In its second season and operating a new processing plant, Dakota Aggregates LLC mines on 700 hectares in the visionary University of Minnesota Outreach, Research and Education (UMore) Park.
Located in Rosemount near the Twin Cities, the mine serves the metropolitan area with a wide variety of construction aggregate products. The operation was designed with innovation in mind, particularly where material handling is concerned. The site spans 4.8km from north to south, and a mile and a half from east to west.
Consequently, overland conveyor systems were chosen to efficiently transfer material from the face to the processing facility, while eliminating the costly use and resulting emission streams of loaders and haul trucks, and providing quiet operation while minimising energy use and lowering operating costs per tonne.
Initially, the challenge for Dakota Aggregates was finding a lower cost overland alternative to custom-engineered, conventional overland systems – and, most importantly, one that would allow it to easily and quickly reconfigure its overland systems to accommodate changing mining requirements each season.
Dakota Aggregates has a 40-year lease on the university-owned land, where melting glaciers left behind a thick blanket of high quality sand and gravel thousands of years ago. Mining this deposit is part of the overall sustainability focus of UMore Park. A few of the benefits of this initiative are that the local region taps into the cost efficiencies of a valuable and nearby source of aggregate products, while the university realises an additional long-term revenue source. And for every tonne of gravel mined, a portion of the profit goes into a scholarship fund for geology and civil engineering students at the university. It’s a win-win for all and an example of innovation at its best.
With the latter spirit in mind, Dakota Aggregates approached its material handling challenges by consulting with Superior Industries, a manufacturer of material processing and handling systems and components. Superior had recently launched its Zipline conveyor, a pre-engineered, modular overland conveying system designed for quick and almost tool-free installation. Dakota Aggregates is one of the first producers in the US to take advantage of this new overland conveying solution.
“It was refreshing to share our input on the system with the engineers at Superior and to work with them on various enhancements to this new product,” said Stacey Hannover, operations manager for the Dakota Aggregates plant, which processes more than 1.5 million tonnes of aggregate products annually."
The site mines from its furthest boundary and back towards the processing plant.
“While we are generally pulling conveyors out and shortening the distance of conveying, we can easily add on sections in other areas of the operation,” Hannover said. “We needed flexibility at the right price point. With the Zipline conveyor, we have ease of assembly and ease of on-site portability.”
The operation utilises 1494m of modular conveyor sections (at lengths of three metres each and belt widths of 762mm to 914mm), which is currently divided into six different overland systems of 152m to up to 305m.
“It’s easy to reconfigure any one of our modular overland systems to cost-effectively meet our changing requirements each year,” Hannover said. “As an example, during this season, we easily pulled 76m out of one system.
“Also, while we generally operate on level ground, next season we will be moving a section to accommodate material transfer on an area with a 15 per cent incline.”
He said installation was “pretty much a breeze. Once we got the pattern down, three crew members marched right down the conveyor corridor and were able to assemble 76m of overland conveyor sections in a 10-hour day.” The crew used a forklift and a skid steer loader, with no need for cranes or other heavy equipment.
“We began with the mission of being tool-free in installation requirements regarding the entire intermediate area between the head and tail sections,” said Travis Thooft, a member of the Superior Industries engineering team.
This required creating a new type of “fastening system” that is structurally sound and reliable, yet is quick and easy to use in the field.
“When you consider the typical way to put things together, the industry standard is basically weld or bolt,” Thooft said.
“We took it a step further by eliminating bolts and replacing them where possible with a ‘fixed-pin’ connection. We wanted to eliminate the need to bring out a set of wrenches for most installations.”
Thooft estimated the new design could cut installation time by up to 75 per cent.
“Basically, you hook in one end and then the other, with the whole set-up for a three-metre section taking just about five minutes,” he said.
Thooft said the specification process started by defining the overall length of the overland system, and the required output. The system includes a pre-engineered head assembly and tail section, and is designed with off the shelf components for easy sourcing of replacement idlers and pulleys.
“Producers can customise with options such as self-aligning troughing idlers or special return trainers, idler guards and belt cleaners; or a longer or different type of gravity take-up, for example,” he said.
When compared with the spec-by-spec, highly engineered system, Thooft said the Zipline conveyor system was a lower cost overland alternative. “While it’s lighter in weight, it offers the structural strength of the conventional overland system. Its big advantage is its ‘modularity factor and unique fastening system’, which allows easy structural additions in the future, and easy site reconfigurations as needed.
“It also allows operations to choose (depending upon the project) between renting modular sections from their local equipment dealer or purchasing a package of sections that they can customise within a given set of parameters.”
Driving overland solutions
What are the key drivers behind more operations turning to overland conveyor solutions?
Certainly overland conveyors offer cost-effective material transport within a wide spectrum of capacities – and when used in place of loaders and haul trucks, operations are significantly reducing fuel costs and expenses due to labour, workers’ compensation, training, emissions, maintenance and engine depreciation.
Another key driver is ever-tightening environmental regulations. While individual mobile haulage units emit and stir noise and air pollution along the entire transfer path, overland conveyor systems offer quiet and environmentally sound material transport.
With the advent of the pre-engineered and quick to install, modular overland system, producers such as Dakota Aggregates can acquire a system with a lesser initial capital investment than conventional systems, and can operate with greater efficiency, flexibility and sustainability into the future.
Superior Industries’ modular conveyor systems and mobile stackers are available in Australia through 888 Screening & Crushing Equipment (west coast) and Mobile Conveying Systems (east coast).
Source: Superior Industries