PROCESS STEAM CARBON REDUCTION IN A HIGH-TEMPERATURE ALUMINA REFINERY

To achieve decarbonisation targets, the process steam load for alumina refineries will need to be increasingly provided by renewable energy. In Australia, this energy is likely to be predominately sourced from wind and solar electricity with significant grid firming required to achieve 24x7 supply. For Queensland Alumina Limited, a high temperature refinery using double streaming digestion technology, direct fuel switching to electricity-based steam generation is likely to increase the site electrical load to ten times the current base load. An alternative approach, based on modifying the process flowsheet utilising Double Digestion technology to reduce the quantity and quality of process steam requirements and the subsequent implementation of waste heat recovery and steam compression systems prior to fuel switching has been proposed. To facilitate flowsheet development, extensive laboratory testing and targeted pilot plant testing in a purpose-built pilot plant facility were used to define critical process parameters for the process flowsheet design. Using these test results a modified process flowsheet based on a Counter Current Double Digestion flowsheet was developed and evaluated using a SysCAD computer simulation of the refinery process. These simulations indicate that this flowsheet will provide a platform for further energy reduction using waste-heat recovery technology to provide up to a 50% reduction in the electricity requirements for process steam generation.