JP2000239072A - Amorphous refractories and waste melting furnaces using them - Google Patents

Abstract

(57) [Problem] To provide a zirconia-silicon carbide amorphous refractory excellent in corrosion resistance and spall resistance which is optimal for a waste melting furnace corresponding to chromium pollution. Kind Code: A1 Abstract: 95 to 50% by weight of fused zirconia particles containing ZrO ₂ monoclinic and containing a glass phase and 5 to 5% of silicon carbide particles
An amorphous refractory comprising 90 to 99% of refractory particles of 0% by weight and 1 to 10% by weight of a binder containing alumina cement.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amorphous refractory which does not contain chromium and is suitable for use in waste melting furnaces and incinerators and is environmentally friendly.

[0002]

2. Description of the Related Art In recent years, the amount of waste generated has been steadily increasing, and its disposal has become a major social problem. For example, in order to treat a huge amount of waste, it is necessary to secure landfill sites. In addition, incineration ash and fly ash generated by incineration of waste, sewage sludge, and the like may also cause secondary pollution depending on the treatment method and disposal location.

[0003] As a countermeasure, it is desired to reduce the volume, detoxify or recycle the waste, and a melting method is attracting attention as one of the measures. The melting method is a method in which inorganic substances in waste are taken out as molten slag to greatly reduce the volume of waste. There are two methods of melting waste: direct pyrolysis of solid waste (garbage, etc.) and melting, and primary incineration of waste in an incinerator, and secondary incineration ash, fly ash, and sewage sludge generated. There is a method of melting.

The chemical composition of incinerated ash, fly ash, sewage sludge and the like is generally 15 to 45% by weight of SiO ₂ and Al ₂ O ₃ 1
0-20 wt%, CaO 5 to 45 wt%, Na ₂ O
1 to 15% by weight. In addition, incineration ash and fly ash include C
Many harmful metals such as d, Pb, Zn, Cu, As, Cr, and Hg are also contained. The sewage sludge, metal is small but contains P ₂ O ₅ is 5 to 15 wt%. Further, a large amount of compounds containing S and Cl as volatile components are contained.

[0005] The degree of erosion of the refractory used in the melting furnace largely depends on the components of the molten slag such as incineration ash, fly ash and sewage sludge charged into the furnace, and the melting temperature. Although the components of the molten slag vary depending on the type of waste, etc., generally, the weight ratio of CaO to SiO ₂ is C
aO / SiO ₂ = about 0.1 to 1.5. On the other hand, it is necessary that the temperature in the melting processing furnace is set to a high temperature of 1400 to 1650 ° C. for melting.

[0006] As refractories that can withstand such processing conditions, refractory materials such as alumina, magnesia, and silica-alumina are known. These refractories easily react with molten slag components and erosion easily proceeds. Tend. Further, the refractory containing carbon has low reactivity with the molten slag component, but tends to be oxidized and consumed when used in a high temperature range.

For this reason, refractories containing chromium oxide are now widely used as refractories exhibiting high corrosion resistance. For example, JP-A-63-30363 and JP-A-6-32162 are known.
8, JP-A-8-48574, JP-A-10-81572, and the like.

Further, refractories which exhibit high corrosion resistance and do not contain chromium oxide have been proposed in Japanese Patent Application Laid-Open Nos. 7-293851, 7-256229 and 2808293.

The higher the content of chromium oxide, the better the corrosion resistance of the refractory containing chromium oxide. However, when used at high temperatures and under atmospheric conditions such as alkali, the chromium oxide in the refractory is harmful to hexavalent. Due to the change to chromium, there is a problem that causes environmental pollution.

Japanese Unexamined Patent Publication No. 7-293851 describes a fired or amorphous refractory containing chromium-free fusible zirconia as a main component, and suggests a compound containing silicon carbide. . It is said that as the refractory, a material further containing zircon, clay and alumina cement, and a material further containing stabilized zirconia are also good. However, considering the refractory joint, it is difficult to obtain a refractory having high corrosion resistance due to decomposition of zircon and an increase in the amount of silica and calcia.

[0011]

SUMMARY OF THE INVENTION The present invention is a refractory excellent in corrosion resistance which can be used in a waste melting furnace,
Further, it is an object of the present invention to provide a low-cost, easy-to-install, irregular-shaped refractory, and to eliminate the problem of environmental pollution caused by harmful hexavalent chromium.

