The flow profile on spiral separators alters with feed rate and this affects the performance of coal spirals in a different way from mineral spirals. The effect of flow rate is examined in terms of mass and volume recovery to coal product and equations are developed for three different spirals, based on the performance recorded in 684 tests covering 198 different coal samples. A generic coal spiral model is also developed based on the total data for the three types of spiral. A set of test data is then reported and examined in detail for each spiral and the anticipated variation in performance, predicted using wash-ability data and the equations developed earlier, is compared with the test results. The importance of selecting and maintaining the correct feed rate to spiral separators is emphasised and distributor performance is discussed. An application of the models to the problem of defining the requirements for an automatic distributor control system is then illustrated.
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