Speedy SAG Mill System Upgrade Minimizes Downtime Costs
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.”
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.
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 allowing Siemens to test new components while the existing system was still running.
Upgrading the electronics provided a challenge as well as an opportunity to devise another innovative solution. Typically, an electronics upgrade involves swapping out old components and in-stalling new parts. This was not an option if Robinson Mining was to keep its mine operating. Instead, Siemens installed all of the new electronics within a compact, portable ‘eContainer,’ that was construct-ed in Indiana, shipped intact to Nevada and hoisted into position on the external platform, which was then enclosed for protection from the elements.
“The benefit of the eContainer was that we could assemble and test it remotely and then hoist it into place; it put us that much further ahead,” said Brunson.
The mill modernization was completed in September 2011. The final switchover took just 72 hours, saving Robinson Mining 18 days of downtime. With the cost of inoperation as high as $100,000/hr, the innovative approach proved worth its weight in gold—and copper.
“Siemens, from the beginning on this project, was willing to listen to us and understand our concerns. This was a very good partnership,” said Brunson.
With the new system up and running, Siemens said Robinson Mining can expect to reap long-term benefits such as greater reliability, along with improved performance and ease of use. The mill’s new digital electronics system provides more precise control and greater diagnos-tic capability. A user-friendly interface delivers information to operators more efficiently, resulting in higher productivi-ty. Energy efficiency also has improved. With the new power conversion system in place, the mill can perform the same amount of work with less energy.
The benefits to Robinson Mining extend beyond just the upgrade, accord-ing to Siemens. Through a comprehensive service strategy, Siemens is provid-ing operators with confidence that the new mill will continue to deliver greater productivity and reliability. The service strategy devised by Siemens includes:
• 24-hour hot line support and monitoring;
• Remote data analysis and diagnostics;
• Semi-annual, on-site preventive main-tenance visits;
• A comprehensive maintenance plan for key equipment; and
• Spare parts management and inventory reliability analysis.
Through remote diagnostics, Siemens experts can monitor and troubleshoot main-tenance issues before they result in a shut-down, and Siemens technicians can be on-site in a matter of hours—crucial advantages for a mine that is more than 200 miles away from the nearest electronics distributor.
Looking back at the whole project, Whittaker summed up the experience of partnering with Siemens to deliver an innovative solution that kept his mine at its most productive. “The project was fun and exciting, and it is a real enhancement to the future of Robinson Nevada Mining.”