JP2001056195A - Heat transfer pipe for heat exchange - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a metal from being corroded and enable high temperature heat recovery even if the metal is exposed to a high temperature corrosive atmosphere for a long time by constituting a non-bonded structure of a heat resistant alloy and a cover material made of a ceramics alloy composite material and providing a structure wherein at least parts of both members are in contact with each other. SOLUTION: A outside of a pipe body 1 made of a heat resistant alloy is covered with a cover member 2 made of a ceramics alloy composite material and both members 1, 2 have non-contact structure and at least parts of the members 1, 2 are in contact with each other. A high temperature gas is allowed to flow outside of an outer surface of the cover member 2 and a fluid to be heated is allowed to flow inside of the heat resisting alloy pipe 2. The ceramics alloy composite material 2 covers outside of the heat resisting alloy pipe 1 and the ceramics alloy composite material 2 and the heat resisting alloy pipe 1 are at least partly in contact with each other. By this constitution, high temperature heat can be recovered from high temperature corrosive environment in high temperature corrosive gases such as waste combustion exhaust gas, coal burning exhaust gas and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to municipal solid waste, coal,
The present invention relates to an electric heat exchanger tube for heat exchange in a heat recovery / utilization system that recovers thermal energy from high temperature combustion exhaust gas of sewage treatment, papermaking sludge, and other industrial wastes through a fluid such as steam or air to generate power.

[0002]

2. Description of the Related Art Exhaust gas generated when municipal solid waste or industrial waste is incinerated contains hydrogen chloride gas, NaCl containing sodium, potassium, etc., KCl, Na ₂ SO _{4 and} other basic salts. The corrosiveness of hydrogen chloride and basic salts increases as the temperature increases. Therefore, in a waste heat boiler that recovers heat from the combustion exhaust gas of municipal solid waste and industrial waste, the steam flowing through the heat exchange tube is generally used to reduce the damage of corrosion damage due to hydrogen chloride and basic salts. It is kept below 300 ° C.

Therefore, in order to recover higher-temperature heat energy from this corrosive environment, as disclosed in JP-A-10-274401, the outer surface of a boiler tube made of a heat-resistant metal is sprayed by a thermal spraying method. A method has been devised in which a heat exchange tube is coated with a ceramic film by a chemical vapor deposition method or a chemical vapor deposition method to improve the high-temperature corrosion resistance. Since the boiler tube is based on metal, it has the toughness necessary for the heat exchange tube, and the surface has
In general, high corrosion resistance in high-temperature exhaust gas was ensured by using ceramics that have excellent high-temperature strength and low wettability with salts and exhibit excellent high-temperature corrosion performance.

[0004]

However, in the above-described conventional heat exchange tubes, since the ceramics and the metal are bonded by a thermal spraying method or a vapor deposition method, if they are exposed to a high-temperature corrosive atmosphere for a long time. Under the influence of the difference in the coefficient of thermal expansion between the ceramic and the metal, the ceramic is easily separated from the metal surface. Then, the metal part where the ceramic has been peeled off starts to corrode. For this reason, there is a problem that this method is insufficient as a method for reliably preventing corrosion of the heat exchange tube.

Accordingly, the present invention has been made to solve the problem of the separation of ceramics and metal due to the difference in thermal expansion without lowering the thermal conductivity. An object of the present invention is to provide a heat exchanger tube for heat exchange that can recover heat at a higher temperature than conventional ones without corrosion of the surface.

[0006]

A heat exchanger tube for heat exchange according to the present invention is provided in a high-temperature gas atmosphere, and performs heat exchange from the high-temperature gas to a fluid to be heated in the heat exchanger tube. The pipe through which the fluid to be heated flows is made of a heat-resistant alloy,
The outside of the heat-resistant alloy tube is covered with a cover material made of a ceramic alloy composite material, and the heat-resistant alloy tube and the cover material made of the ceramic alloy composite material have a non-adhesive structure, and at least a part of both members are in contact with each other. (Claim 1).

