JPS6125673B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a hardened body using coal ash discharged during coal combustion as a main raw material, specifically, adding quicklime or/and slaked lime, dihydrate gypsum, hemihydrate gypsum, or type anhydrous gypsum to coal ash. The present invention relates to a method for producing a hydration-hardened body with high mechanical strength by producing a molded body using a mixed powder made of the above as a raw material, curing the molded body, and then treating the molded body with steam. In recent years, it has become difficult for our country to secure a large amount of oil imports due to the international oil supply instability that has been occurring since the oil crisis, and the development of oil-alternative energy to reduce our dependence on oil has become a national issue. Lime is now being reconsidered as a pillar. There are various issues to overcome in the practical application of coal utilization technology, which is necessary for mass consumption of lime, and among them, the treatment of large amounts of coal ash generated during coal combustion has been highlighted as an important issue. When burning coal, usually almost 10 to 20 of the coal usage
% coal ash is generated. Previously in Japan, approximately 10 to 20% by weight of coal ash was reused as fly ash for cement admixtures, cement raw materials, etc., and the rest was disposed of in landfills. However, with regard to the current method of using fly ash as a raw material for cement, it is not expected that the demand will be sufficient to meet the large amount of coal ash generated in the future, and disposal in landfills is not possible either in sea-surface or land-based landfills. From the standpoint of environmental conservation, it is becoming difficult to secure land for ash dumping. For this reason, when full-scale coal is used in coal-fired power plants, etc., it is extremely difficult to process all of the coal ash using the current coal ash processing methods. is thought to have a major impact on the scale of coal energy use. In addition, effective reuse as a resource is essential for establishing a mass processing method for coal ash. This is based, firstly, on the fact that in our country, which lacks domestic resources, reuse rather than mere disposal directly leads to resource and energy conservation, and secondly, environmental destruction is extremely low. In view of the above points, the present invention was made with the aim of making use of coal ash in large quantities as a resource in the civil engineering and construction fields, and producing a cement-like hardened body with high mechanical strength using coal ash as a raw material. Something,
Coal ash 60-85% by weight, quicklime or/and slaked lime (hereinafter abbreviated as quicklime etc.) 10-25% by weight, 2
A mixed powder consisting of 8-25% by weight of hydrogypsum, hemihydrate gypsum and/or type anhydrous gypsum (hereinafter abbreviated as dihydrate gypsum etc.) is mixed with 10-60%, preferably 30-50% per 100 parts by weight. After adding the amount of water (parts by weight to be added to 100 parts by weight of the powder) and thoroughly kneading the mixture, put the kneaded product into a mold or molding container to form it into a predetermined shape, and then This molded body is heated at a relative humidity of 70 to 100%, preferably 90 to 100%.
1 to 30 days, preferably 2 to 10 days at room temperature
After curing for days, 80~100℃, preferably 95~100℃
The present invention provides a method for producing a hydrated and cured product with high mechanical strength by treating with relatively low-temperature atmospheric pressure steam. Hereinafter, the configuration of the present invention will be explained in detail. In general, the typical properties of coal ash, such as its components, composition, and particle size distribution, greatly depend on the place of production and combustion history of the coal. Firstly, the proportions of ingredients such as SiO ₂ , Al ₂ O ₃ , CaO, Fe ₂ O ₃ , Na ₂ O, K ₂ O differ depending on the place where coal is produced, and secondly, Coal ash generated is mainly pulverized coal combustion ash, and is classified into electrostatic precipitator (EP) ash (raw powder, fine powder, coarse powder), clinker ash, and cinder ash depending on the location and collection method. Particle size distribution is different. Therefore, when producing a high-strength hydrated body by steam treatment using coal ash as the main raw material, the appropriate manufacturing conditions for the hydrated body must be determined depending on the composition and particle size distribution of the coal ash, which is the main raw material. is slightly different. Factors that have a large contribution rate as production conditions are the blending ratio of raw coal ash, quicklime, etc., dihydrate gypsum, etc., steam treatment conditions (temperature, time), and coal ash pulverization conditions. Note that atmospheric pressure steam is used as the steam due to the strength of the processing equipment. Further, curing is usually performed in an atmosphere at room temperature. The main component of the hydrated hardened body produced by steam treatment is ettringite (3CaO・Al ₂ O ₃・3CaSO ₄・
