Migration of inert materials during coking of molded coal

Abstract

Since the maldistribution of substances with poor melting and expansion properties decreases the strength of coke, we investigated whether these substances gather or disperse during coking process. Coal briquettes (before coking) and cokes (after coking) containing a predetermined amount of alumina beads were prepared. These beads constituted 2–15 vol% of the samples. A three-dimensional analytical object was constructed by X-ray CT images of coal briquette or coke with alumina beads, and isolated alumina beads were extracted from analytical objects by image processing. The number of isolated alumina beads increased after coking in any mixing ratios. Therefore, it was shown that the alumina beads dispersed each other during coking. The observed result could be attributed to the expansion of pores near the contact points between agglomerated alumina beads, resulting in the expulsion of the beads. At the lower part of the sample, where the effect of expansion was small, the same ash before and after carbonization can be found. Focusing on the area near the ash, alumina beads with the same distance from the same ash are observed before and after the coking. This indicates that there are alumina beads that have not moved during coking. The reason why the alumina beads did not move may be using low fluidity coal and high-density coal briquette as the raw material of coke. This suggests that the high-density coal briquette may prevent the coke strength from decreasing due to the suppression of insoluble matter agglomeration.