Prediction of evolution characteristics of alkali metal compounds in coal combustion/gasification from coal properties

Abstract

A series of experiments has been conducted to study the transformations of the organically bound inorganic elements and inherent sodium chloride under conditions relevant to fluidized bed combustion of low rank coals. Large coal particles (5.5–9.0 mm) were suspended in a convective gas flow in a single particle furnace operated at 700–830 °C. The experiments were performed under pyrolysis as well as combustion conditions. The product particles withdrawn from the furnace at various residence times were analysed using chemical methods, X-ray diffraction and electron microscopy. It was found that the transformations of the inorganic matter in high sodium, high sulphur low rank coals result in the formation of a molten ash layer on the char surface, providing evidence of the formation of low melting point eutectics. The molten ash consisted of a matrix of mixed alkali sulphates. The findings are expected to assist in explaining the role of the inorganic matter in causing operational problems during the fluidized bed combustion of low quality, low rank coals.