Swelling and plastic properties of coal devolatilized at elevated pressures of H 2 and He : Influences of added iron oxides

Abstract

The influences of Fe 2O 3 and Fe 3O 4 additives on the swelling and plastic properties of a low volatile bituminous coal devolatilized at elevated pressures of H 2 and He were characterized using a high-pressure microdilatometer. The results indicate that added Fe 2O 3 or Fe 3O 4 destroyed the thermoplastic properties of coal at low pressures (< 1.0 M Pa H 2 or He). In general, Fe 2O 3 appeared to serve as a stronger decaking additive than Fe 3O 4. The presence of either additive increased solid yield during coal pyrolysis. The reduction in the thermoplastic properties by the additives is explained by suggesting that Fe 2O 3 and Fe 3O 4 had a catalytic effect that facilitated char-forming reactions during coal pyrolysis. In addition, a chemical role in the case of Fe 2O 3 (conversion of Fe 2O 3 and Fe 3O 4 and consumption of coal-derived H 2 in the process) was suggested. When coal was devolatilized at elevated pressures of H 2, especially at a slow heating rate (≈ 5 K min −1), the plastic and fluid behaviour of the coal markedly increased. This behaviour is explained by suggesting that the effects of H 2 were to decrease the extent of char-forming reactions and to reduce iron oxides to elemental iron which serves as an excellent hydrogenation catalyst (especially at the longer residence time resulting from a very slow heating rate).