Method of reducing dew point of atmosphere gas in annealing furnace, apparatus for the same and method of producing cold-rolled and annealed steel sheet

Patent metadata

Field	Value
Publication number	US-9657366-B2
Application number	US-201314391077-A
Country	US
Kind code	B2
Filing date	Apr 5, 2013
Priority date	Apr 9, 2012
Publication date	May 23, 2017
Grant date	May 23, 2017

Abstract

Part of an atmosphere gas in a heating zone and/or a soaking zone is sucked out and is cooled through a high-temperature gas passage of a heat exchanger by heat exchange with a gas in a low-temperature gas passage, then cooled through a gas cooler, then dehumidified to a dew point of −45° C. or less in a dryer, then heated through the low-temperature gas passage of the heat exchanger by heat exchange with a gas in the high-temperature gas passage, and returned to the heating zone and/or the soaking zone. Part of gas flowing from the dryer toward the low-temperature gas passage of the heat exchanger is returned to a cooling zone. These can achieve a low dew point of −45° C. or less with high energy efficiency.

First claim

The invention claimed is:

1. An apparatus that reduces a dew point of an atmosphere gas in a continuous annealing furnace that anneals a metal strip in a reducing atmosphere by passing the metal strip through a heating zone and a cooling zone in this order or through a heating zone, a soaking zone, and a cooling zone in this order, comprising:
a circulator including a heat exchanger that exchanges heat between a low-temperature gas and a high-temperature gas, a gas cooler that cools a gas, a dryer that dehumidifies a gas to a dew point of −45° C. or less by utilizing a desiccant or compressor, and a gas distributor,
wherein the apparatus further includes
a first gas passage extending from the heating zone and/or the soaking zone through a gas passage to a high-temperature gas passage which is installed in the heat exchanger and through the gas cooler to the dryer,
a second gas passage extending from the dryer through the gas distributor to a low-temperature gas passage of the heat exchanger and from the heat exchanger to the heating zone and/or the soaking zone, and
a third gas passage that returns part of gas flowing from the dryer toward the low-temperature gas passage of the heat exchanger directly to the cooling zone through the gas distributor but without passing through the heat exchanger.

2. A method of reducing the dew point of a furnace atmosphere gas in a continuous annealing furnace that anneals a metal strip in a reducing atmosphere by passing the metal strip through a heating zone and a cooling zone in this order or through a heating zone, a soaking zone, and a cooling zone in this order, comprising:
(a) providing the apparatus that reduces the dew point of an atmosphere as in a continuous annealing furnace according to claim 1 ;
(b) sucking part of the atmosphere gas from the heating zone and/or the soaking zone;
(c) passing the sucked part of the atmosphere gas through a high-temperature gas passage of the heat exchanger and decreasing the temperature of the sucked part of the atmosphere gas by heat exchange with a gas in a low-temperature gas passage;
(d) passing the part of the atmosphere gas having a decreased temperature through the gas cooler to further cool the part of the atmosphere gas;
(e) dehumidifying the further cooled part of the atmosphere gas to a dew point of −45° C. or less in the dryer;
(f) passing the dehumidified part of the atmosphere gas through the low-temperature gas passage of the heat exchanger to increase the temperature of the dehumidified part of the atmosphere gas by heat exchange with a gas in the high-temperature gas passage;
(g) returning the part of the atmosphere gas having an increased temperature to the heating zone and/or the soaking zone; and
(h) simultaneously with (f) and (g), returning part of gas flowing from the dryer toward the low-temperature gas passage of the heat exchanger directly to the cooling zone without passing through the heat exchanger.

3. A method of producing a cold-rolled and annealed steel sheet, comprising continuously annealing a cold-rolled steel strip, wherein the dew point of an atmosphere gas in a continuous annealing furnace is reduced by the method according to claim 2 during the continuous annealing.

Assignees

• Jfe Steel Corp

Inventors

• Fujii Takamasa
• Iri Masato
• Sato Nobuyuki

Classifications

• C21D1/76

  Adjusting the composition of the atmosphere · CPC title

• F27B9/28

  for treating continuous lengths of work · CPC title

• C21D9/52

  for wires; for strips {; for rods of unlimited length} · CPC title

• C21D9/0006

  Details, accessories not peculiar to any of the following furnaces (control devices C21D11/00) · CPC title

• C21D9/562

  Details · CPC title