JPS6017020A - Direct firing vertical type continuous annealing furnace - Google Patents

Abstract

PURPOSE:To prevent oxidation of a steel strip in a clean heating atmosphere gas furnace by providing an intermediate chamber in which the internal pressure higher than the pressure in a vertical type direct firing heating furnace for the steel strip to be plated in a galvanizing device and the above-described gas furnace is maintained to the intermediate of the two furnaces. CONSTITUTION:A steel strip 5 to be galvanized is heated in a preheating furnace, a vertical type direct firing heating furnace 2 and a clean heating atmosphere gas furnace 3 and is then galvanized. An intermediate chamber 9 having a narrow passage in which the strip 5 passes is provided between the furnace 2 and the furnace 3. The gas in the furnace 3 is fed by a blower 10 into the chamber 9 and at the same time gaseous nitrogen is forced through another pipeline 12 into said chamber. The internal pressure in said chamber is maintained always higher than the pressure in the furnace 2 and the furnace 3 on both sides. Even if the internal pressure of the furnace 2 drops sharply with a change in the combustion condition of fuel, the drop of the internal pressure of the furnace 3 is obviated by the presence of the chamber 9 and therefore the oxidation of the strip 5 by the outdoor air intruded into the furnace 3 and the succeeding unstable galvanization are obviated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a continuous annealing furnace having a vertical direct-fire heating furnace and a non-oxidizing atmosphere gas furnace (soaking furnace, etc.) following the vertical heating furnace.

[Technical background of the invention and its problems]

Figure 1 shows a conventional direct-fired vertical continuous annealing furnace used as hot-dip galvanizing equipment. , having a molten zinc pot 4. The strip 5 is in the preheating furnace 1. It is heated to about 700°C in a direct-fire heating furnace 2, then enters a non-oxidizing atmosphere gas furnace 3, where it is subjected to heat treatments such as soaking, cooling, and over-aging, and then sent to a molten zinc pot 4 where it is plated. . Direct fire heating furnace 2 uses coke oven gas, natural gas, L
This is a furnace that burns PG, etc. directly in the furnace using an open flame burner, and has the feature of being able to rapidly heat the IJ5) with the radiant heat of high-temperature gas. Also, keep the air-fuel ratio below 1 (usually 0).
．． 85 to 0.95), and the gas temperature is 1150
If you heat IJ knob 5 at ~1300℃, it will reach 70℃.
The temperature can be raised to about 0°C with almost no oxidation.

The non-oxidizing atmosphere gas furnace 3 following the direct-fired heating furnace 2 fills the furnace with atmospheric gas (5 to 75% H2, balance N2) through gas supply pipes Ja and 3b, and connects radiant tubes, cooling tubes, etc. This is a furnace in which the strip 5 is indirectly heated and cooled by a heater (not shown) to perform heat treatment.

The strip 5 heated with almost no oxidation in the direct fire heating furnace 2 is then heated in the non-oxidation atmosphere gas furnace 3,
If it is slightly oxidized, it will be completely reduced, and if it is not oxidized, it will be brightly annealed as is.

Because the non-oxidizing atmosphere gas furnace 3 cannot be made completely gas tight due to its structure, the furnace pressure is set to positive pressure (usually 10 to 20 wa H2
O) to prevent outside air from entering.

For this reason, atmospheric gas of about 4C)0 to 100ON is constantly supplied into the furnace. Additionally, the direct-fired heating furnace 2 itself does not need to be gas-tight as does the non-oxidizing atmosphere gas furnace 3, but the oxidizing H2O, CO2f after combustion
In order to discharge the contained waste gas from the chimney 6 of the preheating furnace 1, the furnace pressure of the direct-fired heating furnace 2 is usually kept lower by about 5 to 10 thm H2O than the furnace pressure of the non-oxidizing atmosphere gas furnace 3, and the atmosphere gas and waste gas are Gas is transferred to a non-oxidizing atmosphere gas furnace 3 → Direct fire heating furnace 2 →
The furnace pressure is controlled so that the preheating furnace 1 is guided to the chimney 6. The furnace pressure of the direct-fired heating furnace 2 is usually controlled by sealing the part where the strip 5 enters the preheating furnace 1 with a sealing roll or gas sealing device 7, and with a furnace pressure control dan/4'6a in the flue.

There is no problem with this control in steady state, but direct-fired heating furnace 2
(The direct-fired heating furnace 2 is usually divided into 3 to 4 zones, and the combustion amount can be controlled in each zone, but for combustion stability, the minimum combustion amount in each zone is the maximum combustion amount.) 1/4 to ]15, and there is a sudden change in the amount of waste gas during zone extinguishing and ignition.)
A large damper 6a in the flue controls the furnace pressure of the direct-fired heating furnace 2.
f1ll L is not cut, and the furnace pressure changes rapidly. Due to this influence, the furnace pressure of the non-oxidizing atmosphere gas furnace 3 becomes angular pressure, and a problem occurs in which the IJ 5 is oxidized due to the intrusion of outside air.

