IMPROVED FILTRATION AND WASHING OF AL-HYDRATE PRODUCT: COST SAVINGS BY MODERN FILTER DESIGN

Filtration and washing of Al-hydrate product in alumina refinery plants is usually performed on pan filters since this vacuum rotary filter type is well adapted to the filtration of coarse particles. It is the target to achieve a filter cake that is as dry and free of soda as possible. The single stage process with feeding the precipitation product directly onto a pan filter is a wide spread process design for Al-hydrate product washing. In the last decade BOKELA has introduced a new generation of rotary vacuum filters such as disc, drum and pan filters with new and innovative designs. With this new generation of pan filters, the filtration and washing out of the Al-hydrate product is performed with significantly improved filter capacity, reduced maintenance and operation cost compared to conventional designed pan filters. The most efficient process design, however, is a two stage process. First, deliquoring of the precipitation slurry on disk filters and second, washing of the re-slurried hydrate on a pan filter.