8336
Ind. Eng. Chem. Res. 2007, 46, 8336-8342
Hydrodynamic Observations of Trickle Beds under Filtration Conditions Mohsen Hamidipour,† Faı1c¸ al Larachi,*,† and Zbigniew Ring‡ Department of Chemical Engineering, LaVal UniVersity, Que´ bec, QC, Canada G1K 7P4, and Secondary Upgrading & Refining, National Centre for Upgrading Technology, 1 Oil Patch DriVe, DeVon, AB, Canada T9G 1A8
Experiments were carried out to investigate the evolving hydrodynamics of trickle-bed reactors as altered by the concomitant filtration of a flowing suspension containing micrometer-scale fines. The filtration efficiency, two-phase pressure drop, and bed specific deposit (mass of deposited fines per unit of reactor volume) were monitored using flows of air and a kaolin-containing kerosene suspension to clarify the roles of packing (smooth vs porous collectors), bed height, bed entrance distribution of the suspension, makeup addition in recirculation mode, gas superficial velocity, and flow regime transition. It was observed that deposition did not exhibit a seamless pattern but rather consisted of scattered mesoscale islands of deposits, several collectordiameters in size, separated by relatively large plug-free multiple interconnected pores. These corridors favored the in situ development of bed maldistribution that favored short-circuiting of the flow and leveling off of the bed pressure drop. Contrary to expectation, the transition from trickle flow to pulse flow due to progressive bed obstruction was not systematic, and to occur, it required a minimum clean-bed starting liquid holdup value. 1. Introduction Bitumen and unconventional heavy crude resources in the world exceed the known conventional crude oil resources; Canadian oil sand bitumen could be a valuable alternative to respond to the decreasing trend of high-quality crudes.1 Upgrading of bitumen vacuum bottoms yields so-called bitumen-derived crude (BDC). Primary upgrading via C-rejection (delayed/fluid coking) or H-addition (LC-fining)2 produces a syncrude high in sulfur and nitrogen,3 whereas secondary upgrading, which includes hydrotreating, is necessary to comply with the lowsulfur specifications in the syncrude oil fractions. Heavy gas oil (HGO), representing 40% of BDC liquid yield, is difficult to refine into the fuel boiling range because of its low cetane number3 and also because of its content in fines (
