JP2001220228A - Heat-resistant and corrosion resistant protective tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protective tube having excellent resistance to thermal shock, and capable of being used without being damaged even in a case in which 500-1,000 deg.C difference of the temperature is caused under a thermally severe condition in a refuge incinerator or the like. SOLUTION: This heat-resistant and corrosion-resistant protective tube is composed of a partially stabilized zirconia ceramic consisting essentially of ZrO2, containing 3.0-3.8 wt.% MgO as a stabilizer, and further including 10-60 mol% monoclinic zirconia crystal.

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 a heater, a sensor and the like in a melting furnace such as a refuse incinerator and a refuse incineration ash melting furnace, and other various furnaces.

[0002]

2. Description of the Related Art Garbage discarded from homes 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,
Mg, K, Mn, Cl, Na, and S) contain heavy metal components and toxic contaminants 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. In addition, detoxification of harmful pollutants such as dioxin and furan is being regulated strictly by laws and regulations, so incineration ash and fly ash are collected and re-melted to detoxify harmful pollutants. The need for melting furnaces is growing 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 volume can be reduced to about 1/10.
Harmful pollutants such as dioxin can be decomposed by high heat and made harmless. For these reasons, high-temperature heat treatment in this melting furnace is considered promising. As a high-temperature heat treatment method, a resistance heating method or a plasma arc method, which is a heating method using electricity, from a heating method in which heavy oil or the like is burned is becoming mainstream.

FIG. 2 shows a typical example of a heat treatment in a melting furnace. First, the incineration ash 11 is put into the melting furnace 12 and heated to 1300 to 1500 ° C. by the heating heater 2 as an electric heat source.
Evaporates. The metal element 13 is taken out, rapidly cooled by a cooling device (not shown), and condensed into fine particles. The fine particles are collected by a filter 14 to collect a metal concentrate 15. On the other hand, toxic pollutants such as dioxin and furan are destroyed by heat,
The detoxified gas 16 is released into the atmosphere via a gas processing device. Further, the residue in the melting furnace 12 is taken out as slag (glass) -like granules 17 and is effectively used or finally disposed.

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 and the thermocouple 3 from these substances.

On the other hand, the heater for heating requires a high insulation property from the viewpoint of short-circuit and electric leakage as a heater protection tube for applying a large voltage and a large current. In addition, the thermocouple protection tube needs to be insulated as much as possible in order to cut off electrical noise as much as possible.

Therefore, the heating heater 2 and the thermocouple 3 are covered with a ceramic protective tube 1 having excellent heat resistance, corrosion resistance, insulation and thermal shock resistance. The material of the protective tube 1 is, for example, MgO, Al ₂ O ₃ , M
Ceramics such as gAl ₂ O ₄ are used. As the shape, a shape in which the tip of the protective tube is sealed on one side is generally widely used.

As the MgO-stabilized zirconia, for example, monoclinic zirconia crystals containing 7 to 11 mol% of MgO as disclosed in JP-B-3-53271 and JP-B-3-64468 are disclosed. What contained 55-85 mol% and improved thermal shock resistance was the mainstream.

When the total amount of monoclinic zirconia crystals is increased, microcracks in the sintered body are increased, and the mechanism of stress-induced phase transformation from tetragonal to monoclinic is reduced. However, there is a problem that the mechanical strength and the fracture toughness of the steel are reduced, and they are not suitable for applications requiring high strength. When micro cracks in the sintered body increase,
When used as a protective tube, there is also the problem that corrosive components penetrate into the porcelain through microcracks and significantly degrade corrosion resistance. Further, zirconia is about 300 ° C-50
At a high temperature of 0 ° C. or higher, there is a problem that the volume resistivity of the material becomes small and the insulating property deteriorates, so that it cannot be used in a furnace using an electric heating method.

