JP2006143556A - Manufacturing method for artificial aggregate, and artificial aggregate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for an artificial aggregate using coal ashes as a main raw material, by which method the artificial aggregate having such a low water absorption coefficient and such high strength properties as a natural aggregate has is economically manufactured. <P>SOLUTION: The coal ashes, which are a main raw material, and an adding-component controlling agent and/or a forming aid are together charged into a crusher, and subjected to mixing and crushing which are simultaneously operated. Then the mixed and crushed product, as it is or a formed product of the mixed and crushed product is fired in a rotary kiln. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to a method for producing an artificial aggregate using coal ash as a main raw material and an artificial bone, and in particular, a method for producing an artificial aggregate and an artificial bone using coal ash having a low water absorption rate and high strength as a main raw material. It relates to materials.

With the increase in power demand, the amount of coal ash generated is increasing year by year. In conjunction with this, technological development related to the effective use of coal ash is being addressed in various fields.
For example, many attempts have been made to add various auxiliary raw materials to coal ash and to sinter and densify them to use as aggregates for concrete.

  The demand for aggregates is enormous, so there is great expectation as an effective use destination of coal ash generated in large quantities. However, the chemical composition of coal ash generated by the coal type and boiler type / structure is large. Due to differences, the handling process is difficult in the manufacturing process, and unburned carbon contained in coal ash hinders densification of the aggregate structure. Aggregate is not yet widely used.

  In producing a fired artificial aggregate, the firing method and productivity are greatly affected by the properties of coal ash. It is not an exaggeration to say that the unburnt carbon content and the silica content are the factors that have a particularly influential effect.Some of these are difficult to control the firing, which hinders stable operation and causes variations in aggregate quality. Become.

The biggest cause of the unburned carbon inhibiting the densification of the aggregate fabric is that the component explosively burns in the high temperature zone during firing. When the component is burned during the sintering process of the aggregate tissue, it will be present as bubbles, but not only that, but the surrounding tissue will be distorted, resulting in destruction of the aggregate.
Moreover, when there is much silica content, it becomes easy to cause softening and fusion | bonding with respect to the change of a calcination temperature, and temperature control will become difficult.

  Therefore, Patent Document 1 discloses a granulated product having a predetermined apparent specific gravity and strength by pulverizing coal ash so that the specific surface area of the brain is a predetermined value, and an additive for adjusting the ingredients is contained in the raw material powder. A technique for producing a high-quality artificial aggregate by molding and firing the granulated product is disclosed.

JP-A-61-163152

  However, since the technique disclosed in Patent Document 1 is based on uniform quality of the granulated material to be fired, it is considered that the firing process itself is stable and a uniform artificial bone can be produced. In the technology, molding of a granulated product having a predetermined apparent specific gravity and strength is a complicated operation and is not an economical manufacturing method. Moreover, the pulverization of only the coal ash, which is the main raw material, has not been effective enough to produce a low water absorption and high strength aggregate.

  The present invention has been made in view of the background art described above, and its purpose is a method for producing an artificial aggregate using coal ash as a main raw material, and has a low water absorption rate and high strength comparable to natural aggregates. An object of the present invention is to provide a method for economically manufacturing an artificial aggregate having a property.

  As a result of intensive studies to achieve the above-mentioned object, the present inventors have obtained coal, which is the main raw material, in order to improve the sinterability of the raw material and obtain low water absorption and high strength comparable to natural aggregates. It is not enough to make the ash finer, and it is found that the sinterability and firing stability are dramatically improved by making the component modifier and / or molding aid to be added together. The present invention has been completed.

That is, in the first aspect of the present invention, a component modifier added together with coal ash as the main raw material is put into a pulverizer, mixed pulverization, which is a simultaneous operation of mixing and pulverization, and then the mixed pulverized product is left as it is. A method for producing an artificial aggregate to be fired by a rotary kiln is provided.
The second aspect of the present invention is to add a component modifier and / or a molding aid to be added together with coal ash as a main raw material to a pulverizer, and after performing mixed pulverization, which is a simultaneous operation of mixing and pulverization, An object of the present invention is to provide a method for producing an artificial aggregate in which the mixed pulverized product is molded and the obtained molded product is fired by a rotary kiln.

