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Dewatered Nickel Laterite Tailings Truck Load-Out Bins

Dewatered Nickel Laterite Tailings Truck Load-Out Bins 

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 because of our expertise, special equipment and long history of designing storage and feed arrangements handling very sticky and cohesive bulk solids.

 

The formula for designing a reliable truck load out system handling a cohesive material is to pair a correctly designed storage bin with a feeder that withdraws material evenly from its entire opening. The storage bin geometry, including bin shape and angle of sloping walls, must be chosen such that the stored material will discharge in a mass flow or a first-in, first-out discharge pattern. Further, the storage bin should discharge via a sufficiently wide and long opening, such that the material cannot bridge over the feeder. Finally, the feeder must withdraw material evenly from the full length and width of the bin discharge opening otherwise the whole bin/feeder arrangement will be susceptible to chronic rat holing.

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Kamengo’s Approach and Solution

Prior to starting equipment design, Kamengo conducted material flow testing using a sample of the dewatered nickel laterite. The testing includes a series of bench-scale tests that are used to derive the minimum geometry (angle of sloping walls, sloping wall material, discharge opening) required to reliably discharge a bulk solid. The standard that Kamengo uses, is that if the feeder were removed from the storage bin, it should completely self-empty with only the aid of gravity. If it cannot self-empty, then there is something wrong with the geometry of the storage bin.

 

To confirm both the geometry and suitability of the Kamengo Feeder, Kamengo conducted at-scale pilot testing. The testing included increasing the moisture content of the bulk solid until it was saturated to test the Feeder’s ability to discharge out-of-spec material.

 

In total Kamengo delivered two truck load out storage bins. Each storage bin is paired with a Kamengo Feeder. The strength of the Kamengo Feeder is that it withdraws material evenly from the entire width and length of the bin discharge opening. This is necessary when handling a difficult flowing material. A second advantage of the Kamengo Feeder is that it discharges over the length of the truck bed, allowing the truck to be filled without having to index it forward.

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. 

Platinum Group Metals (PGM) Concentrate Filter Cake Truck Load-Out Bin

Platinum Group Metals (PGM) Concentrate Filter Cake Truck Load-Out Bin  (A)

 

This case study is an example of a Kamengo truck load out bin discharging cohesive PGM filter cake into trucks. What makes this application challenging is that the filter cake will be stored in the storage bin for up to 72 hours and the material gains significant strength at rest. To overcome the shear strength of the bulk solid, the Feeder is discharging from a 10-foot (3m) wide bin opening. This installation went into service in 2020.

The Challenge and Kamengo’s Solution

Kamengo was chosen to deliver two truck load-out storage bins with feeders handling platinum group metals (PGM) concentrate filter cake. Each installation serves a different mine site. Each truck load-out arrangement includes a mass flow storage bin and Kamengo Feeder fitted with an integrated dust control system. Each storage bin is handling a PGM concentrate filter cake, and receives material directly from the filter press. Filter cake is expected to be stored in the storage bin up to 72 hours. To ensure material will not bridge over the Feeder, Kamengo delivered a 10-foot (3m) wide Kamengo Feeder. An advantage of choosing a Kamengo solution, is that the Kamengo Feeder handles loads very efficiently. As a result, a wide Kamengo Feeder is close to a tenth of the cost of an equally wide apron Feeder.

 

Both storage bins are located in a building. To minimize dusting, prior to discharging material into a truck, a Kamengo loading deck with a shroud lowers from the Kamengo Feeder over the truck bed. A dust control system holds the area within the shroud at a slight negative pressure. Air in the truck bed that is displaced by the falling filter cake is circulated first through self-cleaning filters, then through HEPA filters before being expelled into the building. Once the Feeder has completed a set number of strokes, equating the target discharge volume, the loading deck automatically raises.

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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. 

Lithium Carbonate Precipitate Dryer Metering Bin

Lithium Carbonate Precipitate Dryer Metering Bin

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. Kamengo has a long history of designing storage and feed equipment handling cohesive materials.

 

The formula for designing a reliable metering bin handling a cohesive material is to pair a correctly designed storage bin with a feeder that withdraws material evenly from its entire opening. The storage bin geometry, including bin shape and angle of sloping walls, must be chosen such that the stored material will discharge in a mass flow or a first-in, first-out discharge pattern. Further, the storage bin should discharge via a sufficiently wide and long opening, such that the material cannot bridge over the feeder. Finally, the feeder must withdraw material evenly from the full length and width of the bin discharge opening otherwise the whole bin/feeder arrangement will be susceptible to chronic rat holing.

