Development of thermal stresses in reacting media—I. Failure of catalyst particle

Abstract

Analysis of the kinetics of a chemical reaction with heat and mass transfer forms an important part of reactor design. For a strong exothermic reaction, steep steady-state or transient temperature gradients can exist and consequently thermal stresses may develop in reactor walls, catalyst carriers or the solid reaction medium itself. To our knowledge, the important reaction engineering problem of thermal stress development in reacting media has not been addressed in the literature so far. In this paper, which is the first in a series of papers dedicated to the interaction of exothermic chemical reaction with heat and mass transfer, and thermal stress development, an important problem of catalyst support failure, due to excessive thermal stress development, is analysed. Thermal mechanical and chemical effects occur on different time scales and the thermo-elastic and energy equations are solved on two different time scales. On the time scale of mechanical disturbance relaxation, the effect of inertia is included and a thermal shock propagates through the catalyst sphere. On the time scale of thermal relaxation, the solution is obtained numerically for a case where the surface reaction operates in the kinetic state, as well as a case where the reaction jumps to the ignited state. In the latter case, stresses are found to exceed the fracture stress of α-alumina. Thermal stress is found to increase with pellet radius.