| The situation that the main energy of China is relied on coal will not be changed in a long time. As a result, various pollutants was produced. With the increasing awareness of environmental protection and more promulgation of policy, laws and regulations, the pollutants have been controlled. At present, many coal fired plants are equipped with fine particle removal, desulphurization equipment and denitrification facilities, thus dust, SOx and NOx are under control. However, the treatment method for heavy metal mercury is not enough. Therefore, it is meaningful to develop a novel efficient cost-effective sorbents for capturing mercury.Petroleum coke is selected as raw material in this study and alkali is employed as activation to obtain petroleum coke-based activated carbon (PAC) which is regarded as a kind of support. Potassium iodide (KI) or manganese chloride (MnCl2) have been chosen as active materials, and the sorbents were prepared by wet impregnation method and the sorbents were characterized by N2 adsorption, XRD, SEM and FT-IR to analyze the surface properties of sorbents before and after reaction. Experiments were tested in the packed-bed to evaluate the Hg0 removal efficiency under different loading values, temperatures and gas components.The results indicated that PAC showed a certain mercury removal performance, but the efficiency decreased with the increasing temperature. The KI impregnated PAC significantly improved the mercury removal efficiency and removal efficiency can be increased to above 90%. When the impregnation concentration of KI solution is 1.5 g/m3 and the mass percent of active component is 3 wt.%, the sorbent showed better mercury removal performance, and the efficiency showed the trend of increasing in the initial stage and then declined during the temperature of 40-120 ℃, and the best removal efficiency is at 80 ℃, the removal efficiency is above 85% after 3 h reaction. SO2 show the effect of inhibition or promotion; it is dependent on the concentration of SO2 and gas components. The efficiency will be increased under relatively low SO2 concentration and with oxygen in the flue gas, while under the high concentration and without oxygen, the removal efficiency shows the opposite performance. HCl and NO have a positive effect under a certain concentration range. XPS analysis and Hg-TPD have been used to test the sorbents after mercury removal reaction and the results show that the reaction on the surface of the PAC modified with KI is chemical adsorption even at low temperatures.MnCl2 was employed to modify the PAC with various concentration of solution from 0.2 to 0.6 mol/L to expand the range of application of carrier and the reaction temperature window. The results showed that the higher concentration of impregnation solution the better mercury removal performance. The experiments were carried under the temperature with the range of 100 to 250 ℃, the removal efficiency was high and stable(above 90%) at the temperature before 200 ℃ and suddenly dropped when the temperature is above 250℃. The concentration of oxygen have an influence on the mercury performance, and the higher concentration can improve mercury capture and oxidized. In order to explore the mechanism of mercury removal reaction with this series sorbents, CaCl2 impregnation agent and the method of pretreatment of samples impregnated by MnCl2 at higher temperature were employed. With the results of comparative experiments and characterizations, it could be found that MnOx and active Cl both have a promotion effect of PAC modified by MnCl2 on the mercury adsorption. The metal oxide of Mn could oxidize Hg0 and follow the mechanism of Mars-Maessen and the element of Cl promote the mercury removal efficiency could be explained by Eley-Rideal mechanism. |
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