JP3505076B2 - Heating furnace using radiant tube as heat source - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating furnace in which a radiant tube is provided with a pair of heat storage type burners at both ends thereof, and the burners are alternately burned to heat the tube to serve as a heat source. More specifically, the present invention relates to improved placement of radiant tubes within a furnace.

[0002]

2. Description of the Related Art As a heat source in a heating furnace which dislikes a contaminated atmosphere, for example, a sintering furnace used for powder metallurgy of iron-based magnetic materials, heating of a green compact is carried out by using a gas mixture of hydrogen gas, nitrogen, hydrogen and carbon dioxide gas. Electric heating is generally adopted because it is performed in an enclosed reducing atmosphere, requires a furnace temperature of 1100 to 1200 ° C., and requires precise temperature control.

Further, a radiant tube and one radiant tube burner which causes long-flame combustion in the tube may be adopted as a heat source.

[0004]

However, electric heating has a problem of high energy cost. Further, when the radiant tube burner is used as the heat source, the cost is low, but there are technical problems as described below, making it difficult to apply to a sintering furnace that requires precise temperature control. ing. That is, since the combustion progresses in one direction from the one end of the radiant tube toward the exhaust port of the other end, the tube surface temperature in the vicinity of the firing port becomes highest as shown in FIG. 3, and the combustion amount is increased. If it passes, the vicinity of the firing port will be burnt out due to overheating. Therefore, in a sintering furnace that operates at a high temperature of 1100 to 1200 ° C., the vicinity of the burning end of the tube is burned due to overheating.

In order to prevent the burnout of the tube, it is necessary to reduce the temperature of the tube in the vicinity of the firing port to a temperature below the limit of use of the tube material, so the amount of combustion must be reduced. Therefore, the heat transfer amount per tube surface area is limited, and in order to maintain a predetermined furnace temperature, it is necessary to increase the number of tubes to secure the tube surface area. Moreover, it may be difficult to maintain a predetermined furnace temperature in some cases.

Further, the temperature of the combustion gas in the tube lowers toward the exhaust port, and the amount of heat transfer decreases in the lengthwise direction of the tube. Then, there is a large temperature gradient in the length direction of the tube, which shortens the life of the tube.
Further, it is impossible to uniformly heat a material that requires uniform and precise temperature control.

Further, since the amount of heat transfer is proportional to the logarithmic mean temperature difference between the combustion gas temperature and the work temperature, a huge heat transfer area (tube surface area) is required in order to save energy by lowering the exhaust gas temperature. Therefore, it is possible to install a recuperator to recover the exhaust heat and preheat the combustion air, but even in this case, the tube temperature near the heating port must be below the limit temperature, increasing the amount of heat transfer. I can't. Furthermore, even if some heat saving is achieved even if a heat recovery is attempted by providing a recuperator at the tube exhaust port and the other end side for heat exchange between the exhaust gas and the combustion air, the temperature efficiency of the recuperator used is The effect is low due to the low rate of 60% or less.

As described above, it has been difficult to use the conventional radiant tube burner as a heat source for a heating furnace such as a sintering furnace.

An object of the present invention is to provide a heating furnace using a radiant tube as a heat source, which can realize uniform heating not only in the tube length direction but also in the tube-to-tube direction.

[0010]

In order to achieve the above object, the invention according to claim 1 has a heat storage type burner for alternately discharging exhaust gas and supplying combustion air through a heat storage body at both ends of a radiant tube. A radiant tube equipped with a heat storage burner system that alternately burns a pair of burners is provided as a heating source, and the effective surface area ratio of the tubes between adjacent radiant tubes and (tube pitch / tube diameter) ^1/4 Is close to the maximum value, and the ratio of the heat flux of the object to be heated under the tube given by the direct radiation from the two radiant tubes to the heat flux of the object to be heated in the middle of the tube is 1 The tube pitch is set in a range that simultaneously satisfies the values in the vicinity.

