JP3491444B2 - How to use a regenerative preheater - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an object to be heated, for example, by keeping a tundish for continuous casting (hereinafter, also simply referred to as continuous casting) in a non-oxidized state in order to repeatedly use the tundish. The present invention relates to a method of heating the inside of an object (hereinafter also referred to as a heating object) in a predetermined gas atmosphere state.

[0002]

2. Description of the Related Art A tundish that receives molten steel from a ladle and distributes it to a mold does not have a heating element itself. Therefore, when it is used, it is separately heated by a heating means to ensure a pourable temperature. There is a need. In addition, when casting continuously while exchanging multiple tundish (hereinafter also referred to as continuous casting), for example, when the steel type is changed, replace the tundish on standby. ,
There is a usage of the tundish such that the one used until then is kept waiting until the next reuse,
In this way, even the tundish in the standby state needs to be heated to a temperature at which it can be cast at least before being used.

In the case of heating the tundish in this manner, a gas burner provided in the preheating cover of the tundish has conventionally been used as a heating means. A mixture of 110 to 120% of combustion air is fed and burned in the gas burner to heat the inner surface of the tundish to 1200 to 1300 ° C.

However, in this case, a large amount of O ₂ is introduced into the tundish at high temperature, so that the residual steel and residue from the previous use (pre-charging) are oxidized during preheating during the next charging, and FeO and Iron oxides such as Fe ₃ O ₄ are produced.
O components of iron oxide the generated remaining, the Al ₂ O ₃ generated by reaction with Al in the steel in the component of the next charge, as a result, hard Al ₂ O ₃ is Hottohege, blistering, etc. at the lower step Will cause quality defects in the.

There is a demand for establishment of a technique for preventing and preventing such so-called FeO pickup, and at present, various proposals have been made. As one example, for example, Japanese Patent Laid-Open No. 4-
No. 22567 discloses that the amount of combustion air supplied to a preheating gas burner is 70 which is the theoretical required amount of the supplied fuel gas.
A tundish preheating method has been disclosed in which the atmospheric oxygen concentration in the tundish is made lower than in the prior art by setting the content to -100% to prevent the oxidation of residual steel from being suppressed.

Further, Japanese Patent Laid-Open No. 2-37949 discloses that
With the completion of preheating in the tundish as described above, the supply of fuel gas and combustion air is stopped, and at the same time, these residual components remaining in the burner and the residual components of combustion exhaust gas are retained by Ar, which is an inert gas. After being discharged (purged), the fuel gas and the combustion air are burned in the preheating cover as needed, so that the inside of the tundish can be A in a short time.
A gas replacement technique in a tundish is disclosed in which the oxidation of the residual steel is suppressed and prevented by purging with r.

[0007]

However, the heating method itself of the tundish described in the above-mentioned JP-A-4-22567 and JP-A-2-37949,
When using the tundish, as a means of heating it to a temperature at which it can be cast, burn a fuel gas mixed with air in the tundish to heat or heat the inner wall at 1200 to 1300 ° C. Is assumed. Here, for example, in the above-mentioned Japanese Patent Laid-Open No. 4-22567, the amount of combustion air fed is 70 times the amount of fuel gas fed.
However, under such a high temperature, in addition to the remaining O ₂ component, the O component of CO ₂ and H ₂ O, which are the oxidizing components in the generated combustion exhaust gas, may cause residual steel. There is a problem that the oxidation itself of the residual steel cannot be sufficiently suppressed because the iron oxide is generated by the bonding.

In order to suppress this as much as possible, the above-mentioned JP-A-2-
In the heating method for a tundish described in Japanese Patent No. 37949, after the preheating, the purpose is to use Ar, which is an inert gas.
Is blown into the tundish to purge the fuel gas and residual oxygen, thereby replacing the atmosphere with a non-oxidizing atmosphere. However, even if the method of purging the inert gas is improved and the time required to complete the gas replacement after the completion of the preheating can be shortened to some extent, the temperature of the inner wall of the tundish is lowered by this inert gas purging and the heat loss is reduced. However, there is a problem that even the oxidation of the residue due to excess oxygen during heating cannot be prevented.

On the other hand, the above-mentioned Japanese Patent Laid-Open No. 22567/1992.
In the tundish heating method described in the publication, the amount of air to the preheating gas burner is set to the theoretical required amount or less, so that the oxidation of the residual steel is suppressed without performing the inert gas purge. Even if such a problem does not occur, in order to completely prevent the oxidation of the residual steel in the tundish due to the combustion exhaust gas as described above, the combustion air amount supplied to the burner is set to the theoretical air amount of the fuel gas. It should be 50% or less. However, if the supply amount of the combustion air is extremely reduced in this way, there arises a problem of incomplete combustion due to lack of O ₂ at the time of combustion, resulting in high heating cost and explosion-proof and CO treatment for treatment of unburned gas. Safety problems such as measures against poisoning occur.

[0010] The inventors of the present invention, for example, as a measure for solving the above-mentioned problems related to the conventional problems relating to ensuring the temperature at which a reusable tundish can be cast, without involving the above-described combustion in the tundish. The tundish has been reused, that is, has been earnestly studied while conducting various experiments in order to realize a non-preheated and nonoxidized reuse process.

[0011] When reusing the tundish, the present inventors can continue to purge the inside of the tundish with an inert gas heated outside the tundish so that the surface temperature inside the tundish can be cast. It has been found that if the temperature is kept at the lower limit of 850 ° C. or higher, the preheating by the conventional combustion gas in the tundish can be omitted, and the tundish can be reused without preheating and preventing oxidation. .

Various heating means are provided outside the tundish and do not supply the combustion exhaust gas or the atmosphere into the tundish. Various types of heating means can be considered. In particular, the heat storage type preheater uses a small amount of combustion gas. While using, the inert gas can be efficiently heated without mixing the combustion exhaust gas into the inert gas. Therefore, multiple heat storage type preheaters are connected to the tundish, and while one of the heat storage type preheaters that has already heated the heat storage body is heating the inert gas, it is charged into the tundish, and the remaining heat storage -Type preheater sucks (recycles) the inert gas in the tundish while heating the heat storage body with the combustion burner, and exhausts the combustion exhaust gas and the sucked inert gas as exhaust gas and at the same time the inside of the tundish If the positive pressure is continuously maintained, the combustion exhaust gas and the atmosphere will not flow into the tundish. Therefore, the burner capacity of each regenerative preheater can be reduced while reliably suppressing the oxidation of the residual steel. , It is also possible to downsize it and always attach it to the tundish. Of course, this method
It can be applied to any object to be heated that has a predetermined content volume and needs to heat the inside in a non-oxidized state.

However, such a non-oxidizing heating device does not always continue to heat the object to be heated, for example, when the object to be heated is a tundish, and more specifically, it does not heat the object to be heated. The objects are connected when they are heated and separated when heating is not required. In such a situation that it is not necessary to heat the heating object and the heating object itself is separated, there is no energy loss or cost consumption unless the heat storage type preheater is operated. On the other hand, since the heat storage body of the heat storage type preheater continues to radiate and the temperature drops, the heat storage body must be heated again in order to heat the next heating object such as a tundish. Therefore, for example, a plurality of heat storage type preheaters as described above are connected by individual means other than the heating object, and a predetermined gas such as an inert gas is supplied to heat the heat storage body as described above. However, if the specified gas to be supplied is an inert gas, etc., the inert gas must be generated or purchased. Occurs. Further, when the connecting means is not provided, the heated gas is released into the atmosphere, but when the gas is an inert gas, safety problems such as oxygen deficiency occur.

The present invention has been developed in view of these problems, and an object of the present invention is to provide a method of using a regenerative preheater capable of preventing energy loss and cost consumption from being suppressed. .

[0015]

In order to solve the above-mentioned problems, a method of using a heat storage type preheater according to claim 1 of the present invention.
The method has a prescribed content volume and the inside is added in a non-oxidized state.
When heating the heating target that needs to be heated, multiple
Connect the heat storage type preheater of
From any heat storage type preheater, the heat storage body of the heat storage type preheater
Inert gas heated by passing through the
Turn on and put in the heating target from the remaining heat storage type preheater
Intake the generated inert gas and remove the inert gas.
Heat is stored by burning the combustion gas only in the regenerative preheater that draws in heat.
Heating the body, its flue gas and the sucked inert gas
Exhaust as exhaust gas, and switch this alternately
The object to be heated is heated and whether the object to be heated is a heat storage type heater.
When the gas is separated from the
It is characterized in that air is supplied to the heat storage body .

[0016]

Further, in the method of using the heat storage type preheater according to claim 2 of the present invention, the object to be heated is a tundish, the tundish is heated in a non-oxidized state, and the tundish is used. While being used for casting, the supply of inert gas to the heat storage preheater is stopped, and instead air is supplied to continue the operation of the heat storage preheater. is there.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the method of using the heat storage type preheater of the present invention, for example, the object to be heated is a tundish, and has a predetermined internal volume and internal volume. When it is necessary to heat in a non-oxidized state, as described above, a plurality of regenerators are connected to an object to be heated, and a regenerator of any one of the regenerators is used as a regenerator. Inert gas that has passed through and heated is introduced into the object to be heated, and the inert gas introduced into the object to be heated is sucked from the remaining heat storage type preheater, and heat storage that sucks the inert gas. The combustion gas is burned only in the type preheater to heat the heat storage body, the combustion exhaust gas and the sucked inert gas are exhausted as exhaust gas, and these are alternately switched to heat the heating target portion. At this time, when the object to be heated does not require the non-oxidized state and requires heating in a certain predetermined gas atmosphere, the predetermined gas is supplied to the heat storage body instead of the inert gas. Just pass through.

