Control of mercury emission from coal combustor/waste incinerators has been in the limelight for many years. It is especially difficult to remove elemental mercury (Hg) from the combustion flue gases due to its non-reactivity and high volatility. A novel gas phase sorbent precursor injection technique for the control of toxic metal emissions was developed in the Aerosol and Air Quality Research Laboratory. The effectiveness of the proposed technique for the elemental Hg capture is investigated in this thesis.; First, structural characteristics of the in situ generated sorbent particles were studied. The proposed method generated highly agglomerated sorbent particles with small primary particles. This agglomerated structure exhibits large surface area which is ideal for the adsorption process.; Different types of sorbent precursors (Ti, Si, and Ca based) were compared for their ability to capture Hg with and without UV irradiation. While SiO 2 showed no effectiveness for Hg capture, TiO2 in the presence of UV irradiation and CaO were able to capture Hg. In situ generated TiO2 was very effective in the presence of UV irradiation. Hg capture efficiency by CaO and UV irradiated TiO2 was decreased by the addition of SO2 gas into the system. However, higher efficiency was obtained by increasing the feed amount of Ti precursor. In situ generated/UV irradiated TiO2 captured Hg effectively at the elevated temperature condition similar to that of the flue gas entering the electrostatic precipitator in real combustion system.; HCl is one of the major species in flue gases (along with sulfur which was discussed previously) from the coal combustor/waste incinerators that readily reacts with metallic species. Therefore, it is important to examine how the presence of the chlorine species will affect the performance of the in situ Hg capture method. First, gas phase transformation of elemental mercury by HCl was investigated using the simple overall pathway expressed as follows: Hgg+HCl g→HgClg +HgCl2g+&cdots; Finally, the effect of chlorine species (HCl, CH2Cl 2) on the in situ Hg capture was investigated. The TiO2 particles were generated in situ by introducing the Ti precursor into the system before the furnace reactor (1000°C). In situ generated TiO2 particles with UV irradiation were as effective as the chlorine free environment for Hg capture. It is clear from this study that the proposed in situ Hg capture method can be effectively used in combustion flue gas system (with SO2 and HCl as major species).
展开▼
