過渡金屬改質椰殼活性碳同步控制燃煤煙氣中多重污染物(Hg0、SOx、NOx)之研究

Abstract

With the increasing needs for energy sources all over the world, the demand for thermal power is keeping rising. Thermal power is one of the main causes of air pollution since its emissions contain metal contaminants such mercury, as well as acidic gases such as nitrogen oxide and sulfur oxide. In light of such effects on the environment, the US Environmental Protection Agency passed the Mercury and Air Toxics Standards (MATS) in 2011, which is a law that additionally limits the heavy metal and acidic gas emissions along with other toxic pollutants from coal-fired power plants. Absorption has been considered as one of the best techniques to control the pollutants emitted from power plants. The capacity and kinetics of the absorbents, the chemical reactions in gas streams, and overall cost are the key factors to whether or not that absorption can be successful. This research utilizes a commercially available coconut-shell activated carbon paired with various transition metals (5 wt% Mn or 5wt % Cu) in a mixed sequence to investigate its characteristics before and after modification and its capacity to adsorb contaminants. Results showed that after the transition metal modification, the BET surface area of the activated carbon decreased due to the blockage of micropores of the activated carbon by the doped transition metal salt. SEM and XRD results showed that the surface of modified activated carbon was smooth, and the crystal phase of metal oxides were not observed. It is speculated that the modification method was mild and done without using invasive energy; therefore, significant changes in the surface structure of the activated carbon were not occurred. The doped metal oxides can thus be homogenously distributed onto the surface of the activated carbon. The doped metal oxides had marked effects in enhancing the Hg0 removal under both nitrogen and simulated flue gas conditions. At 350 oC, flue gas condition the Hg0 removal efficiency was 34.8-87.5%. Furthermore, Hg0 removal was further increased under simulated flue gas condition as compared to that under nitrogen condition. These results indicate that flue gas components had a positive effect on enhancing the activated carbon's Hg0 removal efficiency. It is worth noting that the activated carbon modified with copper possessed the greatest Hg0 removal of 87.5% and 98.9% at 150 oC and 350 oC, respectively. The presence of NH3 inhibited the oxidation of Hg0. Cu-modified activated carbon also had greater NO reduction of 3.7% and a lower SO2 removal of 14.7%. Consequently, activated carbon modified with copper salt is considered having the greatest potential in simultaneously removing multipollutants from coal-combustion flue gease.