Research On The Chemical Kinetics And Volatilization Behaviour Of Typical Trace Elements In Coal

The trace elements emitted during the coal combustion will greatly damage themankind and the enviroment. They receive the concerns of many researchers more andmore. People know few about the mechanism of kinetics of homogeneous reactionand the emission of the trace element because the amount of the trace elements are rare andthey are difficult to be measured . This paper regards the typical trace elements emitted during thecoal combustion as the targets. Some researches on kinetics model and the characteristic ofvolatilization of trace elements have been done in this thesis. Firstly the reaction order of each component in five homogeneous Hg0 reactionmodels is compared in this paper. The range of the reaction order as well as theapparent activation energy Ea of the whole reaction system are obtained by thecomparison. Reasonable explanation on sudden decrease of the apparent activationenergy Ea at the reaction temperature of 1000K is provided. The reaction componentsconsidered in this study include HCl,Cl2,O2 and the reaction models used in thispaper are commonly acceptable in recent research in this field. The calculation andcomparison results show that Cl2 is a main oxidizer in homogeneous Hg0 reactionmodels, and O2 is an un-neglected factor in mercury oxidation, while HCl has anunnoticeable effect on the oxidation of Hg. This conclusion is consisted with recentresearch results in the literature. Then the partitioning of As and Se species in three different coal combustionsystems were predicted by equilibrium analysis. Then the experimental research onvolatilization behaviour of As and Se was conducted. Finally, the followingconclusions can be drawn: The percentage of volatilization of As and Se increasedwith the increase of the reaction temperature, meanwhile the amount of volatilizationof Se was more larger than that of As under same temperature. Under nitrogencondition, the amount of volatilization of As increased rapidly at the temperature of600-900℃ while Se at 200-600℃. The oxidizing condition was favorable for thevolatilization of As and Se under more lower temperature. SO2 also can improve thevolatilization of As and Se.