Flyash: Characteristics, Problems and Possible Utilization

Flyash is a light coal dust coming out with the gases of coal-fired boilers. The particle size of flyash varies from one sub-micron to several micrometers and mineral admixture, inert material and good Pozzolanic properties [1]. In India, electricity is the main source of power for industries. For enormous reserve of coal in the country, coal-based power generation is the major source of energy, and the coal-generated thermal power stations have been established throughout the country. The need and consumption of power is increasing by leaps and bounds; in 1991 the total installed capacity of all the thermal power stations was 45,000 MW, in 1995 it went up to 54,622 MW, in 2003 it has reached 1,06,245 MW (NTPC Publication, 2003). About 62% of the coal produced in India is utilized for generation of 65% of total electricity. The huge burning of low quality Indian coal results into generation of various byproducts like bottom ash, boiler slag and flyash. Ash is the waste product left after the burning of many combustible substances and “flyash” is the term defined for the finely divided residues those results from the combustion of the ground coal. It is dissipated by fuel gas and wind if not checked by devices like electrostatic precipitators. Primarily the flyash particles consist of Silica and Alumina; carbon and oxides of iron, calcium, magnesium, sulfur, titanium etc. being the secondary ingredients. The location of the energy source, nature of fuel and size of the furnace determine the exact nature and quantity of these compounds. The fine particles may remain suspended in the air from few seconds to several months. The particle size distribution of the particulate matter influences residence time and transfer efficiency [2].