JP3518216B2 - Heating method in furnace - Google Patents

Description

Detailed Description of the Invention

[0001]

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

[0002]

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

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

One of the heat storage type preheaters 2A is a heat storage chamber 5A filled with a heat storage body, a combustion chamber 6A for heating the heat storage body, 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. Also, the other heat storage type preheater 2B is also the same.
The heat storage chamber 5B, the combustion chamber 6B, the burner 7B, the fuel supply line 8B, and the air supply line 9B are provided.

Further, the switching valve 3 is connected to a nitrogen supply line 10 for supplying nitrogen gas to a pair of heat storage type preheaters 2A and 2B, 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. Then, in the suction line 13, the circulation fan 1
2 is installed.

Further, the switching valve 3 switches the nitrogen gas supplied from the nitrogen supply line 10 to the heat storage type preheater 2A on one side or the heat storage type preheater 2B on the other side to store heat in the heat storage chambers 5A, 5A.
The route for sending to B is switched to the route for discharging the nitrogen gas from the tundish 1 that has passed through one of the heat storage type preheaters 2A and 2B to the outside through the exhaust fan 11. Further, when the circulation fan 12 is operated, the nitrogen gas in the tundish 1 is sucked and mixed with the low temperature nitrogen gas supplied from the nitrogen supply line 10, and the heat storage type preheater 2
Supply to either A or 2B.

The nitrogen gas heating step and the regenerator heating step are continuously performed by alternately switching the pair of heat storage type preheaters 2A and 2B at predetermined intervals. That is, in the heat storage body heating step, the heat storage body 5B is sucked and exhausted by the operation of the exhaust fan 11 for the combustion gas in the combustion chamber 6B and the nitrogen gas in the tundish 1 generated by the combustion of the burner 7B.
Heating. Also, the nitrogen gas heating step is performed by the burner 7A.
Of the nitrogen gas in the tundish 1 is sent to the nitrogen supply line 10 as the circulating nitrogen gas for mixing and is passed through the regenerator 5A which has already accumulated heat. To heat the nitrogen gas.

As a result, the nitrogen gas in the tundish 1 can be reused and the nitrogen gas can be heated with high efficiency, and the tundish 1 can be maintained in the non-oxidizing atmosphere.

[0009]

By the way, the conventional heating device shown in FIG. 4 is a nitrogen gas in which a circulating nitrogen gas in the tundish 1 is mixed with a heat storage body (for example, the heat storage body 2A) for performing the nitrogen gas heating step. However, when the circulating nitrogen gas temperature is high or the circulating nitrogen gas amount is large, the nitrogen gas flowing into the heat storage body 2A becomes high in temperature, so the heat storage body 2A
Passes through without taking away the amount of heat stored by.
When this heat storage body 2A finishes the nitrogen gas heating step and switches to the heat storage body heating step, the heat amount of the heat storage body 2A is taken by the exhaust gas and the high temperature exhaust gas is discharged to the outside of the system. Also,
Similarly, when the heat storage body 2B is switched from the nitrogen gas heating step to the heat storage body heating step, the high-temperature exhaust gas is released to the outside of the system.

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

Further, when the heat storage type preheater 2B performs the heat storage body heating step , the nitrogen in the tundish 1 is placed in the combustion chamber 6B.
Although the gas flows in, this nitrogen gas dilutes the heat of the combustion gas generated in the combustion chamber 6B and lowers the flame temperature of the burner 7B. Therefore, if the combustion usage amount of the burner 7B is not increased, the heat storage body 5B It cannot be heated to a sufficiently high temperature. Further, even when the regenerative preheater 2A performs the regenerator heating step, the regenerator 5A cannot be heated to a sufficiently high temperature unless the combustion usage amount of the burner 7A is increased for the same reason.

Therefore, the present invention has been made by paying attention to the unsolved problem of the above-mentioned conventional apparatus, and it is possible to significantly improve the heat loss of exhaust gas and reduce the fuel consumption, thereby heating the furnace. The purpose is to provide a method.

