Dynamic modeling of the methanol synthesis fixed-bed reactor

A dynamic model for a fixed-bed reactor for methanol synthesis is presented. The model is compared with its steady state version. The analysis points out that the numerical stability of the dynamic model is improved by opportunely increasing the level of detail. It is appropriate to introduce the diffusion terms, to work with mass fractions, to select good discretization methods for each term of the model equations. Since these aspects are usually neglected in steady state analysis, this paper investigates step-by-step their implementation, emphasizing their importance (I) in the transformation of an original hyperbolic PDE system into a parabolic PDE system; (II) in removing non-physical oscillations generated by first-order systems that may lead to relevant model prediction errors; and (III) in the approximation of the convection terms using the forward formulation, which is more stable and provides more realistic solutions.

► The computational effort can decrease as the model detail increases.
► Certain steady state assumptions can be no longer valid for the dynamic simulation.
► The selection of terms and phenomena must be carried out looking at the PDE numerical stability.
► High performances allow on-line monitoring and optimal control of the methanol synthesis reactor.
► Temperature and position of the hot spot can be accurately estimated and monitored.