Theoretical and experimental investigations on particle rotation speed in CFB riser

Particle rotation is a common phenomenon in gas–solid two-phase flows. The paper presents theoretical and experimental investigations on particle rotation speed in the gas–solid flow inside a cold CFB riser. The possible particle rotation speed, caused by non-homogeneous flow field and particle collision, and its variation with time were investigated. The average particle rotation speed was predicted with considerations of particle size, average particle collision velocity, particle collision rate and particle number density. It is found that particle collision is the most significant reason for particle rotation. The maximal and average rotation speed for particles with an average size of several hundred micrometers in the CFB riser under typical working condition may be several thousand revolutions per second and several hundred revolutions per second, respectively. The rotation speed of glass beads with an average size of 500μm in the upper dilute zone of a cold CFB riser was measured by using a high speed digital imaging system. The variation of particle rotation speed with time was observed, which is in accordance with the theoretical result. The average rotation speed for glass beads was statistically analyzed based on a large number of particle examples. With several factors taken into account, the experimental result is considered to agree with the theoretical one.