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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) Tall Day Bin

Hog Fuel (Wood Waste) Tall Day Bin

This is an example of a storage bin designed specifically to handle difficult flowing biomass, including stringy woody biomass.

Why Conventional Live Bottom Bins Suffer from Chronic Plugging and Inconsistent Discharge

Standard storage bins used to handle biomass are typically negative taper, and use a live bottom reclaim system such as augers or a stoker.

In summary, live bottom negative taper bins struggle handling biomass because: 1) they allow the stored biomass to compact on itself and place a heavy load on the reclaim system, 2) promote material compaction by driving material against the bin front wall, and 3) withdraw material in a funnel flow discharge pattern, which induces rat-holing.

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Kamengo’s Solution

The solution to a reliable biomass storage bin starts with good bin design and moving away from the negative taper bin to a positive taper bin where the majority of the load in the bin is carried by the bin walls, and where the biomass will accelerate from the storage bin during discharge. However, for reliable discharge, the geometry of the positive taper storage bin must be correct. The most conservative bin shape for handling biomass is a plane flow hopper shape with a wide and long discharge opening. A plane flow hopper only converges in one plane at a time, and is vertical in the opposite plane. The plane flow hopper is the most conservative hopper shape. The purpose of using a conservative bin shape with a long and wide discharge outlet is to employ a geometry where if the Feeder were removed, the entire bin would self-empty with gravity in a mass flow or first-in, first-out discharge pattern.

 

The second half of the solution is to pair the plane flow hopper with a fully-effective feeder – that is a feeder that withdraws material evenly from its entire infeed opening. By definition, to achieve mass flow, where the stored material comes down as a single body, the feeder must withdraw material evenly from its entire opening. If the Feeder withdraws material selectively from the bin discharge outlet, sections of material in the bin will be stagnant and funnel flow will ensue.

 

A great example of a fully-effective feeder is the Kamengo Feeder. In addition to being fully-effective, the Feeder offers consistent metering, and can be made as wide as needed and as long as wanted. As a result, the Kamengo Feeder offers valuable advantages when designing for a difficult flowing fibrous material.

Learn More

To learn more about the physics of storage bin and feeder design as well as the root causes of bin plugging, please download our white paper entitled: The Design of Reliable Storage Bins and Feeders for the Biomass Industry. 

Construction & Demolition Debris Truck Load-Out Bin

Construction & Demolition Debris Truck Load-Out Bin

This is an example of a tall 30,000 cu-ft (825 cu-m) truck load out storage bin designed to handle construction and demolition wood waste and other difficult flowing fibrous materials. 

Why the Material is Challenging

Processed construction and demolition wood waste gains strength very quickly when it is subject to compaction, including compaction under its own weight in a storage bin. When processed C&D wood waste compacts it gains shear strength very quickly. Compact C&D wood waste enough and you will form bricks that have the strength of a cement block. It is this strength that enables the material to bridge over wide openings. 

 

Processed construction and demolition wood waste is a relatively low-density material, and this means that the force supplied by gravity to keep the material moving is less relative to other bulk solids. With gravity being the primary force for emptying the storage bin, it is easy to design a storage and feed system where the strength that C&D wood waste gains under compaction exceeds what gravity can break. These storage bins suffer from erratic discharge and/or chronic plugging. 

 

Processed construction and demolition wood waste is a highly variable material. It can be stringy and have long sticks. A conservative design includes using a wide and long bin opening, steep and lined bin sloping walls, and using a feeder that pulls evenly from the entire opening of the storage bin. 

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

Standard truck load out bins use clam shell gates to control discharge. The problem is that when the clam shell is partially open, a funnel flow discharge pattern is induced, which introduces a high risk of bridging and rat-holing. Further, there is little control in how the truck is filled and the loads that are transferred to the truck. 

Kamengo’s Solution

The solution to a reliable C&D waste truck load out bin that provides a controlled discharge of material has two parts. 

 The first half of the solution is to use a plane flow hopper shape with a wide and long discharge opening. A plane flow hopper only converges in one plane at a time, and is vertical in the opposite plane. The plane flow hopper is the most conservative hopper shape. The purpose of using a conservative bin shape with a long and wide discharge outlet is to employ a geometry where if the Feeder were removed, the entire bin would self-empty with gravity in a mass flow or first-in, first-out discharge pattern. 

 

The second half of the solution is to pair the plane flow hopper with a fully-effective feeder, which withdraws material evenly from its entire opening. A fully effective feeder is, by definition, necessary to actually achieve a mass flow discharge pattern in the hopper, which is necessary when handling a difficult flowing fibrous bulk solid. 

 

Kamengo’s proposal is to use a plane flow shaped truck load-out storage bin with a vertical section and roof to provide up to 30,000 cu-ft (825 cu-m) of live storage. The storage bin has steep sloping walls, and each sloping wall is lined with a single seamless sheet of UHMW. The storage bin has a wide and long 6-foot by 24-foot opening, which is necessary to overcome the bridging dimension of C&D waste. 

 

The storage bin is paired with a Kamengo Feeder. The Kamengo Feeder is capable of filling a range of truck beds. Of critical importance, the Kamengo Feeder withdraws material evenly across both its entire length and width. The result is that the stored material is withdrawn evenly from the full discharge outlet of the truck load out bin. An even withdrawal of material is absolutely required to achieve a first-in, first-out discharge. The Kamengo supplied PLC has a user interface where the truck driver selects their truck-type and is given instructions on starting the loading procedure. Based on the truck type, the Kamengo Feeder, which delivers a consistent, predictable volumetric discharge, will deliver the volume desired for the chosen trailer type. 

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.