JPH061654A - Manufacture of calcia clinker - Google Patents

Abstract

PURPOSE:To manufacture calcined calcia clinker superior in hydration resistance and at a low cost by using a lime stone as a raw material. CONSTITUTION:The size of a crystal of a carbonate constituting the lime stone is <=64mum and the lime stone is pulverized at the size <=150mum and the obtained powder is molded and then the calcia clinker is produced by calcining the molded product at the temp. >=1500 deg.C. At this time, TiO2, ZrO2, Al2O3, CaF2, MgF2 or their mixture can be added to the lime stone powder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing calcia clinker as a raw material for producing refractory materials such as bricks and crucibles for refining metals and alloys, mainly iron and steel.

[0002]

2. Description of the Related Art Calcia has a basic property, a high melting point of about 2600 ° C., a low oxygen dissociation pressure, a high thermal conductivity, etc. It is equipped with Currently, most of the calcia products that take advantage of such properties are obtained by adjusting the particle size of calcia clinker, molding and firing (sintering), and most of the calcia clinker used in this case is It is a melt. Further, a method for obtaining a crucible or the like by calcining calcium carbonate after adjusting the particle size of calcium carbonate without using a calcia clinker and then firing it is disclosed in JP-A-1-290554, but a calcia product obtained by this method is However, it has a weakness against thermal shock, and the method of molding and firing calcia clinker is the main cause. However, as described above, most of the calcia clinker has a disadvantage that the cost is high because the melt is used. In addition, calcia clinker by firing was also considered to reduce costs, but since calcia is originally very hydrated by moisture in the air, etc. It is currently not used. In order to improve the hydration resistance of calcia clinker by this firing, the present inventors have filed Japanese Patent Application No. 2512/1990.
No. 18 (JP-A-4-130046) proposes a method of forming and firing calcium carbonate having a particle size or crystallite size of 0.3 μm or less, and crushing limestone into submicron particles or limestone. It was necessary to hydrate the calcined quicklime and then use as a raw material the calcium carbonate synthesized by blowing carbon dioxide gas. Therefore, further cost reductions have been made, research has been conducted to promote industrialization, and the present invention has been completed.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to produce an inexpensive calcined calcia clinker excellent in hydration resistance by using limestone as a raw material.

[0004]

According to the present invention, the crystal size of the carbonate constituting the raw material limestone is 64 μm (fine crystallinity).
It is limited to the following, and it is characterized in that the particle size is adjusted to 150 μm or less according to the molding means, and after molding, it is baked at 1500 ° C. or higher. The term "fine crystallinity" as used herein means a scale of crystal diameters shown in Table 1. The present invention also provides a method for producing a calcia clinker in which the addition of a small amount of auxiliary agent that does not affect the subsequent steps is sufficient and the hydration resistance is improved.

[0005]

[Table 1]

[0006]

[Operation] Generally, when manufacturing a sintered body close to the theoretical density,
It is known that it is better to reduce the particle size of the raw material powder, but when the present inventors form a limestone powder and fire it to produce a lime sintered body, when it does not depend on the particle size of the limestone powder. I found that there is. As a result of further experiments,
When limestone is fired as a lump, the smaller the size of the crystal of the carbonate forming the limestone (hereinafter abbreviated as the crystal diameter of limestone), the larger the bulk specific gravity of the sintered body. Considering that the crystal size of limestone is the particle size of powder, this is consistent with the fact that the smaller the particle size, the higher the density of the sintered body.
As shown in the table, there is no significant difference in the minor constituents of limestone among the limestones, so the crystal size of limestone is considered to be the most important factor. If limestone having a small crystal diameter of limestone is left as a lump, and crushed to a size of 150 μm or less and fired under the same conditions, the bulk specific gravity is almost the same, but a lump obtained by firing as a lump The aggregate has many cracks, the apparent surface area increases, and the hydration resistance is poor.
Therefore, it is necessary to carry out operations such as crushing and molding in order to prevent cracks from occurring by allowing the molded product to have appropriate voids and absorbing the strain due to shrinkage during firing from the voids, and not to increase the apparent surface area. The crushing is a balance between the apparatus conditions such as the molding method and the crushing method, and the conditions for forming a molded product having a uniform and appropriate void so as not to cause the cost and cracks, but it is about 150 μm or less. Is good. When an auxiliary agent is added, it may be added at the same time during pulverization or mixed with limestone powder obtained by pulverization with a mixer, a ball mill or the like, but in this case, the smaller the particle size of the powder is,
A smaller amount has an effect on hydration resistance, and it is desirable that the amount be about 40 μm or less.

