JPH10185442A - Method for heating furnace interior - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for heating the inside of a furnace by reducing the used amount of fuel by greatly by improving the heat loss of exhaust gas. SOLUTION: A method for heating the inside of a furnace comprises the step of alternately switching heat radiation and heat exhaust of two heat storage type preheaters having combustion chambers 34a, 34b for generating combustion exhaust gas due to combustions of burners 36a, 36b and heat storage units 32a, 32b connected to the chambers. Gas in the furnace again circulated from the furnace interior 22 is fed to the heat-storage preheater 30A. The preheater 30A passes low temperature gas supplied newly via the unit 32a to radiate its heat. The gas in the furnace circulated from the interior 22 is mixed with high temperature gas passes via the unit 32a, and then supplied into the furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for heating a furnace provided with a regenerative preheater for reusing furnace gas.

[0002]

2. Description of the Related Art As a method of heating the inside of a furnace, for example, a tundish for continuous casting, an annealing furnace, or the like is used as in a technique disclosed in Japanese Patent Application Laid-Open No. Hei 8-159664 (hereinafter referred to as "prior art"). In addition, a technique of heating the inside of a furnace in a non-oxidizing atmosphere is known.

FIG. 4 shows a specific heating device according to the prior art, in which the openings 1b, 1b of the lid 1a of the tundish 1 are shown.
A pair of regenerative preheaters 2A and 2B are connected to c. These regenerative preheaters 2A, 2B are connected in series via a switching valve 3.

On the other hand, a regenerative preheater 2A comprises a regenerator 5A filled with a regenerator, a combustion chamber 6A for heating the regenerator, a burner 7A connected to the combustion chamber 6A, and a fuel supply line connected to the burner 7A. 8A and an air supply line 9A. Similarly, the other regenerative preheater 2B also
A heat storage chamber 5B, a combustion chamber 6B, a burner 7B, a fuel supply line 8B, and an air supply line 9B are provided.

A nitrogen supply line 10 for supplying nitrogen gas to a pair of regenerative preheaters 2A and 2B is connected to the switching valve 3, and one end of the lid 1a of the tundish 1 is inserted into the nitrogen supply line 10. The suction line 13 is connected. The suction line 13 includes a circulation fan 1.
2 are interposed.

[0006] The switching valve 3 switches the nitrogen gas supplied from the nitrogen supply line 10 to one regenerative preheater 2A or the other regenerative preheater 2B to regenerate the regenerative type 5A, 5A.
B is switched to a path for feeding nitrogen gas from the inside of the tundish 1 to a path for exhausting nitrogen gas having passed through one of the regenerative preheaters 2A and 2B to the outside via the exhaust fan 11. Further, when the circulation fan 12 is operated, the nitrogen gas in the tundish 1 is sucked, mixed with the low-temperature nitrogen gas supplied from the nitrogen supply line 10 and stored in the regenerative preheater 2.
A or 2B.

[0007] The nitrogen gas heating step and the heat storage element heating step are continuously performed by alternately switching the pair of regenerative preheaters 2A and 2B at predetermined time intervals. That is, the regenerator heating step is performed by sucking and exhausting the combustion gas in the combustion chamber 6B generated by the combustion of the burner 7B and the nitrogen gas in the tundish 1 by operating the exhaust fan 11.
Is heated. Further, the nitrogen gas heating step is performed by the burner 7A.
Is stopped, the circulation fan 12 is operated, a part of the nitrogen gas in the tundish 1 is sent to the nitrogen supply line 10 as the circulating nitrogen gas, mixed and passed through the heat storage body 5A which has already stored heat. To heat the nitrogen gas.

[0008] Thus, the inside of the tundish 1 can be maintained in a non-oxidizing atmosphere while reusing the nitrogen gas in the tundish 1 and heating the nitrogen gas with high efficiency.