With this configuration, the heat-resistant alloy tube and the cover material made of the ceramic alloy composite material are exposed to a high-temperature atmosphere and are not bonded to each other even if they are thermally expanded. No damage caused by interference of the ceramic alloy composite cover material,
Further, the thermal energy of the high-temperature fluid existing outside the ceramic alloy composite material cover material can be transferred to the heated fluid flowing inside the heat-resistant alloy tube for a long time. In addition, since the heat-resistant alloy tube and the ceramic alloy composite material cover material are at least partially in contact with each other, a decrease in thermal conductivity between the ceramic alloy composite material cover material and the heat-resistant alloy tube is prevented. It is more preferable that almost all of the inner surface of the ceramic alloy composite material cover material comes into contact with the outer surface of the heat-resistant alloy tube in terms of improving thermal conductivity. If the ceramic alloy composite material cover material and the heat-resistant alloy tube are completely separated without contact, that is, if there is a gap, a heat insulating layer of gas will be formed there and the thermal conductivity will drop sharply. Is not preferred.

Here, the heat-resistant alloy which is the material of the tube through which the fluid to be heated flows includes, for example, carbon steel / alloy steel for boilers,
Alternatively, stainless steel, heat-resistant steel, Ni-based / Co-based heat-resistant alloys (Inconel, Hastelloy, stellite, etc.) and the like, and chromium, which is a high melting point metal, are also suitable.
Furthermore, the ceramic alloy composite material constituting the cover material includes oxides, carbides, nitrides, borides, silicides,
A wide range of choices, such as carbon, and their mixtures, are possible. For example, Al ₂ O ₃ or Sialon (SiAlNO) is used as an oxide, and SiC or B _{4 is used} as a carbide.
C, AlN, Si ₃ N ₄ as nitride, Ti as boride
MoSi and the like are suitable as B ₂ and silicide.

Further, the ceramic alloy composite material constituting the cover material in the present invention contains Al and AlN,
AlN of 1 wt% or more and 90 wt% or less, (Al + AlN + A
(ON) is a total ratio of 50 wt% or more and 100 wt% or less (claim 2).

[0010] Among ceramic materials, AlN is a material excellent in corrosion resistance to air oxidation and corrosion resistance to various molten metals such as molten steel. In an inert atmosphere, it is also excellent in corrosion resistance to various molten slags such as blast furnace slag. Are better. In addition, it has relatively high hardness, so that it has excellent wear resistance. Further, it has an extremely high thermal conductivity, a low coefficient of thermal expansion, and a relatively low elastic modulus, so that it has a feature that is relatively resistant to thermal shock. As described above, AlN is a material having both excellent corrosion resistance and wear resistance and relatively excellent thermal shock resistance.

[0011] Along with AlN, metallic aluminum A
1 is also a material having extremely good heat conduction, is a metal that is advantageous for reducing thermal shock, and is suitable as a component of a heat transfer tube. In the manufacturing process of ceramic alloy composite material cover material, changes to AlN reacts with N ₂ atmosphere Many Al, become configuration Al is dispersed unreacted during AlN, A
1N enhances the bonding force between the particles.

With this configuration, even if the sintered body receives a thermal shock, AlN has a function of preventing shape deformation, and Al surrounded by AlN has a function of reducing the thermal shock. Therefore, in order to maintain this function, AlN must be contained at least 1 wt% or more. If the content of AlN is less than 1 wt%, the bonding force between the particles is small and insufficient, and 90 wt%.
Exceeding the ratio is undesirable because the properties of the ceramic alloy composite material become closer to ceramics and become brittle. Therefore, the content ratio of AlN is set to 1 wt% or more and 90 wt% or less.

