Focusing the Flow
Tight control of underground mine ventilation system performance can be an ongoing challenge, but software, hardware and service options for drafting better ventilation plans keep expanding.
By Russell A. Carter, Contributing Editor
With a capacity of just eight breaths worth of air, the imaginary can is no bargain — and when it comes to mine ventilation in general, bargains are hard to find. For instance, the huge fans most mines use for primary ventilation purposes aren’t cheap to buy and install, but their purchase price might be considered a bargain compared with the cumulative power costs they accrue over the course of their service lives. And as mines extend to greater depths, the costs and challenges of maintaining proper ventilation and cooling of underground work spaces grow in lockstep with development. It’s an ongoing struggle for underground mine operators — one that regularly demands solutions to thorny technical issues, and involves decisions made from the top of the organization down to the lowest level of the mine regarding everything from the multimillion-dollar funding of a new ventilation shaft to the selection and placement of helper fans in the stopes and workrooms. Unexpected problems in mine ventilation performance and quality can cause a sudden and complete work stoppage lasting for weeks or more, as experienced by Vale’s Coleman operation near Sudbury, Ontario, last November when the company determined that repairs were needed in the mine’s ventilation shaft.
Fortunately, mine ventilation is also an area in which many potentially useful solutions are available, ranging from basic products such as mine doors and ducting to high-tech, mine-wide ventilation- on-demand (VOD) systems that include extensive sensor arrays, asset tracking and energy management capabilities.
A Swing Toward Safety
Until quite recently, mine doors installed to control air flow in underground mines weren’t regarded as sophisticated devices, but increased emphasis on worker safety and efficiency, along with a rising interest in ventilation automation, has resulted in a new generation of door designs that cater to these concerns. For example, American Mine Door’s EcoVent door, introduced to the industry at MINExpo 2016, addresses safety issues encountered when workers open and close doors in zones where the pressure drop from one side of the door to the other is high. EcoVent doors are distributed in the U.S. by Jennmar, which offers a variety of door types, stoppings and other ventilation accessories, and is available through other sales agents in the international market.
Traditional mine doors require miners to open one panel at a time. The EcoVent doors use a patented opposing-wing design in which the wings are connected. When one wing is opening, the other wing also opens simultaneously in the opposite direction. This design, according to the company, uses equalized air pressure to assist the door in opening and closing with little effort. The air pressure does the work instead of the miner, creating a safer work environment for miners as doors will not slam closed, significantly reducing the potential for injuries.
Apart from their safety features, these
“swing type doors,” which are also available
from other suppliers such as Zacon can offer additional advantages in some
applications. A recent paper* highlighted
benefits identified by a Codelco engineering
team that was tasked with choosing a single
door type to be used for ventilation and
fire control throughout the company’s huge
Chuquicamata underground mine project.
Having used “barn door” units — comprising
two panels hinged vertically on the
outside edges and opening from the center
in one direction — exclusively in its operations
in the past, the Codelco engineers
analyzed the drawbacks of this door type
and decided to take a look at other designs
including overhead models as well as the
swing-type or “Z” doors. They determined
that the swing doors offered a number of
benefits for this particular application:
• Because barn doors must be configured, for safety reasons, to open in the direction opposite airflow, a certain number of these doors, once installed, would have to be reinstalled — a two-weeklong operation — to work in the other direction as the mine’s ventilation plan changed throughout the long construction phase. This could adversely impact construction/ production schedules. Swing doors, on the other hand, operate independently of air flow direction.
• Although the swing door models evaluated by the Codelco team could only withstand about half the maximum pressure drop encountered in some areas of the mine, the use of multiple swing doors in an airlock configuration, where needed, could overcome this problem. Supply, installation and maintenance costs for the swing doors were estimated to be about 36% lower than barn doors — significant savings for a project that calls for installation of about 100 ventilation and fire control doors.
• The swing doors required minimal or no additional rock removal for installation, the concrete foundations were smaller than those required for barn doors, and workers could be quickly trained in installation and maintenance procedures.
