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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. 

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) 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. 

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. 

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. 

Poultry Litter Boiler Feed Metering Bins

Poultry Litter Boiler Feed Metering Bin 

 

This case study is an example of boiler feed metering bins that are metering poultry  litter into a power boiler. This installation was delivered in 2007 and operated until 2019 when the plant was decommissioned.

 

This fuel is particularly challenging because it consists of wood waste mixed with poultry  litter. The result is a fuel that is not only fibrous and compactible, but also sticky and corrosive.

The Challenge

This installation was a for a new power plant. The owners, who had built several poultry  litter power plants in the UK prior to this plant in Benson, Minnesota, had experienced a lot of difficulty handling poultry fuel, in particular in delivering an even feed into the boiler at their existing plants. For their first planned plant in the USA, the owners wanted a solution that was capable of reliably metering poultry fuel and ultimately selected the Kamengo Feeder.

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Why Conventional Live-Bottom Feed Systems Suffer from Chronic Bridging and Inconsistent Discharge

The owners had previously used live bottom bins and individual metering bins with screw augers to meter fuel into the boiler of previous plants. These bins suffered from inconsistent discharge and plugging for several reasons. First, the screw augers have a tendency to compact material against the front of the bin wall. As poultry  litter 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 poultry  litter 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, 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 poultry  litter 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 installation, Kamengo supplied eight 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 poultry  litter 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 is necessary to maximize steam delivered to the turbine.

 

There are eight inlets into the boiler, with a Kamengo supplied 430 cu-ft bin, Feeder, screw conveyor and chute with expansion joint for each inlet. The Kamengo equipment receives fuel from a distribution chain conveyor. Fuel is continuously fed into the first seven bins. Level sensors in the seventh and eighth bin indicate to the plant PLC when to start and stop the distribution conveyor. The even feed from the Kamengo bins permitted the plant to forgo a return conveyor.

 

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 subject to failure and wear, its inclusion permits a layout that maximizes storage at the boiler. Kamengo was chosen as the vendor for this project after extensive testing, including feeding the material through our pilot scale Kamengo feeder and bin located in Vancouver, Canada.

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 37-foot tall, 6,000 cu-ft silo used to store and feed hog fuel (wood waste) into a power boiler. The hog fuel at the mill is particularly challenging because it contains hickory bark and can be very stringy.

When Kamengo first met the mill, the plant engineers were exploring options to replace the entire hog fuel feeding system. However, upon learning of a retrofit to a similar size tall bin that Kamengo had completed for a pulp mill in Washington State, USA, the mill found that it could solve its feed issues by retrofitting its existing bin

 

Kamengo replaced the lower half of the bin with a rectangular plane-flow mass flow hopper and Kamengo Feeder. The Kamengo Feeder is ahead of a live bottom bin with screw feeders feeding biomass fuel into the boiler. Since the screw feeders cannot maintain a significant head of material above them, the Kamengo Feeder is used to reliably meter just enough material that the screw feeders can handle to ensure good, steady material discharge into the boiler.

 

This retrofit was completed in 2004.

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Why the Existing Storage and Feed System is Suffering from Chronic Bridging and Inconsistent Discharge

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 6-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.

The existing silo was suffering from chronic plugging for three 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. 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 fixing 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 cut off the bottom portion of the silo, including the cone and replaced it with a plane flow, mass flow hopper and Kamengo Feeder. A plane flow hopper is the most conservative hopper shape.

 

The new hopper converged to wide and long 6-foot wide by 18-foot long discharge 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 new plane flow hopper, 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 plane flow hopper 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 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. This feature is particularly valuable given that the chosen minimum discharge opening of the silo is 6-foot by 18-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.