【作者】 于洁；

【导师】 孙路石； 邱建荣；

【作者基本信息】 华中科技大学 ， 热能工程， 2013， 博士

【摘要】 随着我国经济的快速增长以及城镇化进程的加快，城市生活垃圾产量也急剧增加。目前焚烧法处理城市生活垃圾已逐渐成为我国垃圾处理的主要手段之一，然而垃圾热处理的同时会产生大量的二次污染：飞灰、酸性气体、颗粒物、重金属及二噁英等物质。因此在处理城市生活垃圾的同时如何减少污染物排放成为突出存在的环境问题。基于国内外研究进展，本文以垃圾模拟物和典型城市生活垃圾为研究对象，系统地研究了城市生活垃圾热处理过程中镉、铅、锌和铜四种重金属的迁移行为，并对工业垃圾焚烧炉的底灰和飞灰的物理化学形态进行了分析，这对于掌握热处理过程中重金属的迁移规律和控制提供了重要的参考价值。首先，为了减少实验影响因素和误差，采用垃圾模拟物的方法研究重金属的挥发特性。在实验室流化床台架上研究了停留时间、氧化还原条件、HCl和SO₂对Al₂O₃颗粒中负载的重金属的挥发特性影响。结果表明氧浓度的增加不利于金属氯化物从Al₂O₃颗粒中的挥发。而HCl则通过抑制重金属铝酸盐及氧化物的生成促进了重金属的挥发。SO₂的存在同样促进了重金属从Al2O3颗粒中的挥发。为了更好地研究重金属的动力学挥发特性以及更加深入研究重金属的扩散挥发机理，建立了数学模型模拟了热处理过程中重金属的释放规律。模拟结果表明，扩散系数D对重金属CdCl₂的挥发有非常重要的影响。随着扩散系数的增加，CdCl₂的挥发率也随之增加。孔隙率对CdCl₂的挥发率的影响同样很大。随着孔隙率从0.2增加到0.68，CdCl₂挥发率从20%增加到了40%。重金属的挥发率随着颗粒粒径的减小而迅速增加。颗粒粒径的减小一方面能增加重金属的最大挥发速率，另一方面能够缩短达到最大挥发速率所需要的时间。不同垃圾组份中重金属的含量以及所存在的形态的不同，因而不同组份的垃圾在热处理过程中重金属的挥发特性差异很大。在研究了垃圾模拟物中重金属挥发特性的基础上，选取了不同种类的城市生活垃圾。在快速和慢速燃烧条件下，研究了新闻纸、竹筷、垃圾袋、PVC管及橡胶粉等五种典型城市生活垃圾在不同温度下重金属的挥发特性，并与900oC热解条件下重金属的挥发特性进行了比较。研究表明，在快速燃烧条件下，温度对新闻纸、竹筷和PVC管中重金属的挥发率影响不大，而橡胶粉和垃圾袋中重金属的挥发率则随着燃烧温度的增加而增加。所研究几种垃圾组份中，PVC管和竹筷中重金属挥发率最高，纸次之，而垃圾袋和橡胶粉最低。慢速燃烧条件下重金属的挥发率要低于快速燃烧条件下重金属的挥发率。对于新闻纸、垃圾袋和橡胶粉，热解条件下元素镉和锌的挥发率要高于燃烧条件下镉和锌的挥发率。PVC管中由于含有大量的有机氯元素，燃烧条件下能够生成挥发性更高的金属氯化物，因而在燃烧条件下重金属的挥发率更高。而在热解气氛下，铅和铜的挥发率要低于快速燃烧条件下铅和铜的挥发率。我国城市生活垃圾组份复杂，因而有必要研究不同垃圾组份混烧对重金属的挥发特性影响。实验研究表明，掺烧不同组份的垃圾对底灰中重金属的残存率的影响并非简单的叠加。掺烧橡胶和垃圾袋后，元素镉的残存率略呈增加趋势。掺烧橡胶和织物后，元素铜的残余率变化不大。而掺烧垃圾袋则对铅的挥发有一定的抑制作用。各工况下锌的残存率要略高于铅。掺烧橡胶、PVC管和垃圾袋后，元素锌的残存率大幅增加。掺烧橡胶后，元素铜的残存率增加最大。而掺烧PVC管和垃圾袋后，底灰中铜的残存率略有下降，表明塑料类垃圾中铜相对易挥发。实验研究垃圾热处理过程中重金属的挥发行为与实际焚烧炉中重金属的迁移行为有较大的差别。因而对武汉市某一流化床垃圾焚烧炉产生的底灰和飞灰的物理化学特性进行了研究。研究表明重金属主要富含在较细的底灰以及飞灰中。并且随着底灰粒径的增加，元素镉、铅和锌的析出率大幅增加。而铜的析出率则小幅降低。BCR实验表明铅主要存在于残留态中，从而不易析出到自然环境中。而镉则容易析出到自然环境中。根据飞灰的重金属含量分析以及TCLP实验可以得出，底灰可以直接填埋并不会对环境造成大的危害。然而飞灰在填埋前必须进行预处理。更多还原

