JPH10194821A - Heat and corrosion resistant protective tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve heat and corrosion resistance and to enable use over a long period of time by specifying the average diameter, occupying rate and aspect ratio of pores in the ceramic outer surface layer of a ceramic tubular body with its front end sealed. SOLUTION: A ceramic compsn. having >=2μm average grain diameter and <=3% pore diameter is prepd. by incorporating <=5wt.% impurity components such as SiO2 , CaO, Na2 O and Fe2 O3 into 100 pts.wt. ceramics consisting essentially of >=50mol.% Al2 O3 and <=50mol.% MgO so that the molar ratio of MgO to Al2 O3 is regulated to <=1 and having a crystal phase of MgAl2 O4 and/or Al2 O3 and m.p. of >=2,000 deg.C. The ceramic compsn. is compacted into a tubular body with its front end sealed to obtain a compact forming an inner surface layer 1b. The surface of the compact is coated with a ceramic slurry and the coated compact is fired to form pores having <=20μm average diameter, <=10% occupying rate and an aspect ratio of <=5 only in the outer surface layer 1b of the resultant tubular body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection tube for protecting heaters and sensors in a melting furnace such as a refuse incinerator, a refuse incineration ash reprocessing melting furnace, and other various furnaces.

[0002]

2. Description of the Related Art Garbage discarded from households and companies is burned in incinerators of local governments, and the incinerated ash and fly ash contained in the smoke (elements contained: Si, Al, Fe, Ca, M).
g, K, Mn, Cl, Na, and S) contain heavy metal components and toxic elements 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. I have. In addition, the detoxification of toxic contaminants such as dioxin and furan is being regulated quite strictly by laws and regulations, so incineration ash and fly ash are collected and re-melted to make harmless substances harmless. The need for furnaces is increasing year by year.

[0004] The incinerated ash that has not been burned after being burned in an incinerator can be reduced in volume to about 1/2 to 1/4 of the incinerated ash if it is converted into slag by high-temperature heat treatment. The high-temperature heat treatment method in this melting furnace is considered promising, for example, because it can decompose harmful pollutants with high heat to make them harmless.

[0005] As shown in FIG. 2, the incineration ash 11 is put into a melting furnace 12 and heated to 1300 to 1600 ° C. by a heating heater 2 which is an electric heating source.
The incinerated ash 11 is melted and the contained metal element 13 evaporates. This metal element 13 is taken out and cooled (not shown)
And rapidly condensed to obtain fine particles, which are collected by a filter 15 or the like to collect a metal concentrate 16. On the other hand, toxic substances such as dioxin and furan are destroyed by heat, and the detoxified gas 17 is released into the atmosphere via a gas treatment device. The residue in the melting furnace 12 is slag (glass) -like granules 1
8 to be effectively used or disposed of.

The melting furnace 12 requires a heater 2 for heating and a thermocouple 3 for temperature control. The melted incineration ash 11 is supplied into the melting furnace 12 by molten slag, molten salt, or a vapor component thereof. Therefore, it is necessary to protect the heating heater 2 or the thermocouple 3 from these substances.

Therefore, it has been practiced to cover the heating heater 2 and the thermocouple 3 with a protective tube 1 made of ceramics having excellent heat resistance and corrosion resistance. As the material of the protective tube 1, for example, as shown in Japanese Patent Application Laid-Open No. 51-71312,
composite ceramic of gO-ZrSiO ₂ -Al ₂ O ₃ is used.

[0008]

By the way, when the ash generated by incineration of garbage is reheated, the carbon content of the ash is reduced.
In order to decompose metal elements such as d, Pb, and Zn, and harmful pollutants such as dioxin and furan, 1300 is applied by electric heating.
Detoxification is performed by heating and melting at 1600 ° C., but the protective tube 1 used in the melting furnace 12 is exposed to molten salt, molten slag, steam, or the like formed by melting the incineration ash 11. Therefore, Si, Al, F in these components
e, Ca, and Na gradually penetrate and erode into the ceramics forming the protective tube 1, and gradually deteriorate the strength of the ceramics, causing cracks and breakage, and can be used for a long time. It was not something.

