JP2984142B2 - Single-ended radiant tube and combustion method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single-ended radiant tube.

[0002]

2. Description of the Related Art A radiant tube type heating device is generally used for controlling the atmosphere and temperature in a furnace. The shape of the radiant tube is a U-shaped, straight type or straight type outer tube. A single-end type in which an inner tube is provided inside has been invented and used. Among these, the single-end type radiant tube is the most excellent in terms of temperature distribution, efficiency, and handling. In addition, the temperature distribution is easily uniform, and accurate heating can be performed.

A single-end type radiant tube is provided with an outer tube having a closed end, and an inner tube having an outer diameter smaller than the inner diameter of the outer tube is concentrically arranged so that the inner tube has a gap with the closed portion of the outer tube. Are provided so as to face each other. There is an inner pipe combustion type in which a burner is provided in the inner pipe, and the high temperature combustion gas generated from the burner passes through the inner pipe, heats the outer pipe, and is exhausted.

In recent years, the operating temperature has tended to increase from the standpoint of quality measures of steel sheets and combustion efficiency, and it has been desired to improve the outer tube temperature of the radiant tube. However, in the case of a single-ended radiant tube of the inner tube combustion type, the surface temperature of the outer tube, which is the radiation surface, due to combustion in the inner tube, results in radiation from the inner tube or heat received from the combustion exhaust gas. Yes, generally lower than the temperature of the inner tube. In order to raise the heating temperature of the radiant tube, the method of burning in the inner tube and exhausting in the outer tube is an inefficient structure.

[0005] In order to solve this problem, a structure in which burner combustion is conventionally performed using an inner pipe and combustion gas is exhausted using an outer pipe has been proposed.
Japanese Patent Application No. 2-63625 discloses a structure in which combustion can be performed by an outer tube and combustion gas can be exhausted by an inner tube. 16 and 17 show the structure. The configuration is such that, inside the outer tube 2 whose end is closed, the inner tube 3 is concentric with the outer tube having an outer diameter smaller than the inner diameter of the outer tube, and the end of the inner tube has a gap with the outer tube distal end closing portion. A burner is provided in the gap between the outer tube and the inner tube at the rear end, and the high temperature combustion gas generated by the burner is heated through the gap between the outer tube and the inner tube, and then the inner tube is heated. A single-ended rangant tube characterized by exhausting through a tube.

[0006]

However, Japanese Patent Application No. 2-63625 is excellent as a tube structure for increasing the outer tube surface temperature, but requires improvement in the burner structure. The present inventors have conducted various investigations on the burner structure and temperature distribution in this structure, and found that a premix type porous body was prepared by using a multi-hole burner aiming for uniform combustion in the circumferential direction and using the structure. When installed, the temperature immediately after the burner tended to be too high, and the uniformization of the temperature in the tube length direction was insufficient. The present invention has been made to solve the above-mentioned problems, and provides a radiant tube structure and a combustion method in which the temperature of the outer tube surface is made more uniform.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention relates to a radiant tube burner structure and a combustion method, the constitution of which is as follows. (1) Inside the outer tube whose end is closed, the outer tube has an outer diameter smaller than the inner diameter of the outer tube, and the inner tube is concentric with the inner tube so that the distal end of the inner tube faces the outer tube distal end closed portion with a gap. A burner is provided in the gap between the outer pipe and the inner pipe at the rear end, and the high temperature combustion gas generated from the burner is heated through the gap between the outer pipe and the inner pipe, and then the inner pipe is heated. The first in a single-ended radiant tube that is evacuated
A burner and a second burner are arranged, and the fuel gas holes of the first burner are oriented in the pipe length direction, and the fuel gas holes of the second burner are oriented in the circumferential tangential direction.

Further, air is introduced into the air header portion of the first burner according to the above item (1) in a circumferential tangential direction,
The fuel gas header portion of the burner has a mechanism for introducing fuel gas in a circumferential tangential direction.

