SHAPA Conveying the message
The SHAPA Knowledge Conference was the ideal opportunity to learn how to choose lean or dense phase conveyors
The SHAPA Knowledge Conference held recently at Loughborough offered expert insights into many of the challenges presented by the moving and processing of materials in bulk. A typical example of such a challenge is how to choose between lean or dense phase conveying. Indeed, the first hurdle is to define the terms and discriminate between them.
In general, if the material can reasonably remain airborne in an airstream within a pipe or duct, then it may be a candidate for lean phase conveying. Advantages include low capital cost – only a blower fan instead of compressed air being required as the prime mover – and the ability to deliver a constant stream of product to the next process. Weighing against lean phase conveying, however, is the relatively high running cost, as considerable quantities of air at pressure must be supplied. Maintenance costs and possible downtime must be considered, as high speed blowers will need servicing and ducting that carries material may wear quite rapidly negating the initial capital cost advantages. However, because of its convenience and low height requirements, for example with the conveying pipe connected directly beneath a discharge rotary valve, the case for lean phase may be compelling. Against this, lean phase conveying may be damaging to delicate materials.
So, what of dense phase? The need for a pressure vessel to be fitted beneath the feed hopper increases the height of the system.
But no blower is required, merely relatively small quantities of compressed air to move the bed or “plugs” of material to the receiving vessel. Dense phase conveying is much kinder to the material, resulting in less abrasion or attrition damage, delivering particularly delicate or sensitive material in good condition. For fine powders it maybe the ideal solution, particularly if particle condition is important downstream. By its very nature dense phase conveying is a batching process, the quantity of each delivery being determined by the pressure vessel capacity. Of course, comparisons between and relative merits of the two technologies will necessitate an in-depth study, with the argument well summarised for delegates at the Knowledge Conference by SHAPA member Clyde Materials Handling. Again, pneumatic conveying is just one of a range of means to transport material, other methods including disc-and-rope, drag-link, helical screw, flexible screw and the ubiquitous belt conveyor in all its forms. Material properties and quantity, distance and site conditions all play a part in final selection. Close liaison with an expert supplier to ensure that the materials are properly matched to the handling equipment will pay dividends in the long run – or even in the short run – avoiding well known and lesser known pitfalls. Visit the SHAPA Product Selector at
www.shapa.co.uk for a selection of the best companies with proven competence, for all conveying technologies.
32 Solids & Bulk Handling • November 2010
www.solidsandbulk.co.uk
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