JPH0138069B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field The present invention mainly uses a mixed powder consisting of coal ash and spent desulfurization agent generated during fluidized bed combustion in a fluidized bed consisting of coal as a fuel and coal stone as a desulfurization agent. A method for producing a cured product as a raw material, in detail, adding water to the above mixed powder and kneading it,
After making it into granules or slurry, it is cured (specifically, steam treated after curing in a humid air), and when producing a hardened product, the water content is 3/7 to 6/7 of the plasticity limit of the mixed powder. The present invention relates to a method for producing a cured product, which is characterized in that after sufficient kneading is carried out in advance, water is further added and kneaded. 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 that has been occurring since the 1973 oil crisis. Coal energy development has become a national issue, and coal energy has been highlighted as one of the pillars of energy. Conventionally, pulverized coal combustion has been the main combustion method when coal is used as fuel, but fluidized bed combustion has recently been attracting attention. This fluidized bed combustion method usually employs an in-furnace desulfurization method, in which coal as a fuel and coal stone as a desulfurizing agent for in-furnace desulfurization are input to form a fluidized bed in a boiler. Compared to the conventional pulverized coal combustion method, the fluidized bed combustion method has the following advantages: firstly, the furnace volume is smaller and the boiler volume is smaller; secondly, there are fewer restrictions on the type of fuel coal; It has the advantages of being able to burn at a low temperature of °C, having no problems with ash condensation, and generating little thermal NOX, and fourth, having a large overall heat transfer coefficient on the surface of the heat transfer water tube. On the other hand, there is a problem with ash disposal in the practical application of fluidized bed combustion technology. The ash generated during fluidized bed combustion is composed of so-called coal ash and spent desulfurization agent, and the spent desulfurization agent is composed of anhydrous gypsum, which is a desulfurization product, and unreacted quicklime.
In order to increase the removal efficiency of sulfur oxides in coal combustion gas, that is, the desulfurization rate, the amount of coal stone input is usually set so that the Ca/S molar ratio is 3 to 6, and the temperature is 750 to 850℃. Coal stone becomes quicklime and type anhydrous gypsum through reaction with sulfur oxides, which are discharged together with coal ash. The amount of fluidized bed combustion ash generated varies considerably depending on the type of coal used, desulfurization rate, boiler operating conditions, etc., but normally, the amount of coal ash, type anhydride, and quicklime generated is approximately 15 to 20 times the amount of coal used. Weight%, 1-10% by weight,
It is 1 to 10% by weight. Problems to be Solved by the Invention Conventionally, most of the coal ash generated in Japan has come from pulverized coal combustion, of which about 10 to 20% by weight is reused as fly ash for cement admixtures, cement raw materials, etc., and the rest is recycled as fly ash. It had been disposed of in a landfill. However, the current situation is that it cannot be expected that future large quantities of coal ash will be adequately coped with either by reusing it as a raw material for cement or disposing of it in a landfill. In this way, the treatment method of pulverized coal combustion ash is also becoming a major issue, and fluidized bed combustion ash is also being produced in extremely large quantities during full-scale coal utilization through fluidized bed combustion in coal-fired power plants. Considering that fluidized bed combustion ash is generated, establishing a unique disposal method for fluidized bed combustion ash is an extremely important issue for the practical application of fluidized bed combustion technology. Furthermore, in order to establish a mass disposal system for fluidized bed combustion ash, effective reuse as a resource is essential. First of all, in Japan, where domestic resources are scarce,
This is based on the fact that reuse rather than mere disposal directly leads to resource and energy conservation, and secondly, it causes very little environmental damage. In view of the above points, the present invention was made with the aim of producing a hardened body with high mechanical strength using fluidized bed combustion ash as a raw material, in order to utilize fluidized bed combustion ash in large quantities as a resource in the field of civil engineering and construction. It is something. Means and Effects for Solving the Problems The method for producing a hardened body using fluidized bed combustion ash as a main raw material of the present invention is characterized by fluidized bed combustion in a fluidized bed composed of coal as a fuel and coal stone as a desulfurizing agent. Add quicklime or/and slaked lime to the coal ash and spent desulfurization agent generated during , and type anhydrous gypsum, hemihydrate gypsum or/and dihydrate gypsum are added as necessary to prepare a mixed powder, water is added to this mixed powder, kneaded, and then cured. It is characterized in that water in an amount of 3/7 to 6/7 of the plasticity limit of the powder is added to the mixed powder and thoroughly kneaded in advance, and then water is further added and kneaded. After thoroughly kneading the mixed powder by adding 3/7 to 6/7 of the plasticity limit of water, and then adding water and kneading it into granules or slurry, it is usually pressure-molded or cast-molded. 65 to 90 days after curing in a humid air.
