JP5742950B2 - Method for reducing dew point of atmospheric gas in annealing furnace, apparatus therefor, and method for producing cold-rolled annealed steel sheet - Google Patents

Description

  The present invention belongs to the field of reducing the dew point of atmospheric gas in a continuous annealing furnace and advantageously producing a steel strip with good plating adherence (wetability), and in particular, a method for reducing the dew point of atmospheric gas in an annealing furnace. The present invention relates to an apparatus and a method for producing a cold-rolled annealed steel sheet.

By setting the dew point of the atmospheric gas in the continuous annealing furnace to -45 ° C or less, it becomes possible to suppress the concentration of Mn oxide (surface segregation of Mn) on the steel sheet surface during annealing, and zinc or zinc following annealing It is known that the adhesion of alloy plating is improved (see Non-Patent Document 1).
On the other hand, the following is mentioned as a prior art regarding the dew point reduction method of atmospheric gas in a continuous annealing furnace.
A: A method of distributing and supplying a new low dew point atmospheric gas from outside the furnace every heating zone or soaking zone (see Patent Document 1).
B: A method of exchanging heat between a high temperature atmospheric gas to be circulated and a low temperature dew point ambient gas supplied to the furnace separately by providing a mechanism for circulating the atmospheric gas inside the furnace (patented) Reference 2).
C: A method of exchanging heat between the high-temperature furnace atmosphere gas and the atmosphere gas after dew point reduction outside the furnace, and reducing the dew point with a moisture adsorption filter (see Patent Document 3).

Japanese Unexamined Patent Publication No. 2002-3953 Japanese Unexamined Patent Publication No. Sho 62-290830 Japanese Unexamined Patent Publication No. 11-124622

Iron and steel, 96-1 (2010), pp.11-20

In the prior art A, since a low temperature gas is introduced as it is into a high temperature furnace, a large amount of heating energy is required to maintain the steel strip temperature in the furnace, the gas temperature cannot be controlled, and the energy efficiency is high. Remarkably bad.
Further, in the above-mentioned prior art B, even if the dew point of a newly supplied low-temperature gas is low, only a large amount of dew point in the furnace is mixed with the high atmospheric gas, and the dew point of the atmospheric gas in the furnace is reduced. Is not enough.

  Moreover, in the said prior art C, the temperature of the gas returned to a furnace does not rise completely, and as described in Patent Document 3, the dew point is lowered by a moisture adsorption filter having a low dehumidifying capacity, and the dew point is -30 ° C. Since it is reduced only to the extent, it is not possible to achieve a very low dew point of −45 ° C. or lower, which is the object of the present application. That is, the conventional technique for lowering the dew point in the continuous annealing furnace has a problem that the dew point of −45 ° C. or lower cannot be sufficiently achieved, and the energy efficiency is extremely low. .

  The inventors have intensively studied to solve the above problems, and as a result, a desiccant type or compressor type dryer and circulation device that enables a dew point of −45 ° C. or less to reduce the dew point of the annealing furnace atmosphere gas. Newly reducing the dew point to -45 ° C, and also installing a heat exchanger in the circulation device to allow gas to be heated and cooled, allowing gas to flow into the furnace heating zone and cooling zone ( By devising gas introduction), the inventors have conceived means for improving energy efficiency, and have made the present invention.

