gas, closing a valve for discharging the combustion exhaust gas, then opening a valve for supplying the predetermined gas, and then A valve for supplying the predetermined gas to the heat storage element of the heat exchanger is opened.

According to the present invention, when the heat storage and the gas blowing are switched by any one of the three or more regenerative heat exchangers as described above, the supply of the combustion exhaust gas to the regenerator is first performed. It is necessary to stop, that is, close the valve for that, and then start the supply of the predetermined gas to the heat storage element, that is, open the valve for that purpose, meanwhile, in the heat exchanger, that is, in the vicinity of the heat storage element. Is filled with combustion exhaust gas, and if a predetermined gas supply valve is opened from that state, the filled combustion exhaust gas is sprayed onto the metal strip.
Therefore, a step occurs in which the inside of the regenerative heat exchanger must be purged with the predetermined gas before opening a valve for supplying the predetermined gas to the heat storage element. Valve structures and opening and closing control of those valves are required. That is, by opening the valve for discharging the combustion exhaust gas while opening the valve for purging the predetermined gas, the combustion exhaust gas in the regenerative heat exchanger is discharged, and the heat exchange is performed. The inside of the vessel is purged with a predetermined gas,
Thereafter, by closing the valve for purging the predetermined gas, closing the valve for discharging the flue gas, and then opening the valve for supplying the predetermined gas, the metal zone in the pre-tropical zone is opened. , A predetermined gas heated to a high temperature is reliably blown.

According to a fourth aspect of the present invention, there is provided a continuous heat treatment apparatus for a metal strip for purging the interior of the heat exchanger with the predetermined gas provided in each of the heat storage type heat exchangers. The flow rate of the system is set smaller than the flow rate of the system for supplying the predetermined gas into the pre-tropical zone.

The above-mentioned valve for purging the predetermined gas and the valve for supplying the predetermined gas into the pre-tropical zone may be used in common because the gas passed therethrough is the same. Although it is possible, in the present invention, in the above-mentioned valve opening / closing step, if the valve for discharging the predetermined gas into the pre-tropical area is opened to purge the predetermined gas, the valve for discharging the combustion exhaust gas is opened. Is open and the piping system for exhausting flue gas is generally provided with a fan for sucking it, so it should be discharged from other regenerative heat exchangers to the pre-tropical zone. The high-temperature predetermined gas passes through the regenerative heat exchanger to be purged and is discharged to the outside from a valve for discharging combustion exhaust gas. Therefore, by setting the flow rate of the system for purging the predetermined gas to be smaller than the flow rate of the system for discharging the predetermined gas into the pre-tropical zone, the high temperature from the certain regenerative heat exchanger can be improved. The preheated gas is constantly fed into the pre-tropical zone, and a part thereof purges the inside of the regenerative heat exchanger having the vicinity of the regenerator to be purged. In addition, the flow rate of the system for purging the inside of the heat exchanger is controlled by reducing the diameter of the pipe to be fed, by interposing a throttle damper in the middle of the pipe, or by providing a special piping separately and purging. It is achieved by doing.

[0018]

FIG. 1 shows an embodiment of a continuous annealing furnace for strips (cold rolled steel sheets) in which a continuous heat treatment apparatus for a metal strip according to the present invention is implemented.

FIG. 1 shows the configuration of a vertical continuous annealing furnace for continuously annealing a strip S. This continuous annealing furnace has a coil unwinder, a welding machine, a washing machine and the like in order, not shown. From the incoming equipment, pre-tropical PHS, heating zone HS, level tropical SS, plate temperature control zone (not shown) and heat treatment zone (not shown) for adjusting the plate temperature as needed, and outgoing equipment (not shown) such as shearing machines and winders Be composed. All of these facilities are constructed in a tower-like vertical type in order to reduce the installation area.

