Recent developments in drying and dewatering for low rank coals

Globally, low rank coals are responsible for about half of the world's total coal deposits. However, these low rank coals present a high moisture content, which significantly impacts their utilization processes, including lower power plant efficiency, increased transportation costs, higher CO2 emission, and spontaneous combustion during storage. In order to decrease the energy consumption of low rank coal during the utilization processes, drying and dewatering technologies must be well designed. This review presents recent development in drying and dewatering technologies for low rank coals. Evaporative drying technologies, such as rotary-drying, fluidized-bed drying, hot oil immersion drying, hot oil-immersion drying, as well as non-evaporative drying technologies such as hydrothermal dewatering, mechanical/thermal dewatering, solvent extraction, are summarized in detail. Future research to upgrade low rank-coals, which are deposited in arid geological environments, is also suggested.