JPS58107425A - Method of heating steel strip without oxidation and apparatus therefor - Google Patents

Abstract

PURPOSE:To perform the efficient unoxidizing heat-treatment of a steel strip, in direct flame-type unoxidizing heat-treatment in an apparatus for continuously annealing the steel strip or the like, by making a nozzle for gas fuel movable in a radiant burner and setting the injection angle of air at a specified value. CONSTITUTION:When a steel strip is heated under an unoxidized condition in a continuous annealing oven, a continuous hot-dip zinc-coating apparatus or the like for the steel strip, it is heated by a radiant burner. At the side wall 11a of a burner tile forming the combustion chamber C for a cylindrical burner 11, a plurality of openings 13 for ejecting air A are provided with an angle theta of 60 deg. at most to he connection of the side wall 11a of the tile. Burner nozzles 12 provided with a plurality of openings 14 for ejecting gas fuel F are slidable provided along the axial line, and their top ends are set close to the rear wall 11b of the titled. Combustion is performed by controlling the flow ratio of the air A to the fuel F above 1.5 and the ratio of air below 1.0, to heat the entire inner surface of the combustion chamber C. Consequently, the steel strip is heated under an unoxidized condition with excellent thermal efficiency without the need to previously mix air and fuel.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for non-oxidizing heating of a copper strip.

Continuous annealing furnace for copper strips, continuous galvanizing equipment (CGL)
Conventional direct-fire non-oxidation heating methods, such as those in There is a method of heating the tile by raising the temperature of the inner surface of the tile, mainly through radiation heat transfer from side to side.

As shown in Fig. 1, the high-speed jet burner burns in a combustion chamber 1, ejects a high-temperature gas jet from a narrowed discharge hole 2, and heats the object mainly by convection heat transfer. It has the characteristic of obtaining high heat flux in a relatively low range.

On the other hand, the flame during the combustion reaction hits the copper strip directly, so
Even if the O, O, OH, etc. present in it are non-oxidized, molding is unavoidable.

Radiant burners perform rapid combustion reactions, so
The ffI & metallic air, which has been heated in advance with air and fuel gas, is heated in the second
As shown in the figure, rapid combustion is carried out in the hemispherical recess 3 of the burner tile, the inner surface of the burner tile is heated, and heating is mainly done by radiation heat transfer, which results in high heat flux in areas where the temperature of the heated object is high. It has the characteristics of On the other hand, in this burner, by burning O32 at an air ratio of t,
Since the combustion gas contains reducing unburned components such as CO, H, etc., this combustion gas can not only contact the copper strip and heat it without oxidation, but also reduce the oxide film formed on the copper strip. can do.

Although Radiant-Su is a burner suitable for non-oxidative heating as described above, it has many drawbacks because it is a premixing method. That is, it is dangerous to premix air preheated to a high temperature with fuel gas, and the sensible heat of the exhaust gas must be used to preheat the air. Also, preheating the air is effective in increasing the flame temperature, while increasing the flame temperature is effective for reducing the above-mentioned Co, H, etc., but since air preheating is not possible, non-oxidizing It is also not preferable from the viewpoint of heating.

Furthermore, a premixer, a flashback preventer as a safety device, etc. are indispensable], which raises the problem of increased equipment costs.

Figure 3 shows a CGL heating furnace using a radiant burner. This heating furnace is a three-zone heating furnace consisting of three zones: a first zone 4, a second zone 1, and a third zone 6. In the first zone 4 and the second zone 5, the temperature of the copper strip is relative. Since the oxidation rate of the copper strip is low and the oxidation rate of the copper strip is low, we use a diffusion burner that mainly uses convection heat transfer to obtain high heat flux in a relatively low temperature range, and the combustion air is preheated using exhaust gas as a heat source. Preheat in vessel 1. In the third zone d, a radiant burner mainly using radiant heat transfer is used to reduce the heated and slightly oxidized copper strip that comes in, and to obtain a high heat flux in a high temperature region. This burner has a premixer 8
The mixed warehouse air is fed through a flashback preventer. As mentioned above, in order to save energy, burners with different heat transfer mechanisms are used depending on the temperature of the copper strip, so the piping equipment is complicated), and separate combustion control devices are required for each, so the equipment There are many negative aspects to the above.

This invention was made in view of the above-mentioned circumstances, and its purpose is to provide a method and apparatus for non-oxidizing heating of a steel strip (using a burner) that does not require premixing of air and fuel gas. That is.

