Experimental aspects of combined NOx and SO2 removal from flue-gas mixture in an integrated wet scrubber-electrochemical cell system

Abstract

The objective of this work was to study the effect of some operating conditions on the simultaneous removal of NOx and SO2 from simulated NO–SO2–air flue-gas mixtures in a scrubber column. The gaseous components were absorbed into 6 M HNO3 electrolyte in the scrubber in a counter-current mode, and were oxidatively removed by the Ag(II) mediator oxidant electrochemically generated in an electrochemical cell set-up. The integration of the electrochemical cell with the scrubber set-up ensured continuous regeneration of the Ag(II) mediator and its repeated reuse for NOx and SO2 removal purpose, thereby avoiding: (1) the usage of chemicals continuously for oxidation and (2) the production of secondary waste. The influences of packing material (raschig glass rings, raschig poly(vinylidene) fluoride rings, Jaeger tri-pack perfluoroalkoxy spheres), feed concentrations of NO and SO2 (100–400 ppm NO and 100– 400 ppm SO2), superficial gas velocity (0.061–0.61 m s�1) and liquid velocity (0.012–0.048 m s�1) were investigated. The raschig glass rings with high surface area provided highest NO removal efficiency. NO and NOx showed decreasing abatement at higher feed concentrations. The removal of nitrogen components was faster and also greater, when SO2 co-existed in the feed. Whereas the gas flow rate decreased the removal efficiency, the liquid flow rate increased it for NO and NOx. The flow rate effects were analyzed in terms of gas/liquid residence time and superficial liquid velocity/superficial gas velocity ratio. SO2 removal was total under all conditions