JPS641417B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing a hardened material using coal ash discharged during coal combustion as a main raw material, and more specifically, a method for producing a hardened material using coal ash as a main raw material, and more specifically, a mixed powder made by adding slaked lime and dihydrate gypsum to coal ash as a raw material. The present invention relates to a method for producing a hydrated and hardened body with high mechanical strength by preparing a molded body as a molded body and treating this molded body with steam. [Conventional technology] In recent years, it has become difficult for Japan to secure a large amount of oil imports due to the international oil supply instability since the oil crisis of 1978, and efforts have been made to develop alternative energies to oil in order to reduce the country's dependence on oil. has become a national issue, and coal, a fossil fuel like oil, has become a national issue.
It is being reconsidered as one pillar. There are various issues to overcome in the practical application of coal utilization technology, which is necessary for mass consumption of coal, 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 15-20 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, considering that an extremely large amount of coal ash is generated during full-scale use of coal in coal-fired power plants, it is extremely difficult to treat all of the coal ash using current coal ash processing methods. Coal ash processing and effective utilization technologies are 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, there is extremely little environmental destruction. Previously, Japanese Patent Publication No. 43-21667 describes how limestone powder is used to reduce exhaust gas in heavy oil-fired power plants.
A method of producing concrete using dust after removing SO ₂ and discharged coal ash is disclosed. Furthermore, in JP-A-53-1222, the first raw material is a mixture of anhydrous gypsum and calcium hydroxide or calcium oxide, and the second raw material is a mixture of coal ash and dilute sulfuric acid. A method for producing cement by mixing a first raw material and a second raw material is disclosed. [Problems to be solved by the invention] In the method described in the above-mentioned Japanese Patent Publication No. 43-21667, the ratio range of the mixed powder is not indicated, but as shown in Table 1 on page 2 of the publication, In the case of combination A, the ratio of the thickness is 58.1% {465 ÷ (335
+465)×100}, 33.3% for combination B {306÷
(306 + 306 + 306) x 100}, the ratio of ash is relatively small, and it is not suitable for processing coal ash, which is emitted in large quantities during coal combustion. In addition, when processing with steam, the temperature is relatively high at 180℃ and 10 atm.
High-pressure steam is used (No. 17, left column, page 2 of the bulletin)
line). As described above, the method described in this publication aims to effectively utilize desulfurized limestone powder in heavy oil-fired power plants, so even if relatively high temperature and high pressure steam is used, the compressive strength is 40%.
Kg/cm ² , 70Kg/cm ² (see Table 2 on page 2), which is an extremely low value. In the method described in this publication, as mentioned above, the curing is performed using relatively high-temperature, high-pressure steam at 180°C and 10 atm, so an autoclave is required as manufacturing equipment (page 2, left column 17 of the publication). (see row), the equipment is too large and continuous processing is not possible, so batch processing must be performed, making it unsuitable for processing large amounts of coal ash, and furthermore, the cost of heating energy to maintain the temperature at 180°C is significant. Also, in the method described in the above-mentioned Japanese Patent Application Laid-Open No. 1222-1983, the proportion range of the mixed powder is not indicated, but in the example in the upper left column of page 3 of the publication, coarse coal ash 14.9
%, calcium hydroxide 5.0%, anhydrous gypsum 79.5%
The case is shown in which the proportion of anhydrite is extremely large and the proportion of coal ash is small.
Therefore, it cannot be said to be a preferable method for treating coal ash that is emitted in large quantities during coal combustion. That is, the method described in this publication uses anhydrous gypsum, calcium hydroxide (or calcium oxide), coal ash,
It uses sulfuric acid as a raw material, and dihydrate gypsum after hydration hardening becomes the strength member, and Na ₂ SO ₄ and K ₂ SO ₄ , which are the reaction products of coal ash with sulfuric acid, serve as setting accelerators for anhydrous gypsum. Anhydrous gypsum is the main raw material. On the other hand, the present invention uses coal ash, slaked lime, and dihydrate gypsum as raw materials, and their reaction product (ettringite) becomes a strength member, and coal ash is the main raw material. As described above, the method described in this publication and the present invention differ in the strength development mechanism. Further, this publication does not suggest any technical concept of treating the molded body with normal pressure steam at a relatively low temperature of 80 to 100°C. The present invention was made in view of the above points, and in order to utilize coal ash in large quantities as a resource in the civil engineering and construction fields, the present invention provides a method for producing a hydrated material with high mechanical strength using coal ash as the main raw material. The purpose is to provide [Means and effects for solving the problems] In order to achieve the above object, the method for producing a hardened material using coal ash as a main raw material of the present invention is to reduce the amount of coal ash emitted from coal ash by weight of 60 to 85% by weight. %, slaked lime 10-25
After adding water and kneading a mixed powder consisting of 8-25% by weight of dihydrate gypsum, this kneaded product is molded using a mold or a molding container, and then this molded body is heated to 80-100% by weight. It is designed to be treated with normal pressure steam at ℃. In the method of the present invention, the amount of mixed water (weight % of water added to 100 weight % of powder) is 10 to 60%,
Desirably it is 30-50%. 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. First of all, the proportions of ingredients such as SiO ₂ , Al ₂ O ₃ , CaO, Fe ₂ O ₃ , Na ₂ O, K ₂ O, etc. differ depending on the place where coal is produced. The coal ash generated is mainly pulverized coal combustion ash, and depending on the location and collection method, it may be necessary to use an electrostatic precipitator (EP).
