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:: Outotec Discusses Advances in Flotation Technology, Easy Wins for Difficult Times
Outotec Australia Floatation Manager Dr Robert Coleman says that since the mining boom is over, is more important than ever to optimise current plant performance.
Coleman says that apart for choosing the right staff with the correct skills and experience, it is also vital to choose the right technology. He says that the key is innovative technical solutions, such as low cost new technologies, cost effective upgrades to existing equipment, reduced operating costs and improved wear and maintenance.
This article will look at some key areas in flotation and discuss some recent technical innovations that can return some quick and easy Ďwinsí.
Improving metallurgy - FloatForce
One area that immediately brings rewards to the bottom line is metallurgy. In todayís challenging environment improving the metallurgical performance of a flotation cell can mean the difference between operating at a profit or at a loss. Therefore the impetus for technology providers to introduce highly efficient, flotation machines is huge.
The heart of the mechanical flotation cell is the rotor-stator mechanism. The mechanism mixes the slurry, disperses the air and generates the kinetic turbulent energy required to accelerate the particles and attach them to the bubbles. Outotecís new rotor-stator mechanism, FloatForce, ensures optimised mixing in the flotation cell - ensuring benefits such as enhanced flotation cell hydrodynamics, large air dispersion range with efficient mixing and improved wear life.
Flotation cell operators know well that air deteriorates the performance of impellers. Air occupies the space that should be filled with slurry and in the worst case the pumping stops completely. In all flotation cell mechanisms used today, regardless of how the air is added to the cell, the air is introduced into the central area of the rotor and therefore the mixing efficiency decreases significantly with increasing amounts of air.
So a design that allows no air in this central area of the impeller provides significant benefits to flotation performance. In FloatForce, the rotor design ensures the air is introduced to the impellerís peripheral area and thus the core of the rotor is used only for slurry pumping without diluting it with air (Figure 1). Therefore the mixing capacity is maintained even when the air feed rate is high. Since the slurry flow through the impeller remains high, it is possible to disperse large amounts of air evenly into fine bubbles without any drop-off in mixing and, as a consequence, there is no sanding at the cell bottom.
The new design of the FloatForce stator provides a free inlet with a focus on a critical flow path and a small and well-defined wear area. Changes to the way the stator blades are installed has also improved the time required for maintenance. Straightforward maintenance means less time and less cost.
Another important feature of this design is that the rotor/stator can be easily installed at existing plants - a major feature when reviewing costs.
Another recent innovation, easily installed yet also highly cost effective, is the FlowBooster. The FlowBooster is a pitch blade turbine that is attached to the lower impeller shaft above the normal flotation mechanism located at the bottom of the cell. Outotec in-house CFD results (Figure 2) were analysed by plotting the vector fields, velocity contours and turbulent kinetic energy. In addition, the characteristic volumetric flow rates in the main circulation loops in the tank were analysed from the results and compared.
These results clearly showed that the FlowBooster increases both the primary and secondary mixing flow. The power draw during the CFD simulation increased by approximately 10% compared to performance without the FlowBooster. This result provides the opportunity to distribute the mixing energy in the cell between the bottom and middle thirds of the cell more effectively and slow the mechanism to reduce overall energy consumption.
The FlowBooster has been designed to be reversible, so that that no matter what direction the rotor is turning, the FlowBooster would always pump axially downwards.
The reversible FlowBooster has shown a range of benefits for large flotation cells, including;
Recent test work has shown that when the FloatForce and FlowBooster are installed together, it is possible to slow down the motor speed and reduce the power draw from the mechanism, without affecting the metallurgical performance. This not only leads to significant energy savings but an improvement in metallurgical performance may also be achieved by an increase in coarse particle recovery.
This has successfully been implemented at Codelco Chileís Chuquicamata Concentrator where the specific energy consumption of a 300 m3 TankCell was reduced from 0.66 kW per cubic meter to 0.58 kW per cubic meter (combined mechanism and blower power). This is a savings of approximately 200,000 kWh per year for a single 300 m3 cell. The copper recovery at the same time also increased by 1.5% at a higher concentrate grade.
Optimising maintenance and wear life as maintenance shutdowns are critical in ensuring the processing plant operates efficiently and at full capacity, it is imperative that maintenance tasks are completed in a safe and timely manner.
During the recent mining boom, the skilled labour shortage has resulted in longer scheduled maintenance times and sometimes costly mistakes, adding unnecessary dollars to operating cost. Improved wear and reduced maintenance equals guaranteed cost savings.
Another simple yet highly effective recent innovation is the design of a new Outotec maintenance beam to secure the lower shaft, froth cone and rotor so that maintenance tasks are quicker and safer. Also available are specially designed lifting frames and external maintenance cradles that support the flotation mechanisms - again saving time, money and also creating a safe working environment.
Apart from the new FloatForce mechanism, breakthroughs in the design of the Outotec SkimAir Flash Flotation rotors and stators have led to more than five-fold increases in wear life in some cases. A new discharge pinch valve design for the SkimAir units has also emerged, leading to a more than 10-fold increase in wear life. Furthermore, the capacity of the SkimAir unit has also increased dramatically, going from treating 1200 tph per unit in 1996 (SK-1200) to 1800 tph in 2006, up to the current 2400 tph units currently being installed in Chile.
Finally, tools available for flotation cell control have also been recently improved. Apart from analysers such as the Courier, the FrothMaster 2 froth camera system and the EXACT feed forward level control system, Outotec have recently introduced CellStation. CellStation is a local/field integrated controller for both air and level control, easily expandable and connectable into a full plant wide DCS using Profibus DP ("Ethernet"), eliminating the need for the wiring of 4...20 mA signals. The unit comes fully operational, only requiring minimal configuration in the field, and can therefore provide a control solution without involving expensive third-party system integrators.
In addition, one of the embedded functionalities in the CellStation is the EXACT feed forward level controller, which eliminates the need for a "system set-up", since the algorithm is already in the control logic. CellStation can also be provided with a colour local display to show real-time air and level trends normally only available in the control room.
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