[0013]

In order to solve the problems of the conventional apparatus, the inventors of the present invention reduce the temperature of the exhaust gas discharged to the outside of the system and reduce the amount of exhaust gas discharged to the outside of the system. We thought that the heat loss of exhaust gas could be improved.
In this connection, as shown in FIG. 3, the combustion exhaust gas amount generated in the combustion chamber by the combustion of the burner and the gas amount sucked from the inside of the furnace and passing through the heat storage body (heat storage body passing furnace gas amount) The flame temperature of the burner with respect to the ratio was compared and examined. As a result, it became clear that as the amount of gas in the furnace passing through the regenerator increases, this gas dilutes the heat of the combustion exhaust gas generated in the combustion chamber and the flame temperature of the burner decreases. That is, it was 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 rises and the amount of fuel used can be reduced.

Therefore, the method for heating the inside of the furnace according to claim 1 of the present invention comprises at least two heat storage systems having a combustion chamber for generating combustion exhaust gas by combustion of a burner and a heat storage body connected to the combustion chamber. In the method of heating the inside of the furnace by alternately switching the heat storage type preheater between the heat radiation operation and the exhaust heat recovery operation, the heat storage type preheater that performs the heat radiation operation is While recirculating a part of the furnace gas supplied to the inside of the furnace, the newly supplied low temperature gas is passed through the heat storage body to perform heat dissipation operation, and the high temperature gas that has passed through the heat storage body. Further, the furnace gas circulated from the inside of the furnace was mixed and supplied as high temperature gas of a predetermined temperature into the furnace.

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 heat storage type preheater for performing the exhaust heat recovery operation is operated from the inside of the furnace in the first half of the exhaust heat recovery period. Only the exhaust gas was passed through the heat storage body, and the combustion exhaust gas generated by the combustion of the burner was passed through the heat storage body in the latter part of the exhaust heat recovery period.

Further, the invention of claim 3 is the same as that of claim 1.
Or in the method for heating the inside of the furnace according to 2, immediately after the combustion of the burner of the other heat storage type preheater that is performing the exhaust heat recovery operation is stopped, the combustion exhaust gas in the voids of the heat storage body is expelled to the outside of the system. In order to prevent the gas from entering the inside of the furnace, the in-furnace gas sucked from the inside of the furnace is allowed to pass through the heat storage body.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. The one shown in FIG. 1 is a slab (object to be heated) 2 which is obtained by continuously supplying high temperature nitrogen gas into the heating furnace 22.
4 is a schematic configuration diagram of a heating device for uniformly heating No. 4.

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

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

Burners 36a and 36b are built in the combustion chambers 34a and 34b, respectively.
Fuel supply lines 38a and 38b and air supply lines 40a and 40b are connected to 6a and 36b. And
Fuel supply lines 42a, 38b have fuel supply valves 42a,
42b is 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 between them. An external exhaust line 52 with an exhaust fan 50 interposed is connected to the exhaust line 46. From the position where the external exhaust line 52 is connected, the first heat storage body 3 is connected.
The first exhaust valve 54a is installed in the exhaust line 46 on the 2a side, and the second exhaust valve 54b is installed in the exhaust line 46 on the second heat storage body 32b side.

Further, in the nitrogen gas supply line 28 to which the nitrogen gas is supplied from the main supply line 56, a first nitrogen supply valve 58a is provided on the first heat storage body 32a side from the connection position of the main supply line 56, Second on the second heat storage body 32b side
A nitrogen supply valve 58b is provided.

Further, the first and second combustion chambers 34a, 34a
A furnace gas passage line 60 and a high temperature nitrogen supply line 62 are connected in parallel between b. The above-mentioned 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 this supply line 28.
The first supply control valve 64a is provided on the a side of the second combustion chamber 3
The second supply control valve 64b is provided on the 4b side .

