Mercury speciation and size-specific distribution in filterable and condensable particulate matter from coal combustion.

Particle-bound mercury discharged with fine particulate matter from coal-fired power plants causes atmospheric pollution that impacts human health. In this study, the speciation and size-specific distribution of particle-bound mercury in filterable particulate matter (FPM) from an ultra-low emission power plant and condensable particulate matter (CPM) from an entrained flow reactor were analyzed. Most importantly, particle-bound mercury was enriched in fine particles smaller than 0.02 μm, whose mass fraction was several orders of magnitude higher than that in large particles. Particularly, HgBr2, HgCl2, and HgO were major mercury species in FPM, whereas CPM involves mostly HgCl2 with a small portion of HgBr2. The occurrence of these species was also confirmed by a thermodynamic equilibrium calculation. The results further revealed the effects of air pollution control devices (APCDs) on the speciation of particle-bound mercury. Specifically, an electrostatic precipitator (ESP) removed most particle-bound mercury. Similarly, wet flue gas desulfurization (WFGD) dramatically reduced particle-bound mercury for most particles, except those between 0.1 and 1 μm. At the outlet of WFGD, mercury bound with FPM10 (smaller than 10 μm) is only 0.15% of the total mercury at the inlet of selective catalytic reduction (SCR). This knowledge provides insights that can be used to design and optimize the control strategy for mercury emission in power plants.