Experimental study on plug formation characteristics of a novel draft tube type feeder for vertical pneumatic conveying of coarse particles

Abstract

Plug flow receives attention because of its advantage to reduce particle attrition, pipe wear and energy consumption. A novel non-mechanical draft tube type feeder (DTF) for plug formation is proposed in this study for vertical plug conveying of coarse particles. Particles in the feeder are entrained by gas stream through draft tube direct into the bottom of riser pipe. The plug formation experiments with coarse particles (glass beads particle diameter 4.0mm) are conducted with this novel feeder. Plug formation characteristics are investigated by solids mass flowrate, high frequency pressure fluctuations and high-speed camera measurements. Power spectral density analysis is used to characterize frequency distribution of the high frequency pressure fluctuations. The experimental results show that natural plug formation is successfully achieved by the DTF for the superficial gas velocity ug in the range of 4.86 to 10.16m/s. A “particle cloud” is initially formed by particles entrainment effect in the bottom of riser, then its porosity decreases and length increases by further particles entrainment and pickup to form a plug. The solids mass flowrate shows a good linear relation to the gas mass flowrate. The plug length shows to be stochastic in a certain range around 0.11m, which is mainly attributed to the natural plug formation characteristics of the DTF. This study provides a natural plug formation feeder for vertical plug conveying of coarse particles. The feeder might be used for high temperature and/or high pressure operation environment in which high reliability is required. It might also be used to simplify the feeding device for vertical plug conveying of coarse particles.