JP3368365B2 - Composition for artificial lightweight aggregate and method for producing artificial lightweight aggregate - Google Patents

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 an artificial lightweight aggregate using coal ash.

[0002]

2. Description of the Related Art Consumption of coal has increased with the recent diversification of energy sources. Therefore, the amount of coal ash generated tends to increase, but most of it is discarded as landfill.

In this regard, attempts have been made to use coal ash as a raw material for the production of artificial lightweight aggregates, and some sintered artificial lightweight aggregates have already been put to practical use. However, it is difficult to reduce the weight of the artificial lightweight aggregate, and the specific gravity is at most about 1.4. On the other hand, PC boards and the like used in recent high-rise buildings are required to have higher lightness as they become super-high-rise.

On the other hand, the foam-type artificial lightweight aggregate has a problem that the granules are fused to each other due to melting and vitrification of the surface of the granule in the foaming process, but it is a sintered type. It is superior in that it can be made more lightweight than Therefore, in order to obtain a foam-type artificial lightweight aggregate using coal ash, various methods have been proposed for preventing fusion of the granules.

For example, there is a method of preventing the fusion of the granules by spraying fine powder of silica stone which is high-purity silica and coating the surface of the granules with silica during the production. There is also a method of forming a granulated product having a two-layer structure made of a high melting point substance such as alumina (Japanese Patent Laid-Open No. 4-238845).
issue).

However, when the granulated product having these coating layers is fired by a rotary kiln or the like, the components of the coating layer become fine powder and are mixed into the granulated product due to abrasion between the granulated products, After firing, it becomes necessary to select this. Moreover, since these wear components are completely different from the aggregate components, it is difficult to reuse them, and as a result, a large amount of waste is discharged. Furthermore, high-purity silica used as a coating layer,
Alumina and the like are relatively expensive, so the advantage of using waste materials such as coal ash cannot be fully utilized.

As described above, it is not easy to use waste coal ash as an artificial lightweight aggregate, but on the other hand, there is a strong demand for the development of a utilization technique from the viewpoint of effective use of resources and environmental protection. There is.

[0008]

SUMMARY OF THE INVENTION Therefore, the main object of the present invention is to provide an artificial lightweight aggregate that exhibits excellent lightness and low water absorption by using coal ash.

[0009]

The inventors of the present invention have conducted extensive studies in view of the above-mentioned problems of the prior art, and as a result, the inner core portion of the granulated product containing coal ash as the main component is defined as the outermost shell layer. When firing a granulated product formed of fine powder having the same composition and finer than the outermost shell layer, the characteristics of coal ash, which has been considered to be a defect in the past, are used in reverse. The present invention has been completed by finding that the inner core portion can be preferentially foamed to promote weight reduction while suppressing or preventing fusion.

That is, the present invention relates to the following composition for artificial lightweight aggregate and a method for producing the artificial lightweight aggregate.

1. It is composed of an outermost shell layer containing coal ash powder as a main component and an inner core containing coal ash powder as a main component, and
An artificial lightweight aggregate characterized by comprising a granulated product having a ratio of the average particle size of the powder forming the inner core portion to the average particle size of the powder forming the outermost shell layer is 50% or less. Composition.

2. In a method of manufacturing an artificial lightweight aggregate mainly composed of coal ash, (i) is composed of an outermost shell layer containing coal ash powder as a main component and an inner core part containing coal ash powder as a main component, And (ii) the ratio of the average particle size of the powder forming the inner core portion to the average particle size of the powder forming the outermost shell layer is 5
A method for producing an artificial lightweight aggregate, which comprises firing a granulated product of 0% or less.

The present invention will be described below. As a raw material used as the inner core portion and the outermost shell layer of the granulated product in the present invention, coal ash produced by combustion of coal or the like can be used. In this case, impurities such as unburned carbon may be contained within a range that does not adversely affect the effects of the present invention. If necessary, a crushed material such as shale or a powder such as bentonite may be mixed and used.

The particle shape of coal ash can be any shape such as a large number of spherical particles or particles having a shape close to a spherical shape, a hollow structure, or coarse particles in which a large number of fine spherical particles are incorporated in the hollow portion. Things can be used.
However, since the coal ash having a hollow structure retains air in the hollow portion, it enhances the heat insulating property of each particle and increases the resistance to heat. Therefore, it is preferable for the powder forming the inner core portion to reduce the number of coarse particles having a hollow structure as much as possible in terms of weight reduction.