That is, the present invention is as follows.
(1)
A method for reducing the dew point of the atmosphere gas in a furnace in a continuous annealing furnace in which a metal strip is sequentially passed through a heating zone, a cooling zone, or sequentially passed through a heating zone, a soaking zone, and a cooling zone, and annealed in a reducing atmosphere,
Preparing a circulation device comprising a heat exchanger for exchanging heat between a low temperature gas and a high temperature gas, a gas cooling device for cooling the gas, and a dryer for dehumidifying the gas to a dew point of −45 ° C. or less;
Sucking out part of the heating zone and / or the soaking atmosphere gas (b);
Next, a step (c) of lowering the temperature by exchanging heat with the gas in the low temperature gas flow path through the high temperature gas flow path of the heat exchanger through the part of the atmospheric gas sucked out,
Next, a step (d) of further lowering the temperature by mixing a part of the lowered atmospheric gas with a part of the atmospheric gas sucked out from the cooling zone,
Next, a step (e) of further cooling a part of the atmospheric gas mixed with a part of the atmospheric gas sucked out from the cooling zone and further lowered in temperature through the gas cooling device;
Next, a step (f) of dehumidifying a part of the atmospheric gas further passed through the gas cooling device to a dew point of −45 ° C. or less with the dryer;
Next, the dehumidified part of the atmospheric gas is passed through the low-temperature gas flow path of the heat exchanger to raise the temperature by heat exchange with the gas in the high-temperature gas flow path (g),
Next, a method for reducing the dew point of the atmospheric gas in the annealing furnace, including the step (h) of returning the part of the atmospheric gas whose temperature has been raised to the heating zone and / or the soaking zone.
(2)
The method for reducing the dew point of the atmospheric gas in the annealing furnace according to (1), wherein a part of the gas from the dryer toward the low temperature gas flow path of the heat exchanger is directly returned to the cooling zone without passing through the heat exchanger.
(3)
In an annealing furnace that reduces the dew point of atmospheric gas in a continuous annealing furnace that passes through a metal strip sequentially through heating zone 1 and cooling zone 2 or sequentially passes through heating zone, soaking zone, and cooling zone in a reducing atmosphere. A dew point reducing device for atmospheric gas,
A gas flow path including a heat exchanger 9 for exchanging heat between a low temperature gas and a high temperature gas, a gas cooling device 10 for cooling the gas, a dryer 11 for dehumidifying the gas to a dew point of −45 ° C. or less, and a gas mixer 20 Prepared,
A gas flow path from the heating zone 1 and / or the soaking zone to the hot gas flow path of the heat exchanger 9 through the gas flow path 15 through the gas cooling device 10 to the dryer 11.
Gas flow path 16 that flows from the dryer 11 into the low temperature gas flow path of the heat exchanger 9, and further returns from the heat exchanger 9 to the heating zone and / or the soaking zone,
A dew point reducing apparatus for atmospheric gas in an annealing furnace, comprising a gas flow path 19 connected in a gas mixer 20 to a gas flow path from the cooling zone 2 to the gas dryer 10 to the dryer 11.
(4)
A gas flow path 17 for returning a part of the gas from the dryer 11 to the low temperature gas flow path of the heat exchanger 9 directly to the cooling zone without passing through the heat exchanger 9 via the gas distributor 13 is further provided. The dew point reducing device for atmospheric gas in the annealing furnace as described in (3).
(5)
A method of manufacturing a cold-rolled annealed steel sheet that continuously anneals a cold-rolled steel strip,
A method for producing a cold-rolled annealed steel sheet, wherein the dew point of the atmospheric gas in the furnace in the continuous annealing furnace is reduced by the method of reducing the dew point of the atmospheric gas in the annealing furnace described in (1) or (2) during the continuous annealing.

  According to the present invention, a part of the heating zone and / or the soaking tropic atmosphere gas is sucked out and passed through the high-temperature gas flow path of the heat exchanger to lower the temperature by heat exchange with the gas in the low-temperature gas flow path. Then, the temperature is further lowered by mixing with a part of the atmospheric gas in the cooling zone, then further cooled through the gas cooling device, then dehumidified to a dew point of −45 ° C. or less with the dryer, and then the heat exchanger The temperature is increased by heat exchange with the gas in the high temperature gas flow path through the low temperature gas flow path, and then returned to the heating zone and / or the soaking zone, or more preferably, the heat exchange from the dryer. Since a part of the gas toward the low temperature gas flow path of the furnace is directly returned to the cooling zone without passing through the heat exchanger, the inside of the annealing furnace can reach an extremely low dew point of −45 ° C. or less, and , Energy efficiency will be greatly improved An effect.