A suction line 68 for sucking the high temperature nitrogen gas in the heating furnace 22 by a circulation fan 66 is connected to the in-furnace gas passage line 60. This suction line 68
Of the first circulation control valve 7 on the first combustion chamber 34a side from the connection position of
0a is installed, and the second circulation control valve 70b is installed on the second combustion chamber 34b side.

A control unit for controlling the entire heating device
Is a fuel supply valve 42a, 42b, air
Shutoff valves 44a, 44b, first and second exhaust valves 54a, 5
4b, first and second nitrogen supply valves 58a, 58b, first and second
And second supply control valves 64a, 64b and first and second circulation
The opening / closing switching operation of the control valves 70a and 70b is shown in FIG.
Performed based on sequence control. In addition, at the time shown in FIG.
T₁~ T_FourAnd time point T _Four~ T₇Are set to the same time
There is. Further, the exhaust fan 50 and the circulation fan 66 are connected to each other.
It is assumed to be operating continuously.

First, before the time T ₁ , the first heat storage type preheater 3
Combustion of the burner 36a is stopped by closing the 0A air cutoff valve 44a and the fuel supply valve 42a. And time T
_{In 1} , the nitrogen gas can be supplied by opening the first nitrogen supply valve 58a. 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 side with the supply line 28, and the first circulation control valve 70a is opened to communicate the first combustion chamber 34a side with the suction line 68. .

When this state is continued for the time points T _{1 to} T ₄ , the low temperature nitrogen gas supplied from the main supply line 56 flows into the first heat storage body 32a which has already stored heat to recover the heat quantity. It gets hot. Then, the first heat storage body 32
The nitrogen gas that has passed through a is mixed with nitrogen gas having a temperature lower than the gas temperature supplied to the inside of the furnace that has circulated from the heating furnace 22 via the suction line 68 and the in-furnace gas passage line 60, and has a predetermined high temperature. The nitrogen gas is supplied to the nitrogen gas jetting devices 26a and 26b via the supply line 28. (This step is referred to as heat radiation process.) On the other hand, the second regenerative preheater 30B, at time point T _1,
The second nitrogen supply valve 58b is closed to stop the supply of nitrogen gas. In addition, the second exhaust valve 54b is opened to the second
The heat storage body 32b side communicates with the external exhaust line 52. Further, the second supply control valve 64b is closed to cut off the communication path between the second combustion chamber 34a side and the supply line 28, and the second circulation control valve 70b is opened to the second combustion chamber 34b side and the suction line 68. To communicate.

When this state is continued from time T ₁ to time T ₂ , the nitrogen gas which has heated the slab in the heating furnace 22 is transferred to the second heat storage body 32b side 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 points 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 changed to the second heat storage gas.
The heat storage body 32b collects. (This step is referred to as a step of increasing the temperature of the heat storage body.) Next, at time T ₃ , the air cutoff valve 44b and the fuel supply valve 42b are closed to stop the combustion of the burner 36b, and the second circulation control valve 70b is turned on. The second combustion chamber 3 in the open state
4b side and the suction line 68 are connected, and this state is set at time T
Continue to ₄ . As a result, the high-temperature nitrogen gas generated in the heating passage 22 is discharged from the second combustion chamber 34 immediately after the combustion is stopped.
b and the inside of the 2nd heat storage body 32b, and it exhausts to the external exhaust line 52 side. (This step is referred to as a purging step.) As described above, at the time points T _{1 to} T ₄ , the first heat storage type preheater 30A performs the heat radiation step and the second heat storage type preheater 30B performs the exhaust heat recovery step. At the same time, the step of raising the temperature of the heat storage body 32a is performed in the latter stage of the exhaust heat recovery step, and immediately after that, the purge step is performed. Then, as shown in FIG. 2, at the time points T _{4 to} T ₇ , the second heat storage type preheater 30B switches to the heat radiation step, the first heat storage type preheater 30A switches to the exhaust heat recovery step, and In the latter stage of the exhaust heat recovery process of the heat storage type preheater 30A, the heat storage body temperature raising process and the purging process are performed. Then, the first and second heat storage type 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 passage 22. And heat the slab 24 uniformly.

