JP7675664B2 - Radiant tube type heating device and inner tube - Google Patents

Description

The present invention relates to a radiant tube type heating device and an inner tube.

In general, a radiant tube heating device is a device that supplies fuel gas and combustion air from a burner into a radiant tube, burns them in the radiant tube, and indirectly heats an object to be heated with radiant heat from the radiant tube heated by the generated combustion gas.

In this type of radiant tube heating device, the combustion space is limited, so the radiant tube alone cannot effectively use the heat, and so it is often used with a heat exchanger or heat transfer promoter to increase thermal efficiency.
2. Description of the Related Art A radiant tube heating device having a heat exchanger inside a radiant tube for preheating combustion air with the heat of combustion gas (exhaust gas) is known from the related art, for example, as shown in Patent Document 1.

The radiant tube heating device shown in Patent Document 1 includes a radiant tube with both ends penetrating the furnace body, a combustion burner disposed in the hollow section at one end of the radiant tube, and a heat exchanger disposed in the hollow section at the other end of the radiant tube for preheating the combustion air with the heat of the exhaust gas. This heat exchanger is made of ceramic and includes a cylindrical body, a heat dissipation flow path for the exhaust gas formed in a spiral shape along the outer periphery of the body, a heat absorption flow path for the combustion air formed in a spiral shape inside the body, and a return path for the preheated combustion air formed in the center of the body.

This radiant tube heating device can heat the heat treatment furnace while keeping the atmosphere clean, and is a radiant tube heating device with excellent thermal efficiency and durability.

Furthermore, a radiant tube that has improved structural strength and excellent heat consumption efficiency has been known in the past, for example, as shown in Patent Document 2.
The radiant tube shown in Patent Document 2 has an elliptical cross section with its major axis parallel to the surface of the steel plate being heated and its minor axis perpendicular to the surface of the steel plate.
The radiant tube shown in Patent Document 2 has an elliptical cross section and its major axis is arranged parallel to the surface of the steel plate to be heated, so that the projected area of the radiant tube on the steel plate is larger than that of a radiant tube with a circular cross section. This has the effect of efficiently transferring the heat radiated from the radiant tube to the surface of the steel plate.

Furthermore, as a radiant tube incorporating a heat exchanger with improved heat recovery performance, for example, the one shown in Patent Document 3 is known.
The radiant tube shown in Patent Document 3 has a first partition made of a cylindrical breathable solid arranged within the tube body on the exhaust gas side of the radiant tube at a position corresponding to the heating surface of the heated object of the radiant tube, and a second partition made of a cylindrical breathable solid arranged at a position closer to the exhaust gas outlet than the first partition, and a heat exchanger is provided within a heat exchange chamber surrounded by the first and second partitions, forming a gas flow passage through which high-temperature gas in the radiant tube passes through the first partition, passes through the heat exchange chamber, and then passes through the second partition before being discharged from the exhaust gas outlet.

According to the radiation tube shown in Patent Document 3, the sensible heat of the combustion gas is converted into radiant heat using the first and second partitions made of a breathable solid with high radiation capacity, improving the heat transfer performance into the heating chamber by loading radiant heat onto the tube body of the radiation tube, and improving the heat recovery efficiency by loading radiant heat onto the heat exchanger. In addition, by incorporating the heat exchanger into the radiation tube, it is possible to obtain a radiation tube with a heat exchanger having an extremely compact structure.

JP 2018-17470 A Japanese Utility Model Application Publication No. 2-85207 Japanese Unexamined Patent Publication No. 58-18015

However, the conventional radiant tube type heating device disclosed in Patent Document 1, the radiant tube disclosed in Patent Document 2, and the radiant tube disclosed in Patent Document 3 have the following problems.
In other words, in the case of the radiant tube heating device shown in Patent Document 1, the existing heat exchanger needs to be replaced with a ceramic heat exchanger, and there is a problem that the hurdle for introduction is very high due to reasons such as the high replacement costs.

In addition, when considering the installation of a heat exchanger in the radiant tube shown in Patent Document 2, existing heat exchangers have been developed to fit radiant tubes with a circular cross-sectional shape, so if an existing heat exchanger is installed on a radiant tube with an elliptical cross-sectional shape, the change in the cross-sectional shape of the radiant tube will change the flow of the combustion gas, and there is a problem that sufficient exhaust heat recovery efficiency cannot be obtained in the heat exchanger.

