Mercury speciation and mass distribution of coal-fired power plants in Taiwan using different air pollution control processes

Abstract

ABSTRACT In this study, the mercury (Hg) emission, speciation, and mass distribution of four coal-fired power plants (CFPPs) located at central, southern, and northern Taiwan with various types of air pollution control devices were investigated. Gaseous Hg in the coal-combustion flue gas was sampled by using the Ontario Hydro method, and the solid and liquid samples were collected for understanding the Hg mass balance. The experimental results showed that the total Hg concentrations in flue gases at the inlets of selective catalytic reduction (SCR) varied from 2.984 to 4.692 μg Nm−3, while the total Hg concentrations in the flue gases at the stacks ranged from 0.240 to 0.675 μg Nm−3. These four CFPPs showed similar Hg speciation results at the stacks. The average Hg removal efficiencies of Plants 1 (SCR + electrostatic precipitator [ESP] + wet flue gas desulfurization [WFGD]), 2 (SCR + ESP + WFGD), 3 (SCR + bag filter (BF) + seawater flue gas desulfurization [SWFGD]) and 4 (SCR + BF + SWFGD) were 92.4%, 90.1%, 85.9%, and 84.8%, respectively. Coal was the major raw material in Hg input of CFPPs with a mass flow rate ranging 5.87–12.05 g hr−1. Elemental Hg (Hg0), accounting for 66.4%−97.1% of the total Hg, was the dominant species emitted to the atmosphere. The Hg mass balances for the four CFPPs varied from 86.0% to 117% of the Hg input, suggesting that good mass balances were obtained from the tested CFPPs. Implications: Mercury emissions from coal-fired power plant (CFPPs) have been greatly concerned and should thus be better comprehended. The present study examined the mercury speciation and mass distribution of four CFPPs located at Taiwan. Overall, these CFPPs had similar Hg speciation results at stack and Hg0 was the dominant species emitted to the atmosphere. The selective catalytic reduction (SCR) + electrostatic precipitator (ESP) + wet flue gas desulfurization (WFGD) system had the highest Hg removal efficiency and the Hg mass balances for the four CFPPs varied from 86.0 to 117%. This study helps better understanding the Hg emission inventory of CFPPs and provides useful information for selecting adequate air pollution control devices (APCDs) for Hg control.