An experimental study on the effect of system pressure on char structure of an Australian bituminous coal

A 63-90 mu m size fraction of an Australian bituminous coal sample was fed into a drop tube furnace (DTF) and a pressurized drop tube furnace (PDTF) t o generate chars. A gas temperature of 1573 K and system pressures of 0.1, 0.5, 1.0, and 1.5 MPa were considered. Particle size analysis, scanning ele ctron microscopy (SEM), and image analysis were employed to analyze the cha rs produced in order to investigate the effect of system pressure on the re sultant char structure and morphology. The char character was found to be i nfluenced significantly by the system pressure. Results obtained indicated that the coal and char fragmentation might have occurred during devolatiliz ation at high pressure. The char size (as characterized by the swelling rat io) was also observed to increase with system pressure. The cross-sectional characterization of the char particles indicated that at high pressure the majority of the char particles are of high porosity with thin walls or net work (the group I type) rather than of medium porosity with thicker walls o r network (the group II type) and of low porosity (the group III type). Cha r particles generated at high pressure were also observed to have a higher internal and surface porosity.