In-situ study of the permeability of the plastic layer of Australian coking coals using an advanced permeability test apparatus

This project aimed to develop a new advanced permeability measurement device, and an additional feature to the 4kg coke oven at the University of Newcastle to establish a methodology for the measurement of in-situ plastic layer permeability during the coking of Australian coals. Significant advancements in the understanding of plastic layer formation and chemistry have been achieved over the past years, however, mass transport in the plastic layer during coking remains an area to be explored to further the understanding of coking behaviours of Australian coking coals. It is known that plastic layer permeability greatly influences mass transport between the plastic layer and its adjacent layers In-situ measurements of the permeability of plastic layers as they are formed during the coking process are critical to improve the fundamental understanding of such processes.

To achieve the projects objectives, the investigation was undertaken in a series of steps. An advanced permeability apparatus was designed to conduct synchronised measurements of permeability, thermal swelling, and pyrolysis gas composition during heating. In-situ permeability measurement probes were developed and installed in the lab scale double heated wall coke oven. This technique was employed to observe plastic layer permeability and internal gas pressure (IGP) at various locations when the thermal gradient was applied to the coal charge - conditions similar to industrial scale coke ovens. Five Australian coals varying in rank, maceral composition, and fluidity were selected for the permeability tests developed. In this coal set, we have included a high rank coal with high vitrinite that is likely to generate high oven wall pressure, as specified by the sample provider. The given coals were also used to prepare plastic layer samples which display characteristic layered structures (i.e., particulate coal, plastic layer, and coke/semi-coke) by using the plastic layer sampling technique in the 4kg coke oven. The thermoplastic regions in the samples, more specifically from initial softening layer, intermediate plastic layer and resolidified layer, were scanned by Synchrotron micro-CT and the micro-CT images were analysed by GeoDict, a commercial 3D microstructure image analysis software. This analysis provided detailed quantitative information about the microstructural transition across the plastic layer (i.e. porosity, number of isolated pores, pore throat size distribution and compaction ratio of pore wall structure). The results were correlated with those from the permeability measurement facilities to better understand plastic layer permeability and mass transport processes.

Key findings are described in the final report.