A Study on Emission and Mass Balance of Hg in Coal-fired Power Plants and Cement Kilns

摘要

Mercury (Hg) is one of the most important environmental contaminants, which has raised a global concern because of its toxicity, long-distance transport, persistence, and bioaccumulation in the environment. Considering this, the broad objective of this study was to study mercury behavior in various combustion and incineration sources and to investigate the integrated management technology for mercury emission. To understand mercury behavior at cement kilns (CKs), coal-fired power plants (CPPs), their concentrations at each instream and outstream as well as their mass distribution in the processes were analyzed. Various types of wastes are being frequently burned in the Korean cement industries. The mercury concentrations in flue gas were 3.18-64.66 μg/m~3 in CK-1-3 using fuel and 0.26-3.34 μg/m~3 in CPP-1-3 using bituminous coal. The emission factor was estimated as 11.29-67.42 mg/ton of clinker in CKs and 2.98-16.84 mg/ton of coal in CPPs. Hg emission factors estimation for tested facilities were based on the Hg sampling concentration, flue gas exhaust rate, and coal or quantity of incineration feeding rate or clinker production rate. Approximately, 68-99% of in/out Hg balance was obtained in this study and the major outgoing pathway for Hg was in the fly ash collected in the particulate control device. A large amount of particulate-bound Hg (Hg_P) and over 30% of Hg could be removed by the electrostatic precipitator (ESP), and Hg compounds seemed to be oxidized to Hg~(2+) through the ESP, which resulted in an increase of Hg~(2+). Then, a wet FGD unit could remove Hg~(2+) with a lime slurry scrubber solution and about a quarter of mercury could be emitted to the atmosphere through the stack. Hg speciation changes with the increasing oxidized portion through ESP and the reduction of the absorbed Hg to Hg° in the wet FGD scrubber solution are reported from other investigations. However, these subjects need to be studied more comprehensively through field experiments.