Wet oxidation scrubbing (WOS) for flue-gas desulphurization using sodium chlorite seawater solutions

This paper reports the experimental and modelling results of the absorption of sulphur dioxide by seawater solutions doped with sodium chlorite, a strong oxidant, to improve the conversion of the S-(IV) ions produced by SO2 absorption to the more soluble S-(VI) ones. The experiments show that sodium chlorite oxidation is very fast and determines a constant SO2 solubility regardless of the solution pH, i.e. its alkalinity. However, it was demonstrated the effect of chlorite is alternative but not additive to that of alkalinity. In fact, during tests carried out at acidic pH and with a dosage of chlorite identical to that of carbonate in a natural seawater, the solubility resulted the same as the figure observed for natural seawater. The results show that the absorption increases by increasing the sodium chlorite content because of the higher solubility. Also in this case, the absorption efficiency of sodium chlorite solutions keeps almost constant regardless of the solution pH. This result suggests that the rate controlling step for chemical absorption is the diffusion of chlorite and S-(IV) ions at the gas-liquid interface, with a fast reaction kinetics, similar to the case of reactions with bicarbonate. Finally, a modelling analysis show that ASPEN PLUS (R) simulations provide excellent predictions of SO2 solubility and removal efficiency data.