Physical changes accompanying drying of western US lignites

Experiments have been performed to measure the effect of drying procedures of different degrees of severity on the physical properties of four North Dakota lignites. Moisture desorption-readsorption behaviour was relatively reversible in some cases and irreversible in others. Shrinkage measurements commonly showed volume loss greater than that calculated from moisture loss. The shrinkage was always irreversible, even when drying was relatively incomplete; only ≈ 80% of original volume was regained upon reswelling in water. Severity of drying had a significant effect on measured N 2 surface areas, and on pore size distributions throughout most ranges of pore sizes. All the results are consistent with the view that low-rank coals are essentially colloidal gels, many of whose properties are irreversibly altered by drying.