JPH07232942A - Production of artificial lightweight aggregate - Google Patents

Abstract

PURPOSE:To produce lightweight artificial aggregate having the absolute dry sp. gr. equal to or lower than the absolute dry sp. gr. of shale. CONSTITUTION:The coal ashes from a hopper 1 and the crushed cavity forming materials from a hopper 2 are kneaded together with water 3' in a mixing machine 3 and the mixture is pelletized by a pan type pelletizing machine 4. The resulted pellet nuclei are charged into a pan type pelletizing machine 6 where the kneaded matter of the coal ashes and water sent from the kneading machine 16 is coated and two-layered pellets are formed. The two-layered pellets obtd. in such a manner are charged together with the calcined pellets supplied from a hopper 8' for charging bedding pellets into calcination furnace 9 isolated from the atm. These pellets are calcined under the regulated concn. of O2 in the calcination furnace, by which the lightweight artificial aggregate is obtd.

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 artificial lightweight aggregate applied to lightweight concrete aggregate from coal ash.

[0002]

2. Description of the Related Art As a part of effective utilization technology of coal ash discharged from a coal-fired boiler, a method of manufacturing an artificial lightweight aggregate applied to aggregate of lightweight concrete has been proposed.
The manufacturing method of artificial lightweight aggregate using coal ash is to mix water with a mixture of coal ash and clay, granulate raw pellets with a particle size of 5 to 20 mm using a pan-type pelletizer, and sinter this. To produce product aggregates. At this time, since the absolute dry specific gravity of the sintered product is important, the porosity of the sintered product is increased by increasing the coarse powder mixing ratio of the coal ash to reduce the weight.

For example, according to JP-A-62-256746, the Blaine specific surface area is 2000 to 3800 cm ² / g.
The weight ratio of the coarse powder to the raw material is 60% or more, and the absolute dry specific gravity of the obtained sintered product is 1.27 to 1.43.
It is reported that.

[0004]

The artificial lightweight aggregate (coarse aggregate) is specified in JISA5002, and the absolute dry specific gravity, which is an index for weight reduction, is set to 1.0 to 1.5 for M type. There is. However, currently, the main artificial lightweight aggregates on the market are made from shale, and their absolute dry specific gravity is 1.25 to 1.25.
Since it is 1.35, the artificial lightweight aggregate manufactured from coal ash is required to have the same quality as that of shale, and especially the absolute dry specific gravity is emphasized.

The artificial lightweight aggregate made from shale is manufactured by utilizing the phenomenon that organic substances inside the shale burn and foam when heated externally. On the other hand, when coal ash is used as the raw material, there is no foaming of the coal ash itself, and the weight is reduced due to the disappearance of unburned carbon content and physical voids.

Therefore, even if an artificial lightweight aggregate is produced by the conventional method, a shale equivalent to shale is used unless coarse ash having a specific gravity of about 1.4 and a Blaine specific surface area of about 2000 cm ² / g is used. It is extremely difficult to obtain. The present invention has been made in view of the above circumstances, and provides a method for producing an artificial lightweight aggregate having an absolute dry specific gravity equal to or less than that of shale even when using coal ash as a raw material. It is an issue.

[0007]

In order to solve the above problems, in the method for producing an artificial lightweight aggregate according to the present invention, a cavity forming material or a mixture of a cavity forming material and coal ash is used as a granulation nucleus, and Coal ash is coated on the surface of the granulation nucleus to form a two-layer granulated product,
The method of firing the granulated product is adopted.

In the conventional method, the Blaine specific surface area is 3500 cm.
Clay as a binder was added to the coal ash of about ² / g at 2% by weight based on the coal ash, and the mixture was granulated while pouring water, and then the O ₂ concentration in the firing atmosphere was controlled. About 1100
Although the artificial lightweight aggregate was manufactured by firing at 0 ° C., the absolute dry specific gravity of the obtained artificial lightweight aggregate was about 1.4.

Therefore, in the present invention, in order to reduce the specific gravity of the sintered product, a cavity forming material that burns during firing as described above is used, and the cavity forming material or a mixture of this cavity forming material and coal ash is granulated as a core. Then, a method was adopted in which coal ash was coated as a pellet layer on the surface of the granulation core to form a two-layer granulated product, and this was sintered. As a result, the absolute dry specific gravity of the granulated product can be easily adjusted by changing the particle size ratio of the granulated nucleus / granulated product.