In the ceramic alloy composite material, Al and AlON are dispersed in AlN. Therefore, the content weight ratio of (Al + AlN + AlON) is
When the content is 50 wt% or more and 100 wt% or less, the ceramic alloy composite material cover material has thermal deformation characteristics,
High thermal shock resistance can be maintained. In addition, since nitrides containing aluminum have poor wettability to oxide dust contained in high-temperature exhaust gas, dusts are unlikely to adhere to the ceramic alloy composite material cover material if contained in a considerable amount. It has the characteristic of becoming. Therefore, if the content ratio by weight of (Al + AlN + AlON) is 50 wt% or more, the property of not adhering dust can be effectively exhibited. In the production of the heat transfer tube, AlON may be eliminated, and the weight ratio of Al and AlN alone may be 50 wt% or more and 100 wt% or less.

Here, AlON means Al, O, N
Is a general term for solid liquids such as Al ₁₁ O ₁₅ N, AlO
N, Al ₁₉₈ O ₂₈₈ N ₄ , Al ₂₇ O ₃₉ N, Al ₁₀ N ₈ O ₃ ,
Al ₉ O ₃ N ₇ , SiAl ₇ O ₂ N ₇ and Si ₃ Al ₃ O _4.5 N ₅ are mentioned.

Further, in the present invention, a release agent comprising a compound containing boron or carbon is applied to the outer surface of the heat-resistant alloy tube (claim 3).

By applying the release agent, the slip between the heat-resistant alloy pipe and the ceramic alloy composite material cover material is improved, and the elongation due to the difference in thermal expansion between the two members becomes smoother.

Further, the present invention is characterized in that the porosity of the ceramic alloy composite material is 2% or more and 60% or less (claim 4).

In the production of a cover material made of a ceramic alloy composite material, in order to reduce the porosity to less than 2%, a high-temperature and high-pressure atmosphere is required in the production process, and the production cost rises sharply. Pores in the ceramic alloy composite material are not simple circular holes but have irregular shapes.
Their sizes range from sub-micron or less to several hundred microns in line-to-line distance. In a ceramic alloy composite material having such pores, if the porosity is larger than 60%, dust containing a basic salt easily penetrates into the ceramic alloy composite material, and the corrosion effect reaches even the heat-resistant alloy pipe. Therefore, the lower limit of the porosity is preferably 2%, and the upper limit is preferably 60%.

[0019]

FIG. 1 shows a cross section of a heat exchanger tube for heat exchange according to an embodiment of the present invention. The outside of the tube 1 made of a heat-resistant alloy is covered with a cover material 2 made of a ceramic alloy composite material, and both members 1 and 2 have a non-adhesive structure, and have a structure where at least a part of both members 1 and 2 are in contact with each other. . In the drawing, reference numeral 3 denotes a gap between both members 1 and 2.

A high-temperature gas flows outside the outer surface of the cover material 2 made of a ceramic alloy composite material, and a fluid to be heated passes inside the heat-resistant alloy tube 1. The temperature of the hot gas is 400 ° C ~ 1
At 200 ° C., the ceramic alloy composite material of the cover material 2 is selected depending on the gas atmosphere conditions.

The high-temperature exhaust gas contains HCl and / or SOx. When a high-temperature dust collecting device having an exhaust gas temperature of 300 ° C. or higher is installed in an exhaust gas treatment line, the heat exchange tube for heat exchange of the present invention can be used for high-temperature exhaust gas after dust removal. The fluid to be heated flowing in the heat exchange tube for heat exchange of the present invention represents a combustion exhaust gas containing air, water vapor, and ₂ to 25 vol% (wet basis) of CO _2. The steam can be heated to about 550 ° C. Also, the fluid to be heated can be up to 100
It was confirmed that pressurization up to ata was possible. The thickness of the heat-resistant alloy tube 1 is preferably 3 to 10 mm, and the thickness of the ceramic alloy composite material cover member 2 is preferably 3 to 20 mm.