In this case, the flow of the combustion gas in the tube is reversed at a constant cycle by the high-cycle alternating combustion of the heat storage type burners installed at both ends of the radiant tube, so that the tube temperature is averaged over the entire area and the material to be heated is heated. It is possible to realize uniform heating in the tube axis direction. On the other hand, between two adjacent tubes, the effective surface area ratio of the radiant tube and the reciprocal of (tube pitch / tube diameter) ^1/4 are both close to the maximum value, so the surface of the radiant tube is effectively used. At the same time, if the surface temperature of the tube is lowered and the surface heat load of the tube is the same, it is advantageous in preventing the tube from burning. Moreover, the ratio of the heat flux to the object to be heated directly below the tube and the heat flux to the object to be heated in the middle of the tube is 1
It is near, and it can be said that the heat flux distribution to the object to be heated between the two tubes is averaged and the heat uniformity is high. Therefore, by selecting the tube pitch and the tube diameter that satisfy the above range of the ratio, it is possible to effectively utilize the surface of the tube to lower the temperature of the tube and to uniformly heat the object to be heated.

Further, the invention according to claim 2 is such that the ratio of the effective surface area ratio of the tubes between adjacent radiant tubes and (tube pitch / tube diameter) ^1/4 is 90% or more of the maximum value. And the ratio of the heat flux of the object to be heated directly under the tube given by the direct radiation from the two radiant tubes to the heat flux of the object to be heated in the middle of the tube is 0.9 to 1.1. At the same time, the tube pitch is in a range that satisfies the range. In this case, it is possible to realize a uniform heating property that does not pose a practical problem.

Further, in the invention according to claim 3, the heating furnace is a sintering furnace and a straight tube type radiant tube is used as a heating source. In this case, a reducing atmosphere is formed, and the furnace temperature of 1100 to 1200 ° C. and precise temperature control can be performed therein, and heating conditions suitable for sintering of powder metallurgy can be formed and maintained.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The structure of the present invention will be described below in detail based on an embodiment shown in the drawings.

FIG. 1 shows a sintering furnace as an embodiment of a heating furnace using the radiant tube of the present invention as a heat source. This sintering furnace is suitable for use in powder metallurgy of iron-based magnetic materials, and employs the heat storage type radiant tube burner system 2 as its heat source. Note that the sintering furnace of the present embodiment is particularly structurally different from the conventional sintering furnace except that the heat storage type radiant tube burner system 2 is adopted as a heat source and the arrangement of the radiant tubes 3 is set in a specific relationship. Since there is no difference, detailed explanation is omitted. Reference numeral 1 in the figure
1 is a preheating part, 12 is a high heating part, 13 is a cooling part, 14 is an entrance door, 15 is an intermediate door, 16 is a thermocouple, 17 is a gas inlet for supplying an inert gas or the like, 18 is a mesh conveyor, 1
9 is a water cooling jacket, and 20 is an exit door.

The heat storage type radiant tube burner system 2 is a straight tube type radiant tube 3 which is arranged so as to pass through the side wall of the furnace body 1 and to traverse the inside of the furnace in a horizontal direction orthogonal to the conveying direction of the object to be heated. A pair of radiant tube burners (hereinafter simply referred to as burners) 4a, 4b which are connected to the parts installed outside the furnace at both ends thereof and burn alternately, and for burning the pair of burners 4a, 4b alternately It is composed of a combustion air supply system 5 for selectively supplying air and fuel, an exhaust system 6 and a fuel supply system 7.
The burners 4a and 4b are not particularly limited to a gun structure or the like, but the heat storage body 8 made of honeycomb ceramics or the like is internally provided or directly connected to the outside to connect the exhaust gas and the combustion air to the four-way valve 9. The combustion air at a high temperature (a temperature close to the exhaust gas temperature) obtained by passing the heat storage body 8 alternately through the heat storage body 8 is used for combustion in the closed space in the radiant tube 3. Here, the replacement cycle of the burners 4a and 4b to be operated is a constant time regardless of the presence or absence of combustion. For example, the burner that periodically burns in a short time of about 20 to 30 seconds is switched.

