JPS6252313A - Directly heating burner under reducing condition - Google Patents

Abstract

PURPOSE:To attempt to have non-oxidizing heating under reducing conditions for its steel material by forming a combustion air discharge hole A and a fuel gas discharge hole B in specified directions and specifying the distance from the discharge hole B to the discharge hole A in the axial direction of a burner and the distance from the discharge hole A to the opening of the burner tile. CONSTITUTION:Air discharge holes 2 for the combustion air and fuel gas discharge holes 3 are constituted as follows: a) the air discharge hole 2 for the combustion air is formed with its air injection direction at an angle theta smaller than 60 deg. to the tangential line with respect to the inner circumference of the burner tile 11, 1) the fuel gas discharge hole 3 is formed so that its fuel gas injection direction is not at right angle to the tangential line with respect to the outer circumference of a fuel gas nozzle 7 and yet the fuel gas flow by this arrangement becomes a swirl flow in the direction opposite to the air flow from the discharge holes 2, c) the distance N between the hole 3 and the hole 2 in the axial direction of the burner is made negative when the hole 3 is nearer to the burner tile opening 5 than to the hole 2, and positive when their positions are reversed, and N is set at -0.10-0.25D (D is the inner diameter of the burner), and d) the distance L from the hole 2 to the opening 5 is set at 0.6D-3D (D is the inner diameter of the burner).

Description

[Detailed description of the invention] [Industrial application field] The present invention is a continuous heating furnace (direct heating method) for thin steel sheets such as steel materials, continuous annealing "Fi (CAL), continuous hot dip galvanizing equipment (CGL), etc. This is a direct-fired reduction heating burner used in [ll'1J].

[Prior Art] Conventional methods for direct-fire non-oxidation heating in continuous annealing furnaces for copper strips, ``Mrc hot-dip galvanizing equipment, etc.'' use a general diffusion burner or high-speed jet burner to direct the flame to the copper strip. There are two methods: one method uses a radiant cup burner to raise the temperature of the inner surface of the burner tile, and the other method uses mainly radiant heat transfer from this surface.

As shown in Fig. 16, a high-speed jet burner has a combustion chamber (
8), a high-temperature gas jet is ejected from the constricted discharge hole (9), and heating is mainly done by convection heat transfer, and a high heat flux can be obtained in a range where the temperature of the heated object is relatively low. It has characteristics. On the other hand, since the flame during the combustion reaction directly collides with the copper strip, the 02, O,
Due to Oll et al., slight oxidation is unavoidable even though there is no oxidation.

On the other hand, in order to perform a rapid combustion reaction, a radiant cup burner uses a pre-mixed gas mixture of air and fuel gas, as shown in Fig.
0) to cause rapid combustion and heat up the inner surface of the burner tile,
It mainly heats by radiant heat transfer, and has the characteristic that a high heat flux can be obtained in a region where the temperature of the heated object is high.

On the other hand, by burning with this burner at an air ratio of 1.0 or less, the combustion gas contains reducing unburned components such as Go and 82, so this combustion gas comes into contact with the copper strip and heats it without oxidation. Of course, the oxide film formed on the copper strip can be reduced.

In this way, the radiant burner is suitable for non-oxidation heating, but this burner uses a premixing method, and it is dangerous to premix air that has been preheated to a high temperature with the fuel gas, so preheating the combustion air is not recommended. The drawback is that it cannot be done. For this reason, it is not possible to explicitly recover the exhaust gas by preheating the air, so it is necessary to take other measures for the obvious recovery of the exhaust gas in order to save energy. Furthermore, preheating the air is effective in increasing the flame temperature, and on the other hand, increasing the flame temperature is effective in reducing the reduction effect by the above-mentioned GO, t'z, etc. Therefore, the inability to perform air preheating is not preferable from the viewpoint of non-oxidative heating. Furthermore, a premixer, a flashback preventer as a safety device, etc. are indispensable, which raises the problem of increased equipment costs.

In addition, this type of burner cannot preheat the combustion air, so non-oxidative heating is limited to about 750°C, and there is also the drawback that it cannot be applied in cases where heating in a higher temperature range is required.

The present invention was made in view of such conventional problems,
It is an object of the present invention to provide a direct-fire reduction heating burner that can use preheated air and can heat steel materials in a non-oxidizing and reducing state.