Cover material 2 made of ceramic alloy composite material
As shown in FIG. 1, a cover material 2 made of a ceramic alloy composite material and a heat-resistant alloy
Is at least partially in contact. The heat exchange tube for heat exchange of the present invention does not use a method of bonding ceramics or a corrosion-resistant alloy to the outer surface of a heat-resistant alloy tube by thermal spraying or vapor deposition or other methods, and uses a cover material 2 made of a ceramic alloy composite material like a sleeve. It has a covered shape. Therefore, even if the heat-resistant alloy tube 1 and the ceramic alloy composite material cover material 2 are thermally expanded due to exposure to a high temperature, they are each expanded and do not hinder each other's elongation. The larger the contact area between the outer surface of the heat-resistant alloy tube 1 and the inner surface of the ceramic alloy composite material cover material 2, the greater the heat transfer from the high-temperature exhaust gas flowing outside to the fluid to be heated in the heat-resistant alloy tube 1. The surface roughness of the ceramic alloy composite material cover material 2 is a few microns or more at a large area, and the heat resistant alloy tube 1 and the ceramic alloy composite material cover material 2 thermally expand depending on the temperature. The outer surface of the tube 1 and the inner surface of the ceramic alloy composite cover material 2 are 1
It is extremely difficult to make a full contact with 00%. Heat-resistant alloy tube 1
And the gap between the ceramic alloy composite material cover material 2 is 2
If it is less than mm, the heat transfer is promoted by radiation, so that the expected thermal conductivity can be maintained. Therefore, the gap is preferably 20 mm or less in terms of the distance between the surfaces. Note that the ceramic alloy composite material cover material 2 and the heat-resistant alloy tube 1 do not need to have a perfect circle, and may have an eccentric circle, ellipse, square shape, or irregular shape. Further, the heat-resistant alloy tube 1 and the cover material 2 made of the ceramic alloy composite material do not need to be concentric. Further, the outer surface roughness of the heat-resistant alloy tube 1 may be rough or smooth.

Among the ceramic alloy composite materials, a material composed of AlN + Al + AlON mainly composed of an aluminum element is most preferable for the heat transfer tube of the present invention in terms of performance. Because, in the present invention, the ceramic alloy composite material is desired to have high-temperature corrosion resistance of ceramic properties and ductility of alloy properties, but in this regard, the aluminum element is compared with the main elements forming other ceramic alloy composite materials. Optimum in ductility. Also, the contact surface between the heat-resistant alloy and the ceramic alloy composite material has the advantage that the rate of damage during expansion and contraction is smaller than that of other ceramic alloy composite materials by using an aluminum-based ceramic alloy composite material with excellent ductility. I have.

The ceramic alloy composite material mainly composed of the aluminum element is obtained by, for example, pressing a mixed powder of a low-purity Al source powder and a high-purity Al source powder and sintering the compact. Can be The low-purity Al source powder is, for example, a metal Al or Al alloy powder, Si, M
It may contain an alloying element such as g. The high-purity Al source powder contains, for example, 90 wt% or more of Al. The filling obtained by molding these mixed powders is heated in a nitrogen atmosphere. Al in the powder melts (pure Al has a melting point of 660
Is a ° C., Al-Mg alloy has a melting point lowered to a maximum 450 ° C., in the Al-Si alloy melting point is lowered to a maximum 577 ° C.), is reached 680 ° C., Al a certain amount of atmosphere of N ₂ To form AlN, and a small amount of unreacted Al is dispersed in AlN. Since AlN having ceramic properties forms a film around Al, the commercialized cover material 2 made of a ceramic alloy composite material of AlN + Al + AlON melts and loses its shape even when exposed to a high temperature higher than the melting point of Al. Absent. Further, since the degree of nitriding can be controlled by setting the temperature and pressure during molding and during heating, the AlN concentration that enhances the ceramic properties can be adjusted according to the conditions of the high-temperature exhaust gas and the amount of heat recovered. If the concentration of AlN or Al cannot be set to the set value during molding and heating, Al
N or Al may be supplied between the ceramic alloy composite material and the heat-resistant alloy.

