JPH0894051A - High-temperature corrosion resistant air heater - Google Patents

Abstract

PURPOSE: To provide a high-temperature corrosion resistant air heater which has remarkably excellent corrosion resistance and durability in the high- temperature and high corrosion resistant gas atmosphere of an incinerating furnace. CONSTITUTION: The outside of a heat transfer tube 4 made of a metal heat transfer outer tube 3 and a metal heat transfer inner tube 1 is covered with a fire resistant material protective tube 5. A gap 6 is provided between the tube 5 and the tube 3. The tube 5 is coupled to the tube 4 by a support bolt 16. Protective air holes 18, 19 are provided at the bolt 16. Accordingly, even if thermal expansion difference occurs between the metal for forming the outer tube and the fire resistant material for forming the protective tube, the change due to the thermal expansion is scarcely propagated, and hence the damage, exfoliation, removal, etc., of the tube can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air heater for high temperature corrosion resistance, and more particularly to a thermal energy of a high temperature combustion gas generated in refuse and waste incineration treatment in an urban refuse incinerator or an industrial waste incinerator. TECHNICAL FIELD The present invention relates to an air heater for high temperature corrosion resistance for recovering heat by exchanging heat with low temperature air to effectively utilize heat energy.

[0002]

2. Description of the Related Art In an urban refuse incinerator or an industrial waste incinerator, an air heater is provided in order to recover and effectively use the thermal energy of high temperature combustion gas generated in the incineration of refuse and waste. ing.

The air heater is a device for circulating low-temperature air in a metal heat transfer tube and heating it to a high temperature by heat exchange with a high-temperature combustion gas to recover heat. It is a highly efficient energy resource recovery system that does not adversely affect the global environment. Thus, the recovered thermal energy is effectively used for thermal decomposition of waste, power generation, and other facilities.

The heat transfer tube of the conventional air heater is directly inserted and arranged in the incinerator.

By the way, the combustion gas generated in the municipal waste incinerator and the industrial waste incinerator is a product generated by a reaction with a metal at a high temperature such as chlorine and hydrogen chloride resulting from the garbage and the waste in a short time. It is a highly corrosive gas that contains corrosive substances with extremely high corrosiveness that cause evaporation loss at. Therefore, the heat transfer tubes of air heaters installed in these incinerators and exposed to a high temperature, highly corrosive gas atmosphere, have such high temperatures due to their material and structure. It is required to have sufficient corrosion resistance to the corrosive gases of.

Conventionally, various corrosion resistant alloys have been developed, but no corrosion resistant alloy having sufficient corrosion resistance to the high temperature and highly corrosive gas of such an incinerator has been found.

Therefore, conventionally, as a means for improving the corrosion resistance of an air heater, a stud pin is welded to a metal heat transfer tube, and an amorphous refractory is installed around the stud pin. A refractory brick based on a rectangular parallelepiped is connected to a metal heat transfer tube with vertical and horizontal joints. Such a method is considered.

In these systems, the refractory material acts as a physical barrier against convection and mutual diffusion in the corrosive gas phase, and reaches the surface of the heat transfer tube with corrosive gas such as oxygen and chlorine and gas of the reaction product. Corrosion of the heat transfer tubes is prevented to some extent by the action of suppressing transportation within the phases.

[0009]

However, the above refractory arranging system has the following problems.

That is, in the above case, there is damage to the stud pin, cracking of the irregular-shaped refractory, and local peeling or dropping at the end of the heat transfer tube or the tube vicinity. Also in the above case, the refractory bricks may be locally peeled off or fallen off. Also,
In either case, there is a serious corrosion phenomenon such as damage to the metal heat transfer tube, resulting in an extremely short life of the air heater.

[0011] These materials cause cracks in the refractory due to the difference in thermal expansion between the refractory and the metal heat transfer tube, resulting in corrosive damage to the metal fittings for fixing the refractory, and damage / peeling of the refractory. It is considered that the loss of the corrosion resistance of refractory materials is a major factor.

The present invention solves the above-mentioned conventional problems and provides an air heater in which a heat transfer tube is protected by a refractory material without causing problems such as peeling or damage of the refractory material, high temperature in a incinerator, and highly corrosive gas atmosphere. It is an object of the present invention to provide an air heater for high-temperature corrosion resistance, which is extremely excellent in corrosion resistance and durability.