Furthermore, in the case of the radiant tube shown in Patent Document 3, a support plate with an air hole is provided at the opening on one end of the cylinder (first partition and second partition) surrounding the heat exchanger. If there is a partition with air permeability at the opening on one end of the cylinder, there is a problem that pressure loss increases. There is also a problem that the ventilation part formed in the support plate may be clogged with dust or soot in the combustion gas, causing malfunctions.

The present invention was made to solve this problem, and its purpose is to provide a radiant tube heating device and inner tube that can improve the efficiency of exhaust heat recovery in the heat exchanger installed inside the radiant tube without replacing or modifying the heat exchanger.

In order to solve the above problems, the radiant tube heating device according to one embodiment of the present invention is a radiant tube heating device equipped with a heat exchanger inside a radiant tube, and is characterized by the arrangement of an inner tube having an inner tube body with openings at both ends, which is arranged in the combustion gas flow path between the heat exchanger and the radiant tube so as to surround the outer periphery of the heat exchanger, and a baffle plate portion that suppresses the flow of combustion gas flowing in the combustion gas flow path between the inner tube body and the radiant tube.

Another aspect of the present invention is an inner tube used in the above-mentioned radiant tube heating device, and is characterized in that it has the inner tube body and the baffle plate portion.

The radiant tube heating device and inner cylinder of the present invention can provide a radiant tube heating device and inner cylinder that can improve the exhaust heat recovery efficiency of the heat exchanger installed inside the radiant tube without replacing or modifying the heat exchanger.

1 is a schematic diagram showing the general configuration of a radiant tube heating device according to a first embodiment of the present invention; This is a cross-sectional view taken along line A-A' in Figure 1. 2 is a perspective view of an inner cylinder used in the radiant tube heating device shown in FIG. 1. FIG. 13 is a perspective view showing a modified example of the inner cylinder. 1 is a graph showing the relationship between the combustion gas temperature and the value w/d obtained by dividing the gap w between the inner wall surface of the inner cylinder body and the wall surface of the heat exchanger by the outer diameter d of the heat exchanger. 1 is a graph showing the relationship between pressure loss and the value obtained by dividing the gap w between the inner wall surface of the inner cylinder body and the outer wall surface of the heat exchanger by the outer diameter d of the heat exchanger. 2 of a radiant tube applied to a radiant tube type heating device according to a second embodiment of the present invention. FIG. 11 is a graph showing a comparison of the amount of change in combustion gas temperature in case 1, case 2, and case 3.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments shown below are merely examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention is not limited to the following embodiments in terms of the materials, shapes, structures, arrangements, etc. of the components.
In addition, the drawings are schematic, and therefore, it should be noted that the relationship between thickness and planar dimensions, ratios, etc. may differ from the actual relationship between thickness and planar dimensions, and the drawings may include parts in which the relationship between dimensions and ratios differ from one another.

First Embodiment
FIG. 1 shows a radiant tube heating device according to a first embodiment of the present invention, and the radiant tube heating device 1 includes a radiant tube 10 bent into a substantially M-shape.
One end 10a and the other end 10b of the radiant tube 10 are attached to the furnace wall 2 of the heat treatment furnace so that the radiant tube 10 protrudes into the heat treatment furnace in which the object to be heated is heated. In the first embodiment, the cross-sectional shape of the radiant tube 10 is a circular tube shape with a predetermined plate thickness and an inner diameter D, as shown in Figure 2.
A burner 20 is disposed in the hollow portion 11 on the one end 10a side of the radiant tube 10. The burner 20 supplies fuel gas and combustion air into the radiant tube 10, combusts them in the radiant tube 10, and heats the radiant tube 10 from the inside with the generated combustion gas. The burner 20 is attached to a first member 50 having a fuel gas supply passage 52 for supplying fuel gas and a combustion air supply passage 53 for supplying combustion air. The fuel gas is sent to the burner 20 from a fuel gas supply port 51 provided in the first member 50 through the fuel gas supply passage 52. The combustion air is sent to the burner 20 from a combustion air supply port 54 described later through the combustion air supply passage 53.
The radiant tube 10 is heated by the combustion gas, and the radiant heat is used to heat an object to be heated, for example, a steel plate.

