(216b) Pattern Formation Insights from Computational Fluid Dynamics Modeling of Exothermic Shallow Packed Bed Reactors

Stationary or spatio-temporal patterns of catalytic reactions can cause operating challenges in shallow packed bed reactors with large diameter/depth aspect ratios [1] [2] [3]. Partial ignition patterns were observed in a pilot scale oxidative coupling of methane (OCM) reactor under operating conditions approaching the extinction limit. A computational fluid dynamics (CFD) model based on porous media that has conductive, convective, and effective radiative heat transfer along with global reaction kinetics was developed to understand the role of different physico-chemical processes that control pattern initiation and formation. Results showed that the partial ignition can be triggered by bed nonuniformity (catalyst distribution, activity, etc.), nonuniform initial conditions, flow maldistribution, heat loss through walls, and buoyancy effects. The non-uniform mesh leads to specific pattern formation solution indicating that among all perturbations, bed nonuniformity is dominant. The simulations also reveal the mechanism of pattern locking due to thermal-fluid-chemistry interaction after it is triggered [4]. The stability and robustness of these patterns along with ways to mitigate them will be discussed.

[1]	B. Marwaha and D. Luss, "Hot zones formation in packed bed reactors," Chemical Engineering Science, vol. 58, pp. 733-738, 2003.
[2]	Y. Matros, "Unsteady processes in catalytic reactors," Studies in Surface Science and Catalysis, vol. 22, p. 256, 1985.
[3]	V. Balakotaiah, E. L. Christoforatou and D. H. West, "Transverse concentration and temperature nonuniformities in adiabatic packed-bed catalytic reactors," Chemical Engineering Science, vol. 54, pp. 1725-1734, 1999.
[4]	D. Nguyen and V. Balakotaiah, "Flow maldistribution and hot spots in down-flow packed bed reactors," Chemical Engineering Science, vol. 49, no. 24B, pp. 5489-5505, 1994.