In the method for producing an artificial lightweight aggregate according to the present invention, crushed paper, crushed chaff or sawdust can be used as the cavity forming material of the granulation nucleus. It is preferable that the crushed paper, sawdust, and chaff that form the cavity-forming material be crushed into smaller pieces (usually 5 mm or less) than the granulation nuclei by a crusher or the like.

As the crushed paper, cardboard, newsprint, magazines, other used paper, or recycled paper such as recycled pulp can be used. Further, sawdust is scraps obtained by sawing wood and can usually be used as it is as a granulation nucleus. On the other hand, chaff is a hard skin that appears when brown rice is used, but since it has poor granulation properties, it is crushed before use. In addition to the above materials, the cavity forming material is not limited as long as it is combustible, and may be, for example, dead grass.

In this way, the granulated product is composed of coal ash and the cavity forming material, and the unburned carbon in the coal ash and the cavity forming material are fired, so that the natural material is burned and the natural sintering is performed. A granular sinter is obtained.

The sintering temperature is the temperature at which the maximum shrinkage rate is judged from the high temperature characteristic curve of coal ash shown in FIG.
A region of 100 to 200 ° C. lower than 80 ° C. is appropriate. The structure of the sintered product sintered in this temperature range has a large cavity because the cavity forming material, which is a combustible substance in the granulation nucleus, burns and disappears.

As the coal ash for coating used in the method for producing an artificial lightweight aggregate according to the present invention, it is preferable to use coal ash having a Blaine specific surface area of 4000 cm ² / g or more. When such a coating coal ash is used, the pellet layer around the cavity formed as described above has a specific surface area of 4000
Since it will be covered with fine coal ash of cm ² / g or more,
By firing the granules coated with this fine powder of coal ash having a low porosity, it is possible to manufacture a lightweight aggregate having a significantly low water absorption rate. As a result, this sintered product can sufficiently satisfy the physical property values as an artificial lightweight aggregate.

In the present invention, when firing the two-layer granulated product, the two-layer granulated product is laminated on the grate of the firing furnace which is isolated from the atmosphere, and the natural product contained in the granulated product is laminated. It is preferable to perform firing while controlling the oxygen concentration according to the amount.
By firing in such a controlled manner, an appropriate combustion temperature can be maintained, so that an artificial lightweight aggregate having excellent physical properties can be obtained.

[0016]

EXAMPLES The present invention will be specifically described below based on examples. An embodiment of the present invention will be described with reference to FIG. 1,
Reference numeral 2 denotes a hopper for accommodating the coal ash and the crushed product of the cavity forming material, and the crushed product of the cavity forming material from the hopper 2 and, if necessary, the coal ash from the hopper 1 to the kneading machine 3. It was obtained by pouring water 3 ′ into the kneading machine 3 to knead the crushed product of the cavity-forming material or a mixture of the crushed product of the cavity-forming material and coal ash, and granulating this with the pan-type granulator 4. The granulation nuclei are transported by a belt conveyor 5 and put into a pan-type granulator 6 for coating a pellet layer.

On the other hand, the coal ash from the hopper 1'is kneader 16
The kneaded product is supplied to the kneading machine 16 and is kneaded by pouring water 16 ′ into the kneading machine 16 and is introduced into the pan-type granulator 6 and is kneaded on the surface of the granulation nucleus transported by the belt conveyor 5. A two-layer granulated product obtained by coating the product with two-stage granulation is obtained, and the two-layer granulated product is stored in the hopper 8 for raw pellets.

Reference numeral 8'denotes a bedding bed pellet loading hopper containing a burned product (fired pellets). The pellets are fed from the hopper 8'and the raw pellet loading hopper 8 to a firing furnace 9 isolated from the atmosphere. .

Reference numeral 9'denotes a moving grade of the firing furnace 9,
1 is a suction box 10 provided below the grate 9 '
And 17 is a blower for introducing air to adjust the O ₂ concentration in the firing atmosphere. Reference numeral 14 is a bucket conveyor that sends the pellets fired in the firing furnace 9 to the product recovery hopper 15.

