DYNAMICS OF GAS-PHASE AND SOLID-PHASE REACTIONS IN FIXED-BED REACTORS

Volumetric thermal capacity of solids is higher than that of gases by three orders of magnitude. We show that this leads to a dynamic respon se of a fixed bed reactor involving a solid phase reaction which is sl uggish compared to that involving a gas phase reaction of the same kin etic and thermodynamic parameters. In the dynamic regime where the inl et gas temperature is lower than the initial bed temperature, fixed be d reactors exhibit the wrong way behavior. We show that in this regime , the transient maximum temperature rise and the steepness of the temp erature front are affected by the phase in which reaction occurs, by t he inlet gas temperature and by the volumetric heat transfer rate. The maximum temperature rise in the bed is lower for the solid phase reac tion and decreases with a decrease in the volumetric heat transfer coe fficient. These and other new findings are obtained by our newly devel oped robust, completely implicit spatially and temporally adaptive num erical algorithm which can capture steep moving fronts in fixed bed re actors.