On the other hand, when the heating of an object to be heated such as a tundish is completed and the object to be heated and the heat storage type preheater are separated, a so-called heat retaining operation of the preheater is performed, for example, the plurality of heat storage type preheaters. Connect the vessels to each other with individual piping means,
By switching the supply gas switching means, individual gas such as air is supplied to the heat storage body to any one of the heat storage type preheaters in the same manner as described above, and the heat is supplied through the heat storage body of the heat storage type preheater. In the regenerative preheater that sucks the individual gas such as the air, etc. with the remaining regenerative preheater and sucks the individual gas,
The combustion gas is burned to heat the heat storage body, and the combustion exhaust gas and the individual gas such as the sucked air are exhausted as exhaust gas, and the heat storage body of each heat storage type preheater is heated by alternately switching this. It can be continued and operated continuously. At this time, if the supplied individual gas is air, even if there is no connecting means, there is no risk of oxygen deficiency etc. even if the heated gas is diffused to the atmosphere, and it is purposely generated or purchased. Since it is not necessary to do so, energy loss and cost consumption can be suppressed and prevented accordingly.

[0020]

EXAMPLES Next, a position example of the use of the regenerative preheater according to the present invention with reference to the drawings will be described in detail.

First, the non-oxidative heat retention of a tundish in which the heat storage type preheater of this embodiment and the method of using the same are embodied in FIG. From here, heating to that temperature is described as heat retention). In the tundish 1, each of the openings 1b and 1c of the lid 1a,
The heat storage type preheaters 2A and 2B are connected. In these heat storage type preheaters 2A and 2B, for example, in order to increase the heat transfer area, heat storage chambers 3A and 3B filled with a heat storage body made of spherical or pipe-shaped ceramics or metal, and the heat storage chambers 3A and 3B.
Combustion chambers 4A, 4B for heating the heat storage bodies A, 3B are provided in series in a manner adjacent to each other, and the combustion chambers 4A, 4B are connected to the opening 1b of the tundish 1 via insertion tubes 7A, 7B. The main burners 5A and 5B and the pilot burners 6A and 6B are respectively connected to the combustion chambers 4A and 4B.
To arrange. Between the insertion tubes 7A, 7B and the openings 1b, 1c of the tundish 1, sealing devices 50A, 50B, which will be described later, are interposed to keep the inside of the tundish 1 in an unoxidized state. ing. The nozzles at the bottom of the tundish are not shown.

Next, the heat storage type preheaters 2 similar to each other.
In order to explain the state of piping to A and 2B, one of the heat storage type preheaters 2A will be used for description. First, in the combustion chamber 4A of the heat storage type preheater 2A, the temperature in the combustion chamber 4A will be described. A combustion chamber temperature detector 31A for detecting the temperature and a combustion chamber pressure detector 33A for detecting the pressure in the combustion chamber 4A are attached. Further, a heat storage chamber output side temperature detector 37A for detecting the output side temperature of the heat storage chamber 3A is attached to the output side of the heat storage chamber 3A of the heat storage type preheater 2A, and the heat storage chamber output side temperature detector 37A. A temperature switch (TS) 39A that operates based on the output of

The main burner 5A is connected to an M gas supply source (not shown) through an M gas valve 8A, an M gas cutoff valve 52A, an M gas flow rate adjusting valve 9A and an M gas orifice 10A, and also M The gas valve 8A, the N ₂ shutoff valve 11A for purging the M gas, and the N ₂ pressure reducing valve 12 are connected to an N ₂ supply source (not shown). here,
M gas is a fuel gas, for example, a converter (LD) gas generated in a converter and a coke furnace (C) generated in a coke furnace.
It is a mixed gas of gas and a mixed gas of C gas and blast furnace (B) gas generated in the blast furnace. Instead of these, it is also possible to use fuel gas such as LPG or liquid fuel. An M gas flow rate detector 26A is provided at the orifice 10A to which the M gas is supplied. Further, a diffusion valve 51A is branched and connected to a pipe between the M gas valve 8A and the M gas cutoff valve 52A or the M gas purge N ₂ cutoff valve 11A, and its anti-branch connection end is open to the atmosphere.

Further, the main burner 5A includes an air valve 1
The air supply fan 16 is connected via 3A, the air flow rate adjusting valve 14A, and the air orifice 15A. An air flow rate detector 29A is provided at the air orifice 15A to which combustion air is supplied from the air supply fan 16.

The pilot burner 6A is connected to the M gas supply source through the pilot burner M gas shutoff valve 54, and also includes the pilot burner N ₂ shutoff valve 53 and the N ₂ pressure reducing valve 12. It is connected to the N ₂ supply source through.

On the other hand, the heat storage chamber 3A has an N ₂ valve 17A,
The N ₂ flow control valve 19, the N ₂ orifice 18, the N ₂ shutoff valve 77 for preheating the heat storage chamber, and the N ₂ pressure reducing valve 12 are connected to the N ₂ supply source, and the N ₂ valves 17A, N are connected.
_It is connected to the air supply fan 16 through the ₂ flow rate adjusting valve 19, the N ₂ orifice 18, and the heat storage chamber preheating air cutoff valve 76, and the N ₂ valve 17A, the H ₂ valve 72, the H ₂ flow rate adjusting valve 71, It is connected to an H ₂ supply source (not shown) via the H ₂ orifice 70, and further connected to the exhaust fan 22 via the exhaust valve 20A and the exhaust flow rate or pressure adjusting valve 21A. The N ₂ orifice 18 has the N
N ₂ flow detector 42 for detecting the flow rate of N ₂ supplied from the _second source is provided, in the H ₂ orifice 70 for detecting the flow rate of H ₂ supplied from the H ₂ supply H ₂
A flow rate detector 73 is attached. An exhaust flow rate or pressure detector 35A for detecting the exhaust flow rate from the heat storage chamber 3A is attached between the heat storage chamber 3A and the exhaust valve 20A, and the exhaust flow rate or pressure control valve 21A and the exhaust fan 22 are further provided. An exhaust gas temperature detector 38A for detecting the exhaust gas temperature is attached between the and, and a temperature switch 40A that operates based on the output of the exhaust gas temperature detector 38A is provided. Further, a dilution valve 23A is branched and connected to a pipe between the heat storage chamber 3A and the exhaust valve 20A, and an anti-branch connection end of the dilution valve 23A is manually or automatically flow-controlled valve 24A.
Is open to the atmosphere via (in actual control, as will be described later, since the dilution valve 23A is opened only when the exhaust from the heat storage chamber 3A is being performed, the heat storage chamber 3A is opened). The exhaust of 3A is not opened to the atmosphere through the manual or automatic flow rate adjusting valve 24A).
The exhaust valve 20A and the exhaust flow rate or pressure adjusting valve 21
The exhaust gas analyzer 41A connected to A is for analyzing and detecting the CO concentration and the like in the exhaust gas.

The M gas flow rate of the M gas flow rate control valve 9A is controlled by the M gas flow rate control controller (FIC) 27A, and the air flow rate of the air flow rate control valve 14A is controlled by the air flow rate control controller (FIC) 30A. Although the respective flow rates are controlled, both FICs 27A and 30A can exchange information with each other. Therefore, the M gas FIC 27A detects the M gas flow rate detection value and the combustion chamber temperature detection according to the output from the M gas flow rate detector 26A. The M gas flow rate control of the M gas flow rate adjusting valve 9A is performed as described later according to the detected value of the combustion chamber temperature according to the output from the reactor 31A and the control information from the air FIC 30A, while the air FIC 30A controls the air flow rate. An air flow rate adjusting valve, which will be described later, according to the air flow rate detection value according to the output from the detector 29A and the control information of the M gas FIC 27A. Performing 4A air flow control.

Further, the exhaust flow rate or pressure control valve 21A
The exhaust flow rate or pressure of the
By the exhaust flow rate or pressure indicating controller (F / PIC) 34A reading the detected value of the combustion chamber pressure according to the output from The flow rate or pressure is controlled as described below.

The output of the temperature switch 39A, which operates in response to the output from the heat storage chamber outlet temperature detector 37A, is taken in by a control unit for the entire system (not shown).
Described later regenerative preheater 2A, switched control of 2B, the N ₂ flow rate adjusting valve 9A of the N ₂ gas is an inert gas which will be described later
It is also used for the flow rate control and the like (in this embodiment, it is also used for the flow rate control and the like when the air is used as the input gas to the heat storage type preheater, which will be described later). Further, the output of the temperature switch 40A, which operates in response to the output from the exhaust temperature detector 38A provided near the exhaust fan 22, is also taken in by the control device of the entire system (not shown), and the atmosphere is taken into the exhaust gas. It is used for opening adjustment control of the flow rate adjusting valve 24A (only in the case of automatic control) to be inserted. Further, each of the on-off valves, such as the M gas valve 8A, the air valve 13A, the N ₂ valve 17A, the exhaust valve 20A, the dilution valve 23A, the H ₂ valve 72, etc., has a limit (not shown) that operates at its open / close end. A switch is provided, and the output of the limit switch is also taken in by the control device for the entire system (not shown).
It is used for sequence control described later.