The gas in the firing furnace 9 sucked by the blower 11 is circulated into the firing furnace 9. Again 1
Reference numeral 2 is an ignition device for the firing furnace 9 such as an LPG burner, and 13 is a partition plate of the firing furnace 9. Table 1 shows the properties of the coal ash used in this example. The Blaine specific surface area is 3500 cm ² / g (average viscosity: 25 μm) and 4000 cm ² / g (5 μm).
It is a kind. The finely crushed paper is used by crushing newsprint and passing through a screen of 2 mmφ.

[0021]

[Table 1]

Coal ash is put into a hopper 1 and finely pulverized paper is put into a hopper 2, and these are weighed so as to be a target granulation nucleus raw material and supplied to a kneading machine 3, where 40 to 50 parts by weight of water 3'is supplied. %, And the mixture is kneaded and then granulated by the pan-type granulator 4 via the belt conveyor 5 to the pan-type granulator 6 to coat the pellet layer on the surface of the granulation nucleus.

From the hopper 1 ', coal ash is weighed and supplied to the kneading machine 16 so as to be a target pellet layer raw material,
The kneaded product obtained by adding about 17% by weight of water 16 ′ to the kneaded product is sent to the pan-type granulator 6, where the granulation nucleus is coated with the kneaded product in a two-stage granulation process. A layer granulate is obtained.

The obtained two-layer granulated product is fed from the raw pellet feeding hopper 8 and the fired pellets from the floor laying pellet feeding hopper 8'to the firing furnace 9 which is isolated from the atmosphere at the same time. 2 through drying, ignition, sintering and cooling process
Sintering of the layer granulation is performed. In this sintering, the sintered pellets are put in advance on the Great 9'and spread to a thickness of 30 mm to form a bedding, and then the granules are loaded on it and stacked to a thickness of 200 mm.

Then, while suctioning from the suction box 10 below the grate 9'at a pressure of 30 mmH ₂ O, 300 to 50
After drying with hot air at 0 ° C. for about 10 minutes, the surface layer of the granulated product is ignited by the igniter 12 (ignition temperature 1000 to 1200 ° C.).
In the firing area of the firing furnace 9, the gas amount is 1000 to 1500 Nm ³ / h,
An artificial lightweight aggregate is obtained by controlling the O ₂ concentration to 4 to 13% and sintering for 30 to 60 minutes. The O ₂ concentration is controlled according to the amount of natural substances (unburned carbon in coal ash, finely pulverized paper) contained in the granulated product.

The firing test results using the apparatus shown in FIG. 1 are as follows. In addition, Ag.Loss of aggregate physical properties, absolute dry specific gravity,
The water absorption rate and the crush strength were evaluated according to JIS standards. Table 2
Shows the influence of the blending ratio of finely pulverized paper on the granulation nuclei in coal ash A and B.

[0027]

[Table 2]

The result of the main firing test is a case where the particle size ratio of the granulation nucleus / granulated product is 0.7, and the absolute dry specific gravity is remarkably decreased as the amount of the finely pulverized paper of the granulation nucleus is increased. In the case of 100% crushed paper, it is 1.10 to 1.16. However, although the water absorption rate exceeds the target value when the coal ash A is used, the water absorption rate of the coal ash B is a remarkably low value of about 4.0%. Table 3 shows the effects of the amount of gas at the calcination inlet, the concentration of O ₂ at the calcination inlet, and the calcination temperature in coal ash B.

[0029]

[Table 3]

As a result of the main calcination, the calcination inlet gas amount was 1300.
Nm ³ / h is appropriate. However, in the following 1000 Nm ³ / h it becomes green by shortage gas, at 1500 Nm ³ / h or more fused to sinter is generated by the gas volume overload, resulting in loss of shape.

The firing inlet O ₂ concentration of 8 to 10% is appropriate. However, when it was 4% or less, it was unfired due to lack of O ₂ concentration, and when it was 13% or more, fusion occurred in the sintered product due to excessive O ₂ concentration, and the shape collapsed.

The appropriate firing temperature is 1100 to 1200 ° C. However, at 1000 ° C. or lower, the firing temperature was low, so that it was not fired. At 1300 ° C. or higher, the firing temperature was too high, and fusion occurred in the sintered product, causing the shape to collapse. Table 4 shows the influence of the particle size ratio of the granulation nucleus / granulated product by coal ash B.

