Air Pollution Technology

S.V. Krishnan Acurex Environmental Corporation 4915 Prospectus Drive P.O. Box 13109 Research Triangle Park, NC 27709 Brian K. Gullett U.S. Environmental Protection Agency Air and Energy Engineering Research Laboratory Research Triangle Park, NC 27711 Wojciech Jozewicz Acurex Environmental Corporation 4915 Prospectus Drive P.O. Box 13109 Research Triangle Park, NC 27709

Abstract
The mechanisms and rate of elemental mercury (Hgx) capture by activated carbons have been studied using a bench-scale apparatus. Three types of activated carbons, two of which are thermally activated (PC-100 and FGD) and one with elemental sulfur (S) impregnated in it (HGR), were chosen to study the effects of surface area (approximately 550-1000 m²/g), sorption temperature (23 to 140 °C), and Hgx concentration (30 and 60 ppb of Hgx in nitrogen). Investigations revealed that sorption occurs in active sites in PC-100 and FGD which are either depleted or deactivated upon heat treatment at 140 °C. For HGR, sorption at 23 °C occurred in non-S sites residing in the external surface and sorption at 140 °C primarily occurred through the reaction of Hgx and S. Desorption studies for PC-100 and HGR revealed the sorption mechanism to be a combination of physisorption and chemisorption at 23 °C, whereas chemisorption is the primary route at 140 °C.

Gullett, B. K.; Jozewicz, W.; and Stefanski, L. A. Reaction Kinetics of Ca-Based Sorbents with HCl, Ind. & Eng. Chem. Res., 31(11), 2437-2446, 1992.

Chun Wai Lee Combustion Research Branch Air and Energy Engineering Research Laboratory U. S. Environmental Protection Agency Research Triangle Park, NC 27711

Abstract
A pilot-scale multifuel combustor (MFC) designed to permit research with a variety of solid fuels is currently under development at EPA's Air and Energy Engineering Research Laboratory (AEERL). The MFC is designed with sufficient flexibility so that, with some minimum but critical changes, it can be used for studying the combustion of municipal solid waste (MSW), refuse derived fuel (RDF), biomass fuel, and coal. Three interchangeable stoker grates are designed so the combustor can be operated in spreader stoker, continuous mass burn, or batch feed mass burn firing modes. The thermal output of the facility (580 kW) is sufficient to simulate the critical combustion conditions that occur in full scale systems. The processes controlling pollutant formation and destruction can be studied during combustion in the fuel bed, in the radiant furnace, or in the convective section. The MFC facility will also have the capability of studying the performance of flue gas cleaning devices such as baghouses and scrubbers. After the combustion conditions of the research unit are fully characterized, the initial application of the facility will be focused on studying formation, destruction, and control of pollutant emissions from MSW combustion processes. The effects of waste stream composition, such as the type and the quantity of paper, plastic, metal, and glass, on pollutant emissions and their control will be evaluated.

Gullett, B. K.; Lemieux, P. M.; and Dunn, J. E. The Role of Combustion and Sorbent Parameters in Prevention of Polychlorinated Dibenzo-p-Dioxin and Polychlorinated Dibenzofuran Formation During Waste Combustion, Environ. Sci. Technol. 28(1), 107-118, 1994.

Brian K. Gullett Paul M. Lemieux Air and Energy Engineering Research Laboratory U.S. Environmental Protection Agency Research Triangle Park, North Carolina 27711 and James E. Dunn Department of Mathematical Sciences University of Arkansas Fayetteville, Arkansas 72701

Abstract
This research uses experimental data and a statistical approach to determine the effect of combustion- and sorbent-injection-related parameters on the mechanism of polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran (PCDD and PCDF) formation and prevention in waste combustors. The operation of a pilot-scale combustor was varied to effect different regimes of oxygen (O₂), hydrogen chloride (HCl), and chlorine (Cl₂) concentration; temperature; residence time; quench rate; and sorbent injection. The fly ash loading of a municipal waste combustor was simulated by post-combustion injection of fly ash collected from a full-scale facility. Downstream sampling and analysis indicated significant PCDD and PCDF formation, beyond concentrations on the pre-injected fly ash, at rates conducive to explaining formation in full-scale facilities at particle/gas residence times 5 s. Stepwise regression analyses determined the predictive parameters for four models of PCDD, PCDF, the total of PCDD and PCDF yield, and the partitioning between PCDD and total yield. Substantial prevention of PCDD and PCDF formation can be brought about with upstream sorbent injection for HCl and Cl₂ reduction, control of excess air, and increased quench rate.