JP2001247379A - Formed refractory material and waste melting furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a formed refractory material free from chromium, having excellent corrosion resistance, slug infiltration resistance and spalling resistance and suitable for the furnace for melting waste material. SOLUTION: The objective formed refractory material is produced by compounding 100 pts. of a refractory composition with 0.5-3.5 pts. of sodium aluminate in terms of NaAlO2 and 0.1-1.3 pts. of sorbitol. The sum of spinel particle and dolomite particle in the refractory composition is 80-96% and the amount of fused zirconia particle containing glassy phase is 4-20%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention does not contain chromium,
The present invention relates to a molded refractory suitable for a waste melting furnace for melting waste such as incineration ash.

[0002]

2. Description of the Related Art In recent years, the amount of waste generated has increased rapidly.
The treatment has become a major social problem. 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 takes out the inorganic substances in the waste as molten slag,
This is a method of drastically reducing the volume. As a method for melting waste,
Solid waste (such as garbage) is directly pyrolyzed and melted, and incinerators are primarily incinerated to produce incinerated ash.
There is a method of secondary melting of fly ash and sewage sludge.

In any of the melting methods, the erosion of the refractory used in the melting furnace largely depends on the components of the melting slag such as incineration ash, fly ash, sewage sludge and the like and the melting temperature. . Although the components of the molten slag vary depending on the type of waste and the like, generally, the chemical composition of incinerated ash, fly ash, and dried solidified sewage sludge is SiO ₂ : 1
5 to 45% by mass (hereinafter simply referred to as%), Al ₂ O ₃ : 1
0~20%, CaO: 5~45%, Na 2 O: 1~15
%. In addition, incineration ash and fly ash include Cd, Pb, Z
Many harmful metals such as n, Cu, As, Cr, and Hg are also contained. Sewage sludge contains ₅ to 15% of P ₂ O ₅ , although the amount of metal is small. S and C as volatile components
The compound 1 is also included in a large amount. Further, the temperature in the melting furnace must be as high as 1400 to 1650 ° C.

Therefore, at present, refractories containing chromium oxide are used in waste melting furnaces and the like from the viewpoint of corrosion resistance. The higher the content of chromium oxide, the better the corrosion resistance of refractories containing chromium oxide.However, if chromium oxide in the refractory is used at high temperatures and in atmosphere conditions such as alkali, it changes to harmful hexavalent chromium. May cause environmental pollution problems.

[0005] Examples of the unfired molded refractory containing no chromium include magnesia-carbon, alumina-silicon carbide-carbon, and alumina-based, but the corrosion resistance and spalling resistance are the same as those of the fired molded refractory. Is not sufficient as a refractory for waste melting furnaces.

[0006]

The present invention does not contain chromium and has excellent corrosion resistance, spalling resistance and mechanical strength.
The purpose is to provide molded refractories suitable for waste melting furnaces.

[0007]

The present invention relates to a refractory composition 1
To 00 parts by mass, 0.5 to 3.5 parts by mass of sodium aluminate converted to NaAlO ₂ and 0.1 parts by mass of sorbitol
A molded refractory compounded at a ratio of about 1.3 parts by mass, comprising spinel particles, dolomite particles, and molten zirconia particles containing a glass phase in the refractory composition, wherein the spinel particles in the refractory composition And a dolomite particle having a total content of 80 to 96% and a molten zirconia particle containing a glass phase having a content of 4 to 20%. However, in the above description, the spinel particles refer to particles containing MgAl ₂ O ₄ crystals, containing 23 to 60% of an MgO component in the particles, and having a total amount of the MgO component and the Al ₂ O ₃ component of 95% or more. . Further, the present invention provides a waste melting furnace using at least a part of a furnace wall formed from the molded refractory.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The molded refractory of the present invention (hereinafter referred to as the molded refractory) is obtained by adding a binder and the like to a refractory composition.
Obtained by molding. The molded refractory is usually used as a non-fired product, but may be used as a fired product. The molded refractory comprises a refractory composition, sodium aluminate, and sorbitol. The refractory composition is mainly composed of spinel particles, dolomite particles and molten zirconia particles.
The molten zirconia particles include a glass phase.