Further, according to the present invention, inside the outer tube whose end is closed, the outer tube has an outer diameter smaller than the inner diameter of the outer tube, the inner tube is concentric with the inner tube, and the inner tube has a gap with the outer tube distal end closing portion. And a first burner and a second burner are provided in the gap between the outer pipe and the inner pipe at the rear end, and the high-temperature combustion gas generated from the burner passes through the gap between the outer pipe and the inner pipe. In the method of burning a single-ended radiant tube in which the outer tube is heated and then exhausted through the inner tube, the air ratio of the first burner is increased to more than 1.0, and the second burner is uniformly burned in the circumferential direction. It is characterized in that combustion is performed with an air ratio smaller than 1.0.

As a first burner aiming at uniform combustion in the circumferential direction, a multi-burner having a large number of fuel gas holes of 6 to 40 or a surface combustion in which a porous body is arranged using such a multi-burner structure as a premix device. Burners can also be used. The second burner having an air ratio of less than 1.0 is used in a state where the fuel gas is relatively rich, and ultimately becomes a fuel gas hole for supplying only the fuel gas. A pilot burner for ignition may also be used as the second burner.

[0011]

[Function] In the first burner aiming for uniform combustion in the circumferential direction, the maximum point of combustion is generated immediately after the burner because the fuel gas and the air are uniformly mixed, and the temperature there is highest, and it is located at the tip of the radiant tube. The temperature decreases as the temperature increases. Immediately after the burner, the combustion of the fuel gas and air is not uniform due to uneven mixing of the fuel gas and the fuel gas and air are mixed in a spiral process in the pipe length direction. The maximum point of combustion is near the tip of the tube. When the air ratio of the second burner approaches 1.0 from 1.0, the mixing of the process in which the fuel gas and air spiral spirally in the pipe length direction is promoted, and the maximum point of combustion tends to approach the center of the tube from the tip. .

When the first burner for uniform combustion and the second burner for non-uniform mixing of fuel gas and air are used at the same time, the added temperature distribution is exhibited, and there is an effect of suppressing the generation of each low-temperature portion. . Further, when the air ratio of the first burner is larger than 1.0, the fuel gas of the unburned second burner having the air ratio smaller than 1.0 is thermally decomposed to lower the temperature immediately after the burner. As the air ratio of the second burner approaches 1.0 from 1.0, the amount of unburned fuel gas increases due to a decrease in swirling force due to air and an increase in the amount of supplied gas. As a result, the effect of thermal decomposition becomes significant. The temperature drop immediately after the burner is significant.

The fact that the temperature of the high-temperature portion of the first burner can be reduced is excellent in that the temperature can be lower than the endurable temperature of the material even if the overall temperature is increased accordingly. On the other hand, when the air ratio of the first burner is smaller than 1.0, the temperature immediately after the burner is reduced by the air mainly serving as the second burner whose air ratio is larger than 1.0. The air ratio of the first burner is greater than 1.0 and the air ratio is 1.0.
It is not as remarkable as the temperature drop immediately after the burner when it is smaller than 0.

In order to achieve substantially uniform combustion in the circumferential direction of the first burner, it is necessary that an equal amount of gas is emitted from each of the multiple fuel gas holes and equally emitted from the air holes. . For this purpose, the gas pressure in the header outlet side hole needs to be uniform, and dynamic pressure is likely to be applied in the direction of introduction to the header in the axial direction, and the pressure at some header outlet holes increases, so the gas exiting the header The gas amount and the air amount become uneven in the circumferential direction. Therefore, in order to make it difficult to apply dynamic pressure to the header outlet holes for fuel gas and air and to make the pressure uniform, gas is introduced into the fuel gas header and air header portion of the first burner in a circumferential tangential direction.

The air ratio of the first burner can be increased as long as the combustion gas does not blow off, and is greater than 1.0 and less than 2.0. The air ratio of the second burner is less than 1.0 and is up to 0.0, and the total air ratio is 1.0 to 1.5 from the viewpoint that the total combustion gas used for the first burner and the second burner is completely burned. It is appropriate that the first and second
When the fuel gas amount of each burner is determined and one air ratio is determined, the other air ratio increases the total air ratio from 1.0 to 1.5.
Is determined by the range. It is the same in the present invention that the total air ratio is most preferably 1.0 for the purpose of efficiently obtaining a high temperature. Regarding the dimensions of the radian tube, the outer diameter is 100 mm to 300 mm, and the inner diameter is 50 mm to 250 mm
Can be used as a suitable structure.

