Fine Ore Pile Reclaim (Copper Mine)
This is an example of a large fine ore storage reclaim that is suffering from chronic bridging.
Why the Existing Reclaim System is Suffering From Chronic Bridging and Inconsistent Discharge
The existing storage and feed arrangement consists of a storage building that has a flat floor and is being reclaimed from below through a series of long slots. Material is metered by a belt feeder below each slot. This case study is an example of making funnel flow work when handling a fine material.
In summary, because the storage facility has no sloping walls, but is instead reclaiming the pile through a series of long slots in the floor, the pile is expected to empty in a funnel flow or first-in, last-out discharge pattern. Funnel flow can certainly be made to work when the “effective” discharge outlet is wide and long. However, when the discharge outlet is small, gravity is insufficient to overcome the strength of the bulk solid at the discharge outlet, and hence chronic bridging and rat-holing is expected.
In the case of this facility, below each slot is a tapered chute and a belt feeder. The purpose the tapered chute is to try to even out the discharge by the belt feeder, because it has a propensity to withdraw material selectively from the rear of the slot. However, tapered chutes are only effective over short distances, and the slot is over 44-ft long. In summary, the tapered chute is having little effect, as a result the belt feeder is primarily pulling material from only a short section of the slot. As a result, despite the fact that the slot in the floor is long, effective opening through which material is being discharged (from the perspective of gravity) is small. And when the opening is small, rat-holing can be expected.
The solution to fixing this problem is to replace the chute and belt feeder with a fully-effective feeder. A fully-effective feeder is one where the feeder withdraws material evenly from its entire infeed opening. With a fully effective feeder, the full length and width of the slot is “live”, and with a large effective discharge area, the pile can reliably be discharged in a funnel flow discharge pattern.
A great example of a fully-effective feeder is the Kamengo Feeder. In addition to being fully-effective, the Feeder offers consistent metering, and can be made as wide as needed and as long as wanted. As a result, the Kamengo Feeder offers valuable advantages when designing for a difficult flowing material.
To learn more about the physics of storage bin and feeder design as well as the root causes of bin plugging, please download our white paper entitled: The Design of Reliable Storage Bins and Feeders for the Mining Industry.