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Kamengo’s Approach and Solution

Prior to starting equipment design, Kamengo conducted material flow testing using a sample of the lithium carbonate precipitate. The testing includes a series of bench-scale tests that are used to derive the minimum geometry required to reliably discharge the bulk solid as well as make decisions on the internal geometry of the Kamengo Feeder. The standard that Kamengo uses, is that if the feeder were removed from the storage bin, it should completely self-empty with only the aid of gravity. If it cannot self-empty, then there is something wrong with the geometry of the storage bin.

 

In total Kamengo’s scope of supply included the hopper, Kamengo Feeder and discharge chute. The strength of the Kamengo Feeder is that it withdraws material evenly from the entire width and length of the bin discharge opening. This is necessary when handling a difficult flowing material. A second advantage of the Kamengo Feeder is that it delivers a very consistent feed which is necessary when feeding a bulk solid into a dryer.

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. 

Recycled Shredded Aluminum Tall Metering Bin

Recycled Shredded Aluminum Tall Metering Bin

 

This case study is an example of a Kamengo tall bin metering recycled shredded aluminum into a kiln. What makes this installation challenging is that the material is quite light and has a propensity to intertwine, and thus gain significant strength when compacted. This installation went into service in 2018.

The Challenge

This installation was for a second recycling line feeding a kiln that the plant was installing. On the first recycling line, the metering bin to the kiln, which consisted of a carbon steel plane flow hopper fed by a belt feeder, suffered from inconsistent discharge and chronic hang-ups. To make the line work, the plant needs to keep a low-level of material in the storage bin.

 

When it came to designing the second line, the plant not only desired a metering bin that is reliable, but also wanted to increase the available storage before the kiln. The plant chose a Kamengo Feeder and tall bin.

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Why the Existing Storage and Feed Solution is Suffering from Chronic Plugging and Inconsistent Discharge

The prior metering bin, including belt feeder, on the first line was suffering from chronic plugging for two reasons:

 

  1. The conveying action of the belt feeder, which is shearing material from the storage bin, was compacting the stored shredded aluminum against the front of the bin wall. As shredded aluminum compacts, it gains significant shear strength. With enough compaction, the shredded aluminum gains sufficient shear strength to bridge over the Feeder.
  2. The belt feeder had a tendency to withdraw material from the rear of the bin. This selective withdrawal of material 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 shredded aluminum is quite large – in fact, it is larger than the metering bin. To handle shredded aluminum 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. Further, the discharge outlet for the hopper must be wide and long.

Kamengo’s Solution

The solution to designing a reliable storage bin capable of metering shredded aluminum as two parts:

 

The first half of the solution is to choose a correct bin geometry for handling the shredded aluminum. In this case, Kamengo chose a plane flow hopper shape with steep sloping walls 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. 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 shredded aluminum is approximately 6-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 visit KamengoU.

Wood Waste and Construction Debris Boiler Feed Metering Bins

Wood Waste and Construction Debris Boiler Feed Metering Bins

This case study is an example of a series of Kamengo metering bin feeding construction and demolition debris and other wood waste into one of two power boilers. Each power boiler has six Kamengo metering bins. Each metering bin consists of a Kamengo Feeder, storage hopper with slide gate, long chute and expansion joint. These two installations were put into service in 2018.

 

The Challenge

Conventional metering bins feeding fuel into boilers consists of screw feeders discharging from negative taper storage hoppers. Knowing that these metering bins are known to suffer from chronic plugging and inconsistent discharge, the client selected Kamengo metering bins for its two new power boilers.

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Why Conventional Screw-Type Storage and Feed Solutions Suffer from Chronic Plugging and Inconsistent Discharge

Typical screw augers suffer from many of the challenges typical of conventional feeders. First, the screw augers have a propensity to compact material against the front of the bin wall. As wood fuel is sheared from the storage bin, due to interlocking and friction, the fuel being carried out, carries fuel above it. And this fuel travelling above the outlet is compacted against the bin wall. The problem is that wood waste gains significant strength when it is compacted. Once the fuel above the outlet gains sufficient strength it will bridge over the outlet resulting in inconsistent discharge and plugging. Second, the screw augers withdraw material from the back of its opening, leaving a stagnant pocket of material at the front. This limited withdrawal of material has several consequences. First, it means that not only is gravity acting on a smaller area, but it also means that the stagnant material is allowed to compress and compact over time under its own weight. The more wood waste compacts, the stronger it gets. Eventually the material will be strong enough to form a stable bridge. Second, uneven withdrawal promotes a funnel flow discharge pattern, which promotes rat-holing.

