Fly Ash Cenospheres – A Resourceful Material for Engineering Applications

In India, about 60% of the total power generation comes from thermal power stations operating on fossil fuels like coal and lignite [1]. Presently about 400 million tons of coal and lignite is consumed annually for power generation. Typically, Indian coals have an average ash content of about 45%, thereby leading to generation of around 180 million tons of ash annually as an industrial by product.

Out of the total ash generated, 70 % of this ash comprises of fly ash and the remaining are bottom ash, economizer ash, air-preheater ash, etc. Presently, dry fly ash is being utilized in a big way in value added products like bricks, blocks, pavers, etc., while bulk volumes of fly ash is consumed in blended cement manufacture, different types of concrete, construction of dams, roads, river embankments, etc.

Fly ash also contains about 1.0 % hollow particles called as ‘Cenospheres’ generated during combustion of the pulverized coal at high temperatures in the thermal power plant boilers. Cenospheres is a useful by-product of coal combustion which can be harvested from the ash ponds or by any other methods such as tribo-electric separation, slurry precipitation, pond skimming etc., from fly ash. Fly ash cenospheres are unique in the way that they possess excellent properties such as lightweight, low density, nonmetallic, high melting points. These unique properties make cenospheres a prospective raw material to produce value added products for use in engineering applications. The paper discusses the work carried out at Central Power Research Institute on cenospheres characterization and development of value added products for various applications.