Rigorous modelling of NOxNOx absorption in tray and packed columns

The absorption of NOxNOx into pure water or nitric acid is usually a kinetically controlled operation in which complex reactions in both gas and liquid phases are combined with multicomponent mass transfer. To be able to describe this process adequately, a rigorous general rate-based model for the reactive absorption in tray and packed columns has been developed based on earlier works (see, e.g. [Kenig et al., 2001. Chemical Engineering Science 56, 343–350; Kenig et al., 2003. Chemical Engineering and Technology 6, 631–646]). Heat and multicomponent mass transfer in the film phases, chemical reactions and thermodynamic non-idealities are taken into account. Furthermore, the influence of column internals and hydraulics is considered via relevant correlations. For tray columns, a special consideration of the empty sections above the gas–liquid layer on a tray is included. The model is implemented into the simulation environment Aspen Custom ModelerTM and validated by comparison with experimental data for a pilot scale packed column and an industrial sieve tray column equipped with cooling coils. The simulation results obtained for both column types agree well with the experimental measurements. In addition, the influence of cooling on the process behaviour is studied.