[0009]

Meanwhile, the conventional heating apparatus shown in FIG. 4 uses a nitrogen gas in which a circulating nitrogen gas in the tundish 1 is mixed with a heat storage (for example, a heat storage 2A) for performing a nitrogen gas heating step. When the temperature of the circulating nitrogen gas is high or the amount of the circulating nitrogen gas is large, the temperature of the nitrogen gas flowing into the heat storage body 2A becomes high.
Will pass with little deprivation of the stored heat.
When the regenerator 2A completes the nitrogen gas heating step and switches to the regenerator heating step, the exhaust gas robbs the heat of the regenerator 2A and releases high-temperature exhaust gas out of the system. Also,
Similarly, when the heat storage body 2B switches from the nitrogen gas heating step to the heat storage body heating step, high-temperature exhaust gas is similarly discharged to the outside of the system.

As described above, the conventional heating apparatus has a problem that the temperature of the exhaust gas discharged to the outside of the system increases and the heat loss of the exhaust gas is large, so that the fuel consumption of the burners 7A and 7B increases.

When the regenerative preheater 2B performs the regenerator heating step, nitrogen gas flows into the tundish 1 into the combustion chamber 6B. This nitrogen gas dilutes the heat of the combustion gas generated in the combustion chamber 6B. Since the flame temperature of the burner 7B is lowered, the heat storage body 5B cannot be heated to a sufficiently high temperature unless the amount of combustion of the burner 7B is increased. Also, when the regenerator preheater 2A performs the regenerator heating step, the regenerator 5A cannot be heated to a sufficiently high temperature unless the amount of combustion used by the burner 7A is increased for the same reason.

Accordingly, the present invention has been made in view of the above-mentioned unresolved problems of the conventional apparatus, and it has been found that heating in a furnace capable of greatly improving heat loss of exhaust gas and reducing fuel consumption can be achieved. The aim is to provide a method.

[0013]

In order to solve the problems of the conventional apparatus, the present inventors have proposed to lower the temperature of the exhaust gas discharged outside the system and to reduce the amount of the exhaust gas discharged outside the system. It was thought that the heat loss of the exhaust gas could be improved.
In this connection, as shown in FIG. 3, the amount of combustion exhaust gas generated in the combustion chamber by the combustion of the burner, the amount of gas sucked from the furnace and passing through the regenerator (the amount of gas in the regenerator passing furnace), and And the flame temperature of the burner with respect to the ratio of As a result, it became clear that as the amount of gas in the regenerator passing furnace increased, this gas diluted the heat of the combustion exhaust gas generated in the combustion chamber, and the flame temperature of the burner decreased. That is, it has been found that, when the burner is burned in a state where the amount of gas sucked from the furnace is reduced, the flame temperature of the burner is increased, and the fuel consumption can be reduced.

Therefore, the method for heating the inside of the furnace according to the first aspect of the present invention is characterized in that at least two regenerative storage units having a combustion chamber for generating combustion exhaust gas by burning a burner and a regenerator connected to the combustion chamber. A method of heating the inside of the furnace by alternately switching these regenerative preheaters to a radiating operation and an exhaust heat recovery operation, wherein one of the regenerative preheaters performing the radiating operation is provided in the furnace. A part of the furnace gas supplied to the furnace is circulated again and supplied to the furnace, and a newly supplied low-temperature gas is passed through the heat storage to perform a heat radiation operation, and the high-temperature gas that has passed through the heat storage is The gas in the furnace circulated from the furnace was mixed and supplied to the furnace as a high temperature gas at a predetermined temperature.

According to a second aspect of the present invention, in the method for heating the inside of the furnace according to the first aspect, the other regenerative preheater for performing the exhaust heat recovery operation is connected to the inside of the furnace during the first half of the exhaust heat recovery period. Only the exhaust gas was passed through the regenerator, and in the latter half of the exhaust heat recovery period, the combustion exhaust gas generated by the combustion of the burner was passed through the regenerator.

