JPH05287369A - Burner for directly firing reduction heating and method for directly firing reduction heating - Google Patents

Abstract

PURPOSE:To provide a directly firing reduction heating burner and a reduction heating method, having the reduction zone in stable and wide range at the time of heating a steel strip. CONSTITUTION:At the time of heating the steel strip in a heating furnace by the burner provided with a nozzle composed of plural round-shape discharging holes 2 at the right angle in the tangential direction to a fuel gas passage in the discharging nozzle part at the outlet side of the fuel gas in an inner pipe 3 and to an air flow passage in an outer pipe 4 in the burner, the fuel gas is flowed at the right angle in the tangential direction to the air flow to execute reduction heating to the steel strip. By this method, the steel strip can always be operated in the reduction range and can uniformly be reduction-heated and the stable surface quality on the steel strip is always obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a burner for direct flame reduction heating of thin steel sheets and a direct flame reduction heating method.

[0002]

2. Description of the Related Art As a burner for direct-heating reduction heating and a method of using the burner, for example, Japanese Patent Laid-Open No. 60-779929 discloses an oxide film on the surface of a thin steel sheet by a diffusion burner in which combustion gas is used as an internal flow and air is used as an external flow. Is described to be reduced. Further, as a burner for direct-fire reduction heating and a method of using the burner, Japanese Patent Application Laid-Open No. 3-69972 discloses a fuel gas (or air) in an inner tube and air (or fuel gas) in an outer tube with respect to a central axis of the burner. Direct heating reduction burner and its method in which the air ratio is adjusted to 0.7 to 0.9 and the distance between the steel strip and the bottom of the burner tile is adjusted to 100 to 400 mm for heating. ing.

[0003]

Problems to be Solved by the Invention JP-A-60-7792
In the direct-fire reduction heating method according to Japanese Unexamined Patent Application Publication No. 9-96, the reduction area is narrow, and particularly when the sheet passing speed of the thin steel sheet is high, the thin steel sheet vibrates and deviates from the reduction area, and it is difficult to uniformly reduce and heat the surface of the thin steel sheet. Becomes Further, the thin steel sheet comes into contact with the burner tile, and the surface is flawed to deteriorate the quality. As a solution to this problem, in the burner for direct-fire reduction heating and the method for direct-fire reduction heating according to the above-mentioned Japanese Patent Laid-Open No. 3-69972, a wide reduction region can be obtained when the sheet passing speed of the thin steel sheet is slow, but the sheet passing speed is When applied to a fast heating furnace, a wider reduction area is desired. In order to solve the above problems, the present invention solves a reduction heating burner and a reduction heating method which are stable and have a reduction region in a wide range.

[0004]

SUMMARY OF THE INVENTION A gist of the present invention is a burner for heating a thin steel plate in a heating furnace, wherein a fuel gas outlet side of an inner tube is provided with respect to an air flow path of an outer tube in the burner. The burner for direct-fire reduction heating is characterized in that the discharge nozzle portion is provided with a nozzle formed of a plurality of circular discharge holes at right angles to the tangential direction to the fuel gas flow path.

Further, according to the present invention, when the thin steel sheet is heated in the heating furnace, the fuel gas is provided with a plurality of circular shapes perpendicular to the flow direction of the fuel gas in the tangential direction with respect to the flow direction of the air in the burner. A direct-fire reduction heating method, characterized in that a fuel gas is flown from a nozzle, mixed with the air, and the thin steel sheet is reduced and heated.

[0006]

When the nozzle burner of the present invention is used, the fuel gas can be uniformly split and made to be orthogonal to the air flow, so that the contact area between the fuel gas and air is increased, and the fuel gas and air are strongly mixed. As a result, the fuel gas and the air can be uniformly mixed in the mixed gas discharge hole, unreacted oxygen having oxidizing power in the flame is reduced, and the reducing ability can be maintained or improved to widen the reducing region.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A cross-sectional view of an embodiment burner of the present invention is shown in FIG. FIG. 2 shows an AA cross section of FIG. 1, FIG. 3 shows an enlarged view of the discharge nozzle 7 in FIG. 1, and FIG. 4 shows a BB cross section of FIG. In FIG. 1, the burner tile bottom portion 1 is provided with a double-structure burner including a mixed gas discharge hole 2 of a fuel gas and air, an inner pipe 3, and an outer pipe 4.

