Optimization of microwave dewatering of an Indonesian lignite

Dewatering of an Indonesian lignite with microwave irradiation was optimized to increase dewatering rate and decrease energy consumption. The energy consumption of the microwave dewatering process was affected by different factors, including addition of microwave absorber, diameter-to-height ratio of lignite pile, particle size and initial moisture content of lignite. The experiment results indicated that adding absorber carbon materials (activated carbon and graphite) and metal oxides (Fe3O4, MnO2, etc.) could increase the dewatering rate and decrease the energy consumption. With increased diameter-to-height ratio of lignite pile, dewatering rate initially increased and then decreased. An optimum value exists for diameter-to-height ratio, which presents maximum dewatering rate but with minimum energy consumption. The enhancement of heat accumulation caused by larger particle size increased the dewatering rate of lignite and decreased energy consumption. The energy consumption decreased with increased lignite weight and initial moisture content. However, the energy consumption initially decreased and then increased with enhanced microwave power. Electric power consumption can be well predicted on the basis of the microwave dewatering kinetics of lignite, which can be well described by the Page model under different conditions. (C) 2015 Elsevier B.V. All rights reserved.