Thermomechanical instability in steady operating regime of continuous-flow chemical reactor with fixed catalyzer bed

Abstract

A continuous-flow chemical reactor with fixed bed is a vessel filled with a porous catalyzer through which a liquid or gaseous reagent mixture is filtered. The motion of the mixture in this system is maintained by the pressure differential which compensates for the hydraulic resistance.

The complete system of equations describing the mass-and heat-transfer processes in the continuous-flow chemical reactor includes the mass, momentum, and energy conservation equations [1], Usually, in the study of the existence and stability of steady reactor operating regimes, very simple reactor models are analyzed, in which only the mass-conservation equation in the form of the diffusion equation and the energy-conservation equation in the form of the heat-conduction equation are taken into account. The equation of motion drops out of consideration, since the velocity of the reagent mixture with the reaction products through the reactor is considered given and unvarying for disturbances of the steady operating regime.

The purpose of the present study is to indicate the possibility of instability in the steady-process regime of a chemical reactor, which is associated with the fact that any temperature (and also concentration) variation within the reactor with disturbances of the steady regime will, generally speaking, lead to variation of the mixture viscosity and, consequently, to variation of the hydraulic resistance and the filtration velocity. This interconnection is an additional factor which may have a significant effect on the behavior of disturbances of the steady regime.

In contrast with thermal, kinetic, and thermokinetic instability [2], it is natural to refer to the instability being investigated as thermomechanical instability. Let us consider an example.