Discrete element simulation for pneumatic conveying of granular material

The pneumatic transport of granular material is a common operation frequently employed to transport solid particles from one location to another. It is well established in the literature that different flow regimes can arise in such transportation processes depending on the system geometry and operating conditions used. In this study, the pneumatic transports of solid particles in both vertical and horizontal conveying lines were studied numerically using the discrete element method coupled with computational fluid dynamics. The simulation outputs corresponded well with reported experimental observations in terms of the different flow regimes obtained at different operating conditions. In the vertical pneumatic conveying simulations, two different flow patterns corresponding to the experimentally observed dispersed flow and plug flow regimes were obtained at different gas velocities and solid concentrations. Similarly, the homogeneous flow, stratified flow, moving dunes, and slug flow regimes previously reported to occur in horizontal pneumatic conveying were also reproduced computationally in this study. Solid concentration profiles obtained by spatial averaging along the length of the pipe showed a symmetrical but non-uniform distribution for dispersed flow and an almost flat distribution for plug flow in vertical pneumatic conveying. The profile for stratified flow in horizontal pneumatic conveying showed higher solid concentration near the bottom wall due to the effects of gravitational settling, while that for slug flow was flat. Hysteresis in solid flow rates was observed in vertical pneumatic conveying near the point where transition between the dispersed and plug flow regimes was expected to occur. Solid flow rates were also found to be more sensitive towards the coefficient of friction than the coefficient of restitution of particles and the pipe walls in a sensitivity analysis study of these parameters.