Coal Carbonization: Formation, Properties and Relevance of Microstructures in Resultant Cokes

Abstract

Metallurgical coke is a composite material which when used in the blast furnace has to meet several requirements which are not totally complementary. It is considered that metallurgical coke is a successful compromise in structure and properties. Initially, the microstructures or optical texture of cokes are described. They mainly consist of anisotropic mosaic. Anisotropic carbon in cokes is formed from the homogeneous nucleation of liquid crystals and mesophase from the melt. Factors, physical and chemical, which control the size and shape of optical texture are summarized leading to a discussion of optical textures of cokes from coals of increasing rank. The optical texture of mosaics is relevant to industrial performance. The interlocked, randomly oriented units of the mosaics are more resistant to fracture than isotropic carbon or the more orientated petroleum cokes. Anisotropic carbon is more resistant to gasification than isotropic carbon. The mosaics are less able to develop troublesome gasification fissures than the cokes of larger optical texture. The shringkage fissures of the mosaics created by heat treatment permit some accommodation of internal stresses set up by thermal expansion. The mosaics are more resistant to alkali than the larger optical texture. Cocarbonizations are described which procedure cokes with suitable optical textures. The concepts of ‘hydrogen shuttling’ is introduced to explain the successful use of pitch additives in coal blends.