The release of water-bound and organic sodium from Loy Yang coal during the combustion of single particles in a flat flame

The concentration of atomic sodium in the plume of single brown-coal particles burning in a flat flame environment is measured using quantitative planar laser-induced fluorescence (LIF). A run-of-mine Loy Yang brown coal (LY-ROM) and two Loy Yang brown coals (MTE1 and MTE2) that were processed using Mechanical/Thermal Expression, which removed a fraction of the inherent moisture and concomitant dissolved salts, were investigated. By applying a chemical equilibrium model, at an appropriate location in the flame, the total sodium release is estimated from the measured atomic sodium concentration profile. For LY-ROM, MTE1 and MTE2 the total proportion of sodium release following devolatilisation, as a percentage of the initial sodium in the coals, was 80.9 ± 19.5%, 87.9 ± 19.0% and 93.0 ± 28.0% respectively. Using this data, it is inferred that approximately 67% of water-bound sodium and approximately 100% of the organically-bound sodium is released following devolatilisation. Furthermore, in the present experiments up to 60% of the total sodium is released during the period in which the ash remains within the flat flame, following char combustion. A mechanism is proposed to explain this observation in which Na2O in the ash reacts with ambient water vapour at high temperature.