On the other hand, the other heat storage type preheater 2B side is also constructed similarly to the heat storage type preheater 2A, that is,
The main burner 5B is connected to the M gas supply source via an M gas valve 8B, an M gas flow rate control valve 9B, etc., and
N ₂ shutoff valve 11B for purging M gas and the N ₂ pressure reducing valve 12
Etc. to the N ₂ supply source. Furthermore, the pilot burner 6B, the is connected to the pilot the M gas supply source through the M gas shut-off valve 54 or the like burner, and the pilot burner N ₂ shutoff valve 53 the N ₂
It is connected to the N ₂ supply source via a pressure reducing valve 12 or the like. Further, the combustion chamber 4B includes an air valve 13B and an air flow rate adjusting valve 14
It is connected to the air supply fan 16 via B or the like. Further, the heat storage chamber 3B includes the N ₂ valve 17B, the N ₂ flow rate adjusting valve 19, the heat storage chamber preheating N ₂ cutoff valve 77, and the N ₂ pressure reducing valve 1.
2 is connected to the N ₂ supply source, and is also connected to the air supply fan 16 via the N ₂ valve 17A, the N ₂ flow rate adjusting valve 19, the heat storage chamber preheating air cutoff valve 76, and the like. In addition, the exhaust valve 20B and the exhaust flow rate or pressure adjustment valve 21B
The exhaust system is connected to the exhaust fan 22 through the like, and the exhaust system includes a dilution valve 23B and a manual or automatic control valve 2
4B is branched and connected. Since the other detailed configurations are the same as those of the one regenerative preheater 2A side,
The same constituents are denoted by the same reference numeral with a suffix B, and detailed description thereof will be omitted.

Next, the heat storage type preheaters 2A and 2B and the sealing devices 50A and 50B interposed between them and the openings 1b and 1c of the tundish 1 will be briefly described with reference to FIG. . This heat storage type preheater 2A, 2B
The sealing devices 50A and 50B have a function of surrounding and sealing the outer circumferences of the insertion tubes 7A and 7B as shown in FIG. Reference numeral 301 in the heat storage chamber 3B (3A) is the heat storage body, and the heat storage body 301 is formed in a spherical shape here. This heat storage body 301 is the heat storage chamber 3B (3A) described above.
A large number are accumulated above the heat-resistant net member 302 obliquely arranged above the pipe connection portion 303, and when the heat storage type preheater 2B (2A) is in the state shown in the figure, these heat storage bodies 301 The upper surface of the is in a state as shown by the chain double-dashed line a in the figure according to the angle of repose. However, since the heat storage type preheater 2B (2A) of this embodiment is tilted in the arrow direction in the figure together with the tundish 1 at the time of slag, the spherical heat storage body 301 rolls under its own weight. It stabilizes at the angle of repose indicated by the chain double-dashed line b. Therefore, weirs 304 and 305 as shown in the figure are formed in the heat storage chamber 3B (3A) of the heat storage type preheater 2B (2A) of the present embodiment. Incidentally, the allowable upper limit temperature of the heat storage chamber 3B (3A) outlet side (TCA (TCB) in the figure) mainly depends on the heat resistant upper limit temperature of the heat resistant net member 302.

On the other hand, adjacent to the heat storage chamber 3B (3A)
As described above, the main burner 5 is installed in the combustion chamber 4B (4A).
The burner port of B (5A) is opened, and the M gas and
Combustion air is supplied. Also, this main burner 5B
The pilot burner 6B (6
The burner mouth of A) is opened, and this pilot burner 6B
Using the M gas flame supplied to (6A) as a pilot flame,
The inverter 5B (5A) is ignited. Of these, the main
Ignition and extinction of the burner 5B (5A)
This will be explained in detail using a sequence diagram, but here
A brief explanation of the ignition procedure for the Lot Burner 6B (6A)
Reveal As is known, this kind of pilot burner 6B
When igniting (6A), the surrounding area should not explode sufficiently.
It is assumed that you are in a good environment. More specifically, heat storage
Inside the chamber 3B (3A) and combustion chamber 4B (4A), of course, each pipe
In order to achieve a non-combustion state,
N, which is an inert gas₂Fill with gas (or N₂With gas
Need to be purged). Therefore, the pilot bar concerned
Before igniting the 6B (6A), the M gas shutoff valve 52
B (52A) and diffusion valve 51B (51A) are closed and M
Open the gas valve 8B (8A) to open M for gas purging N₂Occlusion
Open the shutoff valve 11B (11A) to open the main burner 5B (5
N in the pipe to A)₂Purge with. Then the pie
With the M gas shutoff valve 54 for the lot burner closed,
N for ilot burner₂Open the shutoff valve 53 to open the pilot valve.
N inside the piping to the 6A (6A)₂Purge with. Of course
During this period, the N₂Valve 17B (17A) and Dairyu
The exhaust valve 20 with the isolation valve 23B (23A) closed.
B (20A) is opened, combustion chamber 4B (4A) and heat storage chamber
N in 3B (3A) and exhaust pipe₂Purge with. this
In this way, the environment of the pilot burner 6B (6A) is
N₂N for the pilot burner after being purged with
₂Closes shutoff valve 53 and shuts off M gas for pilot burner
Open the valve 54 and ignite the pilot burner 6B (6A)
To do. By doing this, you can safely and securely
The lot burner 6B (6A) can be ignited.

Now, the tip of the insertion tube 7B (7A) extending downward from the combustion chamber 4B (4A) is inserted into the opening 1c (1b) of the lid 1a of the tundish 1, Around the opening 1c (1b) and around the upper surface of the lid 1a and the insertion tube 7B (7A) and the combustion chamber 4B.
Between the lower surface of (4A) and the sealing device 50B described above.
(50A) is provided. In addition, reference numeral 504 in the figure denotes a heat shield ring, which suppresses and prevents unnecessary transfer of heat between the heat storage type preheater 2B (2A) and the tundish 1. Also,
Open the tip of the insertion tube 7B (7A) with the opening 1c (1b).
If it is not inserted into the inside of the container, the airtightness (sealing property) between the insertion tube 7B (7A) and the opening 1c (1b) of the tundish 1 by the sealing device 50B (50A) should be expected.
Is decreased, the N heated from the combustion chamber 4B (4A)
_{When 2} is blown into the tundish 1, the atmosphere containing the O ₂ component flows into the tundish 1 due to the ejector effect generated along with the gas flow, so that the inside of the tundish 1 may not be maintained in an unoxidized state. There is. Therefore, in this embodiment, by inserting the distal end of the insertion tube 7B (7A) into the inside of the opening 1c (1b),
The inflow of air due to the ejector effect of the N ₂ gas flow can be suppressed and prevented.

Next, an outline of the tundish non-oxidizing heat retention method executed in this embodiment will be briefly described with reference to FIG. This tundish non-oxidizing heat retention method,
Now, assuming that the heat storage body in the heat storage chamber of the A type heat storage type preheater A is sufficiently heated, while supplying N ₂ which is an inert gas to the heat storage body of the heat storage type preheater A, the other side B Exhaust is performed from the heat storage chamber of the heat storage type preheater B of the system. At this time, in the combustion chamber of the heat storage type preheater A, M gas and combustion air are not supplied to the main burner and are not burned, and in the combustion chamber of the other heat storage type preheater B, M gas and Combustion air is supplied to burn them. Then, N ₂ which has passed through the gap of the heat storage body of the heat storage type preheater A and has been sufficiently heated is put into the tundish (T / D in the figure), and the other heat storage type preheater B is forcedly exhausted. Therefore, the tundish is sucked (recycled in the figure) into the combustion chamber of the heat storage type preheater B and heats the tundish by convective heat transfer while passing through the tundish. On the other hand, N ₂ recycled to the other heat storage type preheater B
Has a lower thermal energy, that is, a temperature, due to the heat transfer to the tundish, but since the M gas of the main burner is burning in the combustion chamber, the thermal energy of the combustion exhaust gas and itself (recycle N ₂ Since the heat energy of the adjacent heat storage chamber is heated by the heat energy of the above), and the temperature of the exhaust gas made of the mixed gas of the combustion exhaust gas after heating the heat storage body and the recycled N ₂ gas is already sufficiently lowered. ,
Exhaust this.

However, the heat storage type that is heated as described above
The allowable upper limit temperature is also set on the exhaust side (outlet side) of the heat storage chamber of preheater B.
Therefore, the temperature on the outlet side of the heat storage chamber reaches the allowable upper limit temperature.
Or before that, N₂And reverse the exhaust flow
Extinguish the main burner in the combustion chamber of the B-system heat storage type preheater B
The main burner of the combustion chamber of the A-system heat storage type preheater A.
To fire. Therefore, this time, the B-type heat storage system that is fully heated
Sufficiently heated N through the gap of the heat storage body of the preheater B₂
Heat transfer through the tundish
Energy of the combustion exhaust gas of the A-type combustion chamber
Rugie and the N ₂With the residual heat energy of the heat storage room
The heat accumulator is heated and then exhausted. To repeat this
The O component contained in the combustion exhaust gas and the atmosphere is
Since it does not flow into the rush, the tundish
The inside of the tundish is heated by heating the inside of the
Longer heat retention time and the
Almost 100% of the energy is put into the tundish N₂
Energy efficiency can be improved by converting to sensible heat. Less than
Is a technique such as how to enhance such effects.
It is a technique. In addition, two heat storage type preheaters alternate
Short heating (20 to 12)
(0 seconds), the entire heat storage body of each heat storage type preheater
The heat capacity may be small, so each heat storage type preheater is small
Can be converted.