According to the sintering furnace configured as described above, the burners 4a and 4b are burned by using the secondary air that has passed through the heat storage body 8 and has been preheated to a high temperature, for example, 800 ° C. or higher. Alternating at both ends in a short time. Then, for example, the combustion gas generated by the combustion of the one burner 4a is attracted to the exhaust system 6 after passing through the heat storage body 8 of the burner 4b on the other end side while heating the radiant tube 3 and subjected to a predetermined exhaust treatment. And then released into the atmosphere. Therefore, the heat of the exhaust gas is recovered by the heat storage body 8. Then, the heat recovered in the heat storage body 8 is used for preheating the combustion air when the other burner 4b is burned, and is returned to the tube 3 again. As a result, a tube surface temperature distribution as shown in FIG. 3 is formed, and uniform heating is performed in the tube longitudinal direction.

Here, the heat storage body 8 is, for example, a passage cross-sectional area.
Honeycomb shape with constant flow path and straight passages
Ceramics such as alumina, cordierite, murai
It is preferable to use, but it is not particularly limited to
Not a bundle of thin tubes, balls or nuggets
It is also possible to use the shape. Most honeycomb-shaped cell
Ramix has a large heat capacity and high durability, but it is relatively compressed.
Low power loss, alternating exhaust and air supply without stagnation
Therefore, it is preferable. Also, materials other than ceramics, such as
For example, a composite of metal such as hot steel or ceramic and metal
For example, it melts in the pores of ceramics with a porous skeleton
Voluntarily infiltrate the formed metal and oxidize or partially oxidize it.
Nitrids into ceramics, completely filling the pores
Done Al ₂O₃-Al composite, SiC-Al₂O₃-A
It may be manufactured using an l-complex or the like.

As the radiant tube 3, a metal such as heat-resistant cast steel is usually used, but it is not particularly limited to this, and a ceramic tube such as SiC may be used. Ceramic tubes have the advantages of not being oxidized, being lightweight, and containing a small amount of heat (because they have a low specific gravity and can be made thin). As the radiant tube 3, a straight pipe (I type), U type, W
Examples of the shape include a straight tube type radiant tube, which is preferably used as the high temperature section 12 which operates at a furnace temperature of 1100 ° C. or higher. In the high temperature section 12, the surface heat load on the tube 3 (heat transfer amount per surface area of the radiant tube) is increased to increase the furnace temperature and give a large amount of heat to the object W to be heated. The amount of heat transferred from the radiant tube 3 to the object to be heated W depends on the cross-sectional heat load of the radiant tube 3 (heat input per cross-sectional area of the tube 3: heat input = combustion heat + combustion air sensible heat). That is, in order to give a large amount of heat transfer to the object to be heated, the combustion amount is increased to increase the sectional heat load, and if it is small, the combustion amount is reduced to decrease the sectional heat load. The larger the cross-section heat load, the more likely it is to burn due to overheating near the burner firing port. Therefore, from the viewpoint of preventing burnout, the section heat load is naturally limited. On the other hand, the amount of heat transferred to the object to be heated also depends on the surface heat load of the radiant tube. Surface heat load is proportional to cross-section heat load and tube diameter,
Since the tube length is inversely proportional to the tube length, the shorter the tube length, the larger the surface heat load per cross-section heat load, and the more the heat transfer amount per tube can occur without fear of tube burnout.

Since the length of the straight tube type radiant tube corresponds to about half of the U type and about 1/4 of the W type, for the same diameter, about twice the U type per section heat load, A surface heat load that is about four times that of the W type can be applied, the furnace temperature can be raised without fear of tube burning, and a large amount of heat can be applied to the object to be heated. Further, in the U-shaped radiant tube and the W-shaped radiant tube, since the straight pipe is joined by the U vent, the combustion gas in the pipe is reversed at the vent portion, so the temperature of the vent portion becomes higher than that of the straight pipe portion. In some cases, the uniformity of temperature is impaired and precise uniform heating becomes difficult.

Therefore, as the heat storage type radiant tube 3 used in the high temperature section 12, a straight tube type radiant tube is desirable.

Further, in the straight tube type radiant tube, since there is no vent, the pitch between the tubes can be freely set, and the optimum pitch for giving the optimum heat flux distribution to the object W to be heated can be selected. In the U-type and W-type radiant tubes, the pitch Lp between the tubes 3 is about 1.5 of the tube diameter D due to the limitation of the radius of curvature of the vent portion.
It is limited to a certain range of up to 1.7 times, and the heat flux required by the object W to be heated (heat transfer amount per surface area of the object to be heated)
There is also a problem that may occur when the optimum pitch for giving the distribution cannot be selected. On the other hand, since the straight tube type radiant tube does not have such a vent portion, the pitch between the tubes can be freely set.

