Radial flow reactor optimization for highly exothermic selective oxidation reactions

Radial flow reactors (RFR's) with catalyst external to cooling tubes are compared with fixed bed, axial flow cases for highly exothermic, selective oxidation reactions. Steady state, one dimensional mass, heat and momentum balances were integrated for the butane to maleic anhydride (ma) reaction at commercially relevant conditions. “Triangular” kinetics for the main, total oxidation and product decomposition reactions were utilised (Wellauer et al., 1986). From this work, diffusion restrictions in the particles and interphase heat transfer were approximated making the reactor model quasi-heterogeneous. From the literature, heat transfer for radial flow through a packed bed with cooling tubes was estimated in addition to pressure drop for radial flow using flow parameters based on “local” values and including the bed voidage occupied by the cooling tubes. Comparison of the optimal cases at the same ma yields showed significant advantages for RFR's with respect to an increase in productivity, a decrease in reactor volume, lower hotspot temperatures and steam production and a significantly lower pressure drop. Stable operation was predicted for butane concentrations (5 mol %) within flammability limits but below ignition temperatures and well within runaway conditions for axial flow.