  Here, it is preferable that the mixed pulverized product has an average particle size of 15 μm or less and a residue on the 88 μm sieve is 5% by mass or less. Moreover, it is preferable that the addition amount of the said component regulator and / or shaping | molding adjuvant is 1-20 mass%.

Further, the present invention is an artificial aggregate produced by the method of the present invention described above, having an absolutely dry density of 1.5 g / cm ³ or more and 2.3 g / cm ³ or less, and a 24-hour water absorption of 0. An artificial bone having a mass of 1 to 5% by mass and an aggregate having a diameter of 5 mm to 10 mm having a crushing load of 0.5 kN or more, or an aggregate having a diameter of 10 to 15 mm having a crushing load of 1.0 kN or more. The material is provided.

  According to the above-described method for producing an artificial aggregate according to the present invention, not only the coal ash that is the main raw material is pulverized, but also the component modifier and / or molding aid to be added to the pulverizer together with the coal ash. Since the mixing and pulverization, which is a simultaneous operation of mixing and pulverization, is performed, the homogeneity of the raw materials is increased, and this improves the sinterability and firing stability dramatically, and has a low water absorption rate. There is an effect that a high-strength artificial aggregate can be manufactured with high productivity.

  Further, according to the above-described artificial aggregate according to the present invention, since it is an aggregate having high strength and low water absorption that is comparable to natural aggregate, it can be suitably used as a concrete aggregate, and further, coal-fired power generation Since coal ash, which is waste from a place, is used as a main raw material, the invention has an excellent effect from the viewpoint of effective use of waste.

  Hereinafter, embodiments of the method for manufacturing an artificial bone and the artificial bone according to the present invention will be described in detail.

  The coal ash used in the present invention is discharged from a coal-fired power plant or the like, and refers to fly ash or PFBC ash collected by an electric dust collector or the like. These coal ash contains unburned carbon, and the unburned carbon burns during the firing process, but it generates bubbles in the aggregate during combustion, and in extreme cases it is explosive. In general, it is preferable that the amount of unburned carbon is as small as possible. However, in the present invention, the raw material is mixed and pulverized and refined as described later, so that it is incorporated into coal ash. The unburned carbon is exposed to the surface and easily burns, and the decarbonization reaction proceeds quickly in a relatively low temperature zone, and the unburned carbon does not remain until the pellet reaches the high temperature zone. Explosive combustion in the belt will not occur. Therefore, the coal ash used in the present invention does not need to be regulated for unburned carbon.

  In the present invention, at least a component modifier and / or a molding aid is added to the coal ash to adjust its chemical composition.

The said component regulator is added in order to improve the sinterability of coal ash, and various component regulators are added according to the chemical composition of the coal ash to be used.
Examples of main component modifiers include various mineral resources such as silica, clay, alumina, limestone, and dolomite, or processed products thereof. Moreover, as long as a desired amount is contained, various incineration ash such as aluminum ash, garbage incineration ash and sewage sludge incineration ash, and waste such as construction generated soil can be used.

In addition, when the raw material powder is molded and fired by some shaping means such as rolling granulation, stirring granulation, extrusion molding or pressure molding, instead of firing the raw material in a powder state, the moldability In order to impart the above, a molding aid is added to the coal ash.
Examples of the molding aid include various clay minerals, various cements and gypsum, sodium silicate, organic binders, and lignin contained in waste liquid during pulp production.
In addition, some inorganic molding aids such as clay and cement perform the function of component adjusters from their chemical components. If these components can be used to adjust the components of coal ash, the component adjustment described above is intentionally made. There is no need to add any agent.

The addition amount of the above-described component modifier or molding aid is determined according to the properties of the coal ash used, but the recommended addition amount is 1 to 20% by mass, and 3 to 17% by mass. % Is still preferred.
This is because if the addition amount is less than 1% by mass, the granulated product becomes insufficiently densified, and a low water absorption and high strength aggregate cannot be obtained. If added, the amount of coal ash used is reduced, which is not preferable from the viewpoint of effective use of waste.

In the present invention, the coal ash that is the aggregate raw material is mixed and pulverized with the component adjusting agent and / or the molding aid. That is, in the present invention, not only the coal ash as the main raw material is pulverized, but also component adjusting agents and / or molding aids added together with the coal ash are introduced into the pulverizer, and simultaneous operation of mixing and pulverization can be performed. Do some mixing and grinding.
This is because mixing and grinding increases the homogeneity of the raw material powder, which improves the sinterability and also improves the firing stability dramatically.