In the heat storage type radiant tube burner system 2 configured as described above, the number, arrangement direction, etc. of the radiant tubes 3 are selected as necessary. Requires a certain relationship. That is, the ratio of the effective surface area ratio of the tubes between the adjacent radiant tubes and (tube pitch / tube diameter) ^1/4 is ^close to the maximum value, and the tube is given by direct radiation from the two radiant tubes. Having a tube pitch in a range that simultaneously satisfies the ratio of the heat flux of the object to be heated directly below to the heat flux of the object to be heated in the middle of the tube is at the same time uniform heating in the axial direction and width. It is necessary to satisfy both uniform heating in the same direction. When this piping condition is followed, uniform heating of the object W to be heated can be realized. The heating in the tube axis direction and the tube-to-tube direction will be described below. (1) Tube A heat storage type burner in the axial direction is installed at both ends of the radiant tube.
By alternately switching between combustion and exhaust with a short switching time of about 30 seconds, the flow of the combustion gas in the tube is reversed at a constant cycle of a short time, so that the tube temperature is locally changed as shown in FIG. It is possible to realize uniform and precise heating of the material to be heated, since the amount of heat transferred from the tube 3 to the work W is uniform in the tube length direction, and is averaged over the entire tube length direction without forming any peaks. Moreover, since local overheating of the tube 3 is also avoided, it is possible to increase the temperature of the entire tube and increase the amount of heat transfer per tube without fear of burning the tube. Further, since no local high temperature region is generated, low NOx can be realized. In addition, in the heat storage type heat exchange, temperature efficiency of 90% or more can be easily obtained, and high-temperature air close to the exhaust temperature of the tube outlet can be obtained, so that a uniform and high temperature difference can be obtained between the combustion gas and the work. And high energy saving is achieved. That is, it is possible to obtain thermal efficiency comparable to that of electric heating. Therefore, when the power generation efficiency of electricity is set to 35%, raw fuel consumption of 60% or more will be achieved, which not only helps prevent global warming,
The energy cost will be reduced by about 80% or more. Further, when the tube is uniformly heated at the limiting temperature, the amount of heat transfer can be approximately doubled with the same surface area as the conventional type, and the surface area can be halved with the same amount of heat transfer as the conventional type. With the same surface area and the same amount of heat transfer as the conventional type, the peak temperature of the tube decreases, so inexpensive low grade materials with poor heat resistance can be used. The temperature efficiency used in this specification is
In heat exchange between exhaust gas and air, for the inlet temperature of exhaust gas,
The ratio of the temperature at which air is obtained is given by the following formula 1.

[0024]

[Equation 1]

(2) Heating in the tube-to-tube direction Conventionally, uniform heat transfer from the radiant tube to the work is better as the pitch of the radiant tubes is made smaller and densely arranged, and the pitch is increased to separate the radiant tubes. Accordingly, it was thought that the heat transfer at the midpoint between the tubes was delayed and the uniform heat transfer of the work was hindered. Therefore, the pitch of the tubes has been decided mainly from the economical point of view on the assumption that the tubes are arranged as closely as possible. However, in reality, it was difficult to uniformly heat the tubes between the work pieces, and it was found that even if the tube pitch was made smaller by ignoring the economic requirements, the heat transfer could not be kept uniform. .

As a result of various researches conducted by the present inventors on this point, the arrangement pitch L of the radiant tubes is shown.
It was found that there is a correlation between p and the tube diameter D. That is, as a result of detailed examination of the heat transfer from the tube to the work, the uniformity of the heat transfer is not maintained as the pitch of the tube is simply made smaller, as has been conventionally said. There is a region in which the heating uniformity is most maintained in a range having a relationship with the pitch Lp, and even if the relationship between the pitch and the tube diameter is smaller than that, or conversely, there is a uniform heat transfer. I found that it was hindered.

