JP2013060610A - Method of controlling the atmosphere of continuous heat treatment furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for lowering a dew point of the furnace atmosphere, while suppressing the decrease of local temperature in a furnace because a local decrease of temperature in the furnace cannot be prevented without an additional charge of a quantity of heat, when lowering the dew point in the furnace of a continuous annealing furnace by a refiner.SOLUTION: The method of controlling the atmosphere of the continuous annealing furnace includes taking a gas that is a portion of the furnace atmosphere into the refiner 8 installed outside the furnace to dehumidify and deacidify, and injecting it into the furnace again. The gas after dehumidification and deacidification out from the refiner 8 is heat exchanged with a gas to be taken into the refiner 8 by a heat exchanger 7 installed outside the furnace, subsequently heat-exchanged with the furnace atmosphere by an in-furnace heat exchanger 11 installed in the furnace, and then injected in the furnace.

Description

  The present invention relates to a method for adjusting the in-furnace atmosphere of a continuous heat treatment furnace. More specifically, the present invention relates to a continuous heat treatment furnace for reducing the dew point of the in-furnace atmosphere gas of a continuous annealing furnace and advantageously producing a steel sheet with good plating adhesion. The present invention relates to a furnace atmosphere adjustment method.

In a continuous annealing furnace that continuously heat-treats a steel plate (specifically, a strip-shaped steel plate), the dew point of the atmosphere gas in the furnace is − in order to improve the chemical conversion treatment property of the steel plate after heat treatment and the plating property of the high-tensile steel plate. It is known that 45 ° C. or lower is targeted.
In the continuous annealing furnace, the interior of the furnace when the furnace is started up is filled with an atmospheric atmosphere, and moisture in the atmosphere permeates into the furnace and the inside of the furnace wall refractory. Such moisture is gradually removed by operating the furnace, but it is inefficient because it requires an operation of several tens of hours to several days to reach the dew point range in which the steel sheet can be produced. The reason for this is that it takes time until the dew point in the furnace is lowered by gradually supplying moisture that has penetrated into the refractory after the furnace is started up. As one of the conventional furnace atmosphere adjustment methods, atmospheric gas is directly supplied to the furnace space as in Patent Document 1, and 50 ° C. to 120 ° C. from the outermost surface side of the furnace wall refractory toward the furnace space. A method of supplying a low-temperature atmospheric gas is known.

Japanese Patent Application Laid-Open No. 07-173526

  In a continuous annealing furnace, in order to lower the dew point in the furnace atmosphere, gas that is part of the high-temperature atmosphere in the furnace is taken into a refiner that is a dehumidifying / deoxidizing device, and dehumidified / deoxidized. After that, when the method of blowing into the furnace is employed, it is necessary to once cool the taken-in high-temperature gas to near normal temperature in order to perform dehumidification / deoxidation treatment. If the dehumidified and deoxidized gas that has been cooled to near normal temperature is blown into the furnace as it is, the temperature inside the furnace will be excessively lowered, leading to deterioration of the quality of the steel sheet. Therefore, a method is employed in which the gas after dehumidification / deoxidation treatment cooled to near room temperature is heated by exchanging heat with the incorporated high-temperature gas before blowing it into the furnace. .

However, in the heat exchange between the taken-in high-temperature gas and the dehumidified / deoxidized gas cooled to near room temperature, the temperature of the gas after the heat exchange can be raised only to an intermediate temperature between them. First, since the temperature after the heat exchange is lower than the furnace temperature and blowing it into the furnace, a local decrease in the furnace temperature occurs. Therefore, in order to prevent this, it is necessary to apply an additional amount of heat.
In other words, conventionally, when reducing the in-furnace dew point of a continuous annealing furnace with a refiner, there has been a problem that a local decrease in the in-furnace temperature cannot be prevented without additional input of heat.

The inventors have intensively studied to solve the above problems, and as a result, the heat-exchanged gas is further heated by heat exchange with the furnace atmosphere and blown into the furnace to add heat. It was found that local reduction of the furnace temperature could be prevented without charging, and the present invention was made.
That is, the present invention relates to a dehumidification / deoxidation after taking a gas that is a part of the furnace atmosphere into a refiner provided outside the furnace in order to lower the dew point in the furnace atmosphere of the continuous annealing furnace, In the in-furnace atmosphere adjustment method of the continuous annealing furnace, the gas after dehumidification / deoxidation that exits the refiner is heat exchanged with the gas taken into the refiner by a heat exchanger provided outside the furnace, Next, after the heat exchange with the furnace atmosphere is performed in the furnace heat exchanger provided in the furnace, the furnace atmosphere adjustment method of the continuous annealing furnace is characterized by blowing into the furnace.

  According to the present invention, the gas dehumidified and deoxidized by the refiner is heated by exchanging heat with the gas taken into the refiner by a heat exchanger provided outside the furnace, and then the furnace heat provided in the furnace. Since the heat was exchanged with the furnace atmosphere in the exchanger and the temperature was further raised and then blown into the furnace, the gas temperature in the furnace could be brought close to the furnace temperature without additional input of heat. Thus, it is possible to achieve a low dew point in the furnace atmosphere while suppressing a local decrease in the furnace temperature.