[Means for Solving the Problem] For this reason, the present invention provides a plurality of combustion air discharge holes at intervals in the circumferential direction of the inner wall of a cylindrical burner tile with an open tip, and a plurality of combustion air discharge holes inside the burner tile. The basic feature is that the air discharge hole and the combustion gas discharge hole are configured as follows.

(a) The combustion air discharge hole is formed so that its air injection direction has an angle of 60° or less with respect to a tangent to the inner circumference of the burner tile.

(b) Set the fuel gas discharge hole so that the fuel gas injection direction is not perpendicular to the tangent to the outer periphery of the fuel gas nozzle, and the resulting fuel gas flow is in the opposite direction to the air flow from the combustion air discharge hole. Form a swirling flow.

(C) Distance N in the burner axial direction between the fuel gas discharge hole and the combustion air discharge hole: (-) indicates the case where the fuel gas discharge hole is closer to the burner tile opening than the combustion air discharge hole, and (+) indicates the opposite.
In this case, set it to -0.1D to +0.25D (D: burner inner diameter).

(d) Set the distance from the combustion air discharge hole to the burner tile opening to 0.6D to 3D (D: burner inner diameter).

[Function] When the heating burner configured as described above is used at an air ratio of 1.0 or less, a non-equilibrium region is formed in the flame within a predetermined range. That is, in such a heating burner, rapid combustion is achieved by the swirling flow of combustion air from the air discharge hole and the fuel gas discharged from the center of the burner.
Over a predetermined range outside the burner opening, a 111 ft area that contains a large amount of combustion intermediate products (intermediate ions, radicals, etc.) and does not contain any unreacted elements, that is, a non-equilibrium region, is spread over a wide area. Moreover, it forms stably. Figure 8 shows an example of measurement using an ion detection probe of the non-equilibrium region in the flame formed by such a heating burner.The reason why the current value measured by the probe is high is that the ion intensity is high, and therefore it is the result of intermediate combustion products. It means that things exist in many places. According to this, a non-equilibrium region is formed at the burner outlet over a predetermined range outward, and the outside thereof is C
O2.

N20. It is a quasi-equilibrium region containing N2, etc.

Figure 9 shows the reductive heating characteristics of such a heating burner, that is, the limit temperature at which it can be heated without oxidation (the limit temperature for a thin plate of ordinary steel). In the range of 0.85 to 0.95, the steel strip can be heated to about 900°C without oxidation.

[Embodiment] FIGS. 1 and 2 show an embodiment of the present invention.

In the figure, (1) is a cylindrical burner tile that is the burner body, and a plurality of combustion air discharge holes (2) are provided at intervals in the circumferential direction of the burner tile inner wall (6). At the same time, a fuel gas nozzle (7) is provided protruding from the center of the burner tile inner end wall (4).
7), fuel gas discharge holes (3) are formed at intervals in the circumferential direction.

In such a configuration, the combustion air discharge hole (
2) and the fuel gas discharge hole (3) are constructed as follows.

(a) The combustion air discharge hole (2) is formed so that the air injection direction has an angle θ of 60° or less with respect to a tangent to the inner circumference of the burner tile.

(b) The fuel gas discharge hole (3) is arranged so that the fuel gas injection direction is not perpendicular to the tangent to the outer periphery of the fuel gas nozzle, and the resulting fuel gas flow is connected to the combustion air discharge hole (3).
) to form a swirling flow in the opposite direction to the airflow from the airflow.

(C) Fuel gas discharge hole (3) and combustion air discharge hole (
If the burner axial distance N in 2) is set as (-) when the fuel gas discharge hole (3) is closer to the burner tile opening than the combustion air discharge hole (2), and (+) when the opposite is set, - 0,10
~+〇, set to 25D (D: burner inner diameter).

((1) Set the distance IIIL from the combustion air discharge hole (2) to the burner tile opening (5) to 0.6D to 3D (D: burner inner diameter).

Above, the contents of (a) to (d) above will be explained in detail.

