Experimental aspects of combined NO x and SO 2 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 NO x and SO 2 from simulated NO–SO 2–air flue-gas mixtures in a scrubber column. The gaseous components were absorbed into 6 M HNO 3 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 NO x and SO 2 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 SO 2 (100–400 ppm NO and 100–400 ppm SO 2), 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 NO x showed decreasing abatement at higher feed concentrations. The removal of nitrogen components was faster and also greater, when SO 2 co-existed in the feed. Whereas the gas flow rate decreased the removal efficiency, the liquid flow rate increased it for NO and NO x . The flow rate effects were analyzed in terms of gas/liquid residence time and superficial liquid velocity/superficial gas velocity ratio. SO 2 removal was total under all conditions.