Effect of Additive Agents on the Simultaneous Absorption of NO_2 and SO_2 in the Calcium Sulfite Slurry

摘要

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)_2SO_4, and NH_4C1. 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)_2SO_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 S 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)_2SO_4 are used as additives.