Technical and economic justification of the technological scheme of sorption materials production from the coal fly ash

Abstract

Despite the wide range of industrial applications for ash and slag waste, the actual utilization rate of ash disposed at Ukrainian TPPs is close to zero. Dry ash from electrostatic precipitators is used in the production of construction materials to a very limited extent. An analysis of the possibility of producing commercial materials from ash and slag using hydrochemical methods shows that these methods are mainly used in laboratory practice. Taking into account the content of silica in TPP fly ash, which is more than 50% by weight, it is of practical interest to use it to produce zeolite-like materials that have pronounced adsorption properties and can be used in water and gas purification processes. The known processes for obtaining sorption materials based on fly ash involve alkaline treatment of raw materials and hydrothermal synthesis at temperatures of about 100 °C. At the current stage of development of this technology, the main problem is to increase the synthesis capacity to ensure the profitability of production on an industrial scale. In recent years, in many fly ash-producing countries, the most widespread synthesis has been the one involving the high-temperature fusion of fly ash with sodium hydroxide, but this process is practically unfeasible from a technical and economic point of view, as it requires the use of huge furnaces. The methods of ultrasonic processing and hydrodynamic cavitation can be a possible alternative to high-temperature synthesis, and the conditions provide significant economic advantages for potential production. This paper systematically considers the problems of large-scale synthesis of zeolites from fly ash of thermal power plants and discusses the factors that determine the efficiency of hydrothermal synthesis processes in terms of quality and specific yield of product zeolite. Critical analysis of typical technological processes for the synthesis of zeolites based on TPP`s fly ash from showed that hydrothermal synthesis requires the minimum energy consumption and forms very small amount of by-products that require disposal. Unlike fusion synthesis (about 500 °C), the hydrothermal process is possible at much lower temperatures. Also, hydrothermal synthesis enables replacing pure water with less expensive recycled water to save resources. Recommendations are given that may be useful in the development of appropriate production of zeolite materials based on fly ash. Keywords: fly ash, scaling, technological parameters, technical and economic indicators, waste utilization.