JPS6212660A - Heat transmission member for heat exchanger - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] lTo the East, send a second lesson.■ The present invention relates to a heat transfer member for a heat exchanger. .

Next title: Bisono.

Heat exchangers are widely used for purposes such as waste heat recovery and preheating of combustion air in power generation plants, industrial furnaces, iron and metallurgical plants, chemical plants, etc. from the standpoint of energy conservation.

These heat exchangers are of the bulkhead heat transfer type (she
EL type, etc.), a method in which high-temperature gas on the primary side such as combustion gas is passed outside the tube, and heat transfer is conducted through the tube wall to heat the gas on the secondary side, which flows inside.
Jin type, etc.) is known, in which heat is stored by passing high-temperature gas through a honeycomb-structured rotor, and then low-temperature secondary gas is flowed to radiate heat.

Among these methods, the former partition wall heat transfer method is generally used in relatively large heat exchangers mB, and the latter heat storage method is used in small heat exchangers.

The heat transfer member of a heat exchanger is a material used in a heat transfer portion from high temperature gas to low temperature gas in these heat exchangers.

At present, heat-resistant alloys are mainly used as materials for the heat transfer members of this heat exchanger, but heat-resistant alloys do not have sufficient heat resistance and are usually 1. The temperature of the high-temperature gas on the next side that can be used is limited to about 800℃, and when using gas with a higher temperature than this, cooling air etc. must be introduced to raise the temperature to 800℃.
Cooling and heat exchange are performed as follows. Therefore, the temperature of the gas on the secondary side obtained is limited to about 500°C. Therefore, in order to make it possible to use higher temperature gas and perform efficient heat exchange, there is a demand for the development of materials that can withstand temperatures of 1000°C or more for long periods of time, and research into ceramic heat transfer members is underway. It is progressing.

Such heat transfer members are required to have excellent heat resistance, as well as excellent properties such as chemical stability, corrosion resistance, strength, thermal shock resistance, and abrasion resistance. It is desired to have durability. Ceramic members exhibit excellent durability, especially against high temperatures and corrosive gases.
For the heat storage type, lithium ceramics such as cordierite and spongene, aluminum titanate, etc. are used.

Among these, SiC has excellent high-temperature strength, thermal conductivity, corrosion resistance, etc., but it is prone to gas leakage from partition walls, is difficult to make thin walls, and has poor chemical stability against high-temperature combustion gas and heat resistance. It has n points in impact resistance and is also poor in economical efficiency.

Although 3i3Na has better thermal shock resistance than SiC, it is inferior in high temperature strength, chemical stability, etc. In addition, since both SaC and 513N& are made of non-oxides, they have poor oxidation resistance in open atmospheres or oxidizing atmospheres at high temperatures of about 1200°C or higher, and have the disadvantage of being oxidatively decomposed and difficult to use for long periods of time. be.

Cordierite, lithium ceramics, aluminum titanate, etc. used in regenerative heat exchangers have low thermal expansion and excellent oxidation resistance, but they have poor heat resistance. Lithium ceramics are approximately 1000℃, aluminum titanate is approximately 1200℃
Furthermore, corrosion resistance, high temperature stability, high temperature strength, abrasion resistance, etc. are not satisfactory.

As mentioned above, currently known ceramic heat transfer members are not fully satisfactory for use at high temperatures, and are therefore used at temperatures above 1000°C, more preferably at temperatures above 12°C.
It is desired to develop a heat transfer member that can be stably used for a long period of time at temperatures of 00° C. or higher.

Steps for Solving the Problems The present inventor has conducted extensive research in order to find a heat transfer member for a heat exchanger that can withstand use at high temperatures for a long period of time. As a result, heat transfer members made of mullite sintered bodies that satisfy specific conditions can withstand repeated use over long periods of time, even when the heat source is high-temperature gas of 1000°C or higher, or even 1200°C or higher. This discovery led to the completion of the present invention.

That is, the present invention provides 1) a crystal phase consisting of mullite crystals and a glass matrix phase with a surface area ratio of 5% or less, and ii) a thermal expansion coefficient of 5.1 x 10-6/°C or less and a bulk density of 3. The present invention relates to a heat transfer member for a heat exchanger made of a mullite sintered body having an Oa/cm3 or more and a residual expansion coefficient at room temperature of 0.2% or less after heat treatment at 1450° C. for 48 hours.

