JP2843520B2 - Method for producing coal ash solidified material - 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 a solidified coal ash which is a solidified material containing coal ash as a main component, and more particularly to a building material such as a building panel, a soil material such as a roadbed material and a crushed stone,
An object of the present invention is to provide a method for producing an artificial aggregate or the like.

[0002]

2. Description of the Related Art A large amount of coal ash such as fly ash is produced in thermal power plants and various factories utilizing coal as an energy source (about 4 million tons / year). Of these, only about 40% are effectively used, and the remaining 60% are currently landfilled.
However, it is not always easy to secure landfill sites for coal ash, and it is becoming increasingly difficult to secure landfill sites due to the guarantee of fishing rights and the establishment of the Recycling Law. Therefore, effective utilization of coal ash, which is expected to further increase in the future, is an urgent issue.

At present, coal ash is disclosed in
As disclosed in JP-A-17247 and JP-A-4-305044, it has been proposed as one raw material of inorganic building materials, or as disclosed in JP-A-3-16176. It has been proposed as a raw material of the agent. As a special example, as shown in the publication "Nippon Kogyo Shimbun: Constructing Artificial Seabed Mountains with Coal Ash (Issued February 26, 1993)", it has been proposed as a raw material for artificial reefs. ing. Among these proposals, large amounts of coal ash can be expected when used as building materials or as a raw material for artificial reefs.

[0004]

When the above-mentioned coal ash is used as a building material or a raw material for artificial reefs, both are used in the form of a mixture with cement. Although coal ash is used as a main raw material, the mixing ratio is not necessarily high, and when the mixing ratio of coal ash is increased to 50% by weight or more, the strength of the solidified material is reduced. And the utilization of coal ash was at most 40% by weight. In this case, there is also a problem that the dimensional stability against water is poor because a large amount of cement is used. this is,
Alite (3CaO.SiO) in cement clinker
₂ ) and belite (2CaO.SiO ₂ ), etc., and coal ash and these produce calcium silicate hydrate gel (CSH) and calcium hydroxide by a hydration reaction. Because the reaction is slow,
It is understood that a large amount of unreacted alite and belite remain in the solidified product. Further, it is understood that a large amount of calcium hydroxide is generated by the hydration reaction, and this hydrate also has an adverse effect on the dimensional stability. Here, poor dimensional stability with respect to water means that the solidified material has a large volume change due to the dry-wet state.

[0005] A method of autoclaving the composition of coal ash and cement can be considered, but coal ash is added in an amount of 40% by weight.
When mixed as described above, there is a problem that the strength of the solidified product is not sufficiently exhibited even in the autoclave curing. An object of the present invention is to solve such conventional problems and to provide a solidified material having a high mixing ratio of coal ash, high strength, small variation in strength, and good dimensional stability against water. And

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made intensive studies and found that quality control of coal ash (bulk density, average particle size, and aluminum content),
By mixing ratio of coal ash and calcium compound and hydrothermal treatment, it was found that the solidified material was much better than the conventional one. That is, the method for producing a coal ash solidified product of the present invention has a low bulk density of 0.8 g / cm ³ ,
The average particle size is 5 to 40 μm and the aluminum content is Al ₂ O
A step of mixing at most 35% by weight of coal ash in terms of ₃ and a calcium compound in a weight ratio of 40:60 to 95: 5, a step of forming into a predetermined shape, and a step under a temperature of 120 ° C. or higher and a high pressure A hydrothermal treatment step.

The calcium compound is preferably at least one of calcium oxide, calcium hydroxide, calcium carbonate and calcium silicate.

Further, prior to the hydrothermal treatment, 30 to 1
Curing at 00 ° C. is also suitable.

The bulk density is measured according to JIS Z 250
4. The measurement method was used.

[0010]

[Action] For coal ash, the bulk density is 0.8 g / cm ³
As described above, it is preferably 1.0 g / cm ³ or more. If the bulk density is less than 0.8 g / cm ³ , the strength of the coal ash solidified product will not be sufficiently exhibited, and the variation in strength will be large. The average particle size of the coal ash is 5 to 40 μm, preferably 10 to 30 μm. When the average particle size is less than 5 μm, the strength of the solidified product is not sufficiently exhibited, and when the average particle size exceeds 40 μm, the strength is reduced and the variation in the strength is increased. Although the reasons are not clear, it is assumed that coal ash is involved in the strength of the solidified coal ash as aggregate. Therefore, it is considered that the particles of the coal ash having a small bulk density have a large number of hollow particles, resulting in a decrease in strength and an increase in variation in strength. In addition, coal ash having an average particle size of less than 5 μm is considered not to have a strength improving effect because coal ash hardly remains as coal ash particles after autoclave curing as hydrothermal treatment, and coal ash does not participate as aggregate. Can be On the other hand, coal ash having an average particle size of more than 40 μm is considered to be a coal ash particle remaining after autoclaving, but having a too large particle size and acting as a defect. The particle size distribution of the coal ash is 6 times to 1/4 to 4 times the average particle size in terms of improving strength and reducing variation in strength.
A distribution containing 0% or more particles is preferable. Coal ash is preferably fly ash in terms of strength, but bottom ash can also be used by pulverizing.

