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When hoppers are designed without consideration of the actual materials being handled, problems inevitably arise. Follow this guidance to avoid common solidshandling issues, such as erratic flow and no flow
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Pivotal work on the development of the theory of bulk solids flow began in earnest in the early 1950s, when Andrew Jenike applied a solidsmechanics-continuum concept to develop a logical, theoretical approach for understanding and managing solids flow. He developed testing methods, equipment, and design techniques and conducted experiments to confirm and refine his groundbreaking analysis [7].
Prior to Jenike's work, bins and hoppers were typically designed primarily from an architectural or fabrication standpoint (for instance, hopper walls were sloped 30 deg from vertical to reduce the waste of wall materials, or 45 deg to minimize headroom requirements and simplify design calculations). However, extensive experience has shown that designing equipment without regard to the actual bulk materials being handled often leads to flow problems, such as arching, ratholing, erratic flow and even no flow. By measuring the flow properties of a bulk solid, the flow behavior of the material can be predicted, and more reliable hoppers and bins can then be designed.
Competing flow patterns
Two primary flow patterns can occur in a bin or a silo: mass flow and funnel flow (Figure 1). In mass flow, the entire bed of solids is in motion when material is discharged from the outlet. This behavior eliminates the formation of stagnant regions in the vessel, and affords a "first-in, firstout" flow sequence, which provides a more uniform velocity profile during operation. A uniform velocity profile also helps to reduce the effects of sifting segregation.
By contrast, in funnel flow, an active flow channel forms above the outlet, but stagnant material remains (called ratholes) at the periphery of the vessel. Funnel flow can cause erratic flow, exacerbate segregation, reduce the live capacity of a vessel, allow particle degradation (leading to caking and spoilage) in stagnant regions. Depending on the vessel size, funnel flow can also induce high loads on the structure and downstream equipment, due to collapsing ratholes and the formation of eccentric flow channels.
For many materials, flow problems can be eliminated by ensuring that a mass flow pattern exists in...