Ceramics mainly composed of aluminum element
In addition to AlN and Al, heat-resistant
May be blended as long as the substance is not suitable. That is, Ti
O_Two, ZrO_Two, Cr_TwoO_Three, Al_TwoO_Three, SiO_Two, Y
_TwoO_Three, CeO_Two, Sc_TwoO_ThreeOne selected from
Is more than one oxide and also less of these oxides
A composite oxide containing at least one may be contained. Also, B
N, MgB_Two, CaB₆, TiB _Two, ZrB_Two, AlB_Twoof
Even if one or more borides selected from among them enter
Good. Also, B_FourC, TiC, ZrC, Cr_ThreeC_Two, Al_Four
C_ThreeOne or more carbonizations selected from, SiC
Things may enter. Also, TiN, ZrN, Cr _TwoN,
Si_ThreeN_FourOne or more nitrides selected from
You may enter. Si_TwoN_TwoContains oxynitride represented by O
You may. Regarding the composition, in this invention, any composition
There may be. Also, part of Al in AlON is replaced with Si.
May be replaced. However, the molar ratio of Si / Al is 1.0
The following is preferred from the viewpoint of corrosion resistance.

When exposed to a high temperature, the outer surface of the heat-resistant alloy tube 1 is coated with BN or the like to improve the mutual slip between the outer surface of the heat-resistant alloy tube 1 and the inner surface of the ceramic alloy composite cover material 2. A compound containing boron or carbon such as B ₄ C is applied. This functions as a release agent that more effectively prevents the adhesion between the ceramic material and the metal and improves the slip of each. The coating thickness is preferably 1 to 60 microns.

The high-temperature exhaust gas contains H as a corrosive substance.
There is a condensate composed of a gaseous substance such as Cl or SOx and a basic salt such as NaCl or KC1. This condensate forms submicrons on the small scale and forms aggregates on the large scale.
It has a size of about 0 microns. In order to reduce the cost of the heat exchange tube for heat exchange of the present invention, it is effective to increase the porosity of the ceramic alloy composite material to 2% or more. Is likely to erode into ceramic alloy composites, empirically 60
%, The effect of the present invention cannot be exhibited.

FIG. 2 shows a side view and a cross section of the heat exchanger tube for heat exchange according to the present invention. A heat transfer tube for heat exchange is set in an atmosphere in which a high-temperature gas flows, and a fluid to be heated enters the inside of the heat-resistant alloy tube 1 from one end and escapes to the other end. Basically, the outer periphery of the heat-resistant alloy tube 1 exposed to the high-temperature gas is covered with a cover material 2 made of a ceramic alloy composite material. Although not clearly shown in FIG. 2, as described above, the heat-resistant alloy tube 1 and the cover member 2 made of the ceramic alloy composite material have a non-adhesive structure in which at least a part thereof comes into contact.

The flow velocity of the fluid to be heated in the pipe is in accordance with the conventional waste combustion or coal combustion boiler, but the flow velocity may be changed to a lower speed or a higher speed depending on the purpose. Heat-resistant alloy tube 1 through which the fluid to be heated of the heat transfer tube for heat exchange flows 1
The pipe diameter of the pipe may be any number as long as the fluid to be heated flows.
It is preferable to make it 0 A in terms of manufacturing. The length of the heat exchange tube is preferably 1 m to 6 m. When the heat exchange tube for heat exchange becomes longer, the amount of deflection of the heat-resistant alloy tube 1 increases, and there is a fear that the ceramic alloy composite material of the cover material 2 is cracked.
In this case, the problem can be solved by providing a column for supporting the ceramic alloy composite material cover member 2 from the outside and reducing the amount of deflection of the heat-resistant alloy tube 1. In addition, as can be seen from FIG. 2, a long heat transfer tube can be made by welding both ends of the heat-resistant alloy tube 1 that is not covered with the ceramic alloy composite material of the short heat transfer tube.

