【作者】 高洪亮；

【导师】 骆仲泱； 倪明江； 岑可法；

【作者基本信息】 浙江大学 ， 环境工程， 2004， 博士

【摘要】 燃煤汞排放作为大气污染的一个重要来源，其造成的汞污染对生态环境具有很大的直接和潜在的危害。国内外有关燃煤过程中汞的形态转化和控制方法的研究还处于探索阶段，在有效吸附剂的筛选及治汞机理方面的研究也还很薄弱。因此，积极开展汞污染的研究，研究汞脱除的特效吸附剂，研究汞形态的转化规律和合理的治汞方法，对于提高燃烧质量，减轻汞对环境的污染都有重大意义。 首先对单质汞向氧化态汞转化的影响因素进行了实验研究，采用Ontario Hydro方法作为样品取样方法，分别进行了烟气中氯化氢浓度大小、氧气浓度大小、NO浓度大小、二氧化硫浓度大小、反应器出口温度高低以及汞浓度变化对燃煤烟气中汞形态分布的影响。得出如下结论：HCl是燃煤烟气中与汞发生化学反应的主要物质，在未添加HCl的烟气体系中，随反应温度的升高单质汞向氧化态汞转化的转化率先是升高而后降低，NO、O₂、SO₂的存在可以促进汞的氧化；在添加HCl的烟气体系中，随反应温度的升高汞单质汞向氧化态汞转化的转化率升高，烟气中氯化氢的浓度越大，转化率越大；烟气中其他成分对汞的形态转化有一定的影响，NO、O₂的存在可以促进汞的氧化，SO₂的存在则抑制汞的转化；另外，较高的烟气排放温度会提高单质汞向氧化态汞转化的转化率，Hg浓度升高汞转化率下降。 建立了燃煤烟气中汞形态转化的动力学模型，在氯化氢存在的情况下烟气中汞均相气相氧化的总反应速率方程为：(^dCHg/dt=-k×C_Hg^1.78×C_HCl^0.79；总反应速率常数方程为： k=0.029858exp（-12787.5/RT）。通过模型计算，选取基本工况，对烟气中汞的反应过程进行了模拟计算，计算结果与实验结果基本吻合；通过模型分析，选取一些重要影响因素，预测了在一定运行条件下汞形态的转化，结果与汞形态转化实验研究的结果一致。该模型可用于定量预测典型燃煤烟气中汞形态转化的程度。 对吸附剂进行化学改性后，在小型模拟烟气实验台上进行了汞吸附实验筛选，以期获得经济、高效的汞吸附剂。首先进行了吸附剂的改性实验研究。在查阅大量文献基础上，结合现有污水除汞及炼汞工业的废液、废气的除汞方法，尝试性地进行了吸附剂的活性MnO₂浸渍、FeCl₃浸渍、不同温度下渗硫等改性试验。并在固定床上进行了吸附剂的初步筛选。对原吸附剂及其改性吸附剂在固定床上进行了恒温汞吸附实验，初步找出效果较好的吸附剂，筛选出了以下几种有应用前景的吸附剂：活性炭、活性MnO₂浸渍活性炭、三氯化铁浸渍活性炭、600℃渗硫活性炭、活性MnO₂浸渍沸石、活性MnO₂浸渍膨润土、活性MnO₂浸渍蛭石、三氯化铁浸渍蛭石，并研究了不同烟气成分、不同入口汞浓度、不同吸附反应温度、不同炭汞比等因素对汞蒸气吸附作用的影响。 在燃烧石煤的循环流化床电站锅炉上进行了汞排放及控制试验研究。结果表明汞在燃烧产物中的分布因工况不同而不同，燃烧添加石灰石前后汞的分布发生了较大的变化，比较明显的是ESP灰中汞增加，排放大气总汞减少，炉底灰渣中汞和排放大气总汞中固态汞含量变化不是很大，添加石灰石有利于总汞中零价汞的减少。电站除尘器对汞的排放有一定的控制作用，除尘器后烟气中汞的含量明显低于除尘器前；烟气经过除尘器前后气态汞分布变化不大；排入大气的烟气中主要为单质态汞为主。浙江大学博士学位论文 在小型脱汞实验台上进行了燃煤烟气除汞技术的机理试验研究。对固定床实验筛选出来的吸附剂进行了脱汞实际应用研究，对各种脱汞操作工况进行了优选，得出对于未进行化学改性的吸附剂，半干法除汞是最佳操作方式;对于经过化学改性的吸附剂，干喷射吸附剂法除汞是最佳操作方式;由于电厂燃煤烟气除汞过程需要的吸附剂量较大，化学改性具有一定的难度，因此就工程实际应用前景来看半干法除汞是最佳的电厂燃煤烟气除汞技术;在中型燃油实验台上进行了有关的放大应用实验，主要研究了固定床试验所筛选出的几种吸附剂对汞蒸气的吸附效果，以及吸附反应温度、不同碳汞比等因素对汞蒸气吸附作用的影响。对吸附汞后的吸附剂进行了稳定性实验，结果表明被吸附后的汞比较稳定。 通过模型计算，选取基本工况，对活性炭半干法中试塔体内部吸附进行了模拟，结果基本吻合。通过模型分析，选取某些影响因素，预测了在一定运行条件下活性炭吸附剂的吸附量。结果表明，在保证一定C/Hg比的条件下，随着入口浓度增大，单位吸附量也相应增大，活性炭的利用率提高了;改变吸附剂喷入量使炭汞比增大到一定程度时，吸附量曲线增长缓慢，吸附剂的单位吸附量降低，吸附效率增加。较长的接触时间有利于提高吸附效率;在较低的吸附温度下，有利于吸附效率的增加，这是由物理吸附的特点决定的。吸附剂颗粒粒径越小越有利于汞的吸附。 关键词:汞;燃煤锅炉;形态分布;半干法汞排放控制;改性吸附剂;烟气更多还原

