EFFECT OF CHANGING INERTINITE CONCENTRATION ON PYROLYSIS YIELDS AND CHAR REACTIVITIES OF 2 SOUTH-AFRICAN COALS

Pyrolysis experiments have been carried out with sets of inertinite graded samples prepared from two South African coals (Durban Navigation and Vryheid Coronation Collieries). The effects on product distributions of increasing inertinite concentration, and of different heating rates, have been determined. An atmospheric pressure wire-mesh pyrolysis reactor was used during these experiments (1 or 1000 K s(-1) to 700 degrees C with 30 s holding at peak temperature) in order to minimize reactor related effects on the results. Tar and total volatile yields from the South African samples decreased with increasing inertinite concentration; the decrease in yields were in line with those observed for a set of maceral concentrate samples from a UK coal (Point of Ayr) and other Northern Hemisphere coals. Total volatile yields showed no detectable deviations when plotted alongside a correlation based on data from 24 Northern Hemisphere derived coals. Relative combustion reactivities of the chars from the pyrolysis experiments have been determined using a standard TGA-based method, as a function of inertinite contents of the original samples. The lower rank DNC set showed a rapid drop in char combustion reactivity with increasing inertinite concentration. By contrast, the reactivity of the VCC samples showed no sensitivity to changes in maceral concentration. It seems tempting to ascribe this similarity between vitrinites and inertinites of the VCC samples to progressively diminishing differences between macerals of higher rank coals. Clearly, however, many more samples need to be studied before definitive conclusions can be drawn.