Performance and mechanism of CO2 absorption during the simultaneous removal of SO2 and NOx by wet scrubbing process

The co-removal of CO 2 while removing SO 2 and NO x from industrial flue gas has great potential of carbon emission reduction but related research is lacking. In this study, a wet scrubbing process with various urea solutions for desulfurization and denitrification was explored for the possibility of CO 2 absorption. The results showed that the urea-additive solutions were efficient for NO x and SO 2 abatement, but delivered < 10% CO 2 absorption efficiency. The addition of Ca(OH) 2 dramatically enhanced the CO 2 absorption, remained the desulfurization efficiency, unfortunately restricted the denitrification efficiency. Among various operating parameters, pH of solution played a determining role during the absorption. The contradictory pH demands of CO 2 absorption and denitrification were observed and discussed in detail. A higher pH of solution than 10 was favorable for CO 2 absorption, while the oxidizing of NO to NO 2 , NO 2 − or NO 3 − by NaClO 2 was inhibited in this condition. When 7 < pH < 10, it was favorable for the conversion and absorption of NO and NO x . However, the conversion of HCO 3 − to CO 3 2− was significantly inhibited, hence preventing the absorption of CO 2 . Large part of Ca(OH) 2 became CaCO 3 with a finer particle size, which covered the unreacted Ca(OH) 2 surface after the reaction. Kinetic analysis showed that the CO 2 absorption in urea-NaClO 2 -Ca(OH) 2 absorbent was controlled by chemical reaction in early stage, then by ash layer diffusion in later stage.