As part of the project to rebuild their digestion circuit, the Kaiser Gramercy Alumina refinery opted for a version of a Double Digestion circuit which was developed jointly with Alcan International. The Double Digestion circuit makes use of Pressure Decanters operating at digestion temperatures and pressures to separate the mud from the first digestion stage and to redigest the separated mud in a second digestion stage. Gramercy refinery operates on Jamaican bauxite, which is well known for its poor settling and compaction characteristics.
This paper will outline the basic features of the Pressure Decantation Technology, describe the testing program and the results obtained in order to size and predict the performance of the full size vessels. Then the paper will present some of the distinctive features of the installed units. It will finally present results obtained from the operation of these pressure decantation units and compare these results with the predicted performance based on laboratory/pilot scale tests.