Here, the spinel particles are MgAl ₂ O ₄
Containing crystals, containing 23-60% of MgO component in the particles,
In addition, it refers to particles in which the total amount of the MgO component and the Al ₂ O ₃ component is 95% or more, and may be any of an electrofused (fused) spinel and a sintered spinel, or may be used in combination.

These spinel particles are composed of magnesia of seawater and alumina of 23 to 60% of MgO and 40 to 40% of Al ₂ O _3.
It is prepared by a method in which a raw material mixture mixed so as to be in a range of 77% is fired by a rotary kiln, or a method in which the raw material mixture is melted by an electric melting method, cooled, pulverized, and then sized.

In the present invention, the spinel particles consist essentially of an MgO component and an Al ₂ O ₃ component, but may contain unavoidable impurities or other components that do not impair the object and effects of the present invention. Good. The total amount of the MgO component and the Al ₂ O ₃ component is preferably 97% or more. Spinel (Mg
Theoretical composition of Al ₂ O ₄₎ is, MgO component 28%, Al ₂ O ₃
The component is 72%, but in the present invention, even better effects are exhibited by properly using spinel particles having various MgO component: Al ₂ O ₃ component ratios.

In the present specification, Mg in spinel particles
Those having an O component content of 23% or more and less than 33% are referred to as substantially theoretical composition spinel particles, and those having an O component content of 33% or more and 60% or less are referred to as magnesia-excess spinel particles. Periclase crystals are usually precipitated in the magnesia-excess spinel particles.

The spinel particles according to the present invention contain 23-60% of MgO component. If the MgO component is less than 23%, the alumina becomes relatively excessive, so that it reacts with CaO in dolomite particles, which is a main component of the molded refractory, and CaO.A
A low melting point compound such as l ₂ O ₃ is formed, and the corrosion resistance is reduced.
If the MgO component exceeds 60%, although corrosion resistance is present, slag penetration resistance is deteriorated, and systematic spalling is likely to occur. More preferably, the MgO component in the spinel particles is 25 to 50%.

The dolomite particles in the present invention include:
Although natural ones can be used, synthetic dolomite particles of high purity are preferred. Synthetic dolomite particles, for example,
It is obtained by coprecipitating iron hydroxide with magnesium hydroxide to obtain iron-containing magnesium hydroxide, adding lime milk thereto, adding titanium oxide as an antidigestion agent, and firing in a rotary kiln.

When the CaO component in the dolomite particles is 5 to 20
% (Most of the remainder is MgO component). The dolomite particles are easily digested by water, so that the surface of the dolomite particles may be treated with a phosphoric acid solution or the like to improve the digestion resistance.

The molten zirconia particles in the present invention can be obtained by melting and re-solidifying a zirconia raw material by electrofusion or the like, and contains a glass phase. As the molten zirconia particles, those containing a monoclinic ZrO ₂ crystal phase and a glass phase are preferable. Specifically, 1) desiliconized molten zirconia containing a glass phase obtained by desiliconizing zircon, and 2) glass Phase-containing monoclinic fused zirconia, 3) fused glass-containing zirconia-alumina, and the like.

The desiliconized molten zirconia 1) containing a glass phase has a ZrO ₂ content of about 95%, a crystal phase containing monoclinic ZrO ₂ , SiO ₂ , Fe ₂ O ₃ , TiO ₂ , and Al ₂ O. _And a glass phase consisting of ₃ grades. The desiliconized molten zirconia is obtained by desiliconizing the zircon sand, and a predetermined amount of a raw material containing a component capable of forming a desired glass phase is further mixed with the desiliconized molten zirconia and melted by electric arc melting. After the obtained melt is blown off and granulated or poured into a carbon mold, it is cooled, further pulverized, and sized.