32H ₂ O) and various forms of calcium silicate hydrate (XCaO・YSiO ₂・ZH ₂ O), but the one that contributes the most as a strength member is ettringite. First, the relationship between the blending ratio of coal ash, quicklime, dihydrate gypsum, etc. and the properties of the hydrated hardened product is roughly as follows. When the amount of quicklime etc. and/or dihydrate gypsum added in the raw material mixed powder is small, calcium monosulfur aluminate (3CaO・Al ₂ O ₃・CaSO ₄・12H ₂ O) is the main component. The strength of the hydrated hardened product is low, but as the amount of quicklime and/or dihydrate gypsum added increases, the amount of ettringai, which is a strength member, increases and the strength increases. Furthermore, when the amount of quicklime and/or dihydrate gypsum added increases, slaked lime and/or gypsum that does not participate in the reaction occurs during steam treatment, resulting in a decrease in the strength of the hydrated hardened product. Therefore, the amount of added quicklime etc. is 10
-25% by weight, and the amount of dihydrate etc. added is limited to 8-25% by weight. If the blending ratio of quicklime etc. exceeds 30% by weight, a lot of quicklime etc. will remain in the steam treatment, and in a dry atmosphere, the quicklime etc. will turn into calcium carbonate, and the reaction expansion will generate many hair cracks (microcracks). , product quality deteriorates. Furthermore, the steam treatment conditions are mainly determined by treatment temperature and treatment time. Generally, when the steam treatment time is short, the hydrated hardened product consists of a mixture of calcium monosulfo aluminate hydrate, dihydrate gypsum, and ettringite, and its strength is low; The amount produced increases and the strength also increases. Furthermore, if the steam treatment is further carried out for a long period of time and the steam treatment is continued even after the formation of ettringite has been completed, ettringite will decompose into anhydrous gypsum and calcium aluminate hydrate due to its lack of heat resistance, resulting in the formation of a hydrated hardened product. Strength decreases. The particle size distribution of coal ash also has a large effect on the properties of the hydrated hardened material. Generally, as the particle size of coal ash becomes smaller, that is, as the specific surface area becomes larger, the hydrated and hardened material tends to exhibit a predetermined strength in a shorter treatment time. This is because the ettringite formation reaction by steam treatment is a through solution reaction, and the solubility of Al ₂ O ₃ is significantly smaller than that of slaked lime and dihydrate gypsum, and the rate of ettringite formation is
It can be assumed that this is because it depends on the dissolution rate of Al ₂ O ₃ . As mentioned above, the main factors in steam processing are the blending ratio of raw material powder, steam treatment conditions, and particle size distribution of coal ash, but the properties of coal ash vary greatly depending on the place of production and combustion conditions. Coal ash with poor properties cannot exhibit sufficient mechanical strength simply by selecting an appropriate area regarding the above three factors. The use of such coal ash requires suitable pre- or post-treatment operations to increase the reactivity. In the present invention, coal ash is cured for 1 to 30 days in a normal temperature atmosphere with a relative humidity of 70 to 100% as a pretreatment for steam treatment, thereby improving the reactivity of coal ash and hydrating it with high mechanical strength. Manufacture a cured body. Since the most suitable curing conditions vary slightly depending on the properties of the coal ash, it is desirable to determine the appropriate range in advance. In this way, in the present invention, since the blending ratio of coal ash in the raw material is as high as 60 to 85% by weight, it is possible to process a large amount of coal ash, and it is possible to process coal ash in a relatively low temperature of 80 to 100 degrees Celsius using normal pressure steam curing. This makes it possible to have an open structure (no pressure-sealed structure required), simplifying manufacturing equipment, and allowing continuous curing, making it suitable for large-scale processing of coal ash.Moreover, the steam temperature is below 100°C, so waste steam Low-temperature steam such as can be used, reducing energy costs. Next, Examples and Comparative Examples will be described.
