Flue gas interactions of mercury, chlorine, and ash during coal combustion
The interaction between the coal combustion flue gas components mercury, chlorine, and entrained fly ash particulate was investigated experimentally using a 42 MJ- or 40,000-Btu/hr, downfired, combustion system. A low-Cl, Powder River Basis (PRB) subbituminous coal with 0.052 ppm Hg was burned at an excess O{sub 2} concentration of 8.5%. HCI was injected into the hot zone of the furnace at concentrations of 50 and 100 ppmv. Tests involving the injection of 10 {mu}g/m{sup 3} Hg{sup 0} (elemental Hg) and 100 ppmv HCI into a simple heated gas mixture were also conducted. A modified US Environmental Protection Agency (EPA) Method 29 sample train, developed by Radian International and evaluated at the Energy and Environmental Research Center (EERC), was used for determining Hg emission and speciation at the baghouse inlet of the system. EPA Method 26 was used for determining Cl emission and speciation, and on-line analyzers were employed during most tests to monitor total Hg, Hg{sup 0}, HCl, O{sub 2} CO{sub 2}, CO, SO{sub 2}, and NO concentrations. Fly ash was sampled from the baghouse and analyzed for Hg, Cl, and C after each coal test. Baseline testing of the PRB coal indicated that on average 40%, 20%, and 40% of the total Hg in the flue gas was present as particle-associated mercury (Hg[p]), gaseous divalent mercury (Hg{sup 2+}[g]), and gaseous elemental mercury (Hg{sup 0}[g]), respectively. In comparison, Hg speciation of the HCl-spiked flue gases was 10% Hg(p), 30% Hg{sup 2+}(g), and 60% Hg{sup 0}(g). Hg mass balance closures were acceptable (85% {+-} 12%). Cl speciation analyses indicated that >98% of the injected HCl remained as HCl. In the lower-temperature environment of the baghouse, fly ash from the baseline coal test has depleted in Cl relative to the ashes produced from the 50- and 100-ppmv HCl injection tests. Hg concentrations of the baghouse fly ash samples were not directly correlated to ash Cl or C contents. The PRB coal tests indicate that the expected conversions of Hg{sup 0}(g) to Hg(p) and Hg{sup 2+}(g) with HCl injection did not occur. Conversely, HCl injection converted most of the Hg(p) to Hg{sup 0}(g). The injection of Hg{sup 0}(g)-HCl into the simple heated gas mixture resulted in the expected conversion of Hg{sup 0}(g) to Hg{sup 2+}(g) in the combustor. Consequently, the presence of PRB coal combustion flue gas components (i.e., other gases and/or entrained particulate) promoted the remobilization of Hg(p) to Hg{sup 0}(g) during HCl injection.
- Research Organization:
- Univ. of North Dakota, Grand Forks, (US)
- Sponsoring Organization:
- Environmental Protection Agency
- OSTI ID:
- 20012959
- Resource Relation:
- Conference: 23rd International Technical Conference on Coal Utilization and Fuel Systems, Clearwater, FL (US), 03/09/1998--03/13/1998; Other Information: PBD: [1998]; Related Information: In: The proceedings of the 23rd international technical conference on coal utilization and fuel systems, by Sakkestad, B.A. [ed.], 1164 pages.
- Country of Publication:
- United States
- Language:
- English
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