JP2000191363A - Spalling resistant spinel brick - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spinel brick which is excellent in spalling resistance, hardly generates structural degradation even in long term use and is used for cement rotary kiln or lime firing kiln. SOLUTION: A special spinel raw material is prepared by blending magnesia fine powder and alumina fine powder to have a chemical composition of 30-90 wt.% MgO and 10-70 wt.% Al2O3, kneading, molding and drying or further firing the blended material at <=1500 deg.C. The special spinel raw material is added externally by 1-20 wt.% into a blended material having 50-90 wt.% magnesia clinker and 10-50 wt.% spinel clinker as aggregate and the spinel brick is obtained by kneading and molding the blended material and, after that, firing at a high temperature. The stress caused by thermal shock is mitigated scince the spinel brick forms gap around the special spinel raw material by using the special spinel raw material. As a result, thermal spalling resistance is improved and the spinel brick is suitable for a lining material for the cement rotary kiln or the lime firing kiln especially requiring excellent thermal spalling resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spinel brick having excellent spalling resistance used for lining a cement kiln, a lime kiln and the like, and a method for producing the same.

[0002]

2. Description of the Related Art In a rotary kiln for sintering cement clinker, an atmosphere temperature of a sintering zone is 1700-1800 ° C.
This is the most severe, and is subject to abrupt temperature changes accompanying the reaction between the cement raw material and the refractory and the attachment and detachment of the coating. Conventionally, magnesia
Chrome bricks have been used, but after the advent of rotary kilns with suspension pre-heaters, as the kilns became larger, the inner part of the sintering zone was heavily attached and detached from the coating, leading to deterioration of the structure of magnesia-chrome bricks,
Increased brick wear has led to problems in sustaining long-term operation of the kiln.

In addition, it has been found that magnesia-chromic bricks used in recent years show hexavalent chromium which elutes in water, and from the viewpoint of preventing pollution, special disposal is required. There is also a problem that it is necessary to take into consideration, and disposal is costly.

[0004] For that reason, magnesia-spinel brick began to be used from around 1976, and the usage ratio increased rapidly. Magnesia-spinel bricks, unlike magnesia-chromium bricks, do not contain iron oxide, so there is no expansion or shrinkage due to transformation of iron oxide, so that wear due to so-called thermal fatigue is reduced, which is advantageous in terms of durability.

[0005] In addition, since chromium is not contained as in the case of magnesia-chromic brick, there is no need to consider generation of hexavalent chromium, and there is an advantage that no extra disposal cost is required for disposal. is there.

However, the spalling resistance is low due to the high coefficient of thermal expansion, and the thermal conductivity of magnesia-chromium brick is higher, which is disadvantageous in terms of energy saving and improvement is desired. As an improvement measure, magnesia and magnesia-alumina spinel are used as the main aggregate, and carbon or carbon and glassy raw materials are blended to suppress alkali penetration and improve spalling resistance, and zirconia and iron oxide are added. A refractory having improved spalling resistance and stable coating adhesion is disclosed. (For example, Japanese Patent Publication No. 60-34513 and Japanese Patent Application Laid-Open No. Hei 1-305850)

[0007]

However, carbon not only oxidizes during use and causes weakening of the structure, but also raises the thermal conductivity of the brick, which is a problem from the viewpoint of energy saving in recent years.

[0008] The addition of iron oxide causes transformation of the iron oxide due to an oxidizing or reducing atmosphere during use, and when used for a long period of time, causes brittleness of the brick structure and causes a reduction in the service life of the brick. In addition, the addition of zirconia also causes microcracks in the structure and improves the spalling resistance, so that the microcracks are grown over a long period of use, leading to a reduction in service life.

On the other hand, the addition of SiO ₂ or a vitreous raw material is likely to be selectively present in the matrix portion of the brick, so that it easily reacts with cement clinker or the like during use to form a low-melt material. However, even if the addition of these impurities is small, the life of the brick may be shortened.

It is an object of the present invention to provide a refractory brick which solves these problems, has excellent spalling resistance, and hardly causes tissue deterioration even when used for a long period of time.

[0011]

According to the present invention, it has been found that the above object can be achieved by preparing a special spinel material and adjusting the porosity of the spinel material.