Kamengo’s Solution

In contrast to the live bottom bin, the Kamengo Feeder withdraws material evenly from its full opening. Further, the opening of a Kamengo Feeder can be made as wide as needed and as long as desired. Also, because the Kamengo Feeder withdraws material evenly from its entire opening, all of the material above the feeder is in motion during discharge, resulting in a mass flow, or first-in, first-out discharge. Handling a low bulk density, easily compactible bulk solid like construction and demolition debris and other wood waste in mass flow is important to ensuring a reliable system.

 

Finally, the Kamengo Feeder delivers a very steady, predicable discharge of fuel into the boiler. This is necessary for maintaining a predictable and efficient pyrolytic reaction in the boiler.

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 Biomass Industry. 

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. 

Hog Fuel (Wood Waste) Boiler Feed Metering Bins

Hog Fuel (Wood Waste) Boiler Feed Metering Bin

 

This case study highlights the retrofit of four live bottom metering bins that were suffering from chronic plugging at a pulp mill in Port Angeles, Washington State. Kamengo replaced the four metering bins with new bins, Kamengo Feeders, chute and expansion joint. Prior to the retrofit, the plant was experiencing lost steam production and swings in the header pressure, which made it particularly problematic to keep emissions within the plant’s permit. Post retrofit, the plant is producing more steam, and the boiler is able to meet the changing steam demands from the paper plant while maintaining an even header pressure. The retrofit was completed in 2015.

The Challenge

Prior to the retrofit, the pulp mill had four live bottom metering bins, each discharging into one of four spouts into the boiler.

 

Each metering bin consisted of two augers below a negative taper storage bin. Although the boiler was only two years old, the mill was keen to improve the reliability fuel feed into the boiler. The screw feeders had a propensity to compact material at the front of the bin walls as well as rat hole in the storage bin. The mill tried a number of solutions, including installing UHMW along the front of the bin walls. Nothing worked.

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Why the Conventional Screw Feeders Were Suffering from Chronic Plugging and Inconsistent Discharge

The screw augers were suffering from chronic plugging for two reasons:

 

First, the screw augers have a tendency to compact material against the front of the bin wall. Wood waste that is being carried or sheared from the storage bin, through friction or interlocking, carries fuel above it. And this fuel travelling above the screw feeder outlet is compacted against the bin wall. The problem is that wood waste gains significant strength when it is compacted. Once the fuel above the outlet gains sufficient strength it will bridge over the outlet resulting in inconsistent discharge and plugging.

 

Second, the screw augers withdraw material primarily from the rear of the bin. This limited withdrawal of material has several consequences. First, it means that gravity is acting on a smaller area than the total footprint of the screw auger, leaving a stagnant pocket of material at the front of the bin. This tagnant material is allowed to compress and compact over time under its own weight. The more wood waste compacts, the stronger it gets. Eventually the material will be strong enough to form a stable bridge. Second, the uneven withdrawal of fuel by the screw auger promotes a funnel flow discharge pattern, which promotes rat-holing, which will lead to plugging through the center of the bin.

Kamengo’s Solution

In contrast to the screw feeders, the Kamengo Feeder withdraws material evenly from its full opening, while avoiding the compaction that promotes material bridging. Because the Feeder withdraws material evenly from its entire opening, all of the material above the feeder is in motion during discharge, resulting in a mass flow, or first-in, first-out discharge. Handling a low bulk density, easily compactible bulk solid like wood waste in mass flow is important to ensuring a reliable system.

Finally, the Kamengo Feeder delivers a very steady, predicable discharge of fuel into the boiler. This is necessary for maintaining a predictable pyrolytic reaction in the boiler. The steady discharge of fuel from the Kamengo Feeders improved boiler efficiency and resulted in higher steam-output with lower emissions.

