JP2005104804A - Artificial aggregate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the lowering of the yield of good quality product by decreasing the wear of a molded/granulated material in the course of firing, widening a firing temperature range by the control of a liquid forming rate and adding aluminum ash to retard a liquid phase forming rate and prolonging the burning time of unburned carbon contained in coal ash to reduce the residual quantity of the unburned carbon to become a foaming source at a high temperature in a method of manufacturing artificial aggregate using coal ash having large variation of chemical/physical performance. <P>SOLUTION: The artificial aggregate is formed by heating and firing a molded body comprising coal ash, aluminum ash, cement and water. The coal ash is flyash discharged from a coal-fired powder plant and/or clinker ash. The artificial aggregate has a formulation of 27.5-62.5 pts.wt. SiO<SB>2</SB>, 35-55 pts.wt. Al<SB>2</SB>O<SB>3</SB>and 2.5-17.5 pts.wt. CaO as a chemical composition. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an artificial aggregate used for forming concrete and an artificial aggregate as a roadbed material, and more particularly to an artificial aggregate containing aluminum ash.

TECHNICAL FIELD The present invention relates to an artificial aggregate used for forming concrete and an artificial aggregate as a roadbed material, and contributes to the effective use of coal ash and its disposal is considered as a problem socially. It is possible to provide an artificial aggregate that can be used effectively. At thermal power plants that use pulverized coal as fuel, over 4 million tons of coal ash are produced as a by-product. When coal is burned as fuel in a boiler of a thermal power plant, a large amount of fly ash is generated as industrial waste. About half of them are effectively used in the construction of cement concrete, civil engineering, and ceramics. However, the amount of fly ash generated is steadily increasing year by year. From the standpoint of environmental conservation and effective use of resources, it is desirable that the effective use of fly ash be further promoted.

On the other hand, there have been various attempts to use fly ash as a concrete aggregate, but very few have been put into practical use. The cause is that the aggregate cannot be produced in high yield because of the large variation in chemical and physical properties of fly ash.

There are various methods for producing artificial aggregates using coal ash as the main raw material, but in order to obtain high-quality artificial aggregates with low water absorption and high strength that can replace natural crushed stones. A granulation / firing method is generally employed. Manufacture of artificial aggregates by granulation / firing method involves adding and mixing water and component preparation materials to coal ash and granulating and molding with a pan-type pelletizer. Thereafter, it is fired at a maximum temperature of 1100 to 1500 ° C. in a rotary kiln to achieve densification, and a fired artificial aggregate is obtained.

Although many companies and their research and development have tried to establish mass production technology by the above method, it has not yet been realized. The main reason for this is that the physical and chemical properties of coal ash produced as a by-product fluctuate due to differences in the types of coal used as fuel for thermal power generation equipment and combustion conditions, etc. This is because is not realized.

Specifically, this variation in properties causes the following problems in the manufacturing process.
1. During the process in which the molded and granulated product is fired while rolling in a rotary kiln, fine powder is produced by polishing. If this fine powder moves to the high temperature zone as it is together with the molded / granulated product, it promotes the melt adhesion of the molded / granulated product, and as a result, the product yield decreases.
2. If the unburned carbonaceous material is excessively contained in the molded / granulated product, foaming occurs simultaneously with densification, so that a high-density artificial bone cannot be obtained.
3. When the chemical composition of coal ash is different, the firing temperature and the width of obtaining good quality artificial aggregates also change. In particular, when the content of alkali metal and alkaline earth metal is excessive, the firing temperature range is significantly reduced, resulting in a decrease in product yield due to insufficient densification and promotion of melt adhesion.

To solve the above problem 1, there is a technique for adding water and cement when molding and granulating coal ash to improve the abrasion of the molded and granulated product by the hydration reaction product of cement. . However, when cement is added to such an extent that the wear of the molded / granulated product can be improved, the main component of the cement is CaO, so the total amount of alkali metal and alkaline earth metal in the molded / granulated product becomes excessive. End up. As a result, the above three problems are caused.
That is, after the compacted and granulated material is most densified during the firing process, the liquid phase formation rate becomes remarkably faster, so a slight increase in temperature and increase in residence time promotes melt adhesion and increases product recovery. It will decline.

