JP2001048650A - Heat transfer tube for heat exchanger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a heat transfer tube for heat exchanger which can be stably used for a long period of time in a thermal decomposition gasification melting furnace used in a thermally heard environment by forming a tubular heat transfer tube being opened at least at one end and used for a heat exchanger by using a porous ceramic obtained by mixing various types of particles in which each particle is mainly constituted of the crystal phase of SiC and each type of the particles has a specified average particle size. SOLUTION: Particles having an average particle diameter of 5 to 10 μm and particles having an average particle diameter of 0.5 to 1 μm are mixed in the ratio of 1:9 to 3:7. The strength is improved by mixing two types of particles having different average particle sizes. Further, in the case that SiC mainly constituted of the crystal phase of SiC used, a thermal conductivity of >=50 W/m.K is realized and the obtained porous ceramic is excellent in the oxidation resistance under a high temp. oxidizing atmosphere, e.g. when the porous ceramic is heatd to 1,200 deg.C, the amount of the increase in the oxidation is as small as <=0.5%. Moreover, direct oxidation of SiC can be inhibited by forming a dense SiO2 protective coating film having a cristobalite-type crystal structure on the surface of the porous ceramic, because the SiO2 coating film contributes as an oxidation inhibiting film of the SiC being the base material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat exchanger tube for a heat exchanger suitable for recovering heat from high-temperature waste gas of an incinerator or a pyrolysis furnace.

[0002]

2. Description of the Related Art Garbage discarded from homes and companies is burned in incinerators of local governments, and the unburned incineration ash and fly ash contained in flue gas (containing elements: Si, Al, Fe, Ca,
Mg, K, Mn, Cl, Na, and S) contain heavy metal components and toxic contaminants such as dioxin and furan.

Until now, unburned incineration ash after being burned in local government incinerators has been buried as it is in the final disposal site. However, location conditions have become severe, making it difficult to secure a place. In addition, since detoxification of harmful pollutants such as dioxin and furan is being strictly regulated by laws and regulations, a melting furnace that detoxifies harmful pollutants by collecting incinerated ash and fly ash and remelting them. The need for is increasing year by year.

[0004] The incinerated ash after being burned in an incinerator, which is turned into slag by high-temperature heat treatment, can be reduced to 1/2 of the incinerated ash.
The high-temperature heat treatment method in this melting furnace is considered to be promising because its volume can be reduced to about 1/4 and harmful pollutants such as dioxin can be decomposed and detoxified by high heat.

On the other hand, municipal waste incinerators have been installed for the purpose of incinerating municipal waste to reduce the volume of waste. However, from the viewpoint of effective utilization of energy, the heat generated by the incinerated waste gas is reduced. In order to recover energy to the maximum, it is important to recover and utilize the waste heat from the high-temperature waste gas using a heat exchanger.

Conventional heat exchangers have a temperature of 500-60.
Although it was used at 0 ° C., for example, in a pyrolysis gasification and melting furnace that is being commercialized in recent years, it is 1200 to 1300
It is operated at a temperature of ℃, and heat exchange is being performed at 1200 to 1300 ℃ in order to recover and utilize the heat energy in a region where the temperature of the waste gas is high.

In the pyrolysis gasification and melting furnace, the gasification furnace and the melting furnace are integrated.
The waste is heat-treated at a low temperature of ℃ to generate flammable gas and send it to the melting furnace. In the melting furnace, fly ash sent together with combustible gas and tar are burned at a high temperature of about 1300 ° C to make fly ash into slag and completely decompose dioxin and the like. . After this, the waste gas after high-temperature combustion is led to the waste heat boiler, but the heat exchanger is often installed from the melting furnace outlet to the waste heat boiler, and the recovered heat is air It is effectively used for steam generators for preheating and power generation.

FIG. 1 shows an example of a heat exchanger. A heat transfer tube 1 in which one side of a cylindrical body is sealed is arranged so as to protrude from a furnace wall 2 of a gasification and melting furnace toward the inside, and a pipe 3 is arranged inside the heat transfer tube 1. During the operation of the melting furnace, the outside of the heat transfer tube 1 is exposed to a combustion gas of 1200 ° C. or more, and if a heating fluid (air) of about 250 ° C. is sent from the pipe 3 in this state, the inside of the heat transfer tube 1 is At 550 ° C
Heated to a degree and discharged, it acts as a heat exchanger.

