JPH1045463A - Heat and corrosion resistant protective tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve heat resistance, thermal shock resistance, strength and corrosion resistance by using ceramics based on Al2 O3 , MgO spinel or MgO. SOLUTION: Ceramics based on Al2 O3 , MgO spinel or MgO and having >=1,700 deg.C softening point in the air, >=150 deg.C thermal shock resistance ΔT by an in-water dropping method, >=150MPa three-point bending strength and >=2μm average grain diameter is formed into a tubular body with a sealed end to obtain the objective heat and corrosion resistant protective tube 1.

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, S, Na, Pb, and Zn) are detoxified in a reprocessing melting furnace and finally disposed of or effectively used based on the treatment standards according to the revision of the Waste Management Law.

As shown in FIG. 2, in this reprocessing step, incinerated ash 11 is placed in a melting furnace 12 and heated to 1300 to 1600 ° C. by a heater 2 as an electric heating source.
1 melts and the metal element 13 evaporates. This metal element 1
3 is taken out and rapidly cooled by a cooling device (not shown) to be condensed into fine particles, which are collected by the bag filter 15 to collect the heavy metal concentrate 16. On the other hand, the detoxified gas 17 is released to the atmosphere via a gas processing device. In addition, melting furnace 1
The remnants in 2 are taken out as glass granules 18 for effective use or disposal.

[0004] The melting furnace 12 requires a heater 2 for heating and a thermocouple 3 for temperature control. The melted incineration ash 11 is supplied to 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.

[0005] 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.

[0006]

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
Since e, Ca, and Na gradually penetrate into the ceramics forming the protective tube 1, the ceramics are gradually deteriorated and the strength is deteriorated. Did not.

In addition, there has been a problem that, during use at a high temperature for a long time, the battery is deformed by the influence of its own weight, and comes into contact with a heater or a thermocouple to adversely affect the melting furnace system. On the other hand, the temperature of the melting furnace 12 is raised and lowered periodically for maintenance, but there is also a problem that the protective tube 1 is broken by the heat shock at this time.

[0008]

In view of the above, the present invention provides
Softening point in air atmosphere 1700 ° C or more, Thermal shock resistance by water drop method ΔT 150 ° C or more, 3-point bending strength 150
Al ₂ O ₃ , M having an average crystal grain size of 2 μm or more
A tubular heat-resistant and corrosion-resistant protective tube whose end is sealed with gO spinel or MgO ceramics is formed.

Here, the reason why the characteristics of the ceramics are limited to the above range is as follows.

First, a protective tube in a melting furnace or the like is 1300
Since it is used for a long time in a very high temperature environment of １1600 ° C., it is important that no deformation occurs during use. For this reason, in the present invention, ceramics that do not cause softening to at least 1700 ° C. or more are used as the material of the protective tube.

The softening point is defined as 3 × 3 of ceramics.
When the test piece shape is about 15 mm and heated in a TMA (thermomechanical analysis) test device, the length increases with temperature due to thermal expansion, but the length starts to decrease at a certain temperature. That is, this temperature is called a softening point. Therefore, if the softening point is 1700 ° C. or higher, it does not deform at a temperature lower than 1700 ° C., and can be suitably used as a protective tube.

Usually, the melting furnace is operated continuously once if it is operated once, but the temperature is raised and lowered at intervals of several weeks to several months because maintenance such as repair of furnace materials is required. In this case, the shorter the time required for raising and lowering the temperature, the higher the operating rate of the entire system. There are several factors that determine the rate of temperature rise and fall, but if the thermal shock resistance of the ceramic material forming the protective tube is high, the system operation rate can be increased.

Furthermore, the temperature difference between the inside and outside of the protective tube for a melting furnace is about 100 ° C., and a material having low thermal shock resistance may be damaged. To avoid these problems,
ΔT Ceramics having a thermal shock resistance of 150 ° C. or more may be used.

Here, the thermal shock resistance ΔT means that the strength of a ceramic formed into a JIS test piece (3 × 3 × 40 mm) after being dropped into water from a state where the ceramic is maintained at a certain temperature and rapidly cooled is sharply reduced. Such a temperature difference.