2) Monoclinic fused zirconia containing glass phase
A is ZrO_TwoIs about 94% and monoclinic ZrO_Twoincluding
Crystal phase and P_TwoO_Five, Na_TwoO, Al_TwoO_Three, SiO_TwoFrom etc
Glass phase. 3) Molten gill containing glass phase
Konia-alumina is about 40% monoclinic ZrO _TwoAnd about 4
0% corundum (Al_TwoO_Three) And about 20% of SiO
_Two, Al_TwoO_Three, Na_TwoO and the like.

The molten zirconia particles preferably contain a glass phase in an amount of 3 to 25%, particularly preferably 5 to 20%. When the content of the glass phase is less than 3%, the volume change at the transition temperature of zirconia is not sufficiently absorbed, and the zirconia may be weakened due to generation of residual stress. If it exceeds 25%,
Corrosion resistance to molten slag, metal, and glass and high-temperature strength may be reduced. Thus, the glass phase in the molten zirconia particles absorbs the volume change at the transition temperature of zirconia and prevents the collapse of the molten zirconia particles.

On the other hand, when zirconia particles stabilized with MgO, CaO, Y ₂ O _3, etc. which do not contain a glass phase are used as the particles of the molded refractory, the stabilizers MgO, CaO, Y ₂ O _{3 and the} like react with molten metal, molten slag, or glass to cause destabilization. For this reason, the stabilized zirconia particles are preferably contained in the molded refractory in a small amount as much as possible.

In the present invention, the refractory composition contains spinel particles, dolomite particles, and molten zirconia particles containing a glass phase. The total content of spinel particles and dolomite particles is 80 to 96%, and the content of molten zirconia particles is 4%.
~ 20%. If the combined amount of the spinel particles and the dolomite particles is less than 80%, the slag penetration resistance and the spalling resistance will be poor, and if it exceeds 96%, the corrosion resistance will be poor.
If the content of the spinel particles in the refractory composition is less than 25%, it is difficult to obtain sufficient corrosion resistance. If the content is more than 55%, the slag penetration resistance is reduced, so that the content of the spinel particles is preferably 25 to 55%.

4% of molten zirconia particles in the refractory composition
If it is less than 10%, the corrosion resistance and thermal shock resistance will not be sufficiently exhibited, and if it exceeds 20%, the formed molded refractory will be porous and the corrosion resistance will be poor. More preferably, the molten zirconia particles are from 5 to 18% of the refractory composition.

In the molded refractory, the spinel particles, dolomite particles and molten zirconia particles are preferably as large as possible because they mainly constitute the aggregate portion as a refractory composition and characterize the properties as a molded refractory. The total amount of the spinel particles, dolomite particles and molten zirconia particles in the refractory composition is 90% or more, especially 95%.
% Or more is preferable.

In the present invention, the particles in the refractory composition preferably have a particle diameter of 10 μm to 20 mm.
In the present specification, coarse particles refer to particles having a particle diameter of 1.19 mm or more and less than 5 mm, and medium particles refer to particles having a particle diameter of 0.105 mm.
The term “fine particles” refers to particles having a particle diameter of less than 0.105 mm.

In the present invention, the dolomite particles are preferably used as coarse particles in view of digestion resistance and thermal shock resistance.
As the molten zirconia particles, those mainly composed of fine particles are preferable. As the spinel particles, it is preferable to use spinel particles having a substantially theoretical composition and magnesia-excess spinel particles, and it is more preferable to use fine particles alone, medium particles alone, or a mixture of medium particles and fine particles. When the magnesia-excess spinel particles are used together with water, they are easily digested. Therefore, it is preferable to use an anti-digestion agent in combination.

As an antidigestion agent, salts of aluminum hydroxide with citric acid and lactic acid can be preferably used.
Examples of such salts include those having a chemical composition of Al ₂ O ₃ min:
17.5%, lactic acid content: 46.5%, citric acid content: 33%
There is a white powder that is It is preferable that the antidigestion agent is contained in an amount of 0.1 to 1% on the basis of the refractory composition. When the content of the antidigestion agent is less than 0.1%, the antidigestion effect is small and 1%
%, It is not preferable because the formed molded refractory becomes porous.

The molded refractory contains sodium aluminate and sorbitol in addition to the refractory composition. In this molded refractory, it is considered that sodium aluminate functions as a binder and sorbitol functions as a molding aid.