The cold rolled steel sheet is welded in the longitudinal direction irrespective of the specifications of the sheet thickness, material, etc., and is continuously fed from the entrance facility as a series of strips S. After passing through the tropical HS, the isotropy SS, and the necessary plate temperature control zone and the heat treatment zone in order, it is finally cooled to room temperature.

Among them, the heating zone HS and the isotropy SS
Is similar or nearly the same as the existing one, and the heating zone H
S is continuously fed from the inlet facility, and heats the preheated cold-rolled steel sheet to, for example, a recrystallization temperature or higher,
Specifically, the steel sheet is heated such that the furnace temperature is 900 to 950 ° C and the temperature of the strip is 700 to 800 ° C. Then, the heated cold-rolled steel sheet is held for a necessary period of time in the solitary SS, and then falls into the sheet temperature control zone. Therefore, in the vicinity of the strip S passed through the heating zone HS, that is, around each pass, a large number of radiant tubes (not shown) are disposed as in the conventional case, and each radiant tube is heated to a high temperature from a normal burner device. And the flue gas that has passed through the radiant tube is collectively fed to a regenerative heat exchange device described later.

Further, the pre-tropical PHS has a structure as shown in FIG. Among them, the combustion exhaust gas discharged from the radiant tube of the heating zone HS is:
Similarly, the existing convection heat exchanger 1 provided on one side of the pre-tropical PHS through the existing exhaust gas inlet pipe 10i.
1 and then exhausted to the exhaust fan side (not shown) through the existing exhaust gas outlet pipe 10o. The convection type heat exchanger 11 has an existing intake fan 12 for sucking the atmospheric gas (air in this case) in the pre-tropical PHS.
Is supplied through the existing air inlet pipe 13i, and the air heated by the convection heat exchanger 11 is then supplied to the existing air outlet pipe 13i.
o, a strip S passing through the pre-tropical PHS from a diffusion spray device such as a plenum chamber (not shown)
Sprayed on. That is, as described above, a large number of tubes (not shown) are provided in the convective heat exchanger 11, and the air supplied into the tubes is used for convective heat transfer of high-temperature combustion exhaust gas flowing around the tubes. Heated by
The strip S is sprayed from the plenum chamber to heat the strip S.

On the other hand, three different regenerative heat exchangers 1A to 1C are provided on one different side of the pre-tropical PHS. Each of the heat storage type heat exchangers 1A to 1C has a heat storage chamber containing a spherical or short pipe-shaped heat storage body (not shown), and two connection chambers connected to each other so as to be able to ventilate the heat storage chamber. In addition, the existing exhaust gas inlet pipe 10i includes:
The newly installed exhaust gas inlet pipe 14 is branched and the tip is branched into three, and each of the regenerative heat exchangers 1A to 1C is connected via an exhaust gas inlet valve 2A to 2C, respectively. Connected to the connection room. In addition, a new air inlet side pipe 15 with an air supply fan 7 interposed in the middle is also connected to the existing air inlet side pipe 13i, and the distal end thereof is branched into three, and the air inlet side pipe 15 is divided into three. Each of the regenerative heat exchangers 1A to 1C is connected to one of the other connection chambers via the side valves 3A to 3C. In addition, the existing exhaust gas outlet pipe 10
At o, a newly installed exhaust gas outlet pipe 16 is connected in a branched manner, and its tip is branched into three, and each of the exhaust gas outlet valves 4A to 4A is connected.
Via 4C, it is connected to any other connection chamber of each of the regenerative heat exchangers 1A to 1C. A new air outlet pipe 17 is also branched and connected to the existing air outlet pipe 13o, and the distal end thereof is branched into three, and each of them is connected via the air outlet valves 5A to 5C. Heat storage type heat exchanger 1A ~
1C is connected to one of the connection chambers. Further, each of the three distal ends of the air outlet pipe 17 is further branched into two and connected to one of the regenerative heat exchangers 1A to 1C via purge valves 6A to 6C, respectively. It is connected to the. Incidentally, the flow rates of the valves 2A to 5C and the piping systems connected thereto other than the purge valves 6A to 6C and the branch piping system connected thereto are equal to or substantially equal to each other, but the purge valves 6A to 6C and The flow rate of the branch piping system connected thereto is set smaller than the other flow rates. The piping and valve configuration connected to the regenerative heat exchanger 1A are A-system, the piping connected to the regenerative heat exchanger 1B and the valve configuration are B-system, and the piping connected to the regenerative heat exchanger 1C. And the valve configuration is designated as C system.

