Generalized desorption equilibrium equation of lignite in a wide temperature and moisture content range

Brown coal is the most abundant and economically viable source of energy. To increase the efficiency of power generation from brown coal predrying of lignite is probably the first step to be taken. Both air drying, or more energy efficient superheated steam drying, may be considered. For the design of both processes an equilibrium relationship between water activity, moisture content and temperature in a form of working desorption isotherm is needed. This work presents experimentally obtained results of sorption isotherms measurements at seven temperatures and one sorption isobar at atmospheric pressure obtained for Bełchatów brown coal. These results were compared to the results obtained by other authors for Australian and USA coals and due to relatively close fit of all data points one generalized equation of desorption equilibrium was fitted covering a wide range of temperatures from 5 to 260 °C and moisture contents up to 1.5 kg/kg. Adsorption isotherms are not described by the same equation since strong sorptional hysteresis was observed.