Regarding the composition of the coal ash, the aluminum content is 35% by weight or less, preferably 30% by weight in terms of Al ₂ O _3.
% By weight or less. Aluminum content is 35 in terms of Al ₂ O ₃
Exceeding the percentage by weight results in a decrease in the strength of the solidified product and an increase in the variation in the strength. It is considered that hydrogarnet is likely to be generated in the coal ash solidified by the autoclave curing, and this acts as a defect. Regarding the other composition of the coal ash, the Si component is preferably 30 to 80% by weight in terms of SiO ₂ , and the Fe component is preferably 15% by weight or less in terms of Fe ₂ O ₃ in terms of strength characteristics. There is no problem even if the amount is 5% by weight or more. The coal ash can be used not only for pulverized coal ash generally generated but also for coal ash generated from a normal pressure or pressurized fluidized bed combustion power generation system.

When the mixing ratio of the coal ash is less than 40% by weight, the strength and dimensional stability of the solidified coal ash are low, and when it exceeds 95% by weight, the solidified ash hardly solidifies as a solidified coal ash. Cannot be held. Therefore, the mixing ratio of coal ash is 40 to 95% by weight, preferably 70 to 9%.
0% by weight.

The calcium compounds which can be employed in the present invention include calcium oxide, calcium hydroxide, calcium silicate, calcium carbonate and the like. These compounds can be used alone or in combination of two or more. Can be used in combination. From the viewpoint of strength characteristics, powder having an average particle size of 500 μm or less is preferable. Here, examples of the calcium silicate include alite and belite, and various portland cements such as ordinary portland cement including these can also be used. Among these compounds, calcium oxide, calcium hydroxide, and calcium silicate are particularly preferable from the viewpoint of action and effect. The incinerated ash of shellfish can be used because it contains calcium oxide. Further, calcium sulfate such as gypsum is not suitable because a product other than tobermorite is formed.

The autoclave curing temperature is 120 ° C.
As described above, the curing time is preferably 130 to 250 ° C., and the curing time is preferably 2 hours or more. Note that the absolute pressure at a saturated steam temperature of 120 ° C. is about 2 kg / cm ² . If the autoclave curing temperature is lower than 120 ° C., the strength of the coal ash solidified product is not sufficiently exhibited, and the dimensional stability with respect to water is also deteriorated. In the autoclave curing at less than 120 ° C., the generation of tobermorite having an effect of improving strength is small,
Also, calcium hydroxide, which adversely affects dimensional stability,
It is considered that a large amount of calcium silicate remains. In addition, regarding deterioration of dimensional stability, C-S-H
Gels are also thought to have had an effect. In an autoclave curing at a temperature lower than 120 ° C., a large amount of CSH gel remains due to insufficient generation of tobermorite.
The water of the gel changes greatly depending on the dry-wet state. As a result, it is presumed that the volume of the solidified material greatly changes with the ingress and egress of this water, and the dimensional stability is deteriorated. Even when the mixing ratio of coal ash is less than 40% by weight, the dimensional stability is deteriorated, but also in this case, it is considered that the CSH gel in addition to calcium hydroxide and calcium silicate has an adverse effect. . It should be noted that autoclave curing while immersed in water is not preferable.

When the coal ash raw material is formed into a predetermined shape, it is preferable to add a predetermined amount of water to the raw material from the viewpoint of improving strength. The raw material thus prepared is formed into a predetermined shape by press molding, extrusion molding, cast molding, compaction molding, centrifugal compaction molding, or the like.
The amount of added water is 1 to 25 in the press molding with respect to the solid content.
%, 15 to 30% by weight in extrusion molding, 20 to 45% by weight in casting, 15 to 15% in compaction molding
40% by weight is preferred. In this case, a binder, a water reducing agent, a water retention agent, a waterproofing agent, a fluidizing agent, an admixture such as a shrinkage reducing agent may be added, and the strength of the coal ash solidified product may be improved.
Silica sand, igneous rock, blast furnace slag, perlite, ALC debris, glass fiber, fiber, pulp, etc. can also be added for the purpose of adjusting the specific gravity and reducing costs. Examples of the binder include methyl cellulose, ethyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, and polyvinyl alcohol. Examples of the admixture include alkyl allyl sulfonic acid, a highly condensed naphthalene sulfonic acid formalin, a cocondensate of naphthalene sulfonic acid and lignin sulfonic acid, an alkyl allyl sulfonate polymer, an alkyl allyl sulfonate, a formalin condensate of diethyl naphthalene, and olefin / maleic anhydride. Acid co-condensates, polycarboxylates, modified methylol melamine condensates, and the like.

