When a large nickel mine located in the South Pacific purchased two side-by-side truck load bins to handle a sticky, high-moisture content dewatered tailings, the mine chose Kamengo to design and deliver both the storage bins and Feeders.
Kamengo truck load out bin discharging cohesive PGM filter cake from a 3m (10-foot) wide discharge bin into trucks.
When a new Lithium mine located in South America purchased a metering bin to feed lithium carbonate precipitate from its centrifuge discharge to deliver an even feed to its dryer, the mine chose Kamengo to design and deliver both the storage bin and Kamengo Feeder.
Retrofit of a front-loaded metering bin handling rock gypsum and limestone shale rock at a cement plant.
Front-loaded metering bin, operating outside in an artic environment, delivering an even, metered discharge of wet FGD gypsum into a continuous process.
Two Kamengo metering bins receiving cobalt hydroxide filter cake from a filter press and metering the wet cake to a dryer.
This case study is an example of a retrofit of a front-loaded metering bin handling recycled gypsum – a very sticky, cohesive material. The retrofit was completed in 1995.
Prior to the retrofit, the front-loaded bin was discharged via three screw augers. The augers suffered from chronic plugging and the gypsum plant was keen to find a solution. The challenge with this application is that not only did the plant need to find a feeder that could reliably handle the recycled gypsum but that could also deliver a very consistent discharge.
The plant receives recycled gypsum for free but is limited in the amount of recycled gypsum that it can add to its wall-board because of the recycled gypsum’s paper content. Hence, to maximize the recycled gypsum content without exceeding the prescribed limit, the front-loaded bin needs to deliver a very accurate and even discharge. What makes the application further challenging is that the recycled gypsum is stored outside in the rain, making it particularly sticky.
The augers struggled handling the recycled gypsum for two reasons:
The solution to fixing this problem storage and feed system was quite simple: Kamengo raised the storage bin and slipped in a Kamengo Feeder between the bin outlet and screw feeders.
First, Kamengo was able to re-use the existing front-loaded bin because the geometry of the bin, including width and length of the discharge opening, and angle of the bin sloping walls were sufficient to deliver a mass flow or first-in, first-out discharge pattern. Good bin geometry is essential to reliable discharge. The measure of a good bin is that, if the feeder were removed, it should completely self-empty with only the aid of gravity.
By inserting the Kamengo Feeder between the screw feeders and the front-loaded bin, the screw augers were no longer acting as feeders but instead only operated as conveyors. This is because the head of material in the front-loaded storage bin was placed on the Kamengo Feeder, which in-turn delivered a metered discharge onto the augers such that they were never more than one-third full. With no head of material on the screw augers, they are plenty reliable acting as conveyors.
Adding a Kamengo Feeder was necessary to achieve a mass flow discharge in the front-loaded bin. By definition, to achieve mass flow, where the stored material comes down as a single body, the feeder must withdraw material evenly from its entire opening. If the Feeder withdraws material selectively from the bin discharge outlet, sections of material in the bin will be stagnant and funnel flow will ensue.
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 Gypsum Industry.
This is an example of a zinc oxide filter cake metering bin that is suffering from chronic bridging.
The existing storage and feed arrangement consists of pyramid hoppers that converge to square openings. Under the pyramid hoppers is a variable pitch twin-screw feeder. Filter cake falls through breaker bars into the hoppers, from where it is metered by the screw feeder.
In summary, the pyramid hoppers are suffering from chronic plugging because the pyramid hoppers, with four sloping sides converging to a small opening combined with the uneven withdrawal by the screw feeder is inducing a funnel flow discharge pattern. Funnel flow (which is a first-in, last-out discharge pattern) can be made to work with a large discharge outlet. 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.
Further, the shearing action of the screw feeder below the pyramid hoppers is driving the filter cake against the discharge end of each hopper wall, compacting material at the discharge outlet. This compaction is problematic because it builds strength in the material. The more strength a bulk solid has, the wider the opening it can bridge over. As a result, the shearing and compacting action of the screw feeder is contributing to poor discharge from the existing hoppers. In addition, the compaction by the screw feeder is resulting in high loads being transferred to the screw feeder, which may result in high wear and motor tripping.
