The non-isothermal drying characteristics of lignite and prevention strategies for structure damage

Structural damage to lignite during drying may cause dust explosions and pose a safety hazard. In this study, a prevention strategy for drying damage of lignite particles using non-isothermal drying processes is proposed. The isothermal and non-isothermal drying processes of lignite particles were systematically studied using drying curves, drying models, and water transfer coefficients. Temperature changes inside the particles were monitored, and the particle strength after drying was analyzed. The results revealed that the internal temperature of the particles suddenly increased towards the end of the drying period at 170 °C, and the corresponding water vapor pressure significantly increased, thereby increasing the driving force for water transfer during the later stages of drying. However, the water vapor pressure caused serious damage to the particles. For the non-isothermal drying process in which the temperature decreased from high to low, the free water was rapidly and massively removed under high temperature during the early stages of drying, and the vapor pressure decreased during the removal of pore water in the late stage of drying, which meant less damage was caused to the pore structure by the vapor pressure.