That is, 30 to 90% by weight of MgO, A
l ₂ O ₃ 10 to 70 by blending weight% of magnesia fine powder and alumina fine powder so that the chemical composition, kneading them, molding, drying or dried and baked at 1500 ° C. or less, special spinel raw material This special spinel material is used in a composition containing 50 to 90% by weight of magnesia clinker and 10 to 50% by weight of spinel clinker as an aggregate.
２０20% by weight, and these compounds are kneaded,
After molding, high-temperature sintering is performed to obtain spinel brick.

[0013]

In the present invention, the special spinel material is MgO 3
0-90 wt%, Al ₂ O ₃ 10 to 70 wt% of the chemical composition and so as kneading a material obtained by mixing magnesia fine powder and alumina fine powder, molding, obtained by drying, or, dried, 1500 ° C. or less It is obtained by calcining with
This raw material selectively shrinks when the refractory brick is fired, and creates voids inside the brick. The voids can relieve the stress generated when a temperature change is applied, and a refractory brick with improved heat spalling resistance can be obtained.

The porosity of the special spinel material is 10 to 40%.
If it is less than 10%, shrinkage during firing of the brick is small, voids formed in the brick are reduced, stress when a temperature change is applied is difficult to relax, and spalling resistance is poor. In addition, the porosity of the special spinel material is 4
If the amount exceeds 0%, the aggregate is not sintered as sufficiently dense particles due to sintering at the time of manufacturing the spinel brick, so that the corrosion resistance and the alkali permeation resistance are inferior and the durability is reduced.

Accordingly, it is necessary to mix magnesia and alumina, which are the raw materials of the special spinel raw material, with fine powders in order to facilitate spinel formation, and it depends on the press forming pressure during forming and the firing temperature during calcination. Rate 10-40
% In order to easily obtain a special spinel material
It is preferable to set it to 0.090 mm or less.

Further, by mixing the magnesia fine powder and the alumina fine powder, performing wet kneading, adjusting the granules in advance by a spray drying method or the like, and pressing the granules, a more uniform special spinel material can be obtained. .

The amount of the special spinel material thus obtained during the production of the brick is preferably 1 to 20% by weight on the outside, and if it is less than 1%, the amount of voids formed inside the brick during the firing of the brick is reduced. And the effect is not seen.

On the other hand, if the content exceeds 20%, the voids formed inside the brick become too large, resulting in poor corrosion resistance, alkali penetration resistance and abrasion resistance.

Since the particle size of the special spinel raw material varies depending on the amount of addition, it cannot be said unconditionally. However, it is most effective to add the material in an amount of about 5.0 to 0.5 mm. Each void is too large, corrosion resistance,
It causes a decrease in alkali penetration resistance and abrasion resistance. On the other hand, if it is less than 0.5 mm, each void is too small, and the void is easily lost by sintering during brick firing, resulting in poor spoiling resistance.

As the magnesia clinker to be mixed with the brick, any of seawater clinker, sintered clinker and electrofused clinker may be used, but one having a high purity of 99% or more of MgO is used for corrosion resistance. It is preferable from the point of view.

On the other hand, for spinel clinker, M
gO content of 30 to 90% by weight, Al ₂ O ₃ content of 10 to
It is preferable to use a 70% by weight sintered or electrofused clinker that does not contain impurities such as SiO ₂ .

[0022]

The following examples are provided to further clarify the features of the present invention.

First, magnesia fine powder and alumina fine powder having the chemical compositions shown in Table 1 were mixed at the mixing ratio (% by weight) shown in Table 2, added with binder, kneaded, formed by a hydraulic press, dried, Calcination was performed at each temperature to obtain a special spinel material. Table 2 shows the properties of the obtained special spinel raw material. The linear change rate (%) after firing at 1750 ° C. was obtained by examining the linear change rate when the special spinel material subjected to the calcination treatment was fired again at 1750 ° C. In this example, the binder was multivalent. Although an alcohol-based binder was used, the binder is not particularly limited thereto, and various binders such as an aqueous binder and a phenol resin-based binder can be used.

[0024]

[Table 1]

[Table 2] Table 3 shows the chemical compositions of the magnesia clinker and spinel clinker used in this example and comparative examples.