It is a schematic diagram which shows one Embodiment of this invention.

FIG. 1 is a schematic view showing an embodiment of the present invention, in which 1 is a steel plate, 2 is an annealing furnace first heating zone, 3 is an annealing furnace second heating zone, 4 is an in-furnace roll, Is a take-out pipe, 6 is a blower, 7 is a heat exchanger, 8 is a refiner (dehumidification / deoxidation device), 9 is a heat exchanger connection pipe, 10 is a heat exchanger supply pipe in the furnace, and 11 is heat in the furnace An exchanger 12 is a blowing pipe.
As shown in the drawing, in the continuous annealing furnace divided into the first heating zone 2 and the second heating zone 3, when the steel plate 1 is continuously annealed while being continuously passed through the in-furnace roll 4, the second heating zone is used. A gas which is a part of the furnace atmosphere is taken out from 3 through a take-out pipe 5. The extracted gas is sent to the heat exchanger 7 by the blower 6, used as the high temperature side heat medium of the heat exchanger 7, and removed by heat exchange with the low temperature side heat medium of the heat exchanger 7. 8 is cooled to near normal temperature in the refiner 8 and dehumidified and deoxidized. The gas close to room temperature exiting the refiner 8 is taken as the low temperature side heat medium of the heat exchanger 7 via the heat exchanger connecting pipe 9 and is taken out as the high temperature side heat medium of the heat exchanger 7. It is heated by heat exchange with the gas, and becomes a gas whose temperature has been raised to an intermediate temperature between the two.

  The gas exiting the heat exchanger 7 is guided to the in-furnace heat exchanger 11 via the in-furnace heat exchanger supply pipe 10 and is used as a low-temperature side heat medium for the in-furnace heat exchanger 11. The in-furnace heat exchanger 11 is installed in the first heating zone 2, and the high temperature side heat medium is the in-furnace atmosphere of the first heating zone 2. Therefore, the gas exiting the heat exchanger 7 is heated by heat exchange with the furnace atmosphere in the furnace heat exchanger 11 and becomes a gas heated to a temperature closer to the furnace atmosphere temperature, and the blow pipe 12 It is blown into the second heating zone 3 via.

  As the location where the in-furnace heat exchanger 11 is installed, as in this example, the location away from the blowing location (second heating zone 3 in this example) and the location where there is no problem even if the furnace temperature drops somewhat, that is, the furnace It is preferable from the viewpoint of better suppressing the local decrease in the furnace temperature to select a portion having sufficient heating capacity (first heating zone 2 in this example).

As an example of the present invention, in FIG. 1, the processing gas of the refiner 8 is maintained under the condition that the load conditions of the combustion devices in the first heating zone 2 and the second heating zone 3 are kept constant and the furnace temperature is set to 800 ° C. A gas flow is performed along the gas path of FIG. 1 with a flow rate (= injection flow rate) of 200 Nm ³ / h, the gas temperature just before the injection (abbreviated gas temperature for short), and the second pressure after the gas injection. Tropical 3 furnace temperature (abbreviated, second heating zone furnace temperature after blowing) was measured. On the other hand, as a comparative example, in FIG. 1, without using the in-furnace heat exchanger 11, the gas heated in the heat exchanger 7 was directly blown into the second heating zone 3, and other than this, the same as in the present invention example, Similar measurements were made. The results are shown in Table 1.

  From Table 1, in the example of the present invention, the blowing gas temperature is much higher than that of the comparative example, and the furnace temperature of the second heating zone 3 after blowing is much higher than that of the comparative example, and the set furnace temperature (800 ° C.). The temperature drop from can be greatly reduced.

1 Steel plate (For details, strip steel plate)
2 Annealing furnace 1st heating zone 3 Annealing furnace 2nd heating zone 4 In-furnace roll 5 Extraction piping 6 Blower 7 Heat exchanger 8 Dehumidification / deoxidation equipment (refiner)
9 Heat exchanger connecting pipe 10 Furnace heat exchanger supply pipe 11 Furnace heat exchanger 12 Blowing pipe

Claims (1)

  In order to lower the dew point in the furnace atmosphere of a continuous annealing furnace, the gas that is part of the furnace atmosphere is taken into a refiner provided outside the furnace, dehumidified and deoxidized, and then blown into the furnace again. In the furnace atmosphere adjustment method of the furnace, the dehumidified / deoxidized gas exiting the refiner is heat-exchanged with the gas taken into the refiner by a heat exchanger provided outside the furnace, and then provided in the furnace. A method for adjusting the in-furnace atmosphere of a continuous annealing furnace, wherein the heat is exchanged with the in-furnace atmosphere by using an in-furnace heat exchanger and then blown into the furnace.

Images