On the other hand, a heat exchanger 30 is disposed in the combustion gas flow passage 12 on the other end 10b side of the radiant tube 10. The heat exchanger 30 heats the combustion air supplied from the outside by performing heat exchange between the combustion gas (exhaust gas) that has heated the radiant tube 10 and the combustion air, and supplies the heated combustion air to the burner 20 side. The heat exchanger 30 is attached to a second member 60 having a combustion air supply passage 62 and a combustion gas exhaust passage 64. The combustion air is supplied to the heat exchanger 30 from the combustion air supply port 61 through the combustion air supply passage 62, where it is heat exchanged with the combustion gas (exhaust gas) and heated, and is supplied from the air supply port 63 through the air piping 55 to the combustion air supply port 54 provided in the first member 50. Then, as described above, the combustion air is sent from the combustion air supply port 54 through the combustion air supply passage 53 to the burner 20.
The combustion gas (exhaust gas) from which the exhaust heat has been recovered by the heat exchanger 30 is discharged to the outside from a combustion gas exhaust port 65 via a combustion gas exhaust passage 64 .
Here, in the radiant tube heating device 1 of this embodiment, in order to improve the exhaust heat recovery efficiency in the heat exchanger 30, an inner tube 40 is arranged in the combustion gas flow path 12 between the heat exchanger 30 and the other end 10b side of the radiant tube 10, as shown in Figures 1 and 2.

The inner tube 40 includes an inner tube body 41 that surrounds the outer periphery of the heat exchanger 30, and a baffle plate portion 42 that suppresses the flow of combustion gas flowing through the combustion gas flow path 12b between the inner tube body 41 and the radiant tube 10.

The inner tube body 41 is composed of a cylindrical tube having a circular cross-sectional shape, and has openings (not shown) at both ends. It is preferable that this opening is not provided with a mesh-like, honeycomb-like, fiber-like, porous or other breathable partition. If a mesh-like or other breathable partition is provided at this opening, the pressure loss will increase. In addition, the ventilation section formed in the partition may be clogged with dust or soot in the combustion gas, causing a malfunction. For this reason, the inner tube body 41 is shaped to have openings at both ends. In addition, the material of the inner tube body 41 is not particularly limited, but is preferably one that can withstand thermal loads, such as ceramic materials and refractories.

The outer diameter of the inner tube body 41 is smaller than the inner diameter D of the radiant tube 10. The inner diameter of the inner tube body 41 is d+2w, expressed using the outer diameter d of the heat exchanger 30 and the gap w between the inner wall surface of the inner tube body 41 and the outer wall surface of the heat exchanger 30. The length of the inner tube body 41 along the length direction of the radiant tube 10 is not particularly specified, but it is sufficient if it is a length that can cover the entire length of the radiant tube 10 of the heat exchanger 30 along the length direction. In addition, both ends of the inner tube body 41 in the length direction are open and communicate with the combustion gas exhaust passage 64 provided in the second member 60.
1 and 3, the baffle plate 42 is provided at an end of the inner cylinder body 41 in the longitudinal direction, and is formed in a flange disk shape protruding outward from the inner cylinder body 41 to close the combustion gas flow path 12b between the inner cylinder body 41 and the radiant tube 10. The baffle plate 42 and the inner cylinder body 41 are integrally formed. The baffle plate 42 is attached to the second member 60 by mounting bolts (not shown).

In this way, the radiant tube heating device according to the first embodiment of the present invention has an inner tube 40 equipped with an inner tube body 41 arranged in the combustion gas flow path 12 between the heat exchanger 30 and the radiant tube 10 so as to surround the outer periphery of the heat exchanger 30, and a baffle plate portion 42 that suppresses the flow of combustion gas flowing in the combustion gas flow path 12b between the inner tube body 41 and the radiant tube 10.

As a result, the combustion gas flowing through the radiant tube 10 mainly flows through the combustion gas flow path 12a between the heat exchanger 30 and the inner cylinder body 41 of the inner cylinder 40 at the combustion gas flow path 12 on the other end 10b side of the radiant tube 10, and the flow is suppressed by the baffle plate portion 42 in the combustion gas flow path 12b between the inner cylinder body 41 and the radiant tube 10. As a result, in the combustion gas flow path 12a between the heat exchanger 30 and the inner cylinder body 41 of the inner cylinder 40, the flow rate of the combustion gas increases and the Reynolds number improves, the heat transfer performance from the combustion gas to the heat exchanger 30 increases, and the exhaust heat recovery efficiency in the heat exchanger 30 can be improved.

On the other hand, a stagnation area of the combustion gas occurs in the combustion gas flow path 12b between the inner tube body 41 and the radiant tube 10, improving the insulation performance. The installation part of the heat exchanger 30 where the inner tube 40 is arranged is located at the end part (other end 10b) of the radiant tube 10, and is therefore located in the furnace wall 2, most of which is made of insulation material, so there is no need to transfer heat from the combustion gas to the radiant tube 10. The insulation effect caused by the stagnation of the combustion gas increases the temperature of the inner tube body 41 of the inner tube 40, contributing to improving the exhaust heat recovery capacity of the heat exchanger 30.
In this embodiment, in order to improve the exhaust heat recovery efficiency in the heat exchanger 30, there is no need to replace or modify the existing heat exchanger 30.