The heat transfer member of the present invention is made of a mullite sintered body that satisfies the following conditions.

a) The crystalline phase in the sintered body consists of mullite crystals.

In the binary system of AQ203 and 5fO2, the crystal phases that precipitate under normal pressure are AQ203 crystal, mullite crystal, and 5fO2.
It is an iOa crystal (mainly cristobalite crystal). Here, mullite crystal has the chemical formula 3AQtO3・2810
2 (A920371.811% by weight, 810228° 2% by weight) as well as a mullite solid solution.

The crystal phase in the sintered body constituting the heat transfer member of the present invention is
It consists only of mullite crystals, and the diffraction peaks of SiO2 crystals and AQ203 crystals must not be observed in powder X-ray diffraction of the sintered body.

When S t O2 crystals precipitate in a sintered body, a liquid phase is formed during the firing process, which is effective in improving sinterability and strength. Furthermore, at high temperatures, toughness is reduced due to plastic deformation of the liquid phase. Although improvements can be obtained, there are drawbacks as shown below.

That is, due to the difference in thermal expansion coefficient between 5102 crystal and mullite crystal, distortion increases during thermal cycles, and volatile components generated from surrounding wall materials contained in high-temperature gas and alkali elements, sulfur, and vanadium generated from fuel , the ash content is SiO
2, the quality of the 8102 crystal changes, and the durability of the heat transfer member becomes inferior. Furthermore, the presence of 5tO2 crystals is not preferred in order to reduce the coefficient of thermal expansion of the sintered body.

Therefore, in the heat transfer member of the present invention, the Sio2 crystal phase must not exist.

In addition, when A12203 crystals are present, although the thermal conductivity increases, alkali elements from fuel and wall materials react with A+1203 crystals at high temperatures to form β-AQ203 crystals and cause the fibers of the sintered body to increase. Alter and deteriorate. Also,
There also arises the disadvantage that thermal shock resistance decreases due to increased strain and increased residual expansion due to the difference in thermal expansion between the 203 crystal and the mullite crystal. Therefore, in the heat transfer member of the present invention,
AQ203 crystals should also not be present.

Note that mullite crystals are preferably acicular crystals with an aspect ratio of about 2 or more because they have superior thermal properties, mechanical properties, etc. compared to granular crystals.

b) The surface area ratio of the glass matrix phase in the sintered body is 5% or less.

The surface area ratio of the glass matrix phase is measured by the following method.

That is, first, a plate-shaped specimen with a thickness of 1 m or more is cut out from any part of the heat transfer member, and its surface is roughly finished with a diamond grindstone, and then semi-finished with a grindstone of No. 800 or more. Next, diamond grains or red iron grains of 3 μm or less,
After finishing with fine powder such as chromium oxide until it becomes a mirror surface, the surface deposits are removed and the sample is used for measurement. After forming a vapor deposited film on the surface of this sample according to a conventional method, the sample surface is photographed with a magnification of 3000 to 5000 times φ using a scanning electron microscope. This microscopic photograph is referred to as a photographic work. Next, the deposited film was removed from the sample surface, and 0 to 5
After being immersed at ℃ for 24 hours, it is washed and dried, and furthermore, a microscopic photograph is taken in the same manner as above.

This micrograph is referred to as Photo-■. Photographs and ■ are photographs of the same portion of the sample with an area of at least 1000 μm2.

From photography, bubbles, cracks, etc. on the surface of the sample can be observed as concave shapes. The area ratio of the concave portion is calculated by determining the area of the portion observed as concave. From the photo - ■, air bubbles,
In addition to the cracks, the glass matrix portion removed by the HF treatment also becomes concave and i! be noticed. The difference between the area ratio of the recesses calculated from the photograph (■) and the area ratio of the recesses calculated from the photographic process is taken as the surface area ratio of the glass matrix phase in the sample. The glass matrix phase obtained by such a method is produced when the alkali metal oxide mixed in the raw material reacts with AQ203 and 8102 to become a low-melting substance.

