JPH0198889A - Drying furnace - Google Patents

Abstract

PURPOSE: To provide a drying furnace in which an item to be heated is uniformly heated, a heater is not damaged and oil is not ignited by a method wherein there are provided a first group of heaters, a second group of heaters, a heating section for the item by radiant heat, a transferring device for the item to be heated and a hot air supplying device. CONSTITUTION: This drying furnace is used for heating and drying various kinds of foods. A drying furnace A is comprised of a heating section 7 for heating a passing item through radiant heat, a heated item transferring device 8 for transferring the item from an inlet part 7a in the heating section 7 toward an outlet part 7b and a hot air supplying device 9 for circulating a part of combustion gas of a far-infrared ray heater into the heating section 7 as hot air and drying the item. The item fixed to a chain 81 is transferred from the inlet port 7a into the heating section 7 by a driving motor 83 for the transferring device 8. The item is uniformly heated by each of heaters 1 of a first group I of heaters and a second group II of heaters. Since a transferring direction of the item is perpendicular to each of the heaters 1, the heaters 1 are not damaged and oil is not ignited even if water, powder and oil drop from the item.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drying oven suitable for heating, drying, and baking various foods such as meat, fish, beans, and confectionery.

[Prior art] Infrared heaters that use electricity as a heat source have been known as sheathed heaters, but the electricity cost of the heat source is high, so infrared heaters that use gas as fuel have also been developed. For example, as described in Japanese Unexamined Patent Publication No. 59-21913, a zigzag smoke pipe is connected to the tip of a circular combustion chamber, and the combustion exhaust heats the combustion chamber, and heat rays made of infrared rays are emitted from the outer surface of the combustion chamber. , then heat the smoke tube and emit infrared rays from the outside surface of the smoke tube, and then send 1!1L
There are infrared heaters that are emitted outdoors through a chimney.

Conventionally, conveyor type drying ovens for heating and drying foods such as meat and fish have been used in the shell. This conveyor-type drying oven has a large number of upper far-infrared heaters arranged in the upper part and a lower far-infrared heater in the lower part, and heats the food from above and below while conveying the food between these two by a conveyor.

[Problems to be Solved by the Invention] However, in the above-mentioned infrared heater, a temperature gradient is generated in the surface temperature between the base end and the tip end of the smoke tube that emits infrared rays, and this makes it difficult to uniformly and efficiently heat the food. There was a problem in that it was a hindrance. In addition, in conveyor-type drying ovens, if moisture, powder, etc. fall off during grilling of meat, fish, etc., the infrared radiation surface of the lower far-infrared heater may be contaminated, causing the far-infrared heater to heat up. There was a risk that efficiency would decrease or that smoke or ignition would occur if oil etc. fell.

The present invention provides a uniform surface temperature distribution in any direction, making it possible to uniformly and efficiently heat or bake objects to be heated. To provide a drying oven in which there is no fear of staining the far-infrared radiation ceramic coating surface of a far-infrared heater or ignition of oil, etc., even if something falls.

[Means for Solving the Problems] The drying oven of the present invention includes: - a cylindrical airtight metal casing whose side surface is a mounting surface to a fixing member and whose other side surface is a far-infrared emitting ceramic coating surface; A first heater group in which a large number of gas-type far-infrared heaters having a A heating section that heats an object to be heated by thermal radiation, and the object to be heated,
A conveying device for the heated object to be conveyed so as to pass between the first heater group and the second heater group in the heating section and an exhaust hole provided in each of the gas far-infrared heaters. A configuration including a communication tube that communicates between the exhaust device and the inside of the heating section, and a hot air supply device comprising means for selectively supplying the combustion gas mentioned above into the heating section is adopted.

[Functions and Effects of the Invention] The drying oven of the present invention has the following functions and effects due to the above structure.

The far-infrared radiation ceramic coating surface of each far-infrared heater is uniformly heated by the combustion gas, and a uniform surface temperature distribution can be obtained in any direction.

The conveying device allows the heater to pass between the first heater group and the second heater group in the heating section from one side to the other almost perpendicularly to the far-infrared emitting ceramic coating surface of each far-infrared heater. It is possible to uniformly heat the object to be conveyed by the radiant heat from the far-infrared radiation ceramic coating surface of each far-infrared heater, or it is possible to uniformly bake the object to be heated.
Even if moisture, powder, oil, etc. fall from the heated object, there is no risk of damaging the far-infrared radiation ceramic coating surface of the far-infrared heater or igniting the oil, etc. The object to be heated can be heated. Further, the hot air supply device selectively supplies the combustion gas of the far-infrared heater into the heating section as hot air, and by applying the hot air to the heated object, the heated object can be dried.

