Implementatlon of Flow Dlstributlon Controls in the Precipitation of Alumina Hydrate

Queensland Alumina produces smelter grade alumina using the Bayer Process. Central to this process is the precipitation of alumina hydrate from a supersaturated solution of sodium aluminate, through the seeding effect of recycled hydrate. The caustic soda stream, once removed of the dissolved alumina, is recycled for the further addition of bauxite. The control and distribution of this caustic liquor is therefore an essential component of Bayer process operation. QAL operates a number of unit operations in parallel, and distribution of process streams between these parallel units is paramount for process of optimisation Alumina refining is also a high maintenance operation, which means many configurations of the parallel equipment can be operated. This control project involved the allocation of the caustic soda stream throughout the plant, and the distribution of liquor through the precipitation area implementation of this project involved a unique approach to obtain a satisfactory and profitable control scheme. The success of the controls can be attributed mainly to the cross-section of personnel involved in the design, configuration and commissioning of the controls. The project team comprised a mix of instrumentation, process and control engineers, while significant effort was required to ensure operator involvement to facilitate process understanding as well as the ongoing operation of the control schemes.