Simultaneous absorption of SO2 and NOx from simulated flue-gas exploiting the enhancing oxidative ability of aqueous euchlorine as scrubbing solution

Abstract

This paper reports the performances of a pilot-scale Wet Oxidative Scrubber (WOS) in the treatment of a simulated flue-gas containing 500 ppmv SO2 and 1030 ppmv NOx and operated at 60 °C and 1 atm. The scrubber is fed with an oxidizing solution containing NaClO2 at either 0.75 % or 1 % w/w initially at pH > 9 and then acidified to pH down to 3 with HCl, to obtain the additional oxidative contribution given by euchlorine species during the simultaneous absorption. Further experiments of single-component NOx absorption are performed to better understand the role exerted by SO2 in the simultaneous absorption. These experimental tests are carried out to investigate the effect of the acidity of the chlorite-based scrubbing solution on the simultaneous absorption performance of SO2 and NOx, highlighting the intensification with respect to the bare de-NOx system. Experiments also allow determining the optimal dosages and solution pH for a complete and optimized removal of NOx and SOx also being less energy-intensive. For a scrubbing solution under acid-induced conditions (pH = 3), the retrieved results show that the NaClO2 molar dosage needed for a complete simultaneous removal results 3.6 times greater than the total NOx concentration in the flue-gas. This allows an interesting reduction of 83 % in oxidant consumption and a water-saving of 70 % with respect to the same process applied to the simultaneous NOx absorption but without altering the solution pH. Overall, the results confirm the enhancing role exerted by euchlorine deriving from chlorite acidification and sulfur dioxide presence in the flue-gas.