(74a) Understanding Particulate Flow Behavior: Fluidized Bed, Pneumatic Conveying and Membrane Filtration Processes

A key focus of my group is on obtaining mechanistic understandings of particulate flow behavior in practical applications, like fluidized bed, pneumatic conveying and membrane filtration processes.

In fluidized bed systems, many of the probes used to understand hydrodynamics intrude into the environment they are measuring, although assumptions are typically asserted that the intrusive probes do not affect the data collected. This could be a poor assumption in some cases and conditions. In circulating fluidized bed risers, we found that intrusive fiber optic probe measurements consistently mis-predicted the solids concentration compared to the non-intrusive pressure drop measurements. The discrepancy was sensitive to superficial gas velocity, solid circulation rate, probe position and flow direction. Computational fluid dynamics simulations confirmed this, and indicated that particle momentum was lost at the leading edge of the probe and particles were spilling over to the probe tip.

Pneumatic conveying is a common operation in a wide range of chemical industries. A critical parameter for ensuring the efficient operation of pneumatic conveying systems is the minimum pickup velocity, U_pu, defined as the minimum superficial gas velocity required to initiate rolling or suspend a particle initially at rest. In view of the increasing prominence of nano-scale particles, we have attempted to bridge the knowledge gap between the nano- and micro-scale particles by investigating the U_pu of particle diameters traversing both scales. We found that the understanding available on micro-scale particles may not be directly applicable to nano-scale ones.

For membrane filtration processes, which is a key unit operation in water treatment, membrane fouling is the key obstacle that leads to higher energy costs and lower productivity. Solid-liquid fluidization, whereby the fluidized particles mechanically scour the membrane, is a promising energy-efficient means of mitigating membrane fouling. The optimal fluidization condition would give (i) good enhancement of permeate flux, (ii) uniform scouring across the membrane, and (iii) a modest power requirement. We have attempted to correlate the hydrodynamics of the fluidized particles with the extent of membrane fouling mitigation in order to understand and optimize such processes.