Bhubaneswar: All over the world, the biggest producer of electrical energy is the coal-fired thermal power plants. During production of thermal energy from coal, a large amount of fly ash and bottom ash are produced and rejected at the site causing a lot of pollution on the land, water and air. A developing country like India, avails nearly 70 per cent of the total energy required from coal fired thermal power plants using low grade coal with ash content in the range of 37 to 45 per cent. Nearly 55 per cent of the coal produced in the world, is utilised for thermal power generation. “In a typical 130-MW capacity thermal power plant in India, the coal consumption is nearly 85 tonnes per hour while the ash generation is as high as 35 tonnes per hour. Out of this, 80 per cent is fly ash and 20 per cent is bottom ash. It is expected that, in the year 2020, Indian thermal power plant will consume nearly 380 MT of coal and produce 140 MT of ash,” says noted scientist and former director general of Council for Scientific and Industrial Research (CSIR) Professor Dr P.K. Jena. The generation of fly ash from the thermal power plants has increased considerably all over the world due to production of electric energy from abundantly available non-coking coal. At the same time, with imposition of various environmental rules and regulations — efforts are being made to utilise the fly ash. The scientist Dr Jena suggests that fly ash can be utilised in four potential areas such as back-filling of open cast mine pits and stowing underground mines and developing waste land, production of cement, bricks and other building materials, construction and lining of irrigation canals and production of manure for agriculture and soil conditioning. In the open cast mining sector, a large number of mine pits are generated during harnessing the mineral resources particularly in coal sectors. While some of these pits can be kept open for rain water harvesting, a large number of these can be filled up for reclaiming and implementing afforestation programme. For back filling, these areas the fly ash along with over burden will be very useful. In this way, a huge quantity of the fly ash can be utilised, points out the scientist. “The waste lands particularly, the low lying areas can be filled up with fly ash and over this after placing the top soil, plantation programme can be taken up to make these areas green. As the fly ash contains mostly silica with various types of nutrients, it can be used for reconditioning in the alkaline soils for agriculture and tree plantation purposes,” he adds. Clay fly ash bricks, calcium silicate bricks, cellular concrete, mixing with cement in small quantities, fly ash — gypsum products and sintered light weight aggregate are some of the potential items in building construction activities. Fly ash has a number of favourable properties which are suitable to make bricks. As a result, in many countries in the world, these are in production on a large scale. Recently, with the development of fly ash — lime — gypsum (FaL-G) high strength bricks, the utilisation of flyash is considerably enhanced. “In case of FaL-G bricks, instead of hydrated calcium aluminate phases formed from the flyash-lime reaction, the presence of gypsum leads to the formation of calcium sulphoaluminate hydrates which render quick setting and hardening to the product. FaL-G technology has been successfully practised with even low purity of lime and gypsum, obtained as wastes of other industries,” he observes. At present, about 25-30 per cent of total fly ash produced in India is being used in different sectors. In order to have an environment friendly sustainable development, all the fly ash producers need to undertake and encourage others the implementation of above programmes so that, like other developed countries, the fly ash produced in India can be fully utilised. Both the state and the Central governments should provide the necessary technology and give incentives to the fly ash producers and users, contends Dr Jena.
