JP2008291497A - Method of using coal ash for ground material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of using coal ash for a ground material, which is implemented by efficiently separating fine particles by means of a simple structure to eliminate trace elements, and detoxicating the coal ash. <P>SOLUTION: The method of using coal ash for a ground material is composed of: a slurry forming step of forming slurry by adding a surface active agent and an aqueous medium to the coal ash, and agitating and mixing a resultant material; a classifying and separating step of classifying and separating particles of 5 μm or more of the slurry by a classifying and separating means; and a washing step of washing the classified and separated particles of 5 μm or more with clean water. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a coal ash ground materialization method for removing trace elements contained in coal ash (fly ash) discharged from a coal-fired power plant, a coal fired boiler, and the like and using it as a ground material.

  Since coal is a fossil plant, it contains trace elements that the plant has absorbed from the soil. After burning coal, about 15% of coal ash is discharged. The fly ash that scatters in the boiler occupies 70% or more of the coal ash. Trace elements are concentrated in coal ash. Since fly ash is a fine particle, trace elements are eluted when it comes into contact with water, and in some cases, it may exceed the environmental standard value. More than 10 million tons of coal ash is discharged annually from coal-fired power plants, and the amount generated is increasing year by year. Most of the coal ash is used as a raw material for cement. However, cement consumption is gradually decreasing. For this reason, utilization as coal ash embankment and road ground material is essential. The problem here is the elution component, and in particular, control of hexavalent chromium, boron, arsenic and the like is a problem.

As a technique for immobilizing such eluted components, effectiveness has been recognized in methods that have been used for a long time, such as adding cement and gypsum. For example, Japanese Unexamined Patent Application Publication No. 2004-148288 discloses a technique for suppressing elution of hexavalent chromium by adding calcium polysulfide or sodium thiosulfate. Japanese Patent Application Laid-Open No. 2004-97944 discloses a technique for suppressing leaching of boron by adding lime / gypsum to coal ash having an adjusted water content ratio. Japanese Patent Application Laid-Open No. 2001-157884 discloses a technique for suppressing elution of heavy metals with wood vinegar or bamboo vinegar. In addition, as a method for removing the eluted components, a method by washing that has been used for a long time is known, and a method for improving the removal effect by using an additive has been proposed. For example, Japanese Patent Application Laid-Open No. 2003-320342 discloses a technique for removing boron by washing with an acidic aqueous solution.
JP 2004-148288 A JP 2004-97944 A JP 2001-157484 A JP 2003-320342 A

  However, the conventional technique for controlling the eluted components by immobilization does not remove the trace components, and there remains a possibility that the trace elements are re-eluted due to changes in environmental conditions. In addition, the technology for removing trace components by washing is not practical because the labor required for washing is very large and the amount of waste water after washing becomes large.

  As a result of investigating and studying the content of trace components in coal ash, (1) components strongly adsorbed on the surface of coal ash, (2) dissolved in silica, alumina, etc., which are the main components of coal ash It was found that there are two types of ingredients. The elution becomes a problem in the case (1), but this removal is difficult. As a result of the examination, the difficulty of removal is that the trace components are strongly adsorbed to the fine particles of coal ash and unburned carbon particles, and these fine particles are strongly coordinated (aggregated) to the coarse coal ash particles. It turned out to be. For this reason, it has been found that effective removal of such fine particles is an important problem in removing trace components, and those from which fine particles have been removed can be used as a ground material.

  The present invention provides a method for converting coal ash into a ground material that solves the problems of the prior art, efficiently separates fine particles with a simple structure, removes trace elements, renders coal ash harmless, and uses it as a ground material. The purpose is to do.

  In order to solve the above-mentioned problems, the first invention of the present invention is a method for making coal ash into a ground material. A slurrying step is performed by adding a surfactant and an aqueous medium to coal ash, stirring and mixing the slurry, It comprises a classification / separation step of classifying / separating particles of 5 μm or more by a classification / separation means, and a washing step of washing the classified / separated particles of 5 μm or more with clean water.

  This 2nd invention is the ground materialization method of the coal ash of this 1st invention, The said slurrying process adds 0.2 to 3weight% of surfactant with respect to coal ash, 100 to 150% by weight of water is added.

