Coal preparation refers to the treatment of raw coal to enhance its suitability for particular end-uses.
The extent and method of treatment depends on the properties of the coal and its intended purpose. It may require only simple crushing or it may need to go through a complex treatment process to reduce the inorganic mineral impurities.
Around 80 percent of all coal mined in Australia, and most of the black coal destined for export, is washed to provide a twofold advantage:
- it upgrades the quality of the coal; and
- it improves the economics of transportation by removing most of the non-combustible material
The Australian coal industry has developed considerable expertise in coal preparation. This has enabled it to achieve a high degree of quality control in order to meet customer specifications.
Coal preparation is now a sophisticated process. Routine underground sampling of the coal to be mined provides advance information on coal washability and product quality parameters. This information is used by technical staff in the coal preparation plants to predict washery performance and product quality in the medium to long term - a vital factor in securing markets in advance of production and, therefore, enabling forward planning by coal companies.
Reject disposal methods involve isolating both coarse reject material and fine reject material or tailings produced by the coal processing plant. Tailings usually consist of a mixture of fine particles of coal and clay minerals, suspended in water. Tailings dams are constructed to permit the solid matter to settle out of suspension and allow the clean water to be collected and re-used in washing or other mine processes.
Coarse reject material is normally carried from the preparation plant to the disposal site in trucks and, in the case of open-cut mines, may be used to fill the workings from which the coal was extracted. Alternatively, it can be moulded into the topography of the area to be covered later with topsoil and revegetated as part of the mine rehabilitation process.
In summary, effective preparation of coal prior to combustion:
- improves the homogeneity of coal supplied
- reduces transport costs
- improves utilistation efficiency
- produces less ash for disposal at the powerplant, and
- reduces emissions of oxides of sulphur