JPH0693341A - Continuous heat treatment method for steel strip - Google Patents

Abstract

(57) [Summary] (Modified) [Purpose] While preventing the deterioration of the refractory materials that make up the furnace body,
Provided is a continuous heat treatment method for a steel strip capable of efficiently burning unburned components. [Structure] In untwisted exhaust gas combustion using a direct-fire continuous steel strip heat treatment apparatus operating at a combustion air ratio of 1.0 or less, the maximum temperature of the refractory material constituting the furnace body is higher than the service temperature of the refractory material constituting the furnace body. Combustion is performed while controlling the temperature to be in the low temperature range of 20 ° C to 100 ° C, and combustion air is blown into the steel strip from a plurality of positions in the sheet passing direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous heat treatment method for steel strips, which is used for a continuous annealing line for cold rolled steel sheets and stainless steel sheets, a heat treatment line for electromagnetic steel sheets, a hot dip coating line including continuous heat treatment, and the like. To be done.

[0002]

2. Description of the Related Art In a direct-fired heating furnace, the combustion exhaust gas generated in the direct-fired heating zone is introduced into a pretropical zone connected to the inlet side of the direct-fired heating zone, and the combustion exhaust gas preheats the steel strip to generate the exhaust gas. It is designed to reduce heat loss. Moreover, in an open flame heating furnace, the air ratio is set to 0.7 in order to prevent surface oxidation of the steel sheet.
Since the combustion is performed in a state of up to 0.95, the combustion exhaust gas from the open flame heating zone contains a large amount of untwisted components. If the exhaust gas containing the untwisted part is discharged out of the furnace as it is, the heat loss is large. Therefore, the untwisted portion is burned in the region where the exhaust gas temperature is lowered before it is discharged to the outside of the furnace, and the combustion heat is utilized for preheating the steel strip.

As a technique for burning the untwisted component in the combustion exhaust gas as described above, for example, there is a technique disclosed in Japanese Patent Publication No. 53-39848. This is provided with an air nozzle in the pretropical zone of the continuous annealing furnace, sends combustion air into the pretropical zone, and burns untwisted gas in the pretropical zone.

In such a conventional continuous twisting furnace, the air ratio of the heating burner must be reduced in order to suppress the surface oxidation of the steel strip as much as possible. As a result, the untwisted portion is increased, and thus a large amount of untwisted portion is completely burned by excess air in the pretropical zone. Further, the nozzles for blowing the excess air are arranged in one place. Since a large amount of untwisted portion is generated in a direct-fired heating furnace with a significantly small air ratio, it is burned in a region where the gas temperature of the preheating furnace is low, and as a result, the gas temperature is raised to efficiently heat the steel strip. is there. However, combustion in a region where the gas temperature is low does not necessarily allow efficient heating of the steel strip because radiative heat transfer to the steel strip is not sufficiently performed. Further, when the untwisted component is burned in a high-temperature gas atmosphere, the burned gas temperature may reach 1500 ° C. or higher, which deteriorates the refractory material forming the furnace body and shortens the life of the furnace body. There was a point.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a continuous heat treatment method for a steel strip capable of efficiently burning untwisted parts while preventing deterioration of the refractory material constituting the furnace body. I am trying.

[0006]

SUMMARY OF THE INVENTION The present invention is a method for continuously heat treating a steel strip by a heat treatment facility having a preheating zone and an open flame heating zone connected to the preheating zone, in an atmosphere near the exit side of a preheating furnace. In the region where the gas temperature is high, combustion air is blown in parallel to the steel strip from a plurality of positions along the strip passing direction to burn untwisted components in the combustion exhaust gas from the direct-fired heating furnace.