The limestone powder obtained within the scope of the present invention can be molded by a general molding method such as press molding or extrusion molding, and a binder can be used if necessary. Unless a binder containing an alkali metal or a halide is used as the binder, the bulk specific gravity of the sintered body does not increase, and the hydration resistance may decrease. The molding density is 1.1 g / when the molded body is allowed to stand and is baked.
There is no problem if the bulk specific gravity is cm ³ or more, but in the case of a rotary kiln or the like where the compact and the refractory rub against each other, the bulk specific gravity of 1.5 g / cm ³ or more may be used. desirable.

The molded body thus obtained is then fired at a temperature of 1500 ° C. or higher. The decomposition pressure of calcium carbonate reaches about 1 atm at about 900 ° C, so if it is fired at a temperature higher than this, it becomes a lime sinter, but the hydration resistance as a calcia clinker that is a raw material for refractory is improved. 15 to have
A temperature of 00 ° C or higher is required.

[0009]

Example 1 Medium limestone A, fine crystalline limestone B, and microcrystalline limestone C were prepared as raw material limestone. When the fracture surface of each limestone was observed with a scanning electron microscope, the crystal diameters of limestones A, B, and C were 130 μm and 38, respectively.
μm and 5.0 μm. Limestones A, B and C are crushed with a lump of about 35 mm each and a hammer crusher to 150
The powder was classified by μm, and the powder was used as a disc-shaped compact at a pressure of 500 kg / cm ² using a mold having a diameter of 40 mm. Then, the lump and the molded body are set to 1300, 1500, 18
It was baked at 50 ° C. for 3 hours. The temperature of the obtained sintered body is 30 ° C.
The rate of increase in weight when left for 120 hours in saturated vapor pressure was defined as the water absorption rate. Table 2 shows the chemical analysis values of each limestone.
Table 3 shows the bulk specific gravity and water absorption of the sintered body at each temperature.

From Table 3, the smaller the crystal size of limestone, the more lumps,
Both the compact and the sintered body have a large bulk specific gravity and are excellent in hydration resistance. Further, when the crystal diameter is more than medium crystallinity, the bulk specific gravity of the sintered body is remarkably reduced, and the hydration resistance is poor.

When the lumps are fired as they are, the specific gravity of the limestone increases and the difference between the limestone and the compact becomes smaller, but the amount of cracks also increases, so that the specific gravity of the limestone increases and water absorption is increased. The rate is high.

[0012]

[Table 2]

[Table 3]

[0013]

Example 2 0.05, 0.5, 5% by weight of ferric dioxide as a reagent was added to the powders of limestone A and C used in Example 1 and mixed to obtain a sample having a diameter of 40 mm. Molded into a disc at a pressure of 500 kg / cm ² and a temperature of 1500 ° C for 3
Burned for hours. The rate of weight increase when the obtained sintered body was left for 120 hours in a saturated vapor pressure at a temperature of 30 ° C. was taken as the water absorption rate. Table 4 shows the bulk specific gravity and water absorption of each sintered body.

From Table 4, limestone A does not show much effect by adding a small amount of ferric dioxide, but limestone C has a great effect on increasing the bulk specific gravity and decreasing the water absorption. When the amount of ferric dioxide added is increased to about 5%, the limestone A also shows an increase in the bulk density and a decrease in the water absorption rate, but it is considered that addition of more than this causes a decrease in the melting point and the like and cannot maintain the performance as a clinker. To be

[0015]

[Table 4]

[0016]

EFFECTS OF THE INVENTION Calcia refractory, which has not been popularized due to its high cost because of the use of melted calcia clinker as a raw material, even though it has been evaluated as excellent in metal refining, etc. By providing a calcined calcia clinker excellent in hydration resistance at low cost by the method of the present invention, the price of the refractory material is also lowered, and by replacement or sharing with the magnesia refractory material which is currently the mainstream of basic refractory materials, more An excellent metal refining system can be built.

Claims (2)

[Claims] 1. A crystal obtained by crushing the limestone to 150 μm or less after molding the powder, which has an average crystal size of carbonate constituting the limestone of 64 μm (fine crystallinity) or less, and 1500 A method for producing a calcia clinker, which comprises firing at a temperature of ℃ or higher. 2. The limestone powder according to claim 1, wherein SiO ₂ ,
TiO ₂ , ZrO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , CaF
₂ , metal oxides such as MgF ₂ and salts alone or 2
A method for producing a calcia clinker, which comprises adding at least 0.05-5% by weight of a mixture or compound in terms of lime, followed by molding and firing at 1500 ° C or higher.