The effect of gas addition on bubble dynamics in a fluidized bed with flat vertical membranes

This study investigates the hydrodynamics of a fluidized bed with flat vertical membranes for selective species dosing. A custom designed pseudo-2D column, equipped with a multi-chamber area on the back for gas permeation, was used to emulate a membrane assisted fluidized bed (MA-FB). The effect of global and local gas additions on bubble properties, solids hold up, solids circulation patterns and regime transition was investigated using Digital Image Analysis, Particle Image Velocimetry and pressure fluctuation measurements. Gas addition throughout the entire permeable area substantially reduced bubble size and velocity, while increasing the number of bubbles. In addition, a significant reduction in gas channelling through the centre of the column was observed. Concentrating gas addition towards the sides of the column further enhances bubble distribution over the lateral direction and totally removes gas channelling. Gas addition also caused an earlier transition to turbulent fluidization. The estimated bubble-to-emulsion mass transfer rate could be doubled when 30% gas addition was applied in the turbulent regime. These benefits maximise the potential of process intensification for fluidized bed reactor concepts using selective dosing through flat vertical membranes.