 

To minimize disruption to structural steel and the existing slide gates between the distribution chain conveyor and the metering bins, Kamengo kept the upper half of the existing metering bins and replaced everything to the boiler distributor. For each metering, Kamengo supplied a new lower half storage bin, Kamengo Feeder, collection screw conveyor, screw conveyor discharge chute and expansion joint.

 

The screw conveyor is required because the Kamengo Feeder discharges material across its full length. There is no head of material above the screw auger – in fact the screw trough is never more than 1/3 full and only requires a 5HP drive. As such the screw is only acting as a conveyor and not as a feeder.  Although the screw conveyor introduces an additional mechanical item, its inclusion permits a layout that maximizes storage at the boiler.

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 Biomass Industry. 

Hog Fuel (Wood Waste) Tall Day Bin Retrofit

Hog Fuel (Wood Waste) Tall Day Bin Retrofit

 

This case study is an example of a retrofit of a tall 18-foot diameter, 4,000 cu-ft silo used to store and feed hog fuel (wood waste) into a power boiler. This retrofit was completed in 2010.

The Existing System Prior to the Retrofit

Prior to the retrofit, the storage silo converged with a 60-deg cone down to a vibrating hat. The mill could not put more than 3-feet of material in the storage bin before it would plug. This was problematic, because this storage silo was providing critical storage between the hog fuel pile and the power boiler’s metering bins.

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Why the Existing System Suffered From Chronic Plugging

The existing silo was suffering from chronic plugging for two reasons:

 

  1. Poor bin geometry. The sloping walls and discharge opening of the cone 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 too small. The smaller the opening, the less strength a material requires to form a stable arch over the bin outlet that gravity cannot reliably break.
  2. Uneven discharge. The vibrating feeder withdrew material unevenly from the storage bin – pulling material primarily from around the silo walls, leaving behind a relative stagnant core of fuel. 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 wood waste is quite large – in fact, it is larger than the silo diameter. To handle hog fuel (wood waste) reliably without hang-ups, it must be discharged in a mass flow, or a first-in, first-out discharge pattern – where all the material in the storage bin descends as a single body and where all the material in the storage bin is in motion. To do achieve a mass flow discharge pattern, the Feeder must withdraw material evenly from the storage bin’s full discharge outlet.

Kamengo’s Solution

The solution to the silo had two parts:

 

The first half of the solution is to modify the bin geometry of the silo such that it will promote a first-in, first-out discharge pattern. In this case, Kamengo placed insert plates lined with a low friction liner into the silo to construct two plane flow hoppers – one stacked on top of the other, and one 90-degrees to the other. A plane flow hopper 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 insert plates open up to a 6-foot wide by 12-foot long opening. This wide and long opening is required to ensure gravity will always be sufficient to break the strength of the arch that hog fuel would create above the Feeder. In summary, by replacing the cone with the insert plates, Kamengo fixed the geometry of the silo such that if the Feeder were removed, the silo would self-empty with only the aid of gravity. The minimum geometry required for gravity discharge, including minimum slope angle of the insert plates and minimum discharge opening were all selected based on the flow properties of hog fuel.

 

The second half of the solution was to pair the plane flow hoppers 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. This feature is particularly valuable given that the chosen minimum discharge opening of the silo is 6-foot by 12-foot. 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 Biomass Industry. 

Hog Fuel (Wood Waste) Boiler Feed Metering Bins

Hog Fuel (Wood Waste) Boiler Feed Metering Bins 

This case study highlights the retrofit of eight small screw feeders experiencing chronic plugging at a mill in Quesnel, BC. The screw feeders where replaced by four surge bins and feeders. Each Kamengo Feeder feeds a split chute, which in-turn directs the hog fuel into two boiler spouts. Prior to the retrofit, the plant was experiencing lost steam production and swings in the header pressure. Post retrofit, the plant is producing more steam, and the boiler is able to meet the changing steam demands from the paper plant while maintaining an even header pressure. The retrofit was completed in 2015.

The Challenge

Prior to the retrofit, the pulp mill had eight small screw feeders that were experience chronic plugging. Each screw feeder consisted of a single auger with a very small and narrow storage bin above it. Although the mill limited the head of material above the screw augers, the metering bins were very unreliable.

