Engineering & Mining Journal

NOV 2012

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PROCESSING SOLUTIONS Speedy SAG Mill System Upgrade Minimizes Downtime Costs The Robinson gold-copper mine, located just outside the town of Ruth in east-cen- tral Nevada, is owned and operated by the Robinson Nevada Mining Co., now part of Poland's KGHM Polska Miedz SA after that company acquired former Robinson owner Quadra FNX Mining for $2.87 billion earlier this year. The open- pit mine is in the historical Robinson Mining District, which has been active in eastern Nevada since the mid-1800s. The mine's dual-pinion, 11,000-hp SAG mill is a critical link in the produc- tion chain, which requires it to operate all day, every day, all year, except for scheduled maintenance downtime. For more than 20 years Robinson successful- ly employed a Siemens Simine Mill GD system to power and control this mill, and although the mill was in good oper- ating condition and continued to work around-the-clock, its electronic controls were a concern for the mine's mainte- nance team. Spare parts and compo- nents were in short supply for the sys- tem's late-1980s/early-1990s technolo- gy. If a component needed replacement, and one was not readily available, the mine would have to shut down. "The SAG mill is a single point of entry into the facility so once we go down, it all comes to a stop," said Tony Whittaker, process and control supervisor at the mine. This is an expensive proposition, according to Cary Brunson, Robinson's general manager. "It can cost anywhere from $50,000 to $100,000 per hour for a shutdown. It adds up in a hurry." While the risk of an unplanned shut- down was of utmost concern, complete replacement of the mill also carried a big price tag. A typical mill replacement would put the mine and its 600 em- ployees out of production for three weeks. Robinson Mining needed a solu- tion that would allow it to modernize its mill while keeping downtime to an absolute minimum. "Twenty-one days was unacceptable for us to be down," Brunson said. "We went to Siemens and said we needed to do something different, and we came together as partners." www.e-mj.com The Robinson gold-copper mine, shown here, produced 95 million lb of copper in 2011, compared with 109 million lb the preceding year. Following the recent upgrade of its SAG mill control and drive systems, plant maintenance should be less of a concern in meeting its future annual production target. Beginning in 2010, Robinson mine and Siemens began to collaborate to develop not only a plan for an upgrade and migra- tion to a new system, but also a service program to ensure the mill's performance once the modernization was complete. Siemens Solution After evaluating Robinson's mining opera- tions and the existing mill drive system, Siemens proposed an innovative solution that would meet all of the mine's goals. The Siemens team, led by Vinny Matthews, business manager–mining projects, con- cluded that they could upgrade all the power conversion, electronics and automa- tion systems without having to replace the motors. Because the two existing Siemens 5,500-hp motors were still in prime working condition, Robinson Mining could leave them in place and eliminate what would have been the most expensive and time- consuming portion of a typical mill upgrade. Not only would the modernization project solve the mine's concerns about spare parts, but additionally, with a new diagnostics system that offered remote access, the new mill would be faster and easier to troubleshoot, allowing mainte- nance issues to be addressed before they resulted in an unplanned shutdown. Major elements of the proposed pro- ject included: • Modernization of the closed loop con- trol (CLC) system, including drive con- trol and excitation. • Modernization of the power section, in- cluding installation of a new Siemens Sinamics SL150 cycloconverter. • Supply of all equipment, including a new PLC, in a single container. • Remote diagnostic and service capabilities. • High-speed data recording. • Personnel training. The installation and setup was to be carried out in two phases corresponding to the mill's planned shutdown intervals. These planned shutdowns occur about once every five weeks and lasted no longer than 14 hours. Personnel training to familiarize the plant's operators with the new drive and automation systems would be carried out in parallel during the installation period. To complete the project within these brief windows, everything had to be in place when the planned shutdowns began—so Siemens built a platform outside the exist- ing mill upon which it could connect equip- ment through a shared wall. This arrange- ment provided an additional benefit of NOVEMBER 2012 • E&MJ; 127

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