There used to be a time when bins were designed for total volume and placed in any available place of the plant. Poke holes were provided and feed was maintained by manual prodding, lancing, hammering, and by various mechanical flow-promoting devices. Little thought was given to what occurred inside the bins and why materials did not flow. Indeed, such mental effort was hard to justify while low-cost manual labor was plentiful, quality standards low, and rates of feed moderate.
Typical Storage and Flow Problems
In order to design an efficient storage plant or contact-bed reactor it is necessary to be aware of the problems which can arise in flow and storage. The typical problems are:
No flow: a stable arch (dome) or rathole develops within the solid and flow ceases.
Erratic flow: momentary arches form within the solid; ratholes empty out partly or completely, then collapse. Density of the stream swings within wide limits.
Flashing: powders in erratic flow aerate, fluidize and flush. While air-locks can be used to prevent flushing they do not eliminate erratic flow.
Insufficient flow: the volumetric rate of gravity flow through an orifice depends on the stored solid. Coarse dry solids flow at a high rate, closely approaching the