[0025]

[Table 3] Example 2 Table 2 The special spinel raw materials shown in Comparative Examples and the various clinkers shown in Table 3 were blended in the blending ratios (% by weight) shown in Table 4, a binder was added, and after kneading with a fret mill, the mixture was subjected to a friction press. It was pressed into a refractory brick of normal shape.

After appropriately drying the obtained molded body, firing was carried out in a tunnel kiln at 1750 ° C. for 7 hours to obtain a test brick. Using the test brick thus obtained, Table 4
The physical properties and characteristics shown in were evaluated. Test items and measurement methods are as follows.

Bulk specific gravity, apparent porosity: Measured according to a method for measuring the apparent porosity, water absorption and specific gravity of refractory bricks (based on JIS R 2205).

Compressive strength: Measured according to the test method for compressive strength of refractory bricks (based on JIS R 2206).

Spalling resistance test: A 55 × 55 × 230 mm prismatic test piece was cut out from the test brick and placed in an electric furnace having one surface kept at 1400 ° C.
Hold for 5 minutes. Then, the sample was taken out of the furnace and subjected to forced air cooling at room temperature for 15 minutes to repeat a thermal shock by a heating-cooling cycle, which was evaluated by the number of thermal shocks until spalling. The spalling resistance was determined to be better when the number of thermal shocks before spalling was large.

[0030]

[Table 4] Examples 1 to 5 in Table 2 are special spinel raw materials within the scope of the present invention. The reheat shrinkage when fired again at 1750 ° C. is as large as 5 to 12%, and when spinel brick is added during production, voids are easily formed during firing. Comparative Example 1 has a higher magnesia weight percentage than the special spinel raw material of the present invention and a reheat shrinkage rate of 1750 ° C. as small as 1%. The conductivity is not improved, and the effect of adding the special spinel material is not seen. Therefore, the weight percentage of magnesia contained in the special spinel material is preferably set to 90% or less.

Comparative Example 2 has a higher alumina content than the special spinel material of the present invention. As shown in Comparative Example 8, when the special spinel material is used, the special spinel material during firing at 1750 ° C. Because alumina reacts with magnesia clinker and expands, sintering of the brick does not occur, there are many fire cracks, loose bricks of the structure, poor spalling resistance and corrosion resistance, so alumina contained in special spinel Is preferably not more than 70% by weight.

In Comparative Example 3, the effect of calcining at a higher temperature than the special spinel material of the present invention was examined. The shrinkage during calcination was large, and the shrinkage when reheated at 1750 ° C. Small, the shrinkage of the special spinel material during spinel brick firing is small, voids are not easily formed in the brick,
No improvement in the ringing property is observed, and no effect obtained by adding the special spinel raw material is observed. Therefore, the calcination temperature of the special spinel raw material is preferably set to 1500 ° C. or less.

As shown in Comparative Examples 4 and 5, the amount of the special spinel material added is preferably 1 to 20% by weight, and if less than 1%, the effect cannot be obtained, and more than 20%. In some cases, the compressive strength is reduced, and the corrosion resistance, the alkali permeation resistance and the like are poor.

In Examples 5 to 10 of Table 4 using the special spinel raw materials of the present invention shown in Examples 1 and 2 of Table 2, the spalling resistance is improved.

[0035]

By using the special spinel raw material as described above, pores are distributed in the spinel brick brick of the present invention, and the stress due to thermal shock is reduced. As a result, the heat-resistant spalling is improved, and it is particularly suitable for a lining material of a cement rotary kiln requiring excellent heat-resistant spalling.

Claims (2)

[Claims] 1. A spinel brick used for lining of a cement rotary kiln, a lime burning kiln, etc., comprising 50 to 90% by weight of a magnesia clinker and 10 to 50% by weight of a spinel clinker as aggregates.
Chemical composition MgO 30 to 90% by weight, and Al ₂ O ₃ 10 to 70 wt%, a porosity of 10 to 40% of the special spinel material
A spinel brick characterized by adding 1 to 20% by weight, kneading, molding and firing at a high temperature to form voids around a special spinel material. 2. MgO 30-90% by weight, Al ₂ O ₃ 10-70
Magnesia fine powder and alumina fine powder are blended so as to contain by weight, kneaded, molded and dried.
The method for producing a special spinel raw material according to claim 1, wherein the method is obtained by firing at 1500 ° C or lower.