For the above three problems, there is a technique as disclosed in JP-A-10-251048.
Japanese Patent Application Laid-Open No. 10-251048 discloses a method for producing an artificial bone material, which comprises mixing fly ash and fine powder containing silica-alumina having a melting point of 1500 ° C. or more, granulating the mixture, and firing the mixture. It is about. If this technique is used, the expansion of the firing temperature range, which is one of the problems to be solved by the present invention, can be achieved, but the problem of wear of the molded / granulated product cannot be solved. In addition, purchasing a silica-alumina-containing fine powder having a melting point of 1500 ° C. or higher increases the production cost.

On the other hand, there is a technique described in JP-A-11-314950 that uses aluminum ash as a raw material for artificial aggregate.
However, this technique is intended to solidify various finely divided inorganic residues with glass to form an aggregate, and does not solve the above problems, and cement is a constituent requirement. It is not something to do.

In view of the situation as described above, an object of the present invention is a method for producing an artificial aggregate using coal ash having a large variation in chemical and physical properties as a main raw material. Unsolved carbon contained in coal ash is solved by reducing the wear and extending the firing temperature range by controlling the liquid phase formation rate, and at the same time, slowing the liquid phase formation rate by adding aluminum ash. In this case, the combustion time is further increased, thereby reducing the residual amount of unburned carbon that becomes a foaming source at a high temperature and solving the decrease in the yield of non-defective products.

In order to solve the above problems, the first invention of the present application is an artificial aggregate obtained by heating and firing a molded article made of coal ash, aluminum ash, cement, and water (Claim 1).
In the second invention, the coal ash is fly ash and / or clinker ash discharged from a coal-fired power plant, and the artificial aggregate has a chemical composition of 27.5 to 62.5 parts by weight of SiO2 and Al2O3. The artificial bone material according to claim 1, which has a blending composition of 35 to 55 parts by weight and 2.5 to 17.5 parts by weight of CaO (claim 2). According to a third aspect of the present invention, there is provided the artificial bone material according to claims 1 and 2, wherein the aluminum ash is preliminarily heat-treated under an atmosphere condition containing oxygen (invention 3). A fourth invention is the artificial bone material according to claims 1, 2, and 3 (invention 4), wherein the aluminum ash is pulverized in advance under an atmosphere condition containing oxygen.

According to the present invention, it is possible not only to recycle both coal ash and aluminum ash for which an effective treatment measure is desired, but also a problem of mass production technology for artificial aggregates using conventional coal ash as a main raw material. As a raw material, coal ash with a large variation in chemical and physical properties is greatly reduced by greatly reducing the wear and tear of molded and granulated products during firing, and expanding the firing temperature range by controlling the liquid phase formation rate. It provides artificial aggregates by granulation and firing stably with high yield. This aggregate also contributes to the stable supply of aggregates for concrete, etc., which are indispensable for promoting public works.

The best mode for carrying out the present invention will be described below. The composition of SiO2, Al2O3 and CaO in the baked product is that the SiO2 content is 27.5-62.5 parts by weight, the Al2O3 content is 35-55 parts by weight, and the CaO content is 2.5-17. Mixing ingredients such as coal ash produced as a by-product in the coal-fired power generation process, aluminum ash produced as a by-product in the aluminum refining process, cement, and, if necessary, bentonite and clay, so as to be 5 parts by weight To do. If CaO is less than 2.5 parts by weight, the liquid phase formation rate is extremely lowered and the densification temperature rises, leading to an increase in the calorific value, which is not preferable. On the other hand, when CaO exceeds 17.5 parts by weight, expansion of the firing temperature range is not achieved even with addition of a high melting point component by aluminum ash. When the Al2O3 content is less than 35 parts by weight, the chemical composition of the calcined product is the eutectic line or cristobalite, anorsite and wollastonite which is the boundary between cristobalite, mullite and anorthite in the ternary phase diagram of the SiO2-Al2O3-CaO system It becomes located in the vicinity of the eutectic line that is the boundary portion of the liquid crystal, making it difficult to control the liquid phase formation rate. On the other hand, if the amount exceeds 55 parts by weight, the liquid phase formation rate is extremely lowered and the densification temperature rises, leading to an increase in the calorific value, which is not preferable.

In addition to fly ash collected by a dust collector, clinker ash can be used as coal ash. The concentration of the unburned carbonaceous material in the coal ash is preferably less than 8% by weight. As aluminum ash, aluminum dross generated in each process of an aluminum melting factory and an ash treatment factory, residual ash collected by a cyclone, dust collection ash collected by a bag filter, or the like can be used. As the cement, ordinary Portland cement, mixed cement, eco-cement, or the like that generates a hydrated mineral by reaction with water can be used.