It is distinguished into ash (raw powder, fine powder, coarse powder), clinker ash, and cinder ash, each with a different particle size distribution. Therefore, when producing a high-strength hydration-hardened body by steam treatment using coal ash, slaked lime, and dihydrate gypsum as raw materials, hydration-hardening The proper manufacturing conditions for each body are slightly different. Factors that have a large contribution rate as production conditions are pretreatment of coal ash (mainly crushing),
These include the blending ratio of coal ash, slaked lime, and dihydrate gypsum, and steam treatment conditions (temperature, time), etc. Note that atmospheric pressure steam is used as the steam due to the strength of the processing equipment. The relationship between the manufacturing conditions for the raw material powder consisting of coal ash, slaked lime, and dihydrate gypsum and the properties of the hydrated product is roughly as follows. The main components of the hydrated hardened product produced by steam treatment are 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, when the content of dihydrate gypsum in the raw material mixed powder is low, calcium monosulfo aluminate hydrate (3CaO・Al ₂ O ₃・CaSO ₄・12H ₂ O) becomes the main component and becomes a hydrated hardened product. The strength is small, but as the dihydrate gypsum content increases, the amount of ettringite, which is a strength member, increases and the strength increases.
Furthermore, when the amount of dihydrate gypsum added increases, free 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 dihydrate gypsum is limited to 8 to 25% by weight. In addition, when the slaked lime content in the raw material mixed powder is low, calcium monosulfo aluminate hydrate becomes the main component, and the strength of the hydrated hardened product is small, and as the amount of slaked lime added increases, The amount of ettringite produced increases and the strength also increases.
If the amount of slaked lime added is further increased, more slaked lime does not take part in the ettringite production reaction, resulting in a decrease in strength. In other words, if the blending ratio of slaked lime exceeds 30% by weight, a large amount of slaked lime will remain after steam treatment, and in a dry atmosphere, the slaked lime will turn into calcium carbonate, and the reaction expansion will generate many hair cracks (microcracks), resulting in poor product quality. deteriorates. For these reasons, the amount of slaked lime is limited to 10 to 25% by weight. 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 reaction uses coal ash, slaked lime, and dihydrate gypsum as raw materials, and the reaction that produces ettringite through steam treatment is a through solution reaction.
The solubility of Al ₂ O ₃ is significantly lower than that of slaked lime and gypsum, and it can be assumed that this is because the rate of formation of ettringite depends on the rate of dissolution of Al ₂ O ₃ . The steam treatment conditions are mainly determined by the treatment temperature and treatment time, and the appropriate range of the steam conditions also differs depending on the particle size distribution of the coal ash as described above. 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 of produced increases and the strength also increases. If steam treatment is carried out for a long time and steam treatment is continued even after the formation of ettringite has been completed, ettringite lacks heat resistance and decomposes into anhydrous gypsum and calcium aluminate hydrate, and the strength of the hydrated hardened product decreases. descend. Note that if the hydrated hardened product is cured for 1 to 30 days in an atmosphere with a relative humidity of 70 to 100%, the reaction of ettringite and the like will proceed and the strength can be improved. As mentioned above, the manufacturing conditions for the hydrated hardened material largely depend on the properties of the coal ash used as the raw material, and the most suitable coal ash pretreatment (pulverization) conditions and slaked lime that correspond to the components, composition, and particle size distribution of the coal. and 2
It is desirable to select the amount of water gypsum added and the steam treatment conditions (treatment temperature, treatment time). The dihydrate gypsum used in the present invention may be any of natural gypsum and chemical gypsum such as phosphate gypsum, salt-produced gypsum, and wet flue gas desulfurization gypsum.
