Mössbauer analysis of iron phases in brown coal ash and fireside deposits

Abstract

The iron phases present in an electrostatic precipitator ash, an uncooled ash deposit and a cooled superheater ash deposit from Hazelwood Power Station, Australia, burning Morwell brown coal has been examined using Mössbauer spectroscopy. The principal iron phase in the precipitator ash and the uncooled ash deposit from a hot gas offtake was calcium aluminoferrite (Ca2Fe2 − xAlxO5). Minor amounts of hematite (α-Fe2O3) and magnetite (Fe3O4) were also detected in the precipitator ash. The cooled superheater ash deposit contained a (Mg, Fe, Al) oxide spinel as the primary iron phase; small quantities of hematite were also detected in this deposit close to the heat exchanger interface. The formation of these iron phases has been rationalized on the basis of the average composition of coal delivered to the power station and supplementary ash chemistry data obtained from other techniques. The evidence suggests that the calcium aluminoferrite in the precipitator ash is derived from inorganic constituents (distributed throughout the coal organic matrix) and the hematite and magnetite are of mineral origin (discrete particles).