JP2000335978A - Castable refractory material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a castable refractory material improved in spalling resistance without impairing its corrosion resistance by formulating a specific refractory aggregate, refractory ultrafine powder, alumina cement and dispersant. SOLUTION: This castable refractory material comprises 60-89 wt.% of a refractory aggregate adjusted in granular size, 10-25 wt.% of at least one kind of refractory ultrafine powder <=10 μm in particle size, 1-10 wt.% of alumina cement, and 0.01-1 wt.% of a dispersant, wherein at least a part of the refractory aggregate is alumina cement-bound alumina/chromia bats whose content is pref. 5-35 wt.% and whose characteristics are preferably as follows: granular size: 5-10 mm, apparent porosity: 5.0-15.0%: Cr2O3 content: >=10 wt.%, and CaO content: >=0.5-5.0 wt.%. The refractory aggregate is e.g. of fused alumina, magnesia clinker; the refractory ultrafine powder is e.g. of alumina, clay; and the dispersant is e.g. sodium hexametaphosphate, sodium pyrophosphate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chromia-containing low cement castable refractory suitable as a lining material for a furnace for melting and processing ash, sludge, refuse, and the like.

[0002]

2. Description of the Related Art Chromia-containing refractories are widely used as refractory materials for steel, glass melting or cement firing because of their excellent corrosion resistance to molten glass and slag. In recent years, refractories containing a relatively large amount of chromia have tended to be used in furnaces that melt ash, sludge, refuse, and the like. A refractory containing a large amount of chromia has excellent corrosion resistance, but has a drawback of poor spalling resistance. As a method for improving the spalling resistance of a chromia-containing refractory, zirconia is added (JP-A-8-4857).
4, Japanese Patent Publication No. 62-36987), addition of zircon (Japanese Patent Publication No. 62-36986), addition of condensed sodium phosphate and calcium carbonate (Japanese Patent Publication No. 62-19395), Cr ₂ O
Sintering of _3- Al ₂ O ₃ —ZrO ₂ —mineralizer system or utilization of electrofused aggregate (JP-A-3-174369) and addition of a coarse chromia angle (JP-A-6-293570) have been proposed.

[0003]

However, the conventional chromia-containing refractory has a high temperature rising or falling speed,
Moreover, when applied to a frequent furnace, sufficient durability cannot be obtained because of spalling.

An object of the present invention is to improve the spalling resistance of a chromia-containing low cement castable refractory excellent in corrosion resistance without impairing the corrosion resistance.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted various studies to improve the above-mentioned problems, and as a result, have found that it is effective to add a coarse angle of chromia bonded to alumina cement, and completed the present invention. I came to.

That is, the chromia-containing cement castable refractory of the present invention has a particle size adjusted to 65-89% by weight and a particle diameter of 10%, at least a part of which is an alumina-cement-bound alumina-chromia coarse angle.
at least one kind of refractory ultra-fine powder of less than μ, 10 to 25% by weight,
Alumina cement 1-10% by weight, dispersant 0.01-1
% By weight.

[0007]

The chromia-containing low cement castable of the present invention will be described in detail below.

[0008] The particle size of the alumina-cement-bound alumina-chromia coarse angle used in the present invention is not particularly limited.
The best one is about 10 to 5 m / m. At 5 m / m or less, the effect of improving corrosion resistance is great, but the effect of improving thermal shock resistance is small. On the other hand, when particles having a particle diameter of more than 10 m / m are used, the effect of improving thermal shock resistance is large, but the effect of improving corrosion resistance is small.

In the present invention, the addition amount of such alumina cement-bound alumina-chromia coarse angle is 5 to 35.
% By weight. If it is less than 5% by weight, there is little effect on both corrosion resistance and thermal shock resistance, and if it is more than 35% by weight, the corrosion resistance tends to decrease.

[0010] The coarse angle of alumina-chromia bonded to alumina cement used in the present invention can be adjusted, for example, by the following method. 10 to 92% by weight of alumina, 5 to 70% by weight of chromium oxide, 3 to 20% by weight of alumina cement
And 4 to 10% by weight of water are added to a total of 100% by weight and uniformly mixed to form a slurry, which is then poured into a mold to be molded. After curing, the mold is removed, and drying and firing are performed. Firing conditions are 1000-
At 1800 ° C. for 5 to 20 hours. After cooling, pulverize and sieve. It is also possible to replace a part of the alumina with an ultrafine powder material such as silica flour. When the viscosity of the slurry is reduced by adding a dispersant, a dense coarse angle is easily obtained. Table 1 shows an example of the characteristics of the alumina-chromia coarse angle used in the present invention.

[0011]

[Table 1]

Although the physical properties of the alumina-chromia coarse angle bonded with alumina cement vary depending on the chemical composition, the amount of water added, the firing temperature and the firing atmosphere, the apparent porosity is 5.0 to 15.
0% can be preferably used.

The Cr ₂ O ₃ content of the alumina-chromia coarse angle bonded with alumina cement is 5% by weight or more, preferably 10% by weight.
It is preferable that the content is not less than weight%. The use of alumina-cement-bound alumina-chromia coarse angle having a Cr ₂ O ₃ content of 5% by weight or less improves spalling resistance but is not preferable because corrosion resistance is greatly reduced.

