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.
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.
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:
- 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.
- 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.
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.
To learn more about the physics of storage bin and feeder design as well as the root causes of bin plugging, please visit KamengoU.