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.
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.
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.
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.
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.