Wind Power

Monday, February 11, 2008

Nuisances of fly-ash generated by coal-fired power plant:

Nuisances of fly-ash generated by coal-fired power plant:

Thermal Power plants using pulverized coal or lignite as fuel generate large quantities of fly-ash as a by-product. With the increase in commissioning of several super thermal power plants with large capacity and with the increasing use of low grade coal of high ash content, the amount of generation of ash from them is becoming very large. This poses serious ecological problems. Most of the ash generated from the power plants is disposed off in the vicinity of the plant as a waste material covering several hectares of valuable land. Looking into the nuisances poses by fly-ash; it has been well appreciated by everybody and various Government agencies, the need for the safe disposal and effective utilisation of fly-ash. The properties of fly-ash depend on several variables such as coal source, degree of pulverization, design of boiler unit, loading and firing conditions, handling and storage methods etc.

At present in the under-developed country like India, the focus is on demonstration of coal ash related technologies - these include fly-ash characterisation, Hydraulic Structures, Handling and Transportation, Agriculture related studies and Application, Ash Ponds and Dams, Reclamation of Ash Ponds for Human Settlement, Roads and Embankments, Underground Mine Fills etc. Only a small quantity of the total ash produced is utilized in concrete, brick making, soil-stabilization treatment etc. The bulk utilization of ash is yet to begin in full swing.

Fly-ash characterization: - The physical, geotechnical and chemical parameters to characterize fly-ash are the same as those for natural soils, e.g., specific gravity, grain size, Atterberg limits, compaction characteristics, permeability coefficient, shear strength parameters and consolidation parameters.

Fly-ash disposal in Ash Ponds: - Fly-ash is mostly disposed off using either Dry or Wet disposal procedure. (a) In the case of dry disposal method, the fly-ash is transported by truck, chute or conveyor from the power plant to the site of disposal where these are disposed off by constructing a dry embankment (dyke). (b) In wet disposal, the fly-ash is transported as slurry through pipe and disposed off in impoundment called "ash pond". Most of the power plants use wet disposal system.

Environmental concerns: - The ash produced in thermal power plants cause all three environmental risks, such as, air, surface water and groundwater pollution. . Directly related to these concerns is the additional environmental goal of aesthetically enhancing ash disposal facilities. Air pollution is caused by direct emissions of toxic gases from the power plants as well as wind-blown ash dust from ash mound/pond. The air-borne dust can fall in surface water system or soil and may contaminate the water/soil system. The wet system of disposal in most power plants causes discharge of particulate ash directly into the nearby surface water system. The long storage of ash in ponds under wet condition and humid climate can cause leaching of toxic metals from ash and contaminate the underlying soil and ultimately the groundwater system. The environmental aspects of ash disposal should be taken care of in order to minimize air and water pollution. Most of the above environmental problems can be minimized by incorporating engineering measures in the design of ash ponds and continuous monitoring of surface and groundwater water systems.

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