Approximate characteristics of a moving temperature front in a fixed-bed catalytic reactor

The study deals with a nonstationary process of mass and heat transfer acco mpanied by a chemical reaction occurring in a catalytic reactor. Based on t he assumptions of the 'ideal thermal front' in the reactor, approximate sol utions are obtained for the equations that describe the process. Thus, rela tions are derived which define the principal properties of the thermal fron t, namely its propagation velocity in the bed and the maximum temperature o f the front. The above relations express these properties in terms of dimen sionless numbers that characterise the chemical reaction taking place in th e reactor and the operating parameters of the vessel. Good agreement is fou nd between the front properties as calculated using the approximate formula e and those yielded by the integration of the complete model equations, i.e . the exact values. A method is proposed for determining approximate temper ature profiles in the bed, which is by far simpler and less rime-consuming than the integration of a complete set of partial differential equations. B oth the formulae derived and the method proposed for calculating the temper ature profiles along the bed may be useful in the design of reactors with t he periodic reversal of the feed mixture. They enable the effect to be anal ysed of the various operating parameters upon the propagation velocity of t he thermal front and its maximum temperature, without resorting to tedious and time-consuming trial and error methods that require repeated integratio n of the model equations. (C) 1999 Elsevier Science S.A. All rights reserve d.