Engineering & Mining Journal

JUN 2019

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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Page 104 of 115

JUNE 2019 • E&MJ 103 PROCESSING SOLUTIONS tering, raking, prevention of rotating mud beds, process control, and the discharge of thickened solids. It said the new thick- ener builds on this proven performance with a range of innovative new features. For example, vertical load monitoring with the Smart Rake Lift system means the thickener can detect early formation of ro- tating beds, allowing countermeasures to be applied in a timely manner. The system also monitors and actively adjusts the individual hydraulic cylinders to maintain alignment of the rake mech- anism. Incorporating vertical load sensing with plant process data in the Outotec ACT Thickener Optimizer control system means that the solids inventory within the tank can be maintained to ensure a consistent underfl ow density, stable process, and im- proved overall thickener performance. In addition to mechanical improve- ments, process control advances can stabilize and optimize the performance of the paste thickener. Outotec said its ACT Thickener Optimizer utilizes a mul- tivariable controller to manage process changes and the associated delays in the response time of the thickener, which can be challenging for traditional con- trol systems. It can also be confi gured to manage the effects of variable feed types to ensure optimum performance despite changing inputs to the process. The company noted that its paste thickening solutions are designed with ease of maintenance in mind, with a skid-mounted hydraulic power unit for centralized connection of hydraulic hos- ing from the rake lift cylinders and drive unit. Other key design features include: • Low profi le rakes with tie-cable load sharing that minimize rake drive torque requirements; • Rake blades supported by thixoposts to move the rake arm away from the high- est density thickened solids; • High sidewall and steep tank fl oor slope for more effi cient dewatering of fl occu- lated solids and compaction of the bed, as well as better transport of the solids inward toward the tank discharge point; • High-installed drive torque to move the rake blades through beds of thickened solids with high yield stress and viscos- ity; and • Feed systems with break tanks when required for different thickener feed situations, including the patented Vane Feedwell, and break tanks inside the thickener perimeter to save on site lay- out space. Packing Ring Solution Triples Slurry Pump Reliability John Crane, an Illinois, USA-based sup- plier of mechanical seals and other in- dustrial products ranging from power transmission couplings to fi ltration sys- tems, has highlighted a pump reliability solution it provided for one of its mining customers. Management at a large gold mine in the North West Province of South Africa was concerned that downtime and high material costs associated with tail- ings processing operations could cut into profi ts. For years, the mine had used on a certain brand of mechanical packing ring to protect against bearing failures and premature sleeve wear on the horizon- tal slurry pumps used to pump tailings. However, the packing consistently failed, requiring frequent maintenance and re- sulting in low mean time before failure (MTBF). Engineers at the mine began looking for a cost-effective alternative. John Crane personnel conducted a survey of the mine's equipment and found that the root causes of the pump prob- lems could be attributed to low extrusion resistance in the slurry pumps' mechan- ical packing caused by ground rock and process effl uents during operation, result- ing in a seven- to 14-day MTBF rate. After presenting the results to mine engineers, John Crane recommended re- placing the rotary mechanical seals with packing rings designed for extreme-duty mining and rotary equipment. The mine agreed to install John Crane packing rings on slurry pumps that were already inactive because of scheduled mainte- nance. John Crane was given 30 days following the installation to validate its reliability promises. The pumps were fi tted with John Crane K1730 and C1065 packing rings installed in fi ve Warman 14/12 horizon- tal slurry pumps. The K1730 rings are constructed of high-tensile strength, abrasion-resistant fi bers, and offer di- mensional stability, resilience, conform- ability and extrusion resistance. And, according to the company, its C1065 Chemlon Graphite Fiber (CGF) rings fea- ture continuous PTFE fi lament yarns and superior heat dissipation and self-lubri- cating graphite. Each pump had a K1730 ring in- stalled as a bull ring against the neck bush of the pump, with three C1065 rings for increased lubrication to reduce shaft sleeve friction. Trial results showed that the K1730 bull ring prevented slurry from contaminating the C1065 rings in the event of a loss of seal water pressure and that the C1065 rings showed high re- silience to the acid content of the slurry. Since the upgrade, annual packing costs have been reduced by 67% and pump MTBF improved by approximately 350% over the previous installation. Outotec claims its new thickener provides superior ease of operation and reliability for applications that demand a high degree of dewatering, such as tailings, mine backfi ll, and pre-leach and CCD circuits.

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