Further, the invention according to claim 3 is the invention according to claim 1.
Or, in the heating method of the furnace according to 2, immediately after the combustion of the burner of the other regenerative preheater performing the exhaust heat recovery operation is stopped, the combustion exhaust gas in the regenerator cavity is expelled to the outside of the system, and In order to prevent the gas from entering the furnace, the furnace gas sucked from the furnace was passed through the heat storage body.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. The slab (object to be heated) shown in FIG.
FIG. 3 is a schematic configuration diagram of a heating device that uniformly heats the heating device 4.

In the heating furnace 22, a pair of nitrogen gas jetting devices 26a for jetting high-temperature nitrogen gas to the upper and lower surfaces of the slab 24 conveyed in the front and back directions on the paper surface are provided.
26b is provided. These nitrogen gas jet devices 26
A high-temperature nitrogen gas is supplied alternately from the first and second regenerative preheaters 30A and 30B to the supply lines a and 26b via the supply line 28.

First and second regenerative preheaters 30A, 30B
Are first and second heat storage bodies 32a and 32b filled with, for example, alumina balls as a heat storage medium;
a, 32b for heating the first and second combustion chambers 34a, 34b
b.

Each of the combustion chambers 34a, 34b has a built-in burner 36a, 36b.
Fuel supply lines 38a, 38b and air supply lines 40a, 40b are connected to 6a, 36b. And
The fuel supply lines 42a, 38b are connected to the fuel supply lines 38a, 38b.
42b are interposed, and the air supply lines 40a, 40
Air supply valves 44a and 44b are interposed in b.

Further, the first and second heat storage bodies 32a, 32b
An exhaust line 46 and a nitrogen gas supply line 48 are connected in parallel. An external exhaust line 52 having an exhaust fan 50 interposed is connected to the exhaust line 46, and the first heat storage unit 3 is located at a position where the external exhaust line 52 is connected.
A first exhaust valve 54a is interposed in the exhaust line 46 on the 2a side, and a second exhaust valve 54b is interposed in the exhaust line 46 on the second heat storage body 32b side.

In the nitrogen gas supply line 28 to which nitrogen gas is supplied from the main supply line 56, a first nitrogen supply valve 58a is interposed on the first heat storage body 32a side from the connection position of the main supply line 56. The second heat storage body 32b has a second
A nitrogen supply valve 58b is interposed.

Further, the first and second combustion chambers 34a, 34
Between b, a furnace gas passage line 60 and a high-temperature nitrogen supply line 62 are connected in parallel. The above-described supply line 28 is connected to the high-temperature nitrogen supply line 62, and the first combustion chamber 34 is connected from the connection position of the supply line 28.
The first supply control valve 64a is interposed on the side a.
A second supply control valve 64b is interposed in the exhaust line 46 on the 4b side.

The furnace gas passage line 60 is connected to a suction line 68 for sucking high-temperature nitrogen gas in the heating furnace 22 by a circulation fan 66.
The first circulation control valve 7 is located closer to the first combustion chamber 34a than the connection position
0a, and a second circulation control valve 70b is provided on the second combustion chamber 34b side.

Then, a controller for controlling the entire heating device
Rollers (not shown) include fuel supply valves 42a and 42b, air
Shut-off valves 44a, 44b, first and second exhaust valves 54a,
4b, first and second nitrogen supply valves 58a, 58b,
And second supply control valves 64a, 64b and first and second circulations
FIG. 2 shows the switching operation of the control valves 70a and 70b.
This is performed based on the sequence control. At the time shown in FIG.
T₁~ T_FourAnd time T _Four~ T₇Are set at the same time
I have. Further, the exhaust fan 50 and the circulation fan 66 are connected in series.
It shall be operating continuously.

First, before the time point T ₁ , the first regenerative preheater 3
The combustion of the burner 36a is stopped by closing the 0A air shutoff valve 44a and the fuel supply valve 42a. And time T
_{At 1} , the first nitrogen supply valve 58a is opened to supply nitrogen gas. Further, the first exhaust valve 54a is closed to shut off the communication path with the external exhaust line 52. Further, the first supply control valve 64a is opened to communicate the first combustion chamber 34a with the supply line 28, and the first circulation control valve 70a is opened to communicate the first combustion chamber 34a with the suction line 68. .

