How fly ash is hazardous


Fly ash is a very fine powder and tends to travel far in the air. When not properly disposed, it is known to pollute air and water, and causes respiratory problems when inhaled. When it settles on leaves and crops in fields around the power plant, it lowers the yield.

The conventional method used to dispose of both fly ash and bottom ash is to convert them into slurry for impounding in ash ponds around the thermal plants. This method entails long-term problems.

 

The severe problems that arise from such dumping are:

How dumping of fly ash leads to pollution of air, land and water

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India would require 1000 sq Km / 1 Sq m per person for disposal of coal ash by 2015.

when the lagoons are full, four basic options are available:

constructing new lagoons using conventional construction material,

~ hauling of fly ash from the existing lagoons to another disposal site,

raising the existing dyke using conventional constructional material, and

~ raising the dyke using fly ash excavated from the lagoon (’ash dyke’).

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· The construction of ash ponds requires vast tracts of land. This depletes land available for agriculture over a period of time.

· When one ash pond fills up, another has to be built,
at great cost and further loss of agricultural land

· Huge quantities of water are required to convert ash into slurry.

During rains, numerous salts and metallic content in the slurry can leach down to the groundwater and contaminate it.

Disposal problem

The Raichur Thermal Power Station (RTPS), one of Karnataka's major power plants, is situated at Shakthinagar near Devasugur village in Raichur District. Owned by Karnataka Power Corporation Limited (KPCL), RTPS consists of seven units, each capable of generating 210 MW of power. Its total power generation at optimum capacity is 1470 MW per day. RTPS is the power-generating hub of Karnataka and meets 75 per cent of the state's power demand.

 

India has about 70 thermal power plants and 70 per cent of them burn coal to generate power. Various Indian collieries supply the coal, which is known to have a very high ash content of almost 40 to 45 per cent.

India's thermal power plants produce an estimated 100 million tonnes of fly ash per annum. Of this, RTPS alone generates about 1.5 million tonnes at 4,000 tonnes daily. Out of this, 80 per cent is fly ash and 20 per cent bottom ash. This ash needs to be disposed of every day.

 

Primarily, the fly ash is disposed of using either dry or wet disposal scheme. In dry disposal, the fly ash is transported by truck, chute or conveyor at the site and disposed of by constructing a dry embankment (dyke). In wet disposal, the fly ash is transported as slurry through pipe and disposed of in impoundment called "ash pond". Most of the power plants in India use wet disposal system, and


The option of raising the existing dyke is very cost effective because any fly ash used for constructing dyke would, in addition to saving the earth filling cost, enhance disposal capacity of the lagoon.

An important aspect of design of ash dykes is the internal drainage system. The seepage discharge from internal surfaces must be controlled with filters that permit water to escape freely and also to hold particles in place and the piezometric surface on the downstream of the dyke. The internal drainage system consists of construction of rock toe, 0.5m thick sand blanket and sand chimney. After completion of the final section including earth cover the turfing is developed from sod on the downstream slope.





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