Residual moisture reduction of coarse coal using air purging. 2. Pilot scale studies

CSIRO and Novatech Consulting have been developing air purging as a new way of reducing the moisture content of coarse coal product from vibrating basket centrifuges. The process involves injecting a turbulent stream of high velocity air through the coal bed as it traverses the centrifuge basket. This paper describes the results obtained when the process was trialed at pilot scale, following a successful bench-scale study, which was reported previously. ntrepiece of the rig used in the testwork was a pilot-scale, continuous, vibrating-basket centrifuge manufactured specifically for the project by LMPE Pty Ltd. In all respects, the unit was a replica of a full-scale machine. The feedstock was a −6+0.5 mm coal, chosen so that the statistical variations that are inevitably encountered when sampling conventional coarse coal (top size 50 mm) could be minimised. Moisture reduction by air purging was a function of air speed, within the boundaries of the other process parameters (eg coal feed rate, feed solids content, manifold geometry) which were kept constant. At the highest air speed tested, which was ca 60 m/s exiting the manifold, moisture reductions close to 1 wt% were achieved. Halving the air speed to ca 30 m/s more than halved the moisture reduction to 0.4 wt%. Doubling the air flow rate but keeping the air speed constant by inserting another manifold into the centrifuge did not enhance moisture reduction. The encouraging moisture reductions were thought to warrant a full scale trial of air purging, which will be described in a future paper.