(A) (a) The heat transfer from the radiant tube 3 to the object W to be heated is mainly direct radiant heat directly reaching the object W to be heated and reflected heat given by being reflected on the furnace wall (partly). Most of the heat is dissipated into the atmosphere as heat radiated from the furnace wall, but most of it is reflected by the furnace wall and given to the object to be heated as reflected heat).

Here, the adjacent radiant tubes 3,
Among the radiant heat directed from the tube 3 directly to the object W to be heated in the area 3, the dead zones of the adjacent tubes 3 act between the tubes 3 and 3 and do not reach the object W directly. It is the tube central angle α ₁ = π−2 · Sin ⁻¹ {0.5 / (L _p that effectively gives heat to the object W to be heated.
/ D)} can be considered to be representative (FIG. 4).
reference).

Similarly, of the reflected heat reflected by the furnace wall 10 and given to the object W to be heated, it is effective to give heat to the object W to be heated because the dead angle of the tube 3 is adjacent to that of the adjacent tube 3. Considering that the radiant heat passing between and is representative, heat is effectively given to the object to be heated W by α ₂ = π−2 · [Sin ⁻¹ {0.25 / (L _r / D )} + tan ^-1 {2 (L _r / D) / (L _p /
D)} + sin ^-1 [0.5 / {(L _p / D) ² +4 (L _r / D) ² } ^0.5 ]]> 0 where L _r is the distance from the tube center to the furnace wall surface The part represents the reflected heat (see FIG. 5).

That is, between two adjacent tubes 3 and 3, the effective surface area ratio of the radiant tube 3 (effective surface area / total surface area of the tube) ψ is ψ = (α ₁ + α ₂ ) / (2
It is given by π), and the larger the value, the more effectively the surface of the radiant tube is used, and if the surface heat load of the tube is the same, the temperature of the tube is lowered, which is advantageous. However, since the lengths of the tubes are the same, they are omitted. (B) On the other hand, when an equal heat flux is given to the heated object W, the smaller the surface area of the radiant tube 3 with respect to the heat receiving surface area of the heated object W, the larger the surface heat load of the tube required. Therefore, the temperature of the tube rises, and there is a risk of burning the tube.

Here, since the ratio of the heat receiving area of the object to be heated W to the surface area of the tube 3 is given by L _p / (πD), the tube temperature T is expressed by the following equation 2.

[0032]

T ⁴ = (1 / π) (Lp / D) (εw / ε) (Tf ⁴ −Tw ⁴ ) + Tf ⁴ T: Absolute temperature of tube Tf: Absolute temperature of furnace Tw: Absolute of heated object Temperature ε: Emissivity of tube εw: Emissivity of heated object

The smaller T ⁴ is (Lp / D), the smaller
Sai. That is, the smaller the (L _p / D) ^1/4 , the lower the tube temperature, which is advantageous for tube burnout. (C) Therefore, both the above conditions (a) and (b), that is, the effective surface area ratio is large, and (L _p / D)
It is necessary to simultaneously satisfy that the smaller the ^1/4 (in other words, the larger the reciprocal is), the better. Therefore, the maximum value of the numerical values obtained by multiplying these two conditions is the optimum condition.

That is, as shown in FIG. 7, ψ / (L _p /
D) shows the vicinity of the maximum value of ^1/4 (L _p / D) increases the effective surface area, and the appropriate range of the ratio of the pitch and diameter of the radiant tubes for lowering the tube temperature (L _p / D) Will be shown. Here, the value of ψ / (L _p / D) ^1/4 is not limited to the maximum value, and about 90% or more thereof can be adopted as a value that causes no practical problems from the experience of the present inventors.

(B) (a) On the other hand, the heat flux distribution to the object W to be heated between the two tubes 3 and 3 is as follows: According to the ratio of the heat flux to the object W to be heated which is in the middle of 3, it can be said that the closer the ratio is to 1, the higher the average temperature is.

At this time, considering that the reflected heat from the furnace wall 10 is evenly given to the object W to be heated by diffuse reflection,
The size of the heat flux given to the object to be heated W is determined by the tube 3
The heat flux distribution can be evaluated by comparing the heat flux due to direct radiant heat.

