Study on flow characteristics of dilute phase flexible ribbon particles in a fluidised bed riser using particle tracking velocimetry

Flexible ribbon particles tend to rotate, deform (bend) and intertwine with each other in a fluidised bed due to their high flexibility and filamentous shapes. The movements of these particles have a significant influence on the formation of the so-called clusters, which lead to the complex hydrodynamic characteristic and subsequently poor equipment performance. However, there is currently no method for accurately defining and effectively measuring these complex particle movements, especially for their non-translational movements. In this paper, the flow characteristics of these particular flexible ribbon particles in a cold fluidised riser are studied using an improved particle tracking velocimetry (PTV) method. A certain number of characteristic points are selected in the longitudinal direction of a single flexible ribbon particle. The translation and non-translation movements of the characteristic points are defined and measured, and then the motion characteristics of the flexible ribbon particles are obtained. This work aims to provide an insight into this particular type of particle flow and to benefit the design and scale-up of related equipment. It is found that particles are most likely to collide, rotate and deform in the neighbouring wall regions with small superficial gas velocity. However, excessive particle contacts inhibit their free movements. By using regression analysis, an empirical correlation is established among the fractions of particles undergoing movement (both translational and non-translational), mass flow ratio (solid to gas) and particle Reynolds number.