The fineness of the coal ash and the component modifier and / or the molding aid by the above-mentioned mixed pulverization may be mixed and pulverized so that the average particle size is 15 μm or less and the residue on the 88 μm sieve is 5% by mass or less. preferable.
This is because when the average particle size exceeds 15 μm, the sinterability is not sufficiently improved, and when the residue on the 88 μm sieve exceeds 5% by mass, the sinterability is promoted similarly. It is because it cannot be expected. In order to sufficiently improve the sinterability and sintering stability, it is more preferable to carry out mixing and pulverization so that the average particle size is 12 μm or less and the residue on the 88 μm sieve is 2 mass% or less.

  The mixing and pulverization of the coal ash and the component modifier and / or the forming aid is not particularly limited as long as the pulverizer can achieve the above fineness, and includes a batch type and continuous type ball mill, a rod mill, and the like. Various mixing and grinding means such as a medium stirring mill and a roller type vertical mill can be used.

The raw material mixed and pulverized as described above can be directly put into a rotary kiln and fired.
In general, it is said that powder sintering is difficult to obtain a granular or massive sintered product that has been sintered, but in the present invention, as described above, the sinterability of the raw material powder is refined by mixing and grinding. It is also a great feature that it can be sufficiently fired even in a powder state.

  Also, if you want to control the shape and particle size of the product arbitrarily, add the above-mentioned forming aid to the raw material system, mix and pulverize, then roll granulation, stirring granulation, extrusion molding, pressure molding, etc. A desired molded body is formed by the various molding means, and the molded body is put into a rotary kiln and fired.

  A rotary kiln is used for firing as described above. The rotary kiln is extremely stable because it is easy to obtain stable quality aggregates continuously and is suitable for industrial production, as well as the refinement and homogenization of raw materials by the above-mentioned mixing and grinding. Aggregates can be manufactured.

The firing temperature at this time depends on the thermal characteristics of the raw materials used, particularly the properties of the main component, coal ash, but usually 1100 to 1400 ° C. is preferred.
This is because when the firing temperature is less than 1100 ° C., a sufficient sintering reaction does not proceed and an aggregate of desired quality cannot be obtained. Conversely, when the firing temperature exceeds 1400 ° C., the mixed raw material is melted and the operation is continued. This is not preferable because it causes trouble.

  The rotary kiln used here may or may not be provided with a material circulation preheating facility such as a cyclone, a preheater, a waste heat boiler, etc., in an exhaust system such as a cement firing kiln. Further, as fuel, if it is generally used, such as heavy oil, pulverized coal, regenerated oil, LPG, NPG, etc., it may be used alone or in a mixed firing, and the amount of squeezing so as to reach a predetermined firing temperature Adjust. In recent years, in cement kilns, waste plastics, waste tires, and the like have been used as fuel substitutes, but such ones may be used as part of the fuel.

By firing the mixed pulverized raw material by the rotary kiln as described above, the absolute dry density is 1.5 g / cm ³ or more and 2.3 g / cm ³ or less, and the 24-hour water absorption is 0.1 mass% or more and 5 mass% or less. Thus, an artificial aggregate having a crushing load of 5 to 10 mm in diameter of 0.5 kN or more or a crushing load of 10 to 15 mm in diameter of 1.0 kN or more is obtained. It is a high strength, low water absorption aggregate that is inferior.

  Examples of the present invention will be described below together with comparative examples.

  Using coal ash A and B shown in Table 1, ordinary boltland cement (labeled as “OPC” in the table) as a component modifier, bentonite as a molding aid, and the formulation and fineness shown in Table 2 The raw materials were prepared. The raw materials were mixed and pulverized, or only the coal ash was pulverized using a ball mill (diameter 1.5 m, length 5 m).

The raw materials adjusted to the above-mentioned blending and fineness were each confirmed with an electric furnace for easy calcination (the maximum density and the calcination temperature range with low water absorption).
The relationship between the density and the water absorption rate with respect to the firing temperature in this electric furnace test is shown in FIGS.

As is clear from FIG. 1, the absolute dry density increases as the firing temperature increases, and decreases after passing through the maximum point. In the present invention, the absolute dry density range is 1.5 g / cm ³ or more and 2.3 g / cm ³ or less, and the temperature range (“a” ° C. to “b” ° C. in the figure) for realizing this density range is provided. The firing temperature range is based on the absolute dry density.

