MAXIMUM TEMPERATURE IN A REVERSE-FLOW REACTOR WITH 2 INDEPENDENT REACTIONS

Estimates are derived for the maximum bed temperature in a reverse-flo w reactor in which two reactions, having relatively low adiabatic temp erature rise, occur and are mass-transfer limited at the high temperat ure zone in the bed. The estimates are derived using a pseudohomogeneo us model and a step-approximation of the temperature dependence of the observed rate expression. When the switching frequency is very high, the estimate of the bed temperature is given by eq. (16). When the swi tching frequency is very low, the reactions may be completed either in a temperature front moving at a constant velocity and shape, or in tw o consecutive temperature fronts, separated by an almost constant temp erature plateau, with the upper front moving faster than the lower one . The corresponding maximum bed temperature for these two cases is giv en by eqs (29) and (38), respectively. A simple criterion predicts whi ch of the two types of front movement occurs. The estimates show that for reactants with low adiabatic temperature rise, the maximum bed tem perature depends mainly on the critical temperature of the reactions, defined by eq. (8), and only weakly on the switching frequency. When t he two critical temperatures are widely separated and both reactants a re converted in the reactor, the maximum bed temperature is essentiall y independent of the reaction occurring at the lower temperature. (C) 1997 Elsevier Science Ltd.