【作者】 徐鸿；

【导师】 岑可法； 骆仲泱； 倪明江；

【作者基本信息】 浙江大学 ， 工程热物理， 2006， 博士

【摘要】 我国长期依赖燃煤发电的能源结构造成了较严重的环境污染，燃煤电厂排放的烟尘是大气环境中可吸入颗粒物的重要来源之一。可吸入颗粒物尤其是细颗粒物PM_2.5是影响我国空气质量的重要污染物，它不仅影响全球气候环境、破坏生态系统和历史文物，而且流行病学研究也显示对人体健康危害巨大，已引起国际社会的广泛关注。本文依据监测固定源颗粒排放EPA Method 5推荐的实验方法，建立了燃煤锅炉烟气小颗粒等速采样系统和实验流程，采用冲击式尘粒分级仪，对循环流化床燃煤锅炉烟道除尘前后烟尘进行采样实验。测得烟尘气溶胶的浓度分布以及PM₁₀／PM_2.5在除尘前后烟尘所占的比例，并求得电除尘器对PM₁₀、PM_2.5、PM_1.0的分级除尘效率。通过实验研究，分析燃煤锅炉烟道中可吸入颗粒物的重金属含量分布、多环芳烃浓度以及颗粒物的显微结构和微观孔隙特性等特性。研究了挥发性元素Hg和重金属元素Pb和Cd等在PM₁₀／PM_2.5中的分布特点，表明近90％的Hg存在于烟气和飞灰颗粒中，Pb和Cd在烟尘颗粒中的浓度随粒径减小而增加，有在亚微米颗粒上富集的趋势。分析PM₁₀／PM_2.5中多环芳烃含量，得到电除尘器前后颗粒物中多环芳烃的分布，研究表明毒性当量较强的5、6环PAHs更多地吸附在粒径较小的颗粒上。BET氮吸附实验研究表明小颗粒直径减小时，比表面积增加，小于2.5μm粒子比表面积最大，小颗粒更易于在燃烧过程和尾部排放过程中吸附和富集多种有害物质，如重金属、多环芳烃等有机污染以及其它酸性气体等。声波团聚是对载尘气流进行中间预处理，使含有微米和亚微米级颗粒的气溶胶在较高强度声场碰撞、团聚而长大，以提高传统除尘装置除尘效率的一种方法。搭建了声波团聚飞灰颗粒实验装置，主要研究声压、声波频率、停留时间、含尘烟气浓度等试验参数对煤飞灰微粒声波团聚过程的影响。建立了以同向凝聚作用和流体力学作用为主要机理的声波团聚模型。求解颗粒随声波运动的夹带函数，得到夹带因子η与相位角Φ与粒径和声波频率的关系；并求得颗粒间在同向凝聚和流体力学作用力两种机理下团聚频率系数的表达式，分析声强、频率、粒径分布和温度等参变量对于团聚频率系数的影响。建立了烟尘颗粒声波团聚气溶胶动力学方程并进行数值求解，与实验数据进行对比吻合较好，分析了主要参数声压（SPL）、频率、烟尘浓度、团聚时间对声团聚过程的影响，得到较优化的实验参数选取范围。更多还原

【Abstract】 The energy consumes structure depending on coal fired power plants for a long timemake serious pollution to the environment, in China. Coal combustion is one of theimportant sources of Inhalable Particulate (PM₁₀) emission to the atmosphere. PM₁₀,especially PM_2.5 has become the most important air pollutant in our country and hasattracted the world attention at present, since it not only effects the world climate change,destroys ecology system and history architectures, but also has great adverse effects onhuman health according to epidemiological studies.Flue gas sample experiments emitted from coal fired boiler were performed throughan isokinetically designed system according to source emission US EPA Method 5.Particulate samples were extracted from flue gas of CFB boilers using cascade impactors.Particle size distribution and the fraction of PM₁₀/PM_2.5 in flue gas are calculated atupstream and downstream of the electrostatic precipitator and capture efficiencies ofPM₁₀/PM_2.5/PM_1.0 for ESP were derived in the thesis.Heavy metals and PAHs distribution in PM₁₀ from coal fired flue gas were measuredin experiments. Characteristics of surface properties of different size particles wereanalyzed with low-temperature nitrogen absorption BET experiments. Several toxic heavymetals including Hg Cd, Pb etal concentration in particulates was analyzed and the resultshows the concentrations of medium volatility Cd and Pb increase with decreasingparticle size and tends to enrich in submicron particles. Hg is a kind of volatile element,and 90% of Hg exists in flue gas and fly ash. PAHs concentration in PM₁₀/PM_2.5 sampledat inlet and outlet of ESP were measured and results show that 5/6-ring PAHs are moreabsorbed in small particles. BET surface area of segregated particles can be derived fromhysteresis loops and PM_2.5 has the greatest surface area compared to other particles. Thusmany pollutants such as toxic heavy metals, organic matter and acid gas are prone to beabsorbed or enriched in PM_2.5 within combustion and post-combustion environment.Acoustic agglomeration is an aerosol preconditioning procedure to improve theperformance of conventional particle removal devices. Application of high intensityacoustic field to aerosol containing micron and submicron sized particles results in muchincreased rates of particle collisions, adhesions and thus agglomeration. Such increasedparticle sizes process improves the fractional efficiency of conventional particle removaldevices. Acoustic agglomeration experiments were done in traveling wave field withredispersed fly ash, and effect of parameters on agglomeration processes is investigatedsuch as SPL, frequency, retains time and dust loading concentration.Acoustic agglomeration simulation is established based on the orthokinetic andhydrodynamic interaction as main mechanisms. The entrainment factor and phase relationship of particle’s motion compared to acoustic field is computed and they aredependent upon the particle size and frequency. A general expression for the acousticagglomeration frequency function （AAFF）, which measures the agglomeration rate ofparticles in a sound field, has been derived through a statistical approach. The acousticintensity, acoustic frequency, particle size distribution and gas temperature effects on theagglomeration frequency function is analyzed through numerical simulation.Aerosol dynamics equation of flue gas acoustic agglomeration is derived and thenumerical scheme to solve the equations is discussed. The results of the numericalsimulation are compared with the experiments results and have a good agreement. Theeffects of importants parameters on acoustic agglomeration process such as soundpressure level, frequency, mass loading and agglomeration time are calculated anddiscussed and an optimal parameters range were recommended according to thesimulation.更多还原