Investigation on the fluidization dynamics of cohesive geldart B particles using X-ray tomography and pressure fluctuation analysis

Abstract

In many applications of fluidized reactors, the particles processed are cohesive. The presence of inter-particle cohesive force causes different fluidization dynamics compared to non-cohesive system. This paper studied the fluidization dynamics of cohesive Geldart B particles in a three dimensional fluidized bed. X-ray tomography and in-bed pressure fluctuation analysis were conducted to reveal bubble behaviors as well as overall fluidization status. The results show that increasing cohesive force facilitates bubble coalescence, leading to the growth of bubble size. When bubbles grow to similar dimensions to the column cross section, the particles above bubbles are lifted as a particle slug and the fluidization turns to slugging. As the cohesive force increases, the energy distribution of power spectral density of pressure signal changes from mono-modal shape to bi-modal shape where two peaks relate to slugging and normal fluidization respectively. At low static bed heights, no slugging takes place even under high cohesive forces. Therefore, to avoid slugging in the practical application, the static bed height should be kept as low as possible. With further increase in the static bed heights, bubbles keep growing by continuous coalescence and become considerable near the bed surface, which triggers slugging and causes an increase in slugging duration.