  On the other hand, the 24-hour water absorption is as shown in FIG. 2, which decreases with an increase in the firing temperature and fuses in a certain temperature range (“d” ° C. in the figure). In the present invention, the range of the 24-hour water absorption is 0.1% by mass or more and 5% by mass or less, but the temperature (“d” ° C.) when fusing from the upper limit temperature (“c” ° C.) is 24. The firing temperature range is based on the time water absorption rate.

As described above, the firing temperature range can be obtained from two criteria, and the final firing temperature range was determined as follows.

Lower limit of firing temperature: higher “a” ° C. or “c” ° C.
Upper limit of firing temperature: lower of “b” ° C. or “d” ° C.
Firing temperature range: Upper limit of firing temperature-Lower limit of firing temperature

Table 3 shows the firing temperature range of each raw material and the maximum dry density of each raw material obtained by this electric furnace test, determined according to the above criteria.

  The prepared raw material was molded into a particle size of 10 to 30 mm as a powder or with a bread pelletizer (diameter 1.8 m, bread depth 60 cm), and fired using a rotary kiln having a diameter of 1.5 m and a length of 20 m. In addition, about the raw material which shape | molded, it described as "Yes" in Table 2, and about what was thrown in with powder, it described as "No" in Table 2.

The absolutely dry density and 24-hour water absorption rate of the obtained fired pellets were measured by a method according to JIS A 1135, and the crushing load was measured by a method according to JIS Z 8841.
In addition, the particle | grain group with a diameter of 10-15 mm was used for the pellet used for the crushing load test.
Table 3 shows the measurement results of the absolute dry density, 24-hour water absorption rate, and crushing load of the fired pellets obtained from each raw material.

In the examples according to the present invention, that is, in Examples 1 to 6 in which the raw materials were mixed and pulverized, it was confirmed that an artificial bone material having a wide firing temperature range, high density, low water absorption and high strength could be obtained.
Furthermore, the amount of raw material input was about twice that of the comparative example. Such an improvement in productivity is sufficient even when considering the cost of mixing and grinding the raw materials, and the effectiveness of the production method of the present invention was confirmed.
On the other hand, in Comparative Examples 1a to 6b in which the raw materials were not mixed and pulverized, the firing temperature range was extremely narrow, and stable operation was difficult due to problems such as frequent fusion, and both achieved low water absorption and high strength. I couldn't do it.

  As mentioned above, although the Example of this invention was described with the comparative example, this invention is not limited to the above-mentioned Example at all, and within the range of the technical idea of this invention described in the claim Of course, various modifications and changes are possible.

It is the graph which showed notionally the relationship of the absolute dry density with respect to the calcination temperature in an electric furnace test. It is the graph which showed notionally the relationship of the 24-hour water absorption with respect to the calcination temperature in an electric furnace test.

Claims (5)

  A component modifier added together with coal ash which is the main raw material is put into a pulverizer, mixed pulverization which is a simultaneous operation of mixing and pulverization is performed, and then the mixed pulverized product is directly fired by a rotary kiln The manufacturing method of artificial aggregate.   The component adjuster and / or molding aid added together with the coal ash as the main raw material is put into a pulverizer, mixed and pulverized, which is a simultaneous operation of mixing and pulverization, and then the mixed pulverized product is molded and obtained. A method for producing an artificial aggregate, characterized in that the formed product is fired by a rotary kiln.   The method for producing an artificial bone material according to claim 1 or 2, wherein the mixed pulverized product has an average particle diameter of 15 µm or less and a residue on the 88 µm sieve of 5 mass% or less.   The method for producing an artificial bone material according to any one of claims 1 to 3, wherein the additive amount of the component modifier and / or the molding aid is 1 to 20% by mass. An artificial aggregate produced by the method according to any one of claims 1 to 4, wherein the absolute dry density is 1.5 g / cm ³ or more and 2.3 g / cm ³ or less, and the water absorption rate for 24 hours is 0. .1 mass% or more and 5 mass% or less, the crushing load of the aggregate having a diameter of 5 mm to 10 mm is 0.5 kN or more, or the crushing load of the aggregate having a diameter of 10 mm to 15 mm is 1.0 kN or more. An artificial aggregate characterized by

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