The Electric Avenue
Workplace mobility, mechanical familiarity and lack of viable alternative products have kept diesel-powered equipment ubiquitous in underground hardrock operations for decades, but the presence of diesels in deep mines always comes at a price: i.e., the need for, and high cost of providing sufficient ventilation to handle the combustion emissions, heat and moisture generated by conventional hydrocarbon fuel-powered equipment.
For example, Goldcorp’s Borden Lake project, billed as the world’s first all-electric underground gold mine, is expected to reach full production in the second half of 2019 using an all-electric underground fleet of tethered and battery-electric units. According to equipment supplier Sandvik, by eliminating diesels underground and fully electrifying Borden Lake, Goldcorp expects a 70% reduction in greenhouse gases and annual savings of 2 million liters of diesel fuel and 1 million liters of propane. The company also expects to save 35,000 megawatt hours of electricity yearly, due in large part to drastically reduced ventilation needs. The mine reportedly was able to eliminate a return air raise from its layout and reduce the diameter of its intake raise from 5 meters (m) to 4 m, saving additional money in the process.
Illustrative of the kind of equipment employed at Borden Lake are two Sandvik DD422iE electric development jumbos currently in service at the mine, located in Ontario, Canada. These drills use power from an onboard battery during tramming, then tap into the mine’s existing electric infrastructure when drilling. Sandvik’s driveline technology enables the battery to recharge during the drilling cycle, and it will even recharge while the jumbos are tramming downhill, using energy generated by the braking system.
Maclean Engineering, another mobile equipment supplier to Borden Lake, has begun offering battery-powered underground road graders, one of which — based on a Caterpillar 12M platform — was delivered to the mine in April. The grader, modified under a partnership with Ontario-based engineering firm Medatech, features an onboard charging system that travels with the machine, eliminating a need for multiple fixed-location charging stations.
In a recent blog post, Maclean Engineering’s Stuart Lister presented an analysis of the potential savings that could accrue from operating a fleet of its electric underground equipment including a scissor bolter, scissor lift, two cassette trucks and a boom truck. The total annual savings in ventilation costs compared with a similar diesel fleet are estimated at $620,000. When combined with projected fuel and maintenance cost reductions, the total annual savings are almost $855,000.
Lister, the company’s director of marketing, explained that by using a 140% capital pricing assumption for the listed EV equipment compared with diesel, “…a high-tramming unit like a battery boom truck can make up the premium within the first few years of its commissioning. And it delivers those cost savings while improving underground air quality as well as operator comfort, benefits that speak for themselves but aren’t as easy to quantify in a cost savings modeler.” There’s another important aspect, Lister pointed out, arguing that: “…they will be the reason that the question ‘to EV or not to EV’ won’t solely rest, in the long run, on the operational costs savings question - it will be based as much on workers’ expectation that the diesel- free mine should be the new normal.”
Borden Lake is part of a new generation of underground mines that are either being revamped or designed from the beginning to take advantage of technologies that enable enhanced communications, data collection and analysis, and tracking of both machine and labor assets in real or near-real time. In many instances these technologies, which range from RFID tags and sensors to high-speed fiber optic data transmission systems, fit hand and glove with mine operator goals of higher levels of automation, reduced operational costs and risks and improved decision making – and they’re a vital requirement for achieving tight, mine-wide control of a ventilation- on-demand (VOD) plan.
Goldcorp said this was the impetus behind the deployment of a Cisco-designed multi-service, secure IP network at its Éléonore mine, enabling Wi-Fi connectivity underground. The Wi-Fi communications network provides improved visibility of the mine’s operations through continuous tracking of equipment, people, operations, and air quality, enabling mine managers to monitor, manage and fine tune processes and operations in near- or real-time.
Goldcorp said it initially engaged Cisco during Éléonore’s construction phase to provide an IP network that would enable real-time production visibility and control to increase efficiency, reduce costs and improve safety. “The primary business case was worker safety, providing visibility on where workers were in the mine and tying that to Ventilation on Demand,” said Alex Smith, account manager at Cisco Canada. “It’s an open standards network, so supporting applications can be built on top of it.”
