Multi-scale Reduced Order Models for Real Time Simulations of Multi-layered Monolith Reactors

Mingjie  Tu, University of Houston

Mingjie Tu, Ram Ratnakar* and Vemuri Balakotaiah

Department of Chemical and Biomolecular Engineering, University of Houston, TX 77204, USA

*Shell International Exploration and Production Inc, Houston, TX-77082, USA

We use individual phase averaging based on Lyapunov-Schmidt reduction to obtain reduced order model for describing the transient non-isothermal diffusion, convection and reaction processes in a catalytic monolith with two and more porous washcoat layers. These reduced order models are expressed in terms of phase-averaged concentration modes in terms of global equations that correspond to conservation equations for each phase. These global equations also contain the interfacial fluxes determined by the local equations. These local equations are linear in the concentration modes as well as interfacial fluxes and contain inter and intra- phase transfer coefficients. The structure of the multiphase averaged models derived by the L-S method is fundamentally different from the traditional intuitively written models. We illustrate the use of the reduced order models using dual layered monolith reactors used in diesel oxidation catalysts, hydrocarbon traps and in three-way catalysts. For selected cases, we compare the solution of the reduced order model derived by our method with detailed model and traditional multiphase models. These comparisons show that the reduced order model represents the detailed model more accurately while the traditional models fail to capture the effect of transverse diffusion and reactions on interfacial fluxes. While our goal is to reduce computational time for modeling multi-species and multi-layer systems so that real time simulations can be performed, we also illustrate the use of reduced order models to solve inverse problems, i.e.  determination of transport and kinetic parameters from a limited set of experimental data.

Keywords: Lyapunov-Schmidt procedure, Multi-scale averaging, Numerical validation, monolith reactors reactor, internal heat/mass transfer coefficient, external heat/mass transfer coefficient.