[Purpose of the invention]

This invention was made in order to solve the above-mentioned conventional problems, and is a direct-fired vertical type heating furnace that prevents pressure fluctuations in the furnace due to sudden combustion changes from spreading to the non-oxidizing atmosphere gas furnace. The purpose is to provide a continuous annealing furnace.

[Summary of the invention]

In order to achieve the above-mentioned object, this invention provides an intermediate chamber at the connecting part of a vertical direct-fired heating furnace and a non-oxidizing atmosphere gas furnace, which is maintained at an internal pressure higher than the furnace pressure of both furnaces, and Even if the pressure of the heating furnace suddenly drops due to combustion changes, the gas from the non-oxidizing atmosphere gas furnace will not flow to the direct-fired heating furnace.
That is, the present invention is characterized in that even if the furnace pressure of the direct-fired heating furnace suddenly decreases, the furnace pressure of the non-oxidizing atmosphere gas furnace does not decrease suddenly.

[Embodiments of the invention]

Hereinafter, an embodiment of the present invention will be described with reference to the drawings in FIGS. 2 and 3. This embodiment will be described in detail in the conventional direct-fired vertical continuous annealing furnace shown in FIG. , followed by a strip 5 at the connecting part 8 of the non-oxidizing atmosphere gas furnace 3.
An intermediate chamber 9 is provided in which the gap in the part through which the gas passes is made as small as possible, and the other parts are made gas-tight. In this intermediate chamber 9, there is a piping line 11 through which the atmospheric gas of the non-oxidizing atmosphere gas furnace 3 is sucked and delivered by a circulation blower 10, and the furnace pressure of the non-oxidizing atmosphere gas furnace 3 becomes low due to excessive gas draw. To prevent overpowering, a gas replenishment pipe 12 for replenishing N2 from another system is connected, and a pressure control valve 13 built into the piping line 11 controls the internal pressure of the intermediate chamber 9 between the direct-fired heating furnace 2 and the non-heating furnace. The pressure is kept higher than the furnace pressure of the oxidizing atmosphere gas furnace 3. In this way, the atmospheric gas of the furnace 3 sent to the intermediate chamber 9 will constantly flow into both the furnaces 2 and 3 from the IJ tube passage gap on the side wall of the chamber, and therefore the direct flame heating Even if the furnace pressure in the furnace 2 suddenly drops due to combustion changes, the gas in the non-oxidizing atmosphere gas furnace 3 does not flow to the direct-fired heating furnace 2 side, and as a result, the furnace pressure in the furnace 3 suddenly drops. doesn't happen. Note that the internal pressure of the intermediate chamber 9 is 10% lower than the furnace pressure of the non-oxidizing atmosphere gas furnace 3.
~20 am) It is better to set it as high as t20.

FIG. 3 shows an example of the structure of the intermediate chamber 9, in which a sealing roll 14.15f is provided in a portion through which the strip 5 passes. With this structure, the furnaces 2 and 3 are connected from the intermediate chamber 9.
Since the amount of gas flowing to the side decreases, the pipe line 1 is connected to the intermediate chamber 9.
1, the necessary indoor pressure can be obtained even if the amount of gas to be supplied is small.

6- [Effects of the Invention] Since the direct-fired vertical continuous annealing furnace of the present invention is as described below, even if there is a rapid pressure fluctuation in the direct-fired heating furnace, it can maintain a non-oxidizing atmosphere. The furnace pressure of the gas furnace does not drop suddenly, and therefore the furnace pressure of the non-oxidizing atmosphere gas furnace becomes a negative pressure, and the problem of outside air entering and oxidizing the strip can be solved.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram showing a conventional direct-fired vertical continuous annealing furnace used as hot-dip galvanizing equipment, Fig. 2 is a sectional view of essential parts of a continuous annealing furnace according to an embodiment of the present invention, and Fig. 3 FIG. 3 is a sectional view showing an example of the structure of an intermediate chamber. DESCRIPTION OF SYMBOLS 1... Preheating furnace, 2... Vertical direct-fire heating furnace, 3... Non-oxidizing atmosphere gas furnace, 5... Strip, 9... Intermediate chamber, 10... Circulation blower, 11.・・Pipe line, 13・
...Pressure side a valve, J4, Js...Seal roll. Applicant's agent Patent attorney Takehiko Suzue 7- Figure 1

Claims (1)

[Claims] A continuous annealing furnace having a vertical direct-fired heating furnace followed by a non-oxidizing atmosphere gas furnace, characterized in that an intermediate chamber that is maintained at an internal pressure higher than the furnace pressure of both furnaces is provided at the connecting portion of the two furnaces. Direct-fired vertical continuous annealing furnace.