ROM Ore Railcar Unloading Bin
This is an example of a series of rail car unloading hoppers designed to handle large particle as well as difficult flowing cohesive materials.
Conventional Unloading Bins and Why they Suffer from Chronic Plugging and Inconsistent Discharge
A standard railcar unloader uses a series of pyramid hoppers that converge to a small opening that use any of slide gates, basket gates, vibrators or clamshells to control discharge.
In summary, a pyramid hopper with a small opening is a terrible choice of bin shape for handling difficult flowing cohesive materials. The bin shape promotes a funnel flow discharge pattern. Funnel flow (which is a first-in, last-out discharge pattern) can be made to work with large bins with large discharge outlets. However, when the discharge outlet is small, gravity is insufficient to overcome the strength of the bulk solid at the discharge outlet, and hence chronic bridging and rat-holing is expected.
Further, Feeders that operate partially open to control the flow of discharge and do not withdraw material from the full discharge outlet of the hopper all the time are dangerous, because this behavior further promotes a funnel flow discharge pattern and the formation of stable arches and ratholes. A reliable Feeder is “fully effective”, where it withdraws material evenly from the full discharge outlet of the storage above it.
The solution to a reliable railcar unloading hopper that is capable of handling both large particles as well as difficult flowing cohesive materials 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 hoppers with a Kamengo Feeder. The value of the Kamengo Feeder is that it withdraws material evenly from its entire opening, which by definition is necessary to actually achieve a mass flow discharge pattern in the hopper, which is necessary when handling a difficult flowing bulk solid. A further advantage of the Kamengo Feeder is its low profile, which helps to save height and related civil costs.
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 Mining Industry.