[0009]

In view of the above, the present invention provides
In a heat-resistant and corrosion-resistant protective tube formed of a tubular body whose tip is made of ceramic, the average diameter of pores present in at least the outer surface layer of the ceramic is 20 μm or less, the pore occupancy is 10% or less, and the aspect ratio of the pores (long diameter) / Ratio of minor axis) is 5 or less.

That is, in the present invention, it has been found that erosion of the metal element into the protective tube mainly occurs from the pores. Corrosion is reduced by reducing the amount so that Moreover, in the present invention, by setting the aspect ratio of the pore to 5 or less, the pore is rounded to reduce the surface area of the pore,
The erosion of the metal element is reduced.

Further, according to the present invention, the ceramic is
It is characterized by having at least one crystal phase of Al ₂ O ₃ and MgAl ₂ O ₄ . That is, these ceramics are particularly excellent in heat resistance and corrosion resistance, and can further extend the life.

[0012]

Embodiments of the present invention will be described below.

As shown in FIG. 1 (a), the protective tube 1 of the present invention is a tubular body whose tip is made of ceramics and has a cylindrical side surface and a hemispherical tip sealing portion which are smooth. It has a continuous shape on a curved surface.

As shown in FIG. 2, for example, this protective tube 1 is installed in a melting furnace 12 for reprocessing refuse incineration ash so as to cover the heating heater 2 and the thermocouple 3 to protect them. can do. At this time, the protection tube 1 of the present invention
Since it has high heat resistance and corrosion resistance, it can be used for a long time with peace of mind.

The pores present in at least the outer surface layer of the ceramics forming the protective tube 1 have an average diameter of 20 μm.
m, the pore occupancy is 10% or less, and the aspect ratio of the pore is 5 or less. That is, in the protective tube 1 according to the present invention, the pores existing throughout the protective tube 1 may be within the above range, or the pores of only the outer surface layer of the protective tube 1 may be within the above range.

As a specific example of the latter, as shown in FIG. 1 (b), only the outer surface layer 1a of the protective tube 1 has the pores within the above range to improve the corrosion resistance, and the inner surface layer 1b Can also improve heat resistance as a porous body having many pores. Such a protective tube 1 having a double structure can be obtained, for example, by preparing a tubular body from a porous body forming the inner surface layer 1b in advance, applying a slurry to the surface thereof, and firing the slurry.

The reason why the average diameter of the pore is 20 μm or less and the occupation ratio of the pore is 10% or less is that the maximum diameter of the pore is 20 μm or less.
μm or the pore occupancy exceeds 10%,
This is because the erosion element easily penetrates into the ceramics and significantly reduces the life of the protection tube 1.

That is, erosion elements such as Si, Al, Fe, Ca, and Na usually enter from the crystal grain boundaries of the ceramics, degrade the crystal grain boundary portions, weaken the grain boundary strength, and detach the crystals from the base material. The erosion progresses due to, for example, the erosion. If pores exist in the erosion path, the erosion elements can move freely in the pore space. Therefore, the average diameter of the pore is 2
If the thickness exceeds 0 μm or the pore occupancy exceeds 10%, the penetration rate of the eroding element becomes extremely high, and the life of the protection tube is significantly shortened. In addition, there is a problem that the pores in the ceramic are large and the strength of the ceramic itself is reduced as the number of pores increases.

On the other hand, as described above, if the average diameter of the pores existing in the ceramics forming the protective tube 1 is set to 20 μm or less and the pore occupancy is set to 10% or less, the penetration of the eroding elements is delayed and the life is shortened. Can be maintained for a long time.