At Éléonore, Goldcorp worked with turbine and fan manufacturer Howmet to develop a comprehensive ventilation control system using VentSim CONTROL, Howmet’s VOD solution formerly marketed as SmartEXEC. In a case history presented by Howmet, the company explained that the mine has a fresh air capacity of more than 900 kcfm (425 m3/s). The principal ventilation system consists of two Howden Alphair 12300-AMF-6600 exhaust axial fans with a nominal power of 2,000 h (1,471 KWh) each, configured in parallel. There is also an exploration shaft that has two Howden Alphair 11200-AMF- 6600 main intake fans with a nominal power of 750 hp (551.62 KWh), again configured in parallel. The mine also has more than 140 auxiliary and booster fans operated in conjunction with seven dampers and air regulators, and a heating system fueled by propane.
Howmet said it devised an automated system covering all the ventilation equipment in the mine, including the main fans, underground auxiliary fans and airflow regulators. Thirty Ventilation Monitoring Stations (VMS) were installed to determine the quantity and quality of fresh air at various points underground. Each VMS included a flow sensor and three gas sensors to detect CO, NOX and C3H8, and is an integral part of the VentSim CONTROL system.
The mine’s asset tracking system detects the presence of vehicles and personnel underground. Each of 144 vehicles was fitted with a Radio Frequency Identification (RFID) tag that indicates its position in the mine and whether the engine is operating. Everyone working underground was also given a unique RFID tag that connects to one of 254 zone-based Access Points. The data from the tracking system allows ventilation requirements for each zone to be calculated by the VOD logic software. This information is then used to automatically modify the speed of each of 140 underground auxiliary fans, to ensure that each zone of the mine receives enough fresh air.
According to Howmet, the mine initially reported a 43% reduction in mine heating costs, a drop of 56% in underground ventilation electricity costs and a 73% decrease in the cost of surface ventilation electricity. Potential savings, said the company, were expected to increase even more as the mine reaches full capacity.
Based on Éléonore’s experience, secure IP networks are being rolled out at Goldcorp’s Peñasquito, Red Lake and other mining operations. Cisco said it hopes to “bring new insights” to Goldcorp’s Borden Lake mine to support the mine’s connectivity and future automation initiatives.
Automation, battery-powered mobile equipment and higher levels of connectivity also enter into the plans for other underground development projects in Canada’s Sudbury mining district that total an estimated $1.43 billion. Vale plans to initiate early-stage development of its Copper Cliff Deep project at a cost of $760 million. After receiving full corporate approval in early 2018, Glencore is moving ahead with development of the Onaping Depth project, which will cost an about $700 million.
Glencore said it will employ a fully electrified underground mining fleet at Onaping Depth and has been testing various models of battery-powered equipment at its other mines. Vale, likewise, is planning for a battery-powered underground fleet at Copper Cliff Deep and is testing equipment in advance at a nearby operating mine. Spokesmen for both companies said expanded equipment telemetry capabilities, mine-wide Wi-Fi and automation initiatives will be important elements in development plans.
Choices Within Choices
Howden’s VentSim CONTROL, the VOD solution implemented at Éléonore and a number of other mines, is one of several VOD solutions offered by vendors that also include ABB, Bestech and others. Although VOD has gained operator interest and mention in the technical press and scientific literature in recent years, it’s not a new concept: For example, GEFA System, a small Swedish company, has been providing VOD support to iron ore producer LKAB’s underground operations for almost 20 years.
Most of these solutions are scalable,
allowing customers to acquire only the
level of sophistication needed for current
operations and resources yet permitting
future updates as needed. ABB’s SmartVentilation package, for example, can be
configured in three implementation levels:
• SmartBasic – Centralized supervision and control of ventilation equipment from ABB System 800xA Operator workplaces.
• SmartMid – A full-scale VOD solution with automatic control of the ventilation equipment according to actual demand. Ventilation demands are dynamically calculated from mine production schedules and events and event equipment status and location.
• SmartPerfect – Mine Ventilation Optimization using ABB’s SmartAir Optimizer module. ABB said SmartAir, a model-based approach, uses sensor feedbacks and advanced multivariable control technology to perform mine-wide control and optimization of air flows and air quality while minimizing energy consumption in real-time.
