Predicting the impact of SO3 on mercury removal by carbon sorbents

This paper introduces a combined homogeneous and heterogeneous SO3 production mechanism to quantify the interference of SO3 on the capture of Hg by unburned carbon (UBC) and activated carbon sorbents in flue gas from coal-fired power plants. This mechanism was validated against measurements at different locations along the gas cleaning systems at fourteen power plants representing the entire range of coal-S, furnace stoichiometry, and gas cleaning conditions found in commercial applications. The SO3 production mechanism was then integrated into previously validated Hg transformation mechanisms to account for inhibition of Hg oxidation and removal due to SO3 condensation on fly ash, UBC and activated carbon. This analysis was subsequently used to interpret Hg removals for more than two dozen test measurements at Daniel and the Mercury Research Center. These tests included different coal blends, ACI concentrations, conventional and brominated activated carbons, and SO3 concentrations. The simulations clearly identified the tests affected by SO3 interference and predicted the Hg removal by ACI to within 15% of the test measurements for 22 of the 27 tests at these two sites. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.