Blast furnace raw material variations and industry specifications necessitate efforts to identify and control factors that determine the quality of coke. Coke quality is expressed, in part, by its mechanical strength at high temperature, commonly known as coke strength after reaction (CSR). CSR indicates the reactivity of coke towards oxidizing gases and the extent of coke degradation within the blast furnace. The metallurgical coke characteristics that influence its quality are surface area, carbon forms, and chemistry. These parameters, in turn, are controlled by coal blend properties and coking conditions. In this work, the influence of coking rate on coke structural quality is evaluated. Two coking runs were performed using a commercial coal blend carbonized in a pilot-scale moveable wall slot-oven under similar conditions but varying the coking rate from 15.57 to 16.52 mm/hour. Coke fingers were collected intact and sliced incrementally perpendicular to the long axis. The prepared samples were investigated using the CSR test, gas adsorption techniques, optical microscopy, and X-ray diffraction analyses. The results show that an increase in coking rate resulted in a decrease in coke surface area and an increase in coke CSR-a phenomenon arising from rapid coking rate promoting the adhesion of coal particles and improving plasticity during the plastic stage. Coke total porosity, pore size, and cell wall measurements indicate that the accelerated events in a rapid coking process limit pore structural development. Faster coking rate also resulted in more pore elongation and formation of fissures, both of which are caused by strong contractions experienced by the coke bed during re-solidification. We also found that an increase in coking rate led to a decrease in crystallite height and the percentage of large anisotropic carbon forms, indicating that under a faster coking rate, crystals and carbon forms do not have sufficient time to develop.

Impact of coking rate on metallurgical coke quality

246th National Meeting (2013)

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