JP4133757B2 - Combustion control method for heating furnace - Google Patents

Description

  The present invention relates to a combustion control method for a heating furnace in which an extraction door provided at a furnace outlet is intermittently opened to extract a workpiece, and particularly to a continuous heating furnace that heats a slab and supplies it to a hot rolling process. The present invention relates to a combustion control method for a suitable heating furnace.

  A heating furnace such as a slab continuous heating furnace is provided with a pre-tropical zone, a heating zone, and a soaking zone in order from the entrance side. The extraction door provided in is opened and extracted and sent to the next hot rolling process. Since the extraction of the slab is intermittently performed based on a request signal from the hot rolling process, the extraction door is also opened and closed intermittently.

  In such a heating furnace, when the oxygen concentration in the furnace rises to a predetermined level (for example, 5%) or more, an oxide scale is generated on the surface of the slab, and a demoted product is generated as a defect called scale flaw. Therefore, as shown in Patent Document 1, conventionally, the oxygen concentration in the furnace is controlled to be low. Also, the pressure inside the furnace is controlled to maintain a slight positive pressure by opening and closing the furnace pressure damper provided in the chimney on the furnace inlet side, which stabilizes the burner combustion and causes excess scale that causes oxide scale Air is not sucked into the furnace.

However, in such a heating furnace, it is necessary to open the extraction door provided at the furnace outlet when extracting the heated workpiece, and in the continuous heating furnace of the slab, the extraction door is about 30 seconds every time one slab is extracted. be opened. Since a gas flow that flows toward the chimney provided on the furnace inlet side is formed in the furnace, outside air is sucked in as soon as the extraction door is opened, and the furnace pressure varies greatly as shown in FIG. FIG. 4 is a graph in which the extraction door is held open in order to observe the convergence of the furnace pressure fluctuation. As a result, a large amount of oxygen flows into the furnace, the oxygen concentration increases, and oxide scale is generated. As described above, in a heating furnace in which the extraction door needs to be opened, it is difficult to always keep the oxygen concentration low, and it has been difficult to eliminate degraded products due to oxide scale.
Japanese Patent Publication No. 64-6253

  In order to solve the above-described conventional problems, the present invention provides a combustion control method for a heating furnace capable of preventing the generation of demoted products due to oxide scale by suppressing the intake of outside air that occurs when the extraction door is opened. It was made.

  The combustion control method for a heating furnace according to the present invention made to solve the above-described problem is a furnace pressure control when the extraction door for workpiece extraction provided at the outlet of the heating furnace under furnace pressure control is opened. The furnace pressure damper is closed, and the amount of soaking zone burner gas near the outlet of the heating furnace is reduced. The heating furnace is, for example, a slab continuous heating furnace, but is not necessarily limited thereto. It is preferable to close the furnace pressure damper immediately before the extraction door is opened, and to open it immediately before the extraction door is closed. When the extraction door is opened, the soaking zone burner gas amount is reduced to 1/3 or less of the normal time. It is preferable to decrease.

  The combustion control method for a heating furnace of the present invention closes the furnace pressure damper for controlling the furnace pressure when the extraction door for workpiece extraction provided at the outlet of the heating furnace under furnace pressure control is opened. As a result, the gas flow that has been flowing toward the furnace pressure damper on the furnace inlet side is stopped until the whole furnace has a slight positive pressure, so that outside air is not sucked even if the extraction door is opened. As a result, we succeeded in reducing the incidence of demoted products due to oxide scale to less than 1/3 of the conventional one.

  However, when the furnace pressure damper is closed, the pressure is increased to the part close to the outlet side of the heating furnace, so if the furnace pressure damper is simply closed, flames blow out from the furnace, which is dangerous and increases the amount of heat dissipation. The problem arises. For this reason, in the present invention, when the furnace pressure damper is closed, the amount of burner gas in the soaking zone close to the outlet of the heating furnace is reduced, flame is not blown out, and safe operation can be ensured.

Preferred embodiments of the present invention are shown below.
FIG. 1 is a sectional view of a heating furnace 1. In this embodiment, the heating furnace 1 is a slab continuous heating furnace. The inside of the furnace body is partitioned by a partition wall, and a pre-tropical zone 2, a heating zone 3, and a soaking zone 4 are provided in this order from the entrance side. The slab, which is the workpiece W, is heated to a predetermined temperature while being conveyed in the furnace by the walking beam type conveying means 5, and is extracted from the extraction door 6 provided on the furnace outlet side for the next hot rolling process. Sent. The extraction door 6 is opened for about 30 seconds when the slab is sent out by a request signal from the hot rolling process.

  A burner (not shown) is provided in each of the pre-tropical zone 2, the heating zone 3, and the soaking zone 4 to control the furnace temperature and the oxygen concentration in the furnace. By suppressing the oxygen concentration, generation of oxide scale on the surface of the slab can be suppressed. However, if the oxygen concentration is suppressed too much and incomplete combustion occurs, black smoke is generated. Therefore, the oxygen concentration is preferably set appropriately between 0.5 and 2.0%.