When this state is continued from time T ₁ to time T ₄ , the low-temperature nitrogen gas supplied from the main supply line 56 flows into the first heat storage body 32 a which has already stored heat, and recovers heat. High temperature. And the first heat storage body 32
is passed through the suction line 68 and the furnace gas passage line 60, and mixed with nitrogen gas having a lower temperature than the gas supplied to the furnace circulated from the heating furnace 22 to a predetermined high temperature. The nitrogen gas is supplied to the nitrogen gas jetting devices 26a and 26b via the supply line 28 as nitrogen gas. (This step is referred to as heat radiation process.) On the other hand, the second regenerative preheater 30B, at time point T _1,
The supply of the nitrogen gas is stopped by closing the second nitrogen supply valve 58b. In addition, the second exhaust valve 54b is opened so that the second
The heat storage body 32b communicates with the external exhaust line 52. Further, the communication path between the second combustion chamber 34a and the supply line 28 is shut off by closing the second supply control valve 64b, and the second combustion chamber 34b and the suction line 68 are opened by opening the second circulation control valve 70b. To communicate.

When this state is continued for a period from time T _{1 to} T ₂ , the nitrogen gas which has heated the slab in the heating furnace 22 is transferred to the second heat storage body 32 b through the suction line 68 and the furnace gas passage line 60. As it flows, the second heat storage body 32b recovers the sensible heat of the high-temperature nitrogen gas. (This step is referred to as waste heat recovery step.) Then, at time T _2, to initiate combustion of the burner 36b air shutoff valve 44b and the fuel supply valve 42b is opened condition.

When this state is continued for the time T _{2 to} T ₃ , the high-temperature combustion gas generated in the second combustion chamber 34b flows toward the second heat storage body 32b, and the sensible heat of the combustion gas is
The heat storage body 32b collects. (This step is referred to as a high temperature step of the regenerator.) Then, at time T _3, the air shut-off valve 44b and the fuel supply valve 42b to stop the burning of the burner 36b as closed, the second circulation control valve 70b Open the second combustion chamber 3
4b and the suction line 68 are communicated.
Continue until ₄ . As a result, the high-temperature nitrogen gas generated in the heating path 22 is supplied to the second combustion chamber 34 immediately after stopping the combustion.
b and passes through the second heat storage body 32b and is exhausted to the external exhaust line 52 side. (This step is referred to as the purge step.) Thus, at time T ₁ through T _4, the first regenerative preheater 30A performs heat radiation process, second regenerative preheater 30B performs the exhaust heat recovery step At the same time, a step of raising the temperature of the heat storage body 32a is performed at a later stage of the exhaust heat recovery step, and a purging step is performed immediately thereafter. Then, as shown in FIG. 2, at time points T _{4 to} T ₇ , the second regenerative preheater 30 </ b> B switches to the heat release process, the first regenerative preheater 30 </ b> A switches to the exhaust heat recovery process, and In a later stage of the exhaust heat recovery process of the heat storage type preheater 30A, a heat storage body high temperature process and a purge process are performed. Then, the first and second regenerative preheaters 30A and 30B alternately switch to the heat radiation step and the exhaust heat recovery step at predetermined time intervals, thereby continuously supplying high-temperature nitrogen gas into the heating path 22. To uniformly heat the slab 24.