Further, when the obtained molded product is subjected to autoclave curing, particularly when calcium carbonate is used as a calcium compound, the freeze-thaw resistance is improved when the autoclave curing is carried out in a state containing alkali. The reason for this is not clear, but it is assumed that the presence of alkali promotes the reaction between coal ash and the calcium compound, further reducing the porosity in the solidified product and causing the reaction product to become firmly fixed. Is done. Examples of the alkali include an alkali metal hydroxide (eg, NaOH, KOH), an alkali metal carbonate (eg, Na ₂ CO ₃ ), and ammonia. Among these compounds, from the viewpoint of the effect, hydroxides of alkali metals,
Ammonia and alkali metal carbonate are in this order. Of these, alkali metal hydroxides are preferred, and sodium hydroxide is more preferred. Regarding the alkali content in the molded product, the alkali content in the molded product was 0.1 wt.
It is preferably in the range of 001 to 20%, more preferably 0.1 to 20%.
The content is 1 to 10%, and within this range, a solidified product having good freeze-thaw resistance as well as strength and dimensional stability can be obtained. Means for incorporating the alkali into the molded article include means for adding the alkali to the coal ash raw material which is a mixture of coal ash and a calcium compound in the form of a powder or an aqueous solution, means for impregnating the molded article in the form of an aqueous solution, and the like. In particular, a means for incorporating an alkali in the form of an aqueous solution is preferable.

When the obtained molded product is cured at a curing temperature of 30 to 100 ° C., more preferably 40 to 90 ° C. and a curing time of 2 hours or more, more preferably 5 hours or more prior to autoclave curing, it is solidified. It is preferable in improving the strength of the product. Curing includes wet curing, flooded curing, watering curing, and film curing, but wet curing and flooded curing are more preferred.

In the case of casting and compaction, applying vibration during molding can remove entrained air bubbles,
It is preferable in terms of improving strength and shape retention. Vibration amplitude 0.1
5 mm and a frequency of 500-50 Hz are preferable. Also,
In pouring, compacting and press molding, it is also possible to produce a multilayer structure in which different layers of components and the like are formed in multiple layers by dividing the supply of the slurry and granules into the mold several times. By using this multilayer structure, the surface can be colored, which is suitable for road sidewalk boards and building materials whose appearance is regarded as important. Further, the amount of added aggregate or the porosity can be continuously changed, and a material having a gradient function can be produced. In addition, a reinforcing material such as a reinforcing bar can be introduced at the pouring. Also, when the coal ash solidified product is pulverized to a predetermined particle size by a commonly used roll crusher, jaw crusher or the like, it can be used as a quarry, an artificial aggregate, or a roadbed material.

According to the production method of the present invention, the solidified product exhibits a state in which the fine particles of the raw material components are densely packed with each other in the state of the molded product before the autoclave curing which is a hydrothermal treatment. After the autoclave curing, SiO ₂ , Al ₂ O _3,
Each component of a calcium compound such as CaO reacts with Fe ₂ O ₃ or the like to form tobermorite (5CaO · 6Si
O ₂ · 5H ₂ O), and other C-S-H gel (calcium silicate ─ preparative Haidore ─ achieve) is generated. As a result, each of the fine particles constituting the solidified product is mainly coal ash particles, tobermorite crystals, and other CSH gels, and is a hardened body having a small porosity while being firmly fixed to each other, and has a high strength. As a result, a solidified product having small variance in strength and excellent in dimensional stability against water can be obtained.

Therefore, the obtained coal ash solidified product is:
The compressive strength is high, for example, 400 kg / cm ² or more, and the variation in strength is small, so that it can be applied to high-strength concrete products such as concrete panels and concrete piles, and has good dimensional stability against water. Therefore, it can be used in water. Therefore, the solidified coal ash produced by the production method of the present invention can be used in large quantities in a wide range of fields such as building materials such as concrete panels for construction, earth and wood such as roadbed materials and crushed stones, and artificial aggregates. At the same time, since the mixing ratio of coal ash in the raw material of the coal ash solidified material is high, a large amount of coal ash can be used.