As a typical composition, sodium aluminate is represented by NaAlO ₂ or Na ₃ AlO ₃ , and the molar ratio of Na ₂ O / Al ₂ O ₃ is 1.2 to 2.6.
It is considered that sodium aluminate reacts with dolomite, spinel, zirconia, etc. at a relatively low temperature to produce a reactant such as a composite spinel and has an action of generating strength. Cracking and peeling due to poling hardly occur, and corrosion resistance is high.

The amount of sodium aluminate is 0.5 to 3.5 parts by mass in terms of NaAlO _{2 based} on 100 parts by mass of the refractory composition. If the amount of sodium aluminate is less than 0.5 parts by mass, sufficient strength as an unfired molded refractory cannot be obtained, and if it exceeds 3.5 parts by mass, oversintering occurs during use, and Spallability deteriorates. Preferably it is 0.5 to 3 parts by mass. Sodium aluminate may be added in the form of a powder or an aqueous solution.

Although the molded refractory contains sorbitol, it is preferable to use D-sorbitol as a main component which is a powder and easily soluble in water. Sorbitol improves the filling property of the kneaded clay, the lubricity between particles, stabilizes the kneaded clay, suppresses the slaking, has no toxicity, and can provide a molded body with high molding density and high strength. give.

The amount of sorbitol to be added is 10
It is 0.1 to 1.3 parts by mass with respect to 0 parts by mass.
If the amount is less than 0.1 part by mass, the effects of filling and lubricity are difficult to obtain, and if it exceeds 1.3 parts by mass, it disappears during use at high temperatures, leaving pores. More preferably, the amount of sorbitol is 0.3 to 1.0 part by mass. Sorbitol may be added and dissolved in an aqueous solution of sodium aluminate, or may be added as a powder.

The molded refractory is manufactured by kneading and molding the above-mentioned raw materials. In the case of a baked product, it is baked,
In that case, the same effect can be obtained. The method of kneading and molding is no different from the usual refractory manufacturing method. In addition, you may heat and dry after shaping | molding.

First, the coarse particles and the medium particles in the refractory composition are wet-kneaded, and sodium aluminate and sorbitol are added in the form of an aqueous solution or powder. A method in which sorbitol is coated and then fine particles are charged and kneaded is preferable because the kneaded material has good uniformity.

The molding is carried out under pressure by a friction press, an oil press, a rubber press or the like according to the application. When drying by heating, the drying temperature is 100 to 500
C. is preferred. 1600 for firing
It is preferable to bake at １６1650 ° C.

Since the molded refractory contains molten zirconia particles, dolomite particles, spinel particles and sodium aluminate containing a glass phase, it is densified and strengthened during use, has excellent corrosion resistance, and has excellent penetration of molten slag. Less,
Less likely to cause systematic spalling.

The waste melting furnace of the present invention uses the molded refractory for at least a part of the furnace wall. In particular, it is preferable to form the furnace wall in a portion in contact with the molten slag from the molded refractory in terms of corrosion resistance and durability. In this case, SiO ₂ , CaO, Al ₂ O ₃ , F contained in molten slag such as incinerated ash
Components such as e ₂ O ₃ and Na ₂ O react with the molten zirconia particles and the spinel particles, but the reactant with the molten zirconia particles becomes a high melting point substance, and the reactant with the spinel particles becomes the high viscous substance. Therefore, it is considered that the corrosion resistance of the furnace wall formed of the molded refractory hardly decreases. Therefore, by using the molded refractory material, it is possible to form a highly durable furnace wall having excellent slag penetration resistance to molten slag and the like and consequently exhibiting high corrosion resistance and thermal shock resistance. This molded refractory is ideal for waste melting furnaces,
It is also preferably used in various furnaces and incinerators for non-ferrous metals and cement.