[0011]

By the way, when heat-treating ash generated by garbage incineration, Cd contained in the ash,
In order to decompose metal elements such as Pd and Zn and harmful pollutants such as dioxin and furan, 1300-1
Detoxification by heating and melting at 500 ° C.
The protective tube 1 used in 2 is exposed to molten salt, molten slag, steam, or the like formed by melting the incineration ash 11. Therefore, Si, Al, Fe, C
a, Na gradually penetrates and erodes into the ceramics and the furnace material forming the protective tube 1 and gradually deteriorates the ceramics and the furnace material and causes a deterioration in strength, so that cracks or breakage are likely to occur. Melting, etc.
It could not be used for a long time.

As a raw material, when the total amount of monoclinic zirconia crystals is increased as described above, microcracks in the sintered body increase, and a phase transformation mechanism from tetragonal to monoclinic due to stress induction. , The mechanical strength and fracture toughness of the sintered body are reduced, and the sintered body is not suitable for applications requiring high strength. When the microcracks in the sintered body increase, when used as a protective tube, corrosive components penetrate into the porcelain from the microcracks,
There is also a problem that the corrosion resistance is remarkably deteriorated.

[0013]

The present invention comprises ZrO ₂ as a main component, and as a stabilizer, 3.0 to 3.8% by weight of MgO.
And a tubular body made of a partially stabilized zirconia ceramic containing 10 to 60 mol% of monoclinic zirconia crystals to form a heat-resistant and corrosion-resistant protective tube.

Further, the partially stabilized zirconia ceramic has a void area ratio of 0.8 to 2.5%.

Further, an insulating ring formed of a ceramic having a volume resistivity of at least 10 ⁹ Ω · cm at a temperature of 500 ° C. is provided on the outer peripheral surface of the tubular body made of the partially stabilized zirconia ceramic. I do.

[0016]

Embodiments of the present invention will be described below.

As shown in FIG. 1, the protection tube 1 of the present invention comprises:
A tubular body having a closed end, made of partially stabilized zirconia ceramics containing ZrO ₂ as a main component and MgO as a stabilizer, and having a MgO content of 3.0 to 3.8% by weight.
And 10 to 60 mol% of monoclinic zirconia crystals, and a void area ratio of 0.8 to 2.5%.

As shown in FIG. 2, this protective tube 1 is installed in a melting furnace 12 of a refuse incineration ash melting furnace so as to cover a heater 3 and a sensor 3 such as a thermocouple, and contains a lot of corrosive components. Heaters and thermocouples can be protected from furnace gas. The protection tube 1 has an integral structure of ceramics, but may have a structure in which the protection tube 1 is combined with a heat-resistant material such as stainless steel. In addition, the protective tube 1 of the present invention is not limited to the above-described refuse incineration ash melting furnace 12, but may be a protective tube for protecting heaters and various sensors in various melting furnaces and incinerators such as a metal melting furnace and a blast furnace. Can be used as

The shape of the protective tube of the present invention is not limited to a tubular body having a closed end as shown in FIG. 1, but may be a cylindrical body without sealing.

The protective tube formed of the partially stabilized zirconia ceramics of the present invention has MgO of 3.0 to 3.0.
After forming a ceramic raw material containing 3.8% by weight into a predetermined shape, it can be obtained by firing at a maximum firing temperature of 1660 to 1700 ° C and a cooling rate of 80 to 150 ° C / hour.

In the present invention, the content of MgO is adjusted to 3.0.
When the content is less than 3.0% by weight, the total amount of the monoclinic zirconia crystal is increased, and the bending strength, fracture toughness, and corrosion resistance are reduced. If the amount is more than 3.8% by weight, the total amount of the monoclinic zirconia crystals becomes extremely small, and the fracture toughness and the thermal shock resistance decrease. MgO content from 3.6 to 3.8
A particularly desirable range of the content of MgO is from 3.6 to 3.8% by weight because high strength can be maintained when the content is made by weight.

The partially stabilized zirconia sintered body protective tube of the present invention can contain components such as Al ₂ O ₃ and SiO _{2 in} addition to MgO as impurities or additives in the raw material. In particular SiO ₂ is to be contained in the range of 0.1 to 0.5 wt% because reacts with ZrO ₂ to form a zirconium silicate, to inhibit the grain growth of primarily present to crystalline zirconia in the grain boundaries preferable.