Before explaining the control of each valve of the piping system, the operation of the valve in the piping system of FIG. 1 which is not directly involved in the tundish non-oxidizing heat retention method will be briefly described. The pilot burner M gas shutoff valve 54 and the pilot burner N ₂ shutoff valve 53 are both used when igniting and extinguishing the pilot burners 6A and 6B. Further, as described above, after the main burner piping is purged with N ₂ , the M gas purging N ₂ cutoff valves 11A and 11B are closed, and the M gas valves 8A and 8B are closed, and then the pilot burners 6A and 6B are connected. Ignite. Further, the diffusion valves 51A and 51B are connected to the main burners 5
When the fire extinguishing of A and 5B is stopped, the M gas valves 8A, 8B and M
Although the gas shutoff valves 52A and 52B are closed, since the shutoff valves may leak, the M gas shutoff valve 52 is temporarily used.
Even if a leak occurs in A, 52B, this diffusion valve 51A,
By depressurizing with 51B, M gas valves 8A, 8B
It has a function as a safety valve to prevent M gas from flowing into the preheater on the downstream side. Also,
Similarly, when the pilot burners 6A and 6B are ignited, the M gas is supplied to the main burners 5A and 5B by the M gas valves 8A and 8B.
The open / close control is performed by B, and the M gas cutoff valves 52A and 52B are maintained in the normally open state. Further, the manual or automatic flow rate adjusting valves 24A, 24B arranged on the inlet sides of the dilution valves 23A, 23B are always maintained at the set opening degree in the tundish non-oxidizing preheating method of the present embodiment. It Further, the heat storage chamber preheating air stage valve 76 is kept in a normally closed state, and the heat storage chamber preheating N ₂ cutoff valve is kept in a normally opened state.

Next, the control logic of each valve of the piping system will be described according to the sequence chart of FIG. Here, it is assumed that the two heat storage type preheaters have already continued to alternately repeat the heating of the tundish and the heating of the heat storage body.

First, time t₀Then, the B system heat storage type preheat
Vessel 2B to N₂And the A system heat storage type preheater 2A
Et N₂To shift to the recycling mode,
N of the B system₂The valve 17B is opened from the closed state. So
And this time t₀After a predetermined time T101 from the A system N
₂The valve 17A is closed from the open state. At this time, important
The reason is that two N₂Valves 17A and 17B
At the same time, if it is closed and the inside of the tundish 1 becomes negative pressure,
The time t ₀To B
System N₂Time T20 required for the valve 17B to open
0 is also the time t₀To N of A series₂Valve 17A is closed
The above time should be shorter than the required time T102.
It is necessary to set the predetermined time T101. That is, this
The required time T102 is N₂Input / “Combustion + N”₂Lisa
It will be the time required to switch "Eccle". This timer processing work
In more detail, the use of the B-type N
₂The valve 17B is closed to open, and the A system N₂Open and close the valve
Basically, in the operation of₂Valve 17B
After confirming the open signal from the above limit switch,
N of the A system₂Logic to output an open command to valve 17A
It is appropriate to use, but it is clear from the following 1 and 2 equations
In order to reduce the switching time, the combustion time ratio
If the combustion time rate is increased,
It is possible to reduce the amount of combustion per unit, that is, the burner capacity.
Therefore, the preheater can be made smaller and lighter to make it compact.
However, it is advantageous in terms of installation cost and installation space.
Therefore, the timer processing as described above is required.
It

Combustion time rate = θ _B / (θ _B + θ _C ) ... (1) where θ _C : required switching time (M gas valve closing time) θ _B : combustion time (M gas valve opening time) ) Required combustion amount / θ _B = combustion amount per unit combustion time (2) Also, during this period, the A system exhaust valve 20A, the dilution valve 23A, the air valve 13A, and the M gas valve 8A are closed. Similarly, the exhaust flow rate or pressure control valve 21A of the A system is set to a predetermined opening. Further, the H ₂ valve 72 is closed, and the N ₂ flow rate adjusting valve 19 is set to a predetermined opening according to the tundish internal positive pressure holding control described later. Here, the closing of H ₂ valve 72 during the switching, can not be secured a N ₂ flow some trouble occurs during this switching, the input N ₂
This is because it is assumed that the inside H ₂ concentration rises abnormally, and this is avoided to ensure safety. Therefore, if an upper limit value is set for the concentration of H _{2 in} N ₂ to be charged and the H ₂ valve is closed when the upper limit value is exceeded, the H ₂ valve is basically always open. It is also possible. The setting state of the N ₂ flow rate adjusting valve 19 is variable, and its control content will be described later in detail. On the other hand, B system exhaust valve 20B, dilution valve 23B, air valve 1
Both the 3B and M gas valves 8B are closed, and the exhaust flow rate or pressure adjusting valve 21B of the B system is set to a predetermined opening degree.

Next, the dilution valve 23A is adjusted in accordance with the timing of closing the N ₂ valve 17A of the A system.
And the H ₂ valve 72 are opened, and thereafter, a predetermined time T103
After that, the exhaust valve 20A is opened. Here, the exhaust valve 2
By opening the dilution valve 23A before 0A, the pressure wave generated by the opening operation of the exhaust valve 20A can be alleviated. Then, after the predetermined time T104 has elapsed after the exhaust valve 20A of the A system is opened, the air valve 13A of the A system is similarly opened to open the air valve 13A.
After a predetermined time T105 from the opening of the air conditioner, the control of the combustion air flow rate by the A-system air flow rate adjustment valve 14A is started so as to be equal to the air quantity at the end of the previous air ratio control in order to secure the combustion air quantity. To do. After that, after a predetermined time T106, the exhaust flow rate or pressure control by the exhaust flow rate or pressure adjusting valve 21A is started (the details of the control will be described later), and after a predetermined time T107, the A system M gas valve 8A is also opened. It is operated to actually start combustion of the A-system main burner 5A. After the A-system M gas valve 8A is opened, the M gas flow rate adjusting valve 9 is further opened after a predetermined time T108.
At the same time when the M gas flow rate control by A is started, the air flow rate control by the A system air flow rate adjusting valve 14A is changed and set from simple flow rate control to M gas air ratio control. Also,
At the same time as the M gas flow rate control, the N ₂ flow rate adjusting valve 19A
Is closed by a predetermined opening degree (the details of the control will be described later), and after a predetermined time T109, the N ₂ flow rate control valve 19 starts the N ₂ flow rate control. By the way,
Both the M gas valves 8A and 8B of this embodiment are set so as to be opened more slowly than the other valves. this is,
This is to prevent incomplete combustion from being caused by inflow of more M gas than the set value into the main burners 5A and 5B immediately after the M gas valves 8A and 8B are opened in a short time.

While continuing this combustion state, the N _{2 which} has been heated from the B type heat storage type preheater 2B as described above is put into the tundish and recycled to the A type heat storage type preheater 2A. The N ₂ heats the heat storage body 301 of the heat storage chamber 3A of the heat storage type preheater 2A together with the thermal energy of the combustion exhaust gas, and is exhausted through the exhaust valve 20A and the exhaust flow rate or pressure adjusting valve 21A. And, in reality, the A
Temperature detector 37A and temperature switch (T
S) Feedback control is performed by the temperature of the heat storage chamber outlet side detected at 39A. Here, the stable combustion time is the time T109 and the time T110 during which both M gas and air are controlled.
It is expressed as the sum of. After the elapse of the predetermined time T110, for switching operation, first, the M gas air ratio control by the air flow rate adjusting valve 14A of the A system is stopped and the opening is fixed at a predetermined opening. The exhaust gas flow rate or pressure control by the A system exhaust gas flow rate or pressure control valve 21A and the M gas flow rate control by the A system M gas flow rate adjusting valve 9A are stopped. At the same time, the predetermined time T1
After twelve, the N ₂ flow rate control by the N ₂ flow rate adjusting valve 19 is stopped and the opening degree is opened by a predetermined opening degree. Then, after a predetermined time T113, the A-system M gas valve 8A is closed, and after a predetermined time T114 after the M-gas valve 8A is closed, the A-system air valve 13A is similarly closed.

Next, after the A-system air valve 13A is closed, the A-system dilution valve 23A and the exhaust valve are similarly exhausted after a predetermined time T115 obtained from an optimized exhaust gas purge time described later. 20A and 20A are simultaneously closed. Then, the H ₂ valve 72 is also closed in synchronization with the closing operation of the exhaust valve 20A of the A system. This series of N ₂ injection /
In the switching sequence of “combustion + N ₂ recycle”, the exhaust flow rate of the A system or the opening degree of the pressure adjusting valve 21A and N ₂
By appropriately setting the opening degree of the valve 19, the combustion exhaust gas of the M gas and air does not flow into the tundish 1, and the M gas that is combustion gas may flow directly into the exhaust gas. Disappear.

On the other hand, after a predetermined time T116 after the exhaust valve 20A of the A system is closed, the N ₂ valve 17A of the A system is similarly opened, and after a predetermined time T201, the B valve is opened.
The N ₂ valve 17B of the system is closed. At this time, in the same manner as described above, the time required T100 until A system of N ₂ valve 17A is opened is, B type of N ₂ valves from N ₂ valve 17A of the system A has started opening operation The predetermined time T20 is set to be shorter than the time T202 required for 17B to be closed.
It is necessary to set 1.