The average particle size of the powder forming the outermost shell layer is usually about 15 to 150 μm, preferably 25 to 100 μm.
And If it is less than 15 μm, the granules may be fused to each other during firing. When it exceeds 150 μm, not only is the firing not sufficiently performed, but it is difficult to form the outermost shell layer at the time of granulation because the cohesive force of the powder is small, and moreover, it is easy to wear during firing, which is not preferable.

Further, the particle diameter of the powder is 0.1 μm.
It is preferable to contain less than ultrafine powder as much as possible. Therefore, as the coal ash used as the outermost shell layer, the raw powder is usually used as it is, but if only the coarse powder is separated and used as the outermost shell layer without destroying the powder, it will It is possible to increase resistance and prevent fusion more effectively.

Further, in the present invention, pulp waste liquid or the like can be used as a binder, if necessary, in order to enhance the cohesive force of the powder. The amount of the binder used is usually about 0.1 to 5% by weight based on the powder.

The average particle size of the powder forming the inner core of the granulated product of the present invention is 50 times the average particle size of the powder forming the outermost shell layer.
% Or less, preferably 10 to 40%. further,
It is preferable that the powder does not include coarse powder having a particle size of more than 75 μm. An artificial lightweight aggregate is obtained by firing the granulated material at the maximum temperature (hereinafter referred to as "heat resistant temperature") at which the powder forming the outermost shell layer does not soften and melt to cause fusion in the above average particle diameter. If the inner core portion is made of fine powder having an average particle diameter of 50% or less at the time of production, only the inner core portion can be softened and melted and foamed without the granulated product being fused. On the other hand, when the average particle size exceeds 50%, it is not preferable because the inner core cannot be sufficiently softened, melted and foamed by heating up to the heat resistant temperature of the outermost shell layer which prevents fusion.

The powder for forming the inner core portion may be prepared by pulverizing the raw powder in a conventional manner. In this case, the classification method,
Although it can be carried out by a crushing method or the like, it is preferable to use the crushing method in the present invention because the influence of breaking the hollow structure of the particles on the thermal properties becomes larger.

Next, the granulation in the present invention will be described. The basic granulation method in the present invention is a two-step method in which the particles to be the inner core are first granulated, then the outermost shell layer is formed thereon, and the particles are molded into a predetermined particle size, or firing. A method of spraying the powder forming the outermost shell layer can be adopted at times, but in the present invention, the two-step method is preferable. The case of using the two-step method will be described below.

First, fine particles of coal ash are used to granulate the particles to form the inner core. For the granulation method, the method conventionally used for the granulation of coal ash, etc. can be applied as it is. Can be granulated. The particle size of the particles to be the inner core is the sum of the thickness of the outermost shell layer and finally falls within the particle size range of 20 to 5 mm or 15 to 5 mm which is the standard value of JIS A 5002 for aggregates. To be
That is, the volume increase due to foaming (usually about 1.1 to 1.9 times) and the outermost shell layer may be appropriately set depending on the thickness and the like.

Next, the outermost shell layer is formed on the obtained granulated product. The thickness of the outermost shell layer is usually about 0.2 to 3 mm, preferably 0.3 to 1 mm, though it depends on the size of the inner core portion. If it is less than 0.2 mm, not only the effect of preventing fusion is not sufficient, but it also becomes difficult to form a layer having a uniform thickness during granulation. Further, when it exceeds 3 mm, heat transfer to the inner core portion during firing becomes insufficient,
The inner core cannot reach the firing temperature and cannot be foamed. As a result, a large amount of dust is generated due to wear of the outermost shell layer during firing, and more water is absorbed by the outermost shell layer after firing, which leads to an increase in the water absorption rate of the aggregate, or abrasion resistance. As a result, the characteristics as an aggregate are deteriorated.

Subsequently, the granulated product obtained above is fired. The firing temperature is usually about 1100-1350 ° C, preferably 1150-1300 ° C. When the temperature is lower than 1100 ° C, the inner core does not foam, the weight cannot be sufficiently reduced, and the outermost shell is insufficiently sintered, so that the aggregate has a high water absorption rate and is easily worn. Become. If it exceeds 1350 ° C, the powder forming the outermost shell may be melted and fused, which is not preferable. The firing atmosphere may be usually an oxidizing atmosphere.

