Conversion characteristics of Canadian coals subjected to vacuum pyrolysis treatment

Abstract

Bench-scale vacuum pyrolysis experimentation (600°C reaction temperature, 10°C min −1 heating rate, < 0.7 kPa total pressure) was carried out on a set of 20 Canadian coals to examine the role of coal rank and petrographic composition on conversion properties. Yields of solid residues (cokes) are a function of initial coal rank (increasing yields with increase of rank), whereas liptinite-rich coals tend to generate low amounts of coke. Calorific values of the cokes produced from low-rank coals significantly exceed the calorific values determined for the feedstocks. Tar yields are a function of both rank and petrographic composition, with the highest values in the 0.7–1.1% vitrinite reflectance range. Very high tar yields were obtained from liptinite-rich samples (24.4–93.0 wt%). Correlations of chemical and petrographical characteristics of the coals subjected to vacuum pyrolysis treatments displayed well-defined relations in terms of petrographic composition, volatile matter and H/C atomic ratios on the one hand and conversion rates on the other.