In-situ study of plastic layers during coking of six Australian coking coals using a lab-scale coke oven

Abstract

An in-situ study on the formation mechanism of plsatic layer was carried out by using a 4 kg laboratory-scale coke oven under controlled heating conditions. The coke oven rig enabled in-situ measurements of internal gas pressure (IGP) and temperature profiles in five locations in the coal charge and allowed sampling of semi-coke which consisted of the coke/semi-cokes, the plastic layers and loose coal. Six Australian coking coals with varying properties were used in the coking experiments. The semi-coke samples were scanned by micro-CT at the Imaging and Medical Beamline at Australian Synchrotron to study the physical structure transitions inside the thermoplastic regions and investigate the fissure patterns at the coke/semi-coke sides. The thicknesses of the plastic layers in different locations inside the coal charge were estimated from the measured temperature profiles and the initial softening temperatures and the solidification temperatures measured from the Gieseler fluidity tests. The results showed that the thicknesses of the plastic layers increased from the heating wall to the center of the coal charge. The IGP curves measured in different locations were used to obtain the maximum IGP values and the IGP termination temperatures across the coal charge. The difference in the extents of fissuring appeared to influence the maximum IGPs measured at the center of the oven. The higher extent of fissurin appeared to facilitate the release of volatile matterfrom the thermoplsatic region through the semi-coke sides, thus leading to lower maximum IGPs at the center. It was found that the extents of the fissuring and the maximum IGPs at the center were sensitive to the coal properties such as the petrographic properties, Gieseler maximum fluidity and volatile matter content.