Future Technological options for  Increased Fly ash utilisation– A Review

Nearly 73% of India’s total installed power generation capacity is thermal, of which coal-based generation is 90%. Presently 90 million tonnes of fly ash is being generated annually in India, with 65 000 acres of land being occupied by ash ponds. The use of coal of high ash content (30%–50%) contributes to these large volumes of fly ash. By end of 11th five year plan the fly ash generation in the country is estimated to reach 110-120 million TPA. India’s dependence on coal as a source of energy remains unchanged. Thus, it is but natural that fly ash management in the country would be important and of national concern.

Such huge quantities of generation would pose challenging problems, in the form of land usage, health hazards, and environmental dangers. Both in disposal, as well as in utilization of fly ash , utmost care would have to be taken, to safeguard ecological balance of the surroundings.

The percentage fly ash utilisation in the country has registered a significant increase from 3 – 5% in late eighties and early nineties to the present levels of around 13% utilisation . However this growth trend is too minimal considering the total quantities of generation. It should be of knowledge here that there are countries, which have reached levels of 80 – 100 % fly ash utilisation levels.

A recent survey carried out on spatial distribution of the thermal plants in the country indicates that these locations could be broadly classified into four categories:

  • Plants located in major/metro cities and their periphery
  • Plants located near coal pitheads.
  • Plants located near consumer industries (Cement plants).
  • Plants not located under the above categories.

Thus depending on the locations of the generation sites , suitable technological options need to be selected and evolved for enhancing the levels of fly ash utilisation of the country.

In case of thermal plants located near cement plants and near major/metro cities,  the main avenue for utilisation of fly ash would be its maximized usage in Cement & concrete . In the tropical climatic conditions of India , the  fly ash based products are being accepted as the  most effective option for durability and performance . This awareness would help increase its utilisation in these areas of applications.

This paper initially discusses briefly the quality characteristics of the low lime Class – F fly ashes available in the country and illustrates that they are in no way inferior to their European counter parts (low lime Class – F fly ash ), in their pozzolanic activity in blended cements and in their use as inorganic admixtures , in concrete as illustrated by the studies carried out at the authors laboratory.

For furthering the utilisation levels of fly ash in cement & Concrete, some of the newer technological options are discussed in the paper in some details. These options include, Processes for improving the pozzolanic activity of fly ash by processing, Processes for decreasing the combustible  contents in fly ash,  Ash modified clinker technology (AMC technology ) a patented process developed in China  – which produces a fly ash  having cement clinker minerals, Manufacture of Sulpho-aluminate belite cements ,high strength cementitious grouts, cementitious binder and aggregates in  pavement applications etc.

The authors opine that in future, the most common feature in cement plants would be Captive power plants using high ash coals , that would generate fly ash  , which could be a value added option with use of some of the above technologies.

In the case thermal plants located at distance from the consumer industries, besides the presently used technologies for use of fly ash in fly ash bricks, landfill , soil conditioning  etc ,  there could be  other avenues of utilisation which could be looked into,  such as  fly ash as a source  material for alumina with Portland Cement as by – product ,In the manufacture of Zeolites – a raw material for  detergent industry , Production of alum from fly ash ,  for manufacture of artificial soil by SLASH  process – which uses sewage sludge , lime and fly ash – partial use of the SLASH  also improves the crop yield  etc . These technological options could be site specific for maximizing the generated fly ash.

Finally the authors summarize that better acceptance of the fly ash generated in country as a pozzolanic material, selection of an appropriate technology relevant in Indian context and to location of the generation would certainly help increase the levels of its Utilisation.

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