Investigating the conveying mechanism of particulate plugs with stationary layers

This paper presents an investigation into pneumatic conveying mechanism of particulate plugs with stationary layers. A plug flow regime may exist in pneumatic conveying systems operating with high-pressure gradients and low gas velocities. The most significant advantages of transporting particulate materials in a plug form is low energy consumption, low particle attrition and low pipe erosion. However, due to inaccurate approximations of the required pressure gradient of the plug, this kind of conveying processes can lead to pipeline blockage. This study presents a model for predicting pressure loss of particulate plugs that include a pick-up mechanism of a stationary layer of particles to be introduced between the plugs. The mechanism takes into account various parameters including the fraction of stationary layer (alpha), pipe and particulate characteristics, plug velocity and slope of pick-up layer. It was shown that the plug repose angle, theta, plays a very important role in determining the characteristics of plug flow conveying regime. Moreover, it was showed that the bulk density ratio (between the bulk density of the plug and the stationary layer) in some cases may make a significant contribution to pressure loss prediction. The model developed in this study was validated by the experimental measurements of other research teams and good agreement was found. The results of the present work provide information for updating major characteristic variables for pneumatic conveying systems operating as a plug flow. This can be useful both for designers and for future research studies. (C) 2014 Elsevier B.V. All rights reserved.