FEECO International discusses storage handling options for processing sites, and the crucial points to getting it all contained safely, efficiently and cost-efficiently.
Different storage settings characteristic for mining and mineral processing sites demand a range of conveying equipment for carrying, elevating and discharging material. Whether stacking, filling bins or railcars, piling material in a storage building or otherwise, conveying equipment is the heart of the operation.
As such, handling systems hold significant potential to either add to or detract from operational efficiency. From pit to beneficiation, on to loadout, and every storage point in between, efficient, streamlined handling is the result of a carefully configured system. What follows are equipment options in storage handling applications and considerations in system design.
Troughed Belt Conveyors
Designed to carry material horizontally or at slight incline without material spillage, troughed belt conveyors are the most prolific type of handling equipment in storage – the basis for most carrying applications.
From bringing product to the storage site, to transporting it around and loading it out, troughed belt conveyors offer cost-effective, reliable and flexible handling for most settings. They are capable of carrying material with a significant range of physical and chemical characteristics and offer ample opportunity for customization, including various belting options, belt cleaners, take-up types, support structures, drive assemblies, materials of construction, accessories and more.
Stack Out Conveyors
Used in outdoor settings to stockpile material in stockyards, stack out conveyors consist of a stationary belt conveyor set on an angle. Note that these are different from radial stacking conveyors, another similarly designed common conveyor type, but that pivots on its tail and travels along a radial arc. While end support points for stack out conveyors are an option, a “knee brace” is typically used to support the unit at or closer to its midsection, allowing the support to be kept away from the material pile for cleanliness and ease of retrieval.
Stack out conveyors provide a more efficient alternative to wheel loaders and screw conveyors, allowing for reduced dust and less damage to product during stockpiling. Stack out conveyor design must consider several factors; desired pile height, spatial restrictions and conveyor length will dictate angle of the conveyor, as well as number and placement of supports.
Belt trippers increase the flexibility of troughed belt conveyors by allowing material to be discharged at any point along the conveyor’s length. This has made them a favored approach in various storage settings for filling bunkers, hoppers, silos and creating piles along the conveyor length. The tripper is positioned 15-20 feet above maximum pile or container height and can be fixed or movable.
The tripper car, which may be festoon or cable reel powered, can be equipped with a diverter system on the discharge chute to allow for material to be released on either or both sides of the unit, or directly back onto the belt. Material diverted back onto the belt can then be released at the conveyor head pulley.
This “pass through” option allows the material to bypass the tripper car and travel upstream without being discharged to the side. Now acting like a more traditional belt conveyor, the material is discharged from the conveyor head pulley. This helps maximize storage space since the tripper must stop short of the conveyor head pulley. It’s also useful when feeding onto a second conveyor that fills additional storage buildings.
Level indicators can indicate when a container is full, prompting the tripper to move to the next discharge point. Trippers may be set to travel automatically or be controlled remotely. Tripper positioning can be controlled by shaft encoders, laser systems, microwave systems, and/or sector position switches.
In designing a belt tripper for storage applications, several factors must be considered: type of storage (indoor or outdoor), building type, height and length, number of discharge points, discharge locations, travel distance, unit power (cable reel or festoon) and more.
Reversing shuttle conveyors offer an alternative to belt trippers in settings with special requirements, most often for limited overhead space. A shuttle conveyor consists of a rail system-mounted troughed belt conveyor, allowing the conveyor to move across the rails in both directions – useful for building an inline, continuous pile or feeding multiple fixed discharge points.
A shuttle conveyor typically costs more than a tripper, but offers a much-needed solution in low-height settings; tripper conveyors are significantly taller than shuttle conveyors, requiring added head room. As such, trippers are often chosen for large storage buildings where height is not an issue, while shuttle conveyors are a better choice for confined spaces.
The downside to shuttle conveyors is the material feed point must remain in the center of the storage area and the length of the shuttle conveyor needs to be long enough to constantly be under the feed point and still reach the furthest ends of storage. This ultimately limits the amount of space the unit can travel. In contrast, a tripper can move from one conveyor end to the other, allowing it to fill a much larger space and for the material feed point to be at the far end of the building.
Shuttle conveyors additionally require the added consideration of how the unit will be fed, as well as geometric considerations associated with the feed point requirements. Shuttle conveyors also require longer-than-typical skirtboards and impact idlers, depending on the exact layout.
Belt feeders are often used after reclaim conveyors, another common storage conveyor which collects material from storage to bring it to processing or loadout. They are essential in metering material onto a conveyor at a controlled rate using a combination of belt speed and an adjustable slide gate. Belt feeders are often accompanied by a flood hopper and belt scale to monitor and totalize the mass flow rate from the feeder. Considerations in belt feeder design for storage include capacity, material lump size, belt speed, slide gate height and feed hopper opening dimensions.
Bucket elevators are another fundamental component in storage settings, carrying material vertically at high capacities. Bucket elevators may be used to feed weigh hoppers or conveyors on a different floor, fill silos outdoors, or transport material to a loadout conveyor for loading onto a barge or rail cars, among other applications. They are also typically the equipment of choice in feeding the aforementioned equipment (except for stack out conveyors), all of which require material to be lifted and discharged above the equipment. Design considerations include feeding and discharge style (centrifugal or continuous), discharge height and chain- or belt-mounted bucket placement.
Editor’s note: author Dan Baxter works in material handling sales for FEECO International.