(121a) Optimum Conveying Conditions for the Pneumatic Conveying of Polyethylene Pellets and Similar Materials

There are many materials that, when conveyed over a wide range of air flow rates, show a distinct pressure minimum point in their operating characteristics. This is particularly the case with highly permeable materials, but also occurs with polymeric powders and innovatory pneumatic conveying systems that artificially induce permeability into a bulk material by means of by-pass piping.

A brief review will be given of the influence of bulk material properties on conveying performance characteristics before considering in more detail the specific case of permeable materials. For materials that exhibit a pressure minimum point, either an increase or a decrease in air flow rate from this point will result in a decrease in material flow rate, for a given operating pressure.

A means of identifying the location of the pressure minimum point is clearly desirable in terms of optimizing the performance of a conveying system in terms of material flow rate. Equally important, however, is the potential location of any optimum value of specific energy for a conveying system, in terms of air flow rate or conveying line inlet air velocity, since material flow rate reduces with reduction in air flow rate below the pressure minimum point.

Polyethylene pellets will be used in this study and it will be shown how the changing values of the various component pipeline pressure drop elements, with conveying air velocities from low velocity dense phase to high velocity dilute phase conveying, change the balance of system performance.