Experimental Investigation of Inverse Liquid-Solid Fluidized Bed Hydrodynamics

AbstractInverse liquid-solid fluidized beds have recently received increased attention, particularly for use with wastewater treatment bioreactors (i.e., particle-supported biofilms). The flow behaviour of free-rising light particles is especially interesting because their drag coefficients deviate from the standard drag curve. For this reason, the work presented in this thesis was focussed on investigating the minimum fluidization velocity () and the steady-state bed voidage associated with four particles, with densities of 28, 122, 300, and 678 kg/m3, in a conventional inverse fluidization regime. All experimental measurements were completed using a large-scale system comprising a downer column with a diameter of 200 mm and a height of 4.5 m. Substantial deviations from the Wen and Yu correlation predictions were evident in the experimentally determined Umf values due to the limited range of particle properties. A modified Wen and Yu correlation is therefore proposed as a means of improving predictions related to free-rising light particles. The bed voidage associated with the particles studied was also explored experimentally. A proposed force balance model has been developed for predicting bed voidage based on an analysis of the liquid-solid interaction forces acting on a suspended particle. Within the range of solid particle properties examined, the proposed model has demonstrated adequate accuracy with respect to predicting bed voidage in inverse liquid-solid fluidized beds.