Bestech’s NRG1-ECO suite, billed as an
“energy consumption optimization” solution,
is a VOD package that also provides
multiple levels of control typically found in
high-end VOD systems. These include:
• Manual Real-Time — allows user manipulation of devices through a web interface.
• Time of Day Scheduling — automatically adjusts devices at specific times of the day such as the start or end of a shift.
• Event Based — devices will be stopped, started or adjusted based on an operational or programmed event.
• Environmental — responds to environmental sensor networks inside the mine to maintain air quality within regulated parameters.
• Tagging (Activity Based) — integrates with new or existing Real-Time Location Systems (RTLS) to deliver the required air flow based on personnel or vehicle locations in the mine.
The system provides environmental monitoring by logging digital or analog sensor information such as particulate, SO2, CO, NOX, barometric atmospheric pressure, temperature, humidity and air flow, and integrates with new or existing systems from Allen-Bradley, Schneider Electric, Siemens, Cisco, AeroScout, Becker, Varis, Smart Tag, PI and ION, according to the company.
In an article written for Canada’s Ingenium website, Marc Boudreau, president and co-CEO of Bestech, noted that the company, after implementing NRG1-ECO across five levels of the Coleman mine in Sudbury, saw electricity consumption cut by 4.4 MW-h, which adds up to $375,000 in savings per year. And by easing the burden on the power grid, greenhouse gas emissions were reduced by an estimated 780 mt. “If these results were replicated across an entire mine, our technology could help operators save as much as $3 million annually,” said Boudreau.
When Vale opened its Totten copper/ nickel underground mine in Sudbury, Ontario in 2014, the mine’s ventilation was administered manually with all fans, louver and doors controlled by an ABB 800xA DCS from a room on the surface. Ventilation Monitoring Stations (VMS) were installed throughout the mine to report on air velocities, relative humidity, dry bulb temperature and CO level. Using this manual approach, Totten chalked up an estimated 25% savings in annual energy consumption from fans and natural gas heaters.
After implementing a tag and tracking- based mode of ventilation control on one mine level in 2016 and subsequently expanding to additional levels throughout the mine, energy savings ballooned to between 50%-60% compared with baseline energy consumption levels before the upgrade,** which involved introduction of Bestech’s NRG1-ECO control system program coupled with the 800xA DCS. The mine-wide implementation of the higher level of control was a 15-month project that ended in late 2017.
VOD, Meet IoT
The ultimate success of mine-wide VOD at Totten, Éléonore and others depends heavily on the convergence and adaptability of reliable, affordable “connected” Internet of Things (IoT) devices and datacomms systems with evolving mining techniques and underground conditions. Without reliable sensors, robust cabling and efficient wired/wireless interfaces, the demands of real-time VOD would be hard to achieve. Luckily, technology is advancing rapidly. For example, USAbased Strata Worldwide introduced the StrataConnect DigitalBRIDGE, a new underground network solution developed in partnership with RFI Technology Solutions of Australia.
The company said DigitalBRIDGE cable segments can extend up to 6,500 ft (2,000 m) without the need for a repeater or dedicated power source. It can be a stand-alone system or can be used as an extension of existing fiber networks to reach further into and in multiple directions of the mine.
Strata Worldwide CEO Mike Berube said, “The outstanding advantage of the DigitalBRIDGE system is the power and data being transported in a single cable, which provides a high level of flexibility in the system engineering. Operations can configure and reconfigure the network on the fly, and place Ethernet end-point devices anywhere they are required.”
One of those devices might be Maestro Digital Mine’s FanMon primary and booster fan-monitoring system which, according to the company, is the first comprehensive and inexpensive fan monitoring system designed to be permanently installed on primary or booster fans. Data from the device is reliable and repeatable, said Maestro, because the sensors are always in the same location — while portable vibration systems are dependent on sensor location and are subject to human error.
FanMon, according to Maestro, can be incorporated into an alarm or safety shutdown system and provides complete vibration analysis including vibration signatures. Through the device’s Ethernet output, analysis or signature interpretation can be viewed locally or remotely by the fan manufacturer or vibration specialist without the need for expensive travel and wait time.
