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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

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.