The characterisation of different forms of water in low rank coals and some hydrothermally dried products ☆

Abstract

Equilibrium moisture contents were determined at 30 °C for a range of coals (raw and acid-washed) and hydrothermally dried (HTD) coals in desiccators at various relative humidities maintained by saturated salt solutions. The equilibrium moisture content at 15% relative humidity for a Loy Yang Low Ash coal was the same within the limits of error as that obtained from an isotherm generated by a microbalance (Intelligent Gravimetric Analyser). Total non-freezing water values for the coals and HTD products were measured using both 1H NMR and differential scanning calorimetry (DSC). Higher values for the non-freezing water contents were obtained from DSC measurements, possibly because the calculation assumes that the enthalpy of the non-freezing water is constant and equivalent to that of the bulk water. This assumption is almost certainly erroneous and is not made in the calculation of non-freezing water from the 1H NMR results. The values obtained by the 1H NMR method corresponded to relative humidity values equal to about 92% for the raw coals and ≥96% for the HTD products.