Environment Protection

High value-addition to power generation through effective use of fly ash and coal

(N.B.: This paper was presented in the International Seminar on Mineral Processing Technology, MPT-2003, held from 6^th to 8^th February 2003 in Panjim, Goa)

The economics of thermal power stations utilizing high-ash coals can be substantially improved if the constituents in their fly ash (generated while burning coal) are recovered and processed into high-value products.

In relation to National Thermal Power Corporation's coal based operations, sales turnover and profitability can be enhanced several folds by proper utilization of fly ash. Recent advances in mineral processing offer the unique opportunity of reducing the ash content in its coal to levels substantially lower than the 34% currently possible from coal washeries. Modern coal ash and fly ash cleaning technologies include improved column flotation; high density cyclones; selective agglomeration; enhanced gravity separation; spiral separation; electrostatic and triboelectrostatic separation; and high-density and high-intensity magnetic separation.

The new technologies also provide better economical and environmental advantages. In addition, electricity generation from high-ash Indian coals can be a much cleaner, and more remunerative, process than one that produces power from "green fuels" like CNG.

for more information, contact: Director, M. S. Iyengar & Associates (P) Ltd., New Delhi

Alternative perspectives to carbon dioxide stabilization

(N.B.: This paper was presented in the Eight Annual International Pittsburgh Coal Conference, held on 14-18 October 1991, in Pittsburgh, PA, USA)

Increasing deforestation and consumption of commercial energy is raising carbon dioxide levels in the atmosphere in an unbalanced manner. Carbon dioxide molecules trap the sun’s heat, much as a greenhouse does, and this can cause global warming. An estimated 21,400 million metric tonnes of carbon dioxide is added each year and the rate is increasing at about 0.5% per annum. Although it is currently not possible to predict regional temperature, precipitation, and other effects of climatic change with confidence, the two possible consequences with highly adverse impacts that have been identified are the interruption of deep ocean currents and the surging of the West Antarctic Ice Sheet. This could affect temperature and precipitation, with possibly catastrophic repercussions and/or lead to a large influx of fresh water which could alter the salinity of the world's oceans. This would affect both plant and animal populations alike.

The suggestions made to counter this likelihood have ranged from limiting global industrial growth to reflecting the sun's rays back into space through geo-engineering or by the use of space borne mirrors. However, it is unlikely that any of the solutions put forward so far would provide additional benefits. This paper, therefore, seeks to provide better way that will not only curtail carbon dioxide emissions but will also provide economic benefits to society and, at the same time, stimulate industrial growth.

Of the three alternatives outlined, the first is based on the fact that oxidation of carbon to carbon dioxide takes place in two stages, i.e.

C + ½0₂ ---> CO - 111.42 KJ/mol (1)

CO + ½0₂ ---> CO₂ - 283.07 KJ/mol (2)

The second stage, i.e. reaction (2), involves a chain reaction with hydrogen, and hydrogen containing radicals. Therefore, emission of carbon dioxide can be contained by terminating the reaction after the first stage.

The second alternative discusses the reduction, using carbon or hydrogen, of carbon dioxide to carbon monoxide, which can be converted to methanol or synthesis gas by the following reactions:

CO₂ + C ---> 2CO + 171.65 KJ/mol (3)

CO₂ + 3H₂ ---> CH₃0H + H₂O - 49.5 KJ/mol (4)

CO₂+ H₂ ---> CO + H₂O + 41.1 KJ/mol (5)

Thus, zero emission of carbon dioxide can be ensured.

Hydrogen can be supplied from external sources or liberated by the following reactions:

C + H₂O ---> CO + H₂ + 130 KJ/mol (6)

H₂O + CO ---> H₂ + CO₂ - 41.1 KJ/mol (7)

The third alternative discussed is the conversion of carbon dioxide to bio-mass through bio-chemical process, simulating Nature. Blue-green algae, which are a rich source of protein and various valuable minerals, can be synthesized photo-chemically in a system of algae inoculums, alkaline water, trace minerals and carbon dioxide.

for more information, contact: Director, M. S. Iyengar & Associates (P) Ltd., New Delhi

A new approach to processing of coal, bauxite and ilmenite

(NB.: this paper was presented in the International Seminar on Mineral Processing Technology, MPT-2002, held from 3^rd to 5^th January 2002 in the Indian Institute of Science, Bangalore)

Most minerals processing today focus on recovering the main component while rejecting the rest. Recent advances in selective crushing, ultra fine grinding, size separation, and electrostatic, magnetic and optical separation provide an alternative approach to recover the other constituents also, thus increasing value addition and minimizing wastage. One example is a combination of gravity, electrostatic, triboelectrostatic and magnetic separation to obtain low ash coal, while recovering valuable mineral constituents. Another possibility is to recover bauxite constituents through a combination of selective crushing, ultra-fine grinding, and optical, electrostatic, triboelectrostatic and magnetic separation.

for more information, contact: Director, M. S. Iyengar & Associates (P) Ltd., New Delhi

A holistic approach to mineral processing

The main challenge before industry today is to be competitive in a global market-driven economy while conserving the earth’s finite resources for the future. If one views traditional raw material processing in a holistic manner, it would be obvious that old ways, e.g. prospecting, mining, and processing a particular mineral, while discarding other associated ones, have to change.

In India, nearly 100 million tonnes per annum of fly ash is produced when coal is burnt to generate power. Although it contains recoverable carbon, iron oxide, alumina, silica, low and high-density cenospheres, most of this ash is wasted. Yet these same materials are manufactured from other sources using un-sustainable resource-depleting processes. For instance, the carbon black required by the tire industry is produced from imported petroleum feedstock; iron ore is mined and processed for iron and steel, and bauxite for alumina. In turn, the alumina industry discards undigested alumina, iron oxide, silica, titanium dioxide and Rare Earth minerals, while the iron and steel industry wastes alumina, silica, and other equally important minerals. Interestingly, titanium dioxide and Rare Earth minerals are recovered from beach sand, and huge expenditure is incurred to re-habilitate mined areas.

All the above minerals can be sourced from a single source, e.g., Nalco's alumina refining and power generation operations. By applying a holistic approach the company can double its alumina production without incurring expenditure on bauxite mining, material handling, crushing and grinding costs. In addition, it would also increase its sales turn-over by marketing titanium dioxide and other valuable products in an efficient, more cost-effective, and less wasteful manner.

for more information, contact: Director, M. S. Iyengar & Associates (P) Ltd., New Delhi