| Mercury pollution from coal combustion causes enormous damage to global ecology and human health, which has brought great concern worldwide. Oxy-fuel combustion technology is known as one of the most advanced clean coal utilization technologies. A commercial activated carbon was taken as mercury adsorbent to explore the mechanisms of mercury removal and impacts of flue gas components under simulated oxy-fuel combustion flue gases and common air-fuel combustion flue gases respectively, in a fixed bed mercury adsorption system. The mercury speciation and its distribution were conducted in a temperature programmed desorption (TPD) experimental facility. The mercury species mass balance was obtained.The activated carbon samples were characterized by means of N2 adsorption/desorption and Fourier transform infrared spectroscopy (FTIR). The results show that the activated carbon has large specific surface area and developed micro-pores. The main oxygen surface functional groups contain ester groups, carboxyl and phenolic hydroxyl group. The adsorption temperature and atmosphere have obvious effect on surface oxygen functional groups. NO increases the content of ester groups slightly, while SO2 reduces the content of both ester groups and carboxyl groups somewhat. The fixed-bed adsorption experimental results indicate that under a pure CO2 atmosphere conditions, the adsorption of Hg0 by activated carbon is slightly worse than that under a pure N2 atmosphere. When added O2, mercury removal efficiency of the activated carbon under the simulated oxy-fuel combustion flue gas is better than that under the simulated air combustion gases. The mercury removal efficiencies increase with the increase of oxygen concentration. SO2 decreases mercury removal efficiency slightly, while NO greatly improves the mercury removal efficiency. It showed the similar tendency under simulated oxy-fuel combustion gases and air combustion gases.Results of the temperature programmed desorption experiments for the activated carbon adsorbed samples show that:organic matter mercury (Hg-OM) is the main form of mercury adsorped on the surface of activated carbon, in which mercury oxide (HgO) is also exists. O2 joined in adsorption process would obviously increase the content of HgO on the activated carbon surface. CO2 has no change on mercury adsorption form, but reduces the adsorption volume of mercury. The sample is exposed by SO2 is detected HgSO4, while when NO is exposed it significantly increases the amount of adsorpted mercury and produces Hg2 (NO3)2.The mass balance analysis of mercury speciation was measured in tests of mercury adsorption and desorption experiments under two groups of simulated oxy-fuel combustion gases and two groups of air combustion gases. The results show that:there is little difference of the Hg adsorption volume by the activated carbon samples performed under both the simulated air combustion gas and the oxy-fuel combustion gas, indicating that the mass of Hg escaped from the fixed-bed reactor accounts for 62% and 65% respectively. When added SO2 and NO in the simulated flue gases seperately, the activated carbon could almost adsorb all the Hg0. Among the four experiments, only under simulated O2/CO2 atmosphere, Hg2+ in gas phase can be obviously detacted. In the other three experiments, Hg2+ content in gas phase is rarely low. Finally, the results of mercury mass balance of the four groups are between 80%-120%, which proves the reliability of this experimental data. |
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