Further, the melting furnace protective tube is inserted into the furnace through holes provided on the side and ceiling of the melting furnace, depending on its use. Usually the protection tube for the heater is large and heavy,
The protection tube is provided with a flange, and is suspended from the ceiling to be held. Further, since the entire weight of the protection tube is supported only by the flange portion, a material strength of three-point bending strength of 150 MPa or more is required.

As a general theory of ceramic materials,
Among materials of the same material, low-strength materials often have many pores and voids in the material. If voids are present in the material,
The erosion element remarkably penetrates and easily promotes the deterioration, and as a result, the slag resistance is significantly reduced. Therefore, in the present invention, the three-point bending strength of the ceramics forming the protective tube is set to 15
It is limited to 0 MPa or more.

Here, the three-point bending strength can be measured by a method in which a ceramic is formed into a JIS test piece (3 × 3 × 40 mm) and specified in JIS.

Further, in the present invention, the average crystal grain size of the ceramics constituting the protection tube is set to 2 μm or more. If the average crystal grain size is less than 2 μm, erosion elements are remarkably penetrated. This is because it is easier to promote deterioration. That is, in the present invention, the penetration of erosion elements is prevented by increasing the crystal grain size.

The average crystal grain size of the ceramic can be determined by thermal etching the test piece at a temperature lower than the firing temperature by 100 ° C. or by subjecting the test piece to chemical etching in which a corrosive chemical is eroded for a certain period of time. Measure by code method. Specifically, two SEM photographs at a magnification of 1000 are prepared, and when three arbitrary lines are drawn, the length is obtained by dividing the length of the line by the number of particles crossing the line. Further, the voids and the average crystal grain size can be freely adjusted depending on the molding and firing conditions of the raw material.

As ceramics satisfying the above characteristics, ceramics mainly composed of one of Al ₂ O ₃ , MgO spinel and MgO are preferable. Note that Mg
O spinel is represented by MgAl ₂ O ₄ , and MgO and A
It is a compound in which l ₂ O ₃ is bonded at a molar ratio of 1: 1.

In the present invention, Al ₂ which is a main component
The content of O ₃ , MgO spinel, and MgO (hereinafter referred to as purity) is set to 95% by weight or more, and the balance of SiO ₂ and Ca
It is characterized in that the total amount of glass components such as O and Na ₂ O is set to 5% by weight or less. By doing this,
The softening point is 1700 ° C or higher, and the thermal shock resistance ΔT is 150
C or higher.

The bending strength and the average particle size of these ceramics can be adjusted by the particle size of the raw material, the firing conditions, and the like. The bending strength and the average particle size are adjusted to 150 MPa or more and 2 μm or more. It can be manufactured.

It should be noted that ceramics other than those described above, such as mullite, mullite to which zircon is added, and zirconia-dispersed alumina can also be used.

[0024]

Embodiments of the present invention will be described below.

As shown in FIG. 1, the protection tube 1 of the present invention comprises:
It is a tubular body with a sealed end, and has a softening point of 1700 ° C or more in the air atmosphere, and a thermal shock resistance by a water drop method.
It is made of ceramics having a T of 150 ° C. or more and a three-point bending strength of 150 MPa or more and an average crystal grain size of 2 μm or more.

As shown in FIG. 2, this protective tube 1 is installed in a melting furnace 12 for reprocessing refuse incineration ash so as to cover the heater 2 and the thermocouple 3 to protect them. it can. At this time, the above-mentioned ceramics forming the protective tube 1 can be used for a long period of time with a high reliability because of its high heat resistance, thermal shock resistance, strength and corrosion resistance.

The protective tube 1 of the present invention is not limited to the melting furnace 12 for reprocessing the refuse incineration ash, but may be used for protecting heaters and various sensors in various melting furnaces such as a metal melting furnace. It can be used as a protection tube. 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.

[0028]

EXPERIMENTAL EXAMPLE 1 The test piece was evaluated for heat resistance in an environment in a melting furnace for reprocessing refuse incineration ash.

First, small test pieces (outer diameter 40 mm × inner diameter 34 mm × 150 mm) having the shape of the protective tube 1 shown in FIG. 1 were prepared from ceramic materials having different purities shown in Table 1. This test piece was subjected to a heat treatment at 1450 ° C. × 50 hours in a melting furnace 12 for reprocessing waste incineration ash. afterwards,
Measure the warpage of the test piece, warp 50% before and after heat treatment test
Those that had deteriorated were judged to be deformed, and those that were deformed were evaluated as x, and those that were not deformed were evaluated as ○. Each material was formed into a 3 × 3 × 15 mm test piece, and the softening temperature was measured using a TMA test device. The results are as shown in Table 1.

