Retrofit of Wood Chip Chute Suffering From Chronic Plugging
This is an example of when a chute becomes a hopper, and when a conveyor becomes a feeder and plugging ensues.
Why the Chute is Suffering from Chronic Plugging and Bridging
In contrast to a bin or hopper, a chute is where material is continuously flowing and there is no head of material at the outlet. When a chute is flooded such that a head of material builds at the outlet, the chute becomes a hopper and the conveyor on which it discharges onto becomes a feeder. This is problematic because suddenly the chute is subject to minimum geometry constraints needed to avoid bridging and the conveyor needs assume the job of shearing material from the chute.
This is an example where the chute is receiving a flood of material from processes upstream causing a head of material to build in the chute. And because the geometry of the chute is insufficient to act as a hopper, the chute is subject to chronic plugging and is a major headache for the plant.
In summary, because it is carrying a head of material, the chute is not actually a chute, but a hopper and as such, its geometry, including outlet and sloping walls must be sufficiently large and steep to ensure reliable gravity discharge. However, with its four sloping walls and small discharge opening, the chute’s (turned hopper’s) geometry is insufficient, and hence it is subject to chronic plugging.
The easy solutions to fixing these chutes turned hoppers is to either decrease the discharge of material upstream or increase the speed of the conveyor to ensure no head of material builds up in the chute. If the easy solutions are not viable, as in the case of this case study, the plant needs to install a hopper and feeder designed to handle the bulk solid as an intermediary between the chutes and the conveyor.
Choosing a suitable storage and feed system has two components. The first is to choose a bin shape with a wide and long opening, where if the feeder were removed, the hopper would self-empty with only the aid of gravity. Kamengo typically suggests a plane flow hopper (which is a bin shape where the hopper walls only converge in one plane at a time). The plane flow hopper is the most conservative hopper shape.
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 opening – which is necessary for reliable discharge when metering a difficult flowing material from a small hopper. The Kamengo Feeder is a very good choice because not only is it a fully effective feeder, but it can also be made as wide as needed and as long as desired, which opens the range of solutions to fixing a problem storage and feeder system.
To learn more about the physics of storage bin and feeder design as well as the root causes of bin plugging, please visit KamengoU.