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Cobalt-Hydroxide Filter Cake Dryer Feeder

Cobalt-Hydroxide Filter Cake Dryer Feeder 

 

This case study is an example of two Kamengo metering bins receiving cobalt hydroxide filter cake from a filter press and metering the wet cake to a dryer. This installation went into service in 2014. In 2019, the mine purchased an additional three Feeders.

The Challenge

Prior to the retrofit, the mine was discharging cobalt hydroxide filter cake from a filter press into a 60-degree plane flow hopper that necked down to an 18” screw feeder. This metering bin suffered from chronic plugging that was particularly disruptive to the mine operation. The filter press was expected to discharge in 3 minutes, however, to keep the level of material in the storage bin to a minimum, mine operators manual emptied the filter press plate by plate. This exhaustive process took three hours to empty to the filter press.

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Why the Current Storage and Feed Arrangement is Suffering from Chronic Bridging and Inconsistent Discharge

The existing screw feeder metering bin was suffering from chronic plugging for three reasons:

 

  1. Poor bin geometry. The sloping walls and discharge opening of the existing hopper above the screw feeder were insufficient to produce a reliable mass flow or first-in, first-out discharge pattern. First, the sloping walls were too shallow. As a result, material could not slide along the hopper walls, but would instead try to slip within itself in a funnel flow, or first-in, last-out discharge pattern. Second, the discharge opening was to narrow. The narrower the opening, the less strength a material requires to form a stable arch that gravity cannot reliably break.
  2. The conveying action of the screw feeder, which is shearing material from the storage bin, was compacting the stored filter cake against the front of the bin wall. As the filter cake compacts, it gains significant shear strength. With enough compaction, the filter cake gains sufficient shear strength to bridge over the Feeder.
  3. The screw feeder had a propensity to withdraw material from the rear of the bin. This selective withdrawal of material, in addition to shallow sloping walls, induced a funnel flow, or first-in, last-out discharge pattern in the bin. In principle, there is nothing wrong with funnel flow as long as the effective opening of the bin exceeds the bulk solid’s piping dimension (or distance over which the bulk solid can form a stable rat-hole). Unfortunately, the piping dimension for cobalt hydroxide filter cake is quite large – in fact, it is larger than the metering bin. To handle cobalt hydroxide filter cake reliably without hang-ups it must be discharged in mass flow, or a first-in, first-out discharge pattern. To do so, the Feeder must withdraw material evenly from the hopper’s full discharge outlet.

Kamengo’s Solution

The solution to fix this cobalt hydroxide filter cake metering bin was to replace the storage hopper with a hopper with steeper hopper walls and a wide and long opening. The steeper hopper walls were required to promote a mass flow discharge, where material slides along the hopper walls. The wide and long discharge opening was required to ensure the material cannot bridge over the Feeder. By correcting the geometry of the storage bin, if one were to remove the feeder, the hopper would now self-empty with gravity in a mass flow or first-in, first-out discharge pattern. To ensure the entire hopper and feeder arrangement is reliable, Kamengo paired the new hopper with a Kamengo Feeder. The value and necessity of the Kamengo Feeder is that it withdraws material evenly from the entire discharge opening of the storage hopper. By definition, to achieve mass flow, the bulk solid must descend the storage bin as a single body with all the stored material in motion, and the only way to achieve this is for the feeder to 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.

Learn More

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. 

Zinc Concentrate Bagging Bin

Zinc Concentrate Bagging Bin 

 

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.

Why Conventional Bagging Hoppers Suffer from Chronic Plugging and Inconsistent Discharge

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.

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Kamengo’s Solution

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.

Learn More

To learn more about the physics of storage bin and feeder design as well as the root causes of bin plugging, please visit KamengoU.

Dry-Stacked Tailings Filter Cake Truck Load-Out Bin

Dry-Stacked Tailings Filter Cake Truck Load-Out Bin

This is an example of a tall truck load-out bin designed specifically to handle difficult flowing cohesive, high-moisture content dry-stacked tailings filter cake.

Why Conventional Clam Shell Bins Suffer from Chronic Bridging and Inconsistent Discharge

Standard truck load-out bins use a clamshell or slide gates to meter discharge. Unfortunately, many of these systems suffer from chronic bridging and rat-holing.

 

In summary, these bins suffer from chronic plugging because when the clam shell or slide gate is only partially open it induces a funnel flow discharge pattern despite the fact that the geometry of the storage bin may be correct, where if the slide gate or clam shell were removed, the bin would self-empty in a mass flow or first-in, first-out discharge pattern. Funnel flow (which is a first-in, last-out discharge pattern) can be made to work with a very large discharge outlet. However, when the discharge outlet is constricted, gravity is insufficient to overcome the strength of the bulk solid at the discharge outlet, and hence chronic bridging and rat-holing is expected.

 

Ideally, a cohesive bulk solid such as a high-moisture content filter cake should be discharged in mass flow, or a first-in, first-out discharge pattern. The definition of mass flow is that during discharge, the entire mass of stored material comes down as a single body (single mass). To achieve this, material must discharge evenly from the entire discharge outlet of the storage bin. The tell-tale sign that you have mass flow is that material is sliding down the bin walls. In contrast, with funnel flow, material is stagnant along the hopper walls. When the clam shell or slide gate is only partially open, then material is not permitted to withdraw evenly from the entire discharge outlet of the storage bin because the slide gate has limited the “live” opening, causing some sections of material in the storage bin to be stagnant during discharge. The result is a funnel flow discharge pattern.

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Kamengo’s Solution

The solution to a reliable truck load-out storage bin for handling cohesive materials such as high-moisture content filter cake is simple. First, ensure the geometry of the storage bin is correct, 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. Typically, Kamengo would recommend a plane flow hopper with a long and wide discharge opening, as this is among the most conservative bin shapes. Second, pair the storage bin with a fully-effective feeder – that is a feeder that withdraws material evenly from its entire infeed opening. 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.

 

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.

Learn More

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.