When removing sulfur oxides generated during coal combustion,
Another advantage of the present invention is that by using flue gas desulfurization gypsum recovered as dihydrate gypsum, both coal ash and sulfur oxides, which are emissions from coal combustion, can be treated at the same location and at the same time. There is one. After kneading the raw material powder and water in the present invention,
The strength of the molded product formed in a mold before steam treatment is not very high after a short period of room temperature curing, and if there is a risk of damage during handling or transportation, Accordingly, it is also useful to increase the mechanical strength by tamping press molding or the like when producing a molded body before steam treatment. In the method of the present invention, the temperature of atmospheric pressure steam is 80°C.
If the temperature is below 100°C, the rate of ettringite formation is slow, resulting in a small amount of produced crystals and thick crystals that do not exhibit high strength. Since this is more likely to occur, the generated ettringite will be decomposed and high strength will not be developed. Among the limes, slaked lime has the effect of making the hardened body porous and reducing the bulk density, and quicklime has the effect of making the hardened body dense and increasing the bulk density. Furthermore, among gypsum, hemihydrate gypsum has a low solubility.
0.58 (β type), 0.45 (α type) (g anhydride/100g solution
at 50°C), the kneaded material rapidly hardens.
The solution is gypsum dihydrate, which is a saturated aqueous solution, with a solubility of 0.26 (g anhydride/100g solution at 50°C).
The kneaded material does not harden. The solubility of type anhydrous gypsum is
0.21 (g anhydride/100g solution at 50°C), as in the present invention, if there is no curing accelerator, no curing will occur, but if a curing accelerator is present, the solubility will increase and the curing will occur gradually. It has an effect. Therefore, the strength of the molded product upon demolding varies depending on the type of gypsum. As mentioned above, the hardening speed of the coal ash-lime-gypsum mixture, bulk density, and strength of the hardened product differ due to the differences in the actions and effects of coal and gypsum. For this reason, lime and gypsum are used depending on the quality required depending on the purpose. For example, if we focus on the compressive strength of a hardened product, there is a close relationship with the solubility of gypsum; in a quicklime system, the compressive strength of a hardened product using the same coal ash is For slaked lime systems, the compressive strength of the hardened material when using the same coal ash is as follows: hemihydrate gypsum system > dihydrate gypsum system > type anhydrous gypsum system. [Example] 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 instrument 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. Example 1 70 parts of coal ash, 20 parts of slaked lime, 10 parts of dihydrate gypsum, water
45 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, stored in a closed container, and brought into contact with steam at 96° C. for 15 hours to obtain a hydrated and cured body. The properties of the hydrated and cured product were as shown in Table 2. Comparative Example 1 An experiment similar to Example 1 was conducted except that 80 parts of coal ash and 0 parts of dihydrate gypsum (no addition) were used. The properties of the hydrated and cured product were as shown in Table 2. Comparative Example 2 An experiment similar to Example 1 was conducted except that 90 parts of coal ash and 0 parts of slaked lime (no addition) were used. The properties of the hydrated and cured product were as shown in Table 2. Comparative Example 3 The molded article obtained in Example 1 was tested without steam treatment. The results were as shown in Table 2.

〔Effect of the invention〕

As explained above, in the method of the present invention, since the coal ash blending ratio in the raw material is as high as 60 to 85% by weight, a large amount of coal ash can be processed.
In addition, because it uses normal pressure steam curing at a relatively low temperature of 80 to 100°C, an open structure is possible (no pressurized and sealed structure is required), simplifying manufacturing equipment, and continuous curing is possible, making it suitable for large-scale processing of coal ash. Furthermore, since the steam temperature is below 100°C, low-temperature steam such as waste steam can be used, reducing energy costs. According to the method of the present invention, by adding slaked lime and dihydrate gypsum, which are inexpensive raw materials, to coal ash, which is an exhaust product during coal combustion, and subjecting it to steam treatment, a high-strength hardened product can be easily and inexpensively produced. The method of the present invention 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 by effectively utilizing coal ash.

Claims (1)

[Claims] 1 After adding water and kneading a mixed powder consisting of 60 to 85% by weight of coal ash, 10 to 25% by weight of slaked lime, and 8 to 25% by weight of dihydrate gypsum discharged during coal combustion, this kneaded product is A method for producing a hardened body using coal ash as a main raw material, which comprises forming the body using a mold or a molding container, and then treating the formed body with atmospheric pressure steam at 80 to 100°C.