The high total moisture content of coal, especially coal fines, after mining and processing, is one of the major reasons why this resource is not extensively used in subsequent power generation, combustion or other conversion processes.

Taking into account South Africa’s vast reserves of coal fines, comprising high heating values and a generally low sulphur content, a breakthrough in reducing the moisture content of these coal fines would have great potential in creating value.

North-West University School of Chemical and Minerals Engineering associate professor Quentin Campbell, who is part of a research team investigating the moisture adsorption and desorption characteristics of some South African coals, says the mechanisms of moisture adsorption onto coal are as varied and complex as the coal itself.

“This makes transporting and handling the coal from the coalfield to port and beyond difficult when trying to keep the coal as dry as possible.”

A high moisture content significantly affects the handleability, or stickiness, of the coal. It also impacts on the heating value of the product and, if the moisture content changes during transportation, it becomes difficult to quantify for quality purposes.

Campbell explains that this is because the moisture in, and specifically, on coal, is always in equilibrium with the environment. The moisture content can increase or decrease, depending on ambient factors like temperature and humidity. If the coal is loaded at one location in a dry and cold atmosphere, and then trans- ported to a port – where it is usually hot and humid – the moisture content changes.

Currently, not much can be done about controlling moisture changes during transportation. Depending on the economics, it may be an option not to spend too much time drying the coal when it is loaded at the source if it is going to get wet again en route to or at a port, says Campbell.

Moisture adsorption is a natu- ral occurrence, so it cannot be prevented. If the extent and dynamics of the process are known, which can be achieved through research, moisture adsorption can be better managed.

Campbell says that, to understand the mechanisms by which moisture is adsorbed onto fine coal particles, further infor- mation is needed on how this occurs on the surface of the coal.

He and his fellow researchers have concluded a study that specifically examines the role that the amount and type of mineral play in moisture adsorption.