[0021]

Next, the present invention will be described based on embodiments. (Example) Bulk density of 0.8 to 1.4 g / cm as coal ash
^3. Fly ash having an average particle size of 5 to 40 μm (component:
SiO ₂ 30 to 80% by weight, Al ₂ O ₃ 18 to 35% by weight, Fe
₂ O ₃ 15% by weight or less) and, as the calcium compound, four types of calcium oxide, calcium hydroxide, calcium carbonate, and ordinary Portland cement having an average particle size of 1 to 100 μm, and these are appropriately mixed by weight. At the same time, 10 to 30% by weight of water and a water reducing agent were added and mixed to prepare various coal ash raw materials. Press molding is performed at a pressing pressure of 50 kg / cm ² ,
Curing was carried out in a wet state for a time to obtain a disk-shaped solidified body (diameter 120 mm, thickness 50 mm). Cast molding is performed by pouring a coal ash raw material slurry into a mold, performing curing in a wet state at 60 ° C. for 20 hours, and forming a disk-shaped solidified body (120 m in diameter).
m, thickness 50 mm). Then, 120-270 ° C
Autoclave curing was performed for 20 hours under the following temperature conditions.

Next, the embodiment will be described in detail with reference to Table 1. In Example 1, the bulk density was 1.1 g / cm ³ , the average particle size was 13 μm, and the aluminum content was 95% by weight of coal ash, 21% by weight in terms of Al ₂ O ₃ , 2% by weight of calcium oxide, and 3% by weight of calcium hydroxide. 160 ° C using coal ash raw material
And autoclaved. Example 2 has a bulk density of 1.3.
g / cm ³ , average particle size 22 μm, aluminum content is Al ₂ O
Autoclave curing was performed at 180 ° C. using a coal ash raw material containing 90% by weight of 30% by weight of coal ash and 10% by weight of calcium oxide in terms of ₃ conversion. Table 1 below. In Examples 1 and 13, autoclave curing was performed without performing the curing in a wet state.

The appearance of the thus obtained coal ash solidified product was observed, and the compressive strength and dimensional stability against water were measured. The results are shown in Table 1. However, in the observation of the appearance of the coal ash solidified matter, the presence or absence of damage such as cracks in the solidified matter and the strength of morphological retention were judged, and good ones were indicated by ○ and bad ones were indicated by ×. For the measurement of compressive strength, a diameter of 50
A metal plate having a thickness of 1 mm was placed thereon, and pressure was applied to the plate. The other method was performed by an autograph according to JIS A1108. The average of 10 samples was used as the compressive strength, and the standard deviation was used as the dispersion. Dimensional stability was measured by cutting out the obtained coal ash solidified product, preparing a measurement sample of 40 × 50 × 100 mm, placing this sample in a drier, drying at 60 ° C. for 24 hours, cooling to a normal temperature in a desiccator, The dimensional change (%) after immersion in water for 24 hours was shown. The dimensional change rate is
According to the measurement method of JIS A 5418. (Comparative Example) As shown in Table 2, the coal ash had a bulk density of 0.5
To 1.2 g / cm ^3, fly ash (component having an average particle size of 1~60μm: SiO ₂ 30~80 wt%, Al ₂ O ₃ 18
40 wt%, while using Fe ₂ O ₃ 15 wt% or less), as a calcium compound, the average particle diameter 1~100μ
m of calcium oxide, calcium hydroxide, ordinary Portland cement and gypsum. Others were the same as the example. In addition, the comparative example 24 is an autoclave.
Without curing, steam curing was performed at 60 ° C. for 20 hours.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

As is clear from the above description, according to the present invention, a solidified coal ash having a high mixing ratio of coal ash, a high strength, a small variation in strength and a good dimensional stability to water can be obtained. Since it can be applied to a wide range of fields such as building materials, earth and wood, and artificial aggregates, coal ash, which is industrial waste, which has been a problem in the past, can be effectively used in large quantities, and the effect of the present invention is extremely large.

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C04B 28/18 C04B 7/26

Claims (3)

(57) [Claims] (1) a bulk density of at least 0.8 g / cm ³ ,
The average particle size is 5 to 40 μm and the aluminum content is Al ₂ O
A step of mixing at most 35% by weight of coal ash in terms of ₃ and a calcium compound in a weight ratio of 40:60 to 95: 5, a step of forming, and a hydrothermal treatment at a temperature of 120 ° C. or higher and a high pressure. A method for producing a solidified coal ash, comprising a step. 2. The method according to claim 1, wherein the calcium compound is at least one or more of calcium oxide, calcium hydroxide, calcium carbonate, and calcium silicate. 3. The method according to claim 1, wherein said hydrothermal treatment is performed in a range of 30 to 100.
The method for producing a solidified coal ash according to claim 1, comprising a step of curing at a temperature of ° C.