JPH0441623A - Direct-fired heating furnace for steel strip - Google Patents

Abstract

PURPOSE:To reduce the equipment cost and to facilitate furnace pressure control by arranging plural direct-fired heating zones to the traveling direction of a steel strip in the direct-fired heating furnace and providing a waste combustion gas duct communicating with a preheating furnace between the adjacent heating zones. CONSTITUTION:The direct-fired heating zone of a direct-fired heating furnace 3 is bisected into the upper heating zone 13 and the lower heating zone 14, and a group of burners (not shown in the figure) directed toward a band steel S are arranged to the traveling direction of the steel. A separation zone 16 is formed between the heating zones 13 and 14, a waste combustion gas duct 18 communicating with the preheating furnace 2 is provided, the cross-sectional area of the duct 18 is equalized to that of the furnace chamber of the heating furnace 3, and a flow control valve 19 is furnished to the duct. Consequently, the waste combustion gas (b) from the lower heating zone 14 and a part of the waste combustion gas (a) from the upper heating zone 13 are passed through the separation zone 16 and introduced into the preheating furnace 2 through the duct 18.

Description

[Detailed description of the invention] [Industrial application field] This invention relates to a direct-fire heating furnace for steel strip.

The present invention is utilized in continuous annealing lines for cold-rolled deep-drawn steel sheets, stainless steel sheets, heat treatment lines for electrical steel sheets, hot-dip plating lines including continuous heat treatment, and the like.

[Prior Art] Some continuous heat treatment equipment for steel strips is equipped with a direct heating furnace instead of an indirect heating furnace using a radiant tube. A direct-fire heating furnace is equipped with a group of burners directed toward the surface of a running steel strip, and directly heats the steel strip with combustion flame from the burners. Further, a non-oxidizing combustion burner is used as a burner. The non-oxidizing combustion burner directly heats the steel strip with a combustion flame, prevents the formation of oxidized scale, and further reduces the amount of scale by reducing the oxidized scale that has already been generated.

For direct-fired heating furnaces, it is desirable that the combustion flame from the burner is not disturbed. If the combustion flame is turbulent, the steel strip may not be fully exposed to the reducing area of the combustion flame, reducing its reducing ability. On the other hand, in a direct-fired heating furnace, a draft is added that goes toward the entrance side of the steel strip (in the opposite direction to the direction in which the steel strip passes).
The combustion exhaust gas flows toward the entrance side of the steel strip. therefore,
The combustion flame F of the burner 23a located closer to the steel strip entry side is
As shown in Figure 4, the burner 2 flowing from the steel strip outlet side
The flow is disturbed by the combustion scum G of No.3. Due to the turbulence of the combustion flame F, the reducing ability decreases as described above.

Techniques for solving such problems include those disclosed in, for example, Japanese Unexamined Utility Model Publication No. 59-9074, Japanese Unexamined Patent Publication No. 59-59833, or Japanese Unexamined Patent Publication No. 62-20828.

The direct-fired heating furnace for steel strip disclosed in Japanese Utility Model Application Publication No. 59-9074 has a combustion gas flow from a burner that crosses the length direction of the steel strip and the direction in which the heated waste flow is formed. There are partitions to guide you in the right direction.

The direct-fire heating furnace for steel strips disclosed in Japanese Patent Application Laid-Open No. 59-59833 has a plurality of pairs of exhaust gas ports facing each other on each of the facing side walls of the heating chamber. After heating the steel strip, the combustion exhaust gas is discharged from the furnace through the exhaust gas port located above and close to the burner.

Furthermore, in the continuous annealing furnace disclosed in JP-A No. 62-20828, intermediate chambers are provided between the preheating furnace and the direct-fired furnace and between the direct-fired furnace and the indirect heating furnace to prevent the movement of gas in the furnace. It is set up. Additionally, an afterburning chamber is provided in which the combustion exhaust gas in the direct-fired furnace is completely combusted and supplied to the preheating furnace.

[Problems to be Solved by the Invention] The direct-fire heating furnace for steel strips disclosed in Japanese Utility Model Application Publication No. 59-9074 had the following problems. Generally, in order to make the furnace body compact, the distance between the steel strip surface and the furnace wall surface is not very large, for example, about 50 to 300 mm. Additionally, the steel strip running at high speed inside the furnace may flap due to air currents. Therefore, there is a risk that the steel strip may come into contact with the partition and cause plate flaws or damage the partition.

In the direct-fire heating furnace for steel strips disclosed in Japanese Patent Application Laid-Open No. 59-511833, the exhaust gas port penetrates the side wall of the heating chamber, and the penetrating portion needs to be airtight. Furthermore, exhaust gas channels must be provided outside the heating chamber. Therefore, the structure of the furnace becomes complicated and the equipment becomes expensive.