[0013]

The air heater for high temperature corrosion resistance according to claim 1 is provided in a high temperature corrosive gas atmosphere, and heats the air flowing through the heat transfer tube by heat exchange with the high temperature corrosive gas. In the high-temperature corrosion-resistant air heater for heating, the heat transfer tube is a metal heat transfer inner tube having an open end, and the inner tube is coaxial with the inner tube so as to cover the inner tube. A metal heat transfer outer tube having a sealed tip, which is arranged with a gap between the inner tube and the inner tube, and the heated air flows through the inner tube, and then from the open end of the inner tube to the inner tube and the outer tube. A hot-corrosion resistant air heater that is heated by a hot corrosive gas while passing through a gap between the outer tube and the protective tube made of a refractory material with a sealed tip covering the outer tube. Is provided coaxially with and with a gap between the outer tube and the outer tube.

A high temperature corrosion resistant air heater according to a second aspect of the present invention is the heater according to the first aspect, wherein the protective tube has a concave portion provided on an inner surface thereof and a convex portion provided on an outer surface of the outer tube. Is supported by the outer tube by the engagement.

A high temperature corrosion resistant air heater according to a third aspect of the present invention is the heater according to the second aspect, wherein the concave portion of the protective tube is a dovetail hole provided on the inner surface of the sealing end surface of the protective tube, The convex portion of the tube is characterized in that it is a tapered dovetail projection provided on the outer surface of the sealing end surface of the outer tube.

An air heater for high-temperature corrosion resistance according to a fourth aspect is the heater according to any one of the first to third aspects, wherein a part of the air flowing inside the outer tube and the outer tube are provided in the outer tube. It is characterized in that a minute through hole is provided between the protective tube and the protective tube so as to flow out.

An air heater for high-temperature corrosion resistance according to a fifth aspect is the heater according to any one of the first to fourth aspects, characterized in that a corrosion-resistant coating film is formed on the outer surface of the outer tube. .

An air heater for high-temperature corrosion resistance according to a sixth aspect is the heater according to the fifth aspect, wherein the corrosion-resistant coating film is a stable oxide such as alumina, silica, or mullite or spinel containing them. It is a mixed oxide.

An air heater for high temperature corrosion resistance according to a seventh aspect is the heater according to the third aspect, wherein the protrusion is a bolt screwed to the outer tube, and the bolt is provided inside the heat transfer tube. It is characterized in that a vent hole communicating therewith is provided.

An air heater for high-temperature corrosion resistance according to claim 8 is the heater according to any one of claims 1 to 7, wherein the protective tube made of refractory material is subjected to a sealing treatment for filling the pores of the refractory material. It is characterized by being

A high temperature corrosion resistant air heater according to a ninth aspect is the heater according to any one of the first to eighth aspects, wherein the tip end surface of the refractory protection tube is biased by a biasing member. It is characterized in that a recessed portion for receiving the push rod is provided.

[0022]

In the air heater for high-temperature corrosion resistance according to claim 1, since the gap is provided between the heat transfer outer tube and the refractory protection tube, the metal forming the heat transfer outer tube Even if there is a difference in thermal expansion from the refractory material that constitutes the protective tube, changes due to thermal expansion are less likely to propagate to each other, so damage, peeling, dropout, etc. of the protective tube are prevented.

According to the high temperature corrosion resistant air heater of the second and third aspects, since the protection tube can slide relatively freely with respect to the heat transfer outer tube, the protection tube is damaged or peeled off due to the difference in thermal expansion. , Falling off is more reliably prevented. In addition, the support structure between the protection tube and the heat transfer outer tube is simplified, and the support section is minimized to reduce the proportion of the joint portion of the refractory material of the protection tube, which reduces the protection tube and the heat transfer tube. Damage to the hot tube is prevented.

According to the high temperature corrosion resistant air heater of the fourth aspect, the air is flown from the heat transfer outer tube into the gap between the heat transfer outer tube and the protection tube, thereby protecting from the outside of the protection tube. It is possible to reduce the amount of corrosive gas that flows through the tube into the protective tube, and thereby more reliably prevent corrosion of the heat transfer outer tube.

According to the high temperature corrosion resistant air heater of claim 5, the corrosion resistant coating film formed on the outer surface of the heat transfer outer tube enables
The heat transfer outer tube can be more reliably protected from corrosion.

According to the high temperature corrosion resistant air heater of the sixth aspect, a particularly excellent corrosion prevention effect can be obtained.

