Water is a necessary transport medium in coal preparation but its presence in the final product has a negative impact on transportation costs, handleability and specific energy value. A major contribution to the total moisture may be attributed to the ever increasing proportion of fine coal in the total product, which undoubtedly presents the greatest dewatering problems.
The main objective of this study was to develop a process aimed at reducing the moisture content of fine coal cakes to a level comparable to that achieved by thermal drying. In this process, superabsorbents, which are granular cross-linked synthetic co-polymers with excellent water-absorbing properties, are employed to draw water from moist fine coal. The process is characterised by three main stages;
(a) contacting of superabsorbents with high-moisture fine coal
(b) separation of dried fine coal from superabsorbents by screening, and
(c) regeneration of used superabsorbent polymer, taking advantage of its response to changes in such conditions as pH, temperature or electric field.
It is shown that, depending on the polymer dosage and contact time allowed, the moisture content of a filter cake can readily be reduced from, say, 25% to 10% by mass or less. Some fundamental properties of both superabsorbents and fine coal are reviewed, and the factors which influence the absorption of moisture from the fine coal cakes by superbsorbents are identified and investigated. A mechanism by which moisture is transferred from coal surfaces to polymer matrices is proposed. Mathematical models are developed to predict the changes in polymer dimensions and density due to absorption of moisture, and the corresponding reduction in coal moisture content. Further work is also recommended.