Cobenefit of SO3 reduction on mercury capture with activated carbon in coal flue gas

Abstract Parametric experiments were carried out to study the interactions of mercury, SO 3 , and injected activated carbon (AC) in a coal flue gas stream. The levels of SO 3 vapor in flue gas were altered by individually varying flue gas temperature, moisture, or sodium fume injection in the flue gas. Meanwhile, mercury emissions with AC injection (ACI) upstream of an electrostatic precipitator (ESP) were evaluated under varied SO 3 concentrations. SO 3 measurements using a condensation method indicated that low temperature, high moisture content, and sodium fume injection in flue gas shifted SO 3 partitioning from the vapor to particulate phase, subsequently improving mercury capture with ACI. 0.08 g/m 3 of DARCO ® Hg-LH injection only provided approximately 20% mercury reduction across the ESP in a bituminous coal flue gas containing 28 ppm SO 3 , but mercury capture was increased to 80% when the SO 3 vapor concentration was lowered less than 2 ppm. Experimental data clearly demonstrate that elevated SO 3 vapor is the key factor that impedes mercury adsorption on AC, mainly because SO 3 directly competes against mercury for the same binding sites and overwhelmingly consumes all binding sites.