As the firing method, known firing methods such as a rotary kiln method and a sinter strand method can be adopted. However, in the firing method in which the granules pass through the firing zone in a static state such as the sinter-strand method, the granules are in contact with each other in a laminated state, and a load is applied to the granules in the lower layer. Since it is always in a restrained state, even a granulated product having an outermost shell layer (anti-fusion layer) may not fully exhibit the anti-fusion effect at the time of foaming. On the other hand, the rotary kiln method causes some abrasion within the kiln of the fusion preventing layer of the outermost shell layer of the granulated product, but if the thickness of the fusion preventing layer of the outermost shell layer is adjusted during granulation, Since there is no problem of fusion and the granules can be fired without being restrained, it is a suitable method for weight reduction and prevention of fusion due to foaming.

[0025]

In general, the powder becomes easier to be heated as it becomes smaller and the surface area becomes larger. Therefore, softening and melting proceed easily, but coal ash is more greatly affected by the difference in particle size than general powder due to its unique particle structure. That is, if the particle size of coal ash is adjusted by crushing or the like and the particle size is reduced to a specific level, the resistance to heat is reduced compared to the raw powder, the melting point is greatly reduced, and the sintering is performed.
There are significant differences in softening, melting and foaming temperatures. For this reason, the particles of the raw material powder of the inner core of the granulated product are made small, a layer made of particles coarser than the inner core is formed in the outermost shell layer, and the firing is performed at the foaming temperature of the raw material powder of the inner core. For example, due to the difference in resistance to heat due to the difference in particle size, softening, melting and foaming precede in the inner core, and the weight of the fired product can be reduced. On the other hand, the coarse particles forming the outermost shell layer stop at the sintering stage at the same temperature, and can prevent fusion of the granulated substances without melting.

[0026]

The composition for artificial lightweight aggregate of the present invention has a structure in which the granulated product is composed of the specific outermost shell layer and the inner core. Then, according to the manufacturing method of the present invention in which the granulated product is fired, it is possible to promote melting and foaming of the granulated product while avoiding fusion between the granulated products,
It is possible to provide an artificial lightweight aggregate having particularly excellent lightness and low water absorption.

The artificial lightweight aggregate according to the present invention is particularly useful for applications such as PC boards for high-rise buildings, heat insulating materials and soundproofing materials.

[0028]

EXAMPLES Examples and comparative examples will be shown below to further clarify the features of the present invention.

Examples 1 to 3 Coal ash raw powder having a residual uncarbon amount of 8.2% and an average particle size of 33.4 μm was used as a raw material powder for the outermost shell layer, and the raw powder was pulverized and shown in Table 1. Granules having the outermost shell layer shown in Table 1 were obtained by using the fine powder adjusted to the average particle diameter for the inner core portion and performing the granulation by the two-step granulation method using the pan type pelletizer. Next, these were fired at 1200 ° C. to manufacture an artificial lightweight aggregate. The characteristics of the obtained aggregate are shown in Table 1.

[0030]

[Table 1]

Comparative Examples 1 to 6 The same coal ash raw powder as in Example 1 was used, and this was classified to give a powder for an inner core having a particle size ratio of 50 with respect to the average particle size of the raw material powder of the outermost shell layer. The content was adjusted so as to fall within the range of -100%, and granulated in the same manner as in Example 1 to obtain the granulated product shown in Table 1. Then, the artificial lightweight aggregate was manufactured by baking at 1200 ° C and 1250 ° C, respectively. The properties of the obtained aggregate are shown in Table 2.

[0032]

[Table 2]

Examples 4 to 10 As shown in Table 3, the particle diameter of the powder of the inner core portion was made constant, and the particle diameter of the outermost shell layer was changed within the range of the particle diameter ratio of 50% or less.

The same coal ash raw powder as in Example 1 was used. In Examples 4 to 7, crushed powder was used, and Examples 8 to 1 were used.
In No. 0, it was used as it was and the inner core was granulated. As the powder for the outermost shell layer serving as the anti-fusing layer, the same raw powder as in Example 1 was classified, and four types of coarse powder thereof were taken as Examples 4 to 7 and obtained from coal ash of different lots. Three types of powder having a small particle size were used as Examples 8 to 10, respectively. The granulation method and the thickness of the fusion preventing layer of the granulated product were the same as in Example 1.

Next, the obtained granules were fired. In Examples 4 to 7, the outermost shell layer has a heat resistant temperature of 120.
It was fired at 0 ° C., and in Examples 8 to 10, it was the heat resistant temperature of the outermost shell layer and the foaming temperature of the powder forming the inner core portion.
It was baked at 50 ° C. Table 3 shows the properties of the obtained aggregate.

