JP2671936B2 - Preheating method of steel to be treated in annealing furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for preventing dew condensation when preheating exhaust gas in a continuous annealing furnace for steel sheets.

[0002]

2. Description of the Related Art In continuous annealing equipment for steel strips, in order to improve thermal efficiency, a preheating furnace using exhaust gas is provided in front of the annealing furnace, and it is widely used for preheating before introducing the steel strip into the annealing furnace. Has been.

However, when the annealing furnace is started up,
Since the temperature of the jet pre-tropical furnace body is lower than the dew point of the exhaust gas, the exhaust gas that touches the furnace body will not condense, not only will the treated steel strip and equipment be contaminated, but there is a risk that the steam will expand rapidly and explode when the temperature rises. It was

Therefore, as a measure for preventing this dew condensation, for example, in Japanese Patent Laid-Open No. 63-31219, a heat exchange device is provided in a preheating furnace, and preheated air heat-exchanged by exhaust gas from the annealing furnace is used for the preheating furnace. The method of using as a heating gas of is disclosed.

As a result, at the start-up of the annealing furnace, the temperature of the pre-tropical furnace can be made higher than the exhaust gas dew point by the preheated air, and the formation of dew condensation in the preheating furnace can be prevented.

[0006]

However, in such a method, the air that has undergone heat exchange in the heat exchanger is continuously used for preheating even after the start-up, and when the exhaust gas is directly used for preheating. Is less efficient than

An object of the present invention is to prevent dew condensation at the time of start-up in a continuous annealing equipment having a preheating furnace which utilizes exhaust gas from the annealing furnace for preheating a material to be treated by a heat exchanger.
An object of the present invention is to provide a system capable of effectively utilizing the heat quantity of the exhaust gas of the annealing furnace.

[0008]

The method for preheating a steel material to be treated in an annealing furnace according to the present invention is such that at the start-up of the annealing furnace, the inside of the preheating furnace is preheated by the gas exchanged with the exhaust gas from the annealing furnace. When the dew point of the atmosphere in the preheating furnace reaches or exceeds the dew point of the exhaust gas from the annealing furnace, the steel to be treated is preheated by the exhaust gas of the annealing furnace.

[0009]

[0010]

[Operation] When the annealing furnace starts up, the combustion exhaust gas is not introduced into the jet preheating furnace, but the air in the jet preheating zone is circulated and heated through the heat exchanger, and the temperature in the preheating furnace is raised by the preheating air. After the dew point of the exhaust gas is exceeded, switch the system,
By directly introducing the exhaust gas into the jet pretropical zone and then directly blowing the exhaust gas onto the material to be heated, the preheating efficiency can be increased.

[0011]

EXAMPLE An example in which the present invention is applied to an equipment for annealing strip steel sheets after cold rolling will be described.

FIG. 1 shows a strip steel sheet annealing system. In the figure, 1 indicates a continuous annealing furnace, and the strip steel plate S is preheated in a preheating furnace 2 and introduced into the annealing furnace 1. Reference numeral 3 shows an exhaust gas extraction system from the annealing furnace 1. Reference numeral 4 denotes a pressure equalizing heat exchanger (plenum chamber), which passes through an atmosphere gas (air) introduction system 7 of the preheating furnace 2 by a circulation blower 6 in a heat exchange pipe 5 arranged in the plenum chamber 4. The air introduced and further heat-exchanged is introduced into the preheating furnace 2 through the heat exchange gas introduction system 8.

Further, the annealing furnace 1 introduced into the plenum chamber 4 through the exhaust gas extraction system 3 from the annealing furnace 1.
Exhaust gas from the plenum chamber 4 exhaust stack 9
Exhaust gas introduction system 11 that is formed so as to be discharged to the outside air through the discharge system 10 to the exhaust gas, and branches from the exhaust system 10 and is introduced into the preheating furnace 2 to directly preheat the strip steel sheet S.
It also has The exhaust gas introduction system 11 joins the heat exchange gas introduction system 8.

