Review of some physical methods of coal characterization, their application in constitution analysis and relevance to industrial utilization

This report reviews some of the physical methods which have been and are being used to characterize coals in the Penn State/DOE program. These include maceral and reflectance analysis, density, various tests of the plastic behavior of coals, Vickers microhardness, and Hardgrove grindability. The ultimate objective of this program is the establishment of interrelationships between coal properties and industrial behavior. Any characterization of coal, physical or chemical, is likely to be influenced by the petrographic heterogeneity of the particular sample. Further, the behavior of coal during pulverization, cleaning, and most industrial uses also depends upon the proportions and mode of occurrence of the various organic macerals and inorganic minerals. Variability in coal composition and behavior which is due to petrographic differences are modified by the extent to which the coals have been advanced in rank as a result of their thermal histories. Some of the direct methods of measuring petrographic composition and physical rank parameters are discussed. Structural parameters such as aromaticity and the ring index can be derived from certain of the physical constants of coal. The thermoplastic behavior of some coals is controlled by both petrographic composition and rank. The porosity and permeability of coals affects such properties and processes as methane adsorption and drainage, reactivity during gasification, and the production of chars. The complexities of coal structure and behavior often have defied or complicated absolute quantitative analysis, and much of the conventional characterization of coal still relies on established empirical testing.