The feature of the non-oxidation heating method of steel strip of this invention is that when air is discharged from the side wall of the circle IIl lacquered burner tile so as to generate a swirling flow, a cloudy fuel gas is discharged radially from the center of the burner perpendicularly to the axial direction. In addition, the heating device should be heated at a discharge flow velocity ratio of air and fuel gas of 1.5 or more and an air ratio of 1.0 or less, and the heating device should be attached to the side wall of the cylindrical burner tile along a tangent to the side wall. A burner nozzle is provided with an air discharge hole at a maximum angle of 60 degrees to the burner, and the burner nozzle has a gas discharge hole that discharges fuel gas radially perpendicularly to the axial direction from the center of the burner. It is provided so as to be slidable in the axial direction so that the relative position can be changed.

An embodiment of the present invention will be described below with reference to FIGS. 4 and 5. In the figure, reference numeral 11 denotes a main body of a cylindrical burner with one end open forming a combustion chamber C, and a burner nozzle 11 is provided at the center of the burner so as to be slidable in the axial direction. Burner body J7
A plurality of discharge holes 11 for air A that open the combustion chamber CK are provided in the burner tile side 1111 & in the circumferential direction,
This discharge hole 13 is tile 1! The angle I with respect to the tangent to J J a is within a maximum range of 60 degrees. A plurality of gas discharge holes 14 are provided at the tip of the burner nozzle 11 to discharge the fuel gas F radially perpendicularly to the axial direction.

Then, as shown in FIG. 4, retract the burner nozzle 12,
Move the position of the gas discharge hole 14 closer to the tile 4 [11b,
In the state shown in (■) where the air discharge hole IJ is different from the one shown in FIG.
/V, ≧1.5K, the fuel gas r and the air mixture are sufficiently mixed, a flame is formed immediately near the rear surface of the burner tile JJb, and a flame is further formed by the discharged air. The rapid rotation causes the entire inner wall of the combustion chamber C to be heated. As a result, heat transfer characteristics dominated by radiation heat transfer, similar to those of conventional radiant burners, can be obtained. Furthermore, convective heat transfer is also promoted by the high temperature combustion gas that has completed the combustion reaction being rapidly swirled and colliding with the copper strip.

And air ratio 1. By burning at less than O), the oxidized copper strip can be reduced with unburned components such as Co, H, etc. in the high temperature combustion gas, and the copper strip can be efficiently heated without oxidation.

In this case, if the angle of the air discharge hole 11 with respect to the tangent to the side wall is gradually increased, the swirling area will be small and the swirling flow will be disturbed by the jets from the individual discharge holes 1j, making it impossible to obtain a preferable swirling flame. , its upper limit is 60 degrees. On the other hand, if the angle is gradually reduced, as the temperature approaches zero, most of the flame will be attached to the tile side *ix*, and the required flame temperature will no longer be obtained. According to experimental results, a range of 20 to 40 degrees is suitable. Furthermore, if the flow velocity ratio Va/Vl of air and fuel gas is less than 1.5, the flame will be formed radially from the gas discharge hole 14).
The mixture of air and gas becomes insufficient, and the flame extends for a long time from the burner outlet, making it impossible to obtain desired heat transfer characteristics.

According to experimental results, the flow rate ratio is preferably 2 to 3 or more.

Regarding the air ratio, non-oxidative heating of the copper strip is impossible if O3 is present in the flame or combustion gas, so the air ratio is set to 1.0 or less and combustion is performed with less than the theoretical air amount. By doing this, 0.0% is added to the combustion gas. It is possible to perform non-oxidative heating by creating a state in which Co, H, etc. are absent and reducing Co, H, and so on are present.

Next, the results of tests conducted by changing the relative positions of the gas discharge hole 14 and the air discharge hole 13 will be described.

Combustion conditions: Fuel gas; coke oven gas 4700&a/Nrl, air temperature; normal temperature (without preheating)
.

Air ratio: 1.00, combustion amount: 3G000&J/h
The state shown in FIG. 4 where the gas discharge hole 14 and the air discharge hole 1z are aligned, θ The gas discharge hole 14 is moved 15 m from the air discharge hole 12 toward the open end of the sipana, that is, on the downstream side.
The state shown by the imaginary line in Fig. 4 and the radiant burner (Kurei 2) with the conventional @ high-speed jet burner (see Fig. 1)
(See figure) Test results: Burner tile inner surface temperature, burner outlet gas temperature. The flame length (distance from the burner outlet to the flame tip) is shown in the table below, and the heat flux qlo'& j as a function of the temperature of the heated object.
/7·hr is shown in FIG. 6, and the non-oxidation heating characteristics are shown in FIG. 7.

