【作者】 陈勇；

【导师】 陈昌和；

【作者基本信息】 清华大学 ， 动力工程及工程热物理， 2008， 博士

【摘要】 本文采用实验研究和热力学平衡计算对中国垃圾焚烧中Cd、Pb的迁移和转化特性进行了研究。在自行设计和搭建的管式焚烧炉中分别就氯、硫、水分、吸附剂和焚烧温度、停留时间对Cd、Pb迁移和转化特性的影响进行了实验研究。使用吉布斯自由能最小法对垃圾焚烧中Cd、Pb的平衡形态分布进行计算,并与实验数据进行对比分析,取得以下研究成果。氯能有效增强Cd、Pb的挥发特性。有机氯（PVC）和无机氯（NaCl）均能使97%以上的Cd和90%的Pb分布于飞灰中。两种氯对Cd、Pb的迁移和转化特性的影响机理不同。NaCl易与Pb形成PbCl₂,与Cd除易形成CdCl₂外还能直接与其反应生成CdCl₂（NaCl）₆和Na₂CdCl₄。PVC除与Cd、Pb形成氯化物外还易形成相应的氯酸盐Na[Cd（ClO₄）₃]、Pb（ClO4）₂、PbCl₂O₄。不同形态的硫对Cd、Pb迁移和转化特性的影响机理不同。S和Na2S易与Cd形成难挥发性物质CdS,使Cd在底渣中分布分别增加4.2%和20.1%,Na₂SO₄（Na₂SO₃）易与Cd生成CdSO₄,使Cd更多地分布在飞灰中。所有形态的硫均使Pb在底渣中的分布减少25%以上,飞灰中Pb主要以PbSO₄形式存在。烟气中水分对重金属迁移和转化特性的影响主要是对重金属反应化学平衡移动的影响,垃圾中水分的影响则是对燃烧状况的影响。实验表明,吸附剂对Cd吸附能力的大小顺序依次为Al₂O₃>SiO₂>CaO,吸附剂除化学吸附外还具有一定的物理吸附能力。硫、氯能缩短吸附剂对Cd、Pb的有效吸附温度段,但有效吸附温度段内吸附率不受影响,氯能使Al₂O₃对Cd的化学吸附能力丧失。温度主要影响Cd、Pb化合物的蒸气压和垃圾焚烧状况,温度的升高能显著增强重金属的挥发性。当温度低于850℃时,Cd、Pb均不在烟气中分布,当温度为1000℃时,Cd在烟气中的分布为8.49%,Pb在烟气中始终没有分布。焚烧中,重金属的挥发主要集中在初始阶段。在初始阶段3min～6min,停留时间对Cd、Pb迁移特性影响显著,超过6min影响甚微。本文的研究成果对进一步深入认识我国垃圾焚烧中重金属的迁移和转化特性、焚烧炉的设计改进及发展焚烧中和焚烧后重金属的控制技术提供参考。更多还原

【Abstract】 This thesis combines experimental study and thermodynamic equilibrium calculations to explore the characteristics of cadmium （Cd） and lead （Pb） partitioning and speciation during municipal solid waste （MSW） incineration. In the tubular furnace designed and commissioned by the author, experiments were conducted to investigate the impact of chlorine, sulfur, moisture, sorbents and operating conditions （including incineration temperature and residence time） on the partitioning and speciation behaviors of Cd and Pb. After comparing the expetimenatal data with the calculated equilibrium form distributions based on Gibbs Free Energy Minimization, hereby are the findings of this study:Chlorine can effectively increase the volatility of Cd and Pb. Both the organic chlorine （PVC） and inorganic chlorine （NaCl） retain more than 97% Cd and 90% Pb partition in fly ash. However, the mechanisms that influenced the partitioning and speciation behaviors of Cd and Pb with these two forms of Chlorine are different from each other. Inorganic chlorine tends to react with Pb to form PbCl₂, With Cd, CdCl₂ could be easily fromed. NaCl could even react directly with CdCl₂ to form CdCl₂（NaCl）₆ or Na₂CdCl₄. For orgnic chlorine, however, apart from its tendancy to react with Cd and Pb to form chloride as inorganic chlorine does, it also encourages the formation of various chlorates such as Na[Cd（ClO₄）₃], Pb（ClO₄）₂ and PbCl2O4.Different types of sulfur have different impacts on the partitioning and speciation of Cd and Pb. With Cd, S and Na₂S tends to form CdS which is hardly volatile, and increased the retention of Cd in bottom ash by 4.2% and 20.1% respectively. In contrast, Na₂SO₄ （Na₂SO₃） tends to form CdSO₄, which also increases the chance for Cd to remain in fly ash. All forms of sulfur tend to decrease the Pb retention in bottom ash by more than 25%. PbSO4 is the main form of Pb compounds in fly ashThe moisture in flue gas mainly affects the chemical equilibrium shift of heavy metal reactions, whilst the moisture in MSW affects the MSW incineration characteristic. The experimental results indicate that adsorptive capacity order of three sorbents towards Cd is as follows: Al₂O₃>SiO₂>CaO. Besides chemical adsorption, sorbents also process certain physics adsorption capacity. Sulfur and chlorine can narrow the effectiveness temperature range of adsorption. The effective adsorptive capacity is not affected by the presence of sulfur and chlorine, although chlorine might deactivate Al₂O₃ in Cd adsorption.Temperature affects both the vapor pressure of Cd and Pb compounds and MSW incineration characteristic. Temperature increase can significantly enhance the volatility of heavy metals. Cd and Pb do not exist in flue gas if temperature below 850°C. 8.49% Cd partitioned in flue gas when temperature was 950°C. Pb did not transfer into flue gas during the whole experimental temperature range. Cd and Pb were more likely to evaporate at the initial stage. During the initial 3min–6min, residence time had a significantly impact on the migration of Cd and Pb, however, this impact almost completely diminished after 6min.The findings of this study should enhance the understanding of heavy metals behaviors during MSW incineration in China and provide valuable information to the improvement of incineration furnace design and the development of heavy metals control technologyies.更多还原