Achieving mass flow in silos with shallow converging sections using inverted cones

The relatively low amount of attention paid to the bulk solids handling stages within industrial processes, has produced a lackadaisical attitude towards design of the equipment involved in these stages. This is commonly reflected in the manufacturing process by unreliable flow/blockages resulting in uneven packaging and reduced homogeneity of the final product. With the use of appropriate techniques existing equipment can be redesigned to operate reliably, however, the cost associated is often too high for it to be considered as an option. A simple and widely used method to try to overcome these problems is the retrofit of inverted cones. However, the solution often becomes a different sometimes bigger problem as the incorrect dimensioning and positioning of the insert causes preferential draw and offset discharge. The present paper explores and validates a method to achieve mass flow using inverted cones. The method studied was developed by J.R. Johanson [Johanson, 1965] and it is shown that mass flow can be achieved following these guidelines when working with tall silos or silos that are continually fed. However, when working with shorter silos or silos running at lower inventory levels the effectiveness of the method decreases. In answer to this, a modification of the method is presented and the improvement validated.