Therefore, according to the radiant tube heating device 1 of this embodiment, a radiant tube heating device 1 can be provided that can improve the exhaust heat recovery efficiency of the heat exchanger 30 installed in the radiant tube 10 without replacing or modifying the heat exchanger 30.

In this embodiment, the baffle plate portion 42 protrudes outward from the inner tube body 41 and blocks the combustion gas flow path 12b between the inner tube body 41 and the radiant tube 10. This completely prevents the combustion gas from being discharged to the outside from the combustion gas flow path 12b between the inner tube body 41 and the radiant tube 10. Therefore, the combustion gas flowing through the radiant tube 10 flows only through the combustion gas flow path 12a between the heat exchanger 30 and the inner tube body 41 of the inner tube 40 at the combustion gas flow path 12 on the other end 10b side of the radiant tube 10. As a result, in the combustion gas flow path 12a between the heat exchanger 30 and the inner tube body 41 of the inner tube 40, the flow rate of the combustion gas increases and the Reynolds number improves, resulting in an increase in the heat transfer performance from the combustion gas to the heat exchanger 30 and an improvement in the exhaust heat recovery efficiency in the heat exchanger 30.

In addition, in this embodiment, the gap w between the inner wall surface of the inner cylinder body 41 and the outer wall surface of the heat exchanger 30 divided by the outer diameter d of the heat exchanger 30, w/d, is set to 0.06 or more.

The reason for this will be explained. Figure 5 shows the relationship between the combustion gas temperature after passing through the heat exchanger 30 and the value w/d obtained by dividing the gap w between the inner wall surface of the inner tube body 41 and the outer wall surface of the heat exchanger 30 by the outer diameter d of the heat exchanger, when the cross-sectional shape of the radiant tube 10 is a perfect circle with an inner diameter D and a specified plate thickness. Figure 6 also shows the relationship between the pressure loss and the value w/d obtained by dividing the gap w between the inner wall surface of the inner tube body 41 and the outer wall surface of the heat exchanger 30 by the outer diameter d of the heat exchanger 30, when the cross-sectional shape of the radiant tube 10 is a perfect circle with an inner diameter D and a specified plate thickness.

As can be seen from Figure 5, the smaller the w/d, the lower the combustion gas temperature after passing through the heat exchanger 30. This means that the smaller the w/d, the more efficiently the exhaust heat is recovered by the heat exchanger 30.

On the other hand, as can be seen from FIG. 6, the smaller the w/d, the greater the pressure loss. If the pressure loss increases, it becomes impossible to maintain negative pressure inside the radiant tube 10. If the radiant tube 10 is used for a long period of time, cracks may occur in the radiant tube 10. If a crack occurs in the radiant tube 10, and if there is negative pressure inside the radiant tube 10, there is little risk of the combustion gas in the radiant tube 10 leaking into the furnace and exposing the object to be heated to the combustion gas. When w/d<0.06, the pressure loss exceeds approximately 500 Pa and becomes particularly large, so in this embodiment, the inner diameter of the inner tube body 41 and the outer diameter d of the heat exchanger 30 are set so that w/d is 0.06 or more.

On the other hand, as w/d increases, the exhaust heat recovery efficiency decreases as shown in FIG. 5. In this embodiment, the inner cylinder 40, which includes the inner cylinder body 41 and the baffle plate portion 42 that suppresses the flow of combustion gas flowing in the combustion gas flow path between the inner cylinder body 41 and the radiant tube 10, is arranged so that the inner cylinder body 41 surrounds the outer periphery of the heat exchanger 30 and is located between the heat exchanger 30 and the inner wall surface of the radiant tube 10. Therefore, in this embodiment, the gap w that becomes the combustion gas flow path is smaller than the gap (D-d)/2 when the inner cylinder 40 is not present, so that the exhaust heat recovery efficiency is improved compared to when the inner cylinder 40 is not present. Therefore, as long as the inner cylinder 40 can be arranged as described above, there is no particular upper limit value for w/d, but in order to increase the effect of improving the exhaust heat recovery efficiency, it is preferable that the inner diameter d+2w of the inner cylinder body 41 and the outer diameter d of the heat exchanger 30 are set so that w/d is 0.15 or less.

