Carbon sorbent injection is the most promising control technology in reducing mercury emissions from coal-fired power plants. CuCl2-impregnated activated carbon sorbent has demonstrated excellent mercury oxidation and adsorption performance in our previous studies. In our previous study using XAFS shows that mercuric chloride (HgCl2) is a major resultant oxidized mercury compound generated over the CuCl2-impregnated activated carbon sorbent as a result of reaction between elemental mercury and cupric chloride. This study focused on the kinetic adsorption behavior of mercuric chloride vapor onto the CuCl2-impregnated activated carbon sorbent.
The experiments were performed in our lab-scale fixed-bed system at 140 °C by varying inlet HgCl2 concentrations in the range of 5~20 ppbv. Three different sorbents were tested, i.e. raw commercial activated carbon (Norit's DARCO FGD), 4%(wt) CuCl2-impregnated activated carbon, and 8%(wt) CuCl2-impregnated activated carbon. The adsorption capacities of HgCl2 onto raw, 4%, and 8% sorbents were 30 mg, 17 mg, 9 mg HgCl2 per g sorbent, respectively, at 10 ppbv HgCl2. The HgCl2 adsorption capacity of CuCl2-impregnated activated carbon decreased with an increase in CuCl2 loading, suggesting that HgCl2 is adsorbed onto free carbon site. Based on the Langmuir isotherm assumption, a kinetic model of HgCl2 adsorption onto CuCl2-impregnated AC was developed, and the adsorption and desorption rate constants were determined by fitting experimental breakthrough data with the model calculations.
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