Further, in the partially stabilized zirconia sintered body of the present invention, the total amount of the monoclinic zirconia crystals is 10 to 10.
The reason for setting the content to 60 mol% is that the content is preferably within the above range in order to suppress the generation of microcracks in the sintered body and to develop an appropriate phase transformation mechanism. And, in order to control the precipitation amount of the monoclinic zirconia crystal within the above range, the content of MgO is set within the above range, and the maximum temperature during firing is set in the range of 1660 to 1700 ° C. The cooling rate may be set to 80 to 150 ° C./hour.

In order to further improve the thermal shock resistance,
An aging treatment at a temperature of 1150 ° C. for 8 hours or less may be performed.
It has been confirmed that aging treatment for more than 8 hours does not contribute to improvement in thermal shock resistance. On the other hand, it is effective to carry out the aging treatment at 1150 ° C. which is lower than the eutectic temperature range.

The partially stabilized zirconia sintered body of the present invention comprises tetragonal and / or cubic zirconia crystals other than the monoclinic zirconia crystals.

Further, the crystal grain size of the zirconia sintered body greatly affects the strength and toughness. When the maximum sintering temperature is higher than 1700 ° C., the average crystal grain size becomes too coarse as 30 μm or more, resulting in a decrease in strength and toughness. Conversely, when the maximum firing temperature is lower than 1640 ° C., crystals do not grow and are about 5 μm. In this case, densification becomes insufficient, and strength and toughness decrease. Therefore, the average grain size of the partially stabilized zirconia sintered body of the present invention is preferably in the range of 5 to 30 μm.

Further, in the zirconia sintered body of the present invention, the void area ratio has a large effect on thermal shock resistance and abrasion resistance. In the present invention, the void area ratio of the partially stabilized zirconia sintered body is determined. By setting the content to 0.8 to 2.5%, the thermal shock resistance is improved. That is, in order to satisfy both the strength, fracture toughness, and thermal shock resistance, the void area ratio must be within the above range, and by appropriately dispersing an appropriate amount of voids in the sintered body, It greatly contributes to relaxation of thermal shock when a thermal shock is applied, and can improve thermal shock resistance and strength and fracture toughness.

The void area ratio is controlled by a method of adjusting the pulverized particle size of the raw material powder, a method of adjusting the firing conditions, or a method of adding an organic substance having a predetermined particle size to the raw material powder and eliminating it during firing. be able to. For example, when adjusting the pulverized particle size, the finer the pulverization, the smaller the voids of the sintered body can be.However, if the pulverization is excessive, the stabilization mechanism of the zirconia particles weakens, and the monoclinic zirconia after sintering The crystals increase excessively, and the bending strength and the fracture toughness decrease. Further, in this case, voids in the sintered body are significantly reduced, so that when a stress accompanied by a thermal change is applied to the sintered body, the thermal shock cannot be relaxed, resulting in destruction. Conversely, if the amount of pulverization is small and contains coarse particles, firing failure occurs,
This also causes a decrease in bending strength and fracture toughness. Therefore, it is preferable to set the center particle size in the range of 0.6 to 1.2 μm as a standard of the pulverized particle size.

The partially stabilized zirconia ceramics satisfying the above conditions show high values with a bending strength of 680 MPa or more and a fracture toughness of 11 MN / m ^3/2 or more. Further, the thermal shock resistance ΔT can be set to 450 ° C. or more.

As a raw material, MgO powder is added to a raw material powder containing ZrO ₂ as a main component, and the mixture is pulverized and mixed by a ball mill or the like to adjust the central particle diameter to a range of 0.6 to 1.2 μm. An organic binder such as polyvinyl alcohol, polyethylene glycol, acrylate or the like is added as an auxiliary agent, and the mixture is dried and granulated with a spray drier to obtain granules having desired characteristics.

As described above, the partially stabilized zirconia ceramics of the present invention is an excellent material.
There is a property that the volume resistivity is lower than that at room temperature in the temperature range of ° C. Although there is no problem in a furnace that burns heavy oil or the like and uses it as a heat source, in a furnace such as a heater that uses electricity as a heating source, a problem such as short circuit or electric leakage may occur.