Gas inside the radiant tube 10 exists in the gap _WD between the inner wall surface of the radiant tube 10 and the outer wall surface of the inner tube body 41, but flow is suppressed because there is no escape route for the gas. This allows heat to be transferred to the furnace wall 2, and has the effect of suppressing a decrease in heat recovery efficiency. Since the thermal conductivity of air is low, the above effect can be obtained even if the aforementioned gap _WD is small. However, even if the gap _WD = 0, the inner tube 40 can increase the combustion gas flow rate around the heat exchanger 30, so the effect of improving the heat recovery rate can be obtained.

Next, a modified example of the inner cylinder 40 will be described with reference to FIG. 4. As shown in FIG. 4, the baffle plate section 42 constituting the inner cylinder 40 is composed of two baffle plates 42a, 42b installed at a predetermined distance apart at locations other than both ends in the longitudinal direction of the inner cylinder main body 41. Each baffle plate 42a, 42b protrudes outward from the inner cylinder main body 41 by the same length and, although not shown, blocks the combustion gas flow path 12b between the inner cylinder main body 41 and the radiant tube 10.

As a result, even if the inner tube 40 is positioned at an angle toward the combustion gas flow path 12 between the heat exchanger 30 and the radiant tube 10, either one of the two baffles 42a, 42b can reliably block the combustion gas flow path 12b between the inner tube body 41 and the radiant tube 10.
Second Embodiment
Next, a radiant tube type heating device according to a second embodiment of the present invention will be described with reference to Fig. 7. Fig. 7 shows a cross section similar to Fig. 2 of a radiant tube applied to the radiant tube type heating device according to the second embodiment of the present invention.
The radiant tube heating device of the second embodiment of the present invention has the same basic configuration as the radiant tube heating device 1 of the first embodiment shown in Figure 1, but the cross-sectional shape of the radiant tube 10 and the shape of the inner tube 40 are different.

That is, the cross-sectional shape of the radiant tube 10 in the radiant tube heating device according to the second embodiment of the present invention is an elliptical tube shape with a major axis a and a minor axis b for an inner diameter having a given plate thickness, as shown in FIG. 7.

By making the cross-sectional shape of the radiant tube 10 an elliptical tube shape and arranging the radiant tube 10 so that the major axis of the ellipse faces the object to be heated, the projected area of the radiant tube 10 relative to the object to be heated is increased, and the heat radiated from the radiant tube 10 can be efficiently transferred to the object to be heated. In addition, when the radiant tube 10 is used in a vertical furnace, as shown in FIG. 1, the radiant tube 10 is fixed to the furnace wall 2 so that one end side and the other end side of the radiant tube 10 are aligned along the vertical direction. In this case, by making the cross-sectional shape of the radiant tube 10 an elliptical tube shape and arranging the radiant tube 10 so that the major axis of the ellipse in the straight tube section of the radiant tube 10 is vertical, the rigid strength of the radiant tube 10 can be increased in the vertical direction, and deformation of the radiant tube 10 due to the bending moment caused by the weight of the radiant tube 10 can be suppressed.

The inner tube 40, which is disposed in the combustion gas flow path 12 between the heat exchanger 30 and the other end 10b side of the radiant tube 10, includes an inner tube body 41 that surrounds the outer periphery of the heat exchanger 30, and a baffle plate portion 42 that suppresses the flow of combustion gas flowing in the combustion gas flow path 12b between the inner tube body 41 and the radiant tube 10.

The inner tube body 41 is a cylindrical tube having a circular cross-sectional shape, and has openings (not shown) at both ends. It is preferable that the openings are not provided with a mesh-like, honeycomb-like, fiber-like, porous or other breathable partition. The outer diameter of the inner tube body 41 is smaller than the minor diameter b of the radiant tube 10. The inner diameter of the inner tube body 41 is d+2w, expressed using the outer diameter d of the heat exchanger 30 and the gap w between the inner wall surface of the inner tube body 41 and the outer wall surface of the heat exchanger 30. The length of the inner tube body 41 along the length of the radiant tube 10 is not particularly specified, but is set to a length that can cover the entire length of the radiant tube 10 of the heat exchanger 30 along the length of the radiant tube 10.

Here, the baffle plate portion 42 is provided at the end of the inner cylinder body 41 in the longitudinal direction, but unlike the baffle plate portion 42 shown in Figures 1 to 3, it is formed in the shape of a flanged elliptical plate that protrudes outward from the inner cylinder body 41 and is designed to block the combustion gas flow path 12b between the inner cylinder body 41 and the radiant tube 10. The baffle plate portion 42 and the inner cylinder body 41 are formed integrally.

