Process Know-how

Extraction characteristics of bulk materials from silos

Part 1: Basic experimental and theoretical principles

Summary: As part of this work experimental investigations were carried out with a rectangular silo. The main focus was on the stress states during emptying by two silo extraction screws and the relationships between the wall normal stresses, the flow profiles and the torques required for the extraction screws. Among other things it was established that the wall normal stresses are lower in moving zones than in stationary zones. The findings and relationships that were discovered can be reliably applied to industrial plants. Part 1 of the article deals with the basic experimental and theoretical principles and Part 2 deals with the test results.

1    Introduction
Silos have been used for centuries for storing bulk materials. It is important not only that the required quantity of bulk ma­terial can be stored in a silo but also that it can be emptied out of the silo at the required moment. The way the silo is emptied can, depending on the nature of the bulk material, play a central role. Furthermore, mass flow is usually the required flow profile, especially if the bulk material is sensitive to ageing or tends to consolidate with time. Mass flow is understood as the state in which the entire contents of the silo are in motion during the...

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