NUMERICAL PROBLEMS ENCOUNTERED IN THE SIMULATION OF REACTIVE ABSORPTION - DAE INDEX REDUCTION AND CONSISTENT INITIALISATION

A general simulation model able to represent mass transfer in the pres ence of chemical reactions is presented. The model developed describes the behaviour of an absorption column. This model needs to be able to access certain information such as kinetic constants, equilibrium con stants, activity coefficients,:etc. Among these auxilary models, is th e need to be able to calculate the mass flux and compositions at the b oundary of the diffusional Nm. A set of equations describing the film has therefore been developed, and its resolution has proved to be trou blesome. Indeed we have run into two problems that have had to be tack led. The problems encountered are directly due to the nature of the eq uations to be solved, that is a system of differential algebraic equat ions (DAE). These problems arise from the approach desired to treat th e equations, based on Gear's algorithm. The first problem deals with t he solution of high order index systems, and the second involves the n ecessity of having consistent initial conditions. A suitable procedure has been implemented for index reduction, and several. techniques hav e been tested for the obtention of consistent initial conditions. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.