General Considerations for Process Modelling on a thermochemical Basis

Abstract:
Computational thermochemistry is frequently and successfully applied to model high temperature chemical processes. Since thermochemical data is available for a large number of phases and compounds it is possible to consider very large and complicated chemical systems including minor and trace components. However, there are some processes which are on the one hand characterized by very complex chemical conditions, but assuming homogeneous mixing or negligible chemical kinetics due to high temperatures is not quite justified. Since apparently no other method than thermochemistry is available to treat chemically complex systems, kinetic inhibitions and inhomogeneous mixing must be somehow accounted for when setting up a process model. For example, in order to account for incomplete conversion, certain portions of reactands must be excluded from a thermochemical equilibrium calculation. Thus, beyond pure thermodynamic description of a chemical reaction system, thermochemical process modelling also needs analysis of transport and temperature conditions in the considered process. By means of modelling examples it is shown that incorporation of some few simple and plausible assumptions on material transport phenomena into the thermochemical model already leads to significant improvement of simulation results with measurement data.