FIG. 3 shows these valve configurations as a sequence diagram. The opening and closing of these valve configurations are controlled by a process computer (not shown). FIG. 4 shows this control content as a sequence chart. According to the sequence chart of FIG. 4, for example, the A-system and B-system exhaust gas inlet valves 2A and 2B and the exhaust gas outlet valves 4A and 4B are opened, and the C-system air inlet valve 3C and air outlet valve 5C. Is opened and all other valves are closed, that is, in the A-type and B-type regenerative heat exchangers 1A and 1B, the sensible heat of the combustion exhaust gas is stored in the regenerator, and the C that has been stored until then is stored. Assuming that the air sensible heat is increased from the heat storage body of the heat storage type heat exchanger 1C of the system and the high-temperature air is blown from the plenum chamber to the strip, for example, A
When the temperature of the heat storage body of the heat storage type heat exchanger 1A of the system reaches the vicinity of the upper limit value and the heat storage cannot be continued any more, first, the exhaust gas inlet valve 2A of the system A is closed and the combustion exhaust gas is discharged. The heat is not supplied to the heat storage body of the heat storage type heat exchanger 1A of the system. Even in this state, high-temperature air is passed from the C-type regenerative heat exchanger 1C via the air supply fan 7 and the newly installed air outlet pipe 17 to the strip where the hot air is passed through the pre-tropical PHS. Is sprayed on.

When the A-system exhaust gas inlet side valve 2A is completely closed, the A-system purge valve 6A is opened. At this time, although the combustion exhaust gas is still full in the A-system regenerative heat exchanger 1A, the flow rate of the purge valve 6A and the piping system connected thereto is reduced by the C-system air outlet valve 5C. And most of the high-temperature air discharged from the air outlet valve 5C of the C system is still blown to the strip in the pre-tropical PHS, and a part thereof Is supplied from the newly installed air outlet pipe 17 through the A-system purge valve 6A into the A-system regenerative heat exchanger 1A, and the combustion exhaust gas filling the regenerative heat exchanger 1A. Is discharged from the exhaust gas outlet valve 4A of the A system which is still open, whereby the regenerative heat exchanger 1A
The inside is purged with hot air. Of course, during this time, the heat storage body of the A-type heat storage type heat exchanger 1A is further heated by the high-temperature air.

Thus, the A-system regenerative heat exchanger 1A
When the inside is purged with high-temperature air, the purge valve
A is closed, and when the purge valve 6A is completely closed, the exhaust gas outlet valve 4A of the A system is also closed, and the exhaust gas outlet valve 4A is closed.
Is completely closed, the A-system air outlet valve 5A is also opened, and when the air-outside valve 5A is completely opened, the A-system air inlet valve 3A is also opened, and the A-system regenerative heat Exhaust air heated to high temperature from exchanger 1A
Spray on the strip inside. When the A-system air inlet valve 3A is completely opened, the C-system air inlet valve 3C is opened.
When the air inlet valve 3C is completely closed, the C-system air outlet valve 5C is also closed. When the air outlet valve 5C is completely closed, the C-system exhaust gas outlet valve 4C is also opened. ,
When the exhaust gas outlet valve 4C is completely opened, the C-system exhaust gas inlet valve 2C is also opened to store the sensible heat of the combustion exhaust gas in the heat storage body of the C-system regenerative heat exchanger 1C. During this time, after the high-temperature air is blown from the A-system regenerative heat exchanger 1A to the strip as described above, C
Since the discharge of high-temperature air from the regenerative heat exchanger 1C of the system is stopped, high-temperature air is continuously blown to the strip, and there is no variation in the temperature in the strip feeding direction. Of course, during this time, the sensible heat of the combustion exhaust gas continues to be stored in the heat storage body in the B-type heat storage type heat exchanger 1B.

