Impacts of Halogen Additions on Mercury Oxidation, in A Slipstream Selective Catalyst Reduction (SCR), Reactor When Burning Sub-Bituminous Coal

Abstract

This paper presents a comparison of impacts of halogen species on the elemental mercury (Hg(0)) oxidation in a real coal-derived flue gas atmosphere. It is reported there is a higher percentage of Hg(0) in the flue gas when burning sub-bituminous coal (herein Powder River Basin (PRB) coal) and lignite, even with the use of selective catalytic reduction (SCR). The higher Hg(0)concentration in the flue gas makes it difficult to use the wet-FGD process for the mercury emission control in coal-fired utility boilers. Investigation of enhanced Hg(0) oxidation by addition of hydrogen halogens (HF, HCl, HBr, and HI) was conducted in a slipstream reactor with and without SCR catalysts when burning PRB coal. Two commercial SCR catalysts were evaluated. SCR catalyst no. 1 showed higher efficiencies of both NO reduction and Hg(0) oxidation than those of SCR catalyst no. 2. NH3 addition seemed to inhibit the Hg(0) oxidation, which indicated competitive processes between NH3 reduction and Hg(0) oxidation on the surface of SCR catalysts. The hydrogen halogens, in the order of impact on Hg(0) oxidation, were HBr, HI, and HCl or HF. Addition of HBr at approximately 3 ppm could achieve 80% Hg(0) oxidation. Addition of HI at approximately 5 ppm could achieve 40% Hg(0) oxidation. In comparison to the empty reactor, 40% Hg(0) oxidation could be achieved when HCl addition was up to 300 ppm. The enhanced Hg(0) oxidation by addition of HBr and HI seemed not to be correlated to the catalytic effects by both evaluated SCR catalysts. The effectiveness of conversion of hydrogen halogens to halogen molecules or interhalogens seemed to be attributed to their impacts on Hg(0) oxidation.

Mercury emission and speciation of coal-fired power plants in China

“…4a are probably because of the bromine content of coal. There is evidence that bromine species are capable of enhancing the conversion of Hg 0 to Hg 2+ (Liu et al, 2007;Cao et al, 2008b;Niksa et al, 2009). We found there was significant correlation between the Hg 2+ percentage in flue gas released from the tested boilers and the bromine content of coal (see Fig.…”

Mercury Air Emission from Coal-Fired Public Power Sector: Uncertainty and Its Monthly Distribution. Case Study from Poland

“…Increasing the concentration of chlorine in the combustion process facilitates the creation of Hg +2 [4,42]. The amounts of chlorine in Polish hard coals and lignites are derived from studies: [1] and [9].…”

“…The technological structure of APC devices applied before 2010 [47] based on data derived from the ENVIRO database is comparable with data included in this paper. Basing on uncertainty range: A, average estimation; B, low estimation; C high estimation; , no estimation made for 1990 Based on available elaborations [4,17,32,37], also papers and guidelines on uncertainty assessment [10, 13,40,46], the mercury removal efficiencies are assigned with a 30% uncertainty range. Results are presented in Table 13.…”

Oxidation Catalysts for Elemental Mercury in Flue Gases—A Review

“…Pilot-scale results obtained by Cao et al [82] revealed that, in the presence of different commercial SCR catalysts and under PRB (power river basin coal with low sulfur and chlorine contents) coal-derived flue gases, Hg el oxidation was enhanced by the addition of hydrogen halides in the following order: HBr, HI, and HCl or HF. However, it must be considered that the measurement of Hg [21,25,78,83].…”