JP3389436B2 - Heat and corrosion resistant protective tube - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heater and a sensor in a melting furnace such as a refuse incinerator, a refuse incineration ash reprocessing melting furnace, and other various furnaces. It relates to a protection tube for protecting etc. [0002] Garbage discarded from households and companies is burned in incinerators of local governments, and fly ash (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 is reduced to half 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 because it can reduce the volume to about 1/4 and decompose harmful pollutants such as dioxin by high heat to make them harmless. It is. [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, C contained in the ash is not included.
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 quality of the ceramics, causing deterioration in strength. It was not something. In order to solve this problem, if the life of the protective tube 1 is increased by increasing the wall thickness, a temperature difference occurs between the surface layer and the inside due to a temperature change at the time of temperature rise and fall, and the protective tube is broken by thermal stress. Or the heat capacity of the protection tube 1 becomes too large, which makes it difficult to control the temperature inside the furnace. On the other hand, when the thickness of the protective tube 1 is reduced, there is an inconvenience that the life is significantly reduced as described above. [0010] In view of the above, the present invention provides
Ceramics whose main component is MgO spinel whose tip is sealed
A tubular body made of lumps, having an outer diameter d ₁ , an inner diameter d ₂ ,
The wall thickness t satisfies 5 ≦ d ₁ , 1 ≦ d ₂ , (√d ₁ +5) / 7 ≦ t ≦ ( √d ₁ -1.8) /0.3 (both in mm). Smooth tip sealing part and side part of tubular body
End portion of the tubular body while being continuous
Characterized by the fact that the thickness of the
Provide a thermal corrosion protection tube. That is, as a result of various experiments, the optimum range of the wall thickness changes according to the outer diameter of the protection tube. It was found that it could be prevented. Further, according to the present invention, the tip end sealing portion and the side portion of the tubular body forming the protective tube are continuous in a smooth curved shape .
This prevents the occurrence of cracks and the like during temperature rise and fall . Furthermore, the present invention, the thickness of the distal sealing portion of the tubular body forming the protective tube, thicker than the thickness of the side portions
In addition, in the case of a protective tube hanging from the ceiling, if the wall thickness is increased, the weight becomes too heavy. However, if only the sealing portion at the tip is made thicker, the weight can be reduced and the life can be extended. Further, the present invention is characterized in that the ceramics forming the protective tube contains MgO spinel as a main component . That is, these ceramics are particularly excellent in heat resistance and corrosion resistance, and can further extend the life. Embodiments of the present invention will be described below. As shown in FIG. 1 (a), a protective tube 1 of the present invention is a tubular body having a sealed tip made of ceramics, and has a cylindrical side portion 1a and a hemispherical tip sealed portion 1b. Has a smooth curved surface and a continuous shape. In the present invention, the outer diameter d ₁ , inner diameter d ₂ , and wall thickness t of the protective tube 1 are 5 ≦ d ₁ , 1 ≦ d ₂ , (√d ₁ +5) / 7 ≦ t ≦ (√ d ₁ −1.8) /0.3 (both in mm). Here, the reason why 5 ≦ d ₁ and 1 ≦ d ₂ is that when the outer diameter d ₁ is less than 5 mm or the inner diameter d ₂ is less than 1 mm, the above relational expression is not satisfied and the diameter is too small. This is because it is not practical. In addition, the outer diameter d ₁ and the inner diameter d ₂ of the present invention are values measured near the opening of the protective tube 1 at normal temperature, and when not perfectly circular, the average of the outer diameters measured in two directions orthogonal to each other. Calculate by value. The range of the thickness t is (√d ₁ +5) / 7
≦ t ≦ (√d ₁ -1.8) /0.3 is the reason that if the thickness t is less than (√d ₁ +5) / 7, it is liable to corrode during use and the life is shortened. On the other hand, when the thickness t is (√d ₁ -1.