In such a case, ceramics having a volume specific resistance of 10 ⁹ Ω · cm or more at a temperature of 500 ° C., for example, ceramics having a purity of 99% or more and containing Al ₂ O ₃ or MgAl ₂ O ₄ as a main component are used. What is necessary is just to connect via an insulating ring.

As shown in FIG. 3, as an example, between the outer peripheral surface of the protective tube 1 made of partially stabilized zirconia ceramics and the inner peripheral surface of the metal tube 22, the above Al ₂ O ₃ or MgAl ₂
If an insulating ring 24 made of O ₄ is interposed and bonded with an inorganic adhesive, sufficient insulation can be ensured.

The thickness of the insulating ring 24 is 1 mm or more and 10 m.
m or less, and preferably 3 mm or less to ensure thermal shock resistance. The length may be interposed so as to cover the entire area of the contact portion between the protective tube 1 and the metal tube 22. Also,
In order to prevent the protection tube 1 from dropping, the pin 23 may be made of the same material as the insulating ring 24 and may be inserted into the groove 1 a formed in the protection tube 1.

[0035]

EXAMPLE 1 Assuming the environment inside a refuse incineration ash melting furnace, various ceramic materials were manufactured, and a reaction test with the refuse incineration ash was performed. Zr
As for O ₂ , two kinds of materials to which 5% by weight of Y ₂ O ₃ and 3% by weight of MgO were added were prepared and subjected to a reaction test.

First, the incineration ash is composed of Al, C
a, Ash, consisting of Mg, Na, K, Zn, Pb, Si, Fe, Cl, etc., is collected from an incinerator, and a tablet having a diameter of 12 mm, a thickness of 1 mm and a weight of 0.3 g is produced by a dry press machine. did.

Next, tablet test pieces having a diameter of 30 mm × 10 mm were formed from the various ceramics shown in Table 1 by dry press molding, and then fired at a temperature of 1500 ° C. or more in an appropriate atmosphere. A counterbore (diameter 13 mm × depth 1 mm) for accommodating the incinerated ash tablet was formed in advance on each test piece. The characteristic values of various ceramics were measured by the following methods.・ Crystal grain size: SEM photograph of fracture surface is 500 times to 1000 times
The photograph was taken at a magnification of about 2 times and measured from this photograph using the code method. -Bulk specific gravity, bending strength, and volume resistivity were tested and measured based on the JIS method. Insulation: Measured according to the JIS test method. The temperature is room temperature 25 ° C and the maximum test temperature is 500 ° C. If the volume resistivity value is 10 ⁹ Ω · cm or more, ○, otherwise ×
And

In the reaction test, an ash tablet was placed in a counterbore of each ceramic test piece, and the mixture was exposed to air at 1550 ° C.
For 50 hours.

Thereafter, the appearance of each test piece was visually observed, and the presence or absence of melting or cracks was examined. The cross section of each test piece was cut and polished, and the presence or absence of cracks was examined by SEM (about 50 to 200 times), and the wavelength dispersion type EPMA analyzer was used to accelerate the voltage of 15 kV and probe current of 2.0 × 10 ^−7. In A, each element of Si, Ca, and Na was detected and output in a mapping format, and then the diffusion depth (reaction layer) of these elements was examined.

The results are shown in Table 1.
In the table, those with cracks, melting, and reaction layers are indicated by x, and those without cracks are indicated by o.

From these results, it was confirmed that Si ₃ N ₄ and Al ₂ O ₃ were unsuitable due to melting or cracking or a problem in the reaction layer. Although SiC has no problem with cracks, melting, and reaction layers, it has a problem with insulation properties and is unsuitable.

On the other hand, cracks occurred in ZrO ₂ to which Y ₂ O ₃ was added, and a reaction layer with the ash component was observed. ZrO ₂ (partially stabilized) to which MgO is added according to the present invention has no melting or cracking and no reaction layer with the ash component. Thus, it can be seen that it can be used as a heat-resistant and corrosion-resistant protective tube material without any problem.

