Jamil Bundalli In Solutions To Common Problems

Zinc Oxide Filter Cake Metering Bin

This is an example of a zinc oxide filter cake metering bin that is suffering from chronic bridging.

The Existing Hopper and Why it is Suffering from Chronic Plugging and Inconsistent Discharge

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.

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Kamengo’s Solution

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.

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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.

Jamil Bundalli In Solutions To Common Problems

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.

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

Jamil Bundalli In Solutions To Common Problems

Retrofit of Wood Chip Chute Suffering From Chronic Plugging

This is an example of when a chute becomes a hopper, and when a conveyor becomes a feeder and plugging ensues.

Why the Chute is Suffering from Chronic Plugging and Bridging

In contrast to a bin or hopper, a chute is where material is continuously flowing and there is no head of material at the outlet. When a chute is flooded such that a head of material builds at the outlet, the chute becomes a hopper and the conveyor on which it discharges onto becomes a feeder. This is problematic because suddenly the chute is subject to minimum geometry constraints needed to avoid bridging and the conveyor needs assume the job of shearing material from the chute.

This is an example where the chute is receiving a flood of material from processes upstream causing a head of material to build in the chute. And because the geometry of the chute is insufficient to act as a hopper, the chute is subject to chronic plugging and is a major headache for the plant.

In summary, because it is carrying a head of material, the chute is not actually a chute, but a hopper and as such, its geometry, including outlet and sloping walls must be sufficiently large and steep to ensure reliable gravity discharge. However, with its four sloping walls and small discharge opening, the chute’s (turned hopper’s) geometry is insufficient, and hence it is subject to chronic plugging.

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Kamengo’s Solution

The easy solutions to fixing these chutes turned hoppers is to either decrease the discharge of material upstream or increase the speed of the conveyor to ensure no head of material builds up in the chute. If the easy solutions are not viable, as in the case of this case study, the plant needs to install a hopper and feeder designed to handle the bulk solid as an intermediary between the chutes and the conveyor.

Choosing a suitable storage and feed system has two components. The first is to choose a bin shape with a wide and long opening, where if the feeder were removed, the hopper would self-empty with only the aid of gravity. Kamengo typically suggests a plane flow hopper (which is a bin shape where the hopper walls only converge in one plane at a time). The plane flow hopper is the most conservative hopper shape.

The second half of the solution is to pair the plane flow hopper with a fully effective feeder – that is a feeder that withdraws material evenly from its entire opening – which is necessary for reliable discharge when metering a difficult flowing material from a small hopper. The Kamengo Feeder is a very good choice because not only is it a fully effective feeder, but it can also be made as wide as needed and as long as desired, which opens the range of solutions to fixing a problem storage and feeder system.

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

Jamil Bundalli In Solutions To Common Problems

Soda Ash Tall Metering Bin

This is an example of a tall 2,500 cu-ft (70 cu-m) storage bin designed specifically to handle soda ash.

Why Soda Ash is a Difficult Flowing Material and Why Conventional Conical Storage Bins are Inappropriate for the Material.

Soda ash’s granular nature gives it the look and feel of an easy flowing material. However, wall friction testing of the material by Kamengo reveals that a poor choice in bin shape, liner and sloping wall angles will result in: 1) inconsistent discharge; 2) flooding of conveyors; 3) hang-ups; and/or 4) chronic caking and lumping. This is because if any of the above are incorrect, a funnel flow discharge pattern in the storage bin would be induced.

Funnel flow is a first-in, last-out flow pattern where material sluffs from the top down through a core in the storage bin. The challenge with funnel flow is that the majority of material in the storage bin remains stagnant during discharge. The problem is that stagnant material is permitted the opportunity to gain strength as it compacts under its own weight, which promotes caking. Further, as the material gains strength, it is able to bridge over wider openings, eventually leading to stable rat-holes and bridging. The alternative to funnel flow is mass flow. In contrast to funnel flow, mass flow is a first-in, first-out discharge pattern where all of the material in the storage bin is in motion during discharge.