[0016]

Embodiment 1 FIG. 3 shows a cross section of the upper half of the first burner of the present invention when viewed from the side of the tube shaft. The fuel gas header 20 is surrounded on four sides by a partition wall 19, and the upper and lower partition walls 19 form a cylindrical curved surface. There is one fuel gas intake hole 18 on the curved surface of the partition wall 19 on the upper side, and it faces in the circumferential tangential direction. A fuel gas header outlet side hole 21 is provided in the tube axis direction perpendicular to the fuel gas
There is a fuel gas hole 26 ahead of the hole 4.

The air header 23 is a fuel gas header 20.
At a position adjacent to the partition wall 1 in the same manner as the fuel gas header 20.
9, one air intake hole 22 is formed on the curved surface of the upper partition wall 19 and faces in the circumferential tangential direction. An air hole 25 is provided between the fuel gas header outlet side hole 21 and the fuel gas hole 26 in the tube center direction perpendicular to the air intake hole 22. At the time of combustion, the combustion gas 8 is generated in front of the fuel gas hole 26, and the exhaust gas 11 passes through a cylinder formed by the partition wall 19 below the fuel gas header 20.

FIG. 4 shows the first burner of the present invention when viewed from the front of the tube shaft, from the combustion gas 8 side. The fuel gas header 20 forms a hollow cylindrical space from the partition wall 19, and the fuel gas intake hole 18 is directed in the circumferential tangential direction. The air header 23 is located in front of the fuel gas header, forms a hollow columnar space from the partition wall 19 like the fuel gas header 20, and the air intake hole 22 faces in the circumferential tangential direction. Pipes 24 are circumferentially arranged at equal intervals between the partition walls 19 to form fuel gas holes 26. This figure shows a case where the number of fuel gas holes is nine. A hole is formed in the partition wall 19 at an intermediate position between the fuel gas holes, and the air holes 25 are arranged at equal intervals.

The first burner is suitably made of steel from the temperature conditions of the exhaust gas. FIG. 5 shows a case where the number of fuel gas holes is 18 and FIG. 5 shows a case where the number of fuel gas holes is 36. 6 is shown. In each case, circular pipes 24 are arranged at equal intervals on the circumference. First of the present invention
FIG. 5 shows a case where the number of fuel gas holes is 18 and FIG. 6 shows a case where the number of fuel gas holes is 36. FIG. In each case, circular pipes 24 are arranged at equal intervals on a cylinder.

Although the present invention shows an example in which the fuel gas holes 26 and the air holes 25 are arranged at equal intervals, the fuel gas holes 26 and the air holes 25 may be arranged at equal intervals. It is preferable, but not necessarily equal, that a displacement of 20 to 30% with respect to the equal spacing is allowed. Furthermore, the shape of each fuel gas hole 26 in FIGS. 4 to 6 is circular, but may be rectangular. If the number of holes is nine or the like, a method effective for uniform combustion in the circumferential direction is used. is there.

[0021]

Embodiment 2 FIG. 7 shows a cross section of the upper half of the first burner of the present invention when viewed from the side of the tube shaft. The fuel gas header 20 is surrounded on four sides by a partition wall 19, and the upper and lower partition walls 19 form a cylindrical curved surface. There is one fuel gas intake hole 18 on the curved surface of the partition wall 19 on the upper side, and it faces in the circumferential tangential direction. A fuel gas header outlet side hole 21 is provided in the tube axis direction perpendicular to the fuel gas
There is a fuel gas hole 26 ahead of the hole 4.

The air header 23 is a fuel gas header 20
At a position adjacent to the partition wall 1 in the same manner as the fuel gas header 20.
9, one air intake hole 22 is formed on the curved surface of the upper partition wall 19 and faces in the circumferential tangential direction. An air hole 25 is provided between the fuel gas header outlet side hole 21 and the fuel gas hole 26 in the tube center direction perpendicular to the air intake hole 22. A premix portion 27 surrounded by the partition wall 19 and the porous body 15 is provided in front of the fuel gas hole 26. During combustion, the fuel gas 8 is generated forward from the porous body 15 fixed by the presser fitting 28, and the partition wall 19 below the fuel gas header 20 is formed.
Exhaust gas 11 passes through the inside of the cylinder formed by. The second embodiment has a structure in which the premix portion 27, the porous body 15, and the structure shown in the first embodiment are arranged, and various structures described in the first embodiment can be used.