From the table and FIG. 6, it is clear that the gas discharge holes 14 are
In the state (2), which is close to , the heat transfer characteristics are dominated by radiation heat transfer as described above, and a high heat flux is obtained when the copper band temperature is high. On the other hand, in the state θ where the gas discharge hole 14 is moved toward the burner outlet side, a flame, that is, a combustion reaction zone is formed downstream of the air discharge hole IJ, and the burner tile rear wall 11b is hardly heated, and the burner tile rear wall 11b is heated accordingly. Since the combustion gas is obtained and the air plate is given rapid t11 times, the heat transfer characteristics are dominated by convective heat transfer, where the copper strip is heated by the convective heat transfer of the main combustion gas. High heat flux is obtained when the copper band temperature is low. In addition, in the state @ where the discharge hole 14 and the air discharge hole lJ are at the same position, a combined radiation and convection type heat transfer characteristic between the above and θ is obtained. Next, in Figure 7, the horizontal axis shows heating time,
The vertical axis shows the copper strip temperature, and the x mark indicates the non-oxidizing heating limit point, which indicates that the copper strip will oxidize if heated for a long time or if the steel strip temperature I is higher than this limit point. ■ of the burner of the present invention.

In the state of θ, the heating heat flux q is larger than that of a conventional radiant burner, so the heating rate is fast and the copper strip can be heated to a higher temperature without oxidation. Note that if air preheating is performed, non-oxidative heating to even higher temperatures is possible.

As described above, the burner of the present invention has the same parts t-e, j
By simply sliding the 14c burner nozzle 12, the heat transfer mechanism can be changed to obtain an appropriate heat flux depending on the temperature of the object to be heated, and high heating efficiency can be obtained. Moreover, the non-oxidation heating characteristics can be improved compared to the conventional method.

Therefore, with a three-zone copper zone heating furnace divided into three zones,
In order to obtain the highest heat flux depending on the copper strip temperature, the present burner is operated in the θ state in the first zone, the ◎ state in the second zone, and the Φ state in the third zone. The copper strip can be heated efficiently. In addition, it is possible to recover the sensible heat of the exhaust gas by preheating the air without requiring premixing of air and fuel gas, and the reduction action is promoted by increasing the temperature of the combustion gas. It can be heated in the state of Furthermore, equipment costs can be reduced by not requiring any special equipment for premixing, and by using the same type of piping equipment, control equipment, etc. for each zone. In addition, depending on the heating state of the copper strip, the first. The second zone may be omitted.

The present invention is as described above, and can efficiently heat a copper strip without oxidation using a diffusion type rotary burner without requiring premixing of fuel gas and air.

Furthermore, by sliding the burner nozzle and using it as a burner having heat transfer characteristics τ according to the heating temperature of the copper strip), the copper strip can be heated most efficiently.

[Brief explanation of drawings]

1 and 2 are cross-sectional views of a conventional high-speed jet burner and a radiant burner, respectively, FIG. 3 is an explanatory diagram of a three-zone steel strip heating furnace, and FIGS. 4 and 5 are cross-sectional views of a conventional high-speed jet burner and a radiant burner. This shows an example of a thermal device, and Figure 1s4 is a longitudinal cross-sectional view, and Figure 5 is a vertical cross-sectional view.
The figures are a semicircular sectional view taken along the line v-V in FIG. 4, FIG. 6 is an explanatory diagram showing the relationship between the temperature of the heated object and the heat flux, and FIG. 7 is an explanatory diagram showing the non-oxidation heating characteristics. 11.../(-main body, JJ,... burner tile side wall, 12... burner nozzle, 1B-... air discharge hole, 14... gas discharge hole. Applicant's agent Patent attorney Kajie Takehiko Figure 1 Figure 2E 4L Jisotsuen (C0) Figure 7 ho Me 1 Grain (5th generation) Application No. 56-206695 2, Name of the invention: Non-oxidation heating method for copper strip and its device 3, Relationship with the supplementary IF case Patent applicant (412) Nippon Kokan Co., Ltd. 4, Attorney 6, Amendment Subject specification 7, contents of amendment (1) “For air preheating” stated in page 3, line 16 of the specification is amended to “by air preheating” (2) Same as above, page 4, line 2 ``It is effective, but air preheating is not possible,'' in the line 1 is corrected to ``It is effective. Therefore, air preheating is not possible.'' (3) “4700K c” stated on page 8, line 20 of the same
Correct "a l bar" with r 4700 Kcal/as bow.

Claims (1)

[Claims] (1) When heating the copper strip, air is discharged from the side wall of the cylindrical burner tile to create a swirling flow, and fuel gas is discharged radially straight from the center of the burner toward the axial thickness. The discharge flow velocity ratio of the air and fuel gas is set to 1. S or more, and the air ratio is 1. A non-oxidation heating method for a copper strip, characterized in that the copper strip is heated to a temperature of O or less. A burner nozzle that has air discharge holes in the side wall of a cylindrical burner tile at a maximum angle of 60 degrees to the tangent to the side wall, and gas discharge holes that discharge fuel gas radially directly from the center of the burner in the axial direction. An oxidation-free heating device made of a copper strip, which is slidable in the axial direction so that the position of the gas discharge hole can be changed relative to the air discharge hole.