In the case of MgO-stabilized ZrO ₂ , 500 ° C.
At the above-mentioned high temperature, a problem occurs in the insulating property. However, if Al ₂ O ₃ or the like having good insulating property is interposed as an insulating material, it can be used without any problem.

[0044]

[Table 1]

Example 2 As shown in Table 2, 2.0 to 4.5% by weight of MgO was added to ZrO ₂ powder, and pulverized by a ball mill or the like to adjust the average particle diameter to 1 μm. About 4 to 8% of an organic binder such as polyvinyl alcohol was added as a molding aid, and dried and granulated with a spray dryer. Next, the obtained granulated powder was press-molded at a molding pressure of 1 t / cm ² or more to obtain a square bar having a width of 6 mm, a thickness of 5 mm, and a length of 60 mm, which was placed in an atmospheric furnace at about 1660 ° C. to 1700 ° C. Was fired.

The obtained fired body was polished to a width of 4 mm and a thickness of 3 mm, and the bending strength, fracture toughness, apparent specific gravity, and monoclinic ratio were measured. The flexural strength was determined by a normal temperature three-point bending method based on JISR1601, and the fracture toughness K _1C was determined by the indentation method (I.
F. Method), the monoclinic amount was 2θ = 20 with an X-ray diffractometer.
The angle was measured from the range of ° to 40 ° and calculated from the peak intensities of monoclinic zirconia and cubic zirconia.

The void area ratio was measured by measuring an area of 300 μm × 300 μm, which was obtained by magnifying the voids on the mirror-finished sample surface with a microscope using an image analyzer, and averaging the measured areas. .

For the corrosion resistance, a reaction test with incineration ash was conducted. First, as garbage incineration ash, the components are Al, Ca, Mg,
Ash made of Na, K, Zn, Pb, Si, Fe, Cl, etc. is collected from the incinerator and has a diameter of 12 m by a dry press machine.
m, a tablet having a thickness of 1 mm and a weight of 0.3 g was prepared. Next, various ceramics shown in Table 2 were used to obtain a diameter of 30 mm.
× 10mm tablet test piece, after dry pressure molding, 1
It was manufactured by firing at a temperature of about 660 ° C. to 1700 ° C. in an appropriate atmosphere. A counterbore (diameter 13 mm × depth 1 mm) for accommodating the incinerated ash tablet was formed in advance on each test piece. In the reaction test, an ash tablet was placed in the counterbore of each ceramic test piece, and 1550 in air.
A heat treatment at 50 ° C. for 50 hours was applied.

Thereafter, the appearance of each test piece was visually observed, and the presence or absence of melting or cracks was examined. The cross section of each test piece was cut and polished, and the presence or absence of cracks was examined by SEM (about 50 to 200 times), and the wavelength dispersion type EPMA analyzer was used to accelerate the voltage of 15 kV and probe current of 2.0 × 10 ^−7. In A, each element of Si, Ca, and Na was detected and output in a mapping format, and then the diffusion depth (reaction layer) of these elements was examined.

The results are as shown in Table 2.

Regarding corrosion resistance, those having cracks, melting, and reaction layers were indicated by x, and those not having them were indicated by ○.

The thermal shock resistance of the fired body was measured at a predetermined temperature for 15 minutes.
After holding the sample for 20 minutes, the sample was dropped into water at 20 ° C., and the temperature difference at which the strength was deteriorated was indicated as ΔT.

[0053]

[Table 2]

From Table 2, No. In Nos. 1 and 2, MgO content is less than 3.0% by weight, so that they are hardly stabilized, the total amount of monoclinic zirconia increases, volume expansion accompanying transformation increases, cracks occur, and both strength and toughness are low. Value. Conversely, No. 6 and 7 have an MgO content of 3.
Since it is more than 8% by weight, it is stabilized too much and the amount of monoclinic zirconia decreases, the strength strengthening mechanism by phase transformation does not appear, and the strength, toughness and thermal shock resistance are all low.

