Experimental investigation on the generic effects of gas permeation through flat vertical membranes

This work reports the effects of gas extraction through flat vertical membranes on bubble dynamics in a fluidized bed. Bubble properties such as size, number, velocity and shape play a key role in the hydrodynamics and consequently heat and mass transfer characteristics of fluidized bed (membrane) reactors. Thus the main focus of this work is to understand the bubble behaviour over different fluidization velocities, particle sizes, gas extraction rates and gas extraction locations. A pseudo 2D experimental setup with flat vertical porous plates placed at the back of the column was used for simulating gas extraction through a flat vertical membrane in a fluidized bed reactor. A Digital Image Analysis (DIA) experimental technique was applied in order to extract the bubble properties. Experimental results showed that the variation of gas extraction fraction has a minor effect on the bubble dynamics, with significant effects only present for high extraction rates and small particle sizes. Shifting the location of gas extraction more towards the centre of the bed had a larger influence on bubble dynamics. Deactivation of the two outmost membranes created a more uniform lateral bubble distribution profile which would be beneficial for reactor performance. However, deactivation of additional membranes caused the formation of central densified zones which obstructed the rising gas from reaching the central membranes. These effects could be clearly observed for small particles (196 μm), while larger particles (500 μm) showed little or no sensitivity to changes in gas extraction rate or location.