Effect of Additive Agents on the Simultaneous Absorption of NO2 and SO2 in the Calcium Sulfite Slurry

It is known that NO in the flue gas can be effectively converted to NO2 by O-3. The objective of this work is to investigate the feasibility of simultaneously abating NO2 and SO2 from flue gas by liquid-phase conversion. A suite of cost-effective additives for enhancing NO2 absorption through enriching the concentration of sulfite ion, S-IV, in the liquid phase has been evaluated under pH similar to traditional flue-gas desulfurization (FGD). Experiments were conducted in a lab-scale washing tower with CaSO3 slurry, including metal and non-metal additives: FeSO4, FeCl2, Fe-2(SO4)(3), MnSO4, MnCl2, MgSO4, MgCl2, (NH4)(2)SO4, and NH4Cl. All of these additives enhance the absorption efficiency of NO2. Ferrous sulfate, FeSO4, is the most effective additive, with absorption efficiency reaching 95%, but the loss of additive is high because of the oxidation of Fe-II into Fe-III. Ammonium sulfate, (NH4)(2)SO4, has similar absorption efficiency but shows lower loss during absorption. Its absorption efficiency improves with an increasing temperature and decreases with a decreasing pH, although NO2 absorption is still noticeable when pH varies between 5 and 7, which is within the operating range of a typical wet FGD. The presence of O-2 causes a 4% decrease in NO2 removal when MnSO4 and (NH4)(2)SO4 are used as additives.