The Research On The Removal Of Element Mercury From Coal-fired Flue Gas By H₂O₂ Modified Activated Coke

In addition to SO₂,NOx and fly ash will be discharged into the atmosphere,it will also release a certain amount of heavy metals like mercury during coal combustion.Mercury released into the environment has the characteristics of volatile,persistent and bioaccumulation,which has a huge impact on human health and the environment.Additionally,in addition to greenhouse gases,mercury is the only chemical substance which can cause global impact,so the mercury pollution has been drawn serious attention of worldwide.Mercury emissions from coal combustion is the main source of atmospheric mercury,consequently,the development of coal-fired flue gas mercury control technology with prospects is a top priority to control the environmental mercury pollution of China.Due to the fact that there is no equipment for mercury control in the industrial application in China,it is the most economical way to remove Hg from the flue gas through the currently available pollution control devices in coal-fired power plants.Recently,activated coke?AC?has been widely used for desulfurization and it has been reported that AC for simultaneous removal of SO₂ and NOx has been introduced into industrial application.However,simultaneous removal of SO₂,NOx and mercury with AC has been rarely reported by the literature.Therefore,development of a new activated coke adsorbent with excellent mercury removal capacity are of great significance for realizing simultaneous removal of multi-pollutant from the coal-fired flue gas and reducing environmental mercury pollution.This paper introduces the physicochemical properties,existing forms,sources and harm to health as well as the emission standards of 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,technological process and the general situation of AC simultaneous removing SO₂,NOx and mercury are discussed and the regeneration of AC is proposed.Based on these,modified AC by H₂O₂ oxidising was developed and has been used to evaluate the Hg0 removal capacity in the simulated flue gas.In our experiment,modified AC was developed and the optimum parameters were obtained by orthogonal experiment.The effects of some related experiments parameters,including reaction temperature and flue gas components,on Hg0 removal efficiencies were conducted in a lab-scale system.Some physicochemical techniques such as BET,XPS,FT-IR and Beohm titration were employed to characterize the samples.The mass transfer rules of Hg0 and the physic-chemical behavior of Hg0 on the catalyst surface were studied in order to clarify the removal mechanism of Hg0.The experimental results showed that H₂O₂ oxidtion significantly enhanced Hg0 removal efficiency of AC and the optimal sample was AC-10%O-1-3h,with the removal efficiency higher than 90%under the optimal temperature?140 ??.Additionally,the experiment results of effects of flue gas components on Hg0 removal efficiencies showed that the Hg0 removal efficiency is promoted by O2,NO and SO₂ in the flue gas and the higher concerntration of these flue gas components the higher mercury removal efficiency.When O2 was existed with one or both of NO and SO₂,the mecury efficiency was shown an improvment,indicating that O2 has a synergistic effect to Hg0 removal with NO and SO₂.Furthermore,when NH3 or H2O was added into the flue gas,the Hg0 removal capacity was suppressed and the presence of O2 can lighten the suppression of NH3.The analyses of Beohm titration,FT-IR and XPS showed that the acid oxygen containing functional groups of AC were increased by H₂O₂ oxidation and those functional groups had remarkably positive effects on the Hg0 removal.According to Hg 4f XPS analysis,the mercury on the surface of modified AC was mainly in the form of mercuric oxide?HgO?and bits of mercuric chloride?HgCl2?.The reaction mechanism indicated that Hg0 was oxidized to HgO by the acid oxygen containing functional groups after adsorbed on the suface of the sorbent,and the O of those functional groups could be compensated by the O2 in the flue gas.Thus,it indicated that within the range of reaction temperature for activated coke simultaneous removing SO₂ and NOx,the elemental mercury can be effectively removed from the simulated flue gas,which accordingly infer that H₂O₂ modified AC has great potential for simultaneous removing SO₂,NOx and mercury from the flue gas in the existing device.