Some petrographic applications to coal, coke and carbons

Abstract

Petrographic methods have been widely applied in the coking industry especially in predicting coke strength and coke reactivity and to a lesser extent in predicting coking pressure and volume change. Non-maceral microstructure analysis is important in coal characterization; they include various coal types, oxidized coal, brecciation, coarse mineral matter, and miscellaneous materials. The non-maceral microstructure-analysis can be as important, or more important than the maceral analysis in many instances. Coke petrography is a very useful petrographic tool. Different ranks and types of coal produce different carbon forms. Coke petrographic analysis can be used to reconstruct the coal blend and to determine the amount and size of binder and filler phase, and under-coked, burnt coke and depositional carbons. Petrographic techniques have proven important in determining coal tar and pitch quality. The quinoline insolubles can be analyzed microscopically to determine the amount of fine size, low ash material from vapor or gas phase cracking and the amount of material related to coal carryover which is coarser and higher in ash. The tar and pitch quality is often related to the amount and size of the solids. Microscopic techniques have proven useful in the study of composite carbon materials, such as briquettes, electrodes, and “C” cell carbons. As the binder is often optically detectable from the aggregate it can be evaluated in terms of its distribution and wetting ability. Feedstocks also can be evaluated for use in carbon fiber production. Petrography is used in determining the amount, size and distribution of minerals in coal and in grinding studies to determine the degree of liberation of pyrites in coal. It is also used to study feed coals and residues from liquefaction processes. In addition, microscopic techniques are being developed to characterize coal feeds and solid chars or cenospheres produced in combustion. Petrographic data, such as vitrinite reflectance and maceral composition, are used in the International Codification of Coals and is being considered for use in the International Classification of Coals. The use of petrographic techniques is very broad and is developing in scope. The coal petrographer has the tools and, generally, has the background which permits him to expand his analytical repertoire to include many of the diverse applications that relate to coal, coke and carbons.