Demarcation on a new conventional circulating fluidization regime in liquid-solids fluidization via experimental and numerical studies

A new type of liquid-solid circulating fluidized bed, the conventional circulating fluidized bed (CCFB), which operates at superficial liquid velocities below the particle terminal velocity (U_t), was delineated through experimental and numerical studies, in both upward and inverse liquid-solid fluidization systems. The CCFB system was essentially operated in the conventional fluidization regime but with continuous feeding of particles into the liquid inlet end of the fluidization column and particles moving along with the liquid to the other end of the column to achieve solids circulation or circulating fluidization. An extended operating window of the CCFB was numerically studied using the Eulerian-Eulerian two-fluid model based on the existing experimental data. The effects of particle properties and operating conditions on the CCFB were studied. The hydrodynamics in the CCFB were also compared with that in a circulating fluidized bed (CFB). An inverse CCFB using particles with a density lower than the liquid was also investigated by simulations and compared with the upward CCFB. A new flow regime referring to the CCFB operating mode for the liquid-solids fluidization systems, both upwards and inverse, was proposed and situated in between the conventional and circulating fluidized beds.