Nuberical Simulation Of Fixed-Bed Reactor Coupling Exothemal With Endothemal Catalytic Reactions

Monolithic catalysts, which are uni-body structures composed of interconnected cells or channels, are widely used in environmental applications because of low pressure and high gas fluxes, and increasingly in many new reactor application such as chemical and refining process, catalytic combustion, amongst others.In this paper, first, reactive flow, mass transfer and heat transfer characteristics of a honeycomb catalytic reactor were studied under reaction conditions with the catalytic combustion of methane as a model reaction. A two-dimensional reactor model including a set of coupled balance equations of mass, heat and momentum transport is solved by utilizing the CFD method. The reactor model is tested against available data reported in the literature and a good agreement is found. Based on the simulation results, effects of process parameters such as feed composition, inlet velocity, inlet temperature on reactive flows are investigated. The results show that under the simulated conditions, the velocity profiles in channels are parabolic as in the case of laminar tube flows, and radical temperature and concentration gradients is smaller. Comparisons of the model prediction with evaluated values of the conventional Hagen-Poiseuille equation shows that the Hagen-Poiseuille equation under-estimates values of pressure drop in all simulated cases, while the relative deviation, around 40% in most cases, is highly related to the conversion degree and rate of reactions of interest. The value of Nusselt and Sherwood numbers are not the same as those observed in either the constant wall temperature or the constant wall flux cases, and have a high dependence on the reaction rate on the wall and operating conditions such as gas velocity, inlet temperature and inlet reaction concentration. Secondly, a two-dimensional model of catalytic plate reactor coupling endo/exothermal reactions is developed to predict the characteristics of mass, heat and momentum transfer under the reactive conditions. Model equations are solved by using the CFD method. Model predictions proved the feasibility of the reactor concept which takes advantages of an integrated endo/exothermal process. It is found that the ratio of catalyst loading on both channel walls is a key factor affecting reactor performances and need to be carefully adjusted so that the reactor could be operated under the preferred conditions with high conversion and without heat spots. The conductivity of metal channel wall is found to be another decisive factor in that when a high conductivity metal wall is used the heat transfer between the endo/exothermal reactions could be very effective, otherwise heat spots may occur.