According to the high temperature corrosion resistant air heater of claim 7, the protection tube is firmly held to the heat transfer tube, and the bolt surface for this holding is protected by the air layer.
The deterioration of the bolt is prevented.

According to the high temperature corrosion resistant air heater of the eighth aspect, the amount of gas diffused and permeated through the refractory protection tube is reduced.

According to the high temperature corrosion resistant air heater of the ninth aspect, the protection tube made of the refractory material can be pressed and held in the axial direction of the tube.

[0030]

Embodiments of the air heater for high temperature corrosion resistance of the present invention will be described in detail below with reference to the drawings.

1 to 3 are vertical sectional views showing an air heater for high temperature corrosion resistance according to an embodiment of the present invention, and FIG. 4 is a horizontal sectional view showing an installation form of the air heater for high temperature corrosion resistance of the present invention. is there.

Air heater 10 for high temperature corrosion resistance shown in FIG.
Is a metal heat transfer inner tube 1 with an open tip, and this inner tube 1
A heat transfer tube 4 which is arranged coaxially with the inner tube 1 so as to cover the inner tube 1 and is provided with a gap 2 between the inner tube 1 and a metal heat transfer outer tube 3 with a sealed tip. A protective tube 5 made of a refractory material having a sealed tip is provided coaxially with the heat transfer tube 4 and a gap 6 is provided between the heat transfer tube 4 and the outer tube 3 so as to cover the heat transfer tube 4. It is provided.

In this high temperature corrosion resistant air heater 10, the heat transfer tube 4 and the protection tube 5 are arranged so that their axial directions are vertical, and the inner surface of the sealing end surface 5A at the lower end of the protection tube 5 is arranged. The dovetail holes 5a, 5b are provided on the outer surface of the sealing end surface 3A at the lower end of the outer tube 3, and the dovetail holes 5a, 5b of the protective tube 5 are provided on the outer surface.
Dove-shaped protrusions 3a and 3b capable of engaging with b are provided. The protection tube 5 includes the dovetail holes 5a, 5b and the projections 3a, 3
By being engaged with b, it is supported with respect to the heat transfer tube 4.
In the present embodiment, the protection tube 5 has the dovetail holes 5a and 5b.
Is supported with respect to the heat transfer tube 4 only by the engagement of the projections 3a and 3b with each other, and no other supporting function is provided.

Air heater 10 for high temperature corrosion resistance of this embodiment
Is placed in the hot, highly corrosive gas stream (arrow B) of the incinerator. After the air to be heated descends in the heat transfer inner tube 1, the air to be heated rises from the open tip 1A of the inner tube 1 to the gap 2 between the inner tube and the outer tube (arrow A), between which high temperature and high corrosion of the outside occur. Dirty gas flow B
Is heated by.

It should be noted that unillustrated means for introducing heated air and means for taking out heated air are provided on the base end (upper end) side of the heat transfer tube 4 so that the recovered thermal energy can be effectively utilized. Has been done.

In this high-temperature corrosion-resistant air heater 10, the outer surface of the heat transfer tube 4 is covered with the protective tube 5 made of a refractory material, so that it is protected from corrosion due to high temperature and highly corrosive gas. Moreover, since the gap 6 is provided between the heat transfer outer tube 3 and the refractory protection tube 5, the metal forming the heat transfer outer tube 3 and the refractory material configuring the protection tube 5 are provided. Even if a difference in thermal expansion occurs, dimensional changes due to thermal expansion are less likely to be propagated to each other, so that damage, peeling, dropping, etc. of the protective tube 5 are prevented.

In addition, since the protection tube 5 is supported only at the lower end engaging portion with respect to the heat transfer tube 4, and the protection tube 5 can freely slide with respect to the heat transfer outer tube 3, it is caused by the difference in thermal expansion. Damage, peeling, dropping, etc. of the protective tube 5 that occurs is more reliably prevented.

Further, the heat transfer outer tube 3 is prevented from being damaged by the simple supporting structure of the protection tube 5 and the heat transfer outer tube 3 and the low proportion of the joint portion of the refractory material of the protection tube 5. Like

Air heater 10A for high temperature corrosion resistance shown in FIG.
Has a minute through hole 7 formed in the heat transfer outer tube 3, and causes a part of the air flowing inside the outer tube 3 to flow into a gap 6 between the outer tube 3 and the protective tube 5 (arrow It is different from the air heater 10 for high temperature corrosion resistance shown in FIG. 1 in that it is configured as C). The other configurations of the high temperature corrosion resistant air heater 10A are the same as those of the high temperature corrosion resistant air heater 10, and the members having the same functions are designated by the same reference numerals.

