(359d) Influence of Gas Flowrate On Behavior of High Thermal Conductivity Microfibrous Entrapped Catalyst for Exothermic FTS Reaction

Fischer-Tropsch synthesis (FTS) is a highly exothermic reaction with challenging heat transfer issues.   Enhanced heat transfer has been realized by using microfibrous entrapped catalysts (MFEC) to perform FTS in fixed bed reactors.  Pseudo-homogeneous thermal conductivities greater than 9 W/m-K have been obtained using MFEC made from highly conductive copper fibers.  Much larger tubes can be used for FTS using Cu-MFEC than is possible using packed beds of extrudates.  2D (r,z) Simulations and recent experiments indicate that tubes as large as 100 mm ID can safely be used for this highly exothermic reaction without danger of runaway.  The pseudo-homogeneous thermal conductivity of MFEC made from copper, nickel or stainless steel without flow correlates with the electrical conduction through the sintered metal matrix in terms of a junction factor.  In flowing conditions the pseudo-homogeneous thermal conductivity increases linearly with the Reynolds number.  This behavior is investigated by considering the tortuous nature of the sintered fibers.  In the wet-lay papermaking process used to prepare preforms [1] the fibers form in stacks randomly oriented in the horizontal plane.  Sintering produces contact joints between fibers lying in random directions, so the paths through the metal fibers are tortuous.  This effect is accounted for by modeling the tortuous fibers as a separate phase in a segregated temperature, plug flow, fixed bed tubular reactor (ST-PFFBTR) model for FTS.  Heat can flow from the main fiber phase that contacts the wall through the gas phase to the extra fiber phase that does not contact the wall.  Also, the domain of the influence of this separate fiber phase only extends some multiple of the original length of the fibers used to prepare performs by wet-lay papermaking process.  This segregated temperature simulation uses heat transfer correlations to model heat transfer in the reactor without resorting to pseudo-homogeneous thermal conductivity and lumped wall heat transfer coefficients that must be estimated. Flux limiters are applied to make the simulation more robust. 

[1] Harris D. K., Cahela D. R. and Tatarchuk B.J., “Wet layup and sintering of metal-containing microfibrous composites for chemical processing opportunities,” Composites Part A 32 (2001) 1117-1126.