Furthermore, one side of the cylindrical airtight metal casing is used as a mounting surface that contains heat insulating material, and the other side is coated with far-infrared emitting ceramics, minimizing the amount of heat insulating material required. , the effective far-infrared radiation surface is large compared to the size of the casing, and the amount of far-infrared radiation emitted from the casing with the same external shape can be increased.

[Example] An embodiment of the drying oven of the present invention will be described based on the drawings.

1 to 3 show a drying oven to which an embodiment of the present invention is applied.

In the present invention, combustion gas refers to gas generated after a mixture of fuel gas, primary air, and secondary air is combusted, and includes exhaust gas.

A is for heating foods that produce water, powder, or oil when grilling meat, fish, etc., drying foods that require far-infrared radiation in a low-temperature atmosphere such as dried fish, roasting granular products such as beans and sweets, etc. This shows a hybrid drying oven used for heating and drying.

The hybrid drying furnace A includes a heating section 7 that heats the passing object to be heated by thermal radiation, and a conveying device for the object to be heated that transports the object from the inlet section 7a of the heating section 7 toward the outlet section 1b. 8, and a hot air supply device 9 that circulates part of the combustion gas of the far-infrared heater as hot air within the heating section 7 to dry the heated object.

The heating unit 7 includes a first group of gas-type far-infrared heaters (hereinafter referred to as first heaters), which includes two rows of gas-type far-infrared heaters (hereinafter referred to as heaters) 1 arranged in parallel from the top to the bottom in the figure. group), and a large number of second heaters arranged opposite to each other with a predetermined gap inside the first heater group I.
It is equipped with a gas-type far-infrared heater group (hereinafter referred to as the second heater group) (2).

The heating section 7 includes an upper M wall 70, a mounting base 71, a side wall 72, an island wall 73, side walls 74, 75, 76, a side wall 77, a side wall 78,
and a side wall 79.

The upper lid wall 70 is provided at the upper end of the side wall 72 in the drawing, and includes the heat insulating material 30 therein. Up again! Attached to the wall 70 are exhaust lowers 0a and 70b with dampers for adjusting the temperature within the heating section 7 or exhausting combustion gas. Mounting stand 7
1 is fixed to, for example, an indoor floor surface 71a.

The side wall 72 includes a holding portion 72a to which each heater 10 casing 2 of the first heater group is attached, and includes a heat insulating material 32 therein. The island-like wall 13 includes mounting portions 73a and 73b for mounting each heater 1 of the second heater group (2), and includes heat insulating materials 33a and 33b. side wall 74
．． 75 and 76 are provided inside the side wall 12 and at the upper end of the island wall 73 in the drawing, and include heat insulating materials 34, 35, and 36. The side wall 77 includes a mounting portion 77a to which the casing 2 of each heater 1 of the first heater group (2) is mounted, and includes a heat insulating material 31 therein.

The side wall 78 is provided at the lower end of the island wall 73 in the drawing, and includes the heat insulating material 38 therein. The side wall 19 is connected to the first heater group I.
and a mounting part 79a to which the casing 2 of each heater 1 of the second heater group (2) is mounted, and includes a heat insulating material 39 therein. Further, a viewing window 79b is formed in the side wall 79 for viewing the heating state of the heater 1 in the heating section 7.

By selecting the heater 1, this heating section 7 can respond to a wide range of furnace atmospheric humidity (for example, 50° C. to 400° C.) and heat load. Further, the heating section 7 is heated in a direction from the inlet section 7a to the outlet section 7b, and further in the direction from the inlet section 7a to the outlet section 7b.
Since each heater 1 is heated uniformly in the vertical direction as well, the settings are made so that a uniform surface concentration distribution can be obtained in any direction.

4 to 7 show a heater employed in one embodiment of the present invention.

The heater 1 has one end in the longitudinal direction attached to a side wall 79, and has a hexagonal cylindrical airtight gold Wr& casing 2 (arranged in a Wi shape) within the heating section 7, and a heat insulating material included in the casing 2. 3, a combustion cylinder 4 having an elongated rectangular shape and disposed inside the casing 2 in parallel with the casing 2, a gas burner 5 fixed to one end of the casing 2, and an exhaust device 6.

