The effect of added minerals on the pyrolysis products derived from a vitrinite-rich demineralised South African coal

Abstract A better understanding of the behaviour of the inorganic matter present in coal will assist in more cost-effective operations and more consistency in product yield and composition during thermal processing. In this study, the effect of specific major coal minerals on pyrolysis product yield and composition was determined. 5 wt% calcite, dolomite, kaolinite, pyrite, or quartz was added to an acid washed South African medium rank C bituminous coal fraction and pyrolysed using a modified Fischer Assay procedure, using stainless steel retorts, and temperatures of 520 °C, 750 °C and 900 °C. It was found that mineral activity decreased in the order calcite/dolomite ≫ pyrite > kaolinite ⋙ quartz. Calcite and dolomite addition led to a highly significant decrease in tar yield, and tar producers should note this finding as the presence of these minerals in the coal feedstock could have a considerable effect on the tar yield and composition at their operations. Detailed characterization of the measured pyrolysis products provided valuable insight and data for the development of a pyrolysis yield and compositional model based on mineral addition.