Masaki Takaoka*, Nobuo Takeda* and Shigenobu Okajima*
* Department of Environmental and Sanitary Engineering, Faculty of Engineering, Kyoto University
+ Correspondence should be addressed to Masaki Takaoka:
(Yoshida-honmachi, Sakyo-ku, Kyoto-city, 606-01, Japan)
Abstract
The levels of mercury in flue gas from municipal waste incinerators can be reduced by using bag filter, but the mechanism of mercury elimination is not completely understood. We conducted basic experiments with fly ash, calcined fly ash and activated carbon to evaluate important factors for mercury elimination. It was found that the unburned carbon content and gas temperature were important factors for fly ash. In the case of calcined fly ash with activated carbon, the activated carbon content, temperature and hydrogen chloride concentration were important factors. X-ray diffraction analysis indicated that the type of mercury formed in the filter layer was mercury (I) chloride. From these results, we considered that mercury (II) chloride was converted in the filter layer by a two step reaction; that is, adsorption-reduction and reduction-desorption reactions. A mathematical model was suggested based on the two step reaction. The calculated rate constant value of reduction-desorption reaction was much smaller than that of the adsorption-reduction reaction. The mechanism of mercury elimination in the bag filter was adsorption accompanied with chemical reactions.
Key words: mercury, bag filter, fly ash, unburned carbon, adsorption