Nickel and copper are used in everything from cars and appliances to medical instruments and household batteries. As the only primary nickel mining operation in the U.S., Eagle Mine, in western Marquette County in Michigan’s Upper Peninsula, plays a key role in bringing many of these products to market.
The Eagle Mine site is a underground, high-grade, greenfield nickel and copper mine. It's the first mine to be permitted under Michigan’s Part 632, Non-Ferrous Mineral Mining Law. During its estimated eight-year mine life from 2014-22, Eagle Mine is expected to produce 365 million pounds of nickel, 295 million pounds of copper, and trace amounts of other minerals. It's a subsidiary of Canada-based Lundin Mining Corp.
From its 150-acre surface site in Yellow Dog Plains in western MarquetteCounty, the mine accesses its ore body via a mile-long decline tunnel. Ore is removed using the long-hole stope mining method, which mines horizontal spaces, then backfills before mining the remaining spaces. Next, the ore is transported nearly 60 miles to the Humboldt mill in Champion, Mich., which was a brownfield site first used for iron processing during 1950-1980. After it was closed, the mill sat idle for many years before undergoing a $275-million reclamation and renovation, bringing it back into operation in 2014 (Figure 1).
After getting nickel and copper out of the ground at depths up to 1,000 feet, turning it into usable products requires several steps. In the first, ore processing, the mill uses three crushing stages and a grinding stage to reduce large pieces of rock down to the consistency of a sand slurry, which is run through a flotation process to separate the copper and nickel. The two metal slurries are then filtered to reduce moisture so they can be shipped to an offsite smelter. The mining and milling process produces 2,000 metric tonnes per day of high-grade nickel and copper concentrate, which equates to 1.5% of worldwide production.
Wireless watches for wear
The Homboldt mill's heavy industrial applications can wreak havoc on mechanical equipment, and place substantial burdens on the maintenance crews that must keep it running efficiently and safely. As with any mining operation or other processing plant, continuous improvement is required to stay competitive, which often requires adding instrumentation to existing equipment. In our case, after the mill was engineered and the automation system was installed, it was determined that we needed a quick method for installing more measurement devices, especially vibration and temperature monitors on critical equipment.
Unfortunately, adding new points with wired instruments was expensive, would require time to plan and implement, and would disrupt the commissioning and ramp-up schedule. While wireless monitoring wasn't part of the original engineered design, as the project neared completion, we decided the plant would benefit from adding wireless capability. We also saw other areas where additional process measurements could cut costs, improve safety and avoid unplanned downtime.
In our operation, the ability to immediately detect changes in equipment vibration is essential. For example, if a bearing on a ball mill fails without warning, it could cost millions of dollars in repairs and lost production. Dedicated reliability technicians are onsite during the day, but they can’t be here 24/7. If a failure occurred at night or on a weekend when our reliability technicians are off duty, we needed to identify that bearing and related failure, and shut down the affected equipment. Consequently, we decided to install wireless vibration transmitters to alarm in the DCS, so the operators would know they have to shut down the equipment.
After conducting field trials to determine network coverage requirements, we deployed four 1420 Smart Wireless gateways from Emerson Process Management throughout the mill (Figure 2). To link the WirelessHART vibration transmitters to the wireless mesh network, all transmitters were installed with either standard or long-range antennas.
Wireless transmitters were then placed remotely in convenient locations away from the vibration sensors mounted on the mill’s cone crushers and ball mill bearing housings. We also installed wireless vibration monitors on three crushers and two ball mills, which were identified as critical major equipment.
Wireless transmitters provide quick access to vibration measurements without physically walking to the equipment to take readings. Our reliability technicians also use Emerson’s AMS asset management software to identify and proactively manage issues, and avoid unplanned shutdowns.
More measurements aid operations
Beyond vibration monitoring, we installed WirelessHART wireless transmitters in various locations around the mill to measure pressure, level, temperature and pH. We also installed several discrete wireless transmitters so we could get motor run feedback from remote locations.
Wireless temperature transmitters also were installed in remote locations, including pump houses, fire-riser rooms and outdoor sumps. These locations aren't staffed 24/7, and we needed to monitor ambient temperatures to detect freezing or excess heat. We were concerned that heaters could be left off or fail, causing temperatures to drop below freezing. Or the heaters might be left on, which could cause overheating and potential fire hazards.
Also, another digital wireless transmitter was installed at a remote location (Figure 3) where it receives a hardwired input from a water tank heater starter. When the starter pulls in, the auxiliary contact on it closes and sends the transmitter a signal, which is retransmitted to the DCS through the wireless mesh network. We use this information to make sure someone didn't inadvertently shut the heater off in the winter.
Monitoring water at a distance
The mill also has a water treatment plant and a reclaim water tank roughly a mile away from the mill building’s wireless network. Acquiring process information with hardwired transmitters would have created a major hurdle because of the distance over which we’d need to run wiring, but wireless temperature transmitters solved this problem, too.
