Two-fluid simulation of liquid drainage in oscillating packed beds for offshore floating applications

摘要

Three-dimensional modeling of liquid drainage dynamics in vertical, inclined and oscillating packed bed reactors is virtually inexistent in the literature. An attempt was made in this work where liquid drainage dynamics in vertical, inclined and oscillating packed bed reactors was analyzed via an unsteady-state three-dimensional two-fluid hydrodynamic model. Angular oscillations of the packed bed reactor between two angled symmetrical positions and between vertical and inclined position were considered while bed non-uniformity was described using radial porosity distributions. The simulation results highlighted the fully interpretable trends of the transient liquid flow in packed beds and underlined the differences in the transient behavior of the vertical, inclined and oscillating packed bed reactors. Although the initial period of liquid drainage was dominated by gravity regardless of bed configuration, the packed bed angle with respect to gravity direction had a significant impact on the liquid drainage dynamics. Cross-sections along streamwise direction both for static and oscillating inclined positions of the bed highlighted gas-rich uppermost and liquid-rich lowermost domains. Unlike vertical beds for which drainage occurred according to a quasi-plug flow of the liquid core region, drainage of inclined beds underlined 3D liquid flow structures with liquid-rich lowermost cross-sections which accelerated liquid withdrawal. Compared to the inclined bed case, liquid drainage was delayed under oscillating regimes as a result of reverse secondary flows induced by the column motion. The initial drainage process was controlled by the liquid flow in the bed lowermost part whereas oscillations between two symmetrically angled positions led to almost cross-sectionally uniform liquid drainage distribution. This is valuable and it is plausible that at long time the performance of packed bed reactors onboard offshore floating non stationary platforms is insignificantly affected by the oscillations between two symmetrically angled positions. (C) 2016 Elsevier Ltd. All rights reserved.