EUROPEAN STEEL TECHNOLOGY AND APPLICATION DAYS 2017 - ESTAD 2017

It becomes more important to properly prepare raw coal blend for cokemaking since required coke quality has been increasing. In particular, because coal size adjustment is an important operation which strongly affects coke strength, various control technologies for coal size have been developed. General coal size design has been almost based on the well-known Sovaco method. In the method, firstly coal is classified into fine grain group including more active components with high caking property and coarse grain group comprising rich inert components whose caking property is poor. Secondly the inert components group is crushed by closed-circuit system so that the size becomes smaller than the set screen mesh. The method suggested that coke strength is improved due to suppress formation of cracks in coke by intensively crushing and dispersing inert components. On the other hand, in our previous report, a new measurement method for unique coal thermoplasticity, “permeation distance method”, was devised. As a feature of this method, the permeation phenomenon in which thermally plastic coal permeates into the surrounding voids, which is assumed to occur in actual coke ovens, is evaluated under the circumstances experimentally simulating coke oven environment. It was clarified that coal having longer maximum permeation distance forms larger pore and thinner pore-wall structure in coke and that coke strength deteriorated when the coal blend included longer maximum permeation distance coals. In this study, we investigated an influence of coal grain size on permeation distance and coke strength. If permeation distance can be changed by coal size, adverse effect of longer maximum permeation distance coals on coke strength would be reduced. Through the experimental results, effective formulation about optimum grain size of coal blend was explored from a perspective of control of permeation distance.