Coal middling retreatment using high voltage pulse technique. Part 1: Experimental findings

Coal middlings are usually highly intermixed and notorious for economic reprocessing using conventional mechanical methods. In this study, the high voltage pulse (HVP) technique is employed to retreat coarse coal middlings (26.5–37.5 mm) with the purpose of improving middlings processability. Part 1 of this study assesses the breakage characteristics of the coal middlings, the liberation properties and the potential for retreatment via density and size. Part 2 investigates the mineralogical composition, mineralogical texture and granulometric composition to discern the key factors affecting coal middlings processibility. Part 1 of this study includes full densimetric analyses of the coal middlings prior to and after breakage using the electrical disintegration (ED), Electro-hydraulic disintegration (EHD) and roller crusher. The additive contributions from EHD effects in the ED process were experimentally demonstrated. The ash and sulfur deportment by density and size behavior was also investigated. It was concluded that the HVP multiple particle test method was capable of liberating the coal middlings into low and high-density fractions. A theoretical 81.73% organic matter recovery with a sulfur grade of 0.97% and an ash content of 9.02% could be achieved by scavenging just 50.26% mass, and 72.97% of the sulfur remained in the heavy fractions with the mineral matter. The results encouraged the application of HVP retreatment for coal middling, however, not as a direct mean to achieve separation, but as a preparatory process for gravity-based downstream process to achieve middlings deashing and desulfurization.