Effects on coal-kerogen structure induced by low temperature, moist air heat treatments

摘要

The level of the moisture content of coals can be commercially important and hence procedures for its removal have been of much interest for some decades. Closely associated with this problem of how best to remove moisture without degrading a coal has been the role of water under heat treatments of coals. This study shows that water accelerates oxidation during a heat treatment. Data from low temperature heat treatments (70℃ in a moist air stream) show that even at this low temperature, a rapid and substantial reduction in surface area of the coal can be induced. Raising the temperature results in increased addition of oxygen to the coal surface thus raising its hydrophilicity. The balance between surface area reduction and increasing hydrophilicity is shown to be determinative in controlling the level of the equilibrium moisture content and that this balance is coal dependant. Manipulation of these two parameters in a controlled fashion is possible, leading to the formation of a thermally stabilised coal. This product coal characteristically has an irreversibly lowered equilibrium moisture content compared to a comparably oxidatively heat treated sample. In-filling of coal pores by mobilised bitumens is one mechanism which has contributed to the decrease in surface area of the thermally stabilised coals.