When the surface area ratio of the glass matrix phase exceeds 5%, heat is generated between the mullite crystals and the glass matrix phase! ! High-temperature strength decreases due to differences in swelling, and components such as alkali elements, sulfur, and vanadium from fuel and wall materials penetrate preferentially into the glass matrix phase, expanding the structure and reducing strength due to thermal cycles. This is not preferable because it results in poor durability. Glass matrix phase is 3%
It is more preferable to set it as below.

C) The coefficient of thermal expansion is 5.1X10-8/'C or less,
In addition, the residual expansion coefficient at room temperature after heat treatment at 1500° C. for 48 hours is 0.2% or less.

In the present invention, the coefficient of thermal expansion is expressed by the average coefficient of linear expansion when the temperature is raised from room temperature to 800°C at a rate of 5°C/min.

The expansion coefficient of the mullite sintered body differs depending on the components dissolved in the mullite crystal, the components and amounts of the glass matrix phase, and the like. The heat transfer member of the present invention has a coefficient of thermal expansion of 5. It is limited to 1X10-'/'C or less, more preferably 4.9X10-'/'C or less.

Thermal expansion coefficient is 5.1 xl 0- ',/'Ce exceed; This is unsuitable because the difference in expansion becomes large, resulting in large stress, which may lead to breakage.

The residual expansion rate is measured by the following method. That is, first, a rod-shaped sample whose both end surfaces were ground and polished parallel to each other was heated to 1450 mm in an electric furnace.
The specimen is heated to 1,450°C for 48 hours, then slowly cooled. From the length of the sample measured at room temperature before and after the heat treatment, the ratio of elongation remaining after the heat treatment is determined and used as the residual expansion coefficient.

If the residual expansion coefficient exceeds 0.2%, mechanical stress will be applied to the heat transfer member of the bulkhead heat exchanger because both ends are fixed during use, which may cause damage or deformation. This results in poor durability against thermal cycles. Furthermore, poor sealing at the secondary side gas introduction and discharge portions is also unsuitable because it may result in gas leaks. Furthermore, in a heat storage/type exchanger, if the residual expansion rate exceeds 0.2%, thermal shock resistance, corrosion resistance, wear resistance, etc. will decrease. Therefore, the residual expansion rate is 0.2%
It is necessary that the content is below, preferably 0.1% or below.

d) Bulk density shall be 3.0Q/C■3 or more.

If the bulk density is less than 3.0Q/C■3, the mechanical strength will decrease, and the alkaline components contained in the combustion gas will be easily adsorbed to the heat transfer member, causing the alkali components to react with the member. The deterioration of the members becomes significant, resulting in poor durability. Therefore, the bulk density of the heat transfer member is 3. Oa/cm3
It needs to be at least 3.050/
C■ A rating of 3 or higher.

The heat transfer member of the present invention can be produced, for example, by the method shown below.

That is, first, a liquid raw material is prepared by blending an aluminum compound such as alumina sol, aluminum chloride, sulfate, or nitrate with a silicon compound such as silica sol or ethyl silicate at a predetermined AQ/Si ratio. Although it is economically preferable to increase the concentration of the liquid raw material, in order to ensure that both components are uniformly dispersed and to facilitate the formation of mullite crystals, it is necessary to increase the concentration of the liquid raw material to 30% or less in the case of a sol solution and 30% or less in the case of a salt solution. is suitably about 2 mol% or less.

In order to reduce the coefficient of thermal expansion of the sintered body, it is appropriate that the AQ/Si ratio in the liquid raw material is such that AQ203 is below the solid solution limit in mullite.
A12203 is about 69-74% by weight, 8102 is about 26% by weight
The ratio may be set to 31% by weight. Also, AQ20
3 and 5102 are preferably contained in the sintered body in an amount of 98Ii or more. Furthermore, in order to reduce the coefficient of thermal expansion, it is also effective to have a small amount of MQO18203 or the like present in the raw material, and for this purpose, a small amount of MO acid component B may be added to the liquid raw material.