Further, the present invention is characterized in that the aspect ratio of the pores present in the ceramics forming the protective tube 1 is specified to be 5 or less. Here, the aspect ratio of the pore is
Assuming that the longest distance in the cross-sectional shape of the pore is the long diameter and the shortest distance is the short diameter, it is a value calculated by the aspect ratio = long diameter / short diameter. Therefore, when pores having the same volume are present, the smaller the aspect ratio is, the more round the pores are, and the amount of movement of the erosion element can be reduced. When the aspect ratio of the pores exceeds 5, the amount of erosion elements transferred becomes large, and the life of the protection tube 1 is remarkably deteriorated. Therefore, the aspect ratio is specified to be 5 or less.

For example, FIG. 3 shows a schematic diagram of a pore (black portion) having an aspect ratio of 1.2, and FIG. 4 shows a schematic diagram of a pore (black portion) having an aspect ratio of 6.6. When the aspect ratio of the pore exceeds 5 as shown in FIG. 4, the amount of movement of the erosion element in the pore increases, but when the aspect ratio of the pore is 5 or less as shown in FIG. And the amount of movement of the erosion element can be reduced.

In the present invention, the average pore diameter, the pore occupancy, and the pore aspect ratio are measured as follows.

First, after an arbitrary outer surface of the protective tube 1 is mirror-polished, a measuring area of 2.25 × 10 ⁵ μm ² is magnified 200 times by using a pore ratio measuring device including a metal microscope and an image analyzer. The average diameter of the pores in this range and the occupancy of the pores in this area are measured. The same mirror-polished surface was photographed with an electron microscope (SEM) at a magnification of 1000 times. Ten arbitrary pores were selected from the photograph, and the major axis and minor axis were measured to calculate the aspect ratio. It is determined by the average value of the pieces.

The average diameter of the pores, the occupation ratio of the pores, and the aspect ratio of the pores are determined by the firing conditions of the ceramics forming the protective tube 1 and may be fired under the above-mentioned range.

Next, various ceramics can be used as the ceramic constituting the protective tube 1 of the present invention.
In particular, Al ₂ O ₃ , MgO spinel (MgAl ₂ O ₄ ),
Alternatively, those containing MgO as a main component are preferable.

More preferably, 50 mol% or less (28.
6 wt% or less) and 50 mol% or more (71.4).
(% By weight or more) of Al ₂ O ₃ as a main component, and MgO / Al
A ceramic having a molar ratio of ₂ O ₃ of 1 or less (a weight ratio of 0.40 or less) and at least one crystal phase of MgAl ₂ O ₄ and Al ₂ O ₃ is used.

The main components of Al ₂ O ₃ and Mg
With respect to 100 parts by weight of O in total, SiO ₂ , CaO, Na
It is preferable to contain a total of 5 parts by weight or less of impurity components such as ₂ O and Fe ₂ O _{3 so} that the average crystal grain size is 2 μm or more and the porosity is 3% or less.

These MgO spinels (MgAl
Ceramics mainly composed of ₂ O ₄ ) or Al ₂ O ₃ have an extremely high melting point of 2000 ° C. or higher,
It has stable heat resistance and corrosion resistance even at a high temperature of 600 ° C., and is an optimal material for the protective tube 1.

The MgO spinel is MgAl ₂ O ₄
The theoretical stoichiometric ratio is a molar ratio of MgO and Al ₂ O ₃ of 1:
1, a compound bonded at a weight ratio of 28.6: 71.4. When the composition ratio of MgO and Al ₂ O ₃ is variously changed, only MgAl ₂ O ₄ crystals are present at the theoretical stoichiometric ratio.
O + MgAl ₂ O _{4 has} a two-phase crystal structure. On the other hand, when Al ₂ O ₃ is increased more than the theoretical stoichiometric ratio, Al ₂ O ₃ + MgAl
A two-phase crystal structure of ₂ O ₄ results.

The above ceramics contains at least one crystal phase of MgO spinel (MgAl ₂ O ₄ ) and Al ₂ O ₃ , and this crystal phase can be easily analyzed by X-ray diffraction. MgAl ₂ O ₄ and Al ₂ O
_The phrase “comprising at least one or more crystal phases” in ₃ means that peaks of one or more of these crystal phases exist.