If the ratio is larger than 8) /0.3, cracks and the like are likely to occur due to a temperature difference between the surface layer portion and the inside when the temperature rises and falls. That is, as will be described in detail later, various experiments were conducted while changing each dimension. As the outer diameter d ₁ was increased, the optimum thickness t was increased, and in particular, the optimum thickness t was increased in proportion to Δd _1. It has been found that the range of the optimum thickness t changes. Therefore, the optimum range of the wall thickness t is expressed by the above-mentioned formula based on the experimental results. Even if the thickness is within the above range, for a product having a large thickness t or a large-sized product, the holding method at the time of use is difficult because of its own weight. Conversely, a product having a small thickness may be damaged during handling. Occurs. Therefore, the thickness t is (√d
It is preferable to be within the range of ₁ +1) / 3 ≦ t ≦ (√d ₁ -1.4) /0.7. The thickness t is measured at the side surface 1a near the opening of the protective tube 1 or at the center of the tip sealing portion 1b. Preferably, Further, in the protective tube 1 of the present invention, the thickness t 'of the tip sealing portion 1b may be set to be larger than the thickness t of the side portion 1b within the range of the above formula. That is, this protection tube 1
In the case of using the apparatus by hanging it from the ceiling, if the total thickness t is increased, the weight becomes heavy, the burden on the furnace body increases, and the workability and cost also deteriorate. Therefore, if only the thickness t 'of the tip sealing portion 1b, which requires the most corrosion resistance, is made thicker and the thickness t of the side surface portion 1a is made thinner than this, it is possible to increase the corrosion resistance relatively lightly. . For example, as shown in FIG. 1B, if the thickness t 'of only the central portion of the distal end sealing portion 1b is increased, breakage during handling can be prevented. It is preferable that the space between the side surface portion 1b of the protective tube 1 and the distal end sealing portion 1a be continuous in a smooth curved shape. This is because if there is a corner or the like in a continuous portion between the two, cracks or the like are likely to occur from this portion. It should be noted that “continuous in a smooth curved shape” means that there is no sharp edge portion. Further, the shape of the distal end sealing portion 1b is not limited to a hemispherical shape, but may be various shapes. In this case, in order to prevent the occurrence of cracks or the like, a smooth curved surface or a shape in which a curved surface and a flat surface are smoothly continuous may be used. The shape of the opening of the protection tube 1 can be various. For example, it may be a straight shape as shown in FIG. 1, a flange or a threaded portion formed so as to be easily attached to a jig or the like, or a thicker end portion. Next, as the ceramics which constitutes the protection tube 1 of the present invention, those containing MgO spinel (MgAl ₂ O ₄ ) as a main component are used. [0029] In addition, Al ₂ O _3, which forms the principal component and the 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. [0030] These MgO spinel (MgAl ₂ O ₄₎
Ceramics mainly a, the melting point is extremely high as 2000 ° C. or higher, stable heat resistance even in a high temperature of 1,500 to 1,600 ° C., has a corrosion resistance, an optimum material as the protective tube 1. The MgO spinel is represented by MgAl ₂ O ₄ , and the theoretical constant is MgO and Al ₂ O ₃ in a molar ratio of 1: 1,
It is a compound bound in 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. However, when MgO is increased more than the theoretical stoichiometric ratio, MgO + Mg
Al ₂ O _{4 has} a two-phase crystal structure, while the A
When l ₂ O ₃ is increased, a two-phase crystal structure of Al ₂ O ₃ + MgAl ₂ O ₄ is obtained. 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. To include at least one or more crystal phases of MgAl ₂ O ₄ and Al ₂ O ₃ means that there is a peak of one or more of these crystal phases. Furthermore, 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 impurities from being mixed in the manufacturing process. Further, the average crystal grain size of the ceramic and above 2 [mu] m, it is preferable that the porosity of 3% or less. 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. On the other hand, if the porosity exceeds 3%, erosion elements easily enter the pores present in the ceramics, penetrate into the ceramics at a much higher rate than penetrate into the grain boundaries, and significantly promote corrosion. . [0036] These average crystal grain size and porosity can be freely adjusted by the particle size and sintering conditions and the like of the starting material. As shown in FIG. 2, the protective tube 1 of the present invention described above is installed so as to cover the heater 2 and the thermocouple 3 in a melting furnace 12 for reprocessing refuse incineration ash. These can be protected. At this time, the protective tube 1 of the present invention
Can be safely used for a long time because of its high heat resistance and corrosion resistance. [0038] The protective tube 1 of the present invention is not limited to the melting furnace 12 for waste incineration ash reprocessing described above, in various melting furnaces metal melting furnace, in order to protect the heater and various sensors such as 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. EXAMPLE A protective tube 1 having a flange at an opening thereof was made of a ceramic containing MgO spinel as a main component.
