JP2012097312A - Fire extinguishing method of continuous heating furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fire extinguishing method of a continuous heating furnace, capable of reducing the consumption of fuel gas while securing the regulation value of an exhaust gas NOx concentration especially during extinguishing course for suspension of a line in the continuous heating furnace.SOLUTION: In the fire extinguishing method of the continuous heating furnace, during extinguishing course for suspension of the line, fire is extinguished successively from a zone where the final material to be heated extracted from the continuous heating furnace before suspension of the line passes through in the continuous heating furnace.

Description

  The present invention relates to a continuous heating furnace extinguishing method capable of reducing the amount of fuel gas used while complying with the regulation value of exhaust gas NOx concentration at the time of shutdown due to line stoppage (operation stoppage). It is about.

In order to strictly observe the governmental regulations regarding the NOx concentration of exhaust gas, the heating furnace also suppresses the generation of NOx itself and reduces the raw NOx concentration, thereby reducing the exhaust gas NOx concentration, and the O ₂ in the heating furnace. By reducing the concentration, there is a method of lowering the exhaust gas O ₂ concentration to lower the exhaust gas NOx concentration, and various methods have been taken.

For example, a method is employed in which the exhaust gas NOx concentration is lowered by raising the amount of fuel gas used and lowering the air-fuel ratio to lower the furnace O ₂ concentration.

In Patent Documents 1 to 3, a method is adopted in which exhaust gas is supplied to preheated air and reused to lower the in-furnace O ₂ concentration and lower the exhaust gas NOx concentration.

  Incidentally, the exhaust gas NOx concentration is defined by the following equation.

Exhaust gas NOx concentration [ppm] = (Raw NOx concentration [ppm]) × (21% -11%) / (21% −Exhaust gas O ₂ concentration [%])

Japanese Patent Laid-Open No. 52-119407 JP 05-180411 A JP-A-11-302724

However, as described above, the method of lowering the exhaust gas NOx concentration by increasing the amount of fuel gas used, lowering the air-fuel ratio, and lowering the O ₂ concentration in the furnace is unnecessary especially at the time of shutdown due to line stoppage. Fuel gas was used, and the amount of fuel gas used was wasted.

Further, as disclosed in Patent Documents 1 to 3, a method for reducing exhaust gas NOx concentration by reducing the O ₂ concentration in the furnace by supplying exhaust gas to the preheated air and reusing it seems to be described in Patent Document 3. In addition, the exhaust gas NOx concentration is only lowered to about 98 ppm at the maximum, and the capital investment is expensive and the administrative regulation value cannot be sufficiently achieved.

  The present invention has been made in view of the above circumstances, and reduces the amount of fuel gas used in a continuous heating furnace while complying with the regulation value of exhaust gas NOx concentration, particularly at the time of shutdown due to line stoppage. It aims at providing the fire extinguishing method of the continuous heating furnace which can do.

  In order to solve the above problems, the present invention has the following features.

  [1] In a continuous heating furnace, when the line is stopped due to a line stoppage, the fire is sequentially extinguished from the zone through which the final material of the material to be heated extracted from the continuous heating furnace passes before the line stoppage. How to extinguish the heating furnace.

  In the present invention, in a continuous heating furnace, the amount of fuel gas used can be reduced while complying with the regulation value of the exhaust gas NOx concentration, particularly at the time of shutdown due to line stoppage.

  That is, in the present invention, when the continuous heating furnace is shut down due to the line stoppage, the extinguishing material (the material to be heated extracted from the continuous heating furnace before the line stoppage) is sequentially extinguished from the zone through which the final material has passed. Therefore, NOx generated in the local high temperature portion of the flame is reduced, and the amount of fuel gas used in the zone through which the final cut material has passed can be reduced.

  In addition, the material before the continuous heating furnace was shut down (the material was inserted into the continuous heating furnace before the continuous heating furnace was shut down and placed in the continuous heating furnace as it was stopped. Further, there is an effect that the oxide scale of the placement material is reduced by reducing the heat given to the heated material that is heated together with the startup of the continuous heating furnace and extracted after the startup.

It is a figure which shows the continuous heating furnace used in Example 1 of this invention.

  NOx includes fuel NOx generated by oxidation of fuel-derived nitrogen compounds, prompt NOx generated by oxidation of intermediate products, and thermal NOx generated by oxidation of nitrogen in air under a high temperature and high pressure environment, Most of the NOx in the exhaust gas of a continuous heating furnace (hereinafter simply referred to as a heating furnace) is thermal NOx generated in a locally high temperature portion of the burner flame.

In order to reduce the NOx concentration in the exhaust gas of the heating furnace, as described above, there are a method for suppressing the generation of NOx itself (raw NOx) and a method for reducing the O ₂ concentration in the heating furnace.