In general, aluminum ash contains metallic aluminum, aluminum nitride, and the like, and when this comes into contact with water, it explodes or generates gas such as hydrogen, methane, and ammonia. Aluminum ash having a low content such as metallic aluminum and aluminum nitride can be mixed with other raw materials without any pretreatment. On the other hand, aluminum ash containing metal aluminum, aluminum nitride or the like at a level that causes a problem needs to be pretreated prior to mixing so that the metal aluminum and aluminum nitride in the aluminum ash are oxidized or decomposed. Oxidation or decomposition can be performed by means of heating or pulverizing the aluminum ash under atmospheric conditions containing oxygen. Moreover, since the liquid phase formation rate can be delayed by the addition of aluminum ash, there is also an effect of increasing the combustion time of unburned carbon contained in the coal ash. Thereby, since the residual amount of unburned carbon that becomes a foaming source at a high temperature is reduced, it is possible to suppress a decrease in non-defective product yield due to poor foaming.

The above blended raw material is granulated while adding water using a granulator such as a bread granulator or an extrusion granulator, and a particle size of about 5 to 20 mm (5 to 13 mm is about 50 in the particle size distribution). %) Granulated body. Although it depends on the granulator, the particle size of the granulated material is adjusted by adjusting the operation of the adjusting mechanism incorporated in the granulator, and if necessary, the particle size is adjusted by sieving after granulation. be able to.

Cement in the blended raw material is added and mixed for the purpose of imparting strength to the molded body, but becomes a strong molded body due to the formation of a hydration reaction mineral between water and cement added during molding. After molding, it can be cured in a natural state, but strength development can also be promoted by means such as steam curing. Thereby, the abrasion of a molded object in a baking process can be reduced.

The granulated body hardened with cement formed in the above step is fired at a firing temperature of 1100 to 1400 ° C. by a rotary kiln to produce an artificial aggregate for concrete or the like. The firing time needs to be about 60 to 120 minutes, and the optimum firing time is set according to the firing temperature. Further, if necessary, an artificial aggregate obtained by firing can be sieved to remove an undesirable particle size as an aggregate.

70 parts by weight of fly ash collected by a dust collector at a coal-fired power plant, 25 parts by weight of aluminum dross residual ash, and 5 parts by weight of ordinary Portland cement were mixed to obtain a blended raw material. 30 parts by weight of water was injected and kneaded to 100 parts by weight of this blended raw material to form a granulated substrate, and a granulated body having a diameter of about 5 to 20 mm was formed with a bread granulator. This was naturally cured in an indoor storage yard for about two weeks to generate cement hydrated minerals and to increase the strength of the granulated body. The chemical composition of the aluminum dross residual ash used in the examples is as follows: metal aluminum = 6.1%, AlN = 14.2%, Al2O3 = 55%, SiO2 = 5.5%, Fe2O3 = 1.4%, MgO = 9.3%, CaO = 1.1%, Na2O = 0.9%, K2O = 0.9% and SO3 = 0.4%.

A direct heating type rotary kiln using heavy oil having an inner diameter of 450 mm and a length of 8.34 m as a fuel was used for the firing equipment. The granulated material is supplied to the rotary kiln at a rate of about 65 kg per hour, fired at a maximum temperature of 1240 ° C. and a residence time in the kiln of about 90 minutes, and a particle size distribution of 70 to 80% has a diameter of 10 to 10%. An artificial aggregate having a size of about 15 mm was obtained.
The obtained artificial aggregate had an absolute dry specific gravity of 2.02 and a 24-hour water absorption rate of about 0.5%, so that it was of a high quality to replace ordinary aggregate.

Concerning artificial aggregates used to form concrete and artificial aggregates as roadbed materials, it contributes to the effective use of coal ash and effectively uses finely powdered aluminum ash, whose disposal is regarded as a social problem. Provided is an artificial aggregate obtained.

Claims (4)

An artificial aggregate obtained by heating and firing a molded product made of coal ash, aluminum ash, cement and water. The coal ash is fly ash and / or clinker ash discharged from a coal-fired power plant, and the artificial aggregate has a chemical composition of 27.5 to 62.5 parts by weight of SiO2, 35 to 55 parts by weight of Al2O3, The artificial bone material according to claim 1, which has a composition of 2.5 to 17.5 parts by weight of CaO. The artificial bone material according to claim 1 or 2, wherein the aluminum ash is heat-treated in advance under an atmosphere condition containing oxygen. The artificial bone according to claim 1, 2, and 3, wherein the aluminum ash is pulverized in advance under an atmospheric condition containing oxygen.