In the casing 2, a wall plate 20a on the lower side in the drawing, which is one side of the outer panel 20, includes the heat insulating material 3, and a part of the side surface 21a is the mounting portions 72a and 73a of the heating unit 1.

This is the mounting surface 21 to 73b. The other side surface of the casing 2, the upper wall plate 20b in the drawing, has an outer surface 22a that is a far-infrared emitting ceramic coating surface (hereinafter abbreviated as far-infrared emitting surface) 22. The far-infrared emitting ceramic coating may be applied to both the front and back sides of the wall board 20b for rust prevention, or may be applied to both the front and back sides of the outer panel 20.

Far-infrared emitting ceramics have blackbody-type infrared characteristics with high emissivity in the entire infrared wavelength region, and far-infrared selective radiation characteristics with high emissivity in the far-infrared region of 7 or more wavelengths. There are two types, and one is used depending on the infrared absorption wavelength characteristics of the object to be heated.

The material of the blackbody type is Mn0z30-70% (for example, 6
5%), Fe2O25-30% (e.g. 20%), 00
03-20% (e.g. 10%), 5i02 0-10%
(e.g. 3%), A42030-30% (e.g. 2%)
It has a composition of

The material of the far infrared selective radiation characteristic type is MO050~1
00% (e.g. 95%), A42030~30% (e.g. 3%), 5i(ho~30% (e.g. 2%)).

Further, inside the casing 2, a partition wall 25 is provided to separate the first chamber 23 in which the combustion cylinder 4 is arranged and the second chamber 24 containing the heat insulating material 3 therein. A trapezoidal side wall 27 is fixed to the first chamber 23 of the illustrated left side wall 26 of the casing 2 via a holding member 27a, and this side wall 2I
The heat insulating material 3 is included between the side wall 26 and the side wall 26 . The side wall 26 is attached to the attachment portion 79a of the heating section 7. Therefore, the casing 2 is attached to the heating section 7 in the vertical direction.

A gas burner 5 is fixed above a right-hand side wall 28 of the casing 2 via a gasket 29 . side wall 2
8 is formed with a rectangular opening 28a and a circular opening 28b, and the outer edge of this side wall 28 is formed with a plurality of screw holes and serves as a mounting portion 28G for attaching to other members. . A fastening hole 28 is provided around the opening 28a to fasten the gas burner 5 with a fastening screw 28d via a gasket 29.
0 is formed.

The heat insulating material 3 is made of ceramic fiber, ceramic wool, glass wool, or the like.

Here, in this embodiment, a part of the side surface 21a of the wall plate 20a of the casing 2 is used as the mounting surface 21 that includes the heat insulating material 3, and the outer surface 22a of the wall plate 20b is used as the far-infrared radiation surface 22. Therefore, the portion of the heat insulating material 3 to be used is reduced to the necessary minimum, and the effective far-infrared radiation surface is greatly reduced compared to the size of the casing 2, making it possible to increase the amount of far-infrared radiation from the casing 2 having the same external shape. The object to be heated can be heated quickly. Furthermore, the amount of heat insulating material 3 used is reduced, and the number of man-hours for installing the heat insulating material 3 is reduced, resulting in lower costs.

The combustion tube 4 has an opening 41 formed at the left end in the drawing, and an opening 42 having a size corresponding to the opening 28a of the side wall 28 at the right end in the drawing. A large number of small holes 44 are formed in the side wall 43 of the combustion tube 4 in a predetermined pattern so that the temperature distribution around the side wall 43 is uniform. The left end of the combustion n4 is fixed to the partition wall 25 of the casing 2 via the holding member 45, and the right end of the combustion n4 is fixed to the side wall 25 of the casing 2 through the holding member 45.
8 is fitted.

Further, in the combustion tube 4, by adjusting the number, diameter, pitch, etc. of the small holes 44, the jetting of combustion gas is adjusted.

8 to 10 show a gas burner 5 adopted in an embodiment of the present invention.

The gas burner 5 is made of gold WA and includes a connecting tube 51 fastened to the combustion tube 4, a tapered tube 53 attached to a gas supply pipe 52 for supplying fuel gas, and a partition tube 54 formed on the connecting tube 51. , a sparker 56 that sends sparks to the tip 55 of the partition tube 54, which is a combustion section, when ignited, and a flame rod 57 that detects the state of the primary combustion flame.

