Current Fly Ash Disposal Practices and Effects
At thermal power plants, fly ash is currently collected / disposed off by using wet or dry systems. In cases, where fly ash collection systems are not very efficient, a portion of it escapes into the atmosphere causing environmental pollution.
Although accurate data about the influence of the polluted atmosphere on the state of health of persons inhabiting the vicinity of the power station is not available, cases of pulmonary diseases, including asthma and silicosis are found to be on the increase. In association with moisture in the atmosphere, fine particles of fly ash often form aerosols which affect visibility around power stations, though to varying extent. Aerosols, being particles in colloidal dispersion and of lower bulk density, take a long time to settle down as fine precipitation of dust. These can thus be carried over considerable distances from the power station.
In the wet system, fly ash is mixed with water and sluiced to settling ponds or dumping areas near the plant. Being cheaper than any other manner of fly ash removal, it is the widely used method at present in India.
Electrostatic precipitation is the most popular and widely used method of emission control today which enables collection of dry fly ash. The characteristics of coal contributes significantly to the characteristics of fly ash collection. After arresting the fly ash in ESP, it is then transported to silos through suction or by pressurized air. When required, this can be obtained in the container for further transportation directly from the silos through chutes at the bottom, or to the delivery point by pipeline using vacuum suction or pressurized air.
Fly Ash - A Resource
Utilization of fly ash can result not only in reducing the magnitude of the environmental problems, but it is also to exploit fly ash as raw material for value added products (and conserve traditional materials), and for extraction of valuable materials.
Amongst many uses that fly ash can be put to, that in building materials is particularly suitable. It is also anticipated, that there would be considerable short-fall in production of various building materials. According to a study, there would be a large short-fall in the production of bricks – to the tune of 25 billion bricks on an estimated demand of 100 billion bricks per year in India by the turn of the century.
Considerable work ahs been done in various research institutions in India for utilization of fly ash. In spite of the recognition of the size of fly ash utilization / disposal problem and availability of technologies appropriate for Indian fly ashes and applications, India utilizes hardly about 3% of the total fly ash generated.
Considering the colossal problem of disposal of fly ash, as well as the opportunities for conserving traditional resources like clay, cement, etc., the manufacturing of fly ash bricks is very important from the nation’s environmental and economic points of view.
Apart from the technological research and development effected by TPPs, academic and R&D institutions, various departments and ministries of the Government of india have taken initiatives in the area of fly ash utilization. Since the area of fly ash utilization involves many disciplines like power, industry, urban development, environment, science and technology, often, these initiatives are by inter-ministerial groups or multi-disciplinary bodies. Some of the main initiatives are discussed below:
- The National Housing Policy (1998) by the Ministry of Urban Development, and subsequent draft policy documents lay stress on promotion of low cost building materials which include fly ash. Building Materials and Technology promotion Council (BMTPC) in 1990, under the aegis of Ministry of Urban Development, as an inter-ministerial apex organization, ahs been involved in coordinating with various PWD schedules, preparation of technology profiles for various fly ash based products, providing inputs of towards technology scanning, fixing of land rent, policy review etc.
- A centrally sponsored scheme National Network of Building Centers was launched in 1988-89 through HUDCO.
- Fiscal measures announced by the Ministry of Finance in its past three annual budgets include exemption/reduction of excise duty on the production of low cost building materials/components; reduction in custom duty on the import of equipment, machinery and capital goods required for the production of building materials such as fly ash bricks; light weight aggregates, light weigh concrete elements etc.
- HUDCO and NHB are extending financial support to promote industrial units for production of building materials based on fly ash.
- The Ministry of Power (MoP) has proposed a legislative measure to curb utilization of top soil for making bricks within a suitable distance like 50 km from the TPPs, and providing fly ash free of charge. Efforts are on in coordination with MoP to increase the utilization of fly ash to the extent of 50% of the production by 2000 AD from the present about 2-3%.
- An inter-ministerial council – National Waste Management Council (MWMC) has been setup under the Ministry of Environment and Forests (MoEF) to utilize industrial wastes.
- A Fly Ash Mission has been constituted with DST (TIFAC0 as the nodal agency and in coordination with MoEF, MoP.