JP2001049379A - Heat transfer tube for heat exchanger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a heat transfer tube capable of recovering heat from high temperature corrosive atmosphere in high efficiency without causing reduction in thermal conductivity by using, at least for the surface layer part of a heat transfer tube, a ceramic alloy composite which contains Al and specific percentage of AlN and in which the percentage of Al+AlN is specified. SOLUTION: At least surface layer part of a heat transfer tube for heat exchanger is constituted of a ceramic alloy composite which contains Al and AlN and in which AlN and Al+AlN are regulated to 1-90 wt.% and 50-100 wt.%, respectively. Preferred wall thickness of the ceramic alloy composite is 3-12 mm. A heat transfer tube 11 is constituted, e.g. of a first layer 11a which is composed of heat resistant metal and where a fluid to be heated is allowed to flow on the inside thereof, a second layer 11b which is composed of non- aluminum ceramic material composed essentially of carbon fiber, and a third layer 11c which is composed of ceramic alloy composite and where high temperature gas is allowed to flow on the outside of the external surface thereof. It is also preferable to apply or infiltrate an ash repellent composed of boron or carbon to or into the external surface of the third layer 11c to prevent the sticking of fly ash dust.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to municipal solid waste, coal,
The present invention relates to a heat exchange tube for heat exchange that performs heat exchange between high-temperature combustion exhaust gas of sewage sludge, papermaking sludge, and other industrial waste and a fluid to be heated that passes through the inside.

[0002]

The exhaust gas generated when incinerating BACKGROUND ART municipal refuse and industrial waste contains hydrogen gas and sodium chloride, NaCl containing potassium, KCl and Na ₂ SO ₄ 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 temperature of the steam flowing through the heat exchange tube is set to reduce the damage of corrosion damage caused by hydrogen chloride and basic salts. In general, the temperature is suppressed to 300 ° C. or less.

In order to recover higher-temperature heat energy from this corrosive environment, for example, as disclosed in Japanese Patent Application Laid-Open No. 5-332508, ceramics are placed in a high temperature region of an exhaust gas flue of a waste incinerator. It is proposed that a high-temperature superheated steam can be obtained by providing a heat exchanger made of stainless steel and producing high-temperature air, and superheating the saturated steam introduced into the heater using the high-temperature air. I have. By turning a turbine for power generation using the superheated steam thus obtained, the efficiency of power generation from a refuse incinerator can be improved.

[0004]

However, even if the heat resistance and the corrosion resistance are simply improved by using a ceramic heat exchanger as described above, if the heat exchanger is exposed to a high-temperature corrosive atmosphere for a long time. At the same time, fly ash containing a basic salt adheres to the outer surface of the ceramic heat exchanger in contact with the high-temperature corrosive gas, and the heat exchange rate is reduced by the deposited layer.

When fly ash adheres to the outer surface of the ceramic heat exchanger, a thermal expansion difference occurs between the fly ash and the ceramic at the fly ash attachment site, and the ceramic is liable to crack.

Further, fly ash that has adhered to the outer surface of the ceramic heat exchanger for a certain period of time has become difficult to remove even with a soot blower, and the fly ash deposited layer has increased.
As a result, the heat transfer coefficient of the ceramic heat exchanger decreases. Therefore, simply using a ceramic heat exchanger,
Highly efficient heat recovery cannot be maintained over a long period of time.

An object of the present invention is to eliminate the accumulation of fly ash and to make it possible to efficiently recover heat from a high-temperature corrosive atmosphere without lowering the thermal conductivity.

[0008]

The heat exchanger tube for heat exchange according to claim 1 of the present invention has the following configuration. That is, in a heat exchange tube for heat exchange provided in a high-temperature gas atmosphere and performing heat exchange between the high-temperature gas and a fluid to be heated passing through the inside, at least the surface layer of the heat transfer tube is made of Al and AlN. AlN is 1wt% or more and 90wt%
% Or less, and the total ratio of Al + AlN is 50% by weight or more and 100% by weight.
% Or less of a ceramic alloy composite material.

In a heat exchanger tube for heat exchange according to a second aspect of the present invention, at least the surface layer of the heat exchanger tube contains Al and AlN, and AlN is at least 1 wt% and at most 90 wt%, and Al + AlN + Al.
It is formed of a ceramic alloy composite material having a total ratio of ON of 50 wt% or more and 100 wt% or less.

[0010] Further, the thickness of the ceramic alloy composite material portion is set to 3 mm or more and 12 mm or less.

The heat transfer tube has an outer surface coated or infiltrated with an ash repellent made of a compound containing boron or carbon.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. Hereinafter, the present invention will be described with reference to the illustrated embodiments. FIG. 1 is a sectional view and a partially enlarged schematic view showing a heat exchange tube for heat exchange according to a first embodiment of the present invention.

