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 bas ket centrifuges. The process involves injecting a turbulent stream of high velocity air through the coal bed as it traverses the centrifuge basket. Th is paper describes the results obtained when the process was trialed at pil ot scale, following a successful bench-scale study, which was reported prev iously. The centrepiece of the rig used in the testwork was a pilot-scale, continuo us, vibrating-basket centrifuge manufactured specifically for the project b y LMPE Pty Ltd. In all respects, the unit was a replica of a full-scale mac hine, The feedstock was a -6+0.5 mm coal, chosen so that the statistical va riations 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 pa rameters (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 ex iting the manifold, moisture reductions close to 1 wt% were achieved. Halvi ng the air speed to ca 30 m/s more than halved the moisture reduction to 0. 4 wt%. Doubling the airflow rare bur keeping the air speed constant by inse rting another manifold into the centrifuge did nor enhance moisture reducti on. The encouraging moisture reductions were thought to warrant a full scal e trial of air purging, which will be described in a future paper. (C) 2001 Elsevier Science Ltd. All rights reserved.