Thermal effect during moisture re-adsorption of dewatered lignite

The adsorption activation energy and heat released from the moisture re-adsorption process of dewatered lignite were calculated and related to the drying and re-adsorption behaviors of Chinese lignite. The re-adsorption type and rate of moisture were discussed based on the surface changes of dewatered lignite determined by nitrogen adsorption and in-situ FTIR techniques. The heat quantities released by 1 g dewatered lignite at 353, 393, and 453 K adsorbing 1 mol moisture were, respectively, 65.0, 68.6, and 70.6 kJ, which were greater than the condensation heat of per gram pure water (44.4 kJ mol(-1)). It was suggested that the water adsorbed by dewatered lignite existed mainly in the physical and chemical adsorption states, in which the physically adsorbed moisture was dominant. With increasing of drying temperature, the collapsing degree of pore structure intensified, which leads to the decline of the amount of physically adsorbed moisture, but the slight increase of chemically adsorbed moisture. The amount of saturated re-adsorption moisture at different temperatures varied linearly with water vapor partial pressure. The re-adsorption process had two obvious segments corresponding to the two types of adsorbed moisture. And the higher the adsorption temperature, the shorter the transition time of two segments. The activation energies of two segments were, respectively, 7.9 and 17.3 kJ mol(-1).