Then, when the temperature of the heat storage body of the B-system regenerative heat exchanger 1B, which continues to store heat, approaches the upper limit, the A-system regenerative heat exchanger 1C is moved from the C-system regenerative heat exchanger 1C. As in the case where the supply of high-temperature air to the heat exchanger 1A is switched, the B-system exhaust gas inlet valve 2B is closed to prevent the combustion exhaust gas from being supplied to the heat storage body of the B-system regenerative heat exchanger 1B. When the B-system exhaust gas inlet side valve 2B is completely closed, the B-system purge valve 6B is opened. At this time, as described above, most of the high-temperature air discharged from the A-system regenerative heat exchanger 1A via the air outlet valve 5A is pre-tropical PHS.
A part of the heat is supplied to the heat storage type heat exchanger 1B of the system B through the purge valve 6B of the system B, and is filled in the heat storage type heat exchanger 1B. The combustion exhaust gas discharged from the B-system exhaust gas outlet valve 4B is purged by the high-temperature air in the regenerative heat exchanger 1B.

Further, when the inside of the B-system regenerative heat exchanger 1B is purged with high-temperature air, the B-system purge valve 6B is closed, and when the purge valve 6B is completely closed, the B-system exhaust gas discharge side is also opened. When the valve 4B is closed and the exhaust gas outlet valve 4B is completely closed, the B-system air outlet valve 5B is opened, and when the air outlet valve 5B is completely opened, the B-system air inlet valve 3B is also opened. Is opened, the air heated to a high temperature is discharged from the heat storage type heat exchanger 1B of the B system, and is blown to the strip in the pre-tropical PHS. And the B-system air inlet side valve 3B
Is completely open, close the air inlet valve 3A of the A system,
When the air inlet valve 3A is completely closed, the A-system air outlet valve 5A is also closed, and when the air outlet valve 5A is completely closed, the A-system exhaust gas outlet valve 4A is also opened, and the exhaust gas is opened. When the outlet valve 4A is completely opened, the A-system exhaust gas inlet valve 2A is similarly opened to store the sensible heat of the combustion exhaust gas in the heat storage body of the A-system regenerative heat exchanger 1A.

When the temperature of the heat storage body of the C-type heat storage type heat exchanger 1C, which continues to store heat, approaches the upper limit, C
Closing the exhaust gas inlet valve 2C of the system to prevent the combustion exhaust gas from being sent to the heat storage body of the heat storage heat exchanger 1C of the C system;
When the C-system exhaust gas inlet side valve 2C is completely closed, the C-system purge valve 6C is opened.
Part of the high-temperature air discharged from the B-system regenerative heat exchanger 1B via the air outlet valve 5B is partially removed from the C-system purge valve 6.
The combustion exhaust gas that has been fed through the C into the C-system regenerative heat exchanger 1C and filled in the regenerative heat exchanger 1C is discharged from the C-system exhaust gas outlet valve 4C, The inside of the regenerative heat exchanger 1C is purged with high-temperature air.
Further, when the inside of the C-system regenerative heat exchanger 1C is purged with high-temperature air, the C-system purge valve 6C is closed, and when the purge valve 6C is completely closed, the C-system exhaust gas outlet valve 4 is also closed.
When C is closed and the exhaust gas outlet valve 4C is completely closed, the C-system air outlet valve 5C is opened, and the air outlet valve 5C is opened.
Is completely opened, the air inlet valve 3C of the C system is opened, and the air heated to a high temperature is discharged from the heat storage type heat exchanger 1C of the C system, and is blown to the strip in the pre-tropical PHS. When the C-system air inlet valve 3C is completely opened, the B-system air inlet valve 3B is closed. When the air inlet valve 3B is completely closed, the B-system air outlet valve 5B is also closed. And when the air outlet valve 5B is completely closed,
When the exhaust gas outlet valve 4B of the system is opened, and the exhaust gas outlet valve 4B of the system is completely opened, the exhaust gas inlet valve 2B of the system B is opened, and the heat storage body of the heat storage heat exchanger 1B of the system B is opened. Stores sensible heat of combustion exhaust gas.

