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Gypsum and Shale Rock Front-Loaded Bin

Gypsum and Shale Rock Front-Loaded Bin

 

This case study is an example of a retrofit of a front-loaded metering bin handling rock gypsum and limestone shale rock. This installation when into service in 2018.

The Challenge

The cement plant uses front end-loaders to unload barges. The plant has a front-loaded metering bin at the wharf that discharges onto a conveyor belt that carries material to either the plant’s covered storage or to silos feeding the plant’s kiln. Prior to the retrofit, the front-loaded metering bin consisted of a pyramid hopper that was discharged via a small 1-foot by 3-foot opening straight onto the conveyor belt below. The discharge opening had a hydraulic flap that was tasked with metering material onto the conveyor belt. Unfortunately, the front-loaded bin never worked. If the plant put any head of material into the bin, it would plug. To compensate, the front-end loaders would spoon feeder material into the hopper, reducing the pyramid hopper to a chute.

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Why the Pyramid Hopper and Belt Feeder Were Suffering from Chronic Plugging and Inconsistent Discharge

The existing pyramid hopper was suffering from chronic plugging for three reasons:

 

  1. Poor bin geometry. The sloping walls and discharge opening of the existing hopper above the belt conveyor 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 belt conveyor below the pyramid hopper, which is shearing material from the storage bin, was compacting the gypsum and limestone against the front of the bin wall. As the stored materials compacted, they would gains significant shear strength. With enough compaction, the stored material would gain sufficient shear strength to bridge over the hopper discharge opening.
  3. The belt conveyor had a propensity to withdraw material from the rear of the pyramid hopper. This selective withdrawal of material, in addition to the 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 gypsum and limestone is quite large – in fact, it is larger than the metering bin. To handle gypsum and limestone 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 front-loaded metering bin was to replace the storage hopper with a hopper with plane flow shape, steeper hopper walls and a wide and long opening. Unlike a pyramid hopper, which converges into two planes, a plane flow hopper only converges in one plane at a time. A plane flow bin shape is the most conversative bin shape and is often necessary when designing for a difficult flowing material. Further, the steeper hopper walls were required to promote a mass flow discharge, where material slides along the hopper walls. The angle for the sloping walls were determined via material flow testing. Finally, the wide and long discharge opening is required to ensure the stored materials 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.

 

The second half of the solution is to ensure the entire hopper and feeder arrangement will discharge in a mass flow or first-in, first-out discharge. To do so, 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 Cement Industry. 

FGD Gypsum Front-Loaded Metering Bin

Wet FGD Gypsum Front-Loaded Metering Bin 

 

This case study is an example of a front-loaded metering bin, operating outside in an artic environment, delivering an even, metered discharge of wet FGD gypsum into a continuous process. This installation when into service in 2012.

The Challenge

Prior to selecting a Kamengo Feeder, the client had previous experience metering FGD gypsum with a screw feeder. The previous bin suffered from heavy material compaction at the screw outlet resulting in chronic plugging. The screw would turn, but no material would come out. For a new plant that is mixing gypsum with tailings, the client went looking for a new solution and chose a Kamengo Feeder.

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Why Conventional Storage and Feed Solutions Often Suffer from Chronic Plugging and Inconsistent Discharge

The existing screw feeder hopper suffered from chronic plugging for two reasons:

 

  1. The conveying action of the screw feeder, which is shearing material from the storage bin, was compacting the gypsum against the front of the bin wall. As the stored material compacts, it gains significant shear strength. With enough compaction, the stored material would gain sufficient shear strength to bridge over the hopper discharge opening.
  2. The screw feeder had a propensity to withdraw material from the rear of the hopper. This selective withdrawal of material, induces 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 wet FGD gypsum is quite large – in fact, it is larger than the metering bin. To handle wet FGD gypsum 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 a reliable front-loaded metering bin handling wet FGD gypsum has two parts:

 

The first half of the solution is to choose a correct bin geometry for handling wet FGD gypsum. In this case, Kamengo chose a plane flow hopper shape with steep sloping walls lined with a low friction liner, and 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 wide and long 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. To determine the minimum geometry, Kamengo conducted material flow characterization testing, which includes a series of bench scale tests, which are used to determine the minimum wall angle and the minimum bin discharge outlet width and length.

 

The second half of the solution is to pair the plane flow hopper with a fully-effective Feeder – in this case 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. 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.

 

Again, discharging in mass flow is often necessary when handling a difficult flowing bulk solid. What makes the Kamengo Feeder unique is that it can be made as wide as needed and as long as desired. The minimum bin discharge outlet width and length to reliably handle FGD Gypsum is approximately 3.5-feet by 12-feet. To achieve mass flow, the Feeder inlet must match this outlet. This is very difficult to do with conventional technologies, but very easy to achieve with a Kamengo Feeder.

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 Gypsum Industry. 

Recycled Gypsum Front-Loaded Metering Bin

Recycled Gypsum Front-Loaded Metering Bin

 

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.

The Existing System Prior to the Retrofit

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.

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Why the Existing System Suffered From Chronic Plugging

The augers struggled handling the recycled gypsum for two reasons:

  1. The conveying action of the screws, which are shearing material from the storage bin, was compacting the recycled gypsum against the front of the bin wall. As the gypsum is compacted, the material gains significant shear strength. Eventually, the compacted gypsum would have sufficient shear strength to bridge over the Feeder.
  2. The screws have a propensity to withdraw material from the rear of the bin. This selective withdrawal of material is inducing 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 recycled gypsum is quite large – in fact, it is larger than the front-loaded bin. To handle recycled gypsum 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 full width and length of the bin discharge outlet.

Kamengo’s Solution

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.

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 Gypsum Industry.