According to the above-mentioned embodiment, the following operational effects can be obtained. First, when the first heat storage type preheater 30A performs the heat radiation process, only the low-temperature nitrogen gas supplied from the main supply line 456 flows into the first heat storage body 32a that has already stored heat, and the first heat storage body 32
The nitrogen gas that has passed through a is mixed with the nitrogen gas that has circulated from inside the heating furnace 22. Therefore, the low-temperature nitrogen gas passing through the first heat storage body 32a takes most of the heat quantity of the first heat storage body 32a, and the first heat storage type preheater 30A completes the heat release step and switches to the exhaust heat recovery step. Even if it crosses, the 1st heat storage body 3
Since most of the heat quantity of 2a is recovered, the exhaust gas passing through the first heat storage body 32a and discharged to the outside of the system has a low temperature. Further, even when the second heat storage type preheater 30B performs the heat dissipation step, only low-temperature nitrogen gas flows into the second heat storage body 32b that has already stored heat, and most of the heat amount of the second heat storage body 32b is taken away, Even if the second heat storage type preheater 30B ends the heat radiation process and switches to the exhaust heat recovery process, the second heat storage body 32
The exhaust gas passing through b and discharged to the outside of the system has a low temperature. Therefore, in the present embodiment, since 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, the fuel consumption of the burners 36a, 36 can be reduced. .

Further, when the second heat storage type preheater 30B performs the exhaust heat recovery step, the nitrogen gas in the heating furnace 22 is passed through the heat storage body 32b in the first half of this step, and the burner 36b is passed in the latter half of the step. 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 the 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 hard to be diluted with the nitrogen gas in the heating furnace 22, so that the flame temperature of the burner 36b does not decrease. Further, even when the first heat storage type preheater 30A performs the exhaust heat recovery process, the combustion exhaust gas in the first combustion chamber 34a remains in the heating furnace 2.
The flame temperature of the burner 36a does not decrease because it is hard to be diluted with the nitrogen gas of 2.

Therefore, the first and second heat storage type preheater 3
When 0A and 30B perform the exhaust heat recovery process, the burner 3
The heat storage body 32 while reducing the fuel consumption of 6a and 36b
The a and 32b can sufficiently store heat. Moreover, as the temperature of the gas supplied from the heat storage bodies 32a and 32b becomes higher, the proportion of the amount of gas circulated from inside the heating furnace 22 can be increased, so that the amount of exhaust gas discharged from the external exhaust line 52 to the outside of the system. Can be reduced and the heat loss of exhaust gas can be improved.

Immediately after the second heat storage type preheater 30B carries out the step of raising the temperature of the heat storage body, the nitrogen gas generated in the heating passage 22 is transferred to the outside via the second combustion chamber 34b and the second heat storage body 32b. Since the purge process of exhausting to the exhaust line 52 side is performed, the combustion exhaust gas flows into the heating furnace 22 and adversely affects the heating of the slab 24 when the second heat storage type preheater 30B next performs the heat release process. There is no fear. Also, the first
Since the heat storage type preheater 30A also performs the purging step immediately after the heat storage body temperature raising step, when the first heat storage type preheater 30A next performs the heat radiation step, the combustion exhaust gas is heated by the heating furnace 22.
There is no possibility that it will flow into the interior and adversely affect 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 described in claim 2, and the purging step corresponds to the invention described in claim 3. Moreover, in the said embodiment, although the heating apparatus which used two heat storage type preheaters 30A and 30B was demonstrated, even if a plurality of heat storage type preheaters are installed, the same effect can be obtained. it can.

