Chemical characterisation of fly ash from coal-fired thermal power plants in India

Abstract

Fly ash samples collected from electrostatic precipitators of coal-fired thermal power plants in India were analysed for major and trace elements using energy dispersive X-ray fluorescence (EDXRF). A few coal samples were also analysed and element concentrations compared with those in fly ash. Concentrations varied widely, but are well within the ranges cited in the literature for various coal types. The samples were classified into six groups according to the ash content of the coals, which varied from 4 (for lignite) to 40%. The concentrations of Zn, Cu, Ni, Cr and V were high in fly ash samples from lignite. Sulphur concentrations were found to be lower than values reported in the literature for other countries. The K/Ca ratios for fly ash from non-lignite coals were found to correlate with their Si and Fe content. Inter-element correlations in the samples showed associations of Si with K; Cu and Zn with Pb; K with Rb; Al and Ca with Sr; and Fe with Ti. The ash/coal ratios for various elements indicate that most of them are enriched, except for S, which is depleted. Copper and Cr show higher enrichment than other elements by a factor of 4. Concentrations of the toxic elements S, Pb, Cr, As and Cu released from a typical thermal power station complex having a total of 1150 MWe installed capacity were estimated from the measured fly ash composition, the total ash content and the partitioning values reported by Page et al., load factor and amount of coal consumed. The concentrations of these elements in air due to their release in the flue gases of the plant do not exceed accepted levels. The enrichment factor of As in fly ash with respect to crustal rock was found to be high and it can be used as a marker element for fly ash samples obtained from an electrostatic precipitator.