The continuous annealing furnace disclosed in Japanese Patent Application Laid-open No. 62-20828 has an intermediate chamber, so the flue for the flue gas becomes long, and an afterburning chamber, which makes the equipment expensive. Furthermore, by providing an intermediate chamber or an afterburning chamber, the flow path for the combustion waste becomes long and complicated, which reduces the accuracy and responsiveness of furnace pressure control, making furnace pressure control complicated and difficult.

Therefore, the present invention aims to reduce equipment costs, facilitate furnace pressure control, and provide continuous heat treatment equipment for steel strips that does not cause plate defects.

[Means for Solving the Problems] The direct-fired heating furnace for steel strip of the present invention includes a direct-fired heating furnace connected to the outlet side of a preheating furnace, in which a group of burners facing the steel strip is arranged along the steel strip threading direction. In the heating furnace, a plurality of direct-fired heating zones having approximately equal lengths are arranged along the steel strip threading direction, and a combustion exhaust gas duct is provided to communicate between adjacent direct-fired heating zones and the preheating furnace. There is.

The number of direct-fired heating zones is determined by the cross-sectional area of the furnace chamber of the direct-fired heating furnace, the combustion capacity of the burner, the draft strength, etc. The greater the number of direct-fired heating zones, the less disturbance of the burner combustion flame caused by the combustion exhaust gas, but the more complicated the structure of the furnace becomes.

From these points, it is appropriate that the number of direct flame heating zones be about 2 to 3. The lengths of the open flame heating zones may be equal to each other, or may be slightly different from each other.

The cross-sectional area of the combustion exhaust gas duct is approximately equal to the cross-sectional area of the furnace chamber of the direct-fired heating furnace. A flow rate regulating valve or a throttle valve may be provided in the middle of the combustion exhaust gas duct. The flow rate adjustment valve or throttle valve adjusts the flow rate of the combustion waste flowing from the direct-fired heating furnace to the preheating furnace via the combustion exhaust gas duct.

The direct-fired heating furnace may be vertical or horizontal.

[For I] It is assumed that there are two direct flame heating zones: an upper heating zone and a lower heating zone. Because the draft applied to the direct-fired heating furnace causes the flue gas to flow back toward the entrance side of the furnace, most of the flue gas in the upper heating zone flows through the inlet side of the direct-fired heating furnace into the preheating furnace. On the other hand, the combustion waste from the lower heating zone and part of the combustion waste from the upper heating zone (generated near the exit side of the upper heating zone) pass through the separation zone that separates the upper and lower heating zones.
The flue gas flows into the preheating furnace through the flue gas duct.

The flow rate of the combustion exhaust gas on the inlet side of the upper heating zone is approximately 1/2 of the combined flow rate of the combustion exhaust gas in both the upper and lower heating zones, and therefore the flow rate is also approximately 1/2. As a result, turbulence of the burner combustion flame in the upper heating zone due to the flue gas flow is significantly reduced. Note that since the flow rate of the combustion exhaust gas on the inlet side of the lower heating zone is the flow rate of the combustion exhaust gas generated in the lower heating zone, the turbulence caused by the combustion exhaust gas flow of the burner combustion flame is small.

The same applies if there are two or more open heating zones.

[Example] Fig. 1 is a schematic diagram of a melt wiping facility equipped with a continuous heat treatment facility according to the present invention.

As shown in FIG. 1, the continuous heat treatment equipment 1 includes a preheating furnace 2, a direct-fired heating furnace 3, a soaking furnace 4, a slow cooling furnace 5, and a rapid cooling furnace 6. The hot-dip plating equipment 8 is provided following the continuous heat treatment equipment 1 and includes a hot-dip plating bath 9.

FIG. 2 is a longitudinal sectional view showing details of the direct-fired heating furnace 3. As shown in FIG.

The inlet side of the direct-fired heating furnace 3 is connected to the preheating furnace 2 via a connecting passage 11.
Further, the outlet sides are respectively connected to soaking furnaces (reference numeral 4 in FIG. 1) via connecting passages 21. The direct-fired heating zone of the direct-fired heating furnace 3 is equally divided into two, an upper heating zone 13 and a lower heating zone 14. In each heating zone 13, 14, a group of burners (not shown) facing the steel strip S are arranged along the steel strip threading direction. Between the two-jaw tropics 13 and 14 there is a separation zone]6. A combustion exhaust gas duct 8 is provided between the preheating furnace 2 and the separation zone 16 to communicate them. The cross-sectional area of the combustion waste duct 18 is equal to the cross-sectional area of the furnace chamber of the direct-fired heating furnace 3. Further, a flow rate regulating valve 19 is attached to the combustion exhaust gas duct 18. The flow rate adjustment valve 19 adjusts the flow rate of the flue gas b flowing into the preheating furnace 2 via the flue gas duct 18, and maintains the pressure difference between the preheating furnace 2 and the separation zone 16 at an appropriate value.

