Bulk solids handling

Paul Boughton

Powders and particulate materials are in almost everything ‐ from the food and drink we consume, to the roads we drive on, the power we use, the paper we write on and the clothes we wear, each is dependent on the use of bulk solid materials in some stage of its production.

However, in spite of the fact that most process engineers use systems that handle and process powders and bulk solids at some point in their career, few ever get any formal training in the subject.

Most manufacturing plants need some method of transporting bulk materials around site, or transporting to the customer. These materials may then be stored in or discharged from hoppers, silos, blenders or mixers, using feeders or screws etc yet the statistics show that more often than not, many plants do not reach full performance, and often over‐run extensively in time and cost to get them operating1.

The reason for this is partly down to a lack of training; of not understanding about the materials being handled.

Every different powder or particulate has a different behaviour, so even if you get one product reliably transported and discharged without hiccups in a particular plant, the chances of the same conditions being as suitable to another (even apparently) similar product are quite slim. Even something as simple as varying the amount of one ingredient in a dry blend of powders, for example, could have a disastrous effect on the handling efficiency. What works for cement will not necessarily work for biomass pellets, what works for coffee granules might not work for recycled plastic,  etc.

Good quality training needs to cover the fundamentals – in other words, the behaviour of powders and bulk solids, the methods used to characterise their properties (not just particle size but flow properties, compressibility, density variation under stress etc) and the process models used to choose equipment design to give good performance in view of the powder properties. 

Most process engineers handling bulk materials will have experienced one or some of these typical issues:

* Lumping or caking of products in silos and hoppers, or during storage causing the alltoo common problem of ‘hammer‐rash’ where hoppers have been beaten to achieve flow;

* De‐blending and separation of materials during the discharge process;

* Irregular dosing of powdered ingredients into sachets or packets;

* Damage to particles during transit around the plant or through discharge;

* Excessive equipment wear;

* Inconsistent behaviour of materials when the component materials are altered in volume, weight, type;

* Excessivedust generation.

Anyone handling bulk materials in a part of their process will benefit from training in the technology surrounding their handling, storage and feeding. Anyone involved in plant design, or the manufacture and supply of equipment used for bulk materials handling will also benefit from the knowledge and experience of the experts in the field. 

Although education can’t completely take the place of experience on the job it’s better than the pervasive, though innocent, ignorance of the science of bulk solids handing that most young engineers have to struggle along with when designing, buying, maintaining and troubleshooting this most dominant class of equipment in industry. 

But for these opportunities to be exploited, management at a senior level has to first recognise that formal training in bulk solids handling ought to be a required discipline, a core skill, for engineering staff at all levels. It is already known from previous experience that the payback in plant efficiency and product quality can be dramatic – but as the Rand report shows, the all‐too‐common practice of NOT applying enough science to bulk solids handling operations often leads to excessive costs, low productivity and compromised quality.

The Wolfson Centre for Bulk Solids Handling Technology provides such training in the form of a range of short courses for Industry where delegates can discuss their own bulk materials handling problems and learn methods available to help solve them.

Topics range from basic materials handling, to storage and discharge of materials, pneumatic conveying issues, equipment purchase, to name but a few. If the pre‐arranged calendar of dates is inconvenient, experts can provide in‐house training for 6 or more attendees, thus enabling a course to be tailored to the needs of the plant.

1. Merrick, Understanding Performance Shortfalls in Pioneer Process Plants, Rand Corporation, 1980.

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