Previous Year Question

Fly Ash is a very fine ash generated mainly in Thermal Power Plants that burn coal or lignite. During coal combustion, the non-combustible mineral matter present in coal is converted into ash.

The very fine and light fraction of this ash is carried upward with the hot flue gases and is called Fly Ash. In contrast, the comparatively heavier ash particles that settle at the bottom of the furnace are called Bottom Ash.

The basic process can therefore be understood as:

Coal combustion → Ash formation → Fine particles carried with flue gas → Fly Ash

Thermal Power Plants use Electrostatic Precipitators (ESPs) and other particulate-control systems to prevent Fly Ash from escaping directly into the atmosphere. If collection, storage or transportation is poorly managed, Fly Ash can contribute to air, soil and water pollution.

Fly Ash mainly contains compounds of Silicon, Aluminium, Iron and Calcium. Its exact composition depends on the type of coal, and it can also contain trace quantities of potentially toxic elements.

Fly Ash is not merely a waste material. Suitable ash is used in cement and concrete, fly-ash bricks, road construction, embankments and mine filling. India also has a regulatory framework for utilisation of Fly Ash generated by Thermal Power Plants.