After the liquid raw material is made into El, the liquid raw material is sufficiently mixed so that AQ and 81 minutes are uniformly dispersed, and a powder in which an aluminum compound and a silicon compound are uniformly mixed is formed from this liquid raw material. Methods for obtaining a powder sample from a liquid raw material include a method in which an aluminum compound and a silicon compound are co-precipitated uniformly and then dried, a method in which a powder sample is obtained by evaporating water from a liquid raw material, and a method in which a powder sample is obtained by spraying a liquid raw material. Examples include a method of thermally decomposing it.

The thus obtained powder sample is roasted at 900 to 1350°C, preferably 980 to 1280°C, in order to reduce dimensional changes in the firing process after molding. If a large amount of unreacted 5102, AQ 203, or amorphous phase exists in the powder sample after roasting, it is preferable because the powder sample is likely to agglomerate or separate in subsequent steps. do not have. Further, in order to reduce residual expansion of the sintered body, it is preferable to mulliteize the powder sample in the roasting process. For this reason, it is appropriate to set the roasting conditions to conditions that will promote the mullite formation of the powder sample, and specifically, the conditions that will cause the X-ray diffraction peak of mullite to appear in the powder sample after roasting. It is preferable to roast it to such an extent that the diffraction peaks of 5I02 and A(1203) do not occur.

The resulting powder sample is then ground and dispersed.

It is preferable that the powder has an average particle size of about 2 μm or less and a specific surface area of about 1/m2/1 or more by pulverization. If the average particle size exceeds 2 μm, defects are likely to occur inside the molded body during molding and firing of the powder, and if the specific surface area is less than 1 m 2 /Q, the sinterability will be poor, which is not preferable. Moreover, by making the powder fine in the crushing process, a sintered body with high density can be obtained. For this reason, it is more preferable that the average particle size of the powder is 1 μm or less. The powder may be pulverized and dispersed in accordance with conventional methods, such as a ball mill,
A vibration mill, attrition mill, centrifugal mill, etc. may be used.

Next, the powder thus prepared is molded into a predetermined shape by a method such as casting, extrusion, or press molding according to a conventional method in the production of ceramics, and then fired to produce the heat transfer material of the present invention. A member for use is obtained. The firing temperature is usually about 1550 to 1750°C under normal pressure.
Preferably, the temperature may be about 1600 to 1650°C.

Generally, as the firing temperature increases, the glass matrix phase increases and the density tends to increase. On the other hand, when the firing temperature is lowered, the glass matrix phase tends to decrease and the density tends to decrease. Furthermore, in order to reduce residual expansion, it is preferable to sinter at a slightly lower temperature for a long time without raising the sintering temperature too high. Also,
In order to increase the aspect ratio, it is preferable not to make the firing temperature too high. Therefore, a specific firing temperature that will yield a sintered body that satisfies the conditions a) to d) above may be appropriately determined depending on the raw material composition, molding conditions, etc. Furthermore, the firing time may be appropriately determined depending on the firing temperature, raw material composition, molding conditions, etc. so as to satisfy the conditions a) to d) above.

In the heat transfer member of the present invention, in order to reduce the amount of glass matrix phase present and to reduce the coefficient of thermal expansion, N
Contains alkaline substances such as a, etc. [ffi is 0 in terms of oxides]
．． It is preferably 210a% or less, and 0.1! Il
More preferably, the content is 1% or less. For this reason, it is preferable to use a raw material with a low impurity content or to perform a dealkalization treatment in the process of preparing the powder sample.

In addition, in order to reduce the coefficient of thermal expansion, it is necessary to add Ca in the raw material.
It is preferable to prevent O from being mixed in.

In the present invention, by preparing a powder sample from a liquid raw material by the method described above, a powder with improved sinterability in which AQ and 3i components are uniformly mixed down to the minute portions can be obtained. Therefore, even when the glass matrix phase and the amount of impurities are small, as in the heat transfer member of the present invention, a mullite sintered body having high strength and excellent thermal shock resistance can be obtained.

11) The heat transfer member of the present invention is made of a mullite sintered body that has excellent heat resistance, low heat resistance, low heat resistance, thermal stability, etc., and has high strength. Has excellent properties.