2 were produced in various dimensions. Each protective tube 1 is hung from the ceiling in a refuse incineration ash reprocessing melting furnace with the tip sealing portion 1b facing the molten slag side, the opening of the protective tube 1 is sealed with a furnace material, and the temperature is reduced from room temperature to 48. The temperature was raised to 1400 ° C. over time, held for 500 hours, and then exposed to an actual environment in which the temperature was lowered. [0040] After that, by performing the appearance check of the protective tube 1, deformation, to confirm the presence or absence of cracks was × what is visible, respectively, are not intended to and ○. Further, the central portion of the distal end sealing portion 1b of the protective tube 1 was cut, the degree of corrosion was visually checked, and the corrosion depth was measured by EPMA analysis. Table 3 shows the ratio between the corrosion depth and the wall thickness.
The evaluation was performed as in 4. The results are as shown in Tables 3 and 4 and FIG. From these results, when the thickness t is smaller than the range of the present invention (Nos. 1, 10 and the like) , there are problems such as deformation at a high temperature because the weight cannot be supported and corrosion penetrates to the inside and breaks. was there. This is because a part of the protection tube 1 is eroded and corroded, and cannot withstand the stress when the surface layer swells.
Probably destroyed. On the other hand, in those wall thickness t is larger than the range of the present invention (Nanba4,13 etc.), erosion from the crack unit that would have occurred during heating was in progress. [0043] In addition, No. In Nos. 6 to 9, the front end sealing portion 1b is flat and the boundary with the side surface portion 1a is formed in an edge shape.
It was unsuitable as protection tube 1. On the other hand, the tip sealing portion 1b is connected to the side surface 1a.
In the case of a semi-spherical shape having a smooth and continuous shape and a thickness t within the range of the present invention, although a slight corrosion is observed on the surface layer, no cracks or the like are observed, and a sufficient life as a protective tube is obtained. It was confirmed to have. [ Table 1] [ Table 2] [ Table 3] [ Table 4] As described above, according to the present invention, the tip is sealed.
From ceramics containing MgO spinel as the main component
Having an outer diameter d ₁ , an inner diameter d ₂ , and a wall thickness t.
_{There, 5 ≦ d 1, 1 ≦} d 2, (√d 1 +5) / 7 ≦ t ≦ (√d 1 -1.8) satisfies /0.3 (both also Unit mm), of the tubular body Smooth tip seal and side
End portion of the tubular body while being continuous
The thickness is made thicker than the thickness of the side surface portion, so that breakage due to thermal stress can be prevented and the life can be extended. In particular, when the protective 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 protective 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 graph showing a relationship between an outer diameter d ₁ and a wall thickness t of a heat and corrosion resistant protective tube. [Description of Reference Numerals] 1: Protection pipe 1a: side surface portion 1b: distal sealing portion d _1: the outer protective tube diameter d _2: inside diameter of the protective tube t: meat protective tube thickness 2: heater 3: Thermocouple 11: incineration ash 12: melting furnace 13: metal element 15: filter 16: heavy metal concentrate 17: gas 18: slag granules

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C04B 35/00-35/50

Claims (1)

(57) [Claims] [Claim 1] Mainly composed of MgO spinel whose tip is sealed
A tubular body made of ceramics having an outer diameter d
₁ , inner diameter d ₂ , thickness t is 5 ≦ d ₁ , 1 ≦ d ₂ , (√d ₁ +5) / 7 ≦ t ≦ (√d ₁ -1.8) /0.3 (All units are mm) meets the tip seal and side portions of the tubular body, smooth
End portion of the tubular body while being continuous
A heat-resistant and corrosion-resistant protective tube, wherein the thickness of the protective tube is greater than the thickness of the side surface .