Tomographic analysis of dry and semi-wet bed fluidization: the effect of small liquid loading and particle size on the bubbling behaviour

Abstract

The hydrodynamic changes resulting from the addition of very small quantities of a non-volatile liquid into a cold conventional fluidized bed has been investigated, and compared with the effects of increasing the particle size in a dry bed. Three different particle mixtures belonging to Group A/B, Group B and Group B/D were assessed. The changes in regime transition velocities, pressure drop, bubble rise velocity, bubble frequency and bubble flow rate have been quantified by employing Electrical Capacitance Tomography measurements. A new analysis method for measuring the effective interparticle forces ( F ip ) and the effective drag force ( F d ) in a dry fluidized bed is described, and the results are presented in terms of different force ratios including the single particle weight ( W). It is shown that the addition of a few drops of liquid (<0.055 wt%) to a dry bed of Group B or B/D introduces similar hydrodynamic changes (except, in terms of bubble frequency) as that of increasing the bed particle size, and these particular changes shift the powders away from Group A/B behaviour. It is also illustrated that for beds of different particle sizes, a typical bubbling behaviour can be achieved at a specific gas velocity, this velocity coincides with the point of equality in hydrodynamic force ratios F d/W, F ip/W and E ip / F d .