FIGS. 3 and 4 show another configuration example of the heat exchange tube for heat exchange obtained from the present invention. FIG. 3 shows a state in which one end of the heat exchange heat transfer tube is closed, and the fluid to be heated is caused to flow through the heat resistant tube 4 provided in the heat resistant alloy tube 1, and the fluid to be heated folds in the gap between the heat resistant tube 4 and the heat resistant alloy tube 1. In a structure in which the fluid to be heated is heated, all portions exposed to a high-temperature gas that applies heat to the fluid to be heated are covered with a cover material 2 made of a ceramic alloy composite material. In the case of this type, the outer diameter of the heat exchange tube for heat exchange is preferably φ30 to 200 mm.

FIG. 4 shows a heat-resistant alloy tube 1 through which a fluid to be heated flows.
Is formed in a U-shape, and an outer portion including a bent portion thereof is covered with a cover material 2 made of a ceramic alloy composite material. The U-shaped bent portion requires more gaps 3 because the thermal expansion deformation of the heat-resistant alloy and the ceramic alloy composite material is more complicated than that of the heat exchanger tube having a straight tube shape.

[0032]

[Examples] (1) In a garbage incineration pilot plant for treating municipal waste and industrial waste, about 95
The following several types of heat exchange tubes for heat exchange were inserted into a high-temperature exhaust gas at 0 ° C. to about 650 ° C. Heat-resistant alloy tube: SUS304-15A Ceramic alloy composite material cover material: Al + AlN +
AlON-90wt% or more, wall thickness -5-10mm, porosity 4
0% heat-resistant alloy tube: SUS304-20A Ceramic alloy composite material cover material: Al + AlN +
AlON-90 wt% or more, wall thickness -6 to 8 mm, porosity 20
% Heat-resistant alloy tube: SUS304-20A, outer surface-BN coating Ceramic alloy composite material cover material: Al-10AlN +
AlON-90 wt% or more, wall thickness -6 to 8 mm, porosity 20
% Heat-resistant alloy tube: SUS304-20A Ceramic alloy composite material cover material: Al ₂ O ₃ -80
wt% or more, the thickness -2～4Mm, the main component of the non-N ₂ of porosity 30% flue _{gas, O 2: 2~16 (vol,} dr
y)%, HCl: 200 to 600 (vol, dry) ppm, SO
x: max 300 (vol, dry) ppm, CO ₂ : 4 to 19 (vol, dry)
dry)%, which is a general exhaust gas atmosphere generated when municipal waste and industrial waste are burned.

As a result of the exposure test, no crack occurred in the ceramic alloy composite material cover material under any conditions. After the exposure test for 600 hours, each heat transfer tube was taken out and the cross-section was observed. As a result, the cross-section of the heat transfer tube with BN applied to the outer surface of the SUS was the same as that at the time of manufacture, and the BN
It was found that the slip of the coating and the cover material made of the ceramic alloy composite material was smoother than that of the heat transfer tube. When steam at an inlet temperature of 300 ° C. to 400 ° C. is used as the fluid to be heated,
At the outlet of heat exchanger tube group for heat exchange, 500 ℃ or more, 100ata
I found the possibility of. When air or waste combustion exhaust gas is used as the fluid to be heated, the temperature is 1000 to 5000 mmAq.
It was confirmed that air and waste combustion exhaust gas of 100 to 400 mmAq could be heated up to 800 ° C. However,
Since the cover material made of the ceramic alloy composite material of the heat transfer tube was mainly composed of Al ₂ O ₃ having relatively low heat conductivity, the heat transfer coefficient was lower than that of the heat transfer tube.