In this high temperature corrosion resistant air heater 10A, air flows out from the outer tube 3 into the gap 6 between the outer tube 3 and the protective tube 5, and the pressure in the gap 6 is positive relative to the external atmosphere. It is kept under pressure. As a result, it is possible to reduce the amount of corrosive gas that reaches the inside of the protective tube 5 through the protective tube 5 from the outside of the protective tube 5, and thus to more reliably prevent the corrosion of the outer tube 3. You can

Air heater 10B for high temperature corrosion resistance shown in FIG.
Differs from the high temperature corrosion resistant air heater 10 shown in FIG. 1 in that a corrosion resistant coating film 8 is formed on the outer surface of the heat transfer outer tube 3. The high-temperature corrosion-resistant air heater 10B is similar to the high-temperature corrosion-resistant air heater 10 in other configurations,
Members having the same function are designated by the same reference numerals. As the material of the corrosion-resistant coating film, a single oxide such as alumina or silica or a mullite containing them, or a complex oxide such as spinel is preferable, and the film thickness is required from the viewpoint of ensuring corrosion resistance, heat cycle resistance, etc. Thickness is chosen.

In the high temperature corrosion resistant air heater 10B, the corrosion resistant coating film 8 formed on the outer surface of the outer tube 3 can protect the outer tube 3 from corrosion more reliably. Also in the heater 10B of FIG. 3, the through hole 7 shown in FIG. 2 may be provided in the heat transfer outer tube 3.

Air heater 10C for high temperature corrosion resistance shown in FIG.
In the above, the outer pipe cap portion 11 is fixed to the tip of the heat transfer outer pipe 3 by welding or the like.
A female screw hole 12 is formed in the. A protective tube cap portion 14 is provided at the tip of the protective tube 5 via a refractory mortar 13. A dovetail hole 15 is recessed in the inner surface of the protective tube cap portion 14, and the head portion of a support bolt 16 having a dovetail-shaped head portion is embedded in the dovetail hole 15.
The threaded rod portion of the support bolt 16 is screwed into the female screw hole 12.

The outer tube cap portion 11 and the support bolt 16 are provided with air holes 17, 18 and 19 for introducing the air in the heat transfer tube 4 to protect the surface of the support bolt 16. The air holes 17 and 18 are connected in a straight line, and the air hole 19 intersects the air hole 18 at a right angle. Other reference numerals indicate the same parts as in FIGS.

Air heater 10D for high temperature corrosion resistance shown in FIG.
In the above, a female screw hole 20 is bored in the tip end surface portion of the heat transfer outer tube 3, and a screw rod portion of the support bolt 16 is screwed into the female screw hole 20. A ring-shaped refractory receiving metal fitting 21 is externally fitted to the support bolt 16, and the protective tube 5 is supported via the refractory receiving metal fitting 21. The support bolt 16 is provided with a hole 22 for allowing air to flow from the air hole 18 into the gap 6. Other reference numerals indicate the same parts as in FIG.

In the high temperature corrosion resistant air heater shown in FIGS. 5 and 6, the protection tube 5 is held very firmly by the support bolt 16. Further, the support bolt 16 has air holes 18 and 19, and the air in the heat transfer tube 4 flows into the air holes 18 and 19, so that the support bolt 16
The surface is protected and its durability is high.

FIG. 7 is a cross-sectional view showing an example of a supporting system of the high temperature corrosion resistant air heater 10E in the incinerator. The high temperature corrosion resistant air heater 10E is connected to the gas flow B in the gas flue 25.
It is inserted in the direction orthogonal to. A recess 26 is provided on the tip surface of the refractory protection tube 5 of the high-temperature corrosion resistant air heater 10E, and the tip of the push rod 27 is inserted into the recess 26. The push rod 27 is biased by a spring 28 and presses the high-temperature corrosion resistant air heater 10E in the right direction in the drawing.
29 indicates a stationary wall.