For a Soda Ash silo, which typically has a relatively large storage volume for the given discharge rate, mass flow is preferred for several reasons. To reduce caking and prevent the stored soda ash from developing the strength needed to form a stable rat-hole, it is preferable for 100% of the stored material to move downwards over the course of a 24 hour period, and not just a small section of stored soda ash that lies within a core over the bin opening. Second, because it can take up to a month to empty a soda ash bin and it may never actually be permitted to fully empty. If the bin is emptying in a funnel flow discharge pattern, sections of soda ash will never leave the bin and simply be permitted to harden and become un-flowable. Third, soda ash is a relatively fine material, and if a stable rat-hole forms and collapses, the material would fluidize and mix with air, causing it to rush from the bin, which would introduce an engulfing hazard around the bin.

Standard soda ash bins are conical shape and discharge from a small opening. Typically, the angle of the cone is too shallow to produce a mass flow discharge pattern, and hence these bins discharge in funnel flow.

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Kamengo’s Solution

The solution to a reliable soda ash bin that provides a very controlled discharge has two parts.

The first half of the solution is to discard the standard cone and replace it with plane flow hoppers with lined and sufficiently steep hopper walls needed to produce a mass flow discharge pattern. 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, which withdraws material evenly from its entire opening. A fully effective feeder is, by definition, necessary to actually achieve a mass flow discharge pattern in the hopper, which is necessary when handling a difficult flowing fibrous bulk solid.

Kamengo’s solution employs a Kamengo Feeder with a wide and long 3-foot by 10-foot opening. Of critical importance, the Kamengo Feeder withdraws material evenly across both its entire length and width. The result is that the stored material is withdrawn evenly from the full discharge outlet of the soda ash bin. An even withdrawal of material is absolutely required to achieve a mass flow or first-in, first-out discharge. The Feeder delivers batches of soda ash to a screw conveyor below, which in turn, provides a final metering into the process.

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

Jamil Bundalli In Solutions To Common Problems

ROM Coal Ore Truck Load-Out Bin

This is an example of a 53,000 ft3 (1,500 m3) ROM Coal Ore Truck Load-Out Bin.

Why Conventional Truck Load-Out Bins Suffer from Chronic Bridging and Uncontrolled Discharge

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.

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Kamengo’s Solution

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.

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Jamil Bundalli In Solutions To Common Problems

ROM Ore Metering Bin

This is an example of a rock ore bin handling a mix of large particles and fines that is suffering from chronic bridging. It is a good example of an instance where the behavior of the Feeder is inducing rat-holing and bridging.

The Existing Storage and Feed Arrangement and Why it is Suffering from Chronic Plugging and Inconsistent Discharge

The existing bin consists of a narrow 6.5-foot diameter ore pass leading to a short hopper and an apron feeder.

In summary, the bin is suffering from chronic plugging because the apron feeder is withdrawing material preferentially from rear of the hopper, which is inducing a funnel flow discharge pattern that is extending up into the ore pass. 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.

The alternative to a funnel flow discharge pattern is mass flow. Mass flow is a first-in, first-out discharge pattern where 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 hopper walls. In contrast, with funnel flow, material is stagnant along the hopper walls. When the feeder withdraws material preferentially from one side of the hopper, then material is not permitted to withdraw evenly from the entire discharge outlet of the storage bin. The result is stagnant material along the bin walls and a funnel flow discharge pattern.

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Kamengo’s Solution

The solution to fixing this problem bin has two parts.

The first half of the solution is to discard the existing hopper and replace it with a plane flow hopper with sufficiently steep hopper walls needed to produce a mass flow discharge pattern. 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.

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Jamil Bundalli In Solutions To Common Problems

Ship Unloader Metering Bin

This is an example of a ship unloading hopper designed specifically to handle difficult flowing cohesive materials such as gypsum and bauxite.

Why Conventional Ship Unloading Hoppers Suffer from Chronic Bridging and Inconsistent Discharge

Standard ship unloading hoppers use a pyramid hopper that converge to a small opening that use a slide gate or clamshell to control discharge.

In summary, a pyramid hopper with a small opening is a poor choice of bin shape for handling difficult flowing cohesive materials such as gypsum or bauxite. First, the bin shape 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 ship unloading hopper that is capable of handling difficult flowing cohesive materials has two parts. The first half of the solution is to use 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 Kamengo Feeder. The value of the Kamengo Feeder is that it 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.

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

Jamil Bundalli In Solutions To Common Problems

ROM Ore Railcar Unloading Bin

This is an example of a series of rail car unloading hoppers designed to handle large particle as well as difficult flowing cohesive materials.

