The advantages of vacuum-treatment in the thermal upgrading of low-rank coals on the improvement of dewatering and devolatilization

A new upgrading method for low-rank coals by a combined process of vacuum drying and tar coating has been developed, and some advantages have been observed. This upgrading technique is able to produce upgraded coals comparable to a bituminous coal; the surface of the coals can be effectively coated in order to suppress low-temperature oxidation and spontaneous combustion. The dewatering rate in the vacuum drying stage at 200 °C reached up to 93.81%, and degree of devolatilization significantly increased with elevation of upgrading temperature, from 15.7% at 200 °C to 35.9% at 300 °C. Furthermore, the specific surface area and susceptibility toward the low-temperature oxidation of coals were influenced by the upgrading treatment.