A particularly useful feature, said the company, is its ability to provide natural resonant frequency protection. Many fans have resonant frequencies below their normal operating speed; operating at resonant frequencies can cause high vibration levels that, if uncorrected, will cause damage. Depending on which component of the assembly is in resonance, the vibrations can cause a wide range of problems, from annoying noise to destructive failure. Shafts, bearings, and foundations are particularly susceptible to problems with resonance.
New fan motors now often use variable frequency drives to reduce energy consumption. Properly matching fan airflow delivery to mine load requirements reduces the fan’s rotational speed. Because slowing a fan increases the risk of encountering a resonant frequency, VFDs should be programmed to avoid operating at these frequencies. FanMon can help identify the natural frequency of the total installed installation by monitoring vibration levels while taking the fan through its entire rotation speed range.
However, the latest generation of VFDs may be smart enough to avoid that problem altogether. For example, ABB said its low-voltage AC drives automatically “jump over” fan speeds that cause mechanical resonance. In addition, according to the company, its drives allow “flying starts” to restart fans that are already spinning and offer lower reactive power consumption and a reduced need for compensation equipment when compared with other control methods.
Getting the Facts About Fans
Few mines can achieve adequate ventilation without fan assistance, but unless a fan is correctly selected for the application, ventilation is likely to be inefficient and overly expensive. Identifying and specifying fan requirements without complete knowledge about a product and its installation can be a risky and complicated process, with opportunities for error at almost any stage. Experts such as D.J. Brake, principal consultant and director, Mine Ventilation Australia, and adjunct associate professor of Resources Engineering at Monash University, recommend a turn-key arrangement in which a single supplier handles all aspects of mechanical, electrical and civil works for a given fan installation.
For companies that want to proceed on their own — and for prospective fan buyers in general — Jason Lionberger, operations manager at Western Precision Manufacturing, a Colorado-based supplier of standard and custom-built mining fans under the SMJ brand, offered a few suggestions.
“Spend a lot of time upfront thinking about what your current needs are and how they might change down the road. Often, we have buyers that want to save money up front, so they pass on options/ configurations that might be useful later. A good example would be silencers. We offer a few different silencer designs, standard and extreme duty. Customers typically decline the extra cost for the extreme duty variety based on cost, but later upgrade. Another example is a fan mounted on a crawler. Crawlers can be expensive but make advancing or moving the fan much easier. That time savings adds up over the life of a fan. And, have multiple suppliers provide a quote. It never hurts to see what other fan manufacturers can offer.
“Regarding material, design and warranty, most fan manufacturers have standards that they use based on the required performance, size, operating conditions, etc,” Lionberger said. “Most manufacturers build units that are very similar in design, performance, and warranty. Customer service, delivery, and price are often what really differentiates competitors.”
Some of the key considerations buyers
should carefully evaluate before purchasing
a fan are:
• Pressure and quantity requirements throughout the mine life.
• Nature of air to be handled – density, humidity, temperature, etc.
• Unidirectional or bidirectional flow required.
• Type and capacity of driving shaft or power available.
• Cost requirements and budget.
• Space requirements and availability.
Lionberger’s company also repairs and rebuilds mine fans, and he sees every day the common mistakes made by operators that can shorten fan service life. “Most fans fail first because of motor problems,” he explained. “Lack of maintenance (grease issues, over-current, impeller imbalance) is often the case. It is important to make sure the motor is operating within its designed parameters and that it is being maintained.
“Don’t delay maintenance or a rebuild until the fan fails. An example would be an impeller that is severely worn. This in turn lowers the fan performance and because of the imbalance of the impeller causes the motor bearings to fail. The issue could have been fixed with an impeller rebuild, but now the impeller and the motor must be repaired. Keep spare parts on hand. This minimizes downtime in the event of a failure and will save money by not having to order a rush rebuild or component.
“A fan rebuild typically consists of teardown, sandblast, weld/mechanical inspection, impeller rebuild (new blades, trim OD, dynamic balance), silencer repacking, motor rebuild, starter inspection, paint, assembly and testing. Rebuild costs really depend on the scope of work and the condition of the components. For example, it’ll be a much lower cost if the fan motor does not require a rebuild. A fan rebuild will typically cost one-fourth the price of a new fan.”