The heat exchange tube for heat exchange according to the first embodiment is provided in a high-temperature gas atmosphere, and performs heat exchange between the high-temperature gas and a fluid to be heated passing therethrough.
Contains Al and AlN, AlN is 1 wt% or more and 90 wt% or less, and the total proportion of Al + AlN + AlON is 50 wt% or more and 1 wt% or more.
It is formed of a ceramic alloy composite material having a thickness of not more than 00 wt% and a thickness of not less than 3 mm and not more than 12 mm.

Here, aluminum nitride, AlN
Is a material having excellent corrosion resistance to air oxidation and corrosion resistance to various molten metals such as hot metal and molten steel among ceramic materials. In an inert atmosphere, it is also excellent in corrosion resistance to various molten slags such as blast furnace slag. In addition, since it has relatively high hardness, it has excellent wear resistance, and further has 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. In other words, AlN
A material that has both excellent corrosion resistance and wear resistance, and relatively excellent thermal shock resistance.

AlN, together with AlN, which is metallic aluminum
Is also a material having extremely good thermal conductivity and a metal that is advantageous in reducing thermal shock, and is suitable as a component of the heat transfer tube 1. In the manufacturing process of ceramic alloy composite material, changes to AlN reacts with N ₂ atmosphere Many Al, become configuration unreacted Al in AlN are dispersed binding AlN is between the particles as in FIG. 1 Strengthen power.

Such a ceramic alloy composite material mainly composed of an 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. Obtained by

The low-purity Al source powder is, for example, a metal Al or Al alloy powder, and may contain alloying elements such as Si and Mg. The high-purity Al source powder contains, for example, 90 wt% or more of Al. When the filler obtained by heat-molding these mixed powders is heated in a nitrogen atmosphere, Al in the powder is melted (pure Al has a melting point of 660 ° C., whereas Al-Mg alloy has a maximum melting point of 450 ° C.). The melting point drops to 5% for Al-Si alloys.
When the temperature reaches 680 ° C., a certain amount of Al reacts with N _{2 in} the atmosphere to change to AlN,
A structure is obtained in which a small amount of unreacted Al is dispersed in AlN. Depending on the nitriding conditions, the AlN concentration at the surface of the tube body in contact with the high-temperature gas of the ceramic alloy composite material forming the surface layer of the heat transfer tube 1 can be made higher than at other cross-sections.

With this structure, even if the sintered body receives a thermal shock, the AlN has a function of preventing the shape deformation of the AlN, and the Al surrounded by the 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 if it exceeds 90 wt%, the properties of the ceramic alloy composite material approach ceramics and become brittle, which is not preferable. Therefore,
The content ratio of AlN is 1 to 90 wt%.

Further, this ceramic alloy composite material includes:
Al and AlON are dispersed in AlN. Here AlON
Is a general term for solid liquids of Al, O, and N. For example, Al ₁₁ O
₁₆ N, AlON, 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, Si 3 Al 3 O 4.5 N
₅ can be mentioned. When the content ratio of Al + AlN + AlON is not less than 50% by weight and not more than 100% by weight, the ceramic alloy composite material can absorb a thermal shock while having a thermal deformation characteristic.

The nitride containing aluminum has poor wettability with the fly ash of the oxide contained in the high-temperature exhaust gas (hereinafter referred to as ash repellency), so that the weight percentage of Al + AlN + AlON is 50 wt%. With the above, the property of preventing fly ash dust from adhering (ash repellency) is effectively exhibited.

In the process of manufacturing the heat transfer tube 1, AlON
Is possible. Therefore, AlON was removed and only Al and AlN were used, and the weight ratio was 50 wt%.
It may be configured to be at least 100 wt% or less, and even such a ceramic alloy composite material can absorb thermal shock while having thermal deformation characteristics.

In any case, the thickness of the heat transfer tube 1 is 3 to 12
mm is preferred. If the wall thickness is less than 3 mm, there is a problem in strength with respect to the pressure of the fluid to be heated. If the wall thickness is more than 12 mm, a heat gradient occurs in the thickness direction during heat exchange, causing cracks in the ceramic alloy composite material. It will be easier.

The heat transfer tube made of the ceramic alloy composite material has been described by taking a tube having a perfect circular cross section as an example. However, the heat transfer tube is not necessarily required to be a perfect circle, but an eccentric circle, ellipse, square, or Irregular shapes are acceptable.

Embodiment 2 FIG. FIG. 2 is a cross-sectional view showing a heat exchange tube for heat exchange according to a second embodiment of the present invention. In the figure, the same parts as those in the first embodiment (FIG. 1) are designated by the same reference numerals. is there.