The connecting cylinder 51 is open at the left end in the figure, and has a flange 51b formed around the outer periphery of the opening 51a, and a right side wall 51 in the figure.
51C of secondary air intake ports arranged in multiple rows on the outer periphery of d;
The cylindrical portion 51e connecting the flange 51b and the side wall 51d has holes 51f and 51Q through which the sparker 56 and frame rod 57 are inserted, respectively. Flange 5
A large number of fastening holes 51h are formed in 1b.

The gas supply pipe 52 has l1lrfl depending on whether it is energized or not.
A fuel gas control unit is provided, such as an NWA type on-off valve (not shown) that adjusts the flow rate of fuel gas, and a flow rate adjustment valve (not shown) that adjusts the flow rate of fuel gas.

The tapered shape n53 has a number of primary air intake ports 53a arranged above and below a nozzle 52b in which a plurality of fuel gas ejection holes 52a are arranged in a row on the side of the fuel gas supply pipe 52.
The gas supply pipe 52 is attached to the gas supply pipe 52 so as to gradually increase from the side toward the connecting cylinder 51.

The partition tube 54 has an inner peripheral edge 54a of the side wall 51d of the connection tube 51.
It protrudes in parallel to the cylindrical portion 51e of the connecting cylinder 51 toward the direction of the combustion cylinder 4. A sparker 56 is installed in the partition tube 54.
A hole 54b is formed through which the tip of the frame rod 57 and the tip of the frame rod 57 are respectively inserted.

The exhaust device 6 includes a scroll casing 61 that houses a blower (not visible in the figure), and the scroll casing 6.
1 and the exhaust hole 11 formed in each heater 1 through a connecting pipe 6.
2, and an exhaust vR65 that exhausts combustion gas discharged from the scroll casing 61 through a branch pipe 64.

The blower is driven by a drive motor 68 via a drive shaft 67, a belt 66, and the like.

The scroll casing 61 forms an inlet 61 a for sucking combustion gas through the exhaust pipe 63 and a discharge port 61 b for discharging the combustion gas into the branch pipe 64 .

The conveyance device 8 can sandwich various objects to be heated, hang them,
A chain 81 to which conveyance jigs for tying or tying are attached at predetermined intervals, a drive motor 83 that operates the chain 81 along a predetermined conveyance path 82, and a large number of 1-liss 84a to 84i.
Equipped with. The conveyance path 82 in the heating section 1 is provided at a predetermined distance (for example, 150 mm each) from each heater 1 of the first heater group I and the second heater group 2. The drive unit 83 uses a continuously variable lotus motor,
The conveyance jig is conveyed at a conveyance speed of 0 to 12 m/sin, for example. The driving field controller 83 has a pulley 83a and a belt 8.
The pulley 84a is driven via the pulley 3b. Further, the drive motor 83 is provided in a device drive section 85 disposed on the right side of the mounting base 71 in the drawing.

The hot air supply device 9 is a means for selectively supplying combustion gas into the heating section 7, and is provided with a flow rate regulating valve 90 for regulating the flow rate of the combustion gas, and is arranged from the branch pipe 64 to the device drive section 85. a communicating tube 91, and a nozzle 9 that discharges hot air from the communicating tube 91 to the inlet section 1a and outlet section 7b of the heating section 1.
2.93 and a gas burner 95 which is a hot air generator for reheating hot air.

This hot air supply device 9 is configured to circulate and supply a portion of the combustion gas to the heating section 7 again as hot air by adjusting the exhaust supply of combustion gas using a flow rate regulating valve 90 .

The operation of the drying oven A of this embodiment will be explained based on the drawings.

When a start switch (not shown) is turned on, the drive motor 68 is energized and the blower rotates. The primary air is supplied to the primary air intake port 53a by the negative pressure caused by the rotation of this blower.
From there, it is supplied into the tapered cylinder 53 and partition cylinder 54 of the gas burner 5. In addition, the on-off valve attached to the gas supply pipe 52 is opened, and the flow rate adjustment valve is opened to obtain a desired gas flow rate, so that the fuel gas is supplied from the fuel gas injection hole 52a to the tapered shape 1i53 of the gas burner 5 and the partition. It is supplied into the cylinder 54. Then, the primary air and fuel gas are mixed in the tip 55 of the partition tube 54 of the gas burner 5, ignited by a spark by the sparker 56, and combustion starts at the tip 55 of the partition tube 54.