Conventional Unloading Bins and Why they Suffer from Chronic Plugging and Inconsistent Discharge

A standard railcar unloader uses a series of pyramid hoppers that converge to a small opening that use any of slide gates, basket gates, vibrators or clamshells to control discharge.

In summary, a pyramid hopper with a small opening is a terrible choice of bin shape for handling difficult flowing cohesive materials. The bin shape 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.

Further, Feeders that operate partially open to control the flow of discharge and do not withdraw material from the full discharge outlet of the hopper all the time are dangerous, because this behavior further promotes a funnel flow discharge pattern and the formation of stable arches and ratholes. A reliable Feeder is “fully effective”, where it withdraws material evenly from the full discharge outlet of the storage above it.

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Kamengo’s Solution

The solution to a reliable railcar unloading hopper that is capable of handling both large particles as well as difficult flowing cohesive materials has two parts. The first half of the solution is to use 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 hoppers with a Kamengo Feeder. The value of the Kamengo Feeder is that it 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 bulk solid. A further advantage of the Kamengo Feeder is its low profile, which helps to save height and related civil costs.

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Jamil Bundalli In Solutions To Common Problems

Wet Phosphate Rock Receiving Hopper

This is an example of a series of wet phosphate rock receiving bins that are suffering from chronic bridging and rat-holing. It is a good example of poor bin geometry combined with uneven discharge that is resulting in inconsistent discharge.

The Existing Hopper and Why it is Suffering from Chronic Plugging and Inconsistent Discharge

The existing bins consists of a pyramid hopper stacked on top of a plane flow hopper that is stacked on top of a second small pyramid hopper. Wet phosphate rock is withdrawn from the hopper via a belt feeder, which is preferentially withdrawing material from the rear of the bin outlet.

The combination of the small openings and pyramid shape at the discharge combined with the behaviour of the belt feeder is resulting in a funnel flow or first-in, last-out discharge. 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 alternative to funnel flow is mass flow, which is 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.

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Kamengo’s Solution

The solution to fixing this problem storage and feed system has two parts. The first half of the solution is to replace the lower pyramid hopper with a plane flow hopper with a wide and long opening. The wide and long discharge opening is required to overcome the bridging dimension of wet phosphate rock. Overcoming the bridging dimension is necessary to ensure that the material cannot bridge over the feeder. Changing the bin geometry will promote a mass flow discharge. Mass flow is a first-in, first-out discharge pattern.

The second half of the solution is to pair the new plane flow hoppers with a fully-effective feeder – that is a feeder that withdraws material evenly from its entire infeed opening. Again, 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.

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Jamil Bundalli In Solutions To Common Problems

Metallurgical Coal Railcar Load-Out

This is an example of a met coal railcar loadout bin that is suffering from chronic bridging and rat-holing. It is a good example of poor bin geometry combined with uneven discharge that is resulting in inconsistent discharge.

The Existing Storage and Feed Arrangement and Why it is Suffering from Chronic Plugging and Inconsistent Discharge

The existing bin consists of of twin funnel flow (first-in, last-out) pyramid hoppers leading to small square discharge openings. One discharge opening is metered with a screw feeder and the other is metered using a clamshell gate.

The combination of the small openings and multiple shallow walls as well as the behavior of the feeders results in a hopper that cannot reliably discharged with only gravity. Because the discharge openings are small one would expect a tendency for stable rat-holes to form over the openings, and for the bins to suffer from erratic discharge. Finally, a consequence of having a first-in, last-out discharge is that stagnant material is left along the silo walls. Stagnant material will gain strength over time, further creating the conditions for plugging and erratic discharge.

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Kamengo’s Solution

The solution to fixing this problem storage and feed system has two parts. The first half of the solution is to reconfigure the hopper to include steep sloped walls, and move away from pyramid style hoppers to more conservative plane flow hoppers with a wide and long discharge opening. The wide and long discharge opening is required to overcome the bridging dimension of met coal. Overcoming the bridging dimension is necessary to ensure that the material cannot bridge over the feeder.

Changing the bin geometry will promote a mass flow discharge. Mass flow is 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). The tell-tale sign that you have mass flow is that material is sliding down the bin walls. To achieve this, material must discharge evenly from the entire discharge outlet of the storage bin. This requirement leads to the second half of the solution.

The second half of the solution is to pair each plane flow hopper with a fully-effective feeder – that is a feeder that withdraws material evenly from its entire infeed opening. Again, 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.

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