【Abstract】 With the rapid development of economy and accelerated process of urbanization，theamount of municipal solid waste（MSW） has increased substantially. Due to the advantagesof high ability of minimization and eliminating the bacteria and virus, thermal treatment ofMSW is gradually becoming major means of handling MSW. However, thermal treatmentof MSW can give rise to secondary pollutions: fly ashes, acid gases, particulates, heavymetals and Dioxin, and so on. Therefore, it is increasingly turning into one of the majorenvironmental problems that how to effectively dispose the MSW and control pollutionemissions at the same time. Based on the research progress at home and abroad, thebehavior and partitioning of Cd, Pb, Zn and Cu were studied systematically during thethermal treatment of model solid waste and representative MSW, which is of greatsignificance in the understanding of the heavy metals behavior and control.To begin with, the influence of reaction times, redox conditions, water and mineralmatrice on metal chlorides volatilization during thermal treatment of model solid waste in afluidized bed reactor was investigated. The results showed that increasing oxygenconcentration and water can inhibit the vaporization of heavy metals by forming involatilecompound. Nevertheless, HCl can promote the heavy metal release by preventing theformation of metal aluminates and metal oxides. SO₂also had positive effects on thevaporization of heavy metals.To thoroughly and deeply understand the kinetic vaporization behavior of heavymetals and study the diffusion mechanisms of heavy metals through the particles, amathematical model was established to predict the behavior of CdCl₂and studied the effectof different parameters. Through the simulation, it can be observed that diffusioncoefficient played an important effect on the heavy metals vaporization. The vaporizationamount increased rapidly with the diffusion coefficient increasd. The porosity of particlesalso had significant effect. The vaporization amount of increased from20%to40%whenthat porosity of particles increased from0.2to0.68. The smaller the diameter of particles,the higher the vaporization rate of heavy metals. The heavy metals in the different MSW components may behave differently during thethermal treatment, since the amount and form of heavy metals in the different wastefractions varied. On the basis of previous studies, different categories of MSW weresampled. The behavior of Cd, Pb, Cu and Zn in the Paper, Disposable bamboo chopsticks（DC）, Garbage bags （GB）, PVC pipe （PVC） and Tire were studied at the different reactiontemperatures under the conditions of rapid and slow combustion. Moreover, pyrolysisexperiments at900oC were conducted to outline the effect of redox conditions on heavymetals behaviors. It was found that incineration temperature made little difference in thevaporization of heavy metals in paper, DC and PVC. Nevertheless, the volatilization rate ofheavy metals in GB and tire increased with the increase in incineration temperature. Amongthese five waste components, the volatilization rate of heavy metals in PVC and DC washighest; the paper lied next while GB and tire were lowest. The volatilization rate of heavymetals at condition of slow combustion was much lower than that at condition of rapidcombustion. The volatilization rate of Cd and Zn in paper, GB and tire under the conditionof pyrolysis was higher than that at combustion condition. Because PVC contained asignificant amount of chlorine，more volatile metal chlorides could be formed undercombustion conditions which contributed to the higher volatilization rate of heavy metals.Under N2atmosphere, the volatilization rate of Cu and Pb was much lower than that undercombustion conditions for all wastes.Due to the complexity of MSW, there was the necessity to study the effects ofco-combustion between different compositions of MSW on the heavy metals behaviors.The results revealed the nonlinear relationships between the partitioning of heavy metalsand the fuel mixtures. The retention rate of Cd in residues showed a upward trend with theco-combustion of tire and GB. As to lead, the retention rate changed little with the tire andtextile co-fired, while GB had negative effects on the vaporization of Pb. Compared withlead, the retention rate of zinc was a little higher. With the co-combustion of tire, PVC andGB, more zinc could be retained in the residues. The percentage of copper retained in theresidues was increased significantly when the tire was co-fired, while that of copperdecreased slightly with the PVC and GB co-fired, indicating that the copper in plastic wastewould be vaporized more easily. Due to the disparity of the heavy metals partitioning between in industrial incineratorand in experimental reactor, a study of the physical and chemical characteristics of fly ashand bottom ash from a fluidized bed incinerator in Wuhan was carried out. The resultsshowed that the heavy metals were preferentially concentrated in the finer bottom ashes andfly ash particles. BCR results demonstrated that Pb were mainly bound into the matrix andwould not be easily released under natural conditions, while Cd compounds may bereleased easily into the natural environment. According to the chemical characterisation ofresiduals and the leachates, only the bottom ash can be landfilled directly. Nevertheless, flyash must be treated before landfilled.更多还原