Hot Lime Silo Retrofit
This is an example of a hot lime silo that is suffering from chronic bridging. It is a good example of poor bin geometry combined with uneven discharge that is resulting in chronic bridging.
Why the Existing Storage and Feed Arrangement is Suffering from Chronic Plugging and Inconsistent Discharge
The existing bin consists of a 25-foot diameter silo and 55-deg cone that converges to a 2-foot diameter opening that is fitted with a basket gate.
In summary, the silo is suffering from chronic plugging because the shallow cone and the behavior of the basket gate are inducing a funnel flow discharge pattern. Funnel flow (which is a first-in, last-out discharge pattern) can be made to work with a large discharge outlet. 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.
The solution to fixing this problem storage and feed system has two parts. The first half of the solution is to replace the bottom half of the cone with a mass flow chisel hopper with a wide and long opening. The result is an expanded flow bin, with the lower half of the storage silo emptying in mass flow and upper portion emptying in funnel flow. As long as the funnel flow portion is emptied completely on a regular basis the storage bin geometry will be reliable.
Mass flow is a first-in, first-out discharge pattern. The definition of mass flow is that during discharge, the entire mass of stored material comes down as a single body (single mass). The tell-tale sign that you have mass flow is that material is sliding down the bin walls. To achieve this, material must discharge evenly from the entire discharge outlet of the storage bin. This requirement leads to the second half of the solution.
The second half of the solution is to pair the plane flow chisel hopper with a fully-effective feeder – that is a feeder that withdraws material evenly from its entire infeed opening. Again, 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 material.
To learn more about the physics of storage bin and feeder design as well as the root causes of bin plugging, please visit KamengoU.