In order to reduce the O ₂ concentration in the heating furnace, it is necessary to lower the air-fuel ratio, but in order to perform appropriate flow rate control of the combustion air, it is necessary to set the flow rate of the combustion air to a certain amount or more. Further, if the on-off valve of the combustion air piping is not fully closed, air will enter the heating furnace even after the burner is extinguished, and this will increase the O ₂ concentration in the heating furnace. Therefore, conventionally, by lowering the relatively O ₂ concentration by increasing the flow rate of the fuel gas it has been performed operations to reduce the NOx concentration.

  At that time, in order to secure the flow rate of the fuel gas, if the flow rate of the fuel gas is increased in a specific zone, the material to be heated (for example, steel slab) in the zone is overheated, which causes the generation of oxide scale. Therefore, it was necessary to operate the entire zone without extinguishing the fire gas while increasing the flow rate of the fuel gas until the final cut material was extracted from the heating furnace. Therefore, when the heating furnace is shut down, excessive use of fuel gas is generated, which leads to deterioration of the fuel consumption rate.

  Therefore, as a result of intensive studies, the present inventors have sequentially reduced the number of burner flames by sequentially extinguishing fire from the zone through which the final material of the cut-off material has passed when the heating furnace is brought down due to line stoppage. The inventors conceived of suppressing the generation of thermal NOx and lowering the NOx concentration in the exhaust gas.

Conventionally, it was thought that extinguishing a part of the burner of the heating furnace would increase the O ₂ concentration in the heating furnace due to the intruding air from the outside and increase the NOx concentration in the exhaust gas. Although the O ₂ concentration in the heating furnace increases, the number of burner flames decreases and the local high temperature region decreases, so the generation of thermal NOx is suppressed, so the NOx concentration in the exhaust gas increases. That's not to say. That is, the generation of thermal NOx is about 1300 ° C. or higher, the furnace temperature is lower than this, and the local high temperature portion of the burner flame is about 1700 ° C. or higher. Therefore, if the number of burner flames is reduced, NOx is reduced. It is reduced.

  In addition, with the rest of the heating furnace, the placement material that is placed in the heating furnace as it is is conventionally heated until the cutting material is extracted from the heating furnace. As a result of exposure, oxide scales frequently appeared on the surface, causing problems such as yield loss and wrinkle generation.

  On the other hand, according to the present invention, by sequentially extinguishing fire from the zone through which the final material of the cut material has passed, the placement material starts to cool from that point, and the oxide scale generated on the surface is reduced, resulting in a good yield. And reducing wrinkle problems.

  As Example 1 of the present invention, using a continuous heating furnace 10A, 10B shown in FIGS. 1A and 1B, a plurality of steel pieces (slabs) having a width of 1594 to 2304 mm were sequentially charged and heated. Later, it was continuously heated to the final material 21z of the cutting material 21, and then the continuous heating furnaces 10A and 10B were put into a resting state. The continuous heating furnaces 10A and 10B have three zones of a pre-tropical zone 11, a heating zone 12, and a soaking zone 13, respectively. In FIG. 1, 14 is an inlet, 15 is an extraction port, 18 is a burner, and 19 is exhaust gas.

  As an example of the present invention, after the final material 21z of the cutting material 21 passes through the pre-tropical zone 11, the pre-tropical zone 11 is immediately extinguished, and after the final material 21z of the cutting material 21 passes through the heating zone 12, the The heating zone 12 was extinguished, and after the final material 21z of the cutting material 21 passed the soaking zone 13, the soaking zone 13 was quickly extinguished.

As a result, in the example of the present invention, it was possible to achieve a reduction in fuel consumption by sequentially extinguishing the zones and a reduction in exhaust gas NOx concentration by suppressing the generation of thermal NOx. Although the O ₂ concentration increased, the exhaust gas NOx concentration was always below the administrative regulation value.

On the other hand, as a conventional example, the final material 21z of the cutting material 21 is kept warm without extinguishing after passing through the pre-tropical zone 11 and the heating zone 12, and the final material 21z of the cutting material 21 passes through the soaking zone 13. And after extracting from the extraction port 15, the whole heating furnace was extinguished. In the meantime, the flow rate of the fuel gas remained increased to reduce the O ₂ concentration.

  As a result, in the conventional example, the exhaust gas NOx concentration was lower than the administrative regulation value, but the fuel consumption rate was high and was poor.

10A Continuous heating furnace 10B Continuous heating furnace 11 Pre-tropical zone 12 Heating zone 13 Soaking zone 14 Loading port 15 Extraction port 18 Burner 19 Exhaust gas 21 Cutting material 21z Final material of cutting material 22 Inserting material

Claims (1)

  In the continuous heating furnace, the fire is sequentially extinguished from the zone through which the final material of the material to be heated extracted from the continuous heating furnace passes before the line stoppage at the time of shutdown due to the line stoppage. Fire extinguishing method.

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