Numerical and experimental studies of catalytic combustion in a packed bed reactor.

摘要

A one-dimensional, non-equillibrium mathematical model of the catalytic combustion in a packed bed reactor was developed. The model includes heat conduction, convective and radiative heat transfer, axial diffusion, and accounts for both homogeneous (gas-phase) and heterogeneous (surface) reactions of the Arrhenius type. The unsteady state equations of conservation of mass, chemical species, and energy with appropriate boundary and initial conditions were solved using a finite-difference procedure. Numerical simulation was conducted with mainly lean premixed preheated methane-air mixtures over platinum and a binary mixture of Co3O4/Cr2O 3 catalysts for a range of equivalence ratios, approach velocities, and inlet temperatures for three different cases: (i) inert bed (gas-phase), (ii) heterogeneous reaction only, and (iii) both heterogeneous and homogeneous reactions. The effects of the bed porosity, solid thermal conductivity, and bed length on methane conversion were also studied. It was found that the solid thermal conductivity has a strong influence on methane conversion when both homogeneous and heterogeneous reactions were included. The results also showed that the bed length affected the methane oxidation significantly especially when the bed porosity was greater than 0.45.; The catalytic combustion of other gaseous-fuels (ethane, propane, carbon monoxide, and hydrogen) over platinum and binary mixture of Co3O 4/Cr2O3 catalysts was also examined numerically. The results show that the conversion of these fuels exhibits similar behavior; i.e. the conversion of the fuel increased with an increase in the inlet temperature and equivalence ratio, and a decrease in the approach velocity. It was also found that the complete conversion of hydrogen took place at much lower inlet temperatures than those required for the complete conversion of other fuels. The obtained results are consistent with the reactivity of theses fuels as well as with the observed experimental trends.; Experimental studies for model validation were also conducted for the catalytic oxidation of lean methane-air mixtures within the packed bed reactor. The model developed together with the corresponding experimental data was used to establish the kinetic data for global surface reaction (the activation energy and the pre-exponential factor), over platinum and Co3O 4/Cr2O3 catalysts for the fuels employed within the packed bed reactor.