In this way, even in the radiant tube type heating device according to the second embodiment, an inner tube 40 is arranged with an inner tube body 41 arranged in the combustion gas flow path 12 between the heat exchanger 30 and the radiant tube 41 so as to surround the outer periphery of the heat exchanger 30, and a baffle plate portion 42 that suppresses the flow of combustion gas flowing in the combustion gas flow path 12b between the inner tube body 41 and the radiant tube 10.

As a result, the combustion gas flowing through the radiant tube 10 mainly flows through the combustion gas flow path 12a between the heat exchanger 30 and the inner cylinder body 41 of the inner cylinder 40 at the combustion gas flow path 12 on the other end 10b side of the radiant tube 10, and the flow is suppressed by the baffle plate portion 41b in the combustion gas flow path 12b between the inner cylinder body 41 and the radiant tube 10. As a result, in the combustion gas flow path 12a between the heat exchanger 30 and the inner cylinder body 41 of the inner cylinder 40, the flow rate of the combustion gas increases and the Reynolds number improves, the heat transfer performance from the combustion gas to the heat exchanger 30 increases, and the exhaust heat recovery efficiency in the heat exchanger 30 can be improved.

Here, if the cross-sectional shape of the radiant tube 10 is elliptical as in the second embodiment, the cross-sectional area of the combustion gas flow path 12 between the heat exchanger 30 is often larger than when the cross-sectional shape of the radiant tube 10 is a perfect circle. In this case, the flow rate of the combustion gas flowing through the combustion gas flow path 12 is slowed down, which leads to a problem that the heat transfer performance from the combustion gas to the heat exchanger 30 is deteriorated and the exhaust heat recovery efficiency in the heat exchanger 30 is reduced.

In contrast, the radiant tube heating device according to the second embodiment solves this problem by disposing an inner tube 40 in the combustion gas flow path 12 between the heat exchanger 30 and the radiant tube 10, the inner tube 40 having an inner tube body 41 that surrounds the outer periphery of the heat exchanger 30 and a baffle plate portion 42 that suppresses the flow of combustion gas flowing in the combustion gas flow path 12b between the inner tube body 41 and the radiant tube 10.

A stagnation area of the combustion gas occurs in the combustion gas flow path 12b between the inner tube body 41 and the radiant tube 10, improving the insulation performance. The installation part of the heat exchanger 30 where the inner tube 40 is arranged is located at the end part (other end 10b) of the radiant tube 10, and is therefore located in the furnace wall 2, most of which is made of insulation material, so there is no need to transfer heat from the combustion gas to the radiant tube 10. The insulation effect caused by the stagnation of the combustion gas increases the temperature of the inner tube body 41 of the inner tube 40, contributing to improving the exhaust heat recovery capacity of the heat exchanger 30.

And when the cross-sectional shape of the radiant tube 10 is elliptical, there is no need to replace or modify the existing heat exchanger 30 in order to improve the exhaust heat recovery efficiency in the heat exchanger 30.

Therefore, according to the radiant tube heating device 1 of the second embodiment, a radiant tube heating device can be provided that can improve the exhaust heat recovery efficiency of the heat exchanger 30 installed in the radiant tube 10 without replacing or modifying the heat exchanger 30.

In the second embodiment, the baffle plate portion 42 is formed in the shape of a flange elliptical plate protruding outward from the inner cylinder body 41, and blocks the combustion gas flow path 12b between the inner cylinder body 41 and the radiant tube 10, which has an elliptical cross section. This completely prevents the combustion gas from being discharged to the outside from the combustion gas flow path 12b between the inner cylinder body 41 and the radiant tube 10. Therefore, the combustion gas flowing in the radiant tube 10 flows only in the combustion gas flow path 12a between the heat exchanger 30 and the inner cylinder body 41 of the inner cylinder 40 at the combustion gas flow path 12 on the other end 10b side of the radiant tube 10. As a result, in the combustion gas flow path 12a between the heat exchanger 30 and the inner cylinder body 41 of the inner cylinder 40, the flow rate of the combustion gas is further increased and the Reynolds number is further improved, the heat transfer performance from the combustion gas to the heat exchanger 30 is further improved, and the exhaust heat recovery efficiency in the heat exchanger 30 can be further improved.