Protective tube 5 for high temperature corrosion resistant air heater 10E
The rear end portion is fitted to an annular receiving seat 31 provided on the stationary wall 30. The stationary wall 31 is provided with a case 32 for taking out air (air mixed with gas) from the gap 6 between the heat transfer tube 4 and the protection tube 5 of the high-temperature corrosion resistant air heater 10E. . Air is sent into the heat transfer inner tube 1, and the heated air is taken out from between the heat transfer outer tube 3 and the heat transfer inner tube 1.

According to the installation structure of the air heater for high temperature corrosion resistance of FIG. 7, since the compression load in the axial direction of the tube is applied to the protection tube 5 by the spring 28, the protection tube 5 has no or almost no bending stress. It can be prevented. As a result, the durability of the protective tube 5 made of refractory material is significantly enhanced.

When the air heater for high-temperature corrosion resistance is installed in the hanging direction, if the same spring pushes upward in the axial direction of the tube, the protective tube 5 is not subjected to tensile stress at all or almost. Similarly, the durability of the protective tube 5 is enhanced.

In the air heater for high temperature corrosion resistance of the present invention, the metal constituting the heat transfer tube is preferably SUS310 or the like which has excellent heat resistance and corrosion resistance. In addition, the wall thickness of the inner tube and the outer tube of the heat transfer tube is 4 to 4 in terms of strength, durability, weight and the like.
It is preferably about 6 mm.

The inner diameter of the inner tube serving as the air passage is 30 to 7
The width of the gap between the outer pipe and the inner pipe (1/2 of the difference between the inner diameter of the outer pipe and the outer diameter of the inner pipe) is preferably 10 to 30 mm.

As the refractory material constituting the protection tube made of the refractory material, a refractory material that does not form a low melting point compound even when it reacts with the components in the refuse incineration ash is suitable, for example, a high alumina refractory material or a chromia refractory material. Materials, silicon carbide refractories, etc. are preferred.

The wall thickness of the protective tube is preferably about 20 to 35 mm from the viewpoint of ensuring heat transfer efficiency and corrosion resistance. Also, if the gap between the protective tube and the heat transfer outer tube (1/2 of the difference between the inner diameter of the protection tube and the outer diameter of the outer tube) is too large, the heat transfer efficiency decreases, and the air heater is large. On the contrary, if it is too small, the damage due to the difference in thermal expansion cannot be sufficiently prevented.
It is preferably about 2 mm.

By subjecting the refractory material to the sealing treatment, the amount of gas diffused and permeated through the protective tube can be remarkably reduced, and the corrosion resistance of the refractory material itself can be enhanced. To perform the sealing treatment, the refractory protective tube may be immersed in a liquid such as alumina sol or alumina slurry for closing the pores of the refractory material, and then dried and fired. By performing such a pore-sealing treatment, for example, the average pore diameter before the treatment was about 10 μm, but the average pore diameter can be reduced to 5 μm or less.

There is no particular limitation on the arrangement of such a high temperature corrosion resistant air heater of the present invention in the incinerator. Generally, when dust is difficult to adhere, a large heat transfer effective surface is taken. Therefore, if it is installed in an isolated manner, and dust is likely to adhere to it, in the case of Fig. 4 (a) (when the protective tube 5 is a circular tube), (b)
As shown in (when the protective tube 5 is a square tube), it is preferable to install a plurality of sets.

[0057]

As described in detail above, according to the air heater for high temperature corrosion resistance of the present invention, in the air heater in which the heat transfer tube is protected by the refractory, there is no problem of peeling or damage of the refractory,
Therefore, the corrosion of the heat transfer tube is remarkably reduced, and the air heater for high-temperature corrosion resistance is provided which is excellent in corrosion resistance and durability in the high temperature and highly corrosive gas atmosphere of the incinerator.

According to the high-temperature corrosion-resistant air heater of the second and third aspects, damage, peeling, dropping, etc. of the protective tube can be prevented more reliably.

According to the high temperature corrosion resistant air heater of the fourth and fifth aspects, the corrosion of the heat transfer tube can be prevented more reliably.

According to the high temperature corrosion resistant air heater of claim 6, a particularly excellent corrosion prevention effect can be obtained.

In the high-temperature corrosion-resistant air heater according to claim 7, the protective tube is stably supported by the heat transfer tube and is excellent in durability.

In the air heater for high temperature corrosion resistance according to the eighth aspect, the amount of gas diffused and permeated through the protective tube made of the refractory material and reaching the gap between the outer tube and the protective tube is extremely small, and the corrosion resistance of the outer tube is reduced. In addition to being increased, the corrosion resistance of the refractory protection tube itself is also high.

