Sodium and calcium have often been removed in the casthouse by the direct injection of chlorine gas to molten aluminium in the holding furnace.
Increased emphasis on HSE considerations have led to the adoption of alternative technologies at many smelters.
In a co-operative project between Rio Tinto Alcan and VHE an earlier Alcan process has been modified and further developed. The process uses aluminium fluoride (AlF3) as a flux, added directly into a vortex generated in the molten aluminium by a rotor. A test rig was designed, fabricated and erected by VHE at Rio Tinto Alcan Iceland's Straumsvík smelter, ISAL. Experimental work demonstrated that very low sodium levels could be achieved.
Following successful completion of the development work, Rio Tinto Alcan specified a full scale metal cleaning project to be built at ISAL, comprising four stations each equipped with twin rotor vortex generators and injecting aluminium fluoride with argon gas. All stations are fed from an elevated silo using a dense flow system. Gaseous discharges are vented to the existing dry scrubbers.
VHE has subsequently designed and installed a similar system at another smelter in Europe.
VHE - Vélaverkstæði Hjalta Einarssonar ehf. – established over 40 years ago - is a global leader in the primary aluminium industry. The VHE Group designs and manufactures world-class industrial machinery and supplies goods and site services to clients worldwide.
Further information is at www.vhe.is