The waste gas contains H ₂ O, CO
₂ , O ₂ , a large amount of dust and hydrogen chloride (HCl) gas, etc. are contained.
ppm. In addition, since the Ca component contained in the dust and the HCl component in the gas are highly corrosive, excellent corrosion resistance is required. Tokiko Sho 60-21
Japanese Patent No. 6192 discloses that a coating layer of stainless steel or Cr-Ni alloy steel is formed on the surface of a normal steel pipe to be used as a heat exchanger tube for the heat exchanger.

[0010]

However, in the pyrolysis gasification and melting furnace, the temperature distribution in the furnace fluctuates within the range of 500 to 1400 ° C. depending on the type of refuse to be burned and the operating condition of the incinerator. Heat transfer tubes installed for this purpose are required to have high thermal shock resistance. For this purpose, it is effective to make the heat transfer tube porous, but in this case, not only the problem that the heat conductivity is reduced and the function as the heat transfer tube cannot be sufficiently performed occurs, but also the surface area increases and the refuse incinerator The contact area with the corrosive gas inside increases, the corrosion resistance also decreases, the erosion causes holes in the heat transfer tube itself, and the heated air inside the heat transfer tube leaks out of the tube. Has caused a problem that the strength is reduced due to the influence of the material and the material is easily damaged during handling.

When ash generated by garbage incineration is subjected to heat treatment, the ash is heated at 1200 ° C. or more to decompose metal elements such as Cd, Pd and Zn and harmful pollutants such as dioxin and furan contained in the ash. Detoxification by melting treatment, but the heat transfer tube used in this melting furnace is exposed to molten salt, steam of molten slag, HCl gas, etc. formed by melting of incineration ash. Therefore, Si, Al, F in these components
e, Ca, Na, and Cl gradually penetrate and erode into the material constituting the heat transfer tube, and the material constituting the heat transfer tube gradually deteriorates in strength and deteriorates in strength. Or, since the required heat exchange is not performed, it has been desired to extend the service life.

Generally, copper and copper alloys having high thermal conductivity are used as heat transfer tubes for heat exchangers for low temperatures, but hydrogen chloride exceeding 1200 ° C. and requiring corrosion resistance is required. There is no suitable material in the high concentration area. As mentioned above, in Japanese Patent Publication No. 60-216192,
A coating layer of stainless steel or Cr-Ni alloy steel is formed on the surface of ordinary steel pipes to improve high-temperature corrosion.
It could not be used in the temperature range.

[0013] Therefore, in a temperature environment of about 1200 ° C, and in the presence of highly corrosive dust and HCl gas, 1500 to 20
Various ceramic materials having excellent corrosion resistance and heat resistance have been devised in a use environment having about 00 ppm. However, most of the materials are easily broken at high temperatures due to thermal expansion and have poor thermal shock resistance.

[0014]

In view of the above, the present invention provides
In a heat exchanger tube for a heat exchanger, which is formed of a cylindrical body having at least one end opened and through which a heat exchange fluid is circulated, a particle having an average diameter of 5 to 10 μm and an average diameter of 5 to 10 μm is mainly composed of a SiC crystal phase. 5-1 μm particles in a weight ratio of 1: 9 to
It is characterized by being formed of porous ceramics mixed at a ratio of 3: 7.

The above porous ceramic has a porosity of 5
２０20%, thermal conductivity 50 W / mK or more, JIS 4-point bending strength 100 MPa or more, thermal shock (drop in water) ΔT =
It is characterized by being able to maintain 60% or more of room temperature strength at 800 ° C.

Further, the porous ceramics is characterized in that the weight increase due to oxidation up to 1200 ° C. in the atmosphere is 0.5% or less.

The porous ceramics described above are made of dense SiO ₂ having a cristobalite type crystal structure on the surface.
A protection film is formed.

