A study on the mechanism of the evolution of carbon structures during the coking process of Australian coking coals

As a permeable and supportive material in blast furnaces, coke is required to maintain optimum strength and reactivity. It is believed that the carbon structures of coke will ultimately determine its quality. When coking coals are heated in a coke oven, complex chemical reactions such as the release of volatiles, the formation of radicals, hydrogen transfer, crosslinking, and resolidification take place during the carbonisation process. These reactions have profound impacts on the formation of the carbon structures in the plastic layer and, subsequently, on the coke structure. The transformation of chemical structures during the coking process depends on factors such as the properties of the parent coals and operating conditions. Coking coals exhibit fluid-like behaviour and form a plastic layer when the temperature of the coal bed reaches above 350 C. Following the plastic layer stage, after the temperature reaches above 500 C, crosslinking, re-polymerisation and condensation reactions occur, leaving a solid porous residue, namely, semi-coke and coke. Accompanying the formation of the semi-cokes during the heat treatment process is the release of volatile matters, e.g., H2, CO, CO2 and CH4, from the structures of the compounds, leading to the formation of C-C bonds, and consequently shaping the carbon structure of coke. Due to the limited resources of premium coking coals, more research on the underlying mechanisms of the structural transformations during the coking process will provide more information for coal blending techniques and for predicting the final coke quality based on coal properties.