[0023]

Embodiment 3 FIGS. 8A and 8B show the second burner of the present invention when viewed from the tube axis direction and when viewed from the side of the tube axis. The fuel gas 8 and the air 9 are mixed with the spark plug 16
The gas holes 29 are arranged so as to be supplied in a circumferential tangential direction of the heat insulating ring 12 having a hollow cylindrical shape. In this embodiment, a pilot burner for the purpose of ignition is also used as the second burner. Ignition is performed using the ignition plug 16 provided near the fuel gas hole 26. Since the ring is heated directly by a flame, ceramics are suitable from the viewpoint of heat resistance.
In order to suppress heat transfer from the outer tube 2 during heating, heat insulation is preferable.

[0024]

Embodiment 4 FIGS. 9A and 9B show a second example in which the second burner of the present invention is viewed from the tube axis direction and a second example in which the second burner is viewed from the side of the tube axis. FIG. 9 shows a gas hole 29 in the heat insulating ring 12.
Are arranged in two holes, the gas holes 29 are arranged so that the fuel gas 8 and the air 9 are supplied through the ignition plug 16 in the circumferential tangential direction of the hollow cylindrical heat insulating ring 12, and the other is provided. The gas holes 29 are arranged so that only the fuel gas 8 is supplied and the gas holes 29 are supplied in the circumferential tangential direction of the heat insulating ring 12.

[0025]

[Embodiment 5] Fig. 1 shows an embodiment showing a schematic configuration of the entire single-ended radiant tube according to the present invention. A hole is made in one side of the experimental furnace wall 1, a radiant tube is made to penetrate, and the other end of the radiant tube is held by the other furnace wall 1. About 2 m of SiC-Si ceramic tube outer tube 2
The ceramic inner tube 3 is installed. The outer tube 2 is fixed to the burner via a flange 5. In addition, outer tube 2
Has an outer diameter of about 215 mm, a wall thickness of about 6 mm, an inner diameter of the inner tube 3 of about 160 mm, and a wall thickness of 6 mm.

The first burner has a fuel gas header 20 and an air header 23 arranged in parallel in the tube axis direction.
A pipe is provided in the fuel gas header outlet side hole 21, and the fuel gas holes 26 at the tip thereof are arranged at regular intervals of 40 degrees in the circumferential direction facing the pipe length direction, and the air holes 25 are also 40 degrees between the fuel gas pipes. It is arranged every. The second burner 14 is the first
Place immediately after burner. The ignition is performed using the ignition plug 16 provided near the fuel gas hole 26 of the second burner. A spacer 10 was provided at the lower part of the tip of the inner tube to maintain a constant interval between the inner tube 3 and the outer tube 2, and the combustion exhaust gas 11 was passed through the inner tube and exhausted to the outside. A thermocouple was set on the outer tube, and the temperature distribution at each site was measured.

The first burner 13 and the second burner 14 are respectively 3.2 and 0.8000 Kcal / hr using fuel mixed with 35% of methane gas and 65% of hydrogen gas.
3, the air ratio of the second burner 14 is 0.25.
0 was set. FIG. 10 shows the temperature measurement results. As Comparative Example 1, a test result of 40,000 Kcal / hr and an air ratio of 1.0 for the first burner when the second burner of the present structure was not used was also described. As is clear from FIG. 10, 300 m from the flange
It can be seen that the temperature rises by m and the temperature distribution hardly increases thereafter, and the temperature distribution is almost uniform. On the other hand, in the case of Comparative Example 1, after the temperature rises from the flange to 300 mm, the temperature monotonously falls to about 2000 mm in the tube, and the temperature distribution is not uniform.

[0028]

Embodiment 6 In a combustion experiment according to the present invention, in a radiant tube having a structure similar to that of the fifth embodiment, the fuel gas of the first burner and the second burner is supplied to the calorie of 20,000,000 Kcal.
/ Hr, and the air ratio was 2.0 and 0.0, respectively. As Comparative Example 2, a case where the fuel gas of the first burner and the fuel gas of the second burner were set to 13,000 Kcal / hr and 270,000 Kcal / hr, respectively was performed. FIG. 11 shows the temperature measurement results in this case.
As is clear from FIG.
The temperature rises to 0 mm, and then there is a slight rise in temperature, but the temperature distribution is almost uniform. On the other hand, in Comparative Example 2, the temperature increased from the flange to 1600 mm, and the temperature distribution was not uniform.