[0018]

The heat transfer tube for a heat exchanger is mainly composed of a crystal phase of SiC, and has an average diameter of 5 to 10 μm and an average diameter of 0.5 to 1 μm.
Is made of porous ceramics mixed at a weight ratio of 1: 9 to 3: 7, the heat shock resistance can be remarkably increased as compared with a dense heat transfer tube. In a pyrolysis gasification and melting furnace under a severe environment where the temperature in the furnace rises and falls, it can be stably used as a heat exchanger tube for a heat exchanger for a long period of time.

The strength can be improved by mixing two kinds of particles having different particle diameters. Furthermore, the thermal conductivity can be improved to 50 W / mK or more by using a crystalline phase of SiC as a main component, and the increase in oxidation of the porous ceramics up to 1200 ° C. is as small as 0.5% or less, in a high-temperature oxidizing atmosphere. Has excellent oxidation resistance.

Further, by forming a dense SiO ₂ protective film having a cristobalite-type crystal structure on the surface of the porous ceramics, the SiO ₂ film can oxidize SiC as a base material even in a high-temperature atmosphere. It acts as a protective film and acts to prevent direct oxidation. Further, when a fluid for heat exchange is circulated in the heat transfer tube, the fluid can be prevented from leaking from the pores of the porous ceramics forming the heat transfer tube.

[0021]

Embodiments of the present invention will be described below.

In the heat exchanger shown in FIG. 1, a heat transfer tube 1 in which one surface of a cylindrical body is sealed is arranged so as to protrude inward from a furnace wall 2 of a gasification and melting furnace. In which a pipe 3 is arranged. During the operation of the melting furnace, the outside of the heat transfer tube 1 is exposed to a combustion gas of 1200 ° C. or more, and if a heating fluid (air) of about 250 ° C. is sent from the pipe 3 in this state, the inside of the heat transfer tube 1 is At about 550 ° C. and discharged, and acts as a heat exchanger.

In the present invention, the heat transfer tube 1 is composed mainly of a crystal phase of SiC, and has a particle having an average diameter of 5 to 10 μm and an average diameter of 0.5 to 10 μm.
It is formed of a porous ceramic in which particles having a size of １1 μm are mixed at a weight ratio of 1: 9 to 3: 7.

This porous ceramic has a dense SiO ₂ protective film having a cristobalite-type crystal structure formed on the surface. The weight increase due to oxidation up to 1200 ° C. in the atmosphere is 0.5% or less, and the porosity is 5%. ~ 20%, thermal conductivity 5
It is formed of a ceramic material capable of maintaining 0 W / mK or more, JIS 4-point bending strength of 100 MPa or more, thermal shock resistance of ΔT = 800 ° C. and 60% or more of room temperature strength.

For this reason, even when used in a gasification and melting furnace having good thermal shock resistance and a large thermal shock, the heat transfer tube 1 does not crack and does not cause problems such as leakage of the heating fluid. . Further, since only the SiO ₂ film having the cristobalite type crystal structure is formed on the surface of the heat transfer tube 1, the heat exchange can be performed well without the heating fluid leaking from the pores of the porous body.

Here, in particular, mainly the crystal phase of SiC is used,
The reason that the particles having an average diameter of 5 to 10 μm and the particles having an average diameter of 0.5 to 1 μm are mixed at a weight ratio of 1: 9 to 3: 7 is to form a strong structure and obtain a heat transfer tube having high strength. It is.
For example, when a porous ceramics body is formed only of SiC particles having an average diameter of 5 to 10 μm in an N ₂ atmosphere at a temperature of 2000 ° C. and baked, the porosity is 48% and the strength is 13 MPa.
Although porous ceramics can be obtained, the porosity is too large and not only the heating fluid leaks from the pores but also the strength itself as a ceramic body is too low.
When the porous ceramic body is supported in the vertical direction with respect to the furnace wall, the porous ceramic body is damaged by its own weight.