(1) Municipal waste is partially oxidized to about 1000
Heat-resistant alloy tube: heat-resistant tube for boiler STBA28-20A Ceramic alloy composite material cover material: Al + AlN-
90 wt%, Al ₂ O ₃ -7 wt%, wall thickness -6 to 7 mm, porosity 25% Heat-resistant alloy tube: Heat-resistant tube for boiler STBA28-20A Ceramic alloy composite material cover material: SiC-95 wt
%, A heat exchange tube having a wall thickness of -6 to 7 mm and a porosity of 2% was inserted. The fluid to be heated is steam and air.

As a result of conducting a heat exchange test in a reducing atmosphere having a CO concentration of 5 to 15 (vol, dry)%, since the high-temperature gas was a reducing gas, SiC and AlN were mostly oxidized and deteriorated. No good heat exchange could be performed.

(3) In the flue gas of coal, sewage sludge dewatered cake and dry sludge incinerator, heat-resistant alloy pipes: two types of heat-resistant pipes for boilers STBA28-40A and 65A Ceramic alloy composite material cover material: SiC- 95wt
% Or more, the thickness - of about 7 mm, the coaxial tube shape (Figure 3 or equivalent) heat-resistant alloy tube: two ceramic alloy composite material made cover member for the boiler heat pipe STBA28-20A and 50A: Al ₂ O ₃ -95
wt% or more, wall thickness-about 3 mm, coaxial tube shape (equivalent to Fig. 3), heat-resistant alloy tube: two types of heat-resistant tubes for boilers STBA28-15A and 20A Ceramic alloy composite material cover material: Al + AlN-
A heat exchanger tube for heat exchange having a U-tube shape (equivalent to FIG. 4) having a thickness of -6 to 10 mm and a thickness of 90% or more was inserted.

As a result of the test, several hundred (vol, dry) ppm of SOx is contained in the flue gas of coal and sewage sludge, but even under these conditions, the heat transfer tube is not corroded and the power generation efficiency is 30% or more. It has been found that it is possible to recover high-temperature and high-pressure steam and to recover high-temperature air and high-temperature combustion exhaust gas.

[0038]

As described above, the heat exchanger tube for heat exchange of the present invention has excellent toughness of a tube made of a heat-resistant alloy and the properties of both ceramics and metal constituting a cover material covering its outer surface. Combined with the excellent high-temperature corrosion resistance of ceramic alloy composite materials that have not been used in the past due to the high-temperature corrosive environment in waste flue gas, coal flue gas, sewage sludge flue gas, and other industrial waste flue gas. It is possible to recover the heat of the air.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a heat exchanger tube for heat exchange according to an embodiment of the present invention.

FIG. 2 is a side view and a cross-sectional view of the heat exchange tube for heat exchange of the present invention.

FIG. 3 is a cross-sectional view showing another embodiment of the present invention.

FIG. 4 is a sectional view showing still another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heat resistant alloy pipe 2 Ceramic alloy composite material cover material 3 Air gap 4 Heat resistant tube

Claims (4)

[Claims] 1. A heat exchange tube for heat exchange provided in a high temperature gas atmosphere and exchanging heat from the high temperature gas to a fluid to be heated in a heat transfer tube, wherein the tube through which the fluid to be heated flows is made of a heat-resistant alloy. The outside of the alloy pipe is covered with a cover material made of a ceramic alloy composite material, and the heat-resistant alloy pipe and the cover material made of the ceramic alloy composite material have a non-adhesive structure, and at least a part of both members are in contact with each other. Heat transfer tube for heat exchange. 2. The ceramic alloy composite material constituting the cover material contains Al and AlN, wherein AlN is 1 wt% or more and 90 wt% or less, and the total ratio of (Al + AlN + AlON) is 50 wt% or more and 100 wt% or less. The heat exchange tube for heat exchange according to claim 1. 3. The heat exchanger tube for heat exchange according to claim 1, wherein a release agent made of a compound containing boron or carbon is applied to an outer surface of the heat-resistant alloy tube. 4. The porosity of the ceramic alloy composite material is 2% or more and 60% or less.
The heat exchanger tube for heat exchange according to any one of claims 1 to 3.