Next, the operation of the continuous annealing furnace according to the present embodiment will be described. First, in order to facilitate understanding, a current, that is, a conventional continuous annealing furnace will be described. As shown in FIG. 8, this conventional continuous annealing furnace supplies combustion exhaust gas obtained from a radiant tube in the heating zone to a convection heat exchanger and is disposed in the convection heat exchanger. Air is supplied into the tube, and the air in the tube is heated by convective heat transfer from the sensible heat of the combustion exhaust gas, and is blown onto the strip in the pre-tropical zone to heat (preheat) the strip. The set temperature of the strip fed from the heating zone is 800 ° C.

In the above-mentioned heating zone, as shown in FIG.
M gas (name of mixed gas of blast furnace gas and coke oven gas)
The combustion heat of the fuel gas is supplied from the burner device and the radiant tube, and is substantially the same as the heat dissipated from the furnace body or the HN gas (hydrogen-nitrogen mixed gas for reducing the inside of the furnace into a reducing atmosphere). Although there is heat loss due to the discharge and heat loss in the cooling of the roll chamber for cooling the hearth roll, the heat dissipated and lost is not so large. This is the heat loss of the combustion exhaust gas, and the strip sensible heat is neglected because it is necessary to achieve the target temperature of the object to be heated. In this conventional continuous annealing furnace, the flow rate of the combustion exhaust gas is about 63000 Nm ³ / H, and the combustion exhaust gas at that time reaches the convection heat exchanger by the heat dissipated from the duct while passing through the duct (pipe). 6 at the time
Lowers to 40 ° C. In the convection heat exchanger, only the air sensible heat of 298 ° C. can be recovered from the sensible heat of the flue gas. 40 on the side
The sensible heat of the strip in ° C. can only be increased up to 120 ° C. on the outlet side of the pre-tropical zone, ie on the inlet side of the heating zone. Therefore, the furnace temperature in the heating zone must be set to 941 ° C., and the fuel consumption rate in this heating zone is a high value of 238 Mcal / t. The flow rate of air supplied / recycled to the pre-tropical zone in the conventional continuous annealing furnace is about 1300.
00Nm ³ / H, which is very large. This is because, in order to blow low-temperature air to the strip and raise the temperature of the strip as much as possible, as is clear from the action formula of convection heat transfer, the flow rate of air blown to the strip is increased. Because it must be.

On the other hand, as described above, the efficiency of recovering the sensible heat of the flue gas by the regenerative heat exchanger of the present embodiment is very high, so that the air regenerating heat exchanger heats the sensible heat of the air blown to the strip in the pre-tropical zone. Increasing the heat, that is, the temperature of the air blown to the strip, thereby increasing the temperature of the strip delivered to the heating zone, and ultimately lowering the temperature within the heating zone, ie the radiant tube. The high-temperature life of the radiant tube is prolonged, and the cost per unit is reduced by reducing the unit fuel consumption in the heating zone. In this embodiment, as shown in FIG. 5, the temperature in the heating zone (furnace temperature in the figure), that is, the temperature of the radiant tube, can be 926 ° C., which is 15 ° C. lower than the current temperature. The set temperature of the strip fed from the heating zone is 800 ° C., the same as the current temperature.