On the other hand, in the embodiment of the present invention, No.
Nos. 3 to 5 have an MgO content of 3.0 to 3.8% by weight and a total monoclinic zirconia content of 10 to 60 mol%, a bending strength of 680 MPa or more, and a fracture toughness of 11 MN / m.
It turns out that a high numerical value is shown with ^3/2 or more.

As for the corrosion resistance, the MgO content was 3.0 to 3.0.
It is good when the amount of monoclinic crystal is less than 60 mol% at 3.8% by weight, and when it is more than this, a reaction layer is observed and the material is unsuitable as a material for a protective tube.

Therefore, the content of MgO must be in the range of 3.0 to 3.8% by weight in order to satisfy the strength, fracture toughness and corrosion resistance. The void area ratio is 0.8 ~
2.5% is an appropriate value. Example 3 As an example of the present invention, No. 3 in Table 2 was used. The protective tubes made of the materials Nos. 1 and 4 were assembled in an actual furnace, and a comparative test was performed on an actual machine. The protective tube shape shown in FIG. 1 having an outer diameter of 30 mm, an inner diameter of 20 mm, a thickness t of 5 mm, and a length of 500 mm was manufactured. The actual test was performed in a fluidized-bed gasification and melting furnace at an operating temperature of 1300 ° C., and the atmosphere composition was O ₂ 5% and CO ₂ 95
% And the HCl concentration is about 1000 ppm.

As a result of the actual machine test, One protection tube is about 6
The through-hole was generated in the protective tube at 00 hours, and the life was shortened. It was confirmed that the protective tube of No. 4 had a life of about 1200 hours, which proved that it could be used for a long time.

[0059]

As described above, according to the present invention, ZrO ₂
As a main component, containing 3.0 to 3.8% by weight of MgO as a stabilizer, and monoclinic zirconia crystals of 10 to 10.
By forming the heat-resistant and corrosion-resistant protective tube with a partially stabilized zirconia ceramic containing 60 mol%, excellent thermal shock resistance can be obtained, and a temperature difference of 500 to 1000 ° C. in a thermally severe environment such as a garbage incinerator. It can be used without damage even if it occurs.

Further, by connecting this via an insulating ring made of ceramics having a volume specific resistance of 10 ⁹ Ω · cm or more at a temperature of 500 ° C., heat resistance, corrosion resistance,
Excellent in insulation and thermal shock resistance, and can be used well for a long time.

The heat and corrosion resistant protective tube of the present invention is excellent in heat resistance, corrosion resistance, insulation and thermal shock resistance and can be used satisfactorily for a long period of time. It can be suitably used as a protective tube for a thermocouple for measuring the ambient temperature and slag temperature in a melting furnace and other incinerators in a temperature range exceeding 1000 ° C., or as a protective tube for protecting other sensors and heaters.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a protection tube for a refuse incineration ash melting furnace according to an embodiment of the present invention.

FIG. 2 is a schematic view showing a refuse incineration ash melting furnace.

FIG. 3 is a cross-sectional view showing another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1; Protection tube 2; Heating heater 3; Thermocouple 11; Incineration ash 12; Melting furnace 13; Metal element 14; Filter 15; Metal concentrate 16; Glass 17; Slag (glass) -like granules 22; Metal cylinder 23; Fixing pin 24; insulating ring

Claims (3)

[Claims] 1. A The ZrO ₂ as a main component, comprises 3.0 to 3.8 wt% of MgO as a stabilizer, and partially stabilized zirconia ceramics containing zirconia crystals monoclinic 10 to 60 mol% Is formed in a tubular body. 2. A heat and corrosion resistant protective tube according to claim 1, wherein said partially stabilized zirconia ceramic has a void area ratio of 0.8 to 2.5%. 3. A tubular body made of the partially stabilized zirconia ceramic according to claim 1 or 2, which has a temperature of 500
A heat-resistant and corrosion-resistant protective tube comprising an insulating ring formed of a ceramic having a volume specific resistance at 10 ° C. of 10 ⁹ Ω · cm or more.