A rate based reactor model for BiodeNOx absorber units

The reactive absorption of NO in aqueous solutions of FeII(EDTA), resulting in the formation of a nitrosyl complex, FeII(EDTA)(NO), is a key step of the BiodeNOx process for the removal of NOx from industrial flue gas. Oxygen present in the flue gas will also absorb and oxidize FeII(EDTA). This is an undesired reaction, because the resulting FeIII(EDTA) does not react with NO. To explore the industrial applicability of the process, a rate based model for the simultaneous reactive absorption of NO and O2 in aqueous FeII(EDTA) solutions in a counter current packed column has been developed. The effect of process conditions on absorber performance (NO removal efficiency, selectivity, FeII(EDTA) conversion) have been assessed. Using standard conditions, the column height needed to remove 90% of an initial 250 ppm of NO was less than 1 m. The amount of oxidized iron was approximately equal to the amount of the nitrosyl complex, even though oxygen was present in a 200-fold excess over NO. The absorber performance was particularly dependent on the operating temperature, where lower temperatures favoured both the NO removal efficiency and selectivity. Remarkably, the model indicated that overdesign of the absorber can result in decreasing absorber performance.