The heat exchanger tube for heat exchange according to the second embodiment is provided in a high-temperature gas atmosphere, and performs heat exchange between the high-temperature gas and a fluid to be heated passing therethrough.
Has a three-layer structure 11a, 11b, and 11c, and includes the same ceramic alloy composite material as that described in the first embodiment, that is, Al and AlN in the three-layer surface layer portion.
lN is 1 wt% or more and 90 wt% or less, the total ratio of Al + AlN is 50 wt% or more and 100 wt% or less, and the wall thickness is 3 mm or more and 12 mm.
The following ceramic alloy composite material, or containing Al and AlN, wherein AlN is 1 wt% or more and 90 wt% or less, Al + AlN + Al
The total percentage of ON content is 50 wt% or more and 100 wt%
% Or less, and a ceramic alloy composite material having a thickness of 3 mm or more and 12 mm or less is used. Note that the heat transfer tube 11 is not limited to this three-layer structure, and may be formed in a single layer, two layers, or three or more layers according to the purpose. It is important to use the above-mentioned ceramic alloy composite material for the surface layer portion.

The outer surface of the heat transfer tube 11 is coated or infiltrated (for example, at a high temperature of 800 ° C.) with a compound containing boron such as BN or B ₄ C or a carbon-containing compound such as SiC or graphite. Since these have better ash repellency than the above-mentioned AlN-containing ceramic alloy composite material, they prevent fly ash from attaching more than AlN-containing ceramic alloy composite material. The thickness to be applied or infiltrated is preferably 1 to 400 microns, and when the heat transfer tube 1 is used for a long period of time, for example, it is repeatedly applied or infiltrated to the outer surface of the heat transfer tube every year. Thereby, the ash repelling effect can be maintained.

From such a ceramic alloy composite material,
The hot gas flows outside the outer surface of the heat transfer tube 11
The fluid to be heated passes through the inside of the first layer (inner tube) 11a. high temperature
The temperature of the gas is between 400 ° C and 1200 ° C and the gas atmosphere
The material for forming the inner layer is selected depending on the conditions. This
Here, a 4 mm thick heat-resistant metal (eg, SU
S304) Non-Al-based ceramic material for the second layer 11b
(Material mainly composed of carbon fiber) was used. In high temperature exhaust gas
Contains HCl or SOx, or both.
ing. The fluid to be heated flowing through the heat transfer tube 11 is empty.
Gas, water vapor, CO _TwoContaining 2 to 25 vol% (wet base)
Exhaust gas can be used.
800 ° C. In case of steam, heat to about 550 ° C.
Can be.

Also in this case, the thickness of the outermost layer portion 11c made of the ceramic alloy composite material of the heat transfer tube 11 is 3 to 12 mm.
Since it was set to, it was easy to secure a strength surface with respect to the pressure of the fluid to be heated, and it was possible to prevent a thermal gradient from occurring in the thickness direction.

Although the layers 11a, 11b, and 11c including the surface layer made of the ceramic alloy composite material have all been described with reference to a heat transfer tube whose cross section is a perfect circle, it is not limited to a perfect circle. It is not necessary to do so, and an eccentric circle, ellipse, square, or irregular shape may be used. Surface layer (third layer) made of ceramic alloy composite material
The inner layer (second layer) made of a non-Al-based ceramic material and the innermost layer (first layer) made of a heat-resistant metal need not be concentric.

The ceramic alloy composite material mainly composed of aluminum used in the present invention includes AlN,
In addition to Al, a substance having good heat resistance, for example, an oxide, a boride, a carbide, a nitride, an oxynitride, or the like may be blended. The usable oxides include TiO ₂ , ZrO ₂ , and Cr ₂
O ₃ , Al ₂ O ₃ , SiO ₂ , Y ₂ O ₃ , CeO ₂ , Sc ₂ O _3, etc.
As borides, BN, MgB ₂ , CaB ₆ , TiB ₂ , Zr
Examples of carbides such as B ₂ and AlB ₂ include B ₄ C, TiC, and Zr.
Ti, such as C, Cr ₃ C ₂ , Al ₄ C ₃ , and SiC, is Ti
_{N, ZrN, Cr 2 N,} Si 3 N 4 or the like, S is the oxynitride etc.
i ₂ N ₂ O and the like can be mentioned, and one or more of them may be selected. Further, a composite oxide containing at least one of the oxides may be blended. The composition may be any composition.

The length of each of the heat transfer tubes 1 and 11 in each of the above embodiments is preferably 6 m or less. When such heat transfer tubes 1 and 11 are long, the ceramic alloy composite material is easily broken, and in the case of the heat transfer tube 11 having a multi-layer structure, it is easy to peel off.

