Comprehensive study on the efficient superheated steam drying kinetics of the low rank coal from Belchatow deposit in Poland

Lignite, a low-rank coal, is characterized by low calorific value, mostly attributed to its considerable water content. Upgrading the quality of this energy carrier, which benefits coal-fired power plant's thermal efficiency, can be effectively realized by means of drying. The kinetics of superheated steam drying was studied for 30 mm spherical samples from Belchatow lignite mine in Poland. The experiment featured simultaneous and continuous measurements of weight and temperature. The drying kinetics, described by curves of moisture content, drying rate and temperature profile, were evaluated using the data acquired. The present study is a follow-up of analogical examination conducted on 5 and 10 mm objects from the same lignite deposit. The appearance of the sample throughout the process was video-recorded. Widespread cracking and shrinkage, which differ depending on the conditions, along with series of droplets typical for larger sample, were observed. The examined particles were suitable for predictions of thermodynamically derived drying rate and time, as proposed previously for smaller particles. However, in comparison they exhibit more uniform density distribution. Extensive investigation, revealing features of variously-sized samples as well as diameter dependence of drying behavior, is required for purposes of designing industrial drying system dedicated to specific type of coal.