Further, in the melting furnace, S in the ash component
Erosive elements such as i, Al, Fe, Ca, and Na erode into the crystal grain boundaries in the ceramics forming the protective tube 1 and corrode and alter the ceramics. Therefore, as the ceramics forming the protective tube 1, S is added to 100 parts by weight of the main component.
When the total amount of impurity components such as iO ₂ , CaO, Na ₂ O, and Fe ₂ O ₃ is 5 parts by weight or less, the glass components constituting the crystal grain boundaries can be reduced, and the penetration of erosion elements can be prevented.

In order to reduce the amount of the impurity component to 5 parts by weight or less, it is only necessary to use a high-purity primary material of MgO and Al ₂ O ₃ in advance and to prevent the impurity from being mixed in the manufacturing process.

Further, it is preferable that the average crystal grain size of the ceramic is 2 μm or more. This is because, when the average grain size is less than 2 μm, when the erosion element enters the grain boundaries, the strength of the grain boundaries between the crystals is weakened, the crystals are detached from the base material, and the erosion easily progresses. This is because the life of the protection tube is significantly reduced due to the generation of through-holes and the like. This average crystal grain size can be freely adjusted depending on the grain size of the starting material, firing conditions, and the like.

Further, regarding the thickness t of the protective tube 1,
It is preferable to be thin from the viewpoint of thermal shock resistance and thermal efficiency, but it is preferable to be thick from the viewpoint of protection and production, and it is generally preferable that the wall thickness t is 3 mm or more. It is also possible to partially change the thickness t. For example, the thickness of the spherical end sealing portion can be formed larger than other portions.

As shown in FIG. 2, the protective tube 1 of the present invention described above can be suitably used in a melting furnace 12 for reprocessing refuse incineration ash. In a melting furnace, it can be used as a protective tube for protecting a heater, various sensors, and the like. Alternatively, it can be suitably used in various furnaces such as a refuse incinerator, a firing furnace for ceramics and the like, and other devices that provide a high-temperature corrosive atmosphere.

[0036]

Example 1 Assuming the environment inside a refuse incineration ash melting furnace, Al ₂ O ₃ and M
A sample composed of ceramics containing gO spinel as a main component was prepared and subjected to a reaction test with incineration ash.

First, as incineration ash, the components are Al, Ca,
The incineration ash consisting of Mg, Na, K, Si, Fe, Cl, etc. is collected from the incinerator, and the diameter is 12 mm by a dry press machine.
× A tablet having a thickness of 1 mm and a weight of 0.3 g was prepared.

Next, ceramics having various compositions shown in Table 1 having a diameter of 30 mm × thickness of 10 mm and a counterbore for inserting an incinerated ash tablet (diameter of 13 mm × depth of 1 mm).
The tablet test piece which has this was produced. In addition, No. 4
Nos. 12 to 12 have only the crystal phase of MgAl ₂ O ₄ and have the same composition, but have different pore diameters and the like by mixing materials having different sinterability and raw material primary particle size.

With respect to each test piece, the crystal phase, bulk specific gravity, porosity, bending strength, average pore diameter, pore occupancy, and pore aspect ratio were measured.

Here, for the crystal phase, an X-ray diffractometer was used, the conditions were as follows: a Cu tube was used, the voltage was 50 kV, the current was 200 mA, the measurement range was 2θ = 10-90 °, and the full scale was 3 × 10 Analysis was performed at ⁴ to 10 × 10 ⁴ cps. The bulk specific gravity, porosity, and bending strength were tested and measured based on the JIS method.

Further, with respect to the average pore diameter and the pore occupancy, the surface of the test piece was mirror-polished, and then the measurement area was 2.25 × 10 ⁵ μm using a pore ratio measuring device comprising a metal microscope and an image analyzer. ² was measured at a magnification of 200 times, and the average diameter of pores in this range and the pore occupancy in this area were measured. For the pore aspect ratio,
The same mirror-polished surface was measured with an electron microscope (SEM) for 100
A photograph magnified 0 times was taken, ten arbitrary pores were selected from the photograph, the major axis and the minor axis were measured, the aspect ratio was calculated, and the average value of the ten was determined.