  A chimney 8 having a furnace pressure damper 7 for controlling the furnace pressure is installed on the inlet side of the heating furnace 1, and the gas in the furnace is sucked through the furnace pressure damper 7 by the draft of the chimney 8. For this reason, a gas flow 9 is always formed in the furnace from the outlet side to the inlet side. By adjusting the opening degree of the furnace pressure damper 7, furnace pressure control is performed so that the furnace pressure is maintained at a slight plus pressure.

  Although the above content is the same as before, in the present invention, when the extraction door 6 for workpiece extraction is opened, the furnace pressure damper 7 for controlling the furnace pressure is closed. As a result, the suction effect due to the draft of the chimney 8 is cut off and the pressure in the furnace is increased, so that the intake of outside air from the open extraction door 6 as in the prior art is suppressed, and the oxide scale is prevented. In addition, since the furnace pressure fluctuation has already started if the furnace pressure damper 7 is closed after the extraction door 6 starts to open, it is preferable to close the furnace pressure damper 7 immediately before the extraction door 6 is opened. For this reason, in this embodiment, the furnace pressure damper 7 is closed by a request signal from a hot rolling process that is issued before the extraction door 6 is opened. As a result, the furnace pressure fluctuation can be greatly reduced as shown in the graph of FIG.

  In the present invention, closing the furnace pressure damper 7 does not necessarily mean that the furnace pressure damper 7 is completely closed, but means that the damper opening is clearly reduced compared to the normal time.

  However, when the furnace pressure damper 7 is closed and the pressure in the furnace is increased in this way, the flame 10 is blown out from the furnace when the extraction door 6 is opened as shown in FIG. In addition, there is a problem that wasteful heat dissipation increases. Therefore, in the present invention, by operating the soaking zone 4 burner control device 11 close to the outlet of the heating furnace 1 almost simultaneously with closing the furnace pressure damper 7, the amount of gas supplied to the soaking zone 4 burner is reduced, Eliminate flame 10 blowout.

  In order to eliminate the blowing of flame, it is preferable to extremely reduce the amount of gas when the extraction door 6 is opened, but on the other hand, the temperature of the soaking zone 4 will drop. Therefore, in the present invention, the amount of gas supplied to the soaking zone 4 burner when the extraction door 6 is opened is preferably about 1/10 to 1/3 of the normal amount of gas. In this embodiment, the flame 10 was completely prevented from being blown out by reducing the gas amount to approximately 1/5. Note that the furnace pressure damper 7 is preferably reopened immediately before the extraction door 6 is closed, which makes it possible to suppress furnace pressure fluctuations. For the pretropical zone 2 and the heating zone 3, there is no need to change the gas amount.

  By adopting the combustion control method of the present invention described above, since the outside air is not sucked even when the extraction door 6 is opened, the generation rate of demoted products due to the oxide scale is reduced to 1/3 or less of the conventional one. I succeeded in making it happen. In addition, since the inside of the furnace has a positive pressure, there is no blowout of flames, so that safe operation can be ensured and useless heat dissipation can be prevented.

  In the above embodiment, the heating furnace 1 is a continuous heating furnace of a slab. However, the present invention is of a type in which the extraction door 6 is opened and closed intermittently, and is widely applied to heating furnaces that dislike the suction of outside air into the furnace. It is something that can be done.

It is sectional drawing of the heating furnace in embodiment of this invention. It is a graph which shows the furnace pressure fluctuation | variation at the time of opening the extraction door in embodiment of this invention. It is sectional drawing which shows a mode that a flame blows out from the inside of a furnace when an extraction door is opened. It is a graph which shows the furnace pressure fluctuation | variation at the time of opening the extraction door in the conventional heating furnace.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Pre-tropical zone 3 Heating zone 4 Soaking zone 5 Conveying means 6 Extraction door 7 Furnace pressure damper 8 Chimney 9 Gas flow in the furnace 10 Flame 11 Burner control device

Claims (4)

  When the extraction door for workpiece extraction provided at the outlet of the heating furnace under furnace pressure control is opened, the furnace pressure damper for furnace pressure control is closed and the amount of burner gas in the soaking zone close to the outlet of the heating furnace A method for controlling the combustion of a heating furnace, characterized by reducing the amount of heat.   2. The combustion control method for a heating furnace according to claim 1, wherein the heating furnace is a continuous heating furnace for a slab.   2. The combustion control method for a heating furnace according to claim 1, wherein the furnace pressure damper is closed immediately before the extraction door is opened, and is opened immediately before the extraction door is closed. The method for controlling combustion in a heating furnace according to claim 1, wherein when the extraction door is opened, the amount of burner gas in the soaking zone is reduced to 1/3 or less of the normal time.

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