Fuel gas (or air) flows in the inner pipe 3 in the burner in parallel with the burner axis, but the circular shape of the fuel gas (or air) provided in the tangential direction of the discharge nozzle 7 The flow is branched from the discharge hole 5. Air (or fuel gas) flows in the outer tube 4 in parallel with the burner axis. The split fuel gas (or air) and air (or fuel gas) are mixed in the fuel gas and air mixing section 6 at right angles. The mixed gas of the fuel gas and the air flows into the mixed gas discharge hole 2 through the mixed gas uniform portion 8.

FIG. 2 shows the case where the mixed gas discharge holes 2 are five holes. In the figure, the mixed gas discharge holes 2 are evenly arranged in the circumferential direction around the center. An enlarged view of the discharge nozzle 7 is shown in FIG. 3, and a sectional view of the discharge nozzle 7 is shown in FIG.

In FIG. 3, the fuel gas flows in a direction perpendicular to the discharge nozzle 7 from the circular discharge hole 5 provided in the discharge nozzle 7, and mixes at right angles with the air. In FIG. 4, the fuel gas is evenly distributed in the tangential direction of the discharge nozzle 7 from the circular discharge hole 5 provided in the discharge nozzle 7.

Next, the numerical analysis of the mixed state of the fuel gas and air of the burner of the present invention will be described. Numerical analysis is PHOENICS (Parablic Hyper), which is a thermal-hydraulic analysis software of CHAM, which is often used for flow analysis.
bolic Or Elliptic Numeric
al-Integrar-ation Code Seri
es), and a two-dimensional steady model of laminar flow in a cylindrical coordinate system. An example of numerical analysis of the mixed state of fuel gas and air is shown below.

As an example of calculation, LPG is used as the fuel gas,
Fuel gas velocity 1.9m / s, air velocity 22.0m / s
Numerical analysis was performed on the mixed state of fuel gas and air at an air ratio (amount indicating how many times the stoichiometric ratio of air was supplied to a fixed amount of fuel) 0.8.

FIG. 9 shows a schematic diagram of the gas flow in the fuel gas / air mixing portion 6 and the mixed gas uniform portion 8 of the burner of the present invention. The arrows in the figure indicate the flow directions of fuel gas, air, and a mixed gas of fuel gas and air. In the mixed gas uniform portion 8, the mixed gas of the fuel gas and the air is recirculated and the residence time is increased, so that the mixing property is promoted.

Ratio of fuel gas in the mixed gas discharge hole 2 of the burner of the present invention (ratio of fuel gas in the mixed gas)
Is shown in FIG. In FIG. 11, the horizontal axis represents the radial distance from the center of the mixed gas discharge hole 2, and the vertical axis represents the fuel gas ratio. Since the difference in the fuel gas ratio between the center and the end of the mixed gas discharge hole 2 is small, the fuel gas is evenly distributed.

An example of reduction heating experiment of a thin steel sheet using the burner of the present invention will be shown below. Vertical 22 pre-oxidized in the atmosphere
The reducibility of the surface of a thin steel plate having a thickness of 0 mm, a width of 220 mm, and a thickness of 1.6 mm is shown in relation to the air ratio and the distance from the burner tile bottom 1. Using a burner with 5 mixed gas discharge holes, fuel: L
PG, burning capacity: heated at 50,000 kcal / h, the reduction area is the gloss color of the steel sheet surface, that is, if the oxide film on the steel sheet surface is reduced after heating and the surface exhibits a metallic luster, the reduction area (○ mark), If the surface became black due to an increase in the oxide film, it was evaluated as an oxidized region (x mark).

FIG. 13 shows the reduction region in the burner of the present invention. The horizontal axis of FIG. 13 represents the distance from the burner tile bottom portion 1, and the vertical axis represents the air ratio. The burner of the present invention has a reduction region with an air ratio of 0.7 to 0.95 and burner tile bottoms 1 to 10
The reduction region exists in a wide range of 0 to 500 mm.

For comparison, a conventional burner in which fuel gas and air are flown in parallel to the central axis of the burner is used under the same conditions for the flow rates of the fuel gas and air of the present invention. A flow analysis is shown. FIG. 10 shows a gas flow state in the mixed gas uniform portion 8 of the conventional burner. As shown in FIG. 10, in the mixed gas uniform portion 8, the air and the fuel gas flow in parallel, so the contact area between the air and the fuel gas is small and the residence time of the mixed gas is short, so that the fuel and the air cannot be mixed uniformly. ..

