Maceral separation from coal by the Reflux Classifier

• The Reflux Classifier was utilised to divide two coals into different fractions by varying the supplied water flow rate.
• The wide channel model appeared to be the most applicable model to predict maceral separation in this set up.
• Products obtained at lower flow rate contained lower particle density, were richer in vitrinite and lower in ash yield.
• The mineral matter bounded in macerals influenced the separations as mineral matter was largely associated with inertinite.

The Reflux Classifier (RC) is a separation technique which has been used in the coal and mineral processing industries. It uses water as a medium, and is therefore a suitable preparation device for studies on coking coal as other separation techniques may change coking properties. The separation process was conducted by using a channel spacing of 3 mm between two adjacent plates (a deviation from the previous 1.77-mm spacing which promoted laminar flow). The 3-mm channel gap which equated to nominal particle size of coking coal in coke oven charge could lead to a transition from laminar to turbulent flow in the separation process. By changing water flow rate in the separation system, two coals, one coking coal and one thermal coal with particle size of − 210 + 100 μm, were separated into different fractions. The fractions contained vitrinite-rich and inetinite-rich concentrates with vitrinite concentration between 28–84% for the coking coal and 20–75% for the thermal coal. In both coals, telovitrinite and semifusinite were the two maceral components of which concentration varied the most. The products relative density and ash yield both decreased with increasing vitrinite content without any apparent changes in the particle size distribution. The mineral content had a significant impact on maceral separation, especially in vitrinite-rich concentrates obtained at low water flow rates.