ROLE OF MOISTURE IN COAL STRUCTURE AND THE EFFECTS OF DRYING UPON THEACCESSIBILITY OF COAL STRUCTURE

This paper is concerned with the colloidal gel nature of coals and wha t impacts this has upon several properties of practical significance. Water is shown to be a good swelling agent for coals ranging in rank f rom lignites up to high-volatile bituminous, and the coals shrink when dried from the as-mined state. Shrinkage upon drying is correlated by volumetric shrinkage (%) = 0.863 (moisture content, wt %)-0.162. Shri nkage of this magnitude suggests that measurements of ''surface areas' ' of dried coals will provide an erroneous estimate of true accessibil ity of coal structure. In addition, the presence of moisture in the st ructure of coals serves to significantly enhance the rate of uptake of solvents by the coal. There is a strong analogy with enhancement, by water, of diffusive transport in hydrophilic polymers. The process of drying or heat treatment of coal at temperatures above 373 K can signi ficantly affect both the cross-link density of coal (as inferred from pyridine solvent swelling) and the rate of subsequent solvent uptake b y the coal.