JPH0717418B2 - Manufacturing method of artificial lightweight aggregate - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

TECHNICAL FIELD The present invention relates to a method for producing artificial lightweight aggregate by adding fly ash to the waste mud generated when the sand is washed with water, kneading and granulating, and drying and firing the granulated product.

[Prior art]

Aggregates for concrete are required to be clean and must not contain harmful substances such as dust, clay, silt and organic substances. Since these substances significantly reduce the strength of concrete, when manufacturing aggregate for concrete from natural mountain sand, if it is not fired, wash it with water so that the aggregate does not contain dust, mud, organic matter, etc. Is obligatory. Waste mud generated when the sand is washed with water (hereinafter referred to as mud, most of which is silt) has a very small particle size (most of which is 5μ to 74μ) and has a water content ratio. 90 ~
It is a soft substance that contains a large amount of 100% water. Therefore, if the mud is directly landfilled, there is a problem that the disposal site will remain soft and the ground will not harden, hindering the effective use of the land. In order to effectively use the landfill site, the drainage of the landfill site is promoted by the sand drain method, etc. to consolidate the ground, and the surface layer is mixed with a solidifying material such as cement or lime to an appropriate depth to remove the soil. After increasing the strength, a method such as further covering with a thick layer using gravel or mountain soil is performed. However, even with such a method, it takes a long time for the ground at the disposal site to harden and harden, so in recent years, cement and lime have been mixed with mud to improve the strength of mud and landfill, and A method of dewatering and then landfilling is also being considered. As described above, the conventional mud treatment method is intended to stabilize the soil quality by using the solidifying agent. However, in order to dispose of a large amount of mud, a disposal site that accepts it is necessary. In addition to mud, solidification agents and new mountain soil for covering the surface layer are added, so the disposal site is a vast land. Had to be. As described above, the mud generated when the natural mountain sand is washed with water has many problems in disposal due to its nature. On the other hand, a large amount of fly ash generated from lime thermal power plants and lime boilers is partly used for fly ash cement, but most of it is landfilled.
However, from the current state of landfills in Japan, it is clear that the situation of accepting these large amounts of mud and fly ash as they are will be tight in the near future. Conventionally, as a method of manufacturing a lightweight aggregate using fly ash, for example, there are methods described in Japanese Patent Publication Nos. 38-25820 and 39-11234. In the former method, a clay slurry or pulp waste liquid is dripped into fine coal ash (fly ash) in a granulator to obtain spherical granules, which are 1100-1500.
Sintering at ℃ causes volatilization of moisture inside to generate pores. Also, the latter method, after dropping the slurry clay into the fly ash and granulating it, heat it in a rotary kiln to make ferrous oxide in the fly ash ferric oxide, and with the oxygen generated at that time. Foam. During the foaming and firing, the particles and the melting surfaces of the particles may adhere to each other. Therefore, the inorganic material powder having a relatively high melting point is adhered to the surface in the kiln to prevent the caking of the granulated material.

[Problems to be Solved by the Invention]

However, as in the latter method of the related art, even if the high melting point inorganic powder is separately coated to prevent caking of the granulated material in the foaming and firing step, the granulation step in the previous step is performed. If a large amount of water is included, the water will float on the surface of the granulated product, and due to the water on the surface of the granulated product, the granulated products will adhere to each other before they are put into the kiln. Cause a decrease in This becomes even larger than the clay slurry when the kneaded product with fly ash becomes the mud content (silt content) containing a large amount of water as described above. Therefore, an object of the present invention is to provide granulated materials even if the mud content kneaded with fly ash and granulated contains a large amount of water such as waste mud generated when the sand is washed with water. It is possible to accurately prevent the adherence of granules, and thus improve the yield, sphericity, work efficiency, etc. of the granulated product, and also to obtain an artificial aggregate with high performance such as water absorption and crushing strength as a product. Especially.