In this embodiment, since the temperature inside the furnace can be reduced as a result, the supply amount of the M gas, which is the fuel gas, is reduced. As a result, the flow rate of the combustion exhaust gas is reduced by about 6000Nm ³ / H little about 57000Nm
³ / H, and the exhaust gas temperature at that time is 66
It will be 9 ° C. This combustion exhaust gas is dissipated by duct heat.
When it reaches the regenerative heat exchanger, the temperature drops to 626 ° C. In the regenerative heat exchanger, the high heat recovery efficiency reduces the sensible heat of the combustion exhaust gas to 570 ° C.
The sensible heat of the air can be recovered, sent to the pre-tropical zone and sprayed on the strip, so that the sensible heat of 40 ° C. at the inlet of the pre-tropical zone is changed to the outlet of the pre-tropical zone, that is, the heating zone. On the inlet side, the temperature can be raised to 210 ° C., which is 90 ° C. higher than before, and by feeding this to the heating zone, the furnace temperature of 926 ° C. is achieved, and the unit fuel consumption in the heating zone is reduced from the conventional level. 216.6Mcal / t lower 216.6
Mcal / t was able to be reduced. The air flow fed / recycled to the preheating zone in the present embodiment, approximately conventionally 68000Nm ³ / H be less about 62000Nm ³ /
H was able to be reduced. This is because the temperature of the air blown to the strip is much higher than in the past, and the temperature of the strip can be increased efficiently even with a small flow rate, and in this sense, the energy efficiency of the present embodiment is high.

Next, a description will be given of the effect of improving the life by reducing the temperature of the radiant tube. In FIG. 6, the vertical axis represents the stress generated on the radiant tube, and the horizontal axis represents the material-specific constant P value expressed by the following equation.
Average Rupture Strength) and minimum rupture stress (Mi
nimum Rupture Strength). The average rupture stress indicates the relationship between the generated stress that has the highest probability of rupture of the radiant tube and the constant P value according to experimental statistics, and the minimum rupture stress is 95% of the probability that rupture can be avoided with a probability. It shows the relationship between the stress and the constant P value. Further, the generated stress applied to the radiant tube is, for example, a bending stress due to the tube's own weight,
It is given from the sum of the thermal stress in the axial direction, the thermal stress in the cross-sectional direction, the thermal stress in the circumferential direction, and the like, and all except the bending stress are given as a function of the temperature at which the radiant tube is generated. The sum of the stresses generated in the radiant tube in the present embodiment was about 0.852 kgf / mm ² . Therefore, the constant P value according to the minimum breaking stress curve of FIG. 6 is about 36.5.
become.

P = T · (23 + log (t)) exp (−3) (1) where T is a radiant tube temperature, that is, a furnace temperature, and t is a life time. Next, the constant P value is fixed, a function of the life time t based on the furnace temperature (radiant tube temperature) T is obtained, and this is expressed as the estimated radiant tube life years in FIG. As is clear from the above equation (1), the life time (year of life) t is represented by an exponential function of the reciprocal of the radiant tube temperature (furnace temperature) T. A significant temperature reduction has a significant effect on the life expectancy. For example, at the current furnace temperature of 941 ° C., the estimated life of only 5.5 years is reduced by only 15 ° C. 926.
Extended to 12 years more than doubled in ° C. As previously mentioned,
In the heating zone of a continuous annealing furnace having one hundred to several hundreds of radiant tubes in an integrated furnace, this effect is very large,
Not only the material cost of a simple radiant tube, but also the human cost merit required for maintenance and maintenance such as replacement of a broken radiant tube is great.

In the above embodiment, only the case where the gas blown to the strip in the pre-tropical zone is air is described in detail, but the gas blown to the strip in the pre-tropical zone is any other gas. There may be. Also,
The metal strip subjected to the continuous heat treatment is not limited to the strip. The method of spraying the strip may be either a slit nozzle or a multi-hole type.

