Korean J. Chem. Eng., 22(2), 208-213 (2005) 208 † To whom correspondence should be addressed. E-mail: hklee@kier.re.kr Simultaneous Removal of SO 2 and NO by Sodium Chlorite Solution in Wetted-Wall Column Hyung-Keun Lee † , Bal Raj Deshwal* and Kyung-Seun Yoo* Flue Gas Treatment Centre, Korea Institute of Energy Research, Daejeon 305-600, Korea *Department of Environmental Engineering, Kwangwoon University, Seoul 139-701, Korea (Received 29 April 2004 • accepted 8 December 2004) Abstract-The effect of feeding rate of NaClO 2 solution, inlet SO 2 and NO concentration, [NaClO 2 ]/[SO 2 +NO] molar ratio (η), L/G ratio and, solution pH on the simultaneous removal of SO x /NO x has been investigated in a wetted-wall column. Both SO x and NO x removal efficiencies are enhanced with the increasing feeding rate of NaClO 2 solution and attain a steady state. NO x removal efficiency increases with increasing SO 2 concentration, but SO x removal remains unaffected with increasing NO concentration. In an acidic medium, DeSO x and DeNO x efficiency increased with in- creasing [NaClO 2 ]/[SO 2 +NO x ] molar ratio and attained a steady state. NO x removal starts only after the complete re- moval of SO x . The excess of NaClO 2 does not enhance NO x removal efficiency. Solution pH does not affect the DeSO x and DeNO x efficiency. The maximum SO x and NO x removal efficiencies achieved at the typical operating conditions of commercialized FGD processes are about 100 and 67%, respectively. Key words: NaClO 2 , Wetted Wall Column, Removal Efficiency, DeSO x , DeNO x INTRODUCTION Sulfur oxides (SO x ) and nitrogen oxides (NO x ) are the major air pollutants which are emitted from stationary sources such as power plants, incinerators and combustors. The most effective technology for SO 2 removal is flue gas desulphurization (FGD). Commercial processes for the removal of SO 2 use limestone slurry as a scrub- bing solution. These wet FGD processes have been widely accepted because of lower cost, simple operation and higher SO x removal efficiency compared to other processes [Cooper and Alley, 1994]. Technologies for the NO x removal can be divided into combus- tion control and post-combustion treatment. Combustion control aims at reducing the NO x formation during the combustion of fossil fuel. Post-combustion methods include a variety of techniques such as selective non-catalytic reduction (SNCR), selective catalytic re- duction (SCR), thermal DeNO x and scrubbing etc. SNCR approaches require higher reaction temperature (about 900-1,000 o C) with an elaborate temperature control to avoid ammonia breakthrough or effective NO x emission control [Lyon, 1987]. Catalytic reduction methods can remove the NO x with an efficiency of 80 to 95%. Re- cent developments in SCR include the use of activated carbon and zeolites (CuZSM-5 and FeZSM-5) [Heck and Farrauto, 1995; Feng and Hall, 1996]. However, SCR processes require the higher oper- ating cost and additional space. Catalytic poisoning due to SO 2 laden flue gas is another major drawback of SCR processes, which reduces the life of catalyst and makes the process inconsistent. Among these technologies, scrubbing methods are economically most competi- tive and have the advantage of controlling other acid gases and par- ticulates at the same time [Yang et al., 1996]. In spite of successful commercial operation of individual desulfur- ization and denitrification processes, considerable attention has been focused on the simultaneous removal of SO 2 and NO x in a single reactor considering the capital investment, operating cost, and the space for equipment. The FGD process is being quite efficiently used in incinerators and boilers, so if minor adjustment in it may work for simultaneous removal of SO 2 and NO x then it will prove a more compact and cost effective technology for the future. Interest has been focused on the additives to oxidize insoluble NO to soluble NO 2 which can be absorbed into alkaline solution. Various oxidants such as H 2 O 2 [de Pavia and Kachan, 1998], KMnO 4 [Brogren et al., 1997; Chu et al., 2001], organic hydroperoxides [Per - lmutter et al., 1993], peracids [Littlejohn and Chang, 1990], NaClO 2 [Brogren et al., 1998; Sada et al., 1978; Hsu et al., 1998], and fer- rous-chelating agents [Shi et al., 1997; Harriott et al., 1993] have been investigated, and NaClO 2 has been found the most promising chemical for NO oxidation. Simultaneous removal of NO and SO 2 using NaClO 2 solution has also been reported by several research- ers [Yang and Shaw, 1988, Adewuyi et al., 1999; Chien and Chu, 2000]. Most of the work done till now has concentrated more or less on batchwise experimentation. Combined DeSO x and DeNO x results from the continuous operation of gas-liquid contactors may be helpful for successful application of wet DeNO x process com- bined with wet FGD processes. Thus, the present study is aimed at investigating the effect of various operating variables on the simul- taneous removal of SO 2 and NO from flue gas in the wetted wall column using sodium chlorite solution. EXPERIMENTAL 1. Experimental Apparatus A schematic diagram of the experimental system is shown in Fig. 1. This system consists of a simulated flue gas supply unit, co-cur- rent wetted wall column, gas analyzing system, and data acquisition system. The solution pH was continuously controlled by pH control - ler (KFC-MK-250) interfaced with personal computer using NaOH