【作者】 詹靖；

【导师】 徐明厚；

【作者基本信息】 华中科技大学 ， 热能工程， 2004， 硕士

【摘要】 燃煤过程中产生的痕量元素会对人类和环境造成很大的破坏作用,越来越受到国内外众多学者的关注。但是由于痕量元素含量稀少,检测难度大等原因,对于煤燃烧过程中痕量元素的释放机理以及痕量元素的均相反应动力学机理等方面的研究一直进展缓慢。本文以燃煤过程中的典型痕量元素作为对象,对它们的化学动力学模型和挥发特性做了一些初探性的研究。 首先本文以国内外的几种汞的均相氧化反应机理模型为研究对象,对这几种反应模型中各种组分的反应级数进行了比较和研究,从而得出了整个反应系统的反应级数的范围。与此同时,文中对各模型的表观活化能进行了比较,并对各反应系统的表观活化能在T=1000K附近的突降现象给出了可能的解释。本文所考虑的反应物组分包括HCl,Cl2,O2,采用的反应机理模型都是近年来所公认的比较成熟的模型。通过相应的计算和比较发现,Cl2为汞均相氧化模型中的主要氧化剂,O2亦为反应系统中一个不可忽视的因素,而HCl对于汞的氧化贡献较小。这一结果与近年来的报道是一致的。 其次本文运用热平衡分析法对不同气氛下三种煤样的燃烧系统中As, Se物质的分布及含量进行了预报,并以此来指导实验方案的设计,最后,进行相应的实验研究,来探究燃煤过程中As, Se的挥发行为特性。从研究结果我们可以得出:As, Se的挥发量都随着温度的升高而增加,并且Se的挥发百分比要比As要大。在氮气气氛下,As挥发量大幅提升的现象发生在 600-900℃这一温度范围, 而Se的大量挥发现象比As要早,大约在 200-600℃的温度范围内。氧化性气氛有助于As,Se在更低的温度下的挥发。SO2在某一温度范围内对于两种痕量元素的挥发有微弱的促进作用。更多还原

【Abstract】 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.更多还原