Simultaneous Absorption of NOx and SO2 into Water and Acids under High Pressures

Scrubbing of SO2 and NOx from oxy-fuel combustion flue gas under a high pressure has been well recognized as an effective technique for flue gas purification. Experiments were performed in a bubbling column under high pressure to explore the absorption products and the SO2 selectivity during simultaneous absorption of SO2 and NOx. The main absorption product in liquid phase at pH > 1 was identified as hydroxylamine disulfonic acid (HADS), which was then quantified by the Raman spectroscopy. The N2O concentration in gas phase was estimated by the nitrogen mass balance across the system. Results showed that N2O and HADS were produced dominantly by the reaction between HNO2 and HSO3- at pH > 1, and this followed the Raschig mechanism. However, the absorption of SO2 was promoted while the absorption of NOx was inhibited, and this followed the lead chamber mechanism. Based on the quantification of the nitrogen and sulfur related products in both gas and liquid phase, about 48%-56% NQ and 14%-17% SO2 were consumed by the Raschig mechanism, and 15%-23% SO2 was consumed by the lead chamber mechanism in the pH range 1.09-1.72. For simultaneous absorption of NOx and SO2, SO2 was completely absorbed in different solutions except in the 18.4 mol/L H2SO4. A high concentration of H2SO4 suppressed the absorption of NOx but cannot achieve selective absorption of SO2 without absorbing NO. HNO3 concentration did not have appreciable effect on NOx absorption efficiency in the concentration range 0.1-1 mol/L. When the concentration of HNO3 was 15 mol/L, NQ was no longer absorbed into liquid solution. The mixed acids produced by the simultaneous absorption of NOx and SO2 can cause severe corrosion to a 316L stainless steel tube.