Effect Of Additive Oxidants On Mercury Transformation And Removal Efficiency For Coal Combustion

In the foreseeable future,coal still keeps the dominated position in China energy.The majority of which is used by the combustion process for power generation.Trace mercury?Hg?from coal combustionis one of the most toxic heavy metals for atmospheric environment.Therefore,it is of importance to further understand the release behavior of Hgfor developing th eoxidants to decrease Hg emission from coal-fired power stations.In this thesis,a set of temperature-programmed combustion apparatus and two kinds of analysis methods?Zeeman vapor atomic absorption spectrometry and Ontario absorption?are combined to investigate the Hg releasecharacteristics from coal combustion process and the effect of oxidizing agents on Hg removal efficiency.Moreover,the Hg⁰ and Hg²⁺ are distinguished from flue gas and the removal mechanism is explored in this study.Two types of coals and a kind of coal gangue are used to investigate the Hg release behaviors and transformationcharacteristics during combustion processes.The experimental results show that Hg release is directly related to its formation within coals,and the release rules have obvious difference for the different coal samples.For the samples used in this study,Hg is completely released when the temperature is higher than 800 ?.Hg⁰ is the majority of Hg in the flue gas,the minority of Hg²⁺ is likely due to Cl or other similar elements in coal and the operational condition of combustion process.Three kinds of coal samples and one kind of coal gangue were used to study the effect of additive oxidants on mercury and removal efficiency for coal combustion.First,before combustion experiment was carried out on the blank sample coal combustion products was determined,the results show that the smoke of the coal sample in Hg⁰ content can reach more than 60% of the total mercury,human should be improved removal rate.Choice of strong oxidizing oxidant and multiphase exist,therefore chose six HBr,KI,NH₄I,Ca Br₂,NH₄Br halogens,such as salt and compound experiments,including mercury effect is the worst for k I,on equipment corrosion is gets bigger,so this paper NH₄I,CaBr₂,NH₄Br three kinds of antioxidants are discussed.Combustion experiment results confirm that NH₄I is suitable for the coal of mercury content is relatively low,CaBr₂ is added in the coal and coal gangue high mercury mercury works best,and NH₄Br effect is always in the middle level.So don't think for the selection of oxidant is invariable,depends on the specific characteristics of coal sample choose different oxidant,because both the properties of antioxidant properties and coal nature determines the shape of the combustion products.Experiment combustion heating rate of the reaction time is also important factors that influence measuring results show that the heating rate of adding antioxidant effect is very small coke coal sample gas mercury forms to ignore.