A new model of coal-water interaction and relevance for dewatering

Abstract

This project is concerned with a basic scientific question concerning the properties of coM-to what extent is the ability of coal to hold moisture a manifestation of the web-known ability of coal to swell, when exposed to good solvents? The question implies that the longheld belief that coal holds a significant portion of its moisture by classical capillary condensation processes, is possibly in error. This seems to be a very real possibility for low rank coals-i.e. lignites. To explore this hypothesis further requires an examination of the basic phenomena governing the swelling of coals in good solvents. This is the focus of the first part of this project. The possibility that coal holds a significant portion of its moisture by solvent swelling mechanisms leads to an interesting technical issue, lt is well known that simple drying of low rank coals at minemouth is ineffective because the process is reversible, to a significant degree. The economic advantages of pre-shipment drying have however dictated a search for "permanent" drying procedures. These have been developed by largely empirical means, and involve mild pyrolytic treatments of the coals in oil, steam or liquid water itself. The idea has always been to pyrolytically remove oxygen groups, which are assumed to be those that hold water most strongly by hydrogen bonding. The treatments have been designed to minimize tar formation and decrepitation of the particles, both highly undesirable. In relation to the present new hypothesis concerning water retention, it is likely that a sound approach to permanent drying would involve highly crosslinking the coal at mild drying conditions. The crosslinked coal could not swell sufficiently to hold much water, lt is identifying processes to achieve this goal, that constitute the objective of the second phase of this work.