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An implementation of a simplified microkinetics model in three-dimensional computational fluid dynamics (CFD) simulations of an ethylene oxide fixed-bed reactor is proposed. An existing microkinetics model in the literature is simplified to a model with general rate expressions to reduce the complexity of the computations. It then is coupled with CFD simulations of flow in the fixed bed and transport inside the catalyst particles. Illustrative CFD simulations are carried out in a randomly packed bed of 120 spherical particles, which take into account surface species under steady-state conditions in the particles. The proposed approach represents a practical method to integrate simplified surface chemistry with a realistic-scale fixed bed for more in-depth analysis. It is shown that the surface coverages can be greatly affected by the surrounding flow conditions; furthermore, the effects of transport limitations, products, and different inlet compositions on the ethylene oxide selectivity are studied. [ABSTRACT FROM AUTHOR]

A newvelocity-based approach to fixed bed radial heat transferis presented. Axial and radial velocity components were averaged fromdetailed 3D computational fluid dynamics (CFD) fixed bed simulationsof computer-generated beds of spheres and used to model radial thermalconvection. The convection terms were coupled with a radially varyingstagnant bed thermal conductivity in a 2D pseudocontinuum fixed-bedheat transfer model. The usual effective radial thermal conductivity krand apparent wall heat transfer coefficient hwwere not used, and there were no adjustableparameters. The radial and axial temperature variation predicted bythe velocity-based model agreed well with the angular-averaged temperaturesfrom the detailed 3D CFD simulations over the range 80 ≤ Re≤ 1900 and for N= 3.96, 5.96,and 7.99. [ABSTRACT FROM AUTHOR]

Complex interactions between steam methane reforming reaction rates, conduction, and diffusion inside cylindrical catalyst particles with holes, and the external flow and temperature fields near the heated tube wall were shown in detail using computational fluid dynamics and compared to prior work on full cylinders. This work highlights the differences caused by the particle features. Simulations were done under industrial tube inlet conditions at a constant pressure drop for one-, three-, four-, and six-hole cylinders. Heat and mass fluxes were within 10% for all particle surfaces; the holes provided the reactant good access to the particles. The six-hole catalyst particles offered the best temperature distribution and reaction rate. However, the four-hole particles gave a higher mass flow rate and lower tube-wall temperature for a set pressure drop. [ABSTRACT FROM AUTHOR]