Re-Emission of Mercury from Activated Carbon in Coal Combustion Flue Gas
AIChE Annual Meeting
Monday, November 14, 2016 - 10:00am to 12:30pm
Currently there are concerns that AC has the capability of re-emitting already adsorbed Hg during unit start up due to ramps in temperature, sulfur trioxide (SO3) concentration, or both. While the release of Hg is known to occur, the cause of re-emission is not well understood. The objective of this study is to investigate the factors that might have an impact on the re-emission of Hg from AC under a flue gas environment. In this study, the AC samples were exposed to Hg in flue gas composed of either only combustion products (N2, O2, CO2 and H2O) or a simulated flue gas (combustion products with NO and SO2) to evaluate its capture capabilities. After being saturated with Hg in the flue gas mixture, the AC samples were subjected to a SO3 concentration ramp (2 to 20ppm), a temperature ramp (from 105 °C to 205 °C) and both SO3 and temperature ramp in order to understand how these conditions influence Hg re-emission. Temperature was found to be the main factor impacting re-emission resulting in the release of up to 40% of the Hg fed to the reactor. Ramping the SO3 concentration independently had a negligible effect on emission/reemission, while ramping both the SO3 concentration and temperature together showed a similar trend to that of the temperature ramp only.