Dear patel

It is not possible to explain how to determine hopper/ bin dicharge size, however Discharge size of bin/hopper is governed by following

1.0 material lump size

2.0 material discharge capacity

3.0 Flowablity of material

4.0 Downside equipment size

A R SINGH ■

The outlet size of a bin must be adequate to avoid structural arching, cohesive arching and also ratholing, if the hopper is not of mass flow design.

The first decision in hopper design is to select an appropiate flow regime for the duty, the choice being mass flow, expanded flow and non-mass flow. The second decision is the hopper shape. There are many options, but the main ones are circular and cone, rectangual and pyramid, rectangular and chisel, circular and transition ot chisel, with variants of eccentricity and sophisticated shapes, such as Sigma Two relief.

The next step is to measure the wall friction of the porduct on a surface identical to that of the hopper wall construction. This will establish the slope of wall required for slip during flow or self clearing of the container.

Finally, the size of opening is determined by shear tests and lump size measurements. The methodolgy and techniques are well established for product testing and calculating this value, which of course depends on the shape of opening and the form of flow pattern.

Whilst finding the critical size of opening for reliable gravity flow is the most technical demanding of these tasks, there are many more options for dealing with this aspect, both for initial design and for retrofit if the size is inadequate, than the other more simple decisions. It is also important to note that a feeder is an integral part of a hopper design and optimum performance relies on a sound interface, so it is best to deal with experienced suppliers if in any doubt at all, because the cost of problems can well outweigh marginal differentials of supply cost and sometime exceed the equipment cost altogether.

Technical articles expanding on these points are avalaible from lyn@ajax.co.uk ■

Dear Rajendra,

If you are not handling "fines", but coarse granular particles, I can send you equations that I have used with success for many years to calculate the hopper opening.

Regards,

Amrit Agarwal

Consulting Engineer

Pneumatic Conveying Consulting

Email: polypcc@aol.com

Ph and Fax: 304 346 5125 ■