In comparison with this, the porous ceramic of the present invention has a high active energy and an average diameter of 0.5 to 1 μm.
m particles enter the gaps between the contact surfaces of the particles having an average diameter of 5 to 10 μm and increase the contact surface between the particles to promote sintering. Therefore, the porosity is 5 to 20%, the strength is 100 MPa or more, and there is no leakage of the heating fluid. Not only can a porosity in a range be obtained, but also a strength can be obtained that forms a stronger structure and does not break under the influence of its own weight even when supported on the furnace wall at any angle.

When a dense SiC ceramic body is used as the material of the heat transfer tube 1, the thermal shock resistance is ΔT = 45.
At a temperature higher than about 0 ° C., the strength is remarkably reduced to about 20 to 30%. In comparison with this, the porous ceramic body of the present invention has ΔT = 800 ° C. and 60% of room temperature strength. As the above can be maintained, the thermal shock resistance can be significantly increased, and in a pyrolysis gasification and melting furnace under a severe environment where the furnace temperature rises and falls depending on the type of combustion refuse, It can be used stably for a long time as a heat transfer tube.

Further, in a heat exchanger tube for a heat exchanger, a commercially available refractory (a composite porous ceramic refractory material of Si ₃ N ₄ and SiC) having a similar porosity in terms of thermal conductivity which is an important parameter. ) Is about 20 W / mK, whereas the porous ceramic material of the present invention mainly composed of a crystal phase of SiC can be improved to 50 W / mK or more.

The reason why the average particle diameter and the mixing weight ratio are set in the above ranges in the present invention is that if the average particle size and the mixing weight ratio are outside these ranges, the porosity becomes too large and the heating fluid flowing through the heat transfer tube 1 leaks to the outside. Not only does this cause a phenomenon in which either the thermal conductivity decreases significantly or the thermal shock resistance decreases due to a dense body, and the durability decreases significantly with respect to the temperature difference in the gasification melting furnace. This is because there is a danger that it will occur.

In the present invention, the above particle size refers to the crystal particle size in the final sintered body, which can be measured by observing the cross section of the sintered body with an electron microscope or the like. However, in the case of porous ceramics, there is almost no grain growth, so that two kinds of raw materials within this range may be mixed to obtain the above particle diameter.

Further, the porous ceramic of the present invention has only a cristobalite-type SiO ₂ film on the surface, so that the oxidation increase up to 1200 ° C. is as small as 0.5% or less. Such as the commercially available porous ceramic (SiC-Si ₃ N ₄ composite refractory) with similar porosity oxidation weight gain is 1.3% and a low corrosion resistance. In this regard, both Si
When the crystal morphology of the O ₂ film was examined by X-ray analysis, commercially available refractories were cristobalite type (about 2% at 500 ° C.).
In addition to the above, a tridymite type having a different coefficient of thermal expansion (elongation of about 1.2% at 500 ° C.) is generated. ₂ Defects are likely to occur in the film. Therefore, when the base material is exposed to the air atmosphere, oxidation proceeds. It is presumed that the repetition of the above results in an increase in the amount of oxidation as a result as compared with the material having a cristobalite type crystal structure of the present invention.

The two crystal types are present in the commercially available SiO ₂ film of refractory because the oxidation start temperature of the material itself is 830.
Because it is easy to oxidize as fast as ° C., the crystal of SiO ₂ is quartz →
Tridymite → easy to cause transformation of cristobalite,
This is because the next oxidation proceeds while the above-mentioned crystal transformation between tridymite and cristobalite is not completed, and as a result, two crystal forms remain. In comparison, the material of the present invention has an oxidation start temperature as low as 1090 ° C., and it is considered that only cristobalite crystals generated at a high temperature remain. Furthermore,
Commercially available refractories contain a large amount of impurities such as Fe (Fe content of the material of the present invention: 0.02%, Fe content of commercial refractory: 0.1%).
2%), and the susceptibility to transformation between tridymite and cristobalite is also considered to be a factor for the existence of two crystal forms.