[0037]

EXAMPLES Examples of the present invention (Examples 1 to 10) and comparative examples (Examples 11 to 18) will be described below. Tables 1 and 2 show the raw material mixing ratio (unit: parts by mass) of the test sample. The test sample is prepared by adding sodium aluminate, sorbitol, and an antidigestion agent (all of which are external to the refractory composition,%) to a predetermined amount of the refractory composition, and further adding water (to the refractory composition, ,%) Were added and kneaded, followed by pressure molding (98 MPa) into a parallel shape by a friction press. Then, Example 1
About Example 16 was dried at 200 ° C. for 24 hours.

The raw materials in Tables 1 and 2 are as follows. Particle A: Desiliconized zirconia particles and fine particles are used. Particle B: Molten zirconia particles and fine particles obtained by mixing particle A with a glass phase forming component and performing arc melting. Particles C: Particles A, alumina, and a glass phase-forming component are mixed, and arc-fused to use fused zirconia-corundum particles and fine particles. Particle D: stabilized zirconia particles obtained by adding MgO to high-purity zirconia and arc melting, and using fine particles containing 4% of MgO. Particles E: Spinel particles of approximately theoretical composition (sintered product), medium particles used. Particle F: Magnesia excess spinel particles (sintered product), coarse or fine particles are used.

Particles G: Dolomite particles. It was produced by the following method. Iron sulfate and lime milk were added to and mixed with seawater containing MgCl ₂ and MgSO ₄ to obtain iron-containing magnesium hydroxide. A mixture of lime milk and TiO ₂ was added to the mixture, and the mixture was molded and fired in a rotary kiln to obtain a synthetic dolomite clinker. This was treated with phosphoric acid, pulverized and sized to obtain dolomite particles. The chemical composition of the obtained dolomite particles is expressed as a mass ratio of CaO: 16.
_{~17%, Al 2 O 3:} 1.2, Fe 2 O 3: 0.4%, P
₂ O ₅ : 0.7%, TiO ₂ : 1.0%, the balance being MgO. Dolomite particles were used as coarse particles.

Unfired 1: magnesia-chromia (Mg
O: 62%, Cr ₂ O ₃ : 23%). Amorphous 1: Alumina amorphous refractory containing 96% Al ₂ O ₃ . Amorphous 2: Alumina-chromia amorphous refractory containing 10% Cr ₂ O ₃ . Aluminate: sodium aluminate having a molar ratio of Na ₂ O / Al ₂ O _{3 of} 1.2. Sorbitol: powder. Alumina cement: Al ₂ O ₃ min: 73%, CaO min: 2
With a specific surface area of 6000 cm ² / g at 6%. Antidigestion agent: a mixed salt composed of aluminum hydroxide, citric acid and lactic acid (trade name: Taxelum AS-300, manufactured by Taki Kagaku Co., Ltd.). Dispersant: sodium tripolyphosphate.

Table 3 shows the chemical composition, crystal morphology and glass phase ratio of particles A to D, and Table 4 shows the chemical composition and crystal morphology of particles E and F. In Examples 17 and 18, alumina particles having a particle diameter of 5 μm or less were used in addition to the alumina cement.

[Evaluation Results] Using the test specimens obtained in Examples 1 to 18, the characteristics were measured and evaluated, and the results are shown in Tables 1 and 2. Evaluation items and measurement methods are as follows. Bulk density (g / cm ³ ): Refractory test method (JIS R22)
05).

The flexural strength was determined to be 30 × 15 from the specimen.
A test piece having a size of × 100 mm was cut out and measured at room temperature as a three-point bending strength. Flexural strength A (MPa): 3-point flexural strength after heat treatment at 200 ° C. for 24 hours. Bending strength B (MPa): Three-point bending strength after heat treatment at 1000 ° C. for 3 hours. Flexural strength C (MPa): Three-point flexural strength after heat treatment at 1500 ° C. for 3 hours.

Thermal shock resistance (times): 55 × from the test sample
A 55 × 230 mm prismatic test piece is cut out. The end of the test piece in the longitudinal direction was placed in an electric furnace maintained at 1300 ° C.
After holding for 5 minutes, a cycle of taking out of the furnace and holding at room temperature for 15 minutes was repeated, and the number of times until peeling occurred was measured. The number of cycles was limited to 25 times.
The thermal shock resistance is better when the number of times until peeling occurs is larger. In addition, the thing which does not have peeling at the time of repeating 25 times was represented as 25+ in the table.