[Means for Solving the Problems]

Since the water content of mud (silt) is usually 90 to 100%, dehydration treatment is performed. As the dehydration method, a natural dehydration method of leaving it in an indoor soil, a mechanical dehydration method using a filter press, a dehydration method using waste heat from an incinerator or the like is selected depending on the situation. When using the mud stored in the mud disposal pit, the water content varies depending on the layer height of the pit, so the extracted mud should be thoroughly mixed with a shovel in the soil to make the water content uniform. It is necessary to plan.
The water content of mud is reduced to 30-40% by dewatering. Mix the dewatered mud and fly ash and knead thoroughly with a kneader. A part of the kneaded raw material is dried using waste heat from an incinerator or the like, and pulverized by a ball mill or the like to obtain a dry powder (dry powder). The amount of fly ash is 99 to 20% of the total weight. The kneaded mixture of raw materials is first mixed with added water by using a pan-type granulator and the like.
It is added so as to coat the surface of the compounded raw material from the part c in FIG. Generally JIS A
Target the granularity specified in 5002. Since most of the mud and fly ash used as raw materials are fine particles, the amount of added water and the position of addition, the angle and rotation speed of the granulator, and the feed amount and feed position of the raw material are adjusted without using a binder. Granules are possible. When the pan type granulator 1 shown in FIG. 1 is used for granulation, it is preferable to add the kneading raw material from the part a and add the added water to the part b. The reason for coating dry powder of the same raw material in the granulation process is not only to improve the granulation property, sphericity, yield, etc. at the time of granulation, but also to improve the performance such as water absorption and crush strength of the product. Is. When this dry powder coating operation is performed, the amount of fly ash mixed is allowed to be 99 to 20%, which also has the advantage of increasing the degree of freedom in selecting raw materials. When granulation is performed using a pan type granulator, a product having a large particle size or a small particle size distribution is generated in the product. Therefore, use 20 mm and 5 mm sieves to satisfy the JIS standard.
Remove 5 mm above and 5 mm below. The removed material is returned to the kneading step again and used as a part of the raw material. Since the granulated product has a water content of 50 to 60%, if the baking in the next step is performed as it is, bursting will occur due to rapid water evaporation, so it is necessary to perform drying in advance. Next, the granulated product is fired at a high temperature of about 1200 ° C. using a firing device such as a rotary kiln. When firing is carried out at a high temperature, unburned carbon content in fly ash and organic matter in the mud content are burned and gasified, so that it is possible to manufacture a lightweight aggregate with many pores.

[Action]