  The third invention is a premixing step in which, in the slurry ashing method of the first or second invention of the first or second invention, first, a final addition amount of 2/3 of an aqueous medium is added and stirred and mixed. It is characterized by providing. The surfactant may be added to a 2/3 aqueous medium or may be added to a 1/3 aqueous medium to be added later.

  The fourth aspect of the present invention is the second classifying / classifying method according to any one of the first to third aspects of the present invention, wherein the classified and separated particles of 5 μm or more are further classified and separated by 50 μm or more. A separation step is provided.

  The fifth aspect of the present invention is the method for converting a ground material of coal ash according to any one of the first to fourth aspects of the invention to separate floating particles and unburned carbon floating on the water surface from the remaining water in the washing step, and then It is characterized in that particles having a size of 5 μm or less are separated from water by centrifugation to obtain a cement raw material, and the water from which the solid content has been separated is added as a surfactant and used as a surfactant aqueous solution in the slurrying step.

A slurrying step of adding a surfactant and an aqueous medium to the coal ash of the present invention and stirring and mixing to form a slurry; and a classification / separation step of classifying / separating particles of 5 μm or more by the classification / separation means of the slurry; With a structure comprising a washing step of washing the classified and separated particles of 5 μm or more with clean water, the fine particles strongly agglomerated into the coarse particles in the slurrying step are separated and dispersed in the surfactant aqueous solution, followed by Fine particles are separated from particles of 5 μm or more in the classification / separation process. Furthermore, fine particles, floating particles, and unburned carbon adhering to the particles of 5 μm or more are removed in the cleaning process, so it contains a large amount of trace elements. Can be separated efficiently.
In the slurrying process, a configuration including a premixing process in which an aqueous medium having a final addition amount of 2/3 is first added and stirred and mixed can generate a strong shearing force. At this time, fine particles can be peeled off. it can. The surfactant may be added to this premixed water or may be added to the remaining mixed water.
Coal ash having a different particle size according to the use as the ground material can be prepared by a configuration including a second classification / separation step of classifying / separating the classified / separated particles of 5 μm or more and further separating / separating particles of 50 μm or more.
Floating particles floating on the water surface and unburned carbon are separated from the remaining water in the washing process, and then the particles of 5 μm or less are separated from the remaining water by centrifugation to make cement raw material. With the configuration in which the activator is added and used as the surfactant aqueous solution in the slurrying step, the cleaning water can be used without waste and the post-treatment is facilitated. Even if the slurrying process is carried out again with the water after washing in which the concentration of the trace element is increased, the trace element can be removed in the subsequent washing process.

  The method for converting coal ash into a ground material according to the present invention will be described in the order of steps. In the slurrying step, a surfactant and an aqueous medium are added to coal ash and mixed with stirring to form a slurry. As the aqueous medium, tap water, well water, rain water, etc., which are easily available are used. Examples of the surfactant used include an anionic surfactant and a nonionic surfactant. Anionic surfactants such as naphthalene sulfonate and lignin sulfonate are inexpensive and suitable.

  The surfactant is added in an amount of 0.2 to 3% by weight, preferably 0.5 to 1.5% by weight, based on the coal ash. If it is 0.2% by weight or less, the effect of adding a surfactant is hardly obtained, and if it is 3% by weight or more, unburned carbon in coal ash is eluted and the slurry becomes blackish and post-treatment becomes difficult. The aqueous medium is added in an amount of 100 to 150% by weight based on the coal ash. When the amount of the aqueous medium is 100% by weight or less, the viscosity becomes high, and the classification and separation effect deteriorates. When the amount is 150% by weight or more, coal ash is likely to precipitate, causing clogging in the process or wastewater treatment amount. Problems such as swelling occur. Further, as will be described later, it is necessary to effectively produce a precipitate of fluorine and boron.

  Coal ash has fine particles strongly aggregated on the surface of coarse particles. In order to classify and separate the fine particles, it is necessary to separate the fine particles aggregated on the surface of the coarse particles. Therefore, in this invention, surfactant and an aqueous medium are added to coal ash, and it stirs and mixes to make a slurry. In the process of stirring and mixing in the water to which the surfactant is added, fine particles that have been strongly aggregated on the surface of the coarse particles are separated to form a slurry uniformly dispersed in the aqueous surfactant solution.