Treat with normal pressure steam at a relatively low temperature of ℃. Alternatively, the above-mentioned granules may be cured in a humid air without being molded, and further treated with normal pressure steam at 65 to 90°C. Further, the cured product obtained by treatment with atmospheric pressure steam may be pulverized into granular cured products with a particle size of 40 mm or less. Hereinafter, the configuration of the present invention will be explained in detail. In general, the component composition, which is a typical property of fluidized bed combustion ash, largely depends on the type of coal used. First of all, SiO ₂ , which is a combustion residue, depends on the place where the coal is produced.
The blending ratio of components such as Al ₂ O ₃ , CaO, Fe ₂ O ₃ , Na ₂ O, K ₂ O is different, and secondly, the desulfurization product, anhydrous gypsum and non-type anhydrous gypsum, depends on the sulfur content in the coal. The content of quicklime, which is a desulfurizing agent in the reaction, is different. Therefore, when producing a high-strength hardened body by steam treatment using fluidized bed combustion ash as a main raw material, the appropriate manufacturing conditions for the hardened body differ depending on the properties of the fluidized bed combustion ash. The main manufacturing conditions are the amount of quicklime etc. and/or molded anhydrous gypsum etc. added when necessary;
These include kneading conditions, moist air curing conditions, and steam treatment conditions. The relationship between the manufacturing conditions of a hardened body using fluidized bed combustion ash as the main raw material and the properties of the hardened body is roughly as follows. The main component of the hardened material produced by steam treatment is ettrin guide (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 the ettrin guide. First, when the content of anhydrous gypsum and/or quicklime in the raw material mixed powder is low, calcium monosulfur aluminate hydrate (3CaO・Al ₂ O ₃・CaSO ₄・12H ₂ O) is the main Although the strength of the cured product is small, as the content of anhydrous gypsum and/or the content of quicklime increases, the amount of ettrin guide increases and the strength of the cured product also increases. In addition, type anhydrous gypsum and/or
Alternatively, when the quicklime content increases, free gypsum and/or slaked lime that does not participate in the reaction occurs during steam treatment, resulting in a decrease in the strength of the hardened product. The optimum composition of ingredients that maximizes the mechanical strength of the hardened material by steam treatment is 60 to 85% by weight of coal ash other than quicklime and molded anhydrous gypsum, 10 to 25% by weight of quicklime, and 5 to 25% by weight of molded anhydrous gypsum. be. When the quicklime content and/or the type anhydrous gypsum content is less than the optimum component mix, it is necessary to add the quicklime content and/or the type anhydrous gypsum. When adding, slaked lime may be used instead of quicklime, and hemihydrate gypsum and/or dihydrate gypsum may be used instead of type anhydrous gypsum. If the blending ratio of slaked lime exceeds 30% by weight, a large amount of slaked lime will remain after steam treatment, and the slaked lime will turn into calcium carbonate in a dry atmosphere, and the reaction expansion at that time will generate many hair cracks (microcracks), which will deteriorate the product. quality deteriorates. On the other hand, kneading conditions also have a large effect on the properties of the cured product. The quicklime in the fluidized bed combustion ash is coated with ordinary anhydrous gypsum, so the digestion reaction rate with water is slower than that of uncoated quicklime. A high-strength cured product can be produced by kneading and treating with atmospheric pressure steam. However, if the quicklime in the fluidized bed combustion ash is not sufficiently covered with molded anhydrous gypsum, or if the proportion of quicklime is high, if the mixed powder is kneaded with a predetermined amount of water at once, rapid digestion will occur. The temperature of the kneaded material rises rapidly due to the reaction, and the coagulation and hardening reaction progresses, impeding transportability and making it difficult to produce a high-strength cured product even by atmospheric pressure steam treatment. In such a case, if the hydration reaction such as Ettlin Guide does not proceed and the water necessary for the digestion of quicklime is mixed in advance, and after the digestion of quicklime has progressed sufficiently, water is added and kneaded. A high-strength cured product can be produced by subjecting it to atmospheric pressure steam treatment. The appropriate amount of water to be added during preliminary kneading is 3/7 to 6/7 of the plasticity limit of the mixed powder. In other words, if it is less than 3/7 of the plasticity limit, it will take a long time for the digestion reaction of quicklime to complete, and if it is more than 6/7, the digestion reaction of quicklime and the hydration reaction of ettringite etc. will proceed rapidly. This is because it solidifies and hardens. The preliminary kneading time depends on the activity level of quicklime,