That is, between the two tubes 3 and 3,
The heat flux ratio ξ given by the direct radiation from the tube 3 to the object to be heated W located immediately below and in the middle of the tube is given by the following mathematical expression 3 (see FIG. 6).

[0038]

[Equation 3]

Here, it can be said that the condition that ξ in the above equation is 1 is the most uniform, but in reality, a value that approximates 1 due to heat conduction in the object W to be heated, for example, 0.9-1. 1
Ratio of tube pitch and diameter (L _p / D)
Even in the range of, the pitch can be regarded as an appropriate pitch for uniform heating (see FIG. 8).

[0040] Therefore (C), simultaneously satisfy the appropriate range of ξ is given by the _{ψ / (L p / D)} 1/4 of proper range given (B) by _{(A) (L p / D} ) ,
This shows the range of the optimum pitch of the radiant tube that enables the temperature of the tube to be lowered by effectively utilizing the surface of the tube and allows the object to be heated to be uniformly heated (FIG. 9).
reference). (Example 1) The ratio of the distance Lr from the tube center to the furnace wall (ceiling) to the radiant tube diameter D and the distance Lw to the object W to be heated is Lr / D = 1.5, Lw / D = 3.
In the above case, the relationship is as shown in FIG. Here, the tube diameter D can be obtained as the tube diameter D, since the combustion amount per tube is determined when the surface heat load of the tube, which is generally required under various heating conditions, is determined. Therefore, it is most preferable to arrange the tubes at a pitch of 4.3 times the tube diameter D in order to obtain uniform heating. In addition, ψ / which is considered to be a practically preferable range
An appropriate pitch range in the case of satisfying 90% or more of the maximum value of (L _p / D) ^1/4 and simultaneously satisfying that ξ is in the range of 0.9 to 1.1 is: The tube diameter D was about 2.1 to 5.3.

The above-described embodiment is an example of a preferred embodiment of the present invention, but the present invention is not limited to this, and various modifications can be made without departing from the gist of the present invention. For example, in the present embodiment, an example of a sintering furnace has been mainly described, but the present invention is not particularly limited to this, and it goes without saying that the present invention is applicable to all heating furnaces using a radiant tube burner as a heat source.

[0042]

As is apparent from the above description, according to the invention described in claim 1, the flow of the combustion gas in the radiant tube is kept constant by the high cycle alternating combustion of the heat storage type burners provided at both ends of the tube. Since the temperature is reversed in a cycle, the tube temperature is averaged over the entire area, and the material to be heated can be uniformly heated in the tube axis direction. On the other hand, between two adjacent tubes, the effective surface area ratio of the radiant tube and (L
_Since both the reciprocals of _p / D) ^1/4 are close to the maximum value, the surface of the radiant tube is effectively used and the surface temperature of the tube decreases, and if the tube surface heat load is the same, the tube will burn out. It is advantageous for prevention. Moreover, the ratio of the heat flux to the object to be heated directly below the tube and the heat flux to the object to be heated in the middle of the tube is close to 1, and the heat flux distribution to the object to be heated between the two tubes is averaged. It can be said that the soaking property is high. Therefore, by selecting the tube pitch and the tube diameter that satisfy the above range of the ratio, it is possible to effectively utilize the surface of the tube to lower the temperature of the tube and to uniformly heat the object to be heated. By alternating combustion of the heat storage type burners equipped at both ends of the radiant tube,
Since the flow of the combustion gas in the tube is reversed at a constant cycle, the tube temperature becomes uniform in the tube axis direction, and precise uniform heating of the material to be heated can be realized. Further, the heating between the tubes also maintains uniformity.

Therefore, the heating of the work can be reduced not only in the longitudinal direction of the tube but also in the tube pitch direction orthogonal thereto.

The invention according to claim 2 is such that the ratio of the effective surface area ratio of the tubes between adjacent radiant tubes and the ratio (tube pitch / tube diameter) ^1/4 is 90% or more of the maximum value. And the ratio of the heat flux of the object to be heated directly under the tube given by the direct radiation from the two radiant tubes to the heat flux of the object to be heated in the middle of the tube is 0.9 to 1.1. At the same time, the tube pitch is in a range that satisfies the range. In this case, it is possible to realize a uniform heating property that does not pose a practical problem.

