JPH0228534B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a granular hardened material using coal ash as a main raw material discharged during coal combustion, and more specifically, to coal ash, slaked lime or/and quicklime, and dihydrate gypsum, hemihydrate gypsum or/and type anhydrous gypsum are added to the coal ash. The present invention relates to a method for producing a granular cured product by stirring the added powder mixture with moisture, forming it into granules, and then treating the mixture with atmospheric pressure steam at 80 to 100°C. In recent years, the development of alternative energy sources for oil in order to reduce our dependence on oil has become a national issue in our country, and coal energy is attracting attention as one of the pillars of energy. One of the challenges in the practical application of coal utilization technology to cope with the large consumption of coal as a primary energy source is the problem of processing and disposing of large amounts of coal ash generated during coal combustion. Approximately 10-20wt% of coal usage during coal combustion
of coal ash is generated. The so-called pulverized coal combustion ash generated from a typical pulverized coal combustion boiler is classified into bottom ash, cinder ash, and fly ash, depending on where it is generated, of which fly ash accounts for the majority of the amount generated. Conventionally, in Japan, a portion of fly ash has been reused as cement admixtures, cement raw materials, etc., and the rest has been disposed of in landfills. however,
By reusing conventional methods, we cannot expect demand to increase enough to cope with the huge amount of coal ash that will be generated in the future. With the tightening of regulations related to environmental conservation, it is becoming difficult to secure land for coal ash disposal. It is expected that it will be difficult to dispose of all the coal ash that is generated. In addition, when considering methods for mass disposal of coal ash, it is important to reuse coal ash as a resource rather than simply dumping it, as Japan is lacking in domestic resources. In view of the above-mentioned points, the present invention was made with the aim of enabling mass consumption of coal ash by producing a granular hardened material whose main raw material is coal ash. / and quicklime (hereinafter abbreviated as slaked lime, etc.) 10-25wt%, 2
Water gypsum, hemihydrate gypsum or/and type anhydrous gypsum (hereinafter abbreviated as dihydrate gypsum, etc.) 8~25wt
% to the mixed powder, add 20 to 80 wt% of water (wt% of water added to 100 wt% of powder), stir, knead, and form into granules. By treating with atmospheric pressure steam, the roadbed part, roadbed part, embankment part,
The present invention provides a method for manufacturing a granular hardened body suitable for civil engineering materials used for backfilling parts and backfilling materials. Hereinafter, the configuration of the present invention will be explained in detail. In general, the typical properties of coal ash, such as components, composition, and particle size distribution, greatly depend on the coal's production area and combustion history. First of all, it depends on where the coal comes from.
The blending ratios of constituent components such as SiO ₂ , Al ₂ O ₃ , CaO, Na ₂ O, and K ₂ O are different. Secondly, the coal ash currently generated in Japan is mainly pulverized coal combustion ash. Particle size distribution varies depending on location and collection method. For this reason, when producing civil engineering materials by pulverizing the hardened material obtained by using coal ash as the main raw material through atmospheric pressure steam treatment, the appropriate production conditions differ slightly depending on the component composition and particle size distribution of the coal ash. Factors that have a large contribution rate as manufacturing conditions are the mixing ratio of raw material powder, amount of water mixed, kneading method, humid air curing conditions, and steam treatment conditions. Note that normal pressure steam is used during the steam treatment. The main component of the hardened material produced by steam treatment is ettringite (3CaO・Al ₂ O ₃・3CaSO ₄・
32H ₂ O), various forms of calcium silicate hydrate (xCaO.ySiO _{2.zH 2} O), but ettringite contributes most to early strength development.
Therefore, the appropriate blending ratio of raw material powder is the one that is most convenient for the production of ettringite, and the amount of additives such as slaked lime is limited to 10 to 25 wt%, and the amount of additives such as dihydrate gypsum is limited to 8 to 25 wt%. . In this way, when manufacturing granular hardened bodies using coal ash as the main raw material, the amount of other raw materials added, the amount of water mixed,
It is necessary to appropriately select the stirring method and steam treatment. In order to achieve mass consumption of coal ash with the granular hardened material of the present invention, it is desirable to use it as a civil engineering material.
The field of road materials, backfill materials and ground improvement materials is suitable, and for this purpose it is necessary that the granular hardened bodies have an irregular shape and a wide particle size distribution. Therefore, the stirring method when molding raw material mixed powder into granules with water is as follows.
It is preferable to use a stirrer that is fixed to the container and has stirring blades. A fixed container type stirrer stirs powder by rotating a ribbon, screw, etc. inside a fixed stirring tank. Further, after the atmospheric pressure steam treatment step, it is also suitable to perform a crushing treatment if necessary. This is because the atmospheric pressure steam treatment increases the adhesion strength when the particles formed by the stirring treatment are adhered to each other, which adversely affects the particle size distribution. Suitable crushing treatments include, for example, a method using a drop impact, a method using a sieve if necessary, and a method in which two rotors are rotated in opposite directions. The main features of the granular hardened material according to the present invention when used as civil engineering materials such as road materials, backfill materials, and ground improvement materials are as follows. First, it has a unit volume weight that is considerably smaller than conventional similar materials such as crushed stone and gravel, and yet exhibits ground bearing capacity that is almost equivalent to crushed stone and gravel. That is,
The objective is to exhibit the same ground bearing capacity even with 1/2 to 2/3 the weight of crushed stone or gravel. Second, road sections and backfill sections are usually in wet or humid conditions, and in such environments, the granular hardened material of the present invention has the characteristic that the ground bearing capacity increases over time. It is. Next, examples will be described. The raw material coal ash in the examples is commercially available fly ash, and the composition and properties are shown in Table 1. Plain specific surface area measurement is performed using Shimadzu's powder specific surface area measuring device SS-100.
The air permeation method was used. Table 2 shows the manufacturing conditions for the granular cured product. Table 3 shows the properties of the granular hardened body as a civil engineering material, and Table 4 shows a comparison with other civil engineering materials. 78 parts by weight of coal ash with the composition shown in Table 1, 13 parts by weight of slaked lime
parts by weight, 9 parts by weight of dihydrate gypsum, and 25 parts by weight of water were formed into granules while stirring and kneading for 3 minutes at 150 rpm in a container equipped with a stirrer, and treated with atmospheric pressure steam at 92°C for 15 hours (second (see table). The particle size of the granular hardened material is 5mm.
It was below. The properties of the granular hardened product thus obtained as a civil engineering material are as shown in Table 3.