Next, the dilution valve 23B and the H ₂ valve 72 are opened in the same manner as described above at the timing when the N ₂ valve 17B of the B system is closed, and then the exhaust gas is exhausted after a predetermined time T203. The valve 20B is opened. Then, the air valve 13B of the B system is similarly opened after a predetermined time T204 after the exhaust valve 20B of the B system is opened, and the air valve 13B is opened for the predetermined time T.
After 205, similarly to the above, the B system air flow rate adjusting valve 14B
Control of the flow rate of combustion air is started. Then, after a predetermined time T206, the exhaust gas flow rate or pressure control valve 2 is similarly operated as described above.
Exhaust flow rate or pressure control by 1B is started, and after that, after a predetermined time T207, the B system M gas valve 8B is similarly opened to actually start combustion of the B system main burner 5B. After the valve 8B is opened, the M gas flow rate control valve 9B starts the M gas flow rate control after a predetermined time T208, and at the same time, the air flow rate control of the B system air flow rate control valve 14B is simply performed. To M gas air ratio control. Also, the above M
Simultaneously with the gas flow rate control, the N ₂ flow rate adjusting valve 19B is closed by a predetermined opening degree, and after a predetermined time T209,
The N ₂ flow rate control by the N ₂ flow rate adjusting valve 19 is started.

While continuing this combustion state, N _{2 which} has been heated from the A-system heat storage type preheater 2A as described above is fed into the tundish and recycled to the B-type heat storage type preheater 2B. The N ₂ heats the heat storage body 301 of the heat storage chamber 3B of the heat storage type preheater 2B together with the thermal energy of the combustion exhaust gas, and is exhausted through the exhaust valve 20A and the exhaust flow rate or pressure adjusting valve 21A. Then, similarly to the above, after the stable combustion time T210 has elapsed, the M gas air ratio control by the air flow rate adjusting valve 14B of the B system is stopped to fix the opening to a predetermined opening, and then the predetermined time T211. After that, similarly, the exhaust flow rate or pressure control by the B system exhaust flow rate or pressure control valve 21B and the M gas flow rate control by the B system M gas flow rate adjusting valve 9B are stopped. At the same time, after a predetermined time T212, the N ₂ flow rate control by the N ₂ flow rate adjusting valve 19 is stopped and the opening degree is opened by a predetermined opening degree. After that, after a predetermined time T213, the B system M gas valve 8B is closed, and after a predetermined time T114 after the M gas valve 8B is closed, the B system air valve 13B is also closed, and then , After the predetermined time T215 obtained from the optimized exhaust gas purge time, the same B
The dilution valve 23B and the exhaust valve 20B of the system are simultaneously closed, and H is synchronized with the closing operation of the exhaust valve 20B.
_{The 2} valve 72 is also closed. In the switching sequence of this series of N ₂ charging / “combustion + N ₂ recycling”, the above B
System exhaust flow rate or pressure control valve 21B opening and N ₂ valve 1
By appropriately setting the opening degree of 9, the combustion exhaust gas of the M gas and air will not flow into the tundish 1, and the M gas that is combustion gas will not flow directly into the exhaust gas. .

When temporarily suspending the combustion of the main burners 5A and 5B of the heat storage type preheaters 2A and 2B, the stop of the air flow rate control by the air flow rate adjusting valves 14A and 14B precedes. This is because the air flow rate is a cascade control of the M gas flow rate, and the order of restarting the combustion is to safely start the combustion after stabilizing the control of the air flow rate and the exhaust gas flow rate. Also, N ₂ input / “combustion + N ₂ recycling” in the steady state
The switching is performed when the set time by the so-called timer has elapsed, but other than this, the pattern in which this switching command is output in a non-steady state is as follows: (1) When the exhaust gas temperature exceeds the upper limit, And when maintaining thermal efficiency, (2)
There are three patterns: when the device itself is protected when the temperature of the heat storage chamber exit side exceeds the upper limit, (3) when the device itself is protected when the combustion chamber temperature exceeds the upper limit,
Of these, the switching pattern of (1) is not considered to be abnormal because the exhaust gas temperature is lowered by dilution, but the switching patterns of (2) and (3) function as an interlock at the time of abnormality.

Next, the combustion exhaust gas pattern in the logic is
For setting the charging time and controlling the flow rate / pressure of each gas.
Explain. First, the combustion in the combustion chamber of each heat storage type preheater
Finish firing, N₂Input / “Combustion + N” ₂Recycling
When switching the mode, next N₂Heat storage type
Because the combustion exhaust gas remained in the preheater and its piping system,
Is the N₂Combustion exhaust gas is also thrown into the tundish.
It will be entered. CO in this combustion exhaust gas₂And H₂O
Since it contains a large amount of oxidizing gas components such as
Is combined with the residual steel, and at the start of the next casting, as described above
Al₂O₃Will be formed. Therefore, this combustion exhaust gas
After purging₂Need to start
It However, combustion in the combustion chamber of each heat storage type preheater
When finished, put it in the combustion chamber, heat storage chamber and exhaust pipe.
Is still full of combustion exhaust gas, and the exhaust gas temperature at each site
The degrees are very different. Also, the temperature at each site
Is the combustion exhaust gas flow rate / input N₂Flow rate / recycle N₂Flow
Combustion required for actual operating patterns as it depends on the amount
Exhaust gas purge time must be set. Here, below
The combustion exhaust gas purge time t is set according to the equation (3).
It was

T = t _F + t _R + t _W (3) where t _F = V _F / (V _G × (273 + T _F ) / 273) × α ₁ t _R = V _R / (V _G × ( _{273 + T R) / 273)} × α 2 t W = V W / (V G × (273 + T W) / 273) was _{× α 3, V G (Nm} 3 / sec):. exhaust gas flow rate T _F (℃) · V _F (m ^3): a combustion chamber temperature and volume _{T R (℃) · V R} (m 3): regenerator temperature and volume _{T W (℃) · V W} (m 3): piping temperature and volume alpha ₁ ~ Α ₃ : It is a constant.

Here, the combustion chamber volume V _F , the heat storage chamber volume V _R , and the pipe inner volume V _W are known, and N _{2 is} input / “combustion + N ₂ ” from the heat storage chamber allowable temperature in the logic.
The combustion chamber temperature T _F , the heat storage chamber temperature T _R , and the pipe internal temperature T _W when switching the “recycling” mode are almost stable. Therefore, when these are sampled by an experiment or the like, the exhaust gas flow rate V _G is used as a parameter and the exhaust gas concerned. A combustion exhaust gas purge time t that linearly decreases with an increase in the flow rate V _G is calculated. Therefore, the combustion exhaust gas purge time t can be optimized from the assumed actual exhaust gas flow rate V _G.

Next, during normal combustion in the above logic,
That is, in a predetermined time T111, the control time represented by the sum of the T211 to the stable combustion time T110, T210 and control end, the turned flow and recycling flow rate of the N ₂ about the control of the opening degree of N ₂ flow rate adjusting valve 19 The setting method will be described. The actual input flow rate of N ₂ needs to be precisely set in consideration of the exhaust gas flow rate to be described later, but here, only the transfer of thermal energy will be considered.

First, FIG. 5 is an excerpt of the periphery of the heat storage type preheater for exhaust gas in the piping system. In FIG. 5, the combustion chamber temperature detected by the combustion chamber temperature detectors 31A, 31B is shown. T ₁ , the temperature detector 37 on the outlet side of the heat storage chamber
Assuming that the heat storage chamber outlet temperature detected by A and 37B is T ₂ , the heat receiving amount Q _G of the heat storage unit per unit time is as the heat energy stored in the heat storage unit at the time of combustion of this heat storage type preheater. It is expressed by equation 4.

Q _G = (V ₁ + V ₂ ) × C _PG × (T ₁ −T ₂ ) ... (4) where C _{PG is} the specific heat of the mixed gas (exhaust gas) of the combustion exhaust gas and the recycled N ₂ gas. V ₁ : Flow rate of combustion exhaust gas V ₂ : Flow rate of recycled N ₂ .

Further, in the figure, a single unit from the heat storage chamber to the outside is shown.
The amount of heat dissipated per hour is Q₁Therefore, the real heat storage
Heat storage amount Q'of the body per unit time_GIs expressed by the following 5 formula
It   Q '_G= (V₁+ V₂) × C_PG× (T₁-T₂) -Q₁        ……… (Five) Now, the N which is an inert gas₂Set the input flow rate at the time of input
When determining the value, the amount of heat stored in the heat storage body is set to N as described above.₂
If there is no heat exchange with
Lower temperature of heat storage such as heat-resistant net member 302 below rises
Then, there arises a problem of heat resistance of the device structure. On the other hand, N₂amount
Input more than necessary is the input N ₂Low gas temperature
It causes the following, and interferes with the gas supply for heating purposes.
That is, there is a problem in that the heated product is not heated. Since
From above, input N by heat exchange₂Temperature T_NIs the combustion chamber
Temperature T₁Since it becomes the following, N before heat exchange₂Temperature to T_N0When
Then, the most effective input N₂Flow rate V_NSatisfies the following 6 formulas
Therefore, if you use the above 3 formulas to organize, the following 7
It becomes like a formula. Here, the combustion exhaust gas flow rate V₁Is the combustion chamber
The following 7 formulas are recycled because they are controlled by the temperature of
N₂Flow rate V₂And input N₂Flow rate V_NWhen deciding the setting value of
It becomes a constraint condition.

[0054] _{Q 'G = V N × C} PN × (T 1 -T N0) ......... (6) ∴V N = (V G × C PG × (T 1 -T 2) -Q 1) / ( C _PN × (T ₁ −T _N0 )) (7) where C _PN is the specific heat of N ₂ .

