Investigation on elemental mercury removal and antideactivation performance of modified SCR catalysts

Abstract

The ever-growing concern of mercury exhausted from coal-fired boiler is driving the requirement for using novel catalysts with stable Hg 0 removal efficiency. However, the influences of flue gas components on Hg 0 removal performance of modified and deactivated catalysts have been seldom investigated previously. The antideactivation ability of modified catalysts is still unclear. In this study, cerium (Ce) and zirconium (Zr) were utilized to modify the honeycomb V 2 O 5 -WO 3 /TiO 2 catalysts. Sodium (Na) was doped on the rudimentary and modified catalysts by impregnation method to obtain deactivated catalysts. Elemental mercury removal efficiency of the catalysts was measured using a lab-scale experimental system under various working conditions. Characterization of the catalysts was conducted to further analyze the mechanism of Hg 0 removal process. Physical adsorption plays an important role in Hg 0 removal over catalysts in the atmosphere of N 2 and O 2 . The introduction of SO 2 has an adverse effect on Hg 0 removal because of the competitive adsorption. NO and HCl motivate the Hg 0 removal through different mechanisms whereas NH 3 has little effect on the removal efficiency. Mars-Maessen mode could be responsible for the excellent Hg 0 removal performance and the splendid antideactivation ability of Ce-modified catalysts. The efficiency of Zr-modified catalysts is lower due to the decline of vanadium content.

Elemental Mercury Removal over CeO2/TiO2 Catalyst Prepared by Sol–Gel Method

“…However, the efficiency started to decrease when the temperature was higher than 350 • C, which agrees well with some literature [12,19]. Nevertheless, the trend in Figure 3 seems to conflict with the result of our previous work, which is that the Hg 0 removal efficiency declined monotonically as the reaction temperature increased [8]. That is understandable because only Hg 0 , O 2 , and N 2 existed in the flue gas of reference [8], so physical adsorption was the dominant removal mechanism for elemental mercury.…”

“…Nevertheless, the trend in Figure 3 seems to conflict with the result of our previous work, which is that the Hg 0 removal efficiency declined monotonically as the reaction temperature increased [8]. That is understandable because only Hg 0 , O 2 , and N 2 existed in the flue gas of reference [8], so physical adsorption was the dominant removal mechanism for elemental mercury. In comparison, the chemical reaction played a vital role in this study, since all flue gas components were considered in the simulated flue gas.…”

“…Ce0.5Ti-V showed higher efficiency than Ce0.5Ti because vanadium oxides, just like cerium oxides, could provide abundant lattice oxygen, which is quite important for the oxidation of Hg 0 . The process could also be explained by Equations (6)- (8). When the ratio of NH 3 to NO was 1:1, the efficiency of Ce0.5Ti-V remained higher than 91% under various NO and NH 3 concentrations, as shown in Figure 5d.…”

Evaluation of FeIIEDTA‐NO reduction by thiourea dioxide in NO removal with FeIIEDTA

“…2 Therefore, the emissions of NO x and SO 2 have been rigorously controlled and regulated by environment protection department of the world. 4 But it is difficult for SCR to achieve the purpose of desulfurization. 3 It is difficult to remove NO (accounting for 95% in NO x ) with wet process because of poor solvability of NO in water.…”

“…For this reason, several approaches have been refined to improve NO absorption; one of which is selective catalytic reduction (SCR). 4 But it is difficult for SCR to achieve the purpose of desulfurization. So adding oxidizing agents like KMnO 4,5 NaClO 2,6,7 NaClO, 8 and H 2 O 2, 9 for oxidizing NO into more soluble NO 2 and chelating agents 10,11 to unite NO, draws more interest, in which the removal of NO and SO 2 could be simultaneously finished off in a single process or equipment in wet process.…”