Next, a sintered ash tablet was placed in the counterbore of each test piece and heat-treated at 1550 ° C. in the atmosphere for 50 hours. Thereafter, the appearance of each test piece was visually observed, and the presence or absence of melting or cracks was examined. In addition, each specimen was cut and polished on a cross section by SEM (50 to 2).
00 times) to check for cracks and EPMA
In the analyzer, acceleration voltage 15 kV, probe current 2.0 ×
After detecting elements of Si, Fe, Ca, Na, and K at 10 ^-7 A and outputting them in a mapping format, the diffusion depth of these elements was measured to check for the presence or absence of a reaction layer.

The results are shown in Tables 1 and 2. In Table 2, those having cracks / melting and reaction layers were represented by x, and those not present were represented by ○.

From the results, the average pore diameter, the pore occupancy,
Those having any of the pore aspect ratios out of the range of the present invention (Nos. 1 to 3, 10 to 12, and 15) have a reaction layer, which indicates that the erosion elements easily enter. On the other hand, the embodiment of the present invention (Nos. 4 to 9, 13, 1)
In Nos. 4, 16), there was no melting or cracking, and no reaction layer with the incineration ash component was observed, indicating that it can be suitably used as the protective tube 1 of the melting furnace.

[0045]

[Table 1]

[0046]

[Table 2]

Example 2 As an example of the present invention, No. 1 in Table 1 was used. Nos. 4 and 16 were used. Twelve materials, each having an outer diameter of 180 mm, an inner diameter of 160 mm, and a thickness t of 10 m
The protective tube 1 shown in FIG. 1 and having a length of 800 mm was prepared.
This protective tube 1 was subjected to an actual machine test in a refuse incineration ash melting furnace 12 shown in FIG. 2 to examine the life at a temperature of 1500 ° C. The life is a time until a crack or a through hole or the like occurs in the protection tube 1 due to corrosion.

As shown in Table 3, it was proved that the protective tube 1 of the present invention can be used in a refuse incineration ash melting furnace for 2000 hours.

[0049]

[Table 3]

[0050]

As described above, according to the present invention, in a heat-resistant and corrosion-resistant protective tube comprising a tubular body whose tip is made of ceramic, the average diameter of pores present in at least the outer surface layer of the ceramic is 20 μm or less. , Pore occupancy is 10% or less, pore aspect ratio (ratio of major axis / minor axis)
Is 5 or less, heat resistance and corrosion resistance can be increased and used for a long period of time.

In particular, if the protection tube of the present invention is used in a melting furnace for reprocessing refuse incineration ash, erosion of metal elements contained in the incineration ash can be prevented, and the protection tube can be used safely for a long period of time.

[Brief description of the drawings]

FIGS. 1A and 1B are cross-sectional views showing a heat and corrosion resistant protective tube of the present invention.

FIG. 2 is a schematic view showing a refuse incineration ash reprocessing device using the heat and corrosion resistant protective tube of the present invention.

FIG. 3 is a schematic view showing a shape of a ceramic pore forming a heat-resistant and corrosion-resistant protective tube.

FIG. 4 is a schematic diagram showing the shape of a ceramic pore forming a heat-resistant and corrosion-resistant protective tube.

[Explanation of symbols]

 1: Protection tube 2: Heating heater 3: Thermocouple 11: Incineration ash 12: Melting furnace 13: Metal element 15: Filter 16: Heavy metal concentrate 17: Gas 18: Slag granules

Claims (2)

[Claims] 1. A tubular body of which the tip is made of ceramic and which has a closed end, wherein an average diameter of pores present in at least an outer surface layer of the ceramics is 20 μm or less, a pore occupancy is 10% or less, and an aspect ratio of the pores. A heat-resistant and corrosion-resistant protective tube having a ratio of (major axis / minor axis) of 5 or less. 2. The method according to claim 1, wherein the ceramic is Al ₂ O ₃ , MgA.
heat corrosion protection tube according to claim 1, wherein the at least one crystal phase of l ₂ O _4.