  In the slurrying step, a preliminary mixing step may be performed in which an aqueous medium having a final addition amount of about 2/3 is added to the coal ash and stirred. The surfactant may be added to a 2/3 aqueous medium or may be added to a 1/3 aqueous medium to be added later. By mixing premixed water and coal ash corresponding to 2/3 of the required final addition amount and pre-stirring, a strong shearing force can be generated, and fine particles can be peeled off at this time.

  The slurry produced in the slurrying step is classified and separated into particles having a particle size of 5 μm or more and particles having a particle size of less than 5 μm in a classification and separation step such as watering or sieving. Since it is a slurry in which fine particles and coarse particles are uniformly dispersed, dust is not generated in the classification and separation step. From the classified and separated slurry in which particles of 5 μm or less are dispersed, particles of 5 μm or less are separated by a centrifugal separator, and the separated particles of 5 μm or less are used as a cement material. The aqueous surfactant solution from which the solid content has been removed is used again in the slurrying step.

  In the case of coal ash containing a large amount of coarse particles, the classified and separated particles of 5 μm or more are classified and separated into 50 μm or more and 5 to 50 μm in the second classification separation step. Since coarse particles are easy to use as a ground material, particles having a particle size of 50 μm or more and 5 to 50 μm may be separately washed in a washing step to obtain ground materials having different particle sizes.

  The classified and separated particles of 5 μm or more are washed by a washing step. The washing step has a function of washing and separating fine particles and trace components remaining on the surface of particles of 5 μm or more, and floating and separating light floating components and unburned carbon on the washing water surface. The amount of wash water is 30-50% of the aqueous medium added in the slurrying step. The particles of 5 μm or more after washing are used as the ground material.

  The washing water after washing contains particles having a size of 5 μm or less and trace components separated from the surface of the particles having a size of 5 μm or more. The washed water after washing is put into a centrifugal separator to separate solid particles of 5 μm or less, and the separated solid particles of 5 μm or less are used as a cement material. Although trace components remain in the washed water after the solid content is separated, a surfactant is added and reused in the slurrying step. The trace component in the wash water after washing can be easily washed and separated in the washing process after the slurrying process, so that there is no problem. By reusing washing water, the amount of water used can be reduced, and the amount of post-treatment can be reduced.

  Table 1 below shows the results of carrying out the method for converting the ground material of coal ash of the present invention to different types of A, B, C, and D4 types of coal ash.

  As shown in Table 1, it can be seen that the leaching component is largely separated from the coal ash by the method for converting the ground material of coal ash according to the present invention. However, since D-type arsenic has a specifically high elution concentration, it is necessary to perform secondary treatment. In addition, regarding boron and fluorine, mass balance does not match between A type and C type. This is because a chemical reaction between the components occurred in the classification separation process under a high solid content concentration. That is, the calcium contained in the coal ash reacts with boron and fluorine under high pH to generate and precipitate calcium borate and calcium fluoride, respectively. When the amount of added water increases, the amount of precipitation decreases, and the amount of elution of boron and the like cannot be reduced.

  As described above, the coal ash ground materialization method of the present invention can achieve extremely high separation efficiency, and secondary elution of boron and fluorine can be suppressed, and the separated particles of 5 μm or more can be used as the ground material. Fully available.

Claims (5)

A slurrying step of adding a surfactant and an aqueous medium to coal ash and stirring and mixing to make a slurry; a classification / separation step of classifying / separating particles of 5 μm or more by means of classifying / separating the slurry; and classification / separation A method for converting coal ash into a ground material, comprising a washing step of washing particles having a size of 5 μm or more with clean water. The said slurrying process adds 0.2 to 3 weight% of surfactant with respect to coal ash, and adds 100 to 150 weight% of water with respect to coal ash. Of coal ash ground material. 3. The method according to claim 1, further comprising a premixing step of first adding a final addition amount of 2/3 of the aqueous medium and stirring and mixing in the slurrying step. The ground materialization of coal ash according to any one of claims 1 to 3, further comprising a second classification / separation step of classifying / separating the classified / separated particles of 5 μm or more into particles of 50 μm or more. Method. Floating particles floating on the water surface and unburned carbon are separated from the remaining water in the washing process, and then the particles of 5 μm or less are separated from the remaining water by centrifugation to make cement raw material. A method for converting coal ash into a ground material, comprising adding an activator to use as an aqueous surfactant solution in the slurrying step.