Experimental study on rotary triboelectric separation of low-rank coal macerals with surface modification

The enrichment of vitrinite can enhance the oil yield and conversion rate in low-rank coal liquefaction. The work evaluated the effects of surface modification on the rotary triboelectric separation of macerals. Permittivity and charge-mass ratio analysis of vitrinite and inertinite under various modified conditions demonstrated that kerosene and diesel were excellent modifiers since they keep the permittivity of macerals at a low level. The largest difference in triboelectric charge of vitrinite and inertinite was obtained when 3.0 kg/t kerosene was adopted as modifier. Rotary triboelectric separation of untreated low-rank coal indicated that the optimal separation, i.e., a vitrinite content of 65.45% and a recovery of 69.89%, was obtained at a feed rate of 1.5 g/s, a friction wheel speed of 3000 rpm, and a separation voltage of 30 kV. Under the optimum operating conditions, the optimal rotary triboelectric separation under surface modification, i.e., a vitrinite content of 69.78% and a recovery of 73.52%, was achieved when the coal was treated by 3.0 kg/t kerosene. The results demonstrated that surface modification significantly improved the rotary triboelectric separation by changing the surface electrical properties of macerals, while the excessive dosage of the modified reagent was unfavorable to achieving optimal separation.