Fundamental investigation of plug conveying of cohesionless particles in a vertical pipe (pressure drop and friction of a stationary plug)

Abstract

A stationary packed bed of cohesionless particles is set up in a vertical pipe for the fundamental study of plug conveying. The effect of flow acceleration or deceleration on the pressure drop of the plug is investigated first. It is found that the pressure drop increases due to the flow acceleration and vice versa. Next, the following three kinds of experiments were made for the study of friction characteristics: 1. Friction between the plug and moving wall without air flow, 2. Friction between the plug and wall with downward air flow, 3. Friction between the plug and wall with upward air flow. The results are compared with the theory established in powder mechanics. The state of stress being of the active or passive case is discussed. Finally the problem of particles raining down from the back of the plug is studied. It is shown that the air velocity necessary to support the particles can be calculated based on a simple analysis of pressure distribution around the particles.

Flow regime diagram for vertical pneumatic conveying and fluidized bed systems

“…Note that the velocity which relates to the transition between the plug flow regime and blockage of the pipeline is absent from the diagram, that is because of a very poor theoretical and empirical basis presents in the literature. The literature proposes some theoretical models [8,50] conditions by comparing the friction, drag, gravity and adhesion forces, however the experimental basis of those models is inadequate. The non-dimensional terms of the diagram enable us to find a suitable flow state for any particle or gas property.…”

Pressure fluctuation instability in vertical plug formation of coarse particles with a non-mechanical feeder

“…Plug conveying receives continuous interests in recent years, due to the advantages of low particle attrition, low pipeline wear, and low energy consumption (Konrad, 1986;Rawat and Kalman, 2017). As summarized in our previous work (Li et al, 2018), previous studies on plug conveying mainly focused on pressure drop (e.g., Tsuji and Asano, 1990;Pan and Wypych, 1997;Shaul and Kalman, 2015;Kofu, 2016), stress and friction force (e.g., Tsuji et al, 1992;Mi and Wypych, 1995;Pahk et al, 2013;Shaul and Kalman, 2014;Nied et al, 2017), plug motion behavior (e.g., Strauβ et al, 2006;Sturm et al, 2010;Lecreps et al, 2014;Rawat and Kalman, 2017), and transport boundaries (e.g., Wypych and Yi, 2003;Setia et al, 2015), with little attention paid to the process of plug formation.…”