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The Research on the Removal of Element Mercury from Coal-fired Flue Gas by Modified Desulfurization-activated Coke

Author: TaoShaSha
Tutor: LiCaiTing
School: Hunan University
Course: Environmental Engineering
Keywords: coal-fired flue gas catalytic oxidation mercury activated coke CeCl3 CeO2
CLC: X701
Type: Master's thesis
Year: 2013
Downloads: 7
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Abstract


Mercury is one of world-wild concerned pollutants because of its volatility,persistence, bioaccumulation and high toxicity to human health and environment. Theemission of mercury from coal-fired utilities is the main anthropogenic air pollutionsource for countries utilizing coal as their principal energy input. Consequently,development of technologies governing and controlling mercury emission fromcoal-fired power plants has become an urgent issue for the countries using coal astheir principal energy input. Based on the situation of our country and existingpollution control devices in coal-fired power plants, it is the most economical way toremove Hg from the flue gas through the currently available pollution control devices.Recently activated coke has been widely used for desulfurization and it is reportedthat activated coke for simultaneous removal of SO2and NOxhas also been introducedin industry application. However, simultaneous removal of SO2, NOxand mercurywith activated coke is still weak and need further research. Therefore, studying themechanism of removal of mercury with activated coke and development of newactivated coke adsorbents are of great significance for realizing simultaneous removalof SO2, NOx, mercury and improving the combustion quality and reducing mercurypollution.This paper introduces the physicochemical properties, existing forms and harm tohealth of mercury, and discusses the sources of mercury. It also presents the researchprogress of mercury control technologies for coal-fired power plants. Then, thestructure, properties of activated coke and its application in the field of environmentprotection have also been stated. Furthermore, the theories, technological process andthe general situation of activated coke simultaneous removing SO2, NOxand mercuryare discussed. Based on these, modified activated coke （AC） using CeCl3wasdeveloped and used to evaluate the effects on Hg0removal to produce an effectivemercury emission control strategy for coal power plants.In our experiment, modified AC was developed and some related experimentsparameters including the CeCl3loading value, reaction temperature and flue gascomponents for evaluating the effects on Hg0removal efficiencies were conducted ina lab-scale system. Some physicochemical techniques such as BET, XRD, SEM-EDXand XPS were employed to characterize the samples. The mass transfer rules of Hg0 and the physic-chemical behavior of Hg0on the catalyst surface were studied in orderto clarify the removal mechanism of Hg0.The experimental results showed that CeCl3significantly enhanced Hg0removalefficiency of AC. The optimal CeCl3loading value and reaction temperature wasaround6%and170oC, respectively. Additionally, the experiment results of effects offlue gas components on Hg0removal efficiencies showed that when O2was present inthe flue gas, NO and SO2were observed to promote Hg0oxidation. However, in theabsence of O2, SO2showed an insignificant inhibition on Hg0removal. Furthermore,when H2O was added into the flue gas, the Hg0removal capacity had a slightdeclination. The analyses of XRD and XPS showed that CexOyand C-Cl weregenerated on the surface of AICC and those active elements had remarkably positiveeffects on the Hg0removal. And according to Hg4f XPS analysis, the mercury on thesurface of AICC was mainly in the form of mercuric oxide （HgO） and mercuricchloride （HgCl2）. The reaction mechanism indicated that Hg0oxidation was achievedthrough two pathways: one was that Hg0bond with CeO2and was converted by thecatalytic oxidation of valence variable cerium; the other was that Hg0reacted withC-Cl on the sample and was oxidized favored by chloride presence. Thus, it indicatedthat within the range of reaction temperature for activated coke simultaneousremoving SO2and NOx, the elemental mercury can be effectively removed from thesimulated flue gas, which accordingly infer that CeCl3/AC has great potential forsimultaneous removing SO2, NOxand mercury from the flue gas in the existingdevice.

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CLC: > Environmental science, safety science > Processing and comprehensive utilization of waste > General issues > Exhaust gas processing and utilization
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