[0012]

According to the present invention, there is provided a refractory particle comprising mainly fused zirconia particles and silicon carbide particles.
~ 99% by weight and binder 1 containing alumina cement
An amorphous refractory containing 30 to 100% by weight, wherein the content of alumina cement in the binder is 30 to 100% by weight, and the content of molten zirconia particles in the refractory particles is 50 to 95%. % By weight, the content of silicon carbide particles is 5 to 5
A zirconia-silicon carbide amorphous refractory, characterized in that the content is 0% by weight.

Further, the present invention provides a waste melting furnace using these amorphous refractories for a part of a furnace wall.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The amorphous refractory of the present invention contains 90 to 99% by weight of refractory particles mainly composed of fused zirconia particles and silicon carbide particles.

Here, the molten zirconia particles are zirconia.
Near raw materials are melted by electrofusion and re-solidified to obtain
As the molten zirconia particles, monoclinic Z
rO _TwoThose containing a crystal phase and a glass phase are preferred, and
Specifically, the following may be mentioned.

For example, desiliconized molten zirconia obtained by desiliconizing zircon, monoclinic molten zirconia containing a glass phase, and zirconia-alumina-based molten zirconia-corundum containing a glass phase.

The desiliconized molten zirconia has a ZrO ₂ content of about 95%.
% Of a ZrO ₂ crystal phase containing a monoclinic crystal,
O ₂ , Fe ₂ O ₃ , TiO ₂ , and a glass phase composed of Al ₂ O _{3 and the} like. The monoclinic molten zirconia containing a glass phase contains about 94% by weight of ZrO ₂ , and contains a monoclinic ZrO ₂ crystal phase, P ₂ O ₅ , Na ₂ O, Al ₂ O ₃ and S ₂ O _3.
a glass phase made of iO ₂ or the like. This glass phase covers around the monoclinic ZrO ₂ crystal as the refractory particles.

The zirconia-alumina molten zirconia-corundum containing a glass phase is about 40% by weight.
A crystalline phase formed by monoclinic ZrO ₂ of about 40% by weight of corundum and SiO ₂ , Al ₂ O ₃ , and Na ₂
O and about 20% by weight of a glass phase.

Here, the molten zirconia particles preferably contain a glass phase in an amount of 3 to 25% by weight, particularly preferably 5 to 20% by weight.

When the content of the glass phase is less than 3% by weight, the volume change at the transition temperature of zirconia is not sufficiently absorbed, and the zirconia is weakened by the generation of residual stress.
If it is larger, the corrosion resistance to molten slag, metal and glass and the high-temperature strength decrease. Thus, monoclinic ZrO
_The glass phase present around the _two crystals absorbs the volume change at the zirconia transition temperature and prevents the refractory particles from collapsing.

On the other hand, when molten zirconia stabilized with MgO, CaO, Y ₂ O ₃ or the like is used as refractory particles, the stabilizers MgO, CaO, and Y ₂ O ₃ are used as molten metal, molten slag, or Reacts with glass to cause destabilization. Therefore, the refractory particles made of the stabilized molten zirconia collapse at the transition temperature and cannot maintain the shape, and thus are not preferable as aggregates of the amorphous refractory. Therefore, it is preferable to keep the content of the stabilized molten zirconia as small as possible.

The molten zirconia particles in the present invention are obtained, for example, as follows. A raw material obtained by mixing a predetermined amount of a zircon sand material or a molten zirconia obtained by desiliconizing zircon sand, and a raw material having a component capable of forming a desired glass phase, or desiliconized molten zirconia, alumina, and SiO forming a glass phase ₂ , Al ₂ O ₃ , N
A raw material obtained by mixing a predetermined amount of a ₂ O is melted by electric arc melting, and the obtained melt is blown off to be granulated or cast into a carbon mold, and then cooled. This is pulverized and adjusted as refractory particles.

In the present invention, as the silicon carbide particles, generally well-known silicon carbide particles can be used, and generally, a mixture of silica stone and a carbon raw material and pulverized after being synthesized in an electric resistance furnace are used. And those prepared as refractory particles can be used.

In the amorphous refractory of the present invention, the molten zirconia particles and the silicon carbide particles mainly constitute an aggregate portion and are characterized by refractory properties. Therefore, in order to exhibit the characteristics of the molten zirconia particles and silicon carbide particles, it is preferable that the content of these particles is as large as possible. Specifically, the total amount of the fused zirconia particles and silicon carbide particles in the refractory particles is preferably set to 85% by weight or more.