The reason why the air injection direction of the air discharge hole (2) has an angle θ with respect to the tangent to the inner circumference of the burner tile is to generate a swirling flow in the combustion air within the burner tile, and this swirling flow causes the burner A negative pressure region is formed inside, which promotes combustion by recirculating the gas, thereby creating a suitable non-equilibrium region. This air injection angle θ is at most 60°, preferably 20 to 4
By setting it to 0', the swirling property of the airflow can be stably obtained.

For such a combustion air discharge hole (3), a fuel gas discharge hole (3) provided in the circumferential direction of the fuel gas nozzle (7)
As shown in Fig. 7(b), the injection direction is not perpendicular to the tangent to the outer circumference of the fuel nozzle, and the resulting fuel gas flow is opposite to the air flow from the combustion air discharge hole (2). The swirling flow is formed so as to be a swirling flow that collides with the air swirling flow from the opposite direction. The fuel gas discharge hole (3) is configured in this manner by attaching an angle θ to the injection direction of the combustion air as shown in FIG. This is because when the flame is injected from the burner opening (outlet), the temperature distribution of the flame coming out from the burner opening (exit) becomes uneven, and as a result, both the reduction characteristics and the heating characteristics tend to vary according to this temperature distribution, and the air swirl flow On the other hand, by forming a swirling flow in the opposite direction in the fuel gas, such a deviation can be appropriately eliminated.

As mentioned above, the heating burner of the present invention creates a swirling flow of combustion air within the burner tile by attaching an angle θ to the air injection direction, thereby realizing rapid combustion and reducing reduction containing intermediate reaction products. It forms a region.

However, according to studies conducted by the present inventors, if the direction of injection of combustion air is simply angled, the swirling force of the air flow is too strong, creating a strong negative pressure region within the flame. It was found that deviations were likely to occur in the flame temperature distribution. Therefore, the present invention aims at flattening the flame temperature distribution by actively forming a fuel gas swirl flow in the opposite direction to the air swirl flow, thereby weakening the swirling force in the radial direction of the air flow.

FIG. 10 shows the heating burner of the present invention shown in FIG. 7(b),
An example of the burner radial direction gas temperature distribution with respect to the comparative burner shown in FIG. 7(a) is shown. In the figure, the dashed line 0 indicates the present invention example, and the solid line 0 indicates the comparative example, but as is clear from this, the burner of the comparative example shows a significant temperature increase in the center of the burner, which is believed to be due to negative pressure. In contrast, in the burner of the present invention, such a temperature drop is improved and a relatively uniform temperature distribution is obtained in the radial direction.

When the burner axial inner rectangle 111N of the fuel gas discharge hole (3) and the air discharge hole (2) is on the (-) side, the gas temperature is high and combustion intermediate products are also highly distributed over a wide range. However, on the other hand, 31i211tO2 (unreacted 02) tends to be distributed long in the axial direction. In order to appropriately form the non-equilibrium region that is the object of the present invention, it is necessary to minimize the remaining distance of the free 02 in the burner axial direction, and its limit is -0.10.

If N is on the (+) side, a proper non-equilibrium region will be formed, but if it becomes too large, the inner end wall of the burner tile will be heated to over 1400°C, which is undesirable, and it will be difficult to protect the SiC on the inner end wall of the burner tile. The limit is +0.250. Figure 11 shows the burner axial distance from the burner opening and the gas temperature in the burner tile when the burner axial distance N between the fuel gas discharge hole (3) and the air discharge hole (2) is -0,250. ,
02 concentration and ionic strength, and according to this, when N is on the (-) side,
The remaining distance in the axial direction of the free 02 is 11iL.

It has been shown that there is a large presence of

Figure 12 shows the burner axial inner rectangle 1 of the fuel gas hole and air discharge hole.
This shows the relationship between 11N and the remaining axial distance LO of the free 02. According to this, when N becomes larger than -0, 1D on the (-) side, LO increases rapidly, and this On the (-) side, the limit is -0,1D7. on the other hand,
FIG. 13 shows the relationship between the burner axial distance from the burner opening, 02111 degrees, ion strength, and gas temperature when N is +0.1D.

According to FIGS. 12 and 13, if N is on the (+) side, there is no problem with 02) rJ degrees, and there is an appropriate non-equilibrium region at a distance of 0.5D or more from the burner outlet. is formed.

