Theoretical and Experimental Approaches to the Carbonization of Coal and Coal Blends

Abstract

Mechanisms of carbonization of fluid systems from pitches and coals of different origin and rank to form anisotropic cokes are discussed. The concept of nematic liquid crystals and mesophase is introduced. The origins of optical texture in cokes and the chemical and physical factors which control the size and shape of optical texture are explained. The significance of optical texture in metallurgical cokes is analysed in terms of coke strength and chemical reactivity. Laboratory experimental approaches include control over carbonization procedures, the examination of polished surfaces of resultant cokes by optical microscopy, the use of scanning electron microscopy to monitor changes induced by thermal treatment and gasification of cokes, as well as point-countin g of optical texture and the use of microstrength testing procedures. Modern technological approaches to the successful use of coals of several ranks to make metallurgical coke include blending of coals sometimes with pitch additions. The resultant enhancement of coke strength is explained in terms of the development of suitable optical texture from solutions of coal in coal or of pitch in coal. Hydrogen transfer reactions are important here. The use of breeze additions in coal blends is commented upon. Metallurgical coke is used in the blast furnace as an energy source, a chemical reducing agent and to provide permeability and support for the furnace load. To fulfil these functions and maintain blast furnace performance the coke must maintain its size within an optimum range. It must therefore be able to maintain its mechanical strength and to withstand degradation due to gasifi­ cation in carbon dioxide, abrasion, compressive forces and thermal shock in the furnace. Prime coking coals of volatile content 19-33% are becoming scarce in Western Europe and Japan and economic necessity dictates the need for the development of blending