Moisture removal behaviour of single hard lignite particle during drying and quantitative characterization for its surface damage

Abstract

It is extremely meaningful to study the damage behaviour of lignite for safe operation during the drying process. In this study, a single hard lignite particle (SHLP) was prepared for drying. The drying characteristics of an SHLP were described, and its drying kinetics were studied from the perspective of the drying model and effective diffusion coefficient (Deff). The development of surface cracks in drying were obtained, and the changes in surface damage were quantitatively described by relative crack rate (RCR). The results showed that the drying process for an SHLP was divided into three stages following the slope of the drying curve. The rapid removal of a large proportion of moisture mainly occurred in stage I. The Page model is the best model for describing the drying of an SHLP. In addition, Deff increased with increasing drying time. High temperature promoted the moisture transfer from the inside to the surface of an SHLP. Finally, surface cracks on the SHLP developed rapidly in the early drying stage; specifically, the primary cracks widened and lengthened, and the small cracks mainly attached to the primary cracks. In the later drying stage, cracks shrank and cracks in the branch structure closed. High drying temperature made the RCR of an SHLP reach the maximum value more quickly in stage I.