Cyclic Operation Strategies in Trickle Beds and Electrical Capacitance Tomography Imaging of Filtration Dynamics

Abstract

The dynamics of propagating liquid pulsations generated via various cyclic operation strategies in trickle beds was monitored through electrical capacitance tomography (ECT) for gas and liquid superficial velocities in the range of trickle flow regime. The characteristics of ON-OFF liquid, ON-OFF gas, and gas/liquid alternating cyclic operations were compared in terms of mean liquid holdup, pressure drop, pulsation intensity, pulsation propagation velocity, and spatial maldistribution maps of liquid holdup and liquid pulsation propagation velocity. The morphological features of liquid holdup pulsations as a function of cycle frequency were characterized in terms of breakthrough, plateau, and decay times. Gas/liquid alternating cyclic strategy was shown to produce long-lived liquid pulsations under the applied operating conditions and thus could be viewed as a new process intensification means to achieve uniform phase holdup and velocity distributions. In ON-OFF liquid cyclic operation, pulsation velocity did not increase along the bed unlike the ON-OFF gas and gas/liquid alternating cyclic modes where increased pulsation velocities were able to give rise to pulse flow regime. The gas/liquid alternating cyclic operation resulted in the shortest breakthrough and decay times and the longest plateau time, thus approaching the ideal square-shaped inlet pulsations for symmetrical splits. ECT imaging was also used to scrutinize the dynamics of local deposition of fines in trickle beds fed with kaolin suspensions under the three cyclic operations. Data revealed that applying ON-OFF gas and gas/ liquid alternating cyclic methods resulted in significant reduction of fines deposition. This suggests new practical solutions for possible industrial implementation of self-cleaning modulation strategies of trickle beds subject to unwanted filtration during suspension flows.

Hydrodynamics of inclined packed beds under flow modulation ‐ CFD simulation and experimental validation

“…Such leap was ascribed to resumption of the gas flow during gas ON portion whereby the gas-liquid interaction is enhanced and the excess liquid is forced out of the bed. 12,35 Figures 11a1-c1 demonstrate that the morphology of liquid waves generated by gas/liquid alternating cyclic operation (5 s liquid-5 s gas, U g 5 0-12.2 cm/s, U l 5 2-0 mm/s) was also captured by the CFD model. This cyclic strategy is in fact a combination of liquid and gas cyclic operations.…”

“…The measured capacitance maps were converted to normalized permittivity per-pixel distributions (32 3 32 pixels per image) through a Tikhonov reconstruction algorithm discussed elsewhere. 35,36 The ECT sensor was calibrated between the lowest (fully drained) and highest (fully flooded) permittivity limits to generate per-pixel dynamic liquid saturations from the corresponding normalized mixture permittivity data. 36 The limiting cases of drained and flooded beds were assigned to bed states of 0% (low reference) and 100% (high reference) liquid saturation, respectively.…”

“…For additional details on the application of ECT technique, data processing, and validation in the vertical and inclined packed beds, our group's previous studies can be consulted. 7,12,17,[35][36][37] Eulerian CFD Model A 3D unsteady-state Eulerian multifluid CFD model was used to simulate the hydrodynamics of inclined gas-liquid cocurrent downflow packed beds under cyclic operation. The Eulerian approach treated gas, liquid, and solid phases as mutually interacting interpenetrating continua.…”

Modulation of suspension electrical conductivity to counter fines plugging in trickle-bed reactors

“…8 The effect of periodic flow perturbations on the extent of filtration was experimentally investigated where the velocity of suspension and/or gas can be switched back and forth between specified levels. 9 Among the tested approaches, gas/liquid alternating cyclic operation gave the best results in terms of deposition removal.…”

Experimental Study on Liquid Spread and Maldistribution in the Trickle Bed Reactor Using Electrical Resistance Tomography

“…A liquid rich zone flushes down the stagnant liquid and causes complete wetting of catalytic particles. In order to eliminate problems involved in trickle flow operation, few studies (6,7,8) suggest operating in natural pulsating flow or periodic gas-liquid feed strategy that induces pseudo pulsating flow at rather low time averaged flow than that of naturally occurred. However, complex equipment and scale-up problems prevent practical applications.…”