The content ratio of the molten zirconia particles and the silicon carbide particles in the refractory particles is 95 to 50% by weight of the molten zirconia particles and 5 to 5% by weight of the silicon carbide particles.
50% by weight. If the amount of the silicon carbide particles is less than 5% by weight, the corrosion resistance and thermal shock resistance characteristic of silicon carbide cannot be sufficiently exhibited, and if the amount is more than 50% by weight, the corrosion resistance deteriorates.

Most of the refractory particles in the present invention constitute an aggregate portion as an amorphous refractory. Usually, various particle sizes can be used, but in general, 10 μm to
It is preferable to select an appropriate particle size within the range of 20 mm.

As a binder, alumina cement is used.
What contains １００100% by weight is used. This allows
The applied amorphous refractory can maintain sufficient dry strength and high temperature strength. As the alumina cement, generally, various alumina cements containing calcium aluminate as a main component can be used.

As the binder, it is preferable to use ultrafine oxide powder together with alumina cement. By replacing a part of the alumina cement with the ultrafine powder, the formed amorphous refractory can be densified and the hot strength and the corrosion resistance can be further improved.

As the oxide ultrafine powder, for example, SiO ₂
Alternatively, a material composed of Al ₂ O ₃ can be used. The particle size of the oxide ultrafine powder is preferably 10 μm or less, particularly preferably 5 μm or less.

The refractory of the present invention contains 90 to 99% by weight of the refractory particles, whereas the binder contains 1 to
10% by weight. In particular, refractory particles of 92-97
%, And preferably containing 3 to 8% by weight of a binder.

The amorphous refractory of the present invention is used by adding a predetermined amount of water at the time of construction. However, in order to exhibit the function of the refractory particles more effectively, an antioxidant, a dispersant or a curing regulator is used. It is preferable to use an amorphous refractory containing

The antioxidant is preferably contained in an amount of 0.1 to 2 parts by weight based on 100 parts by weight of the total amount of the refractory particles and the binder. This antioxidant has an effect of preventing silicon carbide from being oxidized. When the content of the antioxidant is 0.1 parts by weight or less, the antioxidant effect of the silicon carbide particles is small,
If it is more than 2 parts by weight, vitreous is formed from low temperature,
The corrosion resistance of the silicon carbide particles decreases.

As the antioxidant, boron carbide is preferable, and in particular, boron carbide particles having a particle size of 50 μm or less are preferably used.

The ultrafine powder S added as a binder
iO ₂ , the glass phase in the molten zirconia particles, and the like exhibit properties as a binder and also exhibit an effect of preventing oxidation of silicon carbide particles at high temperatures.

Next, regarding the dispersing agent and the curing regulator, these are added to reduce the influence of the workability of the irregular-shaped refractory and the influence of the working temperature, and any one can be used. .

In the present invention, sodium tripolyphosphate, β-naphthalene sulfonates and the like can be preferably used as dispersants. The dispersant is preferably contained in an amount of 0.02 to 0.2 parts by weight based on 100 parts by weight of the total amount of the refractory particles and the binder.

As the curing regulator, there are a curing accelerator and a curing retarder. As the curing accelerator, quick lime and lithium carbonate can be preferably used, and as the curing retarder, oxalic acid, boric acid and the like can be preferably used. In addition, since the hardening of the alumina cement is slow at a low temperature of 15 ° C. or less and the hardening is fast at a temperature of 30 ° C. or more, it is necessary to adjust the addition amount of the hardening regulator depending on the temperature at the time of construction. Generally, it is preferable that the curing modifier is contained in the range of 0.05 to 0.2 parts by weight based on 100 parts by weight of the total amount of the refractory particles and the binder.

The dispersant and the curing modifier may be added to the mixture of the refractory particles and the binder in advance or dissolved or suspended in water added during kneading.

The amorphous refractory of the present invention has excellent corrosion resistance, penetration resistance and spall resistance to molten metal, molten slag, glass, etc., so that it can be applied to furnace walls of waste melting furnaces, incinerators, etc. Can be used.

[0040]

The amorphous refractory of the present invention contains fusing zirconia particles containing a glass phase and silicon carbide particles, so that it can be easily constructed, and the formed amorphous refractory becomes dense.

