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THE FLY ASH COMPOSITION AND STRUCTURE OF KAZAN CENTRAL HEATING AND POWER PLANT
Abstract
Ash and slag waste constitutes a significant part of the waste of heating and power plant (CHP) complexes operating on solid energetic fuel. For the most part, this by-product does not find further application, accumulating in ash dumps. Meanwhile, taking into account the global trend towards the involvement of ash and slag waste in industrial processing, it is necessary to predict their recycling in Russia. However, for recommend recycling type of ash and slag it is necessary to know their structural and material characteristics. To this end, a study was conducted on ash and slag waste generated at the Kazan CHP. The main research methods were X-ray, optical microscopic and electron microscopic (SEM) analyzes. According to the technological scheme of solid energy fuel combustion at the CHP plant, two structural and genetic types of products of combustion of coal are formed: slag and fly ash. Slags are formed as a result of sintering the aluminosilicate melt in the lower part of the furnace space of boiler units, in the so-called slag-washing mines. According to the X-ray analysis data, they are 99.0% composed of an amorphous phase, which gives a wide halo on the diffractograms. Crystalline compounds make up only 1.0% in a structureless mass; they are mainly represented by quartz (SiO2), its high-temperature modification ?-cristobalite (?-SiO2) and kirsheenite (Ca,Fe[SiO4]). Fly ash is a finely dispersed material consisting of particles of different composition and structure - products of thermal decomposition of the ash component of coal fuel. Aluminosilicate microspheres composed of an amorphous substance are predominant. The crystalline phases are in a smaller amount; among them are quartz (SiO2), mullite (Al4SiO8), magnetite (FeFe2O4) and hematite (Fe2O3). The results of the semi-quantitative spectral analysis show that fly ash is more enriched with various trace elements than slag. This is due to the ability of chemical elements to become gaseous at temperatures more 1000°C, and subsequently condense on the surface of the ash particles when the flue gases are cooled. At the same time, concentrations of potentially hazardous chemical elements in fly ash and slag do not exceed their clarke contents in the Earth's crust. Thus, the research results show that ash and slag wastes of the Kazan CHP do not contain environmentally hazardous components. This allows them to be recommended for recycling in the production of building materials.
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