Further, reference numeral 12 denotes an exhaust system of exhaust gas from the preheating furnace 2 in which exhaust gas from the preheating furnace 2 is discharged into the outside air through an exhaust chimney 9, and a hot water boiler 13 and an exhaust fan 14 are provided in the path. It is provided. Further, on-off valves 15, 16, 17 are provided in the atmosphere gas (air) introduction system 7, the heat exchange gas introduction system 8 and the exhaust gas exhaust system 10 respectively.
Further, in the exhaust gas introduction system 11, an on-off valve 18 is also provided in front of the confluence with the heat exchange gas introduction system 8. Reference numeral 19 denotes a nozzle for blowing exhaust gas onto the strip steel plate S in the preheating furnace 2.

In such an apparatus having the introduction control system of the annealing furnace, when the annealing furnace 1 is started up, the exhaust gas of the annealing furnace 1 is not directly introduced into the preheating furnace 2, but the air in the jet pretropical zone is plenum. The temperature in the preheating furnace is raised to a temperature above the dew point of the exhaust gas of the annealing furnace 1 by the preheated air passing through the heat exchange gas introduction system 8 that can circulate and raise the temperature through the chamber 4.

At the start of the annealing furnace, the valve 18 is closed and the valve 17 is opened, so that the combustion exhaust gas from the annealing furnace 1 is not introduced into the preheating furnace but is discharged to the chimney 9. On the other hand, the air in the preheating furnace 2 is supplied to the plenum chamber 4 by the circulation blower 6.
After passing through the heat exchange pipe 5 therein, the temperature is raised to 200 ° C. by the exhaust gas, and the temperature is again introduced into the preheating furnace 2. This allows
The temperature inside the preheating furnace 2 is raised above the dew point of the combustion exhaust gas. After that, the valves 15 and 16 are closed to stop the operation of the circulation blower 6, the valve 18 is opened, and the exhaust gas of the annealing furnace 1 is sprayed from the nozzle 19 onto the strip steel plate S in the preheating furnace 2 to discharge the exhaust gas to the exhaust system 12. Is exhausted to the chimney 9 by the action of the fan 14.

[0017]

According to the present invention, the following effects can be obtained.

(1) When the line of the annealing furnace starts up,
Since the exhaust gas from the annealing furnace is not introduced into the preheating furnace, no condensation occurs on the inner wall of the jet preheating zone.

(2) During normal operation, since the exhaust gas from the annealing furnace is directly used for preheating, the preheating temperature can be raised, and the thermal efficiency is further improved.

[Brief description of the drawings]

FIG. 1 shows an example system applied to an annealing system for strip steel sheets as an example of the present invention.

[Explanation of symbols]

 S Strip steel plate 1 Continuous annealing furnace 2 Preheating furnace 3 Extraction system of exhaust gas from annealing furnace 4 Pressure equalizing heat exchanger (plenum chamber) 5 Heat exchange pipe 6 Circulating blower 7 Preheating furnace atmosphere gas (air) introduction system 8 Heat Exchange gas introduction system 9 Exhaust chimney 10 Exhaust system to chimney 11 Exhaust gas introduction system 12 Exhaust gas exhaust system from preheating furnace 13 Hot water boiler 14 Exhaust fan 15, 16, 17, 18 Open / close valve 19 Exhaust gas blowing nozzle

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiharu Matsunaga 46-59 Nakahara, Tobata-ku, Kitakyushu, Fukuoka Prefecture Nippon Steel Co., Ltd. Machinery & Plant Business Department (56) Reference JP 63-157819 (JP) , A) Jikkouhei 3-22266 (JP, Y2)

Claims (1)

(57) [Claims] 1. When the annealing furnace is started up, the inside of the preheating furnace is preheated by the gas exchanged with the exhaust gas from the annealing furnace,
A preheating method for a steel material to be treated in an annealing furnace, wherein when the dew point of the atmosphere in the preheating furnace reaches or exceeds the dew point of the exhaust gas from the annealing furnace by this preheating, the steel material to be treated is preheated by the exhaust gas of the annealing furnace.