The CaO content of the alumina-chromia coarse angle bonded with alumina cement is preferably 0.5 to 5.0%. C
If the aO content is 0.5% or less, there is no effect of improving the spalling resistance. If the aO content is 5.0% or more, a dense coarse angle cannot be obtained, leading to a decrease in corrosion resistance.

If the sintering temperature of the alumina cemented alumina / chromia coarse angle is less than 1000 ° C., the sintering is insufficient, so that the castables containing the same are deteriorated in corrosion resistance and at the same time, the fluidity of the castables is reduced by Ca ⁺⁺ ions eluted. There is also a problem that impairs. 1800 ° C
Firing at the above-mentioned high temperature is not suitable because it results in oversintering and high pulverization costs.

The refractory aggregate used in the present invention includes fused alumina or sintered alumina having an Al ₂ O ₃ content of 95% by weight or more, chromia coarse angle, magnesia clinker and picrochromite having an MgO content of 95% or more. , Electrofused magcroclinker, spinel clinker and the like can be used. In addition, raw materials such as bauxite, mullite, and zircon can be used, but the total SiO ₂ content in the castable refractory is 6%.
The amount must be limited so as to be less than% by weight. If the SiO ₂ content exceeds 6% by weight, the corrosion resistance to molten slag such as ash, sludge, and refuse decreases.

As the refractory ultrafine powder, alumina, chromium oxide, clay, silica flour and the like are preferable. By using particles having a small particle size of 10 μ or less, fluidity is improved and a dense construction body can be obtained.

The alumina cement preferably has an Al ₂ O ₃ content of 70% by weight or more. If the amount is less than 1% by weight, sufficient strength cannot be obtained. When the content is 10% by weight or more, the corrosion resistance of the castable is reduced.

The dispersant disperses the alumina cement and the refractory ultrafine powder to reduce the water and improve the fluidity of the castable refractory. For example, sodium hexametaphosphate, sodium tripolyphosphate, sodium pyrophosphate and the like are used. The amount of addition is 0.01 to 1% by weight on the outside.

As long as the above-mentioned properties are satisfied as the alumina-chromia coarse angle combined with alumina cement, alumina-chromia castable waste used in various plants can also be used. After removing the slag attached to the waste material, the slag is roughly crushed, baked at the above-mentioned temperature, and then crushed to adjust the particle size, whereby a required product can be obtained. In this case, firing in the presence of a reducing agent such as coke is a preferable method because the chromium component can be stabilized.

Hereinafter, embodiments of the present invention will be described.

[0022]

Examples All of the conventional examples, examples and comparative examples are shown in Table 2.
The raw materials shown in Table 3 were blended in the proportions shown in Table 3, 5 to 6% by weight of water was added, and the mixture was kneaded for 3 minutes.
Pour into a parallel test frame of × 114 × 230mm,
After curing at 20 ° C. for 24 hours, the frame was removed. 110 ° C x 2
The apparent porosity and the compressive strength of the dried specimen dried for 4 hours and the fired specimen fired at 1400 ° C. for 3 hours were measured. Table 3 also shows the physical property values. The measuring method of each physical property is as follows.

Thermal shock resistance: 65 × 114 × 230 m / m
A 65 × 114 mm surface of the parallel-shaped specimen was kept in an electric furnace maintained at 1400 ° C. for 15 minutes, and then taken out of the furnace and forcedly cooled for 15 minutes. Evaluation was made based on the number of work cycles up to spalling. The thermal shock resistance is better when the number of repetitions of the work cycle up to spalling is larger.

Erosion test: performed by the rotating drum method. Sample shape: 50 × 50 × 230 mm Slag: CaO 22.6%, SiO ₂ 44.1%, Al ₂ O ₃ 13.2%, MgO 2.7% Fe ₂ O ₃ 11. 7%, others 5.7% Temperature: Hold at 1650 ° C for 12 hours. The amount of erosion is shown assuming that the amount of erosion of Conventional Example 2 (containing 7% of chromium oxide) is 100. The smaller the numerical value of the amount of erosion, the smaller the erosion.

Apparent porosity: 65 × 114 × 230 mm parallel specimens were treated at each temperature and determined according to JISR2205.

Compressive strength: A specimen molded to a size of 65 × 114 × 230 mm was judged based on JISR2206.

[0027]

[Table 2]

[0028]

[Table 3]

[0029]

According to the present invention, the thermal shock resistance of the chromia-containing low-cement castable refractory can be improved without lowering the corrosion resistance, so that high durability can be expected even under severe operating conditions of an industrial waste melting furnace.

Claims (1)

[Claims] 1. A fire-resistant aggregate 60 to 8 having a grain size adjusted.
Chromia-containing low cement comprising 9% by weight, 10% to 30% by weight of at least one refractory ultrafine powder having a particle diameter of 10 μm or less, 1% to 10% by weight of alumina cement, and 0.01% to 1% by weight of dispersant. A low-cement castable refractory containing chromia, wherein at least a part of the refractory aggregate has an alumina-cement-bound alumina-chromia coarse angle.