However, when N is increased to the (+) side, the inner end wall (4) of the burner tile is heated, so that the distance 11t in FIG.
As shown in the graph of the relationship between N and the temperature Tb of the burner tile inner end wall (4), at -1-0,250, Tb is 140
0°C or higher, and therefore, considering that the material of the inner end wall is SiC, it is preferable to set the temperature to -1-0,250 or lower in terms of the heat resistance limit. From the above, regarding the burner center axis distance N between the combustion gas discharge hole and the air discharge hole, -0, 1[)=
The range is preferably 0.259.

The distance from the air discharge hole (2) to the burner tile frontage (5) has a close relationship with the formation range of the non-equilibrium region. That is, if L exceeds 3D, the non-equilibrium region will be formed only in the portion immediately after the burner tile opening, which is not preferable. on the other hand,
When L is less than 0.6D, the flame becomes a petal-shaped flame immediately after the burner tile opens, and an appropriate non-equilibrium region cannot be stably obtained on the burner central axis. Therefore 0.6D~3. O.D.
It is preferable to set L within the range of .

When continuously heating a steel plate, the distance between the burner tile opening (5) and the steel plate must be kept at a certain distance or more (usually about i00MR or more), otherwise the steel plate may come into contact with the burner during threading. Therefore, it is preferable that the non-equilibrium region in the flame be formed in as wide a range as possible, including the copper strip passing position located at a predetermined distance from the burner opening side. Figure 15 shows distance 111tL and burner 1? Non-equilibrium g from i1 mouth
The end of area A (the end on the anti-burner side, for example A in Fig. 13)
The relationship between the distance LR and the point LR is investigated. According to this, when L exceeds 3D, the non-equilibrium region is formed only immediately after the burner tile opening, and is hardly formed in front of it. As L becomes smaller, the range in which the non-equilibrium region is formed expands, but in the region (X) where L is less than 0 or 6D, the flame becomes a petal-shaped radial flame immediately after the burner tile opens, and it is located on the burner axis. An appropriate non-equilibrium region is not stably formed. From the above, the distance f from the air discharge hole (2) to the burner tile frontage (5)
It is desirable that f1L is in the range of 0.6D to 3.0D.

In the present invention, in the above configuration, the air injection direction of the combustion air discharge hole (2) and the fuel gas discharge hole (3)
In addition to the above inclination angle, the inclination angle toward the burner front side relative to the radial direction of the burner tile can be set in the fuel gas injection direction, thereby further relaxing the air swirling flow and flattening the combustion gas temperature distribution. can be achieved.

Figure 3, Figures 4 and 5 show examples of such a structure, and Figure 3 shows an example of such a structure in which the air discharge hole (2) has an inclination angle α1 toward the burner opening side in the injection direction. This is what I did. Also, Figures 4 and 5 show the l of the fuel gas discharge hole (3).
l111) An angle of inclination toward the burner frontage side is attached in the j direction. Note that it goes without saying that a configuration combining both of these structures can be adopted.

Further, FIG. 6 shows another embodiment.

In this embodiment, at least the inner wall of the burner tile on the side where the combustion air discharge hole is formed and the opening of the tip is provided with a widening angle α2 such that the inner diameter of the burner increases toward the opening of the tip. By adding the spread angle α2,
The flame from the burner opening spreads, allowing a wide heating area for steel plates and the like. Note that if this spread angle α2 is increased, a circulation region (negative pressure region) will be formed outside the burner, making it impossible to perform stable rapid combustion. In order to form an equilibrium region, the range is preferably 25° or less.

[Effects of the Invention] According to the heating burner of the present invention described above, a region having a uniform temperature distribution and strong reducing power is stably formed in the flame, and steel materials can be properly heated in a non-oxidized and reduced state. Can be heated. Also, since there is no need to premix combustion air and fuel gas, preheated air can be used instead of combustion air.
To enable economical heating furnace operation by effectively utilizing the sensible heat of exhaust gas. Furthermore, since preheated air can be used, the non-oxidation heating limit of conventional radiant burners is 750℃.
However, non-oxidizing heating is possible up to about 900°C, and it can be suitably used for heating steel materials that require high-temperature annealing. Furthermore, since the flame temperature is increased by using preheated air, the reduction action itself by intermediate reaction products can be effectively improved compared to conventional radiant burners. Furthermore, since the temperature distribution of the flame in the direction of the large diameter of the bar can be flattened, a wide non-equilibrium region with stable heating and reduction characteristics can be formed, and stable and reliable non-oxidation and reductive heating can be achieved. Close. In particular, since such a wide non-equilibrium region can be formed, 3! In the subsequent heat treatment, the steel strip can be heated without causing any variation in the heating temperature or reducibility in the width direction.In addition, since the distance between the burner and the copper strip can be relatively large, it is possible to heat the steel strip with poor shape. There is an advantage that contact with the burner can be appropriately prevented even when heating is required.