Further, in the above-described embodiment, only the case where the combustion exhaust gas is only from the radiant tube of the heating zone has been described in detail. However, the combustion exhaust gas only needs to include at least the one from the heating zone. Accordingly, for example, a high-temperature gas such as the combustion exhaust gas from the soot and the exhaust gas from other facilities may be used in combination.

Further, in the above embodiment, only the continuous annealing furnace for continuously annealing the strip has been described in detail, but the continuous heat treatment apparatus of the present invention may be any continuous heat treatment apparatus having at least a heating zone and a pre-tropical zone. Can be similarly diverted.

[0039]

As described above, according to the continuous heat treatment apparatus for a metal strip according to the first aspect of the present invention, the combustion exhaust gas supplied to a radiant tube of a heating zone from a plurality of burners and discharged therefrom is observed. The heat is collectively stored in a heat storage unit of a large-scale regenerative heat exchange device, and a predetermined gas such as air is supplied to the heat storage unit to convert the sensible heat of the combustion exhaust gas into the sensible heat of the predetermined gas. Collected and collected, this gas is pre-heated by spraying this gas onto a metal band such as a strip within the pre-tropical zone, so that the gas passes through a heat storage body in a heat storage type heat exchanger. By raising the temperature of the predetermined gas to a sufficiently high temperature and directly blowing the high-temperature gas onto the metal strip, the temperature of the metal strip becomes significantly higher than in the past. Therefore, the temperature rise of the metal strip required in the heating zone is small, and the temperature required for the radiant tube can be reduced accordingly, and the rupture life of the radiant tube in such a high temperature range is greatly increased. In addition to the improvement, it is possible to reduce the unit fuel consumption supplied to the burner device.

According to the continuous heat treatment apparatus for a metal strip according to the second aspect of the present invention, three or more heat storage type heat exchangers are used, and at least one of the heat storage type heat exchangers stores heat in a heat storage body. The sensible heat of the exhaust gas is recovered as the sensible heat of the predetermined gas, and the sensible heat of the combustion exhaust gas is stored in the regenerator of the regenerative heat exchanger by spraying the sensible heat of the predetermined gas onto the metal strip in the pre-tropical zone. Since the opening and closing control of the control valve is sequentially performed, a predetermined high-temperature gas can be continuously blown from at least one regenerative heat exchanger to the metal strip, and the temperature of the metal strip in the feeding direction can be increased. , And at the same time, the sensible heat of the combustion exhaust gas can be efficiently stored in the regenerator in the remaining regenerative heat exchanger.

Further, according to the continuous heat treatment apparatus for a metal strip according to the third aspect of the present invention, the valve for discharging the combustion exhaust gas is opened while the valve for purging the predetermined gas is opened. By doing so, the combustion exhaust gas in the regenerative heat exchanger is discharged, the inside of the heat exchanger is purged with a predetermined gas, and after that, a valve for purging the predetermined gas is closed, and then the combustion is started. By closing the valve for discharging the exhaust gas and then opening the valve for discharging the predetermined gas, the predetermined gas heated to a high temperature is reliably blown onto the metal zone in the pre-tropical zone.

According to the apparatus for continuously heat-treating a metal strip according to claim 4 of the present invention, the flow rate of the system for purging the predetermined gas is controlled by the system for discharging the predetermined gas into the pre-tropical zone. By setting the flow rate to be smaller than the predetermined flow rate, the predetermined gas heated to a high temperature from another regenerative heat exchanger is constantly discharged into the pre-tropical zone, and a part of the gas is purged by a part thereof. The inside is reliably purged.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment in which a continuous heat treatment apparatus for a metal strip of the present invention is developed in a continuous annealing furnace.

FIG. 2 is a schematic configuration diagram of a pre-tropical zone in the continuous annealing furnace shown in FIG.