It is the schematic which shows the prior art example 1. FIG. It is the schematic which shows the prior art example 2. It is the schematic which shows the circulation system of the prior art example 2. FIG. It is the schematic which shows the prior art example 3. It is the schematic which shows the circulation system of the prior art example 3. 6 is a schematic diagram showing a comparative example 1. FIG. 2 is a schematic diagram showing a circulation system of Comparative Example 1. FIG. It is the schematic which shows the example 1 of this invention. It is the schematic which shows the circulation system of the example 1 of this invention. It is the schematic which shows Example 2 of this invention. It is the schematic which shows the circulation system of the example 2 of this invention.

  When a cold-rolled steel strip is continuously annealed and subsequently plated with zinc or a zinc alloy, the adhesion of the plating is greatly influenced by the dew point in the annealing furnace. It is known that this is due to the abundance of Mn oxide on the surface of the steel strip. If the dew point is around -10 ° C, the Mn oxide is present inside the oxide film on the surface of the steel strip and is present on the surface. If there is almost no dew point and the dew point is −45 ° C. or less, almost no Mn oxide is produced. When the dew point in the middle is around −35 ° C. (−15 ° C. to −40 ° C.), a large amount of Mn oxide is formed on the surface of the steel strip and inhibits adhesion of plating. Therefore, in order to achieve an extremely low dew point in order to prevent the Mn oxide steel strip surface from being concentrated, a circulation device with a dryer enabling a dew point of −45 ° C. or lower was newly installed in the annealing furnace. .

  Here, attention was focused on the temperature of the atmospheric gas (hereinafter referred to as “suction gas”) sucked from the furnace into the circulation device and the temperature of the atmospheric gas (hereinafter referred to as “introduction gas”) introduced from the circulation device into the furnace. In an annealing furnace, the required atmospheric gas temperature differs depending on the heating zone, soaking zone, cooling zone, and the like. In other words, the sucked gas is cooled to about room temperature by the gas cooling device before entering the dryer, dehumidified by the dryer, and introduced again into the furnace. Since the high temperature necessary for annealing the steel strip cannot be maintained, it is required to raise the temperature of the gas introduced from the circulation device.

  Therefore, the present inventors have adopted a method of installing a heat exchanger between the furnace and the gas cooling device. That is, high-temperature gas (suction gas) sucked from the furnace heating zone and soaking zone is cooled by the cooling device before entering the dryer, so if the thermal energy due to this temperature difference is used, it is cooled by the gas cooling device. The temperature of the gas dehumidified by the dryer can be raised again, and the heating energy is the heat energy discarded by the gas cooling device, so that the energy can be effectively used. High-temperature gas sucked from the furnace heating zone and soaking zone is passed through a heat exchanger, then cooled with a gas cooling device, dehumidified with a dryer, heated again with a heat exchanger, and heated again with a furnace. Return to.

Here, since the temperature of the gas after heat exchange of the high-temperature gas sucked from the heating zone or soaking zone may be higher than the gas temperature of the cooling zone, the low temperature sucked from the cooling zone to the gas after the heat exchange It is advantageous that the energy for further cooling in the subsequent gas cooling apparatus can be reduced by mixing these gases.
Furthermore, since the gas temperature after cooling by the gas cooling device is lower than the temperature of the cooling zone of the furnace, a part of the gas cooled by the gas cooling device and dehumidified by the dryer is directly returned to the cooling zone without passing through the heat exchanger. Since the cooling zone can be made at a lower temperature and a lower dew point, energy efficiency is further improved.

  The dryer used in the present invention is made of activated alumina presented in Patent Document 3, and is not a low dehumidifying ability such as a moisture adsorption filter that is alternately operated and stopped, but is not calcium oxide, zeolite, silica gel, chloride Those having a strong dehumidifying ability such as a desiccant system that continuously dehumidifies using calcium or a compressor system that uses alternative chlorofluorocarbon are better.

