Impact of weathering on coal properties and evolution of coke quality described by optical and mechanical parameters

Changes of coals properties due to weathering and its impact on the properties of derived cokes were investigated. Four coking coals collected from Polish coal mines were stored for one year in order to simulate weathering conditions. Samples of fresh and weathered coals were analysed in terms of different coking properties, e.g. fluidity, contraction, thickness and gas permeability of the plastic layer. All coals were also pyrolysed and the optical and mechanical properties of the produced cokes were determined. Results showed that the fluidity clearly decreased with elongation of the storage time. Other coking properties of coals also changed with the storage time in different ways depending on their rank and initial fluidity. Oxidation of all coal samples resulted in a shift of the observed texture of derived cokes towards smaller (worse ordered) textures. However, it was found that the coke from 6-month stored Budryk coal, referring to the coke originated from the respective fresh coal, is characterized with slightly better quality, in terms of reflectance and coke post-reactive strength, CSR. No significant changes in quality of other coke samples were observed.