When the amorphous refractory of the present invention is used for a waste melting furnace wall, Si contained in molten slag of incinerated ash and fly ash is used.
Although components such as O ₂ , CaO, Al ₂ O ₃ , Fe ₂ O ₃ , and Na ₂ O react with ZrO ₂ and SiC in the amorphous refractory, the reaction product becomes a high melting point material. It is considered that the corrosion resistance is unlikely to decrease. In addition, since silicon carbide particles exhibit high viscosity at high temperatures, it is possible to suppress the penetration of molten slag.

Accordingly, the amorphous refractory of the present invention has excellent resistance to penetration by molten slag and the like, and as a result, exhibits excellent corrosion resistance and spall resistance.

[0043]

EXAMPLES Examples and comparative examples of the present invention will be described below. Examples 1 to 9 are examples of the present invention, and Example 10
Examples 17 to 17 are comparative examples.

Each raw material was weighed so that the mixing ratio shown in Tables 1 and 2 was obtained, and water was added while mixing with a universal mixer to obtain a kneaded product. This is 40mm × 40mm × 16
The mold was cast into a 0 mm mold or a mold conforming to each test item while vibrating with a vibrator, cured for a predetermined time, demolded, and dried at 110 ° C. for 24 hours to obtain a test specimen. Tables 1 and 2 show the mixing ratios of the raw materials and the evaluation results of the obtained specimens.

[0045]

[Table 1]

[0046]

[Table 2]

In Tables 1 and 2, the molten zirconia particles A are the molten zirconia particles (desiliconized zirconia) obtained by desiliconization of zircon, and the molten zirconia particles B are the desiliconized zirconia and the glass phase. The components to be formed are mixed, and the molten zirconia particles obtained by arc melting,
The molten zirconia particles C are made of desiliconized zirconia, alumina,
And zirconia-corundum particles obtained by mixing and arc-melting components for forming a desired glass. Further, molten zirconia D (stabilized product) is obtained by adding MgO to desiliconized zirconia to stabilize zirconia, and the content ratio of MgO is 4% by weight.

Table 3 shows the chemical components, crystal morphology and glass phase ratio (% by weight) of the molten zirconia particles A to D.

[0049]

[Table 3]

In addition, these various molten zirconia particles have a coarse particle size of 5 to 1.19 mm and a medium size of 1.19 to 0.1 mm.
The grain size was adjusted to 0.05 mm, and the fine grains were adjusted to 0.105 mm or less. The particle size mixing ratios of the various molten zirconia particles are all 45% coarse, 25% medium, and 30% fine.

As the silicon carbide particles, silicon carbide particles obtained by mixing silica stone and a carbon raw material, synthesizing them in a resistance heating furnace, and pulverizing them were used. The silicon carbide particles have a purity of 97%, and include carbon, Fe and the like as impurities. The silicon carbide particles used were a mixture of fine particles (0.105 mm or less) and medium particles (1.19 to 0.105 mm).

As the alumina cement as a binder,
The main component is CaO and Al ₂ O ₃ , and Al ₂ O ₃
The one having a content of 75% and a specific surface area of 6000 cm ² / g was used. Also, as a binder, the particle size is 5 μm.
The following ultra-fine powder of Al ₂ O _{3 and} the ultra-fine powder of SiO ₂ having a particle size of 5 μm or less were used.

The boron carbide used as the antioxidant had a particle size of 10 μm or less. In addition, sodium tripolyphosphate was used as a dispersant. The amounts of boron carbide, sodium tripolyphosphate, and added water in Tables 1 and 2 are each based on the total amount of the refractory particles and the binder.
It is a weight part when it is set to 00 parts by weight.

As comparative examples, an amorphous refractory containing molten zirconia D as refractory particles and containing a binder containing alumina cement (Example 15) and an alumina refractory containing 96% of Al ₂ O ₃ were used. (Example 16) and Al ₂ O ₃
Specimens _{-Cr 2 O 3 (Cr 2 O} 3 10 wt% content) based monolithic refractory (Example 17) were also prepared.

[Evaluation Results] Using the specimens obtained in Examples 1 to 17, the physical properties and characteristics shown in Tables 1 and 2 were evaluated. Test items and measurement methods are as follows.

The bulk specific gravity can be determined by a general refractory test method (JIS R).
2205).