The raw material coal ash in Examples and Comparative Examples is commercially available fly ash, and its properties are shown in Table 1.

[Table] According to X-ray diffraction analysis, the chemical components of raw coal ash include a large amount of quartz (α-SiO ₂ ), a medium amount of mullite (3Al ₂ O ₃・2SiO ₂ ), and a small amount of magnetite (Fe _{3 O4} ) was observed. The test methods for coal ash and hydrated hardened bodies are shown below. The Blaine specific surface area was measured using a powder specific surface area measuring device model SS-100 manufactured by Shimadzu Corporation, using the air permeation method. The bending strength test uses 20× as a test piece.
A 20 x 80 (mm) piece was used, and the MKS improved universal strength testing machine manufactured by Marubishi Kagaku Seisakusho was used as the testing device. The test method was a three-point bending method. In the compressive strength test, a 20 x 20 x 20 (mm) test piece was used, and an Instron universal testing machine (maximum load: 10 tons) was used as the test device. The test method was based on the constant deflection rate method. Note that in the Examples and Comparative Examples, atmospheric pressure steam was used as the steam. Comparative example: 70 parts coal ash, 20 parts quicklime, 10 parts dihydrate gypsum, water
40 parts were mixed to form a slurry, and this slurry was poured into a mold to obtain a molded body. This molded body was demolded and stored in an airtight container without curing at 97°C.
A hydrated hardened product was obtained by contacting with water vapor for 15 hours. The properties of the hydrated and cured product were as shown in Table 2. Example 1 70 parts of coal ash, 20 parts of quicklime, 10 parts of dihydrate gypsum, water
40 parts were mixed to form a slurry, and this slurry was injected into a mold to obtain a molded article (the following is the same as the comparative example). Relative humidity 95 to 100 when demolding this molded body
%, and after curing for one day in a normal temperature atmosphere at a temperature of 21 to 23°C, a hydrated hardened product was obtained by contacting with steam at 97°C for 15 hours. The properties of the hydrated and cured product were as shown in Table 2. Example 2 The molded product obtained in Example 1 was heated to a relative humidity of 95 to
After curing for 2 days in a normal temperature atmosphere at a temperature of 21 to 23°C, the product was brought into contact with steam at 97°C for 15 days to obtain a hydrated hardened product. The properties of the hydrated and cured product were as shown in Table 2. Example 3 The molded product obtained in Example 1 was heated to a relative humidity of 95 to
After curing for 3 days in a normal temperature atmosphere at a temperature of 21 to 23°C, the product was brought into contact with steam at 97°C for 15 hours to obtain a hydrated hardened product. The properties of the hydrated and cured product were as shown in Table 2. Example 4 The molded article obtained in Example 1 was heated to a relative humidity of 95 to
After curing for 7 days in a normal temperature atmosphere at a temperature of 21 to 23°C, the product was brought into contact with steam at 97°C for 15 hours to obtain a hydrated hardened product. The properties of the hydrated and cured product were as shown in Table 2.

[Table] As explained above, according to the present invention, raw coal or/and slaked coal, which is an inexpensive raw material, and dihydrate gypsum, hemihydrate gypsum, or/and By adding molded anhydrous gypsum and pre-curing the molded product before steam treatment, it is possible to easily and inexpensively produce a high-strength hardened product, and the present invention makes effective use of coal ash. It is extremely useful as a technology that contributes to the production of various building materials and structural materials in the fields of civil engineering and architecture.

Claims (1)

[Claims] 1 60-85% by weight of coal ash discharged during coal combustion, 10-25% by weight of quicklime and/or slaked lime,
After adding 10 to 60 parts by weight of water to 100 parts by weight of a mixed powder consisting of 8 to 25% by weight of dihydrate gypsum, hemihydrate gypsum, and/or molded anhydrous gypsum and kneading, this kneaded product is molded or molded. It is molded using a molding container, etc., and then the molded body is cured for 1 to 30 days in a normal temperature atmosphere with a relative humidity of 70 to 100%, and then heated to 80 to 100℃.
A method for producing a hardened material using coal ash as a main raw material, characterized by treating it with atmospheric pressure steam.