From these results, low-purity alumina and S
A material having a low softening point, such as iO ₂ , was deformed (partially melted) by the heat treatment, and it was confirmed that the material was unsuitable as a material for the protective tube 1. On the other hand, no deformation was observed in the material having a softening point of 1700 ° C. or higher, and it was confirmed that the material was suitable as a material for the protective tube 1.

[0031]

[Table 1]

EXPERIMENTAL EXAMPLE 2 Reprocessing of refuse incineration ash Assuming a situation in which the temperature was raised and lowered for maintenance in an environment inside the melting furnace, the test piece was heat-treated under several raising and lowering conditions.

First, an outer diameter of 180 mm, an inner diameter of 160 mm, and a length of 800 were used for some ceramics as shown in Table 2.
mm protective tube 1 was prepared and used as a test piece.

Next, each of the test pieces was heated in a melting furnace 12 for reprocessing refuse incineration ash under various heating and cooling conditions as shown in Table 2 to 1450.
3 cycles of heat treatment were performed at 2 ° C. for 2 hours. Thereafter, the appearance of each test piece was visually observed to check for cracks. Further, the cross section of each test piece was examined for cracks by SEM.

The results are as shown in Table 2. In the table, those with breakage and cracks were indicated by x, and those without damage were indicated by ○.

At the same time, the JIS bending test piece shape (3 × 4 ×
The thermal shock resistance ΔT was measured by a water drop test at 40 L). The thermal shock test method is as follows. High temperature (T
The test piece kept in 1) is dropped in water at room temperature (T0) and rapidly cooled. The flexural strength of the quenched sample is measured, and a characteristic curve of the strength and the cooling temperature difference (T1-T0) is created. The temperature at which the strength sharply decreases is represented by ΔT.

From these results, ΔT such as SiO ₂
It was confirmed that even a material having a small temperature was not unusable in a real environment if the temperature rise / fall time was prolonged. However, in an actual environment, a sudden temperature drop due to a sudden stop of the power supply or the like is assumed, and thus, in this experiment, SiO ₂ broken by natural cooling at the time of temperature drop is inappropriate. Also practically, a material having high thermal shock resistance of at least ΔT150 or more is desirable, and Al ₂ O ₃ , M
It can be seen that gO spinel and MgO should be used.

[0038]

[Table 2]

EXPERIMENTAL EXAMPLE 3 A reaction test was performed between test pieces of MgO spinel ceramics having different material strengths and incineration ash.

First, as incineration ash, the main components are Si, Al,
The incinerated ash composed of Fe, Ca, K, Mn, Cl, S, Na, Pb, Zn, etc. was collected from the incinerator, and tablets having a diameter of 12 mm × 1 mm and a weight of 0.3 g were produced by dry pressure molding.

Next, test pieces having a diameter of 30 mm and a thickness of 10 mm were prepared from several MgO spinel ceramics having different material strengths obtained by arranging two kinds of MgO spinel ceramic primary materials having different average particle diameters. Then, an incinerated ash tablet was placed on each of the test pieces, and heat treatment was performed at 1450 ° C. for 50 hours in the atmosphere.

Thereafter, the outer diameter of the test piece before and after the test was measured to check for swelling. Further, with respect to the cross section obtained by cutting each test piece, each element of Si, Fe, Ca, and Na was detected by EPMA analysis, and the presence or absence of a reaction layer of these elements was examined. These results are shown in Table 3.

Regarding the swelling, those having a larger outer diameter of 0.1% or more were judged to be swollen, and were represented by x.
Also, according to the EPMA result, even one of the above four elements is 0.5 mm
Those in which the above reaction layers were observed were represented by x.

From these results, in the test specimens having low material strengths shown in the materials C, D, and E, that is, the test specimens having many voids, the erosion by the above elements contained in the incineration ash was observed, and the test specimens swelled. Was obtained, and it was confirmed that this was unsuitable as a protective tube material. Although the material E did not swell, it is considered that there were too many voids and all the incineration ash components permeated the voids, and there was no erosion into the grain boundary phase that would cause swelling.

