The principal aim of this thesis was to develop a mathematical model for prediction of the partitioning performance of dense medium cyclones in coal preparation applications. To ensure relevance to the Australian coal industry the study would concentrate on cyclones of the Dutch State Mines design, using magnetite medium and treating raw coal with a maximum particle size in the range 10-40mm. The model should be suitable for use in the optimisation of all phases of a coal mining project including
• matching the resource to product market specifications
• flowsheet design and selection of separators
• day-to-day production optimisation of the performance of individual separators with due regard to their roles in the entire plant.
Unlike most relationships presented in the literature, the selected independent variables are dimensions, parameters or operating conditions that can be readily selected or controlled.
The study has encompassed the generation of a large base of unusually comprehensive plant performance data using density tracers as well as more conventional techniques for the determination of size-by-size density partitioning performance. These data have been supplemented by studies in the pilot plant environment where certain parameters may be varied over very wide ranges while maintaining precise control of conditions.
Data from other sources were also utilised in the development of a model which recognises the roles of medium behaviour parameters as controllers or indicators of coal partitioning behaviour. Model predictions are compared with an unrelated set of industrial data, and a step-by-step example of circuit design is presented. The model has been successfully utilised as a guide to procedures for realising yield improvements in operating plants.
In the course of the investigations two causes of serious yield losses were identified. They are
• surging loss of high quality coal to rejects as a result of an excessive tendency to accumulate large particles of intermediate density within the cyclone, and
• misplacement of clean coal to rejects caused by insufficient medium-to-coal ratio in the overflow.
The model flags situations where one or other of these mechanisms may impinge on efficient separation.
It is concluded that a model which meets all the above requirements has been developed, and examples of its application are presented. Its range of application is detailed, and recommendations are presented for further work.