【作者】 麻银娟；

【导师】 宋党育；

【作者基本信息】 河南理工大学 ， 地质工程， 2011， 硕士

【摘要】 煤燃烧所造成的大气污染给人类健康带来了极大的危害,特别是亚微米量级颗粒形式存在的重金属及其化合物因为其相当大的毒性而备受人类关注。因而燃煤过程中痕量元素的排放控制研究也成为治理燃煤污染中一个新的前沿领域。本文以煤中易挥发元素Hg、As、Pb为研究对象,以焦作无烟煤和平顶山烟煤为原煤样品,通过热力学平衡模拟分析及实验室燃烧试验相结合的方法对其在添加添加剂前后迁移转化、富集行为及添加剂机理进行了研究,为进一步研究控制煤中重金属污染奠定了基础。（1）本文首先应用了FactSage模拟分析了Hg、As、Pb等挥发性元素在燃烧中的迁移转化及形态分布,考虑了硫,氯元素对其形态分布的影响。模拟结果表明在氧化性气氛下产物固相范围会更宽一些:单质汞是Hg的热力学稳定形式;砷元素在温度升高到700K以后全部转化为气相砷的氧化物;Pb在850K之前以固态PbCO₃与Pb₃O₄,在高温阶段主要以气态PbO存在。氧化性气氛下硫、氯元素与Pb有着很强的结合性,随着Cl/S比的升高,PbCl₄存在的温度范围越宽;氯元素对的As的平衡分布基本没什么影响,硫元素在还原性低温气氛与As有着很强的结合性;对于Hg元素,随着S/Cl比的升高,单质汞的温度范围变宽,增强了单质汞的排放。（2）再次应用了FactSage模拟分析了Hg、As、Pb等挥发性元素在氧化性气氛下加入添加剂之后燃烧时的迁移转化及形态分布。结果表明Al₂O₃与SiO₂对Pb的挥发都有抑制作用,而Al₂O₃在400¹100K效果更好,同时硫、氯元素对添加剂的吸附效果影响很大,加入一定的含钠矿物有助于达到一个更好的吸附效果;而任何添加剂对Hg的形态分布的影响都不大;钙质添加剂使砷元素形态在400¹300K发生了一定的变化,主要以砷的固相物质存在,其中在750¹200K之间生成是砷酸钙,而Ca/S比增大,砷酸钙作为固相的温度范围越宽,Ca/S=10时达到最大。（3）采用高温管式电炉在设定温度下进行煤粉燃烧试验,燃烧气氛为氧化性气氛,将底灰应用先进的微波消解技术进行样品预处理,应用ICP-MS及原子荧光光谱仪等测试手段,分析了加入添加剂前后Hg、As、Pb元素在底灰中的含量分布。结果表明:Hg元素极易挥发,从化学角度讲添加剂对Hg的控制没有作用,这与模拟结果相符;Pb元素有在底灰中富集的趋势,并随温度的升高,其富集趋势减小;四种添加剂对Pb、As的吸附效果随温度、煤种、添加剂种类的不同而不同。模拟结果与实验结果在对重金属控制温度上存在差异。（4）结合模拟研究与试验研究,从化学吸附机理来看,添加剂与煤自身存在着一些的化学活性位,它们与痕量元素发生化学反应,从而生成不易分解的物质而固定在灰中。更多还原

【Abstract】 Air pollution caused by coal combustion brings great harm on human health, especially the heavy metals and their compounds in the form of submicron particles are caught much attention, as they have relatively high toxicity. Therefore, the research on emission control of trace elements in coal combustion has been a new frontier field.In this paper, volatile elements in coal such as Hg, As, Pb are selected as research object, Jiaozuo anthracite and Pingdingshan bituminous as raw coal samples, thermodynamic equilibrium simulation analysis combined with combustion test in laboratory is used to research migration-transformation, enrichment behavior and absorption mechanism of trace elements before and after the additives are added. It lays foundation for pollution control on trace elements in coal in the further study.（1）The FactSage software was firstly applied to simulate migration-transformation and distribution of the volatile elements Hg, As and Pb in coal combustion, the effect of S and Cl on distribution was taken into consideration. Simulation result shows that solid phase of products maybe a little wider under oxidizing atmosphere: Elemental mercury is the thermodynamically stable form of mercury; arsenic transforms into gaseous oxide of arsenic totally when temperature rises to 700K; prior to 850K, the forms of Pb are solid PbCO₃ and Pb₃O₄, while at high temperature gaseous the main form is PbO. Under oxidizing atmosphere, element S and Cl have strong combination with Pb, with the increase of the ration of Cl/S, the temperature range of PbCl₄ becomes wider. The effect of element Cl on the balance distribution of As is little, element S has strong combination with As; as for Hg, with the increase of S/Cl, the temperature of elemental Hg becomes wider, too, which indicates that emission of elemental Hg is enhanced.（2）The Factsage was also applied to simulate migration-transformation and distribution of Hg, As and Pb in combustion after additives were added under oxidizing atmosphere. The result shows that Al₂O₃ and SiO₂ can inhibit the volatilization of Pb, at the temperature 400¹100K, the effect of Al₂O₃ is even better, at the same time, Cl and S have great influence on absorption effect of additives, and adding some sodium minerals can help to reach a better absorption effect. However, any additive has little influence on distribution of Hg. Additives of calcium make the distribution of As change in certain extent at 400¹300K, mainly occurring in the form of solid As（at 750¹200K, arsenic calcium）. As the Ca/S ratio increases, the temperature range of arsenic calcium becomes wider, and when Ca/S=10 reaches to the maximum.（3）High-temperature tube furnace was applied to burn pulverized coal samples at the given temperature under oxidizing atmosphere. Advanced microwave digestion method was used to treat bottom ash; ICP-MS and AFS were applied to analyze the content distribution of Hg, As, Pb in bottom ash before and after the additives were added. The result shows that Hg volatilizes very easily, additives has no control on Hg form the perspective of chemistry, which accords with simulation result; Pb and As have enrichment trend in bottom ash, and with the increase of temperature, the trend becomes less. The absorption effect of four additives is different as the difference of temperature, coal and additive type. There are some differences between simulation and experiment in heavy metal control temperature.（4）Combined with simulation study and experimental research, from the perspective of chemical absorption mechanism, additives and coal chemical itself have some active sites, which react with trace elements to produce the materials that not easily break down, then fix in the ashes.更多还原