Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr
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MARCH 2017 • E&MJ 59 www.e-mj.com PROCESSING SOLUTIONS • Up to 10% increase in throughput at the same particle size. Benefi ts of Measuring Individual Cyclones Until now, there has been no instrumen- tation on individual cyclones, making it very diffi cult to identify cyclones that are performing poorly and to quantify this ef- fect on the grind-classifi cation process. A single poorly performing cyclone can have a signifi cant impact on the entire grinding and classifi cation circuit and cause se- vere disruption to downstream processes. The major impacts include, but are not limited to: • Extended downtime due to cell, slurry line or tank blockages. • Lost effi ciency due to poor coarse parti- cle recovery. The root causes of these events are varied, but are commonly a cyclone blockage (rub- ber liner, object) or exceeding the cyclone capacity, which is defi ned by pressure, fl ow and the cyclone dimensions. An example of a cyclone (Cyclone 7) entering an out-of- class state following a 10% increase in the SAG mill feed is shown in Figure 2. Due to the short-circuiting of the cyclone feed, the load on the remaining cyclones is reduced, as inferred by the lower particle size pro- duct each cyclone produces. Once cyclone 7 is closed, the cyclone feed fl ow and pres- sure recover, and after a surge in cyclone pressure, another two cyclones start to per- form poorly for 10 minutes after which they are closed. In addition to out-of-class events like in Figure 2, cyclones in a cluster perform differently under normal operation. This can be due to items such as uneven fl ow distribution and wear rate variability. PST enables active cyclone control, whereby the optimum particle size distribution is produced by ensuring coarse cyclones are closed. For example: At a specifi ed time in- terval, the coarsest cyclone is closed if it is more than 1 sigma above the me- dian PST signal. Simultaneously another cyclone is opened to keep the pressure disturbance minimized. Data from a concentrator with a known recovery as a function of particle size was used to model the recovery per cyclone as a function of the PST signal. The results of the active cyclone control were then simulated using the following strategy: 1. Every 30 minutes, the coarsest cy- clone is closed, if it is more than 1 sigma above the median PST signal. 2. When it is closed, its signal is replaced with the median (i.e., statistically the new cyclone gives the median grind). The recovery and the copper losses to tails were then recalculated to get ap- proximately $2 million per year in savings with active cyclone control. This does not include the benefi ts of out-of-class cyclone detection or global particle size control, which can be an order of magni- tude higher in value. Dylan Cirulis is a metallurgical engi- neer and the CYCLONEtrac product line manager for CiDRA Minerals Processing. His current focus is process optimiza- tion using new technology for particle size measurement in comminution cir- cuits. Prior to joining CiDRA, he spent fi ve years with Rio Tinto in technical and operations roles at the Kennecott Utah Copper Concentrator. * Cirulis, D., Dunford, S., Snyder, J., Bartsch, E., Roth- man, P., Maron, R., Newton, D., O'Keefe, C., and Mercu- ri, J., Process optimization using real team tracking of coarse material in individual cyclone overfl ow streams, Metplant 2015 Conference Proceedings, Perth, Australia. Figure 1—Example of PST-based control. Figure 2—Example of a poorly performing cyclone.