IMPROVING RED MUD FLOCCULATION AT AUGHINISH ALUMINA LIMITED
Peloquin, G., Baxter, H., Simard, G, Kocaefe, D. and Bui, R.T.
Proper flocculation is essential in obtaining good performance of the liquor decanters and washers in the separation of red mud from liquor. The feed well is a key element helping to distribute and mix the flocculant with the incoming red mud slurry. At Aughinish Alumina Limited, the solid-liquid separation circuit is composed of six large diameter (41 m) thickeners operated in series. The ever-increasing mud load handled by the plant necessitated improvements in the efficiency of the circuit. A computational fluid dynamics (CFD) model of the operation of the feed well was developed to evaluate the performance of the existing feed well and the impact of modifications. The model simulates the two-phase flow of liquor and solid in the feed well. It is implemented in the commercial software CFX.
Several cases were simulated and the best configuration was selected to suggest modifications to the feed well. Initially, the feed well of a washer was modified in the spring of 2000. The modifications yielded a reduction in flocculant use, lowering of the settling interface and improvement in the underflow solids content. Subsequently, all feed wells have been, or will be modified as they become available. This paper describes the CFD model. It then details results of some of the cases run. Finally, the results observed in the plant with the modified feed wells are presented.