Thin-layer drying characteristics and modeling of lignite under supercritical carbon dioxide extraction and the evolution of pore structure and reactivity

In this study, the drying characteristics and kinetics of two typical lignites were investigated by using supercritical carbon dioxide (SCCO2) at mild temperature (62-102 °C). The drying characteristics results show that SCCO2 extraction drying has advantages over conventional drying such as better heat transfer and faster diffusion rate. Seven previous thin-layer models and a new proposed model were applied to analyze the lignite drying kinetics, and the proposed model obtained the best fit to the lignite drying process in all of the models. Apparent diffusion coefficients of moisture in SCCO2 drying are higher compared with conventional drying method. The activation energies for the diffusion process of two typical lignites are 10.5561 and 11.6218 kJ/mol, which are far lower in comparison to conventional drying process. The pore structure and gasification reactivity of drying lignite were analyzed and both of them have an obvious improvement after the SCCO2 drying process.