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Why Do Bulk Solids Handling Problems Occur?

For many plants it is almost a given that when new ingredients or sources of material are introduced into the process that problems will develop with respect to the handling and storage of these materials.

By Richard Farnish – Principal Research Fellow Department of Mechanical & Design Engineering of University of Greenwich

richard farnish

Richard Farnish – Principal Research Fellow Department of Mechanical & Design Engineering of University of Greenwich

Some of the reason for these problems stems from a failure to fully appreciate the importance of investing into the design or procurement of good quality bulk solids handling equipment.

For many engineers the topic of bulk solids handling is one that is hard to identify with – since it embodies a very wide range of applied technical areas into a single ‘subject area’.

A cursory examination of the ‘state of the art’ for bulk solids handling equipment quickly reveals that many types are very similar in design and operating capability – which also adds complication for engineers (that are not well versed in the topic) when evaluating tender documents. A failure to appreciate the need for an appropriate scale of budget leads to a more tightly controlled CAPEX.

This fact combined with a range of tender documents that will likely offer a range of different engineered solutions for a single plant requirement often leads to the successful tender being characterised more by compliance with (or being below) the budget limit than by technical excellence – especially since all submissions will carry process guarantees.

One of the reasons why such variations in engineering proposals can be generated is sometimes due to vaguely written specifications that lack sufficient technical rigour upon which to base a fully informed design.

A balance should be made between allowing sufficient latitude for suppliers to implement their specialist knowledge with the specification framework and ensuring the inclusion of key technical points to steer their collective responses in a concerted way. 

This may sound like common sense for the initiation of a tendering process for any industry – but it is all the more critical for the process industries that work with powder or granular materials. The storage and handling characteristics of bulk materials make them very sensitive to the finer points equipment or system designs – which is one reason why so many plants experience problems.

Void pressure test rig / Bulk Solids Handling Problems

An example of the dilemma that can develop relates to the seemingly simple task of procuring a storage silo. Often the main guidance in the specification will focus upon spatial constraints and vessel volume requirements.

Reference to the materials to be handled is likely to range from virtually absent (i.e. just its name) to uninformative from a design perspective (angle of repose, tapped bulk density, median particle size). Consideration as to how the material is likely to behave when passed through the equipment is usually limited to “….discharge reliably…” – again, not very helpful in a practical sense if it transpires that the material is time dependant (requiring first in – first out flow), segregable (needing designed counter measures and mass flow in many cases) or the process requires a consistent and repeatable flow of material from the storage vessel.

Too often the implications of not realising these design/operational requirements are not fully considered at the project planning stage. A failure to request these types of operational conditions often leads to ambiguity in the written requirements – the most fundamental of which is whether core flow or mass flow is a process requirement.

Whether a supplier will seek clarification of what is actually needed is unlikely if the specification is interpreted as being a definitive document. In such instances a failure to make clear reference to how the process is intended to work (or how the equipment is intended to integrate with existing plant) can be taken as an indication that no special considerations for design exist.

This, in effect, can give suppliers a relatively free hand to fall back on previous experience and standard equipment ranges to compose their response. Thus a common specification can generate quite diverse options between suppliers.

Conclusion

It makes commercial sense to avoid unnecessary expenditure, however this should always be balanced against the long term risk of operational problems if the selected equipment is not technically sound for the duty asked of it.

Although good reference works relating to bulk solids handling are by no means prolific – there are some very useful courses out there that can provide a good foundation in the subject and could serve to help avoid some costly mistakes

there are some very useful courses out there that can provide a good foundation in the subject and could serve to help avoid some costly mistakes
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