On the other hand, as shown in materials A and B, in a material having a high bending strength of 150 MPa or more, that is, a test piece having a small number of voids, no swelling due to erosion of the incineration ash component was observed, and no reaction layer was observed. It can be seen that it can be used as a protective tube material without any problem.

[0046]

[Table 3]

Experimental Example 4 Assuming the environment inside the melting furnace for reprocessing of refuse incineration ash, a reaction test was conducted between the MgO spinel ceramics and the refuse incineration ash with several average crystal grain sizes varied.

First, as incineration ash, the main components are Si, Al,
The incinerated ash composed of Fe, Ca, K, Mn, Cl, S, Na, Pb, Zn, etc. was collected from the incinerator, and tablets having a diameter of 12 mm × 1 mm and a weight of 0.3 g were produced by dry pressure molding.

Next, as shown in Table 4, test pieces having a diameter of 30 mm and a thickness of 10 mm were prepared from MgO spinel ceramics having different average crystal grain diameters obtained by changing the firing conditions. Then, an incinerated ash tablet was placed on each of the test pieces, and heat treatment was performed at 1450 ° C. for 50 hours in the atmosphere.

Thereafter, the outer diameter of the test piece before and after the test was measured to check for swelling. Further, with respect to the cross section obtained by cutting each test piece, each element of Si, Fe, Ca, and Na was detected by EPMA analysis, and the presence or absence of a reaction layer of these elements was examined.

The results are as shown in Table 4. Also in this experiment, judgment was made according to the same criterion as in Experiment Example 3;
It was represented by x.

From these results, it was found that in the test pieces having small average crystal grain diameters shown in materials A, B, F, and G, erosion by the above elements contained in the incinerated ash was observed, and the test pieces swelled. However, it was confirmed that it was unsuitable as a protective tube material. On the other hand, in the test pieces having an average crystal grain size of 2 μm or more shown in materials C, D, E, and H, no swelling or the like due to erosion of the incineration ash component was observed, and no reaction layer was observed. It turns out that it can be used as a protective tube material without a problem.

[0053]

[Table 4]

Experimental Example 5 MgO spinel, Al ₂ O ₃ , and MgO as ceramics within the scope of the present invention, and MgO spinel having a crystal grain size of less than 2 μm and M, which are out of the scope of the present invention, as comparative examples
Using a total of five types of ceramics of gO, an outer diameter of 180
A protective tube for a heater having a diameter of 160 mm, an inner diameter of 160 mm, and a length of 800 mm was produced, and a test operation was actually performed in a refuse incineration ash reprocessing melting furnace, and the life at a reprocessing temperature of 1450 ° C. was confirmed.

Table 5 shows the results. Although the MgO spinel and MgO of the comparative example were broken at the time of confirmation at 500 hours, the MgO spinel, Al ₂ O ₃ , Mg
O was operating without any problem even with a very small amount of corrosion even at the time of confirmation at 1000 hours. Thus, it was demonstrated that the use of the protective tube of the present invention has at least twice the life of the protective tube outside the present invention in a refuse incineration ash reprocessing and melting furnace.

[0056]

[Table 5]

[0057]

As described above, according to the present invention, the softening point in the air atmosphere is 1700 ° C. or more, the thermal shock resistance by the water drop method ΔT 150 ° C. or more, the three-point bending strength 150 MPa or more, the average crystal grain size 2 μm By forming the heat-resistant and corrosion-resistant protective tube from the above ceramics, it is excellent in heat resistance, thermal shock resistance, strength and corrosion resistance, so that it can be used satisfactorily for a long time. In particular, when used in a melting furnace for reprocessing refuse incineration ash, erosion of metal elements contained in the incineration ash can be prevented, and the life can be extended.

[Brief description of the drawings]

FIG. 1 is a sectional view 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.

[Explanation of symbols]

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

Claims (2)

[Claims] (1) a softening point of 1700 ° C. or more in an air atmosphere;
A heat-resistant and corrosion-resistant protective tube characterized by forming a tubular body whose tip is sealed with ceramics having a thermal shock resistance of at least 150 ° C. and a three-point bending strength of 150 MPa or more and an average crystal grain size of 2 μm or more by a water drop method. 2. The heat-resistant and corrosion-resistant protective tube according to claim 1, wherein the protective tube is made of a ceramic mainly composed of one of Al ₂ O ₃ , MgO spinel and MgO.