Furthermore, in the radiant tube heating device of the second embodiment, the gap w between the inner wall surface of the inner tube body 41 and the outer wall surface of the heat exchanger 30 divided by the outer diameter d of the heat exchanger 30, w/d, is 0.06 or more.
As a result, similarly to the radiant tube heating device according to the first embodiment, it is possible to improve the exhaust heat recovery efficiency in the heat exchanger 30 while avoiding large pressure losses.

In addition, when the cross-sectional shape of the radiant tube 10 is an elliptical tube shape, the size of the gap W _a in the major axis direction and the gap W _c in the minor axis direction in the cross-section of the radiant tube 10 between the inner tube body 41 and the radiant tube 10 are different. In this case, even if the gaps W _a and W _c are small, the effect of suppressing the decrease in heat recovery efficiency can be obtained. However, even if gap W _a = gap W _c = 0, the inner tube 40 can increase the combustion gas flow speed around the heat exchanger 30, so the effect of improving the heat recovery rate can be obtained.

The above describes an embodiment of the present invention, but the present invention is not limited to this and various modifications and improvements can be made.

For example, in the radiant tube heating device according to the first and second embodiments, the baffle plate portion 42 is not limited to protruding outward from the inner tube body 41, so long as it suppresses the flow of combustion gas flowing in the combustion gas flow passage 12b between the inner tube body 41 and the radiant tube 10. In addition, the baffle plate portion 42 does not necessarily need to be formed integrally with the inner tube body 41.

Furthermore, in the radiant tube heating devices of the first and second embodiments, the baffle plate portion 42 does not necessarily need to block the combustion gas flow path 12b between the inner tube body 41 and the radiant tube 10, as long as it is capable of suppressing the flow of combustion gas flowing within the combustion gas flow path 12b between the inner tube body 41 and the radiant tube 10.
Furthermore, the cross-sectional shape of the radiant tube 10 is not limited to a perfect circle or an ellipse.
Furthermore, when the gap between the inner wall surface of the inner cylinder body 41 and the outer wall surface of the heat exchanger 30 is w and the outer diameter of the heat exchanger is d, w/d does not necessarily need to be 0.06 or more.
Moreover, the inner cylinder body 41 and the heat exchanger 30 do not necessarily need to be concentric.

To verify the effects of the present invention, the change in the sensible heat of the exhaust gas discharged outside the heat treatment furnace was measured for an example of the present invention in which an inner tube 40 was placed in the combustion gas flow path 12 between the radiant tube 10, which has an elliptical cross-sectional shape as shown in Figure 7, and the heat exchanger 30, and for a comparative example in which an inner tube 40 was not placed in the combustion gas flow path 12 between the radiant tube 10, which has an elliptical cross-sectional shape, and the heat exchanger 30.

The cross-sectional shape of the radiant tube 10 is an elliptical tube with a major axis a of 234 mm and a minor axis b of 186 mm. The outer diameter of the inner tube body 41 of the inner tube 40 is 186 mm, and the inner diameter is 182 mm. The length of the inner tube body 41 in the longitudinal direction is from the inner end of the radiant tube 10 (the intersection with the outer surface of the furnace wall 2) to the tip of the heat exchanger 30. The baffle plate portion 42 is a flange disk shape that protrudes outward (up and down in FIG. 3) from the longitudinal end of the inner tube body 41, as in FIG. 3, and blocks the combustion gas flow path 12b between the inner tube body 41 and the radiant tube 10.

The amount of fuel gas and the amount of combustion air fed into the radiant tube heating device were adjusted to be uniform, and the change in the sensible heat of the exhaust gas discharged from the heat treatment furnace to the outside was measured. When the calorific value of the fed fuel gas was taken as 100%, the sensible heat of the exhaust gas in the present invention example was reduced by 1% compared to the comparative example. Since the heat that could not be used in the heat treatment furnace is discharged as sensible heat of the exhaust gas, the reduction in the sensible heat of the exhaust gas means that the recovery of the exhaust heat in the heat exchanger 30 has been improved. Therefore, as a result of measuring the change in the sensible heat of the exhaust gas, it was found that the recovery of the exhaust heat in the heat exchanger 30 in the present invention example was improved compared to the comparative example.
Further, the amount of change in the combustion gas temperature after passing through the heat exchanger 30 was investigated for each of the following cases 1, 2, and 3. The results of the investigation are shown in FIG.

