GOSFORD-based Eimco Process Equipment (previously known as Baker Process) has supplied three vertical pressure filters to the new Guizhou alumina plant in China after winning the $US1 million contract in June 2000.
The deal follows a $US3 million contract won in March 2000 to supply six deep cone paste thickeners to the Guizhou plant.
The vertical pressure filters form the final polishing stage in the site's Bayer circuit. By extracting alumina hydrate - held in suspension in the overflow from the thickeners - they reduce the concentration of solids in the filtrate from approximately 200mg/L to 10mg/L.
The 8 metre tall VPFs supplied to Guizhou have a four metre internal diameter. Each incorporates twenty one filter leaves, with a total filtration area of 440m2 and a filtration capacity of approximately 1m3/hr/m2.
The vessel is insulated to maintain the temperature of the process and feed material at around 104ºC to prevent precipitation of alumina scale.
The VPFs were fabricated in Western Australia and shipped to Shanghai. From there they were transported by barge along the Yangtse River, then by road to the Guizhou site.
According to Simon Courtenay, Eimco's project manager for Guizhou, one of the main advantages of the Eimco VPF is that it is a closed, self-sluicing system thereby increasing productivity and offering a safer environment for plant operators.
"Conventional filters have an average cycle time of 18 hours, after which operation is halted for around two hours, while the filter is opened and cleaned manually,” he said.
“The Eimco system is PLC-controlled and has an operating cycle of four hours, after which it is automatically taken off-line for a half-hour auto-wash and drain cycle, with the vessel closed.
“Every 10 to 12 cycles a caustic wash is injected to descale the leaves and clean the vessel interior. The head is bolted onto the shell and only needs to be opened every three months to change the filter cloths.
"Eimco VPFs were developed specifically for the alumina industry and can be readily adapted to meet individual client specifications," he said.
The Guizhou plant is due for commissioning in October 2001.