Bench-scale testing of elemental mercury (Hg 0 ) sorption on selected activated carbon sorbents was conducted to develop a better understanding of the interaction among the sorbent, flue gas constituents, and Hg 0. The results of the fixed-bed testing under simulated lignite combustion flue gas composition for activated carbons showed some initial breakthrough followed by increased mercury (Hg) capture for up to ϳ4.8 hr. After breakthrough, the Hg in the effluent stream was primarily in an oxidized form (Ͼ90%). Aliquots of selected activated carbons were exposed to simulated flue gas containing Hg 0 vapor for varying time intervals to explore surface chemistry changes as the initial breakthrough, Hg capture, and oxidation occurred. The samples were analyzed by X-ray photoelectron spectroscopy to determine changes in the abundance and forms of sulfur, chlorine, oxygen, and nitrogen moieties as a result of interactions of flue gas components on the activated carbon surface during the sorption process. The data are best explained by a competition between the bound hydrogen chloride (HCl) and increasing sulfur [S(VI)] for a basic carbon binding site.

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Activated carbons were produced from two European biomasses such as olive residue and wheat straw. The leaching pretreatment is used to study the effect of chlorine and alkali metals on the mercury capture efficiency. The activated carbons were tested for mercury capture in a bench scale reactor against the commercial grade activated carbon NORIT DARCO Hg as well as an activated carbon developed at the Energy and Environmental Research Center (EERC) from lignite. The mercury capture tests showed that the untreated biomass-derived activated carbons performed fair-to-very good compared to the commercial catalyst and better compared to the lignite-derived activated carbon. The leached biomass-derived carbons were seen to have poor performance in the case of the olive residue and similar performance to that of the lignite-derived carbon in the case of the wheat straw.

U.S. Environmental Protection Agency (EPA) Method 26A is the recommended procedure for capturing and speciating halogen (X 2 ) and hydrogen halide (HX) stack emissions from combustion sources. Previous evaluation studies of Method 26A have focused primarily on hydrogen chloride (HCl) speciation. Capture efficiency, bias, and the potential interference of Cl 2 at high levels (>20 ppm [µg/m 3 ]) and NH 4 Cl in the flue gas stream have been investigated. It has been suggested that precise Cl 2 measurement and accuracy in quantifying HX or X 2 using Method 26A are difficult to achieve at Cl 2 concentrations <5 ppm; however, no performance data exist to support this. Coal contains low levels of Cl, in the range of 5-2000 ppmw, which results in the presence of HCl and Cl 2 in the products of combustion. HCl is the predominant Cl compound formed in the high-temperature combustion process, and it persists in the gas as the products of combustion cool. Concentrations of Cl 2 in coal combustion flue gas at stack temperatures typically do not exceed 5 ppm. For this research, bench-scale experiments using simulated combustion flue gas were designed to validate the ability of Method 26A to speciate low levels of Cl 2 accurately. This paper presents the results of the bench-scale tests. The effect of various flue gas components is discussed. The results indicate that SO 2 is the only component in coal combustion flue gas that has an appreciable effect on Cl 2 distribution in IMPLICATIONS The presence of Cl-containing species in combustion effluents is of concern because their emission to the atmosphere can lead to the formation of pollutants such as dioxins and certain Hg compounds. EPA Method 26A is the recommended procedure for measuring the gaseous Cl species HCl and Cl gas in the products of combustion. This study evaluates the effect of SO 2 and other simulated coal combustion flue gas components on the accuracy of EPA Method 26A on the basis of bench-scale tests where low levels of Cl gas were spiked into the flue gas stream. The results indicate that Method 26A cannot speciate low levels of Cl accurately in a coal combustion flue gas stream without modification.Method 26A impingers, and that Method 26A cannot accurately speciate HCl and Cl 2 in coal combustion flue gas without modification. BACKGROUNDSampling and quantitation of stack gas emissions from hazardous waste combustors and from boilers and industrial furnaces co-firing hazardous waste are required as part of the Resource Conservation and Recovery Act (RCRA) permitting process. HCl and Cl 2 are currently regulated. Under RCRA, HCl emissions from municipal incinerators are regulated. Both HCl and Cl 2 are listed among the 189 hazardous air pollutants (HAPs) in the Clean Air Act Amendments of 1990.