The outer diameter of the heat transfer tubes 1 and 11 in each of the above embodiments is preferably 200 mm or less. Outer diameter is 2
When it is larger than 00 mm, the ceramic alloy composite material is easily broken.

In the following, three types of heat exchange tubes for heat exchange according to the present invention having at least a surface layer made of a ceramic alloy composite material are placed in a high-temperature exhaust gas having an exhaust gas temperature of about 950 ° C. to 750 ° C. of a municipal waste incineration pilot plant. Insert, as the fluid to be heated, steam with an inlet temperature of 150 to 400 ° C and 1
A test example using air at 20 to 300 ° C. and waste flue gas will be described. Test Example 1 Single layer structure: Al-based ceramic alloy (Al + A
LN-90 wt% or more), an outer diameter of 40 mm and a wall thickness of 4 mm. Test example 2. Three-layer structure: the first layer is SUS30 from the inner side
4 (thickness 4 mm), the second layer is a layer mainly composed of carbon fiber, and the third layer (the outermost layer) is an Al-based ceramic alloy (Al + ALN).
-90 wt% or more, wall thickness 4 mm) and outer diameter 40 mm. Test Example 3 Three-layer structure: the first layer is SUS30 from the inner side
4 (thickness 4 mm), the second layer is a layer mainly composed of carbon fiber, and the third layer (the outermost layer) is an Al-based ceramic alloy (Al + ALN).
-90 wt% or more, wall thickness 4 mm), outer diameter 40 mm, 20 μm of BN was applied to the outer surface of the tube.

As a result of the exposure test, it was confirmed that in all of the test examples, the amount of thinning on the outer surface of the heat transfer tube was slight, and stable heat exchange was possible over a long period of time. Further, in this test, it was confirmed that the heat transfer tube coated with BN of Test Example 3 had a smaller wall loss by 70% or more than the other Test Examples 1 and 2. The main component of the exhaust gas heat exchanger tube is exposed in the test examples, in addition to _{N 2, O 2: 2~16%} , HCl:
_{100~500ppm, SOx: max300ppm, CO 2} : 5
１８18%, but no cracks occurred in the heat transfer tubes of any of the test examples.

[0035]

As described above, according to the present invention, at least the surface layer portion of the heat transfer tube is made of a ceramic alloy composite material made of a nitride containing aluminum, so that the ash repellency is good and the heat transfer tube outside The deposition of fly ash on the surface was eliminated, and heat could be efficiently recovered from a high-temperature corrosive atmosphere without lowering the thermal conductivity. Therefore, waste flue gas,
High-temperature heat, which had not been used before, could be recovered from the high-temperature corrosive environment in the coal combustion exhaust gas, sewage sludge combustion exhaust gas, and other industrial waste combustion exhaust gas.

In addition, since the thickness of the ceramic alloy composite material portion is set to 3 mm or more and 12 mm or less, it is easy to secure a strength surface against the pressure of the fluid to be heated, and it is possible to prevent a heat gradient from occurring in the thickness direction. .

Further, since the outer surface of the heat transfer tube is coated or infiltrated with an ash repellent made of a compound containing boron or carbon, which has higher ash repellency than a nitride containing aluminum, the ash repelling effect is further enhanced. I was able to.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view and a partially enlarged schematic view illustrating a heat exchange tube for heat exchange according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a heat exchanger tube for heat exchange according to a second embodiment of the present invention.

[Explanation of symbols]

 1,11 heat transfer tubes

Claims (4)

[Claims] 1. A heat exchange tube for heat exchange provided in a high temperature gas atmosphere and performing heat exchange between the high temperature gas and a fluid to be heated passing therethrough, wherein at least a surface layer portion of the heat transfer tube is: Containing Al and AlN,
A heat exchanger tube for heat exchange, comprising a ceramic alloy composite material in which AlN is 1 wt% or more and 90 wt% or less, and a total ratio of Al + AlN is 50 wt% or more and 100 wt% or less. 2. A heat exchange tube for heat exchange provided in a high temperature gas atmosphere and performing heat exchange between the high temperature gas and a fluid to be heated passing therethrough, wherein at least a surface portion of the heat transfer tube is: Containing Al and AlN,
AlN is 1wt% or more and 90wt% or less, Al + AlN + AlON
Characterized by being formed of a ceramic alloy composite material having a total ratio of 50 wt% or more and 100 wt% or less. 3. The thickness of the ceramic alloy composite part is 3 mm.
The heat transfer tube for heat exchange according to claim 1, wherein the heat transfer tube is set to be not less than 12 mm. 4. The heat exchanger according to claim 1, wherein an ash repellent made of a compound containing boron or carbon is applied or infiltrated on the outer surface of the heat transfer tube. Heat transfer tubes.