The separation of fine coal has been widely discussed in the coal preparation industry due to its high economic potential. Dense medium cyclone (DMC) is the most efficient equipment available for fine coal separation. However, the industrial application of DMC is far from satisfactory due to operational difficulties and maintenance. In this research, particle settling behavior in a dense medium cyclone was analyzed for improved separation. The calculation result about feed pressure and separation lower limit, which fits the experimental data well, might be a guidance for industrial DMC design and operation. According to the calculation result, it is highly recommended that the separation lower limit be set at 0.2 mm rather than 0.1 mm, because the feed pressure head required for the latter (50 D) is three times higher than the former (15 D).

The comprehensive quality enhancement and grading of coal are crucial methods for unlocking the high value-added and low-carbon utilization of coal resources. In this work, the influence of oily bubbles on the flotation of Shendong Jurassic vitrinite-rich coal and inertinite-rich coal was studied via flotation tests, Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), contact angle detection, and induction time measurements. FT-IR and XPS analyses demonstrated that the surface of inertinite-rich coal contains more hydrophilic oxygen-containing functional groups. Contact angle and induction time measurements showed that the vitrinite-rich coal is more hydrophobic than inertinite-rich coal, and that for both air and oily bubbles, the induction time on the surface of vitrinite-rich coal is shorter than that on the surface of inertinite-rich coal. In addition, rather remarkably, the induction times for both vitrinite-rich coal and inertinite-rich coal are significantly reduced by oily bubbles. Finally, a better flotation performance for oily bubble flotation of vitrinite-rich coal and inertinite-rich coal was found. It appears that oily bubble flotation is an efficient method for enhancing the recovery of vitrinite-rich coal and inertinite-rich coal.