The corrosion resistance index and the slag penetration depth (m
m): 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. Then, while rotating the rotating drum, oxygen propane flame was blown in the axial direction of the rotating drum.
Heated to 600 ° C. With the temperature maintained at 1600 ° C., a synthetic slag of incinerated ash and fly ash was charged into a rotating drum as an erosion material and rotated for 6 hours.

The chemical composition of the synthetic slag is Al ₂ O ₃ : 16
%, CaO: 32%, SiO 2: 32%, Fe 2 O 3: 8
%, K ₂ O: 2%, Na ₂ O: 2%, MgO: 2%, P ₂
O ₅ : 6%. The synthetic slag was tested fresh every 30 minutes.

After cooling the rotating drum, the test piece was taken out and cut, and the erosion amount (mm) and the slag penetration depth (m
m) was measured at each part of the test piece, and the average value was determined.
The ratio of the amount of erosion in each example when the amount of erosion in Example 18 was 100 was calculated as the corrosion resistance index. A small corrosion resistance index indicates that the corrosion resistance is good.

Mass increase rate (%) in digestion resistance test:
Gakushin Method 7 "Drugite Clinker Digestibility Test Method"
The rate of mass increase (%) after holding at 134 ° C. in a 3 atm autoclave for 2 hours was measured. The digestion resistance is better as the mass increase rate is smaller.

[0049]

[Table 1]

[0050]

[Table 2]

[0051]

[Table 3]

[0052]

[Table 4]

[0053]

The refractory molded article according to the present invention has an improved interparticle bond by adding sodium aluminate and sorbitol to a refractory composition containing spinel particles, dolomite particles, and molten zirconia particles containing a glass phase. Since a reactant such as a composite spinel is generated at an extremely low temperature, there is little change in strength and excellent strength characteristics, and furthermore, it has excellent corrosion resistance, slag penetration resistance, and spalling resistance, so that it can be used for a long time. Since the molded refractory does not contain chromium, there is no possibility of causing environmental pollution. Therefore, this molded refractory can replace the chromium-based refractory used in the waste melting furnace and the like.

Claims (9)

[Claims] (1) To 100 parts by mass of a refractory composition, sodium aluminate is added at a ratio of 0.5 to 3.5 parts by mass in terms of NaAlO ₂ and sorbitol is added at a ratio of 0.1 to 1.3 parts by mass. Molded refractory, comprising in the refractory composition, spinel particles, dolomite particles and molten zirconia particles containing a glass phase, the total content of spinel particles and dolomite particles in the refractory composition is 80 to A molded refractory having a content of 96% by mass and 4 to 20% by mass of molten zirconia particles containing a glass phase. However, in the above description, the spinel particles include MgAl ₂ O ₄ crystals, the particles contain 23 to 60% by mass of MgO component, and the MgO component and Al ₂ O ₃
A particle having a total amount of 95% by mass or more. 2. The molded refractory according to claim 1, wherein the content of the glass phase in the molten zirconia particles is 3 to 25% by mass. 3. The molded refractory according to claim 1, wherein the molten zirconia particles contain monoclinic ZrO ₂ crystals. 4. The content of spinel particles in the molded refractory is 2
The molded refractory according to claim 1, 2 or 3, wherein the content is 5 to 55% by mass. 5. A molded refractory according to claim 1, comprising spinel particles having a particle diameter of less than 1.19 mm. 6. The molded refractory according to claim 1, comprising dolomite particles having a particle diameter of 1.19 mm or more and less than 5 mm. 7. The composition according to claim 1, further comprising 0.1 to 1 part by mass of an antidigestion agent in 100 parts by mass of the refractory composition.
7. The molded refractory according to any one of items 6 to 6. 8. The molded refractory according to claim 1, wherein the molded refractory is an unfired molded refractory. 9. A waste melting furnace using the molded refractory according to claim 1 for at least a part of a furnace wall.