At this time, secondary air is supplied from the secondary air intake port 51c between the connecting cylinder 51 of the gas burner 5 and the partition 9i54,
The mixture is completely combusted. Further, by separating the flow of the primary combustion flame and the flow of the secondary air by the partition tube 54, the flow of the primary combustion flame and the flow of the secondary air are rectified, respectively.

Furthermore, when the partition tube 54 becomes red hot due to combustion at the tip 55 of the partition tube 54, the temperature of the air-fuel mixture in the partition tube 54 increases, so the primary combustion flame becomes more stable, and the combustion produced by combustion increases. Gas is introduced into combustion n4.

It is necessary to lower the temperature of the combustion gas by using an appropriate amount of excess air, but the excess air amount is adjusted by the ratio of the supply amount of primary air and secondary air. Since the flow is rectified between the and the partition tube 54,
Tip 55 of partition %i54 stably even in case of excess air
can be burned with.

In addition, the fuel gas and the primary air are not mixed in advance and the partition I
Because of the diffusion combustion that is mixed at the tip 55 of the Q54, it is possible to prevent packfire from occurring within the tapered portion 53 of the gas burner 5, and a large turndown ratio can be achieved.

Combustion gas introduced into the combustion cylinder 4 from the opening 42 through the opening 51a of the connecting cylinder 51 of the gas burner 5 flows through the opening 4.
1 or into the casing 2 from the small holes 44 to uniformly heat the far-infrared radiation surface 22 of the wall plate 20b of the casing 2. Also, by combustion gas (e.g. at 500-600℃)
It is heated uniformly (for example, to 300 to 400°C) by thermal radiation from the heated combustion tube 4.

Therefore, the first heater group and the second heater &T
Far-infrared rays are efficiently radiated from the far-infrared radiation surface 22 of each heater 1 of I.

On the other hand, when the drive motor 83 of the transport device @8 is energized,
The chain 81 begins to move in the direction of the arrow shown in the figure, and the chain 81 is pinched, hung, or tied by the conveyor jig.
1 is carried into the heating section 7 through the inlet section 7a.

The object to be heated carried into the heating section 7 receives far-infrared rays with a uniform surface humidity distribution in all directions from the far-infrared radiation surface 22 of each heater 1 of the first heater group I and the second heater group By radiating heat, it is heated evenly from all directions.

In addition, since the conveyance direction of the heated object is perpendicular to each heater 1 of the first heater group I and the second heater group ■, moisture, powder, oil, etc. may fall from the heated object. Even if there is, there is no fear of staining the far-infrared radiation surface 22 of the heater 1 or igniting the oil, and the object to be heated can be sufficiently heated from both sides. Therefore, when the object to be heated is carried out from the outlet section 7b of the heating section 7, it is in a state where it is uniformly, efficiently and sufficiently heated.

For example, if the latent heat is taken away by the far-infrared radiation surface 22,
The combustion gas (at a temperature of 0 to 300°C) is passed through the exhaust hole 1 of the casing 2.
1, and is sucked into the scroll casing 61 through the exhaust pipe 63 and the suction port 61a.

Thereafter, the combustion gas is discharged from the discharge port 61b to the branch pipe 64, blocked by the closed flow rate regulating valve 90, and discharged to the exhaust pipe 65.

By adjusting the opening degree of this flow mgI regulating valve 90, the branch pipe 64
When supplying part or all of the combustion gas to the heating section 7 as hot air, first set the flow rate adjustment valve 90 to the open side, or open it, and reheat the hot air with the gas burner 95. . Then, the hot air passes through the branch pipe 64 → the communication tube 91 → the supply pipe 94, and enters the heating section 7 from the nozzle 92.93.
is discharged toward the inlet section 7a and the outlet section 7b, and is supplied into the heating section 1. Therefore, the object to be heated while being conveyed within the heating section 7 can be sufficiently dried by the hot air.

Here, the heating part 7 is surrounded by the upper lid wall 10 and the side walls 12.14 to 78 on all sides except the inlet part 7a and the outlet part 1b, so that the heating part 7 can be reliably heated without leaking hot air to other parts. Hot air can be supplied inside.

