Efficient simulation of an ammonia oxidation reactor using a solution mapping approach

Abstract

A highly efficient single channel monolith reactor model for the oxidation of ammonia is implemented. A mechanistic model for ammonia oxidation on platinum is used, and all internal and external mass transfer effects are included. The model efficiency is derived from the use of pre-computed solutions of the mass balance equations. Spline interpolation functions are constructed from pre-computed solutions of the mass balances of one volume element of the reactor model. It is shown that these spline functions reproduce the exact outlet concentrations of the volume element with a relative error of less than 3%. This solution mapping approach allows computation of concentration profiles in the reactor by simple successive calls of the interpolation function without any numerical solution. Outlet concentrations of the complete reactor computed in this way show a relative error of less than 2%. Application of the solution mapping approach speeds up the solution of the concentration profiles by a factor of more than 3200, compared to the numerical solution of the mass balances. In this way one steady state concentration profile in an ammonia oxidation catalyst can be computed in less than 0.003 s, despite the fact that the model uses mechanistic surface kinetics and includes the radial diffusion in the washcoat.