Micro-structured fluidized bed membrane reactors: Solids circulation and densified zones distribution

• The hydrodynamics of a novel membrane assisted micro-structured fluidized bed (MAmFB) is studied in this work.
• Particle Image Velocimetry (PIV) and Digital Image Analysis (DIA) techniques have been used for non invasive study.
• The turbulent fluidization regime with a relatively low gas extraction velocity reduce the densified zones.
• The micro-structured reactors can be used with state-of-the-art membranes with reduced densified zone formation.

The present paper reports an experimental investigation on the hydrodynamics of a novel membrane assisted micro-structured fluidized bed (MAmFB) operated in bubbling or turbulent flow regimes. The effects of gas addition and gas extraction through flat porous membranes confining the fluidized bed on the bubble size distribution, solids holdup distribution and solid circulation patterns have been evaluated by the combination of two non-invasive techniques, viz. Particle Image Velocimetry (PIV) and Digital Image Analysis (DIA). The experimental results show that the micro-structured fluidized bed membrane reactor improves the solid circulation compared with bigger size membrane reactors where the extraction of gas result in parts of the bed that are completely defluidized and stagnant at the membrane walls. However, also in case of small reactors great care has to be paid to the gas extraction velocity relative to the fluidization velocity. All the results indicate that the amount of densified zones (zones where solids lumps with a local solids hold-up close to the minimum solids packing have a much lower velocity than the rest of the emulsion phase) can be reduced drastically by working in the turbulent fluidization regime with a relatively low gas extraction velocity. This study indicates that actual state-of-the-art membranes can be used in the turbulent regime without the formation of densified zones, thus avoiding additional mass transfer resistances (concentration polarization).

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