[0033]

[Table 4]

The particle size ratio satisfying the physical properties of the aggregate is 0.5
It was found to be ~ 0.7. However, when the particle size ratio is 0.3, the absolute dry specific gravity exceeds the standard value,
In the case of 8, the crush strength did not satisfy the target value.

From the above firing test results, the firing conditions of the two-layer granulated product in which the pellet layer is coated on the granulation nucleus in this example are as follows. (1) The compounding ratio of coal ash / paper to the granulation nucleus is 0 to 70/10
0 to 30. (2) The coal ash in the pellet layer covering the granulation core has a Blaine specific surface area of 4000 cm ² / g or more. (3) The particle size ratio of the granulation nucleus / granulated product is 0.5 to 0.7. (4) By controlling the amount of gas at the calcination inlet to 1300 Nm ³ / h and controlling the concentration of O ₂ at the calcination inlet to 8 to 10%, the calcination temperature becomes 1100 to 1200 ° C., and the range of calcination conditions is very narrow. ₂ Controlled furnace is suitable.

The physical properties of the sintered product obtained under the above firing conditions are: absolute dry specific gravity of 1.10 to 1.35 and water absorption of 3.5 to.
The crushing strength was 5.0% and 70 to 110 kg / piece. In addition, a firing test was also conducted on a two-layer granulated product in which the granulation nuclei of sawdust and chaff were made into a pellet layer with coal ash B, but it was confirmed that a sintered product approximately equivalent to the above-mentioned firing test result was obtained. confirmed.

[0037]

According to the present invention, as described above, the cavity forming material (waste paper, sawdust, crushed pieces of chaff, etc.) or the mixture of the cavity forming material and coal ash is used as the granulation nucleus, and the surface layer thereof is formed. Preferably, a sintered product obtained by sintering a two-layer granulated product coated with coal ash having a Blaine specific surface area of 4000 cm ² / g or more is completely dry specific gravity of 1.10 to 1.3 which is sufficiently satisfactory as an artificial lightweight aggregate.
5, it has a physical property of water absorption of 3.5 to 5.0%. This physical property is shale (absolute dry density 1.25 to 1.35, water absorption of 7 to 13).
%).

The above-mentioned physical property values can be set to desired values by changing the particle size ratio of the granulation nucleus / granulated product. Furthermore, by stacking the two-layer granulated product on the grate of a firing furnace isolated from the atmosphere and controlling the oxygen concentration according to the amount of natural substances contained in the granulated product and firing, the excellent physical properties are obtained. An artificial lightweight aggregate can be manufactured.

[Brief description of drawings]

FIG. 1 is a system diagram of an artificial lightweight aggregate manufacturing apparatus for explaining an embodiment of the present invention.

FIG. 2 is a graph showing the high temperature characteristics of coal ash.

[Explanation of symbols]

 1,1 ', 2 Hopper 3 Kneader 3'Water 4 Bread type granulator 5 Belt conveyor 6 Bread type granulator 8 Raw pellet feeding hopper 8'Food bed pellet feeding hopper 9 Baking furnace 9'Great 10 Suction Box 11 Blower 12 Ignition device 13 Partition plate 14 Bucket conveyor 15 Product recovery hopper 16 Kneading machine 16 'Water 17 Blower

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C04B 18/08 A 38/06 G B09B 3/00 303 L

Claims (4)

[Claims] 1. A cavity-forming material or a mixture of a cavity-forming material and coal ash is used as a granulation nucleus, and the surface of the granulation nucleus is coated with coal ash to form a two-layer granulated material, and the granulated material is fired. A method for producing an artificial lightweight aggregate characterized by the following. 2. Crushed paper as a cavity forming material for the granulation nucleus,
The method for producing an artificial lightweight aggregate according to claim 1, wherein at least one of crushed chaff and sawdust is used. 3. The method for producing an artificial lightweight aggregate according to claim 1, wherein coal ash having a Blaine specific surface area of 4000 cm ² / g or more is used as the coating coal ash. 4. The two-layer granulated product is laminated on a grate of a firing furnace isolated from the atmosphere, and is fired while controlling the oxygen concentration according to the amount of natural substances contained in the granulated product. The method for producing an artificial lightweight aggregate according to any one of claims 1 to 3.