[0029]

Embodiment 7 In a combustion experiment according to the present invention, a burner structure similar to that of the radiant tube in the fifth embodiment was replaced with a second burner having the structure shown in the fourth embodiment. . 1st burner,
The fuel gas of the second burner was 2.0, 200,000 Kcal, respectively.
/ Hr, and the air ratio was 1.1 and 0.9, respectively. Also, only air was supplied from the gas hole of the second burner which also serves as a pilot burner, and only fuel gas was supplied from the other gas hole. FIG. 12 shows the temperature measurement result in this case. In addition, Comparative Example 1 described in the item of Example 5 is also shown.

As is clear from FIG. 12, in the seventh embodiment, the temperature rises up to 300 mm from the flange, and then 800
mm, there is a slight temperature drop,
It rises to around 0 mm. Although the temperature fluctuates before 300 mm from the flange, the temperature distribution there is more uniform than that in Comparative Example 1 beyond 300 mm from the flange.

[0031]

[Embodiment 8] In a combustion experiment according to the present invention, a burner structure similar to that of the radiant tube in the fifth embodiment is different from the burner structure of the fifth embodiment in that the second burner is changed to the first burner of the structure shown in the second embodiment. FIG. 2 shows a schematic configuration of the entirety using a radiant tube of a mold type. The fuel gas of the first and second burners is 27,000 Kcal / hr and 13,000 Kcal / hr, respectively, and the air ratio is 1.48 and 0.0, respectively. FIG. 13 shows the temperature measurement results of a radiant tube combustion experiment performed by this apparatus. Incidentally, as Comparative Example 3, the test results of 40,000 Kcal / hr and the air ratio of 1.0 for the first burner when the second burner of the present structure was not used are also shown.

As is clear from FIG. 13, in the case of the eighth embodiment as well, uniformity of the temperature distribution is achieved at about 300 mm or less from the flange. On the other hand, in Comparative Example 3, after the temperature rises from the flange to 300 mm, the temperature decreases monotonously and the temperature distribution is not uniform.

[0033]

Embodiment 9 In a ninth embodiment of a combustion experiment according to the present invention, in a radiant tube having the same structure as in the seventh embodiment, the air ratios of the first burner and the second burner are (1) 1.1 and 0.1, respectively.
5, (2) 1.5, 0.5, (3) 1.5, 0.2, (4)
1.5, 0.7, (6) 2.0, 0.2, (7) 2.0, 0.1
The fuel gas is supplied to the first burner and the second burner such that the total fuel gas including the first and second burner fuel gas is 40,000 Kcal / hr and the total air ratio is 1.0. It was carried out. From the measurement results, the uniformity of the temperature distribution,
FIG. 14 shows the result of evaluating the non-uniformity. FIG. 14 also shows the evaluation results of Examples 5 to 8 and Comparative Example 2.

From FIG. 14, it can be seen that in order to make the temperature distribution uniform, when the air ratio of the first burner is larger than 1.1, there is an upper limit where the air ratio of the second burner is smaller than 1.0. There is a limit to the uniformity of the temperature distribution as shown by a broken line in FIG. The combination range of the air ratio of the first burner and the second burner according to the second aspect of the present invention is in the range where the uniformity shown in FIG. 14 can be achieved.

[0035]

Embodiment 10 In the tenth embodiment of the combustion experiment according to the present invention, a radiant tube having the same structure as that of the fifth embodiment is used as a first example.
The burner fuel gas is 40,000 Kcal / hr, the air ratio is 1.5, and the second burner fuel gas is 20,000 Kcal / h.
r and the air ratio were set to 0.0. FIG. 15 shows the temperature measurement result of the combustion test. Example 6 having a different total fuel gas amount is also shown.

