Identification and characteristics of different flow regimes in a circulating fluidized bed

A series of experiments was conducted in a 0.3-m diameter circulating fluidized bed (CFB) cold model to evaluate the operating flow regimes and their transitions. A single unambiguous experimental method was developed to identify the transitions between CFB operating regimes. Experiments were conducted at riser gas velocities ranging from dense phase turbulent, through fast fluidization (S-shape riser pressure profile), and up to dilute-phase flow regimes. A transient method was applied to a low density, Geldart Type B, cork bed material. Two distinct transition velocities were found by analyzing the time required to empty out all solids from the riser of the CFB after cutting off solids flow. The lowest transition velocity marked the transition between the dense-phase turbulent and the fast fluidization flow regimes, while a higher or second transition represented the transition between the fast fluidization and the dilute-phase flow regimes. Based on the experimental results, the axial pressures and its fluctuations along the riser exhibited markedly distinct profiles in each of the three different operating flow regime regions as defined by these two transport velocities.