Conveying
is necessary, pneumatic conveying is the method of choice. Likewise, with very-high- temperature material, a positive pressure pneumatic conveyor has the advantage. A vacuum system can’t be ruled out, but measures must be taken to protect the air mover and filter media from the heat. If degradation of product during trans-
port is a concern, either system must be properly designed to minimise dam- age. This is where testing becomes particularly important, especially if there are no fixed, measurable criteria for the permissible degree of degradation. Testing can determine how much degradation occurs with each technol- ogy at varying flow rates and operating conditions. Pneumatic conveying has been used to move products as diverse as bran flakes, ice cream sprinkles, bottle caps, capsules and tablets without damage. But experience with certain materials demonstrates that pneumatic conveying can significantly alter its bulk density, much more than with a flexible screw conveyor. A test program will ensure that, whatever the bulk product, it will reach its destination with properties intact.
MATERIAL SOURCE AND DESTINATION Another influence is how material is sourced. When materials are introduced from multiple sources, either sequentially or simultaneously, pneumatic conveyers tend to be the better choice however since pneumatic conveyors require separate receiving equipment at every destination, such as filter receivers, weigh- ing valves or rotary airlock valves, flexible screw conveyors can
Flexible Screw Conveyor
prove the lower cost alternative when deliver- ing to multiple ‘local’ discharge points. For material in bags, drums or boxes, a vacuum conveying system with a pick-up wand can pull material directly from the container. Use of a flexible screw conveyor requires that the containers be dumped or dis- charged into a hopper fitted with an intake adapter. Either technology is suitable for con- veying products being discharged from bulk bags when the bag is properly suspended above a receiving hopper that is equipped with the appropriate intake adapter.
TESTING
While the characteristics of material and process may clearly dictate one technol- ogy over the other, both flexible screw and pneumatic conveyors are suitable for most bulk conveying applications it is therefore prudent to seek expert, unbiased opinion, look to bulk handling specialists with a fully equipped, modern test laboratory with both pneumatic and mechanical bulk handling equipment that can be easily reconfigured to produce objec- tive recommendations based on live trials. ■
For more information contact Flexicon on tel: +44 (0)1227 374710 or visit:
www.flexicon.com
www.solidsandbulk.co.uk
Solids and Bulk Handling June 2012 19
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