The flexural strength A is a three-point flexural strength after heat treatment at 110 ° C. for 24 hours.
The three-point bending strength after firing in an electric furnace at 0 ° C. for 3 hours. The thermal shock resistance was measured by repeating the cycle of quenching the specimen fired at 1300 ° C for 3 hours, holding it in an electric furnace at 1300 ° C for 15 minutes, and then rapidly cooling it to room temperature, until peeling. did. The number of cycles was limited to 25. The thermal shock resistance is better when the number of times until peeling is larger. In addition, the thing which does not have peeling at the time of repeating 25 times was represented as 25+.

The corrosion resistance test was performed by the following method. A plurality of trapezoidal column-shaped test pieces were cut out from the specimen, polished to a predetermined size, and lined in a rotating drum. Subsequently, oxygen propane flame was blown in the axial direction of the drum while rotating the drum, and heated to 1600 ° C. 1
With the temperature maintained at 600 ° C., synthetic slag of incinerated ash and fly ash (CaO / SiO ₂ (weight ratio) =
1.0, chemical composition is Al ₂ O ₃ 16% by weight, Ca
O 32%, SiO ₂ 32%, Fe ₂ O ₃ 8%, K ₂ O
_{2%, Na 2 O 2%} , MgO 2%, P 2 O 5 6
%) Was charged into a drum and rotated for 6 hours. The slag was freshly introduced every 30 minutes and tested.

After cooling the drum, the test piece was taken out and cut, and the erosion amount (mm) and the slag penetration depth (mm) were measured at each part of the test piece, and the average value was obtained. The ratio of the amount of erosion in each example when the amount of erosion in Example 17 was 100 was calculated as the corrosion resistance index. A small corrosion resistance index indicates that the corrosion resistance is good.

The oxidation resistance is 40 mm × 40 mm × 40 m
m was oxidized in an electric furnace at 1500 ° C. for 3 hours, cut in half, and the thickness of the oxide layer from the surface (m
m) is the measured value.

[0061]

According to the present invention, an amorphous refractory containing molten zirconia particles and silicon carbide particles at a predetermined ratio is easy to construct at low cost, and has excellent corrosion resistance to molten metal, molten slag, glass, etc. Has penetration resistance and spall resistance. Furthermore, since it does not contain chromium oxide, no harmful hexavalent chromium is generated, and there is no pollution problem such as environmental pollution.

Accordingly, the amorphous refractory of the present invention can be used for zirconia-chromium, alumina-chromium, magnesia, etc., which are currently used in waste baking furnaces, melting furnaces, and industrial furnaces such as steel, cement, and non-ferrous metals. -It can be replaced with chromium-based refractories, and has great industrial value.

Claims (9)

[Claims] An irregular refractory comprising 90 to 99% by weight of refractory particles mainly composed of molten zirconia particles and silicon carbide particles and 1 to 10% by weight of a binder containing alumina cement. The content of alumina cement in the binder is 30 to 100% by weight, the content of molten zirconia particles in the refractory particles is 50 to 95% by weight, and the content of silicon carbide particles is 5 to 50% by weight. A zirconia-silicon carbide amorphous refractory, characterized in that: 2. The amorphous refractory according to claim 1, wherein the total amount of the fused zirconia particles and the silicon carbide particles in the refractory particles is 85% by weight or more. 3. The amorphous refractory according to claim 1, wherein the molten zirconia particles contain a monoclinic ZrO ₂ crystal phase and a glass phase. 4. The molten zirconia particles have a glass phase of 3 to 2 times.
The amorphous refractory according to claim 3, containing 5% by weight. 5. The amorphous refractory according to claim 1, wherein the binder comprises an ultrafine oxide powder having a particle size of 10 μm or less. 6. The antioxidant is contained in an amount of 0.1 to 2 parts by weight based on 100 parts by weight of the total amount of the refractory particles and the binder.
6. The refractory of any one of claims 1 to 5. 7. The refractory according to claim 6, wherein the antioxidant is boron carbide having a particle size of 50 μm or less. 8. A dispersing agent comprising a total amount of refractory particles and a binder of 1
The amorphous refractory according to any one of claims 1 to 7, comprising 0.02 to 0.2 parts by weight based on 00 parts by weight. 9. A waste melting furnace using the amorphous refractory according to any one of claims 1 to 8 for a furnace wall.