Our water treatment plant processes outflow from the tailings reservoir, and we had multiple requests to install more transmitters after start-up. Because of the equipment layout in the building and the cable tray run near the ceiling, however, there was no quick and easy way to add wired transmitters. One example of our solution was installing a level switch for containment spill indication. The wireless transmitter connected to the switch was installed and working in a couple of hours, compared to running wire to the DCS that would have taken days. Wireless temperature transmitters also were installed in the mill to monitor process water and building temperatures, saving more time and money.
Analyzing all the data
The mill's operators are the main users of the data from its wireless transmitters, and they constantly use it to monitor and improve operations. The more measurements they have, the better they can run the plant by avoiding downtime and improving safety.
Wireless transmitters are connected to the mill's AMS software through its DCS. The asset management software monitors data from all the wireless transmitters, and provides alarm management information and configuration (Figure 4). The AMS software provides frequent and detailed analysis of vibration readings, and helps to plan and manage instrument calibration routes via its Calibration Assistant function.
Recently, we expanded our asset management system to include ValveLink software, which handles control valve diagnostics from our Fisher FieldVue digital valve controllers. This helps us with early identification of valve performance degradation, and lets us plan for repairs during scheduled shutdowns.
Wireless historical data is retained in two locations at Eagle Mine. The data is brought into the historian, which sends it to PI Historian software for use on the business-level network. We’ve found that, along with being useful for root-cause failure analysis, historical data also reinforces safety and operator accountability. If an event occurs, we can look back and see whether an operator acknowledged an alarm and how they responded. This helps keep everyone focused and ready to take action if something goes wrong.
Why choose wireless?
Similar to any industrial manufacturing facility, we had the choice to add new points of measurement using wired or wireless instruments (see sidebar, “Why use wireless at Humboldt Mill?”).
We wanted to start small with just a few instruments, then add more if results were positive. Our plan was greatly facilitated by our local Emerson representative, Novaspect Inc., which provided demo wireless gateways and devices so we could check signal strength and layout our wireless network. This allowed us to use a “try before you buy” approach with a new technology for us.
Configuration of the wireless gateways was simple, and establishing communication with our DCS was accomplished with Novaspect’s assistance. By connecting the wireless data to the DCS, we were able to trend data in the DCS historian, then send it to our PI system for trending. We also installed software to provide the data translation needed to convert wired HART I/O data coming from the DCS to our AMS system.
Is wireless right for your plant?
The decision by Eagle Mine to invest in wireless came mainly from our desire to respond quickly to production requirements without impacting the mill’s commissioning schedule. This was accomplished through reduced installation time by eliminating the need to run extensive wiring throughout the site.
Although our reasons justified wireless in our case, each facility is different. Some of the main points to consider when contemplating wireless are in the sidebar, “Wireless considerations for your facility.”
In some plants, operations staff often asks for more transmitters to monitor processes. Adding wired transmitters requires manpower and installing more conduit and wire. More wired transmitters also require sufficient capacity in the existing I/O system, which you may not have.
If the request for additional transmitters is time-sensitive—operations wants them now—installing wired devices might not be feasible from manpower, cost and capability standpoints. We found wireless transmitters were a much better solution in this case because they can be installed quickly.
Also, battery-operated wireless transmitters can be configured to sample and transmit data at rates ranging from more than a second to once every few hours. If fast updates are needed for control or monitoring, battery life must be considered. Most wireless transmitters have the option of being line-powered, while others can use energy harvesting.
Installation of wireless transmitters is vastly simplified if your plant already has a wireless mesh network in place and your technicians have been trained. Then it’s simply a matter of installing the transmitter, configuring the Network ID/Join key, and watching it automatically connect itself to the gateway’s existing network.
If you're installing a new wireless network and have no experience with wireless, it’s best to get your local wireless representative involved to ensure proper installation. A site survey to determine where to place the gateways may be required to identify potential network gaps.
At the Humboldt mill, we have several applications with long distances from field transmitters to local gateways. To cross these distances, we used a combination of short- and long-distance antennas to make connections. Network gaps were filled by adding wireless adapters to existing transmitters to strengthen the mesh network by acting as a repeater. Users also can benefit by making hardwired devices wirelessly configurable through the AMS system.
By using wireless transmitters, we estimated an $83,000 savings in installation costs compared to wired transmitters. We also were able to complete the installation much quicker with wireless, maintain the commissioning schedule, and realize benefits of expanded equipment monitoring.
The wireless installation also provided measurable maintenance cost advantages. Monitoring temperatures at remote sites saves $3,000 to $10,000 per incident by preventing pumps from freezing and buildings from overheating. Vibration transmitters have also helped prevent unexpected failures of our crushers and ball mills that might have caused prolonged process shutdown, and cost millions in repairs.
Wireless gives us a degree of flexibility not possible with traditional solutions. Our four wireless gateways started with 20 wireless transmitters but we've increased them to 60 along with multiple wireless adapter installs. Because we already have a wireless infrastructure, we can install and configure new devices and begin streaming data in a few hours. Having that level of adaptability and ease-of-use can be crucial, especially when you’re working against the clock.