The fuel gas ratio at the mixed gas discharge hole 2 is shown in FIG.
2 shows. The horizontal axis in FIG. 12 represents the distance in the radial direction from the center of the mixed gas discharge hole 2, and the vertical axis represents the fuel gas ratio.
As shown in FIG. 12, in the mixed gas discharge hole 2, the mixed gas is non-uniform and unmixed because the difference in the combustion gas ratio between the center and the end of the hole is large. Compared to the present invention, the conventional burner
Inadequate mixing of fuel gas and air.

Next, an example of a reduction heating experiment of a thin steel sheet will be shown below, in which the combustion conditions are the same in the same method as the reduction heating experiment of the present invention in the conventional burner in which the fuel gas and the air are made to flow parallel to the central axis of the burner. .. FIG. 14 shows the reduction area in the conventional burner. The horizontal axis of FIG. 14 represents the distance from the burner tile, and the vertical axis represents the air ratio. In the conventional burner, the reduction area has an air ratio of 0.7 to 0.9 and 100 to 400 from the bottom of the burner tile.
There is a reducing region in the range of mm, and the reducing ratio is inferior to that of the present invention when the air ratio is 0.9 or more and the reducing region is not seen at 400 mm or more from the bottom of the burner tile.

The discharge hole nozzles used in the embodiments of the present invention have been described with respect to four discharge holes. However, if the discharge holes are tangential, air and fuel gas can be sufficiently mixed, so that there are five discharge holes. It is also possible to use eight to eight multi-hole nozzles, and the outer shape of the discharge hole nozzle has been described as a circular shape, but it may be a polygonal shape as long as the contact area between air and fuel gas can be sufficiently taken.
Furthermore, the selection of the mixed gas discharge holes used in the present invention is defined by the size of the burner diameter, and the reduction ability does not change even if the number of holes is not limited to 5 in FIG.

[0021]

By using the burner of the present invention, a reduction region can be obtained in a wide range, so that the thin steel plate can always be operated from the reduction region due to vibration of the thin steel plate and the like, and the reduction heating can be performed uniformly. Further, since the distance between the burner tile and the thin steel plate can be widened, stable sheet passing can be performed without the thin steel plate coming into contact with the burner tile, and a stable quality of the thin steel plate surface can always be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of a burner of the present invention.

FIG. 2 is a front view of FIG.

FIG. 3 is a sectional view of the nozzle shape of the present invention.

FIG. 4 is a front view of FIG.

FIG. 5 is a sectional view of a conventional diffusion burner.

FIG. 6 is a front view of FIG.

FIG. 7 is a cross-sectional view of a nozzle shape of a conventional burner.

FIG. 8 is a front view of FIG.

FIG. 9 is an example of gas flow analysis results in the mixing section of the burner of the present invention.

FIG. 10 is an example of a gas flow analysis result in a mixing section of a conventional burner.

FIG. 11 is a chart of a fuel gas ratio (analysis example) in a mixed gas discharge part of the burner of the present invention.

FIG. 12 is a chart of a fuel gas ratio (analysis example) in a mixed gas discharge part of a conventional burner.

FIG. 13 is a chart of an example of a heating experiment result by the burner of the present invention.

FIG. 14 is a chart of an example of a heating experiment result using a conventional diffusion burner.

[Explanation of symbols]

 1 Burner tile bottom 2 Mixed gas discharge hole 3 Inner pipe 4 Outer pipe 5 Discharge hole 6 Mixing part of fuel gas and air 7 Discharge nozzle 8 Uniform part of mixed gas

Claims (2)

[Claims] 1. A burner for heating a thin steel sheet in a heating furnace, wherein a discharge nozzle portion of a fuel gas outlet side of an inner tube is in a fuel gas flow path with respect to an air flow path of an outer tube in the burner. The burner for direct-fire reduction heating is characterized in that it is provided with a nozzle formed of a plurality of circular discharge holes at right angles to the tangential direction. 2. When a thin steel plate is heated in a heating furnace, a plurality of circular nozzles are provided in which a fuel gas is tangential to the flow of fuel gas in a direction perpendicular to the direction of air flow in the burner. A direct-fire reduction heating method comprising flowing a fuel gas, mixing the air with the air, and reducing and heating the thin steel sheet.