The solution to fixing this problem bin has two parts. The first half of the solution is to replace the existing six pyramid hoppers with a single plane flow hopper with steep sloping walls and a wide discharge opening. Doing so fixes the geometry of the hopper such that if the Feeder were removed, the entire bin would self-empty with gravity in a mass flow or first-in, first-out discharge pattern. The second half of the solution is to pair the new long hopper with a Kamengo Feeder. The reason for doing so is that the Kamengo Feeder withdraws material evenly from its entire opening, which by definition is necessary to actually achieve a mass flow discharge pattern in the hopper. If the Feeder instead withdrew material unevenly, a funnel flow discharge pattern would ensue (regardless of the bin geometry), and rat-holing and bridging would occur.
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.
This is an example of a bagging bin designed specifically to handle difficult flowing cohesive materials such as zinc concentrate and cobalt hydroxide filter cake.
Standard bagging bins use small or narrow hoppers discharged using a range of feeders include screw feeders, vibratory feeders, and rotary feeders.
In summary, standard bagging systems suffer from chronic plugging when handling difficult flowing cohesive materials for two reasons: 1) incorrect bin geometry, including poor choice of bin shape, too small openings, and improper choice of sloping wall angles; and 2) the feeder behavior promotes a funnel flow discharge pattern. Funnel flow (which is a first-in, last-out discharge pattern) can be made to work with large bins with large discharge outlets. 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.
The solution to a reliable bagging bin that is capable of handling difficult flowing cohesive materials has two parts. The first half of the solution is to choose a bin with correct geometry. Kamengo typically recommends a plane flow hopper shape with a wide and long discharge opening. A plane flow hopper only converges in one plane at a time, and is vertical in the opposite plane. The plane flow hopper is the most conservative hopper shape. The purpose of using a conservative bin shape with a long and wide discharge outlet is to employ a geometry where if the Feeder were removed, the entire bin would self-empty with gravity in a mass flow or first-in, first-out discharge pattern.
The second half of the solution is to pair the plane flow hopper with a fully effective feeder such as a Kamengo Feeder. A fully effective feeder is one that withdraws material evenly from its entire opening, which by definition is necessary to actually achieve a mass flow discharge pattern in the hopper, which is necessary when handling a difficult flowing, cohesive bulk solid.
To learn more about the physics of storage bin and feeder design as well as the root causes of bin plugging, please visit KamengoU.
This is an example of a 53,000 ft3 (1,500 m3) ROM Coal Ore Truck Load-Out Bin.
A standard ROM truck load out bin consists of a large conical hopper and silo that is discharged using a very large clamshell gate. Unfortunately, these systems suffer from chronic bridging and flooding from collapsing rat-holes.
In summary, a conical hopper is satisfactory bin shape as long as the discharge opening is large and that the hopper is discharged evenly from its entire opening. The challenge with a clamshell gate is that it operates partially open in order to control the flow of discharge. When the opening is not fully live, bridging and the formation of rat-holes should be expected.
The solution to a ROM truck load out bin has two parts.
The first part is to choose a bin shape that promotes reliable discharge. Kamengo’s preferred method for a tall, large storage bin handling a moderately difficult flowing material is to use “expanded flow”. Expanded flow uses a combination of mass flow and funnel flow, and is typically the most cost-effective bin shape for a tall and very large storage bin.
With expanded flow the bottom of the bin discharges in mass flow and the top of the bin discharges in funnel flow. The benefit of expanded flow is that one is able to benefit from the advantages of both flow patterns while minimizing their drawbacks. The expanded flow hopper shown combines a chisel hopper with a funnel flow cone and circular silo. A benefit of this arrangement is that bin wall loads are handled efficiently, reducing the overall cost of the bin.
The second half of the solution is to pair the expanded flow bin with a fully-effective feeder – that is a feeder that withdraws material evenly from its entire infeed opening. This is necessary to achieve mass flow in the lower portion of the bin, and to avoid the formation of rat-holes, which are particularly dangerous for large truck load-out bins. By definition, to achieve mass flow, where the stored material comes down as a single body, the feeder must withdraw material evenly from its entire opening. If the Feeder withdraws material selectively from the bin discharge outlet, sections of material in the bin will be stagnant and rat-holes will form.
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.