According to the above-described embodiment, the following effects can be obtained. First, when the first regenerative preheater 30A performs the heat radiation process, only the low-temperature nitrogen gas supplied from the main supply line 456 flows into the already stored first regenerator 32a, and the first regenerator 32A
The nitrogen gas circulated from inside the heating furnace 22 is mixed with the nitrogen gas that has passed through “a”. Therefore, the low-temperature nitrogen gas passing through the first heat storage body 32a takes most of the heat of the first heat storage body 32a, and the first heat storage type preheater 30A ends the heat radiation process and switches to the exhaust heat recovery process. Even the first heat storage 3
Since most of the heat of 2a is recovered, the exhaust gas discharged through the first heat storage body 32a and discharged outside the system has a low temperature. Also, even when the second regenerative preheater 30B performs the heat radiation process, only the low-temperature nitrogen gas flows into the already stored second regenerator 32b, and deprives most of the heat of the second regenerator 32b. Even if the second regenerative preheater 30B completes the heat radiation process and switches to the exhaust heat recovery process, the second regenerator 32
Exhaust gas discharged outside the system after passing through b has a low temperature. Therefore, in the present embodiment, the temperature of the exhaust gas discharged from the external exhaust line 52 to the outside of the system is lowered to improve the heat loss of the exhaust gas, so that the fuel consumption of the burners 36a and 36 can be reduced. .

When the second regenerative preheater 30B performs the exhaust heat recovery step, the nitrogen gas in the heating furnace 22 is passed through the regenerator 32b in the first half of this step, and the burner 36b Is started, and the high-temperature combustion exhaust gas generated in the second combustion chamber 34b is caused to flow toward the second heat storage body 32b to perform a step of raising the temperature of the heat storage body 32b. At this time, the combustion exhaust gas in the second combustion chamber 34b is not easily diluted with the nitrogen gas in the heating furnace 22, so that the flame temperature of the burner 36b does not decrease. Also, when the first regenerative preheater 30A performs the exhaust heat recovery step, the combustion exhaust gas in the first combustion chamber 34a is heated by the heating furnace 2A.
The flame temperature of the burner 36a does not decrease because it is hardly diluted by the nitrogen gas of No. 2.

Therefore, the first and second regenerative preheaters 3
0A and 30B perform the heat recovery step, the burner 3
6a and 36b while reducing the fuel consumption.
a, 32b can be sufficiently stored. Moreover, as the temperature of the gas supplied from the heat storage bodies 32a and 32b increases, the ratio of the amount of gas circulated from the inside of the heating furnace 22 can also increase, so that the amount of exhaust gas discharged from the external exhaust line 52 to the outside of the system And the heat loss of the exhaust gas can be improved.

Immediately after the second regenerative preheater 30B performs the step of raising the temperature of the regenerator, the nitrogen gas generated in the heating path 22 is supplied to the outside via the second combustion chamber 34b and the second regenerator 32b. Since the purge step of exhausting to the exhaust line 52 is performed, the combustion exhaust gas flows into the heating furnace 22 and adversely affects the heating of the slab 24 when the second regenerative preheater 30B performs the heat radiation step next. There is no fear. Also, the first
Since the regenerative preheater 30A also performs the purging step immediately after performing the heat storage element high-temperature step, the next time the first regenerative preheater 30A performs the heat release step, the combustion exhaust gas is discharged from the heating furnace 22A.
There is no possibility that the slab 24 flows into the slab 24 and adversely affects the heating of the slab 24.

The step of raising the temperature of the heat storage body described in the above embodiment corresponds to the invention of claim 2, and the purging step corresponds to the invention of claim 3. Further, in the above-described embodiment, the heating device using the two regenerative preheaters 30A and 30B has been described. However, even when a plurality of regenerative preheaters are installed, the same operation and effect can be obtained. it can.

Although nitrogen gas is used as a gas for heating the slab 24, other gases such as argon gas may be used. In the present embodiment, the slab 22
Has been described, but when using a tundish or annealing furnace for continuous casting, the same effect can be obtained even when applied to a device that heats the furnace in a non-oxidizing atmosphere. Can be.

[0036]

As described above, according to the heating method in the furnace according to the first aspect, the method of circulating the gas in the furnace is basically performed, so that the amount of gas flowing out of the system is reduced. be able to. Therefore, since the heat loss of the exhaust gas is improved by reducing the amount of the exhaust gas discharged to the outside of the system, the fuel consumption of the burner can be reduced.