Further, in the present invention, by using a porous ceramic which forms a dense SiO ₂ protective film having a cristobalite type crystal structure having a high melting point of 1730 ° C. among the crystal forms of SiO _{2 on} the surface, Even when exposed to an environment with a maximum temperature of 1400 ° C. in the pyrolysis gasification and melting furnace, the SiO ₂ film serves as an antioxidant film for SiC as a base material, and serves to prevent direct oxidation. is there. Further, when a fluid for heat exchange is circulated in the heat transfer tube, it serves to prevent the fluid from leaking out of the pores of the porous ceramics forming the heat transfer tube. Such characteristics contribute to prolonging the life of the heat exchanger itself.

The cristobalite type SiO ₂ film has already been formed after the firing of the porous ceramics. However, in the case where a grinding process is performed to adjust the dimensions after the firing, the temperature is set at 1200 ° C. for one hour. It can be formed by performing the heat treatment maintained as described above.

In FIG. 1, the heat transfer tube 1 having one side sealed is shown.
However, as for the shape, it is possible to suitably use a cylindrical body having both ends opened.

When the heat transfer tube 1 of the present invention is manufactured, a commercially available binder is added to a material obtained by mixing the above-described two kinds of raw materials having different particle diameters in a predetermined range, and an apparatus such as a super mixer is used. Stir and mix. Thereafter, water is added and the dispersibility of the fine particles and coarse particles is sufficiently increased by a device such as a kneader, and the mixture is molded into a predetermined shape by a known method such as extrusion molding.
After the binder is removed at a temperature of 00 to 800 ° C., N ₂ gas is injected in a vacuum furnace and an induction heating furnace for 200 hours.
It can be obtained by firing at a temperature of about 0 ° C. Further, it is also possible to manufacture by performing molding by both wet-type and dry-type pressure molding methods after adding the binder, and firing by the above method. Furthermore, after granulating with a spray drier and molding using a pressure molding method, it can also be fired by the above method. In any case, by adjusting the composition and firing conditions, 12
A ceramic tube that can be used under severe conditions at a temperature of 00 ° C. or higher is obtained.

In order to increase the heat exchange efficiency, the thickness of the ceramic tube 1 is preferably as thin as possible. However, if the thickness is too small, the strength may be insufficient. The above thickness is optimal,
If the thickness is increased, the heat exchange efficiency may be impaired, and it is preferable to keep the thickness within 5 to 15 mm.

[0039]

Embodiment 1 An embodiment of the present invention will be described below.

JIS 4-point bending test piece (thickness 3 mm, width 4
mm, length 45 mm) were formed from SiC materials having different particle sizes, and the porosity, JIS 4-point bending strength, thermal conductivity, and thermal shock resistance were evaluated. Table 1 shows the average raw material particle size and the results of characteristic evaluation.

The following method was used to produce a test piece in order to evaluate the characteristics more realistically.

First, a commercially available binder was added to each having the average raw material particle diameter shown in Table 1, and the mixture was stirred with a super mixer, then water was added and kneaded with a kneader to uniformly disperse the mixture. Diameter 80mm, inside diameter 72m
m, forming a cylindrical body having a length of 50 mm. Thereafter, the formed cylindrical body was dried at 100 ° C. for 1 hour, and dried at 600 ° C. for 10 hours.
After performing degreasing for a time, calcination is performed at 2000 ° C. for 2 hours. From the cylindrical body thus formed, the JIS
A four-point bending test piece was cut out by grinding so that the length direction of the test piece was parallel to the axial direction of the cylindrical body.

As shown in Table 1, Examples 5 and 6 are examples in which two types of SiC raw materials having different particle sizes are mixed. N
o. No. 5 was mixed at a weight ratio of 2: 8, but the particle size was out of the range of the present invention. In No. 6, the particle diameters were 10 μm and 1 μm, but the weight ratio of the two particle diameters was outside the range of the present invention, and none of the above properties could be obtained.

Further, No. Nos. 8 to 10 are also Nos. 5
This is an example in which two kinds of SiC raw materials having different particle diameters are mixed in the same manner as in the above, and the characteristics within the above range cannot be obtained due to the difference in weight ratio.

