It is well recognised that power requirements for pneumatic conveying systems can be somewhat higher than those for alternative conveying systems, particularly when materials are conveyed in 'dilute phase' suspension flow. With pneumatic conveying systems, however, there are various means by which power requirements can be reduced. Conveying air velocity is a primary variable and this parameter has a significant effect, not only on power requirements but on material flow rate in addition. To add to the complexity of the problem, the conveyed material also has a major influence since material properties dictate whether the material can be conveyed at low velocity, in non-suspension flow, or 'dense phase'. Dense phase conveying implies conveying with a high concentration of material and this, in turn, requires a high pressure gradient, which introduces both conveying line pressure drop and conveying distance into the equation. With conveying air velocity having an influence on power requirements and material flow rate, specific energy is an equally important parameter and provides a useful basis of comparison with alternative conveying systems. Conveying data for a range of materials is used to illustrate how power requirements are influenced by air flow rate, and hence conveying air velocity. The additional influence of air supply pressure is also examined, as well as pipeline bore. Dilute phase conveying, and dense phase conveying in both fluidised sliding bed flow and plug flow, are also included since these display very significant differences in performance with respect to low velocity conveying.
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