Although nitrogen gas is used as a gas for heating the slab 24, other gas such as argon gas can be applied. Further, in the present embodiment, the slab 22
The continuous heating device was described, but when using a tundish or an annealing furnace for continuous casting, even if it is applied to a device that heats the furnace in a non-oxidizing atmosphere, the same effect can be obtained. You can

[0036]

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

According to the second aspect of the invention, the effect of the heating method for the furnace according to the first aspect can be obtained, and the other heat storage type preheater for performing the exhaust heat recovery operation is the exhaust heat recovery. Only the exhaust gas from the inside of the furnace is passed to the heat storage body in the first half of the period, and in the latter half of the exhaust heat recovery period, the combustion exhaust gas generated by the combustion of the burner is passed to the heat storage body, and the exhaust gas in the furnace is discharged. Does not dilute the combustion exhaust gas, so the flame temperature of the burner does not decrease. Therefore, according to the present invention, when the heat storage type preheater performs the exhaust heat recovery process, it is possible to store the heat storage body at a sufficiently high temperature while reducing the fuel usage amount of the burner. Therefore, the temperature of the gas inside the furnace can be raised and the ratio of the gas that can be circulated in terms of heat balance increases, so the amount of exhaust gas released to the outside of the system decreases and the heat loss of exhaust gas is improved. You can

Further, according to the invention described in claim 3, the effect of the method for heating the inside of the furnace according to claim 1 or 2 can be obtained, and at the same time, in the other heat storage type preheater performing the exhaust heat recovery operation. Immediately after combustion of the burner is stopped, since the furnace gas sucked from the furnace is made to pass through the heat storage body, even if the other heat storage type preheater is switched from the exhaust heat recovery operation to the heat dissipation step, There is no possibility that the combustion exhaust gas will flow into the furnace and adversely affect the heating of the object to be heated.

[Brief description of drawings]

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

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

FIG. 3 is a chart showing changes in flame temperature of a burner with respect to a ratio of a combustion exhaust gas amount generated in a combustion chamber due to combustion of a burner and a gas amount sucked from a furnace and passing through a heat storage body.

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 method for heating the inside of a furnace.

[Explanation of symbols]

22 heating furnace 24 slab (heated object) 30A, 30B Heat storage type preheater 32a, 32b heat storage body 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

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI F27B 9/36 F27B 9/36 (56) References JP-A-8-159664 (JP, A) JP-A-8-155599 (JP , A) JP 9-53886 (JP, A) JP 9-295110 (JP, A) JP 9-295125 (JP, A) JP 9-295126 (JP, A) JP 9-295127 (JP, A) Actual development Sho 62-198490 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) F27B 9/10 B22D 11/10 310 C21D 1/52 C21D 1 / 76 C21D 9/00 101 F27B 9/36

Claims (3)

(57) [Claims] 1. A heat storage type preheater having at least two heat storage type preheaters each having a combustion chamber for generating combustion exhaust gas by combustion of a burner and a heat storage body connected to the combustion chamber. In the method of heating the inside of the furnace by alternately switching to the heat recovery operation, one of the heat storage type preheaters that performs the heat radiation operation recirculates a part of the furnace gas supplied into the furnace to reheat the furnace. While supplying the inside, the newly supplied low-temperature gas is passed through the heat storage body to perform the heat radiation operation, and the high-temperature gas that has passed through the heat storage body is mixed with the furnace gas circulated from the inside of the furnace, A heating method for a furnace, characterized in that the gas is supplied as a high-temperature gas of a predetermined temperature into the furnace. 2. The other heat storage type preheater for performing the exhaust heat recovery operation allows only the exhaust gas from the inside of the furnace to pass through the heat storage body in the first half of the exhaust heat recovery period, and the burner in the latter half of the exhaust heat recovery period. The method for heating an inside of a furnace according to claim 1, wherein the combustion exhaust gas generated by the combustion of the above is passed through a heat storage body. 3. The in-furnace gas sucked from the inside of the furnace is allowed to pass through the regenerator immediately after the combustion of the burner of the other regenerative preheater performing the exhaust heat recovery operation is stopped. The method for heating the inside of the furnace according to claim 1 or 2.