Hydro Alunorte currently uses vacuum drum filters for red mud filtration and Giulini dry stacking technology for residue storage. Studies have been completed and Hydro is now implementing new technology with a new filtration plant using fast opening filter presses and changing to dry residue storage. The new system, now under construction, will increase the solids content of the residues to 78% w/w solids, decrease the caustic content in the residues, increase the recovery of caustic soda for reuse, reduce the ratio of washing water to red mud solids, significantly decrease the land area needed for residue disposal and lower the amount of surface water to be treated. The new technology is considered to be the most sustainable way forward for the industry.
Instead of using an independent engineering company, Hydro decided to draw on the proven expertise and experience of the filtration equipment supplier for the design and construction of the filtration plant. This paper will give an overview of the most important considerations when designing a filter press plant for red mud. Most important is personnel health and safety in operation and maintenance because the process is abrasive, corrosive, scaling and at high temperature. To achieve high plant availability the filter presses will have less and larger components. The logistics within the plant for storing and changing of filter cloths for the largest filter plates in the world (2.5m x 3.5m) will be important. The plant performance will be controlled by process optimisers.