In addition, No. 1-4 are S of 1-100 μm
This is an example in which a test piece was manufactured using only iC particles and the property was evaluated. The porosity was 5 to 20%, and the JIS 4-point bending strength was 1
100 MPa or more, thermal conductivity of 50 W / mK or more, thermal shock ΔT = 800 ° C., maintaining 60% or more of room temperature strength, cannot satisfy these characteristics, and is not practical as a heat exchanger tube material for heat exchangers It was confirmed that.

On the other hand, no. 7 and No. 7 11-
14 was within the scope of the present invention, and was able to satisfy the above characteristics.

From this example, two types of SiC particles having different particle sizes are used.
When the raw materials are mixed, if the particle size and the weight ratio are not within the range of the present invention, porosity, strength, thermal conductivity, and thermal shock resistance may not provide a practical value as a heat exchanger tube for a heat exchanger. You can check.

[0048]

[Table 1]

Embodiment 2 Next, another embodiment of the present invention will be described.

A heat transfer tube 1 shown in FIG. 1 (Al ₂ O ₃ ),
No. No. 2 (Mullite), No. No. 3 (ZrO ₂ ),
4 {commercial refractory ceramic (material: SiC-Si ₃
N ₄ composite systems)}, No. 5 ｛Material of the present invention (N in Table 1)
o. 12) It was formed of ceramics containing｝ as a main component.

The dimensions of the ceramic tube are 80 mm in outer diameter,
The inner diameter was 72 mm and the total length was 1500 mm. Inside the ceramic tube, a stainless steel pipe 3 having a diameter of 40 mm is set coaxially with the ceramic tube 1 so that air at 300 ° C. can be introduced into the ceramic tube, and the air is heated by the heat recovery unit simulation device of the waste gas treatment device. Then, it was installed so that heat exchange was possible, and a heat resistance test was further performed. In addition, a heat exchange test was also performed, and a case where heated air of 500 ° C. or more was obtained at the outlet of the ceramic tube was determined to be OK.

At the same time, a 3 × 4 × 45 mm test piece of the same material as each heat transfer tube 1 was prepared, and the thermal shock resistance was evaluated using a thermal shock tester. For the evaluation, a temperature difference (ΔT) that can be durable was measured by using an underwater drop method according to JIS.

Further, the thermal conductivity was measured by a laser flash method using a test piece of φ10 × thickness 3 mm.

Further, in the heat recovery simulation device of the waste gas treatment device, after the heat resistance test and the heat exchange test are completed, the inside of the device is kept at 1250 ° C., and the ash generated by incineration of dust is added. Each of the materials was subjected to an exposure test of 1500 HR that was injected and adjusted to the atmosphere in the refuse incinerator. If cracks occur due to corrosion, N
G. Otherwise, it was determined to be OK.

Tables 2 and 3 show the test results.

[0056]

[Table 2]

[0057]

[Table 3]

No. For 1 and 2, the raw material particle size is 1 μm
The thermal shock resistance was ΔT = 300 ° C. or less, cracks occurred, and the compact was NG. Also, in the heat exchange test, the heat conductivity of the material itself was low and 7 W / mK or less even though it was a dense body. Furthermore, regarding the exposure test, 5
Cracks occurred at about 00 HR, and it was NG.

In addition, No. For No. 3, the raw material particle size is 1 μm.
m, but showed good results in the thermal shock test and the thermal test. However, the thermal conductivity of the material itself is as low as 4 W / mK.
Air of 0 ° C. or higher was not obtained, and the result was NG. Further, in the exposure test, cracks and the like due to the influence of corrosion were not observed, and good corrosion resistance was exhibited.

In addition, No. As for No. 4, the average raw material particle diameter was 75 μm for SiC and 1 μm for Si ₃ N _4, and the weight ratio was 3:
7, a porous material having a porosity of about 15%, which is originally a material having high thermal shock resistance, such as SiC and Si ₃
Because the composite of N _4, was not an OK problem with thermal shock test and heat resistance test. The thermal conductivity was 20 W / mK and No. It has more than twice the characteristics as compared with 1, 2 and 3, and it was possible to obtain heated air of 500 ° C. or more without any problem. However, in the exposure test, 10
Although it was good up to 00 hours, the porosity was high and the contact area with the corrosive gas was large, so the surface corrosion proceeded and the wall thickness gradually decreased. It was found in several places. Heating air leaked from that portion, resulting in NG.