Next, an exhaust gas flow rate setting method relating to the opening control of the exhaust gas flow rate adjusting valves 21A, 21B in the normal combustion time in the above logic will be described. First, FIG. 6 also shows an excerpt of the periphery of the heat storage type preheater related to exhaust in the piping system. In FIG. 6, the combustion chamber pressure detected by the combustion chamber pressure detectors 31A and 31B is P ₁ , The exhaust pressure detected by the exhaust flow rate / pressure detectors 35A, 35B (inside the pipe pressure in the figure) is P ₃ , and the supply pressure of the air used as the dilution gas from the dilution valves 23A, 23B (that is, the large pressure). When the atmospheric pressure) is P ₀ and the tundish internal pressure (in the same figure, the furnace or T / D internal pressure) detected by a tundish internal pressure detector (not shown) is P ₂ , the exhaust gas flow rate V is Combustion exhaust gas flow rate V ₁ , recycle N ₂ flow rate V ₂ and dilution gas (dilution) flow rate V ₃ , that is, V = V ₁ + V ₂
+ V ₃ , of which the combustion exhaust gas flow rate V ₁ is 8
It is represented by a formula.

V ₁ = Vm (G ₀ + (m−1) A ₀ ) ... (8) However, Vm: total fuel gas flow rate G ₀ : theoretical combustion gas amount A ₀ : theoretical air amount m: air ratio Is.

Further, the diluent gas (dilution)
Since the flow rate V ₃ is determined by the dilution gas supply pressure (atmospheric pressure) P ₀ and the exhaust pressure differential between the (pipe _{pressure) P 3 (P 0 -P 3} ), for example, pre-diluted gas as shown in FIG. 7 Supply pressure (=
Atmospheric pressure) P ₀ and exhaust pressure (inside pipe pressure) P ₃ differential pressure (P ₀ -P ₃ ) and dilution gas (dilution) flow rate V
₃ is investigated, and the dilution is calculated from the differential pressure (P ₀ −P ₃ ) between the detected dilution gas supply pressure (atmospheric pressure) P ₀ and exhaust pressure (inside pipe pressure) P ₃ at that time. A gas (dilution) flow rate V ₃ can be obtained.

On the other hand, as described above, the relationship between the recycled N ₂ flow rate V ₂ and the input N ₂ flow rate V _N is determined by the above-mentioned equation 7. Therefore, when this input N ₂ flow rate V _N is determined, the recycled N ₂ flow rate V _N is determined. ₂ is obtained. Here, the input N ₂ flow rate V _N
Is determined by the amount of heat required to heat the tundish,
For example, the following formula 11 can be derived from the heat balance formulas represented by formulas 9 and 10 below to set the input N ₂ flow rate V _N.

Q _TD = A _TD × α × (T _GOUT −T _TD ) ... (9) However, Q _TD : heat received by the tundish A _TD : inner surface area of the tundish α: inner surface of the tundish Heat transfer coefficient between N ₂ T _GOUT : Temperature at which the input N ₂ exits the tundish T _TD : Surface temperature inside the tundish Q _G = V _N × C _P × (T _GIN −T _GOUT ) ……… (10 ) However, Q _G: amount of heat introduced N2 is released into the tundish C _P: average specific heat T _GIN of input N2: temperature of the input N2 here, since it is _{Q TD = Q G, V N} = a TD × α × (T _GOUT −T _TD ) / (C _P × (T _GIN −T _GOUT )) (11) Set the exhaust gas flow rate V from the sum of the flow rates V _{1 to} V ₃ thus obtained. , The exhaust gas flow rate or pressure control valve 21A for the control time so that this exhaust gas flow rate V is achieved,
The opening of 21B may be controlled.

The recycle N ₂ flow rate V ₂ can be set as follows. That is, if the tundish internal pressure P ₂ can be detected as described above, the necessary and sufficient condition for securing the amount of recycled N ₂ from the tundish is the tundish internal pressure P 2.
₂ and the combustion chamber pressure P ₁ and the differential pressure (P ₂ -P ₁₎ is to be a positive value. Here, the tundish pressure P ₂ and the combustion chamber pressure P ₁ of the pressure difference between (P ₂ -P ₁₎ and recycled N ₂ flow rate V _2, under comparable temperature and pressure, is in a unique relationship, hence for example advance as shown in FIG. 8 the tundish pressure P ₂ and the combustion chamber pressure P ₁ of the differential pressure (P
₂ -P ₁ ) and the recycle N ₂ flow rate V ₂ are investigated, and the pressure difference (P ₂ -P ₁ ) between the detected tundish internal pressure P ₂ and combustion chamber pressure P ₁ is satisfied. As described above, the recycle N ₂ flow rate V ₂ may be set to control the combustion chamber pressure P _1, and the exhaust gas flow rate V is set accordingly and the exhaust gas flow rate during the control time or The openings of the pressure regulating valves 21A and 21B may be controlled.

Performing such flow rate control of each gas
And at least steady N₂Input / “Combustion + N”₂Resai
Keep the pressure inside the tundish in positive mode
It will be possible to carry. However, N₂Input /
"Combustion + N₂When switching the "recycle" mode,
The pressure inside the tundish cannot be maintained at a positive pressure
Could be. That is, for example, the sequence of FIG.
From the M gas valve 8A closing to the M gas valve 8B
In the required switching time until opening, the combustion exhaust gas flow rate V ₁Is reason
It is theoretically “0”, and therefore, in a significant case, the
Curu N₂Flow rate V₂= (Exhaust gas flow rate V-Dilution
Flow rate V₃), And in such cases
Input N to₂Flow rate V_NAnd the exhaust gas flow rate V is N₂Input
/ "Combustion + N₂The settings are the same as in the steady state of the "recycle" mode.
It was decided that the pressure in the tundish would be negative pressure.
The combustion exhaust gas and the atmosphere into the tundish.
I will

Therefore, such N ₂ input / “combustion + N”
_When switching to " ₂ recycle" mode, as described above, N
_By opening the opening of the ₂ flow rate adjusting valve 19 to increase the input N ₂ flow rate V _N , or closing the opening of the exhaust flow rate or pressure adjusting valves 21A and 21B to decrease the exhaust gas flow rate V,
Keep the pressure in the tundish positive. More specifically, for example, introduced N ₂ flow rate V when _N for increase setting method of the input N ₂ flow rate [Delta] V _N at the time of increasing is described, for example, N ₂ loading / combustion gas flow V when switching modes "combustion + N ₂ Recycling" _{Since 1} becomes “0”, the recycle N ₂ flow rate V _2C at the time of switching is expressed by the following formula 12 with respect to the steady recycle N ₂ flow rate V _2S .

V _2C = V ₁ + V _2S (12) On the other hand, the pressure in the tundish depends on the emission N ₂ flow rate V _W from the tundish opening (slag port, nozzle port, etc.) (V _{The more W, the} higher the pressure in the tundish). Therefore, this diffused N ₂ flow rate V _W is expressed by the following 13 equations.

V _W = V _N −V _2S ...... (13) Therefore, in order to make this diffused N ₂ flow rate V _W constant at the time of switching, the above equations 12 and 13 are connected by an equal sign and arranged. As is clear from this, basically, it is sufficient to increase the input N ₂ flow rate V _N by the combustion gas flow rate V ₁ . In practice, the recycle N ₂ flow rate V _2S during steady operation is set to a value smaller than the limit value so that the internal pressure of the tundish becomes a positive pressure with a margin. Therefore, if the upper limit value of the recycle N ₂ flow rate that can be set during steady operation is set to “V _2S upper limit” and the relationship between the two is investigated in advance, the increased recycle N ₂ flow rate Δ
The following 14 expressions are established using V ₂ .

V _2S upper limit = V _2S + ΔV ₂ (14) However, ΔV ₂ > 0 Further, the minimum value of the emission N ₂ flow rate, which is the minimum required to make the tundish internal pressure a positive pressure, “V _W lower limit” Is expressed by the following formula 15.

[0066] V _W limit = V _N -V _2S upper ......... (15) Thus, to obtain the following 16 formula from the equation (14) and 15 equation to obtain the following 17 formula from this 16 type and the 12 expression.

V _W lower limit = V _N − (V _2S + ΔV ₂ ) ... (16) V _W lower limit = V _N − (V _{2 C} −V ₁ ) −ΔV ₂ = V _N −V _{2 C} + V ₁ −ΔV ₂ (17) Therefore, from this equation 17, in order to make the internal pressure of the tundish a positive pressure, it is sufficient to increase the input N ₂ flow rate V _N by at least “V ₁ −ΔV ₂ ”. Is to set the increased flow N ₂ flow rate ΔV _N so that the following equation 18 is satisfied.

ΔV _N ≧ V ₁ −ΔV ₂ = V ₁ − (V _2S upper limit −V _2S ) ... (18) If the exhaust gas flow rate is reduced during this switching,
The increased input N ₂ flow rate ΔV _N can be further reduced. This is clear if the decrease in the exhaust gas flow rate is considered as the decrease in V ₁ .

In this embodiment, the increase in the input N ₂ flow rate V _N and the decrease in the exhaust gas flow rate V are simultaneously performed in a well-balanced manner so that the above conditions are simultaneously satisfied, so that the tundish internal pressure P ₂ is ensured. It is set to maintain positive pressure. Of course, when the tundish internal pressure P ₂ can be detected as described above, it is possible to change and set the increase amount of the input N ₂ flow rate V _N and the decrease amount of the exhaust gas flow rate V.