Further, in the invention according to the third aspect, the heating furnace is a sintering furnace and a straight tube type radiant tube is used as a heating source. In this case, a reducing atmosphere is formed, and the furnace temperature of 1100 to 1200 ° C. and precise temperature control can be performed therein.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment in which the present invention is applied to a sintering furnace.

FIG. 2 is a schematic configuration diagram showing an embodiment of a heat storage type radiant tube burner system using a straight tube type radiant tube.

FIG. 3 is a graph comparing the distribution state of the tube surface temperature between the heat storage type radiant tube burner system of FIG. 2 and a normal radiant tube burner system.

FIG. 4 is an explanatory diagram showing direct radiation between a tube and an object to be heated.

FIG. 5 is an explanatory diagram showing reflected heat between a tube and an object to be heated.

FIG. 6 is an explanatory diagram showing the uniform heating property of an object to be heated between tubes.

FIG. 7 is a graph showing the relationship between Lp / D and ψ / (L _p / D) ^1/4 .

FIG. 8 is a graph showing the relationship between Lp / D and ξ.

FIG. 9 is a graph showing Lp / D as a relationship between ψ / (L _p / D) ^1/4 and ξ.

[Explanation of symbols]

2 heat storage type radiant tube burner system 3 radiant tubes 4a, 4b heat storage type burner 10 furnace wall (ceiling) W object to be heated D tube diameter Lp tube pitch ψ tube effective surface area ratio ξ heat flux of object to be heated directly under the tube Heat flux ratio of the heated object in the middle of the tube

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification symbol FI F23D 14/12 F23D 14/12 A 14/66 14/66 C F23L 15/02 F23L 15/02 (72) Inventor Kiyota Kiyofumi Kanagawa 2-53, Shirute, Tsurumi-ku, Yokohama-shi, Japan Within Furnace Industry Co., Ltd. (72) Inventor Koichi Fukuda 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Masahiko Inuzuka Toyota City, Aichi Prefecture Toyota Town No. 1 Toyota Automobile Co., Ltd. (72) Inventor Akio Tamura Toyota City, Aichi Prefecture Toyota Town No. 1 Toyota Automobile Co., Ltd. (72) Inventor Masao Hattori 19-18 Sakurada-cho, Atsuta-ku, Nagoya-shi, Aichi Prefecture Toho Gas Co., Ltd. (72) Inventor Toshiharu Shimizu 19-18 Sakurada-cho, Atsuta-ku, Nagoya-shi, Aichi Toho Gas Co., Ltd. (56) Reference JP-A-8-27 8007 (JP, A) JP 10-298642 (JP, A) JP 9-250716 (JP, A) JP 60-149872 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F27B 9/36 B22F 3/10 C21D 1/34 F27D 17/00 101

Claims (3)

(57) [Claims] With claim 1, wherein each of the regenerative burner which performs the exhaust gas and supply of the combustion air alternately to opposite ends of the radiant tube through a regenerator, equipped with a heat storage burner system for burning the pair of burners alternately the Using a radiant tube as a heating source, and the ratio of the effective surface area ratio of the tubes between adjacent radiant tubes and (tube pitch / tube diameter) ^1/4 is close to the maximum value, in the range of simultaneously satisfying a ratio of the heat flux of the object to be heated heat flux of the heated object directly under the tube given by direct radiation and the middle of the radiant tubes from the radiant tube is near 1 A heating furnace using a radiant tube as a heat source, which has a tube pitch. Wherein in a range showing more than 90% of the effective surface area rate (the diameter of the pitch / tube of the tube) ^1/4 of the ratio maximum value of the tube between the adjacent radiant tubes, and the two At the same time, the ratio of the heat flux of the object to be heated directly below the tube and the heat flux of the object to be heated in the middle of the tube, which is given by the direct radiation from the radiant tube of the book, is in the range of 0.9 to 1.1. A heating furnace using a radiant tube as a heat source according to claim 1, having a tube pitch within a range satisfying the conditions. 3. The heating furnace is a sintering furnace, and a straight tube type radiant tube is used as a heating source.
Or a heating furnace using the radiant tube according to 2 as a heat source.