The action and effect of each step of the method for producing an artificial lightweight aggregate of the present invention will be described in detail below. Mud dewatering process: The mud generated by washing with sand and sand has a water content of 90 to 100% as described above, so handling such as transportation is impossible as it is. Therefore, it is left in the indoor soil for natural dehydration, or mechanical dehydration using a filter press or dry dehydration using waste heat. The water content of mud is reduced to 30-40% by dehydration. If it is less than 30%, it will be too dry and the mud will be in the form of dumplings. Mixing process and dry powder manufacturing process: Dehydrated mud and fly ash equivalent to 99 to 20% of the total amount are simultaneously charged into a kneader such as a roller mixer,
Mix and knead thoroughly. Since the degree of kneading greatly affects the granulation property, it is necessary to perform sufficient kneading. The kneaded product can be directly subjected to the next granulation step, but as described above, a part of the kneaded product is incinerated using a dryer for the purpose of improving the granulation property or increasing the granulation speed. It is dried using waste heat from a furnace and finely pulverized by a pulverizer such as a ball mill to produce a dry powder. This dry powder is used as a coating material for the granulated product in the next step. Granulation step: The kneaded product is granulated using a pan-type granulator or the like so as to have a particle size specified in JIS A 5002. As mentioned above, most of the blended raw materials are fine powders, so it is not necessary to use a binder, and the amount of added water and addition position, the angle and rotation speed of the granulator, and the feed amount and feed position of the raw material can be adjusted appropriately. Granules are possible. When a pan-type granulator is used for granulation, it is preferable that the kneading raw material is introduced from part a in FIG. 1 and the added water is added in part b. In addition, the above-mentioned dry powder is added to FIG.
When the granules are added so as to coat the surface of the granulated product, the coating is accurately performed. Granules use 20 mm and 5 mm sieves to meet JIS standards,
Remove 20mm up and 5mm down. The removed material is returned to the kneading step again and used as a part of the raw material to improve the economical efficiency. It is more preferable to add sieves of 15 mm and 10 mm and adjust the particle size appropriately. Drying process: The formed granulated product is dried to such an extent that the granulated products are not fused to each other in the firing process and the granulated product is not collapsed by bursting due to rapid water evaporation. For drying, waste heat from an incinerator or the like may be used, or waste heat or residual heat from a firing furnace in the next step may be used. Firing step: The dried granulated material is fired using a firing furnace such as a rotary kiln, and the optimum firing temperature at this time is 1150 ± 100 ° C. By this firing, the granulated product is sintered (fused) to obtain a granular solidified product. Since mud contains organic matter and fly ash contains unburned carbon, the surface of the sintered solidified product foams when organic matter and unburned carbon burn and gasify. And become porous. However, firing temperature 10
When the temperature is lower than 50 ° C, unburned carbon remains inside the solidified product after firing, and the foamability is low and the standard as a lightweight aggregate is not satisfied. On the other hand, when the firing temperature is higher than 1250 ° C, the solidified products are more likely to be sintered, and the solidified products may be fused or partially collapsed. The solidified product obtained by the above method is insoluble in water,
Since it is porous, it has a low specific gravity and high strength, so it sufficiently satisfies the standard as a lightweight concrete aggregate for structure. To summarize the features of the present invention, in the present invention, a part of the kneading raw material of fly ash and the mud content (silt content) is dried and pulverized into a predetermined dry powder on the surface of the kneading raw material during the granulation step. By adding from a position and coating (for example, the ratio of kneading raw material: dry powder is 9 to 1), the moisture emerging on the surface of the kneading raw material (granulated product) is instantly absorbed by the dry powder, and Prevents deterioration of yield, sphericity and work efficiency due to adhesion. As a result, the performance of the product such as water absorption and crush strength can be improved. The effect of coating with dry powder of the same raw material can be exhibited because both fly ash and silt have excellent water absorption properties, and other dust (for example, ore powder or dust containing a large amount of iron) can be used. Even if added to the surface of the granulated product, the water absorption of the dust is inferior due to fly ash and silt, so that the water on the surface of the granulated product cannot be absorbed, and the same effect cannot be expected. Also, on the surface of the kneading raw material of fly ash and silt,
Even if only fly ash plain or silt plain is added, the granulation property is improved, but satisfactory product specific gravity and crush strength cannot be obtained. That is, as in the present invention, as long as the dry powder obtained by drying and crushing the kneading raw material is not added to the surface of the kneading raw material of fly ash and silt, an artificial lightweight sufficiently satisfying the specific gravity and crushing strength of JIS standard M type. No aggregate can be obtained.