[Brief explanation of the drawing]

1 and 2 show an embodiment of the heating burner of the present invention, FIG. 1 is a longitudinal sectional view, and FIG.
It is a sectional view along a line. FIG. 3 is a longitudinal sectional view showing another embodiment of the heating burner of the present invention. 4 and 5 show the structure of a fuel gas nozzle in another embodiment of the heating burner of the present invention, with FIG. 4 being a longitudinal sectional view and FIG. 5 being a front view. FIG. 6 is a longitudinal sectional view showing an embodiment of the heating burner of the present invention. FIGS. 7(a) and 7(b) show the injection directions of combustion air and fuel gas in the heating burner of the comparative example and the heating burner of the present invention, respectively. FIG. 8 shows an example of measurement of the non-equilibrium region forming range in the heating burner of the present invention. FIG. 9 similarly shows the reduction heating characteristics of the heating burner. Figures 10 to 15 show the characteristics of the heating burner. Figure 10 shows the temperature distribution in the burner radial direction of the heating burner of the present invention and another heating burner as a comparative example, and Figure 11 shows the fuel gas discharge hole. Distance N between and the air discharge hole in the burner axial direction
The relationship between the distance from the burner outlet and the gas YjAm, 0211 degrees, and the ionic strength when D is 10, 25D. Figure 12 shows the distance N and play between the fuel gas discharge hole and the air discharge hole in the burner axial direction. Burner axial remaining distance LO
Figure 13 shows the relationship between the distance from the burner outlet, gas temperature 02F and 14 degrees, and ionic strength when the distance N is →・0.1D, and Figure 14 shows the fuel gas discharge hole and air discharge hole. Figure 15 shows the relationship between the distance N and the burner tile rear wall temperature Tb, and the relationship between the distance ll1L from the air discharge hole to the burner outlet and the distance LR to the end of the nonequilibrium region. FIG. 16 is a sectional view showing a conventional high-speed jet burner, and FIG. 11 is a sectional view showing a conventional radiant burner. In the figure, (1) shows the burner tile, (2) shows the combustion air discharge hole, (3) shows the fuel gas discharge hole, (5) shows the burner tile opening, and (6) shows the burner tile inner wall. Figure 8 Figure 9! 11 Figure 12 Figure 14 Figure 15 Air-gL Keliper 7%'l Angle angle at Loe L No. 16
Figure 17

Claims (1)

[Claims] (1) A plurality of combustion air discharge holes are provided at intervals in the circumferential direction of the inner wall of a cylindrical burner tile with an open tip, and a plurality of fuel gas discharge holes are provided at intervals in the circumferential direction in the inner center of the burner tile. A direct-fired reduction heating burner having a protruding fuel gas nozzle provided with a discharge hole, and having a combustion air discharge hole and a combustion gas discharge hole configured as follows. (a) The combustion air discharge hole is formed so that its air injection direction has an angle of 60° or less with respect to a tangent to the inner circumference of the burner tile. (b) The fuel gas injection direction of the fuel gas discharge hole is non-perpendicular to the tangent to the outer circumference of the fuel gas nozzle, and the resulting fuel gas flow is a swirling flow in the opposite direction to the air flow from the combustion air discharge hole. form like this. (c) Distance N between the fuel gas discharge hole and the combustion air discharge hole in the burner axial direction when the fuel gas discharge hole is closer to the burner tile opening than the combustion air discharge hole (-
), and the opposite is (+), -0.1D to +0.2
Set to 5D (D: burner inner diameter). (d) Set the distance L from the combustion air discharge hole to the burner tile opening to 0.6D to 3D (D: burner inner diameter).