Further, according to the second aspect of the present invention, the effect of the heating method in the furnace according to the first aspect can be obtained, and the other heat storage type preheater which performs the exhaust heat recovery operation is provided with the exhaust heat recovery. In the first half of the period, only the exhaust gas from the furnace is passed through the regenerator, and in the second half of the exhaust heat recovery period, the flue gas generated by the combustion of the burner is passed through the regenerator. Does not dilute the flue gas, so the burner flame temperature does not decrease. Therefore, according to the present invention, when the regenerative preheater performs the exhaust heat recovery step, it is possible to store the heat storage body at a sufficiently high temperature while reducing the fuel consumption of the burner. For this reason, the gas temperature into the furnace can be raised to a high temperature, and the ratio that can be circulated on the heat balance is increased, so that the amount of exhaust gas discharged outside the system is reduced, and the heat loss of the exhaust gas is improved. Can be.

Further, according to the third aspect of the present invention, the effect of the method of heating the inside of the furnace according to the first or second aspect can be obtained, and the other heat storage type preheater performing the exhaust heat recovery operation can be obtained. Immediately after the combustion of the burner is stopped, the in-furnace gas sucked from the furnace is passed through the regenerator, so that the other regenerative preheater switches from the exhaust heat recovery operation to the heat release step, There is no fear that the combustion exhaust gas flows into the furnace and adversely affects the heating of the object to be heated.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a heating device provided with a regenerative preheater according to a method for heating the inside of a furnace according to the present invention.

FIG. 2 is a time chart for switching operation of two regenerative preheaters to which the method for heating the inside of a furnace according to the present invention is applied.

FIG. 3 is a chart showing a change in a flame temperature of a burner with respect to a ratio of an amount of a combustion exhaust gas generated in a combustion chamber by combustion of a burner and an amount of a gas sucked from a furnace and passing through a regenerator.

FIG. 4 is a schematic configuration diagram showing an apparatus for heating the inside of a furnace in a non-oxidizing atmosphere according to a conventional heating method in a furnace.

[Explanation of symbols]

 Reference Signs List 22 heating furnace 24 slab (object to be heated) 30A, 30B regenerative preheater 32a, 32b regenerator 34a, 34b combustion chamber 36a, 36b burner 42a, 42b fuel supply valve 44a, 44b air cutoff valve 46 exhaust line 48 nitrogen gas supply Line 52 External exhaust line 54a, 54b Exhaust valve 56 Main supply line 58a, 58b Nitrogen supply valve 60 Furnace gas passage line 64a, 64b Supply control valve 70a, 70b Circulation control valve

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F27B 9/36 F27B 9/36

Claims (3)

[Claims] An at least two regenerative preheater having a combustion chamber for generating combustion exhaust gas by combustion of a burner and a regenerator connected to the combustion chamber is provided. In the method of heating the inside of the furnace by alternately performing a switching operation with a heat recovery operation, one of the regenerative preheaters performing the heat radiation operation circulates a part of the furnace gas supplied into the furnace again to recycle the furnace. Along with supplying to the inside, a newly supplied low-temperature gas is passed through the heat storage body to perform a heat radiation operation, and the high-temperature gas passed through the heat storage body is mixed with the furnace gas circulated from the furnace, A method for heating the inside of a furnace, wherein the furnace is supplied as a high-temperature gas of a predetermined temperature into the furnace. 2. The other regenerative preheater that performs an exhaust heat recovery operation passes only exhaust gas from the furnace through the heat storage body in the first half of the exhaust heat recovery period and the burner in the second half of the exhaust heat recovery period. The method for heating the inside of a furnace according to claim 1, wherein the combustion exhaust gas generated by the combustion of the gas is passed through a heat storage body. 3. A furnace gas sucked from the furnace is passed through the regenerator immediately after combustion of a burner of the other regenerative preheater performing an exhaust heat recovery operation is stopped. The method for heating the inside of a furnace according to claim 1.