【Abstract】 Mercury emissions from coal-fired power plants as a large emission source to the atmosphere, is recognized the direct and potential risk to both human health and environment. The researches on the methods of mercury control from coal combustion are just carried out in the world. The sifting of effective adsorbents and the researches on the mechanism of mercury speciation transformation and mercury control are very weak too. Therefore it should be done urgently that carrying out the studies on mercury pollution, finding out the effective adsorbents and studying the mechanism of mercury speciation transformation and relevant methods of mercury control. It is very important for improving combustion quality and reducing the environment pollution.A bench-scale experimental is conducted to study effect of flue gas composition on the speciation distribution of mercury in simulated flue gas streams. The test method used here for mercury speciation was the Ontario Hydro Method. The speciation distribution of mercury in different coal-fired flue gas systems including or excluding HC1, different concentration of O2, different concentration of HC1, different temperature at reactor’s exit, different concentration of Hg was studied in typical constituent flue gas systems. The conclusions reached were as follows: In coal-fired flue gas systems without HC1, the conversion ratio of Hg2+ to total Hg increases at low temperature and decreases at higher reaction temperature; In the coal-fired flue gas systems containing HC1, the conversion ratio of Hg2+ to total Hg increase with rise of reaction temperature; higher concentration of NO and O2 can enhance oxidation of Hg; the conversion decreases with increase of SO2 concentration, higher temperature at reactor’s exit can increase the conversion ratio of Hg2+ to total Hg; the conversion ratio of Hg2+ to total Hg decreases with increase of Hg concentration.A kinetic model was developed to predict mercury speciation transformation based on mercury reaction characteristics as determined in mercury speciation transformation tests atdifferent conditions. The kinetic equation is: ; reaction rate is:k = 0.029858exp(-12787.54/RT). The simulation results indicated that the model is capable ofdescribing the test data. It also showed that the reaction temperature, contact time, HC1 inlet content, influenced the mercury speciation transformation.The modification of adsorbents was studied , then selects out effective adsorbents through the experiment on the experimental set-up which can simulate flue gas conditions in the power plant. The research mainly contains three jobs: Firstly, referring to many literatures and the methods of mercury removal in the industry of refining mercury, the experimental modification of adsorbents is made, which includes the reactive MnO2-impregnated adsorbents, the FeCl3-impregnated adsorbents, the sulfur-impregnated adsorbents at various temperatures, etc. Secondly, the preliminary selection of adsorbents is carried out on a fixed bed. The primary adsorbents and modified adsorbents are tested at the constant temperature. The mechanisms andrate of elemental mercury (Hg0) capture by activated carbons and some other modified chemically sorbents have been studied using a bench-scale fixed-bed apparatus. We have screened out some efficient sorbents such as activated carbons were impregnated with MnO2, FeCl3 and sulfur at 600癈, zeolite were impregnated with MnO2, roseite were impregnated with MnO2, FeCl3, and bentonite were impregnated with MnO2. The effects of flue gas composition, inlet mercury concentration, adsorption temperature and ratio of C/Hg were investigated to determine the abilities to remove mercury in simulated flue gas streams.The emission study for mercury was conducted at a 6 MW stone-coal-fired plant for the combustion of a coal with mercury concentration of 0.1209mg/kg. The power plant equipped with a cold-side electrostatic precipitator. During full load operation of the boilers samples of the input and output stream such as coal, coal ash, ESP ash and更多还原