supplied three custom-designed fabric filter plants to the Koniambo project, an open cut nickel mine and metallurgical plant located in the North Province of New Caledonia, 1500km east of Australia.
A joint-venture partnership between Xstrata Nickel, one of the world’s largest global diversified mining businesses and Société Minière du Sud Pacifique (SMSP), a local mining company in the region, the Koniambo complex will be among the world’s lowest cost producers of nickel with initial annual production of 60,000 tonnes of nickel in ferronickel per annum and substantial further high-return, expansion potential.
Initially involved in the fabric filters’ bankable feasibility studies from the project’s early stages in 2004, Outotec was subsequently contracted in 2008 to supply three custom-designed fabric filter plants (baghouses) to the Koniambo site. While the two main fabric filter plants would collect fine nickel laden ore in the gas from the Hammer Mill Flash Dryers (HMFDs), the third would be used to clean gases picked up from various hoods around the nickel plant.
Outotec had previously worked with Koniambo’s engineering and procurement contractors in supplying High Volume Low Pressure (HVLP) pulse jet filter technology. The HVLP technology uses low pressure pulses and a rotating cleaning system, resulting in high reliability, long bag life and low maintenance.
Extensive flow modelling was conducted to ascertain the optimum flow distribution using both physical modelling and Computer Fluid Dynamics (CFD), followed by a scale model, which was tested and also verified by the University of NSW – Research Testing Facilities.
Though Outotec’s original contract scope required the company to split the baghouse components into a number of large modules for shipment and erection at site, it was modified to include full PAM delivery of the fabric filters, which would require careful planning, delivery coordination and detailed route assessment for the large scale modular construction.
The baghouses were constructed on temporary foundations overseas with all steelwork, insulation, cladding, access and stairways installed. Mechanical equipment and piping were fitted and pre-commissioned where possible. This equipment included pulse cleaning systems, complete with pressure vessels, cell ventilation hatches and pulse air piping.
With construction complete, each pre-assembled baghouse was loaded onto the ship using a number of Self-Propelled Modular Transporters (SPMTs), which lifted the baghouses via transport beams attached low on the support structures. Upon arrival in New Caledonia, the SPMTs were once again used to transport the fabric filter plants and lower them into position on the foundations at the nickel plant site.
The two HMFD baghouse filters weighed 1,158 tonne each including transport steel with the secondary filter plant PAM weighing 489 tonne including transport steel, giving a total of 2,805 tonne.
The nickel refining process at Koniambo is unique with the ore milling and drying completed in one process (the Hammer Mill Flash Dryer) and the baghouse integrated into the main process flow sheet. Outotec’s baghouse technology is therefore not solely considered as pollution control equipment but also as solids separation devices, critical in ensuring reliable delivery of feed solids to all downstream equipment.
Each baghouse must be operational in order for its process plant to work, so high availability and reliability are essential. Both baghouses handle flash dryer off-gas when the dryer is operating and calciner off-gas when the flash dryer is not operating.
High dust load and fine particle sizing, combined with high collection efficiency and low emission requirement demanded careful selection of the bag filter material along with careful design of the gas flow path to each filter compartment. In addition, excellent quality control in both bag manufacturing and installation procedures was required for low emissions to be achievable.
The final design incorporated positive isolating guillotine dampers for safe personnel access, without compromising filter performance whilst still fitting within the original footprint constraints.
Outotec delivered the fabric filter technology on time and installed the baghouses without any difficulties. With particulate emissions of less than 20mg/Nm³, the baghouses will minimise any harm to the local environment as well as maximise ore feed to the process with minimum energy consumption. Commissioning of the baghouses and associated infrastructure is due to take place in 2012.