In this regard, exposure tests 500, 100
0,1500 hours later, X-ray analysis of the surface layer near the cross section of each test piece revealed that the more the exposure time, the more the surface
Although ₂ film is produced, however, the crystalline form and cristobalite type, there are two types of tridymite type, a thermal expansion difference between the two crystal forms, its defect portion for defects in the SiO ₂ film It is considered that the holes were corroded and the holes as described above were generated. In addition, the two types of crystal phases appear because the oxidation initiation temperature is 830 ° C., which is faster than 1090 ° C. of the material of the present invention, and the amount of oxidation increase is so large that it is easily oxidized. Two crystal phases remain without being completed, and Fe which activates the transformation between tridymite and cristobalite
It is conceivable that many impurities such as are contained.

As compared with such a comparative example, the No. 1 of the present invention was
For No. 5, the raw material particle diameter having an average diameter of 6 μm and the average diameter of 1 μm
If the material having the above particle size is mixed in a weight ratio of 2: 8 and used as a ceramic porous body for a heat exchanger tube, the heat shock, heat resistance, heat exchange, exposure and all tests are cleared without any problems. It was confirmed that it was possible.

[0063]

As described above, the heat exchanger tube for a heat exchanger, which is formed of a cylindrical body having at least one end opened and through which a heat exchange fluid flows, has a crystal phase of SiC as a main component and an average diameter of 5 mm. Particles of 10 to 10 μm and average diameter of 0.5 to 1 μm
By using a porous ceramic in which particles of m are mixed at a weight ratio of 1: 9 to 3: 7, the thermal shock resistance can be remarkably increased, and the furnace temperature rises and falls depending on the kind of combustion dust. It can be used stably for a long time as a heat exchanger tube for a heat exchanger in a pyrolysis gasification and melting furnace under a severe environment.

The strength can be improved by mixing two kinds of particles having different particle diameters. Furthermore, the thermal conductivity can be improved to 50 W / mK or more by using a crystalline phase of SiC as a main component, and the increase in oxidation of the porous ceramics up to 1200 ° C. is as small as 0.5% or less, in a high-temperature oxidizing atmosphere. Has excellent oxidation resistance. Further, by forming a dense SiO ₂ protective film having a cristobalite-type crystal structure on the surface of the porous ceramic, the SiO ₂ film becomes an antioxidant film of SiC as a base material even in a high-temperature air atmosphere. In addition to serving to prevent direct oxidation, the fluid can be prevented from leaking out of the pores of the porous ceramics forming the heat transfer tube when a heat exchange fluid is allowed to flow through the heat transfer tube.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a heat exchanger tube for a heat exchanger of the present invention.

[Explanation of symbols]

 1: Heat transfer tube 2: Furnace wall 3: Pipe

Claims (4)

[Claims] 1. A heat exchanger tube for a heat exchanger, comprising a tubular body having at least one end opened therein and through which a fluid for heat exchange is circulated.
A heat exchanger tube for a heat exchanger, comprising a porous ceramic in which particles having a particle size of 10 to 10 μm and particles having an average diameter of 0.5 to 1 μm are mixed at a weight ratio of 1: 9 to 3: 7. 2. The method according to claim 1, wherein the porous ceramic has a porosity of 5 to 2.
2. The material according to claim 1, wherein the material has a property of maintaining 0%, a thermal conductivity of 50 W / mK or more, a JIS four-point bending strength of 100 MPa or more, and a thermal shock resistance of ΔT = 800 ° C. of 60% or more of room temperature strength. Heat transfer tubes for heat exchangers. 3. The method according to claim 1, wherein the porous ceramic is made of 120
3. The heat exchanger tube for a heat exchanger according to claim 1, wherein an increase in weight due to oxidation up to 0 ° C. is 0.5% or less. 4. A heat exchanger tube for a heat exchanger according to claim 1, wherein said porous ceramics has a dense SiO ₂ protective film having a cristobalite type crystal structure on the surface.