In Example 10, the temperature rises up to 300 mm from the flange, but the temperature distribution thereafter is almost uniform. When the total fuel gas becomes 60,000 Kcal / hr, the total fuel gas of Example 6 becomes 40,000 Kcal / hr. About 1 compared to Kcal / hr
Almost uniform temperature distribution at 50 ° C high temperature
mm.

[0037]

According to the single-ended radiant tube of the present invention, the temperature can be made uniform in the length direction of the tube and radiant heat can be transferred near the endurance temperature of the tube material, so that the heat treatment time of the steel sheet can be shortened. The production speed is improved, and the quality of the steel sheet is stabilized by uniformizing the temperature in the width direction.

[Brief description of the drawings]

FIG. 1 and FIG. 2 are schematic diagrams of the entire configuration of a single-ended radiant tube of the outer tube combustion inner tube exhaust type according to the present invention, and FIG.
7 are diagrams of an example of a first burner of the present invention, FIGS. 8 and 9 are diagrams of an example of a second burner of the present invention, and FIGS. 10 to 13 and 15 are temperature measurement results of a combustion experiment according to the present invention. FIG. 14 is a view showing the range of combinations of the air ratios of the first and second burners for equalizing the temperature distribution based on the evaluation results of the combustion experiment according to the present invention, and FIGS. 16 and 17 show the conventional outer tube combustion. The figure which shows the whole structure of the single end type radiant tube of an inner pipe exhaust system.

[Explanation of symbols]

1: furnace wall, 2: radiant tube outer tube, 3: radiant tube inner tube, 4: packing, 5: flange, 6: main burner, 7: pilot burner, 8: fuel gas, 9: air, 10: Spacer, 11: Exhaust gas, 12: Heat insulation ring, 13:
1st burner, 14: 2nd burner, 15: Porous body, 16: Spark plug, 17: Cooling air, 1
8: fuel intake hole, 19: partition wall, 20: fuel gas header, 21: fuel gas header outlet side hole, 22: air intake hole, 23: air header, 24: pipe, 25:
Air hole, 26: fuel gas hole, 27: premix portion, 28: presser fitting, 29: gas hole.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Michio Tamura Inventor: 1 Fujimachi, Hirohata-ku, Himeji-shi, Hyogo Nippon Steel Corporation Hirohata Works (56) References JP-A-1-302013 (JP, A ) Japanese Utility Model Application Hei 4-25912 (JP, U) Japanese Utility Model Application Sho 56-89529 (JP, U) Japanese Patent Publication No. 50-35254 (JP, B1) (58) Fields investigated (Int. Cl. ⁶ , DB name) F23D 14/12 F23C 3/00 301

Claims (3)

(57) [Claims] 1. An inner tube having an outer diameter smaller than the inner diameter of the outer tube, the inner tube being concentric with the inner tube inside the outer tube having a closed end, and the inner tube having a gap with the outer tube distal end closing portion. Provided to face each other,
A burner is provided in the gap between the outer pipe and the inner pipe at the rear end, and the high temperature combustion gas generated from the burner is heated through the gap between the outer pipe and the inner pipe, and then exhausted through the inner pipe. In the single-end type radiant tube, the first burner and the second burner are arranged, and the fuel gas holes of the first burner are oriented in the pipe length direction, and the fuel gas holes of the second burner are oriented in the circumferential tangential direction. A single-ended radiant tube characterized by the following: 2. A mechanism for taking air in a circumferential tangential direction into an air header portion of a first burner and a fuel gas in a circumferential tangential direction into a fuel gas header portion of a first burner. 2. The single-ended radiant tube according to 1. 3. An inner tube having an outer diameter smaller than the inner diameter of the outer tube, the inner tube being concentric with the inner tube inside the outer tube, the distal end of which has a gap with the outer tube distal end closed portion. Provided to face each other,
A first burner and a second burner are provided in a gap between the outer pipe and the inner pipe at the rear end, and after the high temperature combustion gas generated from the burner is heated through the gap between the outer pipe and the inner pipe, the inner pipe is heated. In the method of burning a single-ended radiant tube exhausted through a pipe, the air ratio of the first burner is set to be larger than 1.0, the combustion is uniformly performed in the circumferential direction, and the second burner air ratio is set to be larger than 1.0. A method for burning a single-ended radiant tube, characterized in that it is made smaller and burned.