Computational Fluid Dynamics Simulation of Catalytic Reactors

Abstract

Catalytic reactors are generally characterized by the complex interaction of various physical and chemical processes. Monolithic reactors can serve as example, in which partial oxidation and reforming of hydrocarbons, combustion of natural gas, and the reduction of pollutant emissions from automobiles are frequently carried out. Figure 1 illustrates the physics and chemistry in a catalytic combustion monolith that glows at a temperature of about 1300 K due to the exothermic oxidation reactions. In each channel of the monolith, the transport of momentum, energy, and chemical species occurs not only in flow (axial) direction, but also in radial direction. The reactants diffuse to the inner channel wall, which is coated with the catalytic material, where the gaseous species adsorb and react on the surface. The products and intermediates desorb and diffuse back into the bulk flow. Due to the high temperatures, the chemical species may also react homogeneously in the gas phase. In catalytic reactors, the catalyst material is often dispersed in porous structures like washcoats or pellets. Mass transport in the fluid phase and chemical reactions are then superimposed by diffusion of the species to the active catalytic centers in the pores. The temperature distribution depends on the interaction of heat convection and conduction in the fluid, heat release due to chemical reactions, heat transport in the solid material, and thermal radiation. If the feed conditions vary in time and space and/or heat transfer occurs between the reactor and the ambience, a non-uniform temperature distribution over the entire monolith will result, and the behavior will differ from channel to channel.Today, the challenge in catalysis is not only the development of new catalysts to synthesize a desired product, but also the understanding of the interaction of the catalyst with the surrounding reactive flow field. Sometimes, the exploitation of these interactions can lead to

Surface Reaction Kinetics of Steam- and CO2-Reforming as Well as Oxidation of Methane over Nickel-Based Catalysts

“…The approximation is related to the sizes of the computational cells in the flow field simulation, assuming that the local state of the active surface can be represented by means of values for this cell such as coverages (Θ ) and temperature. [50,51]. A surface reaction is expressed as:…”

Steam Reforming of Methane Over Nickel: Development of a Multi-Step Surface Reaction Mechanism

“…Surface reactions are modeled by a mechanism consisting of elementary-step-like reactions using the mean-field approximation [41,42]. Along the channel, the variation of gas-phase composition in axial and radial directions as well as the axial variation of the surface coverage with adsorbed species are taken into account.…”

“…The chemical source terms _ s i due to catalytic reactions are modeled by elementary-step based reaction mechanisms [42][43][44]. Homogeneous gas-phase reactions can be neglected under the conditions (temperature, pressure, residence time) applied in the present study.…”

Mass Transfer Effects in Stagnation Flows on a Porous Catalyst: Water-Gas-Shift Reaction Over Rh/Al2O3

“…where , and a are the pre-exponential factor, temperature exponent and activation energy, and and are the coverage parameters for species , in reaction , respectively [26][27][28].…”