However, in this embodiment, the dilution flow rate of the atmosphere, which is the diluent gas, is not variably adjusted. However, in the case of automatically adjusting this dilution flow rate, for example, N ₂ injection / By increasing the dilution flow rate at the time of switching the mode of “combustion + N ₂ recycle”, it becomes possible to maintain the tundish internal pressure P ₂ at a positive pressure as described above.

Further, in this embodiment, since the oxygen concentration flowing into the tundish can be reduced as much as possible, it is not particularly used, but the oxygen concentration in the tundish is detected if possible. If a means is provided and the above-mentioned positive pressure holding control in the tundish is executed only when the detected oxygen concentration in the tundish exceeds the threshold value, the increase flow rate of the input N ₂ which becomes an unnecessary amount is increased. Since it is possible to prevent the reduction flow rate of the exhaust gas and the exhaust flow rate or the increase flow rate of the dilution, it is possible to save energy and reduce the cost.

By performing the above control contents in combination, it is possible to prevent the combustion exhaust gas and the atmospheric air from being sucked into the tundish. Therefore, it is possible to surely prevent the further oxidation of the residual steel. be able to. By the way, in the present embodiment, it is attempted to substantially eliminate the residual steel oxidation by further creating a reducing atmosphere in the tundish.

Here, for example, when H ₂ is used as a reducing gas for creating a reducing atmosphere in the tundish, the H ₂ is combined with the O component of iron oxide Fe ₃ O ₄ or FeO to generate iron. reduction or, or a state of H ₂ O O components or by oxidizing the iron is iron oxide Fe ₃ O ₄ and FeO, H ₂
FIG. 9 shows a redox equilibrium curve depending on the concentration, the H ₂ O concentration and the temperature.

This redox equilibrium curve is replaced with the H ₂ / H ₂ O concentration ratio, and the temperature-dependent iron redox equilibrium curve is shown in FIG. The figure also shows the iron redox equilibrium curve depending on the temperature of the CO / CO ₂ concentration ratio when CO is used as the reducing gas which can also achieve a reducing atmosphere. In this case, since the target heat retention temperature of the tundish is about 1000 ° C. or higher, the H ₂ / H ₂ O concentration that can reduce iron is about 1 in the above N ₂ atmosphere at such a high temperature. It turns out that it is about 0.5. Therefore, it is advantageous to use H ₂ as the reducing gas because the amount of H ₂ input may be small, so that the concentration of the reducing gas that is input is suppressed below the explosion limit (flammability limit) concentration as described later. It is said that

Here, as is known, the flammability limit of H ₂ when leaking into the air is about 4% or less, so the conditions for adding H ₂ will be considered. Now, assuming that the average O ₂ concentration in the tundish is C _O , the above-mentioned N ₂ flow rate into the tundish is V _N , and the addition H ₂ flow rate into the tundish is V _H , the tundish enters the tundish. H ₂ amount which reacts with the O ₂ (= generated H ₂ O
The quantity) V _{H2 0} is given by the following equation 19.

[0076]   V_H20= 2 x V_N× C_O                                    ……… (19) Therefore, the H ignited in the tundish₂Of which O
H that does not react with₂Quantity V _HrIs given by the following equation 20.

V _Hr = V _H −V _H20 = V _H −2 × V _N × C _O (20) Therefore, the actual input H ₂ amount V _{Hr with} respect to the H ₂ O amount V _H2O generated here. The concentration ratio H ₂ / H ₂ O of is expressed by the left side of the following equation 21.
If the above is satisfied, the relationship between the required average O ₂ concentration C _O , the input N ₂ flow rate V _N , and the added H ₂ flow rate V _H obtained by solving this is given by Equation 22.

[0078]   (V_H-2 x V_N× C_O) / (2 × V_N× C_O) ≧ 1.5 ……… (21) ∴V_H≧ 5 × V_N× C_O                                      ………(twenty two) On the other hand, the input N₂Flow rate V_NAddition H₂Flow rate V_H
Since the flammability limit range of is expressed by the following formula 23, solve it.
Input N obtained by₂Flow rate V_N, Addition H₂Flow rate V _Hconnection of
Becomes formula 24.

[0079]   V_H/ (V_N+ V_H) ≦ 0.04 ……… (23) ∴V_H≤V_N/ 24 ………… (24) The relationship of this 24 formula is shown in FIG.₂Actually as flammability lower limit curve
Shown with a line, and this H ₂Above and below the flammability lower limit curve,
Average O given by equation 2₂Concentration C_OAs a parameter
N₂Input amount-H₂The relationship between the amounts added is indicated by a chain double-dashed line. this
From the above H₂The upper side of the flammability lower limit curve is N in this embodiment.
₂Atmosphere H₂Inflammable range of gas (HN gas in the figure)
Therefore, this H₂Average above the flammability lower limit curve
O₂When the concentration is ≧ 0.7%, a safety problem occurs. Change
And the input N set as described above.₂Flow rate V_Nunder
Therefore, it is not possible to suck combustion exhaust gas and air into the tundish.
If the reduction of iron oxide is promoted efficiently and efficiently,
₂The addition amount may be extremely small, and for example, N in the present embodiment may be added.₂Input
Quantity 1000 Nm³/ H, added H₂Flow rate V_HIs
Only 10 Nm³/ H has been found to be sufficient.

Now, the operation of this embodiment thus implemented will be described. First, when switching between the N ₂ charging / “combustion + N ₂ recycling” mode, the combustion exhaust gas purge time is set to an optimum value, and the charging N ₂ flow rate V is set.
By temporarily increasing _N or adjusting the openings of the dilution flow rate adjusting valves 24A, 24B (here, the reducing gas H ₂ is not added), in the present embodiment, As shown in FIG. 12a, the internal pressure of the tundish (T / D) could always be kept higher than “0”, that is, positive pressure. On the other hand, when switching the N ₂ charging / “combustion + N ₂ recycling” mode, the combustion exhaust gas purge time is optimally set, the charging N ₂ flow rate V _N is temporarily increased, and the dilution flow rate is changed. In the conventional example which is not adjusted, the tundish (T / D) internal pressure is temporarily lower than "0", that is, a negative pressure as shown in FIG. It is expected that combustion exhaust gas and the atmosphere will be sucked into the tundish.

Further, in this way, N ₂ input / “combustion + N ₂
When switching the "recycle" mode, the combustion exhaust gas purge time is optimally set, the input N ₂ flow rate V _N is temporarily increased, and the dilution flow rate adjusting valve 2
FIG. 13a shows the oxygen concentration in the tundish (T / D) of this embodiment by adjusting the opening of 4A and 24B (again, the addition of the reducing gas H ₂ is not performed).
Shown in. As is clear from the figure, the oxygen concentration in the tundish shows a slight peak at the time of switching the N ₂ input / recycling mode for the first time, but the others are stably kept below the target upper limit value. I understand. On the other hand, as shown in FIG. 13b, the oxygen concentration in the tundish (T / D) according to the conventional example in which such a control mode is not performed has a peak at each N ₂ charging / recycling mode switching, which is always constant. It can be seen that the target upper limit has been exceeded.

Further, as described above, N ₂ input / “combustion + N”
_When switching the " ₂ recycle" mode, the combustion exhaust gas purge time is optimally set, the input N ₂ flow rate V _N is temporarily increased, and the openings of the dilution flow rate adjusting valves 24A and 24B are adjusted. (Again, the reducing gas H ₂ is not added).
As shown in FIG. 4, the average O ₂ concentration in the tundish can be greatly reduced from the conventional value, and thus the amount of oxidation of the residual steel can be significantly reduced. By the way, the oxygen concentration in the tundish shown in FIG. 13a or FIG. 14 corresponds to the case where the above-mentioned reducing gas H ₂ is not added, and the inside of the tundish when the reducing gas H ₂ is actually added. It is known that the oxygen concentration is always "0" (below the measurable limit of the gas analyzer).

When the tundish thus heat-treated in the almost completely non-oxidized state and in the state in which the amount of oxidation of the residual steel was significantly reduced was subjected to actual casting, as shown in FIG. to, 1Ch (charge) -th total Hottohege incidence in the casting of, when a conventional a and 100, approximately 32.0 degree in case of no addition of reducing gases H _2, in the case of adding the reducing gas H ₂ is It can be reduced to about 3.5, and the total hot heggling generation rate in the first and second slabs immediately after the start of casting with the reused tundish is 100
Approximately 27.9 when ₂ is not added, reducing gas H
_{When 2} was added, it could be reduced to about 1.1.

Of course, as shown in FIG.
_{2 By using a} heat storage type preheater (burner in the figure),
The elapsed time from the end of casting in which the temperature in the tundish (T / D) is kept above the open hole limit can be greatly lengthened from the past, and the number of stations can be greatly extended.