1. It has excellent mechanical strength, corrosion resistance, etc. even at high temperatures of 1200° C. or higher, and therefore can withstand use even if the wall thickness is reduced when used as a heat transfer member. Therefore, it is possible to improve the thermal efficiency and reduce the weight of the heat exchanger.

2. It has excellent thermal shock resistance, and the temperature difference when introducing the downstream side gas and the secondary side gas can be set high.

3. Good thermal stability against thermal cycles and excellent durability.

4. High durability against corrosive components and dust contained in volatile matter from combustion gas and wall materials.

As mentioned above, the heat transfer member of the present invention has excellent properties and can be used stably for a long period of time as a heat transfer member of a heat exchanger that uses primary gas at a temperature of 1000°C or higher, and even 1200°C. It is particularly useful as a heat transfer member for a partition wall heat transfer type heat exchanger. The heat transfer member of the present invention can also be used as a conveying ceramic roller, a furnace core tube, a sagger, a setter, a burner nozzle, etc., which require similar properties.

1-Direction-1 The present invention will be explained in more detail by showing Examples and Comparative Examples below.

Examples 1 to 2 and Comparative Examples 1 to 4 A solution was prepared by blending a 0.5 mol% aluminum chloride solution and a 20% silica sol solution so that the ratio of AQvO3 to 5i02 was as shown in Table 1. Next, this solution was sufficiently mixed to become homogeneous, and then neutralized and co-precipitated with aqueous ammonia, the precipitate valve was dried, and roasted at 1250° C. to obtain a mullite powder. However, in Example 2, MQ (
The powder was prepared after adding the NO3)2 solution into the liquid sample. Furthermore, in Comparative Example 3, alumina crystals remained in the roasted powder.

Table 1 Next, the above powder was wet-ground in a ball mill for 24 hours and dispersed to obtain a raw material powder. After adding 2% PVA to this raw material powder, a molding pressure of 2 tons/
C12, outer diameter 201m, inner diameter 16mm, length 600s+
The resulting product was molded into a tube shape with a diameter of 1.5 m and fired at each temperature shown in Table 2 for about 3 hours to obtain a mullite sintered body.

The volume ratio of mullite crystals and alumina crystals in the crystal phase of the sintered body, the surface area ratio of the glass matrix phase in the sintered body, the coefficient of thermal expansion, the residual expansion coefficient, and the bulk density are determined as the second
Shown in the table.

Test 1 The tubes of Examples 1 to 2 and Comparative Examples 1 to 4 were used in the flue of a furnace using LPG as fuel, and gas flowed to each part where the temperature of the combustion gas □ was 1350°C, 1300°C, and 1100°C. It was installed so that it was perpendicular to. After each tube reached its respective gas temperature, air at 50° C. was introduced into the tube from one side of the tube, kept at each temperature for 5 hours, and then allowed to cool. This operation includes heating and cooling for 48 hours.
It took time. When this operation was repeated, the number of repetitions until the tube was damaged, cracked, etc., caused gas leakage, and became unusable was determined. Similar tests were also conducted on a tube made of SiC with a bulk density of 2.6 a/cm3 and a tube made of 5 iaN aluminum with a bulk density of 3.1 a/c. The results are shown in Table 3.

Table 3 Test 2 The tubes of Examples 1 to 2 and Comparative Examples 1 to 4 were 5 mm long.
500% vanadium was used as a test piece.
1) I) A corrosion resistance test was carried out by heating 11 sodium with kerosene combustion gas containing 50 EIEl and maintaining each temperature at 1100° C. and 1450° C. for 50 hours. Table 4 shows the results of measuring the bending strength of the ring samples before and after the corrosion resistance test at room temperature.

Table 4 Note: The bending strength after the test is expressed as a ratio to the bending strength before the test.

Test 3 External diameter 21 in the same manner as Examples 1-2 and Comparative Examples 1-4
A spherical heat transfer member with a diameter of m was produced. This spherical heat transfer member was filled into a pipe with an inner diameter of 80 V to a height of 10 CI, and both ends of the pipe were covered with wire mesh made of a heat-resistant alloy. Next, blow high-temperature gas from one end of the pipe with a burner, and
The pipe was heated for 1 minute to bring the temperature at the center of the pipe to 1100°C. Next, after repeating 100 times the operation of blowing 30°C air into the vibrator for 3 minutes in the same direction as the direction in which the high-temperature gas was blown, the heat transfer member was taken out and the presence or absence of cracks was examined.

