MERCURY CONTROL IN MUNICIPAL WASTE COMBUSTORS AND COAL-FIRED UTILITIES

Control of mercury (Hg) emissions from municipal waste combustors (MWC s) and coal-fired utilities has attracted attention due to current and potential regulations. Among several techniques evaluated for Hg cont rol, dry sorbent injection (primarily injection of activated carbon) h as shown promise for consistently removing high levels of Hg from MWC or coal flue gas. However, the performance in terms of amount of Hg re moved per amount of sorbent varies widely between the MWC and coal-fir ed applications and from unit to unit. In this study, we have conducte d bench-scale experiments under conditions simulating MWCs and coal-fi red units to study Hg capture by dry sorbents. The effect of reaction temperature on the capture of different Hg species [Hg-0 and Hg(II)] b y various types of dry sorbents was the focus of bench-scale tests. An attempt has also been made in this study to compare the bench-scale r esults with results obtained from pilot studies and to explain dispari ties in fuel, and unit-specific performance. Our investigations showed that the reaction temperature and Hg species strongly affect Hg contr ol. The results obtained in this suggested the two following mechanism s for Hg capture: i) Capture of Hg-0 by activated carbons is limited b y sorption kinetics, and ii) Capture of mercuric chloride (HgCl2) by a ctivated carbons is limited by collision with carbon particles.