Experimental Study On Removal Of Elemental Mercury From Coal-fired Flue Gas By Fe₂O₃-CeO₂ Modified Activated Coke

Mercury has the characteristics of volatile, persistence and bioaccumulation, which has a huge impact on human health and the environment. The emission of mercury from coal-fired utilities is the main air pollution source for countries utilizing coal as their principal energy input. Consequently, the development of coal-fired flue gas mercury control technology with prospects is a top priority to control the environmental mercury pollution. Using the existing desulfurization and denitration devices to achieve the removal of mercury in flue gas at the same time is an economical way. Currently, as activated coke（AC） owns superior performance and low price, it has been widely applied in coal-fired power plants desulfurization process. Besides, the combined desulfurization and denitration technology over AC is also mature.However, the study of simultaneously removing SO₂, NO_x and mercury is relatively small. Therefore, studying the mechanism of removing mercury with AC and development of new activated coke adsorbents for efficiently realizing simultaneous removal of SO₂, NO_x, mercury has important theoretical and realistic significance.This paper introduces the physicochemical properties, existing forms, sources and harm to healthof mercury. It also presents the research progress of mercury control technologies for coal-fired power plants. Then, the properties of AC and its application in the field of coal-fired flue gas purification have also been stated. Furthermore, the theories of AC simultaneously removing SO₂, NO_x and mercury are discussed and the regeneration of AC is proposed. Based on these, modified AC by Fe₂O₃-CeO₂ was developed and has been used to evaluate the Hg⁰ removal capacity in the simulated coal-firedflue gas.In our experiment, a series of Fe₂O₃-CeO₂/AC samples were prepared. Effects of some parameters, including the mass ratio of Fe₂O₃ and CeO₂, reaction temperatures and flue gas components, on Hg⁰ removal efficiency were investigated. Some physicochemical techniques such as BET, XRD, SEM and XPS were employed to characterize the samples. The mass transfer rules of Hg⁰ and the physic-chemical behavior of Hg⁰ on the samples surface were studied in order to clarify the removal mechanism of Hg⁰.In comparison to virgin AC, Fe₂O₃-CeO₂/AC significantly enhanced Hg⁰ removal efficiency. Hg⁰ removal ability was enhanced with the increase of Fe₂O₃ when loading value was below 3% and then slightly decreased with increasing Fe₂O₃ loading value to 4%. When the mass ratio of Fe₂O₃ and CeO₂ was 3:3, the Hg⁰ removal efficiency reached to a peak value of 88.29%. The experimental results indicated that Hg⁰ removal efficiency increased with increasing the temperature from 50 to 110 °C and then decreased with the temperature rising from 110 to 200 °C.So, the optimal temperature was 110 °C. Besides, it was observed that the flue gas components would affect Hg⁰ removal efficiency, to some degree. O₂ and NO exerted a promotional effect on Hg⁰ removal. SO₂ showed an insignificant inhibition for Hg⁰ removal, however, SO₂ had a promotional effect on removing Hg⁰ with the aid of O₂. Furthermore, when H2O（g） was added into the flue gas, the Hg⁰ removal capacity had a slight declination. The analysis of XPS showed that the main species of mercury on used Fe₃Ce₃/AC was Hg O, which implied that adsorption and catalytic oxidation were included for Hg⁰ removal over Fe₃Ce₃/AC, and catalytic oxidation played the critical role. Meanwhile, the lattice oxygen, chemisorbed oxygen, and/or weaklybonded oxygen species contributed to Hg⁰ oxidation.