ADEQUACY OF LUMPED PARAMETER MODELS FOR SCR REACTORS WITH MONOLITH STRUCTURE

Two- and one-dimensional steady-state isothermal mathematical models of monolith reactors for selective catalytic reduction (SCR) of NO(x) by NH3 are compared for circular, square and triangular geometry, as well as for linear and Rideal kinetics. Solutions for the two-dimensional model demonstrate that, as the reaction rate decreases from infinity to zero, the Sherwood number varies from the values of the Nusselt number characteristic of the Graetz-Nusselt problem with constant wall temperature to those with constant wall heat flux but with peripherally varying temperature. A lumped-parameter treatment, based on similarity with the constant wall temperature heat transfer problem, agrees satisfactorily with the solutions for a far more expensive two-dimensional model. The agreement is excellent for square channels, but the NH3 slip tends to be underestimated in the triangular geometry. The one-dimensional model reproduces successfully experimental effects of the NH3/NO feed ratio, and of the area velocity and the size of monolith channels.