The untwisted portion contained in the combustion exhaust gas from the open flame heating zone is combusted by the blown combustion air. The air ratio is 1.0 or less, and combustion is performed stepwise toward the entrance side of the preheating furnace. At this time, while monitoring the refractory temperature or the combustion gas temperature from the blow-in port near the open flame heating zone, combustion is performed up to a temperature limit value that does not affect the deterioration of the refractory. The limit temperature of the refractory is determined by the constituent components thereof, but in general, a direct-fire reduction furnace having a temperature of 1400 ° C. is used. In order to increase the combustion efficiency, it is preferable to make the gas temperature as high as possible, but in consideration of deterioration of the refractory, it is necessary to control the gas temperature to a temperature 20 ° C. lower than the limit temperature of the refractory. Although there is no restriction on equipment protection on the low temperature side, in order to exert the effect of the present invention, it is preferable that the gas temperature is 100 ° C. lower than the limit temperature of the refractory material. Therefore, the combustion gas temperature is generally 1
Burn while controlling at 300 ° C to 1380 ° C.

In order to effectively use the untwisted portion of the combustion exhaust gas, combustion is performed in a region where the ambient gas temperature is high near the exit side of the preheating furnace. Adjust the amount. It is also possible to monitor the combustion gas temperature instead of the refractory temperature.
The combustion air is blown with the burner parallel to the steel strip surface.
It is preferable to arrange them at appropriate intervals in the sheet passing direction and blow them in parallel so that the combustion air does not directly hit both sides of the steel strip and the steel strip is not oxidized.

The number of injection points of combustion air and the arrangement intervals of the injection burners depend on the structure of the furnace and the volume of the preheating furnace.
It is determined by the amount of combustion exhaust gas and the ratio of untwisted portion. By making the high temperature gas temperature region as long as possible, sufficient radiative heat transfer to the steel strip becomes possible, and the thermal efficiency of the furnace improves. Generally, about two blowing points are suitable. Further, unlike the combustion gas, the untwisted portion in the exhaust gas does not burn rapidly, so the blowing interval is, for example, 0.5 to
About 3 m is preferable.

At the burning location near the open flame heating zone, since the ambient gas temperature is high, it is necessary to adjust the burning amount while monitoring with a thermometer. However, if the atmospheric gas temperature is sufficiently far from the refractory heat resistant temperature in the second and subsequent combustion parts, monitoring with a thermometer can be omitted.

The burner installed in the pre-tropical zone blows combustion air into the combustion exhaust gas to burn the untwisted portion, but a small amount of fuel is used to prevent the burner from extinguishing and to maintain combustion reliably. Supplied from auxiliary burner. The amount of air supplied to the entire preheating furnace is the amount required to completely burn the untwisted gas in the direct heating zone.

[0012]

EXAMPLES The present invention will be further described below based on examples. As shown in FIG. 1, the continuous heat treatment equipment 1 includes a pre-tropical zone 2, an open flame heating zone 3, a soaking zone 4, a slow cooling zone 5 and a quenching zone 6. The open flame heating furnace 3 is provided with a non-oxidizing combustion burner group 10. The air blowing burners for burning the untwisted portion used in the present invention are arranged at two outlets 11 and 12 of the preheat zone 2.
The exhaust gas generated from the burner arranged in the non-oxidizing burner installation range 10 is discharged from the pre-tropical inlet, the heat is recovered by the recuperator 13, and is discharged from the chimney 15 to the outside of the furnace via the exhaust gas blower 14.

FIG. 2 shows the arrangement of the burners 17 at the burner installation position 12 for burning the untwisted gas shown in FIG. The air-blowing burners 17 are arranged on both side surfaces of the steel strip S, and are attached to the furnace body 16 in pairs at intervals in the vertical direction. The distance between the upper and lower burners is 1 m. The same applies to the burner arrangement at the burner arrangement position 11 for combustion of untwisted gas in FIG.