Taking a continuous annealing furnace composed of a heating zone and a cooling zone as an example, the apparatus configuration and gas flow path of the present invention example, comparative example and conventional example are shown in FIGS.
FIG. 1 shows a conventional example 1 described in Patent Document 1, in which new low-temperature atmospheric gas is supplied as it is from the atmospheric gas supply facility 12 to the heating zone 1 and the cooling zone 2.
2 and FIG. 3 show a conventional example 2 described in Patent Document 2, in which the gas sucked out from the cooling zone 2 is put into the circulation device 8 from the flow path 15, passed through the heat exchanger 9, and from the atmospheric gas supply facility 12. The gas is heated and returned from the flow path 16 to the cooling zone 2. Further, a new low-temperature atmospheric gas separately supplied from the gas supply facility 12 is heated by the heat exchanger 9 and introduced into the heating zone 1 from the atmospheric gas pipe 7.

  4 and 5 show a conventional example 3 described in Patent Document 3, in which gas sucked from the heating zone 1 is put into the circulation device 8 from the flow path 15, passed through the heat exchanger 9, and sucked from the heating zone 1. Is cooled with the gas from the moisture adsorption filter 18, dehumidified with the moisture adsorption filter 18 made of activated alumina, heated again through the heat exchanger 9, and returned from the flow path 16 to the heating zone 1. Two moisture adsorption filters 18 were prepared for each device, and were alternately operated and stopped every 3 hours.

  6 and 7 show a comparative example 1, in which the gas sucked out from the heating zone 1 is put into the circulation device 8 through the flow path 15, passed through the heat exchanger 9, cooled with the gas dehumidified by the dryer 11, and gas cooling After further cooling with the apparatus 10, the moisture is dehumidified with the dryer 11, and is again passed through the heat exchanger 9 to be heated with the gas from the heating zone 1 and returned from the flow path 16 to the heating zone 1.

  FIGS. 8 and 9 show Example 1 of the present invention, corresponding to the means (1) and (3) for solving the problem, the gas sucked from the heating zone 1 is put into the circulation device 8 from the flow path 15 and heated. It is cooled with the dehumidified gas from the dryer through the exchanger 9, mixed with the gas separately sucked from the cooling zone 2 through the flow path 19 in the mixer 20, further cooled with the cooling device 10, and then dehumidified with the dryer 11. Then, the gas from the heating zone 1 is heated again and returned from the flow path 16 to the heating zone 1.

  FIGS. 10 and 11 show Example 2 of the present invention, which corresponds to the means (2) and (4) for solving the problem. In addition to Example 1 of the present invention shown in FIGS. The gas is distributed by the gas distributor 13, one of the distributed gases is passed through the heat exchanger 9, heated by the gas from the heating zone 1, returned from the flow path 16 to the heating zone 1, and the other distributed gas Is directly returned from the flow path 17 to the cooling zone 2.

  Table 1 shows the dew point of the sucked gas, the dew point of the introduced gas, and the energy exhausted in the meantime when the conditions of these sucked gas and introduced gas are changed in various ways according to the gas flow paths of the present invention example and the conventional example. It was shown to. According to this table, No. 1 to No. 3 as Invention Example 1 and No. 4 to No. 6 as Invention Example 2 are annealing furnaces as compared with No. 7 to No. 10 as conventional examples. The dew point of the gas to be introduced into the furnace is good at a value lower than the target of −45 ° C., and the dew point in the furnace 21 before the exit side of the annealing furnace is also lower than −45 ° C., and the waste heat energy is small. It can be seen that the energy efficiency is remarkably good.

  Further, the steel strip after continuous annealing was subjected to zinc alloy plating, and the adhesion state of the zinc alloy plating was examined by a JIS-H8504 (g) tape test method (a peeling test method). As a result, No. 1 to No. 6 as examples of the present invention were strong and good in adhesion, but No. 7 to No. 10 as conventional examples had a problem of generating coating defects. there were.

