The combination of BEUMER Group’s sophisticated modelling techniques and use of drones has enabled Knight Hawk Coal’s Prairie Eagle mine, in the Illinois Basin of USA, to reduce its long-term environmental impact.

Drone technology is being used more frequently during project planning, implementation and documentation to optimise the design phase, according to BEUMER. The recorded aerial photos are reconciled with regards to their perspective and evaluated photogrammetrically.

The software calculates a point cloud in order to generate 3D models from the 2D views, ie digital terrain models, allowing stockpile designs to be generated for both greenfield and brownfield developments.

Opened in 2005 as a surface mine, Prairie Eagle was expanded over time to include two underground mines, Knight Hawk’s main coal preparation plant and multiple truck load-out facilities. Now one of the most efficient underground mining plants in the US, according to BEUMER, it produces around 5 Mt/y of coal, of which more than 80% is processed and delivered to the Prairie Eagle preparation plant.

Management was looking for a more sustainable operating solution that reduced its reliance on truck transportation, according to Andrea Prevedello, System Technology Global Sales Director, BEUMER Group, Germany.

“We provided an overland conveyor that transports the coal from the mine to the main processing plant,” he said. “Our conveyor helps the company to considerably reduce its ecological footprint. With this technology, Knight Hawk can significantly reduce its long-term environmental impact compared to using truck transportation.”

BEUMER’s solution at the mine features a single-flight curved conveying system that eliminates the cost of tower steel, and greatly reduces the quantity of components and necessary spare parts, according to the company. It reduces the dust, noise, maintenance and operating costs associated with the transfer points, BEUMER said.

BEUMER not only supplied the conveying solution to Knight Hawk. As a system supplier, the company also supported the mining group in building a stockpile for hard coal.

“The requirements for storing coal are obviously very different from other materials,” Prevedello said. Some of the requirements change if the stockpile is covered and if explosion-proof equipment is needed. Hard coal is very susceptible to spontaneous combustion, which is why the height of the stockpile must, in certain cases, be limited.

Depending on the customer, stockpile dimensions and design can vary. Two layouts are generally available: circular and longitudinal.

“Their dimensioning and design depend on the purpose of the stockpile,” Prevedello said. Space availability and possible future expansions are also critical factors.

The application must also be considered: does, like Knight Hawk, the customer want to store the bulk material temporarily, then continuously feed it for further processing? “Then longitudinal stockpiles are your best choice,” Prevedello said. These structures can also be extended, if necessary, according to BEUMER. The irregular flow of bulk material arrives at the stockpile and can then be continuously introduced to the process.

Circular stockpiles are frequently used for other bulk materials, eg limestone and clay.

Once the layout of the stockpile has been decided on, the next task is to stack the bulk material efficiently. BEUMER also provided these components, such as the stacker, to Prairie Creek.

“Depending on its mobility, the systems can be categorised into three groups,” Prevedello said. The stacker can be stationary, travel on rails, or be circular with endless movement.

If the machine is circular with endless movement, it is positioned on a column in the centre of the stockpile. Over a conveyor bridge installed above the stockpile, the material is transported directly into the axis of rotation of the stacker, and from there distributed centrally. Depending on the stacking method, the boom conveyor can be fixed, or it can be lifted and tilted.

The stacking method of choice depends on whether the bulk material is only temporarily stored, or if it also needs to be blended.

“For simple stockpiling without blending, we provided the simple ‘cone shell method’,” Prevedello said. The stacker only moves up and down, ie does not slew, and the stacker design can be simplified. This method works for longitudinal as well as circular stockpiles, according to BEUMER.

For blending the bulk material, the ‘Chevron method’ can be used. The boom of the stacker starts in its lowest position; the first row is deposited in the centre of the stockpile and the next rows are layered on it. In longitudinal stockpiles, the stacker usually moves in a tilting and slewing motion; in circular stockpiles, the stacker moves in a circulating and luffing motion.

Prevedello said: “The perfect system solution is always an optimal relation between stacker and reclaimer.” Reclaimers such as side reclaimers or bucketwheel reclaimers remove the material as necessary. The best option for the customer depends, again, on the stockpiling task at the end.

Side reclaimers work for both types of stockpiles – longitudinal or circular – with the bulk material reclaimed from the front or the side. When reclaiming from the side, scraper chains move the material on a belt conveyor. Front reclaiming usually uses a rake that, in small side-to-side movements, pushes the material on a scraper chain to be transported further to the conveyor, BEUMER explained. The advantage is the bulk material is reclaimed from the entire cross-sectional area. Bucketwheel reclaimers are generally used when the bulk material, especially large quantities, needs to be blended.

Each operator has their own specific requirements when it comes to the stockpile and stockyard machines.

This is shown in a project BEUMER engineers are currently implementing for a customer in the energy industry. The order includes the delivery of several conveyors, including pipe conveyors, and a ship loader. The challenge: “On the ground where we will install our solution, there can be violent gusts of wind,” Prevedello said. “That’s why we pay special attention to the dimensioning of the steel structure.”

The system provider will be able to hand over a tailor-made system to the customer, with investment expenditure tailored precisely to them, according to BEUMER, which said the expected commissioning is scheduled for the September quarter of 2020.