Evaluation of Coal Compatibility Effect in Coke Strength by Surface Tension of Semi-coke

摘要

Coal compatibility in coke strength is known as the effect that good combination of coals gives high strength coke and bad one gives the opposite in comparison with the strength expected from their average properties. To understand the phenomena of compatibility, we studied a correlation between adhesive strength and surface properties of semi-cokes obtained by heat treatment of coals at 500℃. As a result, we found that when the difference in surface tension between two semi-cokes was large, the strength of coke produced from the mixture of the two raw coals became low. The same tendency was also observed in laboratory scale carbonization tests and this effect was rationalized by high interfacial tension between two semi-cokes in the case that the difference in the surface tension was large, and accordingly, adhesive strength of the interface became low. To apply these findings to a multi-component coal blending technique used for commercial coke production, we proposed a new blending factor, the interfacial tension of a heat-treated coal blend which was derived from surface tensions of semi-cokes from coals in a coal blend, so that deterioration of coke strength was confirmed in commercial oven operation by increasing interfacial tension while other average properties of the blend were kept constant. This new technology 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.