Effect of Additive Agents on the Simultaneous Absorption of NO 2 and SO 2 in the Calcium Sulfite Slurry

It is known that NO in the flue gas can be effectively converted to NO 2 by O 3 . The objective of this work is to investigate the feasibility of simultaneously abating NO 2 and SO 2 from flue gas by liquid-phase conversion. A suite of cost-effective additives for enhancing NO 2 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 CaSO 3 slurry, including metal and non-metal additives: FeSO 4, FeCl 2, Fe 2 (SO 4 ) 3, MnSO 4, MnCl 2, MgSO 4, MgCl 2, (NH 4 ) 2 SO 4, and NH 4 Cl. All of these additives enhance the absorption efficiency of NO 2 . Ferrous sulfate, FeSO 4, 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, (NH 4 ) 2 SO 4, 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 NO 2 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 NO 2 removal when MnSO 4 and (NH 4 ) 2 SO 4 are used as additives.