environmental impact compared to using truck transportation.” Beumer Group not only supplied the conveying solution; it also supported the mining group in building a stockpile for hard coal. “Te requirements for storing coal are obviously very different from other materials,” explains Prevedello. Some of the important requirements are changing if the stockpile is covered and if explosion-proof specific equipment is needed. Hard coal is very susceptible to spontaneous combustion, which is why the height of the stockpile must be in certain cases limited.

CIRCULAR OR LONGITUDINAL STOCKPILE? Depending on the customer, stockpile dimensions and design can vary. Two layouts are generally available: circular and longitudinal. “Teir dimensioning and design depend on the purpose of the stockpile,” says Prevedello. Space availability and possible future expansions are also critical factors. Te application must also be considered: does the customer want to store the bulk material temporarily, then continuously feed it for further processing, like Knight Hawk? “Ten longitudinal stockpiles are your best choice,” states Prevedello. Tey can also be extended, if necessary. Te 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 as well, limestone and clay, for example. Tis is particularly used by cement manufacturers and power plant operators. But back to coal. Once the layout of the stockpile has been decided on, the next task is to stack the bulk material efficiently. Beumer Group also provided these

Aerial view of the coal mine

necessary components such as the stacker. “Depending on its mobility, the systems can be categorised into three groups,” explains Prevedello. Te 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.

IT DEPENDS ON THE METHOD Te stacking method of choice depends on whether the bulk material is only temporarily stored or if it also needs to be blended. Prevedello says, “For simple stockpiling without blending, we provided

The overland conveyor transports the coal from the mine to the main processing plant

with the simple ‘cone shell method’. Te stacker only moves up and down, not slew. Te stacker design can be simpler. Tis method works for longitudinal as well as circular stockpiles. For blending the bulk material however, the Chevron method can be used. Te boom of the stacker starts in its lowest position. Te first row is deposited in the centre of the stockpile, 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.”

EFFICIENT COAL MINING “Te perfect system solution is always an optimal relationship between stacker and reclaimer,” explains Prevedello. Reclaimers such as side reclaimers or bucket wheel remove the material, as necessary. Te best option for the customer depends again on the stockpiling task at end. Side reclaimers work for both types of stockpiles, longitudinal or circular. Te bulk material can be 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. Te advantage is that the bulk material is reclaimed from the entire cross-sectional area. Bucket wheel are used in particular when the bulk material, especially in large quantities, needs to be blended. 37

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