DESCRIPTION OF SYMBOLS 1 Heating zone 2 Cooling zone 3 Steel strip 4 Roll 5 Inlet 6 Inlet 7 Atmospheric gas piping 8 Circulating device 9 Heat exchanger 10 Gas cooling device 11 Dryer (dehumidifier)
12 New atmosphere gas supply equipment 13 Gas distributor 15 Gas flow path from heating zone 16 Gas flow path to return to heating zone 17 Gas flow path to return to cooling zone 18 Moisture adsorption filter 19 Gas flow from cooling zone Path 20 Gas mixer 21 Annealing furnace exit side

Claims (5)

A method for reducing the dew point of the atmosphere gas in a furnace in a continuous annealing furnace in which a metal strip is sequentially passed through a heating zone, a cooling zone, or sequentially passed through a heating zone, a soaking zone, and a cooling zone, and annealed in a reducing atmosphere,
Preparing a circulation device comprising a heat exchanger for exchanging heat between a low temperature gas and a high temperature gas, a gas cooling device for cooling the gas, and a dryer for dehumidifying the gas to a dew point of −45 ° C. or less;
Sucking out part of the heating zone and / or the soaking atmosphere gas (b);
Next, a step (c) of lowering the temperature by exchanging heat with the gas in the low temperature gas flow path through the high temperature gas flow path of the heat exchanger through the part of the atmospheric gas sucked out,
Next, a step (d) of further lowering the temperature by mixing a part of the lowered atmospheric gas with a part of the atmospheric gas sucked out from the cooling zone,
Next, a step (e) of further cooling a part of the atmospheric gas mixed with a part of the atmospheric gas sucked out from the cooling zone and further lowered in temperature through the gas cooling device;
Next, a step (f) of dehumidifying a part of the atmospheric gas further passed through the gas cooling device to a dew point of −45 ° C. or less with the dryer;
Next, the dehumidified part of the atmospheric gas is passed through the low-temperature gas flow path of the heat exchanger to raise the temperature by heat exchange with the gas in the high-temperature gas flow path (g),
Next, a method for reducing the dew point of the atmospheric gas in the annealing furnace, including the step (h) of returning the part of the atmospheric gas whose temperature has been raised to the heating zone and / or the soaking zone.   The method for reducing the dew point of atmospheric gas in an annealing furnace according to claim 1, wherein a part of the gas from the dryer toward the low temperature gas flow path of the heat exchanger is directly returned to the cooling zone without passing through the heat exchanger. In an annealing furnace that reduces the dew point of atmospheric gas in a continuous annealing furnace that passes through a metal strip sequentially through heating zone 1 and cooling zone 2 or sequentially passes through heating zone, soaking zone, and cooling zone in a reducing atmosphere. A dew point reducing device for atmospheric gas,
A heat exchanger 9 for exchanging heat between the low temperature gas and the high temperature gas, a gas cooling device 10 for cooling the gas,
A dryer 11 for dehumidifying the gas to a dew point of −45 ° C. or less, and a gas flow path including a gas mixer 20;
A gas flow path from the heating zone 1 and / or the soaking zone to the hot gas flow path of the heat exchanger 9 through the gas flow path 15 through the gas cooling device 10 to the dryer 11.
Gas flow path 16 that flows from the dryer 11 into the low temperature gas flow path of the heat exchanger 9, and further returns from the heat exchanger 9 to the heating zone and / or the soaking zone,
A dew point reducing apparatus for atmospheric gas in an annealing furnace, comprising a gas flow path 19 connected in a gas mixer 20 to a gas flow path from the cooling zone 2 to the gas cooling apparatus 10 from the heat exchanger 9 .   A gas flow path 17 for returning a part of the gas from the dryer 11 to the low temperature gas flow path of the heat exchanger 9 directly to the cooling zone without passing through the heat exchanger 9 via the gas distributor 13 is further provided. The dew point reducing device for atmospheric gas in an annealing furnace according to claim 3. A method of manufacturing a cold-rolled annealed steel sheet that continuously anneals a cold-rolled steel strip,
The manufacturing method of the cold-rolled annealing steel plate which reduces the dew point of the atmospheric gas in the furnace in the said continuous annealing furnace by the method of reducing the dew point of the atmospheric gas in an annealing furnace according to claim 1 or 2 during the said continuous annealing.

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