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Why the Conventional Screw Feeders Were Suffering from Chronic Plugging and Inconsistent Discharge

The screw augers were suffering from chronic plugging for two reasons:

 

First, the screw augers have a tendency to compact material against the front of the bin wall. Wood waste that is being carried or sheared from the storage bin, through friction or interlocking, carries fuel above it. And this fuel travelling above the screw feeder outlet is compacted against the bin wall. The problem is that wood waste gains significant strength when it is compacted. Once the fuel above the outlet gains sufficient strength it will bridge over the outlet resulting in inconsistent discharge and plugging.

 

Second, the screw augers withdraw material primarily from the rear of the bin. This limited withdrawal of material has several consequences. First, it means that gravity is acting on a smaller area than the total footprint of the screw auger, leaving a stagnant pocket of material at the front of the bin. This tagnant material is allowed to compress and compact over time under its own weight. The more wood waste compacts, the stronger it gets. Eventually the material will be strong enough to form a stable bridge. Second, the uneven withdrawal of fuel by the screw auger promotes a funnel flow discharge pattern, which promotes rat-holing, which will lead to plugging through the center of the bin.

Kamengo’s Solution

In contrast to the screw feeders, the Kamengo Feeder withdraws material evenly from its full opening, while avoiding the compaction that promotes material bridging. Because the Feeder withdraws material evenly from its entire opening, all of the material above the feeder is in motion during discharge, resulting in a mass flow, or first-in, first-out discharge. Handling a low bulk density, easily compactible bulk solid like wood waste in mass flow is important to ensuring a reliable system.

 

Finally, the Kamengo Feeder delivers a very steady, predicable discharge of fuel into the boiler. This is necessary for maintaining a predictable pyrolytic reaction in the boiler. The steady discharge of fuel from the Kamengo Feeders improved boiler efficiency and resulted in higher steam-output with lower emissions.

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 Biomass Industry. 

Hog Fuel (Wood Waste) Boiler Feed Metering Bins

Hog Fuel (Wood Waste) Boiler Feed Metering Bins  

 

This case study is an example of a retrofit of wood waste or hog fuel metering bins that are metering fuel into a power boiler. The retrofit was completed in 2015.

The Challenge

Prior to the retrofit, the pulp mill had a single live bottom bin discharging into five inlets. The bin suffered from chronic plugging causing the mill to either burn gas at a high expense or live with a lower steam output and lower pulp production. To minimize plugging issues, the mill was forced to run the live bottom bin with a very low head of fuel.

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Why the Existing Conventional Screw-Type Feed Bins Were Suffering from Chronic Plugging and Inconsistent Discharge

The live bottom bin suffered from many of the challenges typical of conventional feeders. First, the screw augers have a propensity to compact material against the front of the bin wall. As wood fuel is sheared from the storage bin, due to interlocking and friction, the fuel being carried out carries fuel above it. And this fuel travelling above the outlet is compacted against the bin wall. The problem is that wood waste gains significant strength when it is compacted. Once the fuel above the outlet gains sufficient strength it will bridge over the outlet resulting in inconsistent discharge and plugging. Second, the screw augers withdraw material from the back of its opening, leaving a stagnant pocket of material at the front. This limited withdrawal of material has several consequences. First, it means that not only is gravity acting on a smaller area, but it also means that the stagnant material is allowed to compress and compact over time under its own weight. The more wood waste compacts, the stronger it gets. Eventually the material will be strong enough to form a stable bridge. Second, uneven withdrawal promotes a funnel flow discharge pattern, which promotes rat-holing.

Kamengo’s Solution

In contrast to the live bottom bin, the Kamengo Feeder withdraws material evenly from its full opening. Further, the opening of a Kamengo Feeder can be made as wide as needed and as long as desired. For this retrofit, Kamengo replaced the live bottom bin with five individual metering bins, each with its own Kamengo Feeder. Because the Kamengo Feeder withdraws material evenly from its entire opening, all of the material above the feeder is in motion during discharge, resulting in a mass flow, or first-in, first-out discharge. Handling a low bulk density, easily compactible bulk solid like wood waste in mass flow is important to ensuring a reliable system.

 

Finally, the Kamengo Feeder delivers a very steady, predicable discharge of fuel into the boiler. This is necessary for maintaining a predictable pyrolytic reaction in the boiler. The steady discharge of fuel from the Kamengo Feeders improved boiler efficiency and resulted in higher steam-output with lower emissions.

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 Biomass Industry.