【table】

【table】

[Table] Example 1 78 parts by weight of coal ash and 13 parts by weight of slaked lime having the composition shown in Table 1
Parts by weight, 9 parts by weight of dihydrate gypsum, and 25 parts by weight of water were formed into granules while stirring and kneading for 2 minutes at 150 rpm in a container equipped with a stirrer, and treated with normal pressure steam at 92°C for 15 hours. The particle size distribution of the obtained granular cured product is as follows: particle size of 5 mm or more: 0%, 5 to 1.7 mm: 20%, 1.7 to 0.074
mm: 70%, 0.074 mm or less: 10%, and the properties were as shown in Table 4. Example 2 78 parts by weight of coal ash and 13 parts by weight of slaked lime having the composition shown in Table 1
Parts by weight, 9 parts by weight of dihydrate gypsum, and 25 parts by weight of water were formed into granules while stirring and kneading at 150 rpm for 4 minutes in a container equipped with a stirrer, and treated with normal pressure steam at 92°C for 15 hours. The particle size distribution of the obtained granular cured product is as follows: particle size of 5 mm or more: 0%, 5 to 1.7 mm: 50%, 1.7 to 0.074
mm: 47%, 0.074 mm or less: 3%, and the properties were as shown in Table 4. Comparative Example 1 Particle size: 0.074 mm or less: The properties of 100% fly ash were measured and were as shown in Table 4. Comparative example 2 Particle size 5 mm or more: 0%, 5-1.7 mm: 20%, 1.7-
The characteristics of river sand with a particle size distribution of 0.074 mm: 80% and 0.074 mm or less: 0% were measured and were as shown in Table 4. Comparative example 3 Particle size 5 mm or more: 0%, 5-1.7 mm: 60%, 1.7-
The characteristics of the crushed sand with a particle size distribution of 0.074 mm: 38% and 0.074 mm or less: 2% were measured and were as shown in Table 4. The modified CBR in Table 4 is based on JIS A
1210 (soil compaction test method by compaction), divided into three layers in the vertical direction and tamped each layer 92 times, and soaked in water for 4 days corresponding to a compaction degree of 95% of the maximum dry density This CBR is JIS A.
1211 (subgrade soil bearing capacity ratio test method), diameter 5
It is given by the following formula from the penetration resistance in cm. CBR = Load (Kg) when penetration depth is 2.5mm / 1370 (Kg) x 10
0 [%]

[Table] Tables 3 and 4 show that the granular hardened material obtained by the method of the present invention is an extremely superior civil engineering material compared to conventional materials such as crushed sand and gravel. As explained above, according to the present invention, slaked lime or/and quicklime, dihydrate gypsum, hemihydrate gypsum, and/or type anhydrous gypsum, which are inexpensive raw materials, are added to coal ash, which is an exhaust product during coal combustion. , stirred with moisture and formed into granules, then heated to 80-100℃
It is possible to use the granular hardened body produced by subjecting it to atmospheric pressure steam treatment as a civil engineering material, and the present invention is extremely useful as a technology that contributes to the effective use of coal ash as a material in the civil engineering field. It is.

Claims (1)

[Claims] 1. 60 to 85 wt% of coal ash discharged during coal combustion,
A mixed powder consisting of 10 to 25 wt% of slaked lime or/and quicklime, 8 to 25 wt% of dihydrate gypsum, hemihydrate gypsum or/and type anhydrous gypsum is stirred with water and formed into granules, and then heated at normal pressure at 80 to 100°C. A method for producing a granular hardened material using coal ash as a main raw material, characterized by processing with steam. 2. A method for producing a granular hardened body using coal ash as a main raw material according to claim 1, which comprises performing a steam treatment and then a crushing treatment.