In the open flame heating zone, the fuel is burned by the non-oxidizing combustion burner at an air ratio of 0.8, and the steel strip is heated by open flame. Further, in the open flame heating zone, the exhaust gas is sucked by the blower from the pre-tropical exit side, so the combustion exhaust gas a flows toward the pre-tropical exit side. Here, the amount of air blown into the burner 17 depends on the thermometer 1 installed in the immediate vicinity of the burner 17.
8 burns while adjusting the air ratio to a gas temperature (for example, 1400 ° C.) that does not exceed the upper limit temperature of the refractory.

In FIG. 1, a burner is arranged at 11
Since the temperature is close to the open flame heating zone, the temperature of the exhaust gas generated in the open flame heating zone is high because the amount of radiative heat transfer to the steel strip is small. Therefore, when the amount of untwisted components is large in a direct-fired heating furnace with a large amount of combustion, burning all untwisted components causes the gas temperature to exceed the service temperature of the refractory. At this time, the combustion load is adjusted while monitoring the gas temperature by the thermometer as described above, and the remaining amount is burned by the 12-part burner installed on the pre-tropical inlet side of the 11-part burner. Depending on the amount of combustion in the direct-fired heating furnace, it is possible to burn all the untwisted parts with only 11 parts of the burner.

FIG. 3 shows the gas temperature distribution in the furnace when the untwisted portion is burned according to the present invention. By blowing air from two locations in the latter part of the pre-tropics and burning the untwisted portion, the distance that the steel strip is in contact with the high temperature gas becomes longer.
As a result, radiative heat transfer from the combustion exhaust gas to the steel strip is sufficiently performed in the furnace, and the temperature of the exhaust gas discharged from the furnace is lowered.

[0017]

EFFECTS OF THE INVENTION According to the present invention, in an open-fired furnace, untwisted components are burned while monitoring the refractory temperature or the gas temperature in a region where the temperature of the combustion exhaust gas is high in the latter part of the pre-tropical zone. It is possible to increase the distance that the steel strip is exposed, and as a result, the thermal efficiency of the direct-fired heating furnace is improved by 5%. Further, since the combustion is performed while monitoring the temperature, the refractory material is not deteriorated, and highly efficient heating can be realized.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a configuration of a hot dip galvanizing facility provided with a continuous heat treatment facility of the present invention.

FIG. 2 is an explanatory view showing the arrangement of auxiliary burners in the pre-tropical zone of FIG.

FIG. 3 is an explanatory diagram showing an example of a gas temperature distribution from a pre-tropical zone inlet side to an open flame heating zone outlet side.

[Explanation of symbols]

 1 Continuous heat treatment equipment 2 Pre-tropical zone 3 Direct heating zone 4 Soaking zone 5 Slow cooling zone 6 Quenching zone 8 Hot dip galvanizing equipment 9 Hot dip galvan pot 10 Non-oxidizing burner installation range 11 Burner arrangement position for untwisted gas 12 Untwisted Placement of burner for gas combustion 13 Recuperator 14 Exhaust gas blower 15 Chimney 16 Furnace wall 17 Burner for combustion of untwisted gas 18 Thermometer a Combustion exhaust gas from open flame heating zone b Combustion exhaust gas after untwisted gas combustion s Steel Zone In-furnace gas temperature distribution according to the present invention In-furnace gas temperature distribution according to the conventional method Steel strip temperature distribution according to the present invention Steel strip temperature distribution according to the conventional method

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yuji Enda 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Corporation Stock of Kimitsu Steel Co., Ltd.

Claims (2)

[Claims] 1. In an unburned exhaust gas combustion using a direct-fire continuous steel strip heat treatment apparatus operating at a combustion air ratio of 1.0 or less,
Combusting while controlling the amount of air blown for burning the untwisted portion in the exhaust gas so that the maximum temperature of the refractory material constituting the furnace body falls within a temperature range 20 ° C to 100 ° C lower than the service temperature. A continuous heat treatment method characterized by: 2. Combustion air is passed through at least 2 in the direction of the steel strip.
The air is blown from a plurality of positions or more.
The continuous heat treatment method for a steel strip according to.