The
trickle-to-pulse flow regime transition in silicon-infiltrated
silicon carbide (SiSiC) foam packed fixed bed reactors has been investigated.
Based on the film stability concepts of Grosser et al. [AIChE J.1988341850] as well as Attou and Ferschneider [Chem. Eng. Sci.200055491], two predictive models have been adapted to foams’ specific
geometric parameters. To account for the different nature of solid
foams and their interactions with various fluids, the fixed bed characteristics
(specific surface area and bed porosity) and fluid specific parameters
(gas and liquid density, liquid viscosity, surface tension) have been
incorporated in the model. Ergun parameters and static liquid holdup
which are required for the modeling of the prevailing tractive forces
were determined experimentally. The modeling results were compared
to regime transition measurements performed for SiSiC solid foams
with different linear pore densities (20, 30, and 45 PPI), for different
reactor diameters (50 and 100 mm) and initial liquid distributors
(spray cone nozzle and multipoint distributor) as well as liquids
with various physicochemical properties (water, Tergitol, 50% glycerin)
under ambient operating conditions. Compared to conventional random
fixed bed reactors, the onset of pulsing in solid foam packed fixed
beds is significantly shifted toward larger liquid and gas fluxes
allowing high throughputs in the trickle regime. Moreover, the homogeneity
of initial liquid distribution strongly affects the trickle-to-pulse
flow transition.
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