Drying of lignite during beneficiation in the air dense medium fluidized bed under mild conditions

Abstract

High water content and ash content are major challenges in lignite utilization. The beneficiation processes, between the mining and upgrading, can achieve deashing and dewatering. An air dense medium fluidized bed integrated drying and beneficiation of lignite was designed in the present research. The drying characteristics of lignite in designed fluidized bed under mild conditions were investigated. Results show that for refractory lignite with diameters from 13 mm to 25 mm, the surface water removal efficiency reaches up to 91% and the adhesion efficiency of dense medium decreased to 0.16% at 85 °C for 2 min with original surface water content of 1.2% and air velocity of 3.5 cm/s. The probable error of separation Ep is 0.048 g/cm3 which is much lower than that of common air dense medium fluidized bed. Based on momentum transfer, heat transfer and mass transfer between moist lignite, adhered dense medium, fluidized dense medium and hot air in the fluidized bed, the drying process in lignite beneficiation was detailed explained. During drying in beneficiation, the dense medium adhered on lignite surface play a significant role since they helped moisture transfer from lignite surface to the hot air, realizing the removal of surface water.