As a result, in the heat transfer member of Example 1, cracks were observed in the bulbs from the pipe entrance to the 4th to 6th point, and in the heat transfer member of Example 2, no cracks occurred. There wasn't. Moreover, when air at 30°C is introduced into the pipe from the direction opposite to the direction in which the high-temperature gas is introduced, Example 1 and ? No cracks were observed in the heat transfer members.

On the other hand, in the heat transfer members of Comparative Example 1 and Comparative Example 4, when air was introduced from the same direction as the high-temperature gas, many cracks were observed in the bulbs within about 4 to 5 cm from the pipe entrance. In addition, in the heat transfer members of Comparative Example 2 and Comparative Example 3, many cracks were observed in the spheres at a distance of about 2C from the pipe entrance. Also, Comparative Example 1~
In No. 4, cracks were observed in the ball even when air was introduced into the pipe from the opposite direction.

From the above test results, the heat transfer member of the present invention can be heated to 1000°C.
Even when the above-mentioned high-temperature gas is used as a heat source, it can withstand repeated use, and it is clear that there is little decrease in strength due to combustion gas containing corrosive components such as vanadium and sodium.

(that's all) Agent: Patent attorney Eiji Mitsue.

Procedural Amendment (Sealed) October 1, 1985 Commissioner of the Japan Patent Office Kuro 1) Yu Akira Patent Application No. 148824 of 1985 2 Name of Invention Heat Transfer Member for Heat Exchanger 3 Case with Person Who Makes Amendment Related: Patent Applicant Nippon Kagaku Togyo Co., Ltd. 4 Agent Sawanotsuru Building Sponsored, 2-10 Hirano-cho, Higashi-ku, Osaka 6 The “Scope of Claims” and “Detailed Description of the Invention” in the specification to be amended Contents of section amendment 1 The description of the section of the scope of claims is corrected as shown in the attached sheet.

2. The phrase "Glass matrix phase with a surface area ratio of 5% or less" in lines 2 and 3 on page 6 of the specification is corrected to "Glass matrix phase with a surface area ratio of 5% or less."

3. In the specification, page 8, line 18 to page 9, line 1, ``Glass matrix phase shall be 5% or less.'' has been replaced with ``Glass matrix phase shall be 5% or less by volume.'' I am corrected.

4. In the second line of page 9 of the specification, "Surface area ratio" is corrected to "Content rate."

5. Specification, page 10, line 11 “Surface area percentage.

"Like this" should be corrected as follows.

[Surface area percentage. Since the glass matrix phase exists almost uniformly throughout the sintered body, the area ratio of the glass matrix phase determined by the above method can be taken as the volume % of the glass matrix phase in the sintered body. 6. On page 10 of the specification, line 16, "5% of the glass matrix phase" is corrected to "5% by volume of the glass matrix phase."

7. On page 22 of the specification, line 10, "Surface area percentage" is corrected to "Volume percentage."

8. In Table 2 on page 23 of the specification, "Glass matrix surface area %" is corrected to "Glass matrix phase volume %".

(Above) Claim 1i) consisting of a crystal phase consisting of mullite crystals and a glass matrix phase of 5% by volume or less, ii) having a coefficient of thermal expansion of 5
．． 1x10-8/'C or less, bulk density 3.0g/cf
A heat transfer member for a heat exchanger made of a mullite sintered body having a fi3 or more and a residual expansion coefficient at room temperature of 0.2% or less after heat treatment at 1450° C. for 48 hours.

Claims (1)

[Scope of Claims] 1 i) consisting of a crystal phase consisting of mullite crystals and a glass matrix phase having a surface area ratio of 5% or less, ii) having a coefficient of thermal expansion of 5.1×10^-^6/°C or less and a bulk density of A heat transfer member for a heat exchanger made of a mullite sintered body having a residual expansion coefficient of 3.0 g/cm^3 or more and a residual expansion coefficient of 0.2% or less at room temperature after heat treatment at 1450° C. for 48 hours.