Simultaneous removal of NO x and SO 2 using two-stage O 3 oxidation combined with Ca(OH) 2 absorption
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pISSN: 0256-1115 eISSN: 1975-7220
INVITED REVIEW PAPER
INVITED REVIEW PAPER
Simultaneous removal of NOx and SO2 using two-stage O3 oxidation combined with Ca(OH)2 absorption Yang Zou*,***, Yan Wang*, Xiaolong Liu*,†, Tingyu Zhu*,**,†, Mengkui Tian***, and Maoyu Cai*,*** *Beijing Engineering Research Center of Process Pollution Control, National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China **Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China ***School of Chemistry and Chemical Engineering, Guizhou University, Guiyang, Guizhou 550025, China (Received 27 November 2019 • Revised 11 May 2020 • Accepted 31 May 2020) AbstractThis paper proposes two-stage O3 oxidation combined with Ca(OH)2 for simultaneous removal of NOx and SO2 (NOx: Nitrogen oxides including NO, NO2 and N2O5). In two-stage oxidation, NO was first oxidized to NO2 in an oxidation tube, and NO2 was further oxidized into N2O5 in the spray tower. NOx and SO2 were simultaneously removed in the spray tower. This method can effectively reduce the extra waste of O3 caused by the decomposition of N2O5, especially at high temperature. Effects of various factors on denitrification efficiency were investigated. The results showed that the NOx removal efficiency decreased and O3 extra consumption ratio increased with the increase of oxidation temperature or oxidation reaction time. When the O3/NO molar ratio was 1.8, one-stage O3 oxidation at 150 oC extra wasted 33.3% of O3. With the increase of O3 concentration at site 2, the NOx removal efficiency first increased and then stabilized. Compared with the one-stage O3 oxidation-absorption, the two-stage oxidation-absorption improved NOx removal efficiency from 62.5% to 89%. In addition, the increase of CaSO3 slurry concentration had little effect on the denitrification efficiency. Keywords: Iron Ore Sintering Flue Gas, SO2, NOx, Ozone, Two-stage Oxidation
additives have been explored to improve denitrification efficiency. FeSO4/CaSO3 [37], Fe3+/H2O2 [38], MgSO4/CaSO3 [39], C6H15NO3 (TEA)/MgO [40] and KI/Na2CO3 have been employed for simultaneous purification of SO2 and NO, and the removal efficiency of SO2 and NO was 100% and 70-95%, respectively. Nevertheless, the drawback of high consumption and high cost limits their wide applications industrially. Further oxidation of NO2 to N2O5, which has the highest solubility among NOx species [17], can greatly promote the removal of NOx. Therefore, the deep oxidation technique has gained increasing importance. O3 is an efficient gas phase oxidant with high oxidation selectivity, high oxidation efficiency, fast oxidation rate and no secondary byproducts. Wang et al. [41] studied ozone oxidation combined with Ca(OH)2 absorption and found that 97% of NO and nearly 100% of SO2 were simultaneously removed. Sun et al. [33] confirmed that 87% of NOx and nearly 100% of SO2 coul
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