Although it varies depending on the kneading capacity etc., 10 to 30 minutes is usually suitable. The main factors for curing conditions are curing temperature and curing time. The purpose of the curing treatment is to allow the hydration reaction to proceed slowly, to obtain an appropriate strength that can withstand the expansion of the hydration reaction during steam treatment at 65 to 90°C, and to create a high-strength cured product by steam treatment. That is, if the curing temperature is low or the curing time is short, the strength of the cured product after curing will be reduced, and many cracks will occur due to steam treatment at 65 to 90°C, resulting in a decrease in the strength of the cured product. On the other hand, if the curing temperature is too high, cracks will occur during curing, and if the curing time is too long, the amount of thick crystals will increase, and the amount of oblique crystals produced by steam treatment will decrease, resulting in hardening. Body strength decreases. Furthermore, if the relative humidity is lower than 80%, water will evaporate and the hydration reaction will not proceed sufficiently. Therefore, in order to produce a high-strength cured product, it is appropriate to cure at room temperature to 60°C (preferably 35 to 60°C) and relative humidity of 80% or higher for 5 to 25 hours. Furthermore, by increasing the curing temperature, the curing time can be significantly shortened to produce a high-strength cured product, and the process for industrial large-scale production of the cured product can be significantly simplified. Steam treatment conditions are the main factors of treatment temperature and treatment time. Steam treatment time is generally short or
When the steam treatment temperature is low, the hydrated hardened product consists of a mixture of calcium monosulfo aluminate hydrate, dihydrate gypsum, and ettringite, and its strength is low, and the steam treatment time becomes longer or the steam treatment temperature becomes higher. As the temperature increases, the amount of ettringite produced increases and the strength also increases. If steam treatment is carried out for a long time or if the steam treatment temperature is too high, ettringite lacks heat resistance, so the generated ettringite will decompose into anhydrous gypsum and calcium aluminate hydrate, and the strength of the granular hardened product will decrease. do. Appropriate steam treatment conditions vary depending on the hydration reactivity of the combustion ash, etc. For fluidized bed combustion ash, the temperature is 65 to 90℃.
A high-strength granular hardened product can be obtained by treating with normal pressure steam at a temperature of 5 to 15 hours. Note that as the steam treatment temperature increases, the steam treatment time becomes shorter and a high-strength cured product can be obtained. In this way, when manufacturing a hardened product using fluidized bed combustion ash as the main raw material, the amount of water added, kneading conditions, curing conditions, and steam treatment conditions must be appropriately selected according to the properties of the fluidized bed combustion ash. is necessary. The cured product according to the present invention has high strength and is expected to be used in artificial reefs, civil engineering blocks, etc. Furthermore, by granulating the hardened product of the present invention during kneading or pulverization, it can be expected to be used as civil engineering materials such as road materials, backfill materials, and ground improvement materials. It is. 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. i.e. 1/2 to 2/3 of crushed stone and gravel
The objective is to demonstrate the same ground bearing capacity even with the weight of Second, road sections and backfill sections are usually in wet or highly wet conditions, and in such environments, the granular hardened material according to the present invention has the characteristic that the ground bearing capacity increases over time. It is. Examples Next, examples and comparative examples will be described.
The chemical composition and physical properties of the fluidized bed combustion ash in Examples and Comparative Examples are shown in Table 1, and the proportions of constituent compounds are shown in Table 2.

【table】

[Table] Test methods for fluidized bed combustion ash and hardened material 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 liquid limit is measured based on JIS A 1205 (Soil liquid limit test method), and the plastic limit is
Measured based on JISA1206 (Soil plasticity limit test method). Bending strength test uses 40 x 40 x 160 as a test piece
(mm), 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. For the compressive strength test, a 40 x 40 x 40 (mm) specimen was used, and a universal testing machine (maximum load: 10 tons) manufactured by Instron was used as the testing device. The test method was based on the constant deflection rate method. Modified CBR is JIS A
4, which corresponds to a compaction degree of 95% of the maximum dry density when divided into three layers in the vertical direction and tamped each layer 92 times according to 1210 (Test method for soil compaction by compaction).
It refers to CBR after being immersed in water for a day, and this CBR is JIS A.
1211 (subgrade soil bearing capacity ratio test method), diameter 5
The penetration resistance of a penetration rod of cm is given by the following formula. CBR = Load when penetration depth is 2.5mm (Kg) / 1370 (Kg) x 100
(%) Example 1 100 parts by weight of fluidized bed combustion ash shown in Table 1 was mixed with 20 parts by weight of water.
After adding part by weight and kneading for 15 minutes, 26 parts by weight of water was further added and kneaded for 2 minutes to form a granule.The granule was press-molded at a pressure of 20Kg/cm ² G and heated at 50℃. ,
After curing for 15 hours in a humid atmosphere with a relative humidity of 80% or more,
A cured product was obtained by treatment under normal pressure steam at 80°C for 10 hours. The properties of the cured product were as shown in Table 3. Example 2 Add 30 parts of water to 100 parts by weight of fluidized bed combustion ash shown in Table 1.