In the direct-fired heating furnace 3 configured as described above, the flue gas flows backward toward the furnace entry side due to the raft applied to the direct-fired heating furnace 3, so that the flue gas a in the upper heating zone 13
Most of it flows into the preheating furnace 2 via the inlet side of the direct-fired heating furnace 3. On the other hand, part of the combustion exhaust gas b in the lower heating zone 14 and the combustion exhaust gas a in the upper heating zone 13 pass through the separation zone 16 and flow into the preheating furnace 2 via the combustion exhaust gas duct 18.

The flue gas flow rate at the entrance side of the upper heating zone 13 is approximately 1/2 of the combined flue gas flow rate of both jaws 13 and 14, and is due to the flue gas flow of the burner combustion flame in the upper heating zone 13. Disturbances are significantly reduced. In addition, lower heating zone 1
Since the combustion exhaust gas flow rate on the inlet side of No. 4 is the flow rate of the combustion exhaust gas generated in the lower heating zone 14, the turbulence caused by the combustion exhaust gas flow of the burner combustion flame is small.

FIG. 3 shows an example of plating evaluation of a product hot-dipped with zinc using equipment including the above-mentioned direct-fired heating furnace 3, in comparison with a case using a conventional direct-fired heating furnace.

According to this invention, the scale thickness of the plating original plate is 100
As a result, plating defects due to scale adhesion on the plating original plate hardly occurred. On the other hand, in a conventional direct-fired heating furnace, the scale thickness of the plated original plate was 1000 mm. Additionally, scale from the plating original plate did not adhere to the hearth roll installed in the direct-fired heating furnace.

[Effects of the Invention] According to the present invention, a part of the combustion exhaust gas is extracted by the combustion exhaust gas duct and bypassed to the preheating furnace, and the flow rate of the combustion exhaust gas flowing through the upper direct-fired heating zone is reduced, thereby reducing the turbulence of the combustion flame. I try to prevent this. Therefore, there is no need to provide an exhaust gas passage outside the heating chamber, a cutoff inside the heating chamber, an intermediate chamber, or an afterburning chamber, so the structure of the furnace body is simplified, and equipment costs can be reduced. Furthermore, furnace pressure control becomes easier. Further, since there are no protruding objects such as partitions in the heating chamber, there is no possibility that the steel strip will hit against any protruding objects and cause flaws.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of a melt-blanking facility equipped with continuous heat treatment equipment including a direct-fired heating furnace of the present invention, and Fig. 2 is a vertical cross-sectional view of the direct-fired heating furnace of the continuous heat treatment equipment shown in Fig. 1. , Fig. 3 is a diagram showing an example of plating evaluation of a product hot-dipped with zinc using the equipment including the direct-fired heating furnace of the present invention, in comparison with a case using a conventional direct-fired heating furnace, and Fig. 4 is a diagram illustrating the results of plating evaluation from the burner. 2 is a diagram illustrating a state in which a combustion flame of a combustion engine is disturbed by combustion exhaust gas. 1... Continuous heat treatment equipment, 2... Preheating furnace 2.3...
Direct-fired heating furnace, 4... Soaking furnace, 5... Slow cooling furnace, 6...
・Quiet cooling furnace, 8...Hot-dip coating equipment, 9...Hot-dip plating tank, Moon...Connection path, I 3-...Upper heating zone, +
4--Lower heating zone, ]6--Separation zone, I8--Combustion exhaust gas duct, 19--Flow rate adjustment valve, 21--Connection path, 23--Burner a--Upper heating zone Combustion exhaust gas, b: Combustion exhaust gas from the lower heating zone, F-: Combustion flame from the burner, G: Combustion exhaust gas, S: Steel strip.

Claims (1)

[Claims] 1. In a direct-fired heating furnace connected to the outlet side of the preheating furnace and in which a group of burners facing the steel strip are arranged along the steel strip threading direction, a plurality of direct-fired heating strips of approximately equal length are connected to the steel strip threading direction. A direct-fired heating furnace for steel strip, characterized in that a combustion exhaust gas duct is arranged along the plate direction and communicates between adjacent direct-fired heating zones and the preheating furnace.