FIG. 3 is a sequence diagram of the valve configuration shown in FIG. 2;

FIG. 4 is a sequence chart of the valve configuration shown in FIG. 3;

FIG. 5 is an explanatory diagram of a heat flow of the continuous annealing furnace shown in FIG.

FIG. 6 is a characteristic diagram of a life evaluation of a radiant tube.

FIG. 7 is an explanatory diagram in which the life evaluation characteristic diagram of the radiant tube shown in FIG. 6 is replaced with a relationship with a furnace temperature.

FIG. 8 is a schematic explanatory view of a pre-tropical zone in a conventional continuous annealing furnace.

9 is an explanatory diagram of a heat flow of the continuous annealing furnace shown in FIG.

[Explanation of symbols]

 1A-1C is a regenerative heat exchanger 2A-2C is an exhaust gas inlet valve 3A-3C is an air inlet valve 4A-4C is an exhaust gas outlet valve 5A-5C is an air outlet valve 6A-6C is a purge valve 7 is air Feeding fan S is strip PHS is pre-tropical HS is heating zone SS is uniform tropical

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F27D 17/00 101 F27D 17/00 101G

Claims (4)

[Claims] 1. A heating zone for heating a metal strip continuously supplied by radiant heat from the radiant tube to a predetermined high temperature, comprising a plurality of radiant tubes to which combustion exhaust gases of a plurality of burner devices are respectively supplied. And a regenerative heat that collects the sensible heat of the combustion exhaust gas of the plurality of burners in this heating zone, stores the sensible heat in a heat storage body, and recovers the sensible heat to the gas by sending a predetermined gas to the heat storage body. A continuous heat treatment apparatus for a metal strip, comprising: an exchange device; and a pre-tropical zone that preheats the gas by blowing gas from the regenerative heat exchange device onto the metal zone at the entrance side of the heating zone. 2. The regenerative heat exchanger includes at least three or more regenerative heat exchangers each including a valve for switching between the combustion exhaust gas and a predetermined gas and supplying the gas to the regenerator. From at least one of these regenerative heat exchangers, a predetermined gas obtained by recovering the sensible heat stored in the regenerator is sprayed onto a metal strip, and the sensible heat of the combustion exhaust gas is emitted by the remaining regenerative heat exchanger. The continuous heat treatment apparatus for a metal strip according to claim 1, further comprising control means for sequentially opening and closing the valves of each of the heat storage type heat exchangers so as to store the heat in the heat storage body. 3. Each of the regenerative heat exchangers includes a valve for supplying the combustion exhaust gas to the heat storage element, a valve for supplying the predetermined gas to the heat storage element, and the combustion exhaust gas. A valve for discharging from the regenerator outside the pre-tropical zone and a valve for sending the predetermined gas from the regenerator to the pre-tropical zone;
A valve for branching from the system for supplying the predetermined gas from the heat storage body into the pre-tropical zone and purging the inside of the heat exchanger, wherein the control means includes a heat storage body for each heat storage type heat exchanger. After the valve for supplying the combustion exhaust gas is closed, the valve for purging the inside of the heat exchanger with the predetermined gas is opened, and the valve for purging the inside of the heat exchanger with the predetermined gas is opened. While the valve is open, a valve for discharging the combustion exhaust gas is opened and a valve for supplying a predetermined gas is closed, and a valve for purging the heat exchanger with the predetermined gas is provided. After closing, close the valve for discharging the combustion exhaust gas, then open the valve for delivering the predetermined gas,
3. A valve for supplying the predetermined gas to the heat storage body of the heat exchanger.
2. The continuous heat treatment apparatus for a metal strip according to claim 1. 4. The flow rate of a system for purging the inside of the heat exchanger with the predetermined gas provided in each of the regenerative heat exchangers sends the predetermined gas into the pre-tropical zone. The continuous heat treatment apparatus for a metal strip according to claim 3, wherein the flow rate is set to be smaller than the flow rate of the system.