In case 1, the cross-sectional shape of the radiant tube 10 is a perfect circle with an inner diameter D, a heat exchanger 30 with an outer diameter d is installed in the combustion gas flow path 12 of the radiant tube 10, and the relationship D/d = 1.9 is satisfied. The change in the combustion gas temperature is the difference between the combustion gas temperature after passing through the heat exchanger 30 when no inner tube 40 is installed in the combustion gas flow path 12 between the heat exchanger 30 and the radiant tube 10, and the combustion gas temperature after passing through the heat exchanger 30 when an inner tube 40 with w/d = 0.17 is installed in the combustion gas flow path 12 between the heat exchanger 30 and the radiant tube 10.

In case 2, the cross-sectional shape of the radiant tube 10 is an ellipse with a ratio of the major axis a to the minor axis b of a/b = 1.24, and a heat exchanger 30 with an outer diameter d is installed in the combustion gas flow path 12 of the radiant tube 10, satisfying the relationship of b/d = 1.9 (when the wet edge length is longer than that of a circular radiant tube with the inner diameter D). The change in combustion gas temperature is the difference between the combustion gas temperature after passing through the heat exchanger 30 when no inner tube 40 is installed in the combustion gas flow path 12 between the heat exchanger 30 and the radiant tube 10, and the combustion gas temperature after passing through the heat exchanger 30 when an inner tube 40 with w/d = 0.17 is installed in the combustion gas flow path 12 between the heat exchanger 30 and the radiant tube 10.

In case 3, the cross-sectional shape of the radiant tube 10 is an ellipse with a ratio of the major axis a to the minor axis b of a/b = 1.24, and the wet edge length is the same as that of a circular radiant tube with the inner diameter D. A heat exchanger 30 with an outer diameter d is installed in the combustion gas flow path 12 of the radiant tube 10. The change in combustion gas temperature is the difference between the combustion gas temperature after passing through the heat exchanger 30 when no inner tube 40 is installed in the combustion gas flow path 12 between the heat exchanger 30 and the radiant tube 10, and the combustion gas temperature after passing through the heat exchanger 30 when an inner tube 40 with w/d = 0.17 is installed in the combustion gas flow path 12 between the heat exchanger 30 and the radiant tube 10.

Referring to FIG. 8, it can be seen that the amount of change in the combustion gas temperature in case 2 is greater than the amount of change in the combustion gas temperature in case 1 and the amount of change in the combustion gas temperature in case 3. In other words, the effect of exhaust heat recovery by installing the inner tube 40 is greater when the cross-sectional shape of the radiant tube 10 is elliptical and its wet edge length is greater than that of a circular radiant tube than when the cross-sectional shape of the radiant tube 10 is circular or when the cross-sectional shape of the radiant tube 10 is elliptical and its wet edge length is the same as that of a circular radiant tube.

Reference Signs List 1 Radiant tube heating device 2 Furnace wall 10 Radiant tube 10a One end of radiant tube 10b Other end of radiant tube 11 Hollow portion 12 Combustion gas flow path (between heat exchanger and radiant tube)
12a Combustion gas flow path (between the heat exchanger and the inner cylinder body)
12b Combustion gas flow path (between the inner cylinder body and the radiant tube)
20 burner 30 heat exchanger 40 inner cylinder 41 inner cylinder main body 42 baffle plate portion 42a baffle plate 42b baffle plate 50 first member 51 fuel gas supply port 52 fuel gas supply path 53 combustion air supply path 54 combustion air supply port 55 air piping 60 second member 61 combustion air supply port 62 combustion air supply path 63 air supply port 64 combustion gas exhaust path 65 combustion gas exhaust port

Claims (4)

A radiant tube type heating device equipped with a heat exchanger inside a radiant tube,
an inner cylinder having an inner cylinder body having openings at both ends and disposed in a combustion gas flow path between the heat exchanger and the radiant tube so as to surround an outer periphery of the heat exchanger; and a baffle plate portion for suppressing the flow of combustion gas flowing in the combustion gas flow path between the inner cylinder body and the radiant tube;
A radiant tube type heating device characterized in that when the gap between the inner wall surface of the inner tube body and the outer wall surface of the heat exchanger is w and the outer diameter of the heat exchanger is d, w/d is 0.06 or more and 0.15 or less. The radiant tube heating device according to claim 1, characterized in that the baffle plate protrudes outward from the inner tube body and blocks the combustion gas flow path between the inner tube body and the radiant tube. The radiant tube heating device according to claim 1 or 2, characterized in that the cross-sectional shape of the radiant tube is a perfectly circular tube shape. The radiant tube heating device according to claim 1 or 2, characterized in that the cross-sectional shape of the radiant tube is an elliptical tube shape.

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