[0036]

[Table 3]

Comparative Examples 7 to 14 The same coal ash powder as in Example 2 was classified to obtain fine powder, which was used as the powder for the inner core of Comparative Examples 7 to 10 and the raw powder was used as it is in Comparative Examples 11 to 14. Was used as the powder for the inner core. In addition, as the powder for the anti-fusing layer, the above raw material powder was used in a particle size ratio of 5
What was adjusted to fall within the range of 3 to 84% was used. The granulation method and the thickness of the fusion preventing layer were the same as in Example 1.

After granulation, firing was carried out at 1200 ° C. which is the heat resistant temperature of the fusion preventing layer in Comparative Examples 7 to 10 and 1250 ° C. which is the foaming temperature of the powder of the inner core portion in Comparative Examples 11 to 14. The properties of the obtained fired product are shown in Table 4.

[0039]

[Table 4]

Examples 11 to 18 The same coal ash powder as in Example 1 was used as the powder for the outermost shell layer, and the raw powder was crushed to obtain two kinds of fine powders as shown in Table 5 for the inner core portion. Of powder. Using these, a granulated product was manufactured by the same granulation method as in Example 1. Then, it was fired at 1200 ° C. which is the heat resistant temperature of the fusion preventing layer. Table 5 shows the properties of the obtained aggregate.

[0041]

[Table 5]

Comparative Examples 15 to 18 Granules having the same particle size ratio as that of Example 3,
Comparative Examples 15 to 18, which are granulated products as shown in Table 6 having an average thickness of the outermost shell layer of 3.5 mm or more, were manufactured by the same granulation method as in Example 1. Then, it was fired at 1200 ° C. which is the heat resistant temperature of the fusion preventing layer. Table 6 shows the properties of the obtained aggregate.

[0043]

[Table 6]

As described above, even if the granulated product composed of the outermost shell layer and the inner core portion is used, it is outside the scope of the present invention.
It can be seen that the aggregate 18 has a large specific gravity even if fusion occurs during firing, or even if it can be fired, and has a high water absorption rate, which is still insufficient as an artificial lightweight aggregate. On the other hand, according to the method of the present invention in which a granulated product composed of a specific outermost shell layer and an inner core is fired, there is no fusion and the like, and an artificial lightweight aggregate excellent in lightweightness and low water absorption is provided. It can be seen that

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Nobuyuki Inumaru, No. 2 No. 1 North Building, No. 221 Uchiage, Neyagawa City, Osaka Prefecture, No. 508 (72) Inventor Mitsuhiro Ishii No. 2239-1, Yamadashita, Ayagami-cho, Ayaka-gun, Kagawa Prefecture (72) ) Inventor Takuo Nojiri 4-16-22 Yamanouchi, Sumiyoshi-ku, Osaka-shi, Osaka (72) Inventor Hiroshi Murai 698-5 Mitsui, Tadotsu-cho, Nakatado-gun, Kagawa (72) Yoshikatsu Nishino Osaka-Sayama-shi, Osaka Ikejiri 1-27-19 (56) References JP-A-5-229858 (JP, A) JP-A-4-238845 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) ) C04B 18/08 C04B 18/10 C04B 14/02 C04B 20/10

Claims (4)

(57) [Claims] 1. An average particle of a powder comprising an outermost shell layer containing coal ash powder as a main component and an inner core portion containing coal ash powder as a main component, and forming the outermost shell layer. A composition for artificial lightweight aggregates, comprising a granulated product having a ratio of the average particle diameter of the powder forming the inner core portion to the diameter of 50% or less. 2. The ratio of the average particle diameter of the powder forming the inner core portion to the average particle diameter of the powder forming the outermost shell layer is 10 to 4.
It is 0%, The composition for artificial lightweight aggregates of Claim 1. 3. The composition for artificial lightweight aggregate according to claim 1, wherein the outermost shell layer has a thickness of 0.2 to 3 mm. 4. A method for producing an artificial lightweight aggregate mainly composed of coal ash, comprising: (i) an outermost shell layer mainly composed of coal ash powder and an inner core part mainly composed of coal ash powder. And (ii) a granulated product having a ratio of the average particle size of the powder forming the inner core portion to the average particle size of the powder forming the outermost shell layer is 50% or less. A method for producing an artificial lightweight aggregate characterized by firing.