REMOVAL TECHNOLGIES OF POLLUTANT GASES AND TOXIC HEAVY METALS BY FINE PARTICULATE SORBENTS

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Decrease of landfill place in Japan gives rise to decrease of volume of final waste. Reduction of the emission of dioxins causes high temperature combustion or gasification condition. Also, increase in efficiency by combined cycle power generation with gas turbine needs the high temperature condition. However, its condition causes the toxic metal emissions, which affect human health. Unless such metal emissions could be enough to controlled by flue gas treatment system or dust separation process with hot gas filters, the service life of the gas turbines should be decreased. Objectives of this research is to capture pollutant gases such as hydrochloric acid (HCl) and/or toxic heavy metals as cadmium (Cd) at high temperature by fine particulate sorbent. In first-step experiment focusing on HCl calcium oxide (CaO) of limestone was used as a sorbent. Results by a continuous measurement equipment for HCl showed that conversion of HCl into CaCl_2 is increased with temperature up to 750℃ but … More it is decreased at much higher temperature by melting CaCl_2. Particle size affects on its melting behavior and gives different conversion even at the same reaction temperature. When SO_2 is mixed, the conversion of HCl is decreased by fast formation of CaSO_4. With water, CaCl_2 emits HCl. It suggests that water content in fuel is an important factor to capture Cl by CaO.In second-step experiment on capturing Cd by minerals, kaolinite was used. We already confirmed that as candidates of sorbent to capture Pb and Cd kaolinite could be much effective and halloysite, dickite with similar layer structure are also effective by a batch experiment. In this study by using flow experiment, Cd was supplied as aerozol vapor. Results suggested that the capture yields of cadmium by both filtering of kaolinite are increased with time up to 40 min and decreased at 60 min for any concentration of cadmium. Kaolinite gave a maximum yield of around 40% but it appeared to be independent of the concentration. It is equivalent to the 300μg of cadmium to 1.0g of kaolinite sorbent. Decrease of captured yields at 60 min could be explained by metal leaving sorbent into silica paper and out of these filter. Similar results were also obtained at 800℃. It suggests that metal concentration in flue gases is one of more important parameters as well as temperature and time. Furthermore, effects of particle size and physical and chemical adsorption were measured and described in this report. Less