After adding 16 parts by weight and kneading for 15 minutes, add 16 parts by weight of water.
parts by weight were added, kneaded for 2 minutes to form granules, and the granules were pressure-molded at a pressure of 20 kg/cm ² G at 50°C.
After curing for 15 hours in a humid atmosphere with a relative humidity of 80% or more,
A cured product was obtained by treatment under normal pressure steam at 80°C for 10 hours. The properties of the cured product were as shown in Table 3. Example 3 Add 30 parts of water to 100 parts by weight of fluidized bed combustion ash shown in Table 1.
After adding part by weight and kneading for 15 minutes, 30 parts by weight of water was further added and kneaded for 3 minutes to form a slurry. This slurry was poured into a mold and heated at 50℃ and in a humid atmosphere with a relative humidity of 80% or more for 15 minutes. After curing for an hour, it was treated under normal pressure steam at 80°C for 10 hours to obtain a cured product. The properties of the cured product were as shown in Table 3. Comparative Example 1 Water was added to 100 parts by weight of fluidized bed combustion ash shown in Table 1.
Add 46 parts by weight, knead for 2 minutes to form granules, press-form the granules at a pressure of 20 kg/cm ² G,
After curing for 15 hours in a humid atmosphere at 80°C and relative humidity of 80% or more, the material was treated for 10 hours under normal pressure steam at 80°C to obtain a cured product. The properties of the cured product were as shown in Table 3. Comparative Example 2 Add 60 parts of water to 100 parts by weight of fluidized bed combustion ash shown in Table 1.
Add part by weight, knead for 3 minutes to make a slurry, pour this slurry into a mold, and heat at 50℃ and relative humidity 80%.
After curing in the above humid atmosphere for 15 hours, it was treated under normal pressure steam at 80°C for 10 hours to obtain a cured product. The properties of the cured product were as shown in Table 3.

[Table] Example 3 The cured product shown in Example 2 in Table 3 was crushed using a geo crusher, and 100% by weight of 20 mm or less,
10mm or less 70% by weight, 5mm or less 39% by weight, 1mm or less
A granular cured product having a particle size distribution of 30% by weight and 3% by weight of 0.1 mm or less was obtained. The properties of the granular cured product were as shown in Table 4. Example 4 Add 30 parts of water to 100 parts by weight of fluidized bed combustion ash shown in Table 1.
After adding part by weight and kneading for 15 minutes, further add 16 parts by weight of water and kneading for 2 minutes to form a granule. After curing, treat under normal pressure steam at 80℃ for 10 hours, 100% by weight for 20mm or less, 80% by weight for 10mm or less, 5
A granular cured product was obtained with a particle size distribution of 45% by weight of less than mm, 36% by weight of less than 1mm, and 4% by weight of less than 0.1mm. The properties of this granular cured product were as shown in Table 4. Comparative Example 3 A granular cured product having the same particle size distribution as Example 3 was obtained by pulverizing the pre-pulverized hardened material shown in Comparative Example 1 in Table 3 using a di-yo crusher and adjusting the particle size. The properties of this granular cured product were as shown in Table 4.

[Table] Effects of the Invention As explained above, according to the present invention, fluidized bed combustion ash, which is an exhaust product during coal combustion, is reduced to 3/7 of the plastic limit.
After thoroughly kneading with ~6/7 water, further water is added, kneaded, and then cured in a humid air, and further curing such as atmospheric pressure steam treatment is performed to form a hardened product with high strength and granular form. It is possible to easily produce a hardened product in a short time, and the present invention is applicable to the production of various building materials, structural materials, road materials, backfilling materials, etc. in the fields of civil engineering and construction by effectively utilizing fluidized bed combustion ash. It is extremely useful as a contributing technology.

Claims (1)

[Scope of Claims] 1 Coal ash generated during fluidized bed combustion in a fluidized bed consisting of coal as a fuel and coal stone as a desulfurization agent and a spent desulfurization agent containing 60 to 85% by weight of coal ash, Quicklime or/and slaked lime, and molded anhydrous gypsum, so that the lime content is 10 to 25% by weight and the gypsum content is 5 to 25% by weight.
In the method of preparing a mixed powder by adding hemihydrate gypsum or/and dihydrate gypsum as necessary, adding water to this mixed powder, kneading, and curing,
The main raw material is fluidized bed combustion ash, which is characterized by adding 3/7 to 6/7 of the plasticity limit of water to the mixed powder, thoroughly kneading it in advance, and then adding water and kneading it. Method for producing cured product. 2. A method for producing a hardened body using fluidized bed combustion ash as a main raw material according to claim 1, which comprises pulverizing the cured body into granular hardened bodies having a particle size of 40 mm or less.