According to the high temperature corrosion resistant air heater of claim 9, the bending load and the tensile load applied to the refractory protection tube can be remarkably reduced, and the durability of the refractory protection tube can be enhanced. it can.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an air heater 10 for high temperature corrosion resistance according to an embodiment.

FIG. 2 is a vertical cross-sectional view showing a high temperature corrosion resistant air heater 10A according to an embodiment.

FIG. 3 is a vertical cross-sectional view showing a high temperature corrosion resistant air heater 10B according to an embodiment.

FIG. 4 is a cross-sectional view showing an arrangement of an air heater for high temperature corrosion resistance of the present invention.

FIG. 5 is a vertical cross-sectional view showing a high temperature corrosion resistant air heater 10C according to an embodiment.

FIG. 6 is a vertical cross-sectional view showing a high temperature corrosion resistant air heater 10D according to an embodiment.

FIG. 7 is a cross-sectional view showing an installation example of the high-temperature corrosion-resistant air heater according to the embodiment.

[Explanation of symbols]

1 heat transfer inner tube 2,6 gap 3 heat transfer outer tube 3a, 3b protrusion 5 protection tube 5a, 5b dovetail hole 7 through hole 8 corrosion resistant coating film 10, 10A, 10B, 10C, 10D, 10E high temperature corrosion resistant air Heater 11 Outer tube cap part 14 Protective tube cap part 16 Support bolts 17, 18, 19 Air hole 26 Recessed part 27 Push rod 28 Spring

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hidehiro Kiuchi 3-1-1 Tam, Tamano City, Okayama Prefecture Mitsui Engineering & Shipbuilding Co., Ltd. Tamano Works

Claims (9)

[Claims] 1. An air heater for high-temperature corrosion resistance, which is provided in a high-temperature corrosive gas atmosphere and heats air flowing in the heat-transfer tube by heat exchange with the high-temperature corrosive gas, wherein the heat-transfer tube has a tip. A heat transfer inner tube made of metal, which is opened, is arranged coaxially with the inner tube so as to cover the inner tube, and is provided with a gap between the inner tube and the tip sealed. A metal heat transfer outer tube is provided, and the air to be heated is heated by the hot corrosive gas while passing through the inner tube and then passing through the gap between the inner tube and the outer tube from the open tip of the inner tube. An air heater for high-temperature corrosion resistance, wherein a protective tube made of a refractory material having a sealed tip, which covers the outer tube, is provided coaxially with the outer tube and with a gap between the outer tube and the outer tube. An air heater for high-temperature corrosion resistance, characterized in that 2. The heater according to claim 1, wherein the protection tube is supported by the outer tube by engagement of a recess provided on an inner surface of the protection tube and a projection provided on an outer surface of the outer tube. An air heater for high temperature corrosion resistance. 3. The heater according to claim 2, wherein the concave portion of the protective tube is a dovetail hole provided on the inner surface of the sealing end surface of the protective tube, and the convex portion of the outer tube seals the outer tube. An air heater for high-temperature corrosion resistance, which is a tapered dovetail protrusion provided on the outer surface of the toe surface. 4. The heater according to any one of claims 1 to 3, wherein the outer tube has a minute penetrating portion through which a part of the air flowing through the outer tube flows out between the outer tube and the protection tube. An air heater for high-temperature corrosion resistance, which is provided with holes. 5. The high temperature corrosion resistant air heater according to claim 1, wherein a corrosion resistant coating film is formed on an outer surface of the outer tube. 6. The heater according to claim 5, wherein the corrosion-resistant coating film is a stable oxide, for example, alumina, silica, or a mixed oxide containing them such as mullite or spinel.
An air heater for high-temperature corrosion resistance, characterized in that 7. The heater according to claim 3, wherein the protrusion is a bolt screwed to the outer tube, and the bolt is provided with a vent hole communicating with the inside of the heat transfer tube. A characteristic air heater for high temperature corrosion resistance. 8. The heater according to claim 1, wherein the protective tube made of refractory material is subjected to a sealing treatment for filling pores of the refractory material. Air heater for corrosion. 9. The heater according to claim 1, wherein a concave portion for receiving the push rod urged by the urging member is provided on the tip surface of the refractory protection tube. An air heater for high temperature corrosion resistance.