Further, with the structure of the drying oven A as in this embodiment, the installation space can be reduced, and highly efficient heating and drying can be performed without radiant heat from the heater 1 leaking to other parts.

Further, the drying oven A of this embodiment can be used as a drying oven using only hot air if the combustion of the gas burner 5 of each heater 1 is stopped while the gas burner 95 of the hot air supply device 9 is operating as described above. .

[Other Examples] In this example, the casing is formed into a hexagonal cylinder shape, but the casing may be formed into a semi-cylindrical shape or a cylindrical shape, without departing from the scope of the present invention. The casing may be formed into various shapes.

In this example, the upper wall plate of the outer panel of the casing was coated with far infrared emitting ceramics, but within the scope of the present invention, the wall plates constituting the casing were coated with far infrared emitting ceramics only on the front surface or on both the front and back surfaces. You may do so.

In this embodiment, a gas burner having a connecting tube, a tapered tube, a partition tube, and an ignition device was used, but burners with various structures may be used without departing from the scope of the present invention.

In this embodiment, a drying oven using two sets of the first gas-type far-infrared heater group and the second gas-type far-infrared heater group was provided; Infrared heater! ! A drying furnace using T and a second group of gas-type far-infrared heaters may be provided.

In this example, the drying oven is used to heat materials that produce water, powder, and oil when grilled, such as meat and fish, to dry materials that require far-infrared radiation in a low-temperature atmosphere, such as dried fish, and to roast granular products such as beans and Toyo. The drying oven was used to heat and dry various foods such as roasting, etc., but the drying oven can also be used to heat and dry strip-shaped products such as cloth, thread, and vinyl sheets, and to heat and dry various plastic parts, metal parts, fibers, etc. with hot air. It may be used for heating and drying various articles. When heating and drying a belt-shaped product such as cloth, thread, or vinyl sheet, heating and drying can be performed by removing the chain 81 and rolling the belt-shaped object to be heated on the boot.

In this embodiment, the hot air supply device is connected to the branch pipe of the exhaust device, but the hot air supply device may be directly connected to the sight hole formed in each heater.

In this example, a container, a gutter-like member, etc. to collect moisture, powder, oil, etc. that falls from the heated object was not provided, but a container, gutter-like member, etc. that collects the moisture, powder, oil, etc. that falls from the heated object. etc. may be provided below the inlet and outlet of the heating section.

[Brief explanation of the drawing]

FIG. 1 is a front view showing a hybrid drying oven according to an embodiment of the present invention, FIG. 2 is a side sectional view showing a hybrid drying oven according to an embodiment of the present invention, and FIG. 3 is an embodiment of the present invention. FIG. 4 is a plan view showing a hybrid drying furnace according to an embodiment of the present invention, FIG. FIG. 6 is a plan view showing a casing of the far-infrared heater adopted in the hybrid drying oven according to an embodiment of the present invention; FIG. FIG. 8 is a rear view showing the casing of the far-infrared heater employed in the hybrid-type drying furnace according to an embodiment of the present invention, and FIG. 9 is a front view showing a gas burner according to an embodiment of the present invention, and FIG. 10 is a side sectional view showing a gas burner of a far-infrared heater employed in a hybrid drying oven according to an embodiment of the present invention. It is. In the diagram

Claims (1)

[Claims] A gas-type far-infrared heater having a cylindrical airtight metal casing with one side serving as a mounting surface to a fixed member and the other side serving as a far-infrared emitting ceramic coating surface. a heating section that heats an object to be heated by thermal radiation; , a conveying device for a heated object that conveys the heated object so as to pass between the first heater group and the second heater group in the heating section; a communication tube that communicates between an exhaust device that is connected to an exhaust hole that is connected to the inside of the heating section; and a hot air supply device that includes means for selectively supplying the combustion gas into the heating section. drying oven. 2) The gas-type far-infrared heater is a combustion heater that is disposed in the casing in parallel with the casing, has one end fixed to the casing, and has a number of small holes formed in a predetermined pattern through which combustion gas passes. The drying furnace according to claim 1, comprising a cylinder and a burner fixed to one end of the combustion cylinder. 3) The drying furnace according to claim 1, wherein the hot air supply device is provided with a hot air generator that reheats the hot air. 4) The drying furnace according to claim 3, wherein the hot air generator is a gas burner.