CFD-DEM study on cohesive particles in a spouted bed

Abstract

In the present work, a numerical model is developed by means of CFD-DEM to study the behavior of cohesive particles in a spouted bed. In the model, the magnitude of the cohesive force was assumed as a specified constant which can be related to the cohesive force for molten particles or the liquid bridge force for wet particles. The evolutions of the flow patterns during the spouting processes at different cohesive forces were obtained. Particle concentration, velocity and circulation fluxes were systematically compared between cohesive and non-cohesive particles. Numerical results reveal that introducing the cohesive force will hinder the initiation of spouting from the compacted state of the bed. Increasing the cohesive forces leads to agglomeration, and correspondingly, higher gas velocities are required to break through the upper bed surface. When the cohesive force FCO=5Fg, where Fg is the particle weight, the spouted bed can be operated properly similar to the non-cohesive one. When the cohesive force is further increased to FCO=10Fg, obvious agglomeration appears at the moment of onset of fluidization. Particle concentration in the fountain region decreases apparently at the stable spout state because the cohesive force hinders the particle transfer from annulus to spout. The average particle velocity in the annulus decreases by about 50% compared to the spouted bed of non-cohesive particles at the same spouting gas velocity Us. When the cohesive force FCO=20Fg, de-fluidization happens in the spouted bed. Meanwhile, it is also found that the particle circulation fluxes under stable spouting condition decrease as the cohesive force increases at the same spouting gas velocity.