8th International Congress on Science and Technology of Ironmaking - ICSTI 2018

Reasonable selection of coal brands and blending them for preparing raw material of coke are important to achieve the effective utilization of caking coal and enhancement of coke strength. Coal compatibility, namely “blending effect” has long been an unresolved problem. The effect is deviation between actual strength of coke made from coal blend and estimated strength which is calculated by averaging single coal properties. To understand the effect and develop a new blending technique which can control coal compatibility, we focused on surface tension of softening coals which probably affects adhesion phenomena between coal particles. However there is no method to measure the surface tension of coal at softening temperature. In this study, to overcome this difficulty, we devised a method to measure surface tension of semi-cokes obtained by heat treatment of coals at 500°C as a substitute for softening coals. First, we investigated the relationship between strength of coke made from binary coal blend and difference in the surface tension of semi-cokes made from these coals. As a result, the larger difference in the surface tension between two coal brands, the lower strength coke was produced. Next, the finding was extended to multi-coal blend. The strength of coke was deteriorated with an increase in interfacial tension which is a new proposed factor calculated from the surface tensions of single coal brands used in the coal blend. The blending technique based on interfacial tension enables us to evaluate more precisely the coal compatibility and to select the good combination of coals, which can contribute to the production of high strength coke and effective usage of coking coal resources.