By the way, when the object to be heated is a tundish as in the present embodiment, when the tundish is subjected to continuous casting, or as described above, two tundish are alternately arranged in a cassette type. Even when the tundish is used, the tundish is not connected to the non-oxidizing heating device when the two tundish are exchanged. That is, it is a time during which the object to be heated does not need to be heated and is separated from the heat storage type preheater. At this time, unless each heat storage type preheater is operated, during that time, energy loss and cost consumption as described above do not occur, but the heat storage body of each heat storage type preheater has its temperature lowered due to heat dissipation, When the next tundish is heated, the regenerator must be heated again, at which point,
There is a waste of time, energy loss, and cost consumption. In contrast, for example, the two regenerative preheater comrades, connected via a separate connection pipe or the like, the N ₂ of the input / "combustion + N ₂ Recycle" while supplying the inert gas N ₂ as described above If the heating operation is performed by, the heat storage body of each heat storage type preheater can be continuously heated, and no time waste is generated during the next tundish heating. However, when the gas used is an inert gas such as N _2, it must be produced or purchased for consumption,
Energy loss and cost consumption occur accordingly. Further, regardless of whether or not the two heat storage type preheaters are connected to each other, each heat storage type preheater is controlled while controlling the exhaust gas flow rate and the M gas flow rate so that the recycling flow rate into each combustion chamber is theoretically zero. A heat storage heating method called so-called heat-retaining combustion is also conceivable, in which the heat storage is heated by performing internal combustion, exhausting only the combustion exhaust gas from the heat storage chamber, and performing the N ₂ charging operation. However, in this heat retention combustion, heated N ₂
Since the gas is emitted from the nozzle to the atmosphere, there is a risk of oxygen deficiency and the cost of the input N ₂ amount is consumed.

Therefore, in this embodiment, since the non-oxidative heating as described above is not required, the two regenerative preheaters 2A and 2B are connected to each other by individual connecting pipe means (not shown), The N ₂ cutoff valve 77 for preheating the heat storage chamber is closed and the air shutoff valve 76 for preheating the heat storage chamber is opened, and instead of the N ₂ air is supplied from the air supply fan 16 to the heat storage chamber 3.
The heating operation is performed in the same manner as described above so that it can be supplied into the A and 3B. At this time, as described above, the M gas purging N
_{Since the 2} cutoff valves 11A and 11B and the N ₂ cutoff valve 53 for the pilot burner are in the closed state, N ₂ is not supplied and consumed anywhere, so that energy loss and cost consumption can be suppressed and suppressed accordingly. Also, when heating the place of N ₂ to introduce air / "combustion + recycling" while the heat storage body, the N ₂ flow rate adjusting valve 19 and N ₂ valves 17A, 1
If the flow rate control is performed in the same manner as described above while using 7B for controlling the air flow rate, the pressures in the heat storage chambers 3A, 3B and the combustion chambers 4A, 4B of the heat storage type preheaters 2A, 2B can be appropriately maintained. The heat storage bodies of both heat storage type preheaters 2A and 2B can be continuously heated efficiently. The sequence chart of opening / closing control and flow rate / pressure control of each valve at that time may be exactly the same as that shown in FIG.

In the above embodiment, N 2 was used as the inert gas.
_2. Only the case where H ₂ is used as the reducing gas in the tundish and the superiority of using it are described in detail. However, various gases such as Ar as the inert gas and the aforementioned CO as the reducing gas are used. It is of course possible to use carbon dioxide gas or heavy hydrocarbon. However, when such a carbon C-based reducing gas is used, there is a possibility that it will fall into the flammable range as described above, and therefore it is not only necessary to take additional safety measures, but also solid C is released. That is, it is necessary to suppress the generation of soot, and in order to judge this, it is necessary to carry out a detailed thermodynamic study to set the carbon C-based reducing gas addition flow rate.

Further, in the above-mentioned embodiment, only the case where H ₂ which is a reducing gas is supplied to the supply pipe of N ₂ which is an inert gas has been described in detail, but when the oxygen concentration is extremely low as described above. Since the input H ₂ flow rate may be extremely small, it may be directly supplied to the inside of the heat storage type preheater or the tundish itself without significantly heating it, which almost affects the temperature drop of the tundish. The inventors have also confirmed by experimentation that this is not the case.

When H ₂ or the like is added as the reducing gas, by extinguishing the pilot burner of the preheater on the side into which an inert gas such as N ₂ is fed, a higher level reduction state is obtained. Is easier to obtain. That is, in the case of tundish heating in the example, the combustion exhaust gas flow rate of the pilot burner is N ₂ + H ₂ (inert gas +
Reducing gas) is less than 1%, and oxidizing gas components such as CO ₂ and H ₂ O are about 0.2%, so there is no practical problem even if the pilot burner is not extinguished. When the flow rate of N ₂ + H ₂ (inert gas + reducing gas) is low, by extinguishing the pilot burner of the preheater on the charging side, a high level of non-oxidized or reduced state can be obtained. .

[0090]

As described above, according to the method of using the heat storage type preheater of the present invention, when the object to be heated and the heat storage type preheater are separated, for example, a plurality of heat storage type preheaters are separated from each other. Connect with piping means, switch the supply gas switching means, supply individual gas such as air to the heat storage body of any heat storage type preheater, heat through the heat storage body of the heat storage type preheater In the heat storage type preheater that sucks the individual gas such as the air that is taken in by the remaining heat storage type preheater and sucks the individual gas
The combustion gas is burned to heat the heat storage body, and the combustion exhaust gas and the individual gas such as the sucked air are exhausted as exhaust gas, and the heat storage body of each heat storage type preheater is switched alternately. Can continue to be heated, and if the individual gas supplied is air, it is not necessary to bother to generate or purchase it, so energy loss and cost consumption can be suppressed accordingly. it can.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing a tundish non-oxidizing heat retention device in which a heat storage type preheater of the present invention and a method of using the same are implemented.

FIG. 2 is a cross-sectional view showing an example of the heat storage type preheater and sealing device of FIG.

FIG. 3 is a schematic explanatory diagram of a non-oxidizing heat retention method for the tundish of FIG. 1.

FIG. 4 is a sequence chart of valve opening / closing control of the tundish non-oxidizing heat retention apparatus of FIG.

FIG. 5 is an explanatory diagram for setting an input N ₂ flow rate.

FIG. 6 is an explanatory diagram for setting an exhaust gas flow rate.

FIG. 7 is an explanatory diagram of a diluent gas flow rate used for setting an exhaust gas flow rate.

FIG. 8 is an explanatory diagram of a recycled N ₂ flow rate used for setting an exhaust gas flow rate.

FIG. 9 is an explanatory diagram of redox equilibrium of iron in an H ₂ —H ₂ O atmosphere.

FIG. 10 is an explanatory diagram of redox equilibrium of iron.

FIG. 11 is an explanatory diagram of H ₂ addition conditions.

FIG. 12 is an explanatory diagram of tundish internal pressure.

FIG. 13 is an explanatory diagram of oxygen concentration in the tundish.

FIG. 14 is an explanatory diagram of a residual steel oxidation amount in a tundish.

FIG. 15 is an explanatory diagram of a hot whip occurrence rate.

FIG. 16 is an explanatory diagram of the temperature in the tundish.

[Explanation of symbols]

1 is a tundish (object to be heated) 2A, 2B is a heat storage type preheater (heating means) 3A, 3B is a heat storage chamber 4A, 4B is a combustion chamber 5A, 5B is a main burner 6A, 6B is a pilot burner 7A, 7B is inserted Pipes 8A and 8B are M gas valves (fuel gas valves) 9A and 9B are M gas flow rate control valves (combustion gas flow rate control valves) 13A and 13B are air valves 14A, 14B are air flow rate control valves 16 are air supply fans 17A, 17B is an N ₂ valve (inert gas valve) 19 is an N ₂ flow rate adjusting valve (inert gas flow rate adjusting valve) 20A, 20B is an exhaust valve 21A, 21B is an exhaust flow rate adjusting valve 22, an exhaust fan 23A, 23B is a dilu Deployment valves 50A, 50B seal device 71 is flow rate of H ₂ regulating valves (reducing gas flow rate adjustment valve) 72 H ₂ valves (reducing gas valve) 76 is regenerator preheating air shut-off valve (feed gas switching means) 7 Regenerator 302 is the regenerator preheating N ₂ shutoff valves (supply gas switching means) 301 heat resistance network member

─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-2-37949 (JP, A) JP-A-7-112249 (JP, A) JP-A-6-281350 (JP, A) JP-A-7- 246456 (JP, A) JP 9-53886 (JP, A) JP 4-143047 (JP, A) JP 9-295127 (JP, A) JP 9-295125 (JP, A) JP 9-295126 (JP, A) Patent 2991941 (JP, B2) Patent 3394612 (JP, B2) US Patent 5700240 (US, A) International Publication 96/017215 (WO, A1) (58) Fields investigated (58) Int.Cl. ⁷ , DB name) B22D 11/10 310 B22D 11/10 360 B22D 41/015 F23L 15/02 F27D 7/06

Claims (2)

(57) [Claims] Upon 1. A heating a heating object that need to heat the inside and has a predetermined internal volume in the non-oxidizing conditions, the multiple regenerative preheater is connected to the heating object, of which From one of the heat storage type preheater, the inert gas heated by passing through the heat storage body of the heat storage type preheater is introduced into the heating target object, and the remaining heat storage type preheater enters the heating target object. While sucking the introduced inert gas, the heat storage body is heated by burning the combustion gas only in the heat storage type preheater that sucks the inert gas, and the combustion exhaust gas and the sucked inert gas are exhaust gas. evacuated as, which heats the heating object by switching alternately, the when the heating object is separated from the regenerative heater, for supplying air to the regenerator by switching the supply gas switching means Of the heat storage type preheater characterized by how to use. 2. The object to be heated is a tundish, the tundish is heated in an unoxidized state, and an inert gas for a regenerative preheater is used while the tundish is used for casting. The method of using the heat storage type preheater according to claim 1 , wherein the operation of the heat storage type preheater is continued by supplying the air instead of supplying the heat.