【Example】

Next, examples of the present invention will be described. In the production test of the artificial lightweight aggregate by the method of the present invention, Table-
The mud generated by washing with sand sand having the composition shown in 1 and the fly ash having the composition shown in Table 2 were used. Mud dewatering step and mixing and kneading step: The mud generated by washing with sand and sand with a water content of 95% was naturally dehydrated in the indoor soil to a water content of 35%. Next, the fly ash and the dehydrated mud were put into a roller mixer and kneaded for 10 minutes. Experiments were carried out by changing the mixing ratio of mud and fly ash as shown in Table-3. Dry powder manufacturing process: A part of each blended raw material was dried using a drier, and then pulverized by a ball mill to manufacture a dry powder, which was used as a coating material in the granulated product in the next step. Granulation step: The kneaded material and the dry powder are granulated at the kneading raw material feeding position a, the water addition position b and the dry powder addition position c by the pan type granulator 1 shown in FIG. The following two methods were performed, and the water content of the granules was 50 to 60%. In addition,
In FIG. 1, 2 is a side scraper, 3 is a product discharge port, and the broken line shows the trajectory of the granulated product. (A) Only the kneaded product was granulated for the samples No. 1 to No. 5 in Table-3. (B) After granulating the kneaded product, it was coated with dry powder The feed ratio of the kneaded product and dry powder was 9: 1 by weight. The target was the samples No. 1 to No. 4 in Table-3 and their dry powders. The granulator specifications at this time are as follows. Bread diameter: 900 mm, Bread depth: 150 mm, Bread angle: 52 °, Bread rotation speed: 16 rpm, Blended raw material supply rate: 200 kg / h Adapted to the type of aggregate specified in JIS for the obtained granules Therefore, using 20mm and 5mm sieve, more than 20mm and 5mm
The following granules were cut and only the intermediate was used in the next step. Drying process: The various granulated products obtained by the granulation methods (a) and (b) are set to a furnace temperature of 400 ° C. using an electric furnace, and a drying time is provided for 4 to 5 minutes to obtain a water content ratio of each. Of less than 5%. Firing process: Each dried granulation product obtained in the drying process is heated in a silicon furnace in order to simulate only the firing zone in the furnace.
The temperature was set to 1200 ± 50 ° C. and the firing time was set to 2 to 3 minutes to perform firing. When the surface of the granulated product became a semi-molten state, and at the same time gas was generated inside to form bubbles, and the softened whole expanded, the granulated calcined product was taken out from the calcining zone and air-cooled. The fired granulated product thus obtained was a foam whose surface was covered with a hard shell and which contained a large amount of fine closed cells. The results of the specific gravity test and the crushing strength test performed on the fired granulated product obtained by performing each of the above operations are described below. Table 6 shows the results of absolute dry specific gravity measurement for the granulated and fired product with only the mud content due to the change in the particle size composition. As shown in Table 6 and FIG.
In the medium grain size, the specific gravity standard was not passed as coarse aggregate for classification by aggregate dry specific gravity of JIS A 5002 shown in Table 4 as artificial lightweight aggregate for structure. Therefore, the specific gravity was measured by changing the grain size composition within the standard from the medium grain size to the coarse grain side, but there was no big difference, and it was found that the specific gravity was not affected by the change in the grain size composition ratio. Next, the same test as described above was performed on the granulated and fired product mixed with fly ash according to the method of the present invention. The results are shown in Table 7 and FIG. Further, FIG. 4 shows the relationship between the fly ash mixing ratio and the crush strength of the fired granulated product. As can be seen from the results, the particle size composition satisfies the JIS standard intermediate particle size shown in Table 5, and in the granulated and baked product without the addition of dry powder, the fly ash mixing ratio is 30% or more, and in the dry powder-coated granulated and baked product, Fly ash mix ratio of 20% or more each
It can be seen that the product satisfies JIS standard M class sufficiently. Also,
It can be seen that the crush strength is also a value that can be sufficiently satisfied. That is, compared with the case where dry powder is not added, the fly ash mixing ratio is increased by about 10%, and the degree of freedom in selecting raw materials is improved. From the above results, it is impossible to produce an artificial lightweight aggregate satisfying the JIS standard only with the mud generated when the mountain sand is washed with water, but an artificial produced by mixing fly ash by the method of the present invention. The lightweight aggregate sufficiently satisfies the JIS standard.

【The invention's effect】

As described above, according to the method of the present invention, a coal thermal power generation that has a problem in securing a landfill site and mud generated when the natural mountain sand that has been conventionally problematic in landfill disposal is washed with water. It is possible to manufacture artificial lightweight aggregates that meet JIS standards by performing simple process operations such as dehydration, mixing and kneading, partial dry pulverization, granulation, and firing of fly ash generated at power plants. It is possible to effectively utilize the landfill and alleviate the problem of securing landfill sites. Further, the yield, sphericity, work efficiency, etc. of the granulated product can be improved, and an artificial aggregate having high performance such as water absorption and crushing strength can be obtained as a product.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a positional relationship among a kneaded material feeding position, an added water addition position, and a dry powder addition position in the case of using a bread granulator in the granulation step of the present invention, and FIG. A graph showing the particle size distribution due to the change in the particle size composition of the granulated fired product using only the mud generated by washing with sand and sand, Fig. 3 is a graph showing the relationship between the fly ash mixing ratio and the absolute dry specific gravity, and Fig. 4 is It is a graph which shows the relationship between a fly ash mixing ratio and a crush strength.

Claims (2)

[Claims] 1. A step of dewatering waste mud generated when washing mountain sand with water, a step of mixing and kneading the dewatered mud and fly ash, and a part of the kneaded material is dried and pulverized. An artificial lightweight bone comprising a step of forming a dry powder, a step of granulating the kneaded product, a step of coating the surface of the granulated material with the dry powder, and a step of drying and firing the granulated material coated with the dry powder. Method of manufacturing wood. 2. A water content ratio of 90 to 10 generated when washing sand sand with water.
The method for producing an artificial lightweight aggregate according to claim 1, wherein 0% of the waste mud is dehydrated to a water content ratio of 30 to 40%.