Evolution, using instrumental neutron activation analysis, of the element composition of coal and oil shale fuel at consecutive stages of its combustion

Abstract

Instrumental neutron activation analysis (INAA) was used to measure the concentrations of 40 elements in coal and oil shale and in products of their combustion at power plants: slag, ash from different aggregates and fly ash. Particular attention was paid to the fine size fractions of fly ash because micrometre and sub-micrometre particles are responsible for the long-range transport of air contaminants. The determination limits of all the elements considered were lower than their mean abundances in the Earth's crust. Concentrations of heavy metals, including radioactive U and Th, and also Cr, Co, Ni, Zn, Mo, Cd, Hg, etc., and toxic non-metals (As, Se, Br, Sb) were determined in the initial fuel and in its combustion products at two power plants. The first, in the city of Chengdu (China), was coal-fired; the second, in Estonia, was oil shale-fired. There were many similar features in the changes in the trace element composition of the combustion products at the two types of power station. Most of the elements enriched in fly ash were volatile. The behaviour of these elements, as revealed by INAA, corresponds to the model of volatilization and condensation processes occurring during combustion of solid fuel.