| Summary: | Successful dewatering and filtration of coal fines remain the major obstacles in
preventing the extensive re-use of large reserves of high calorific quality coal
fines as an additional energy source in South Africa. The high levels of final
moisture in coal fines make it uneconomical to transport, handle and use. The
industry is rapidly reaching the limit of current technology of mechanical
dewatering; this limit is defined by fundamental coal properties, like amongst
others, particle size, porosity and mineral content.
This thesis describes research investigating a shift in approach from high
vacuum or pressure systems, to high air flow systems. Results from various
projects at laboratory scale showed that it was possible to decrease the fine
coal filter cake moisture to as low as 15%. This was obtained by allowing air to
flow freely through a filter cake, even at ambient temperatures, and replacing
the necessity for high applied vacuum levels. There was also an increase in the
dewatering rate, as well as a lower breakthrough pressure. Such an approach
can utilise existing equipment with minor modifications.
Other investigations showed that forced air-drying, both at ambient and
elevated temperatures, could be used to overcome this mechanical limit. Again,
an increased air flow rate at ambient pressure was used. Using air drying,
moisture levels down to zero were possible.
These investigations led to the conclusion that increased air flow through a fine
coal cake was more advantageous than an increase in the applied vacuum, or a
longer dewatering time. This new approach to lowering the final moisture
content in coal fines is crucial in any advancement of the use of this largely
untapped energy source. === Thesis (Ph.D. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2006.
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