Ash, as we know is produced whenever combustion of solid materials like coal takes place. Fly ash is one such residue which rises with the gases into the atmosphere. The ash which does not rise is termed as bottom ash. In industrial terminology, fly ash generally refers to ash produced during combustion of coal. Fly ash is generally captured by electrostatic precipitators or other particle filtration equipments before the flue gases reach the chimneys of coal-fired power plants. Fly ash contains large amounts of aluminium silicate along with silicon dioxide (SiO2) and calcium oxide (CaO).
Fly ash is a very fine powder and tends to travel far in the air. If fly ash is not captured and disposed off properly, it can pollute air and water considerably. When inhaled fly ash causes respiratory problems. Fly ash in the air slowly settles on leaves and crops in fields in areas near to thermal power plants and lowers the plant yield
Coal accounts for about 70% of power production in the country. The thermal power plants in India generate an estimated 100 million tonnes of fly ash per annum. The World Bank has already cautioned India that by 2015, disposal of coal ash would require 1000 square kilometres or one square metre of land per person.
Despite the enormity of the problem, fly ash has many advantages and can be successfully used to the benefit of society. The following are some of its advantages
The Ministry of Environment and Forests vide its notification in 2009, has made it mandatory to use :-