【作者】 徐飞；

【导师】 岑可法； 骆仲泱； 方梦祥；

【作者基本信息】 浙江大学 ， 工程热物理， 2009， 博士

【摘要】 燃煤电厂排放的粉尘颗粒、SO2、NO、Hg、PAHs和二恶英等有害物质已经成为我国大气环境污染的重要来源之一。脉冲放电电凝并技术对细微颗粒有较好的荷电凝并效果,而且可以将烟气中的NO、SO2、Hg0转化成易被溶液吸收的成分,同时还可以对粉尘中的PAHs和二恶英等有害物质进行降解。和传统的碱液吸收技术相结合,可协同脱除燃煤电厂烟气中粉尘、NOX、SO2、Hg0、PAHs和二恶英等污染物,使除尘、脱硫、脱硝、脱汞、降解有机污染物的一体化成为可能,从而降低燃煤电厂烟气净化的成本。本文围绕燃煤烟气多种污染物及其控制方法的新兴研究,对脉冲放电电凝并结合碱液吸收烟气多种污染物协同脱除技术开展了实验和机理研究。本文建立了燃煤锅炉烟道排放颗粒物等速采样系统,采用冲击式尘粒分级仪对440t/h循环流化床燃煤锅炉静电除尘器前后烟道烟尘进行采样实验,进行粒径分布、比电阻测量,研究煤种、锅炉负荷、Ca/S和含氧量等运行参数对颗粒物排放特性的影响；同时还研究了不同粒径和燃烧工况下飞灰颗粒的微观孔隙结构。本文搭建了脉冲荷电凝并结合直流收尘实验系统,主要研究脉冲峰值电压、脉冲频率、停留时间、初始粉尘浓度等因素对脉冲电晕放电颗粒荷电以及凝并收尘的影响。实验结果表明：脉冲电晕放电能够实现颗粒非对称双极性荷电,>0.2μm颗粒基本被荷上负电荷,电场荷电是其主要荷电机理；<0.2μm颗粒基本被荷上正电荷,扩散荷电是其主要荷电机理。脉冲电晕荷电颗粒在直流电场中的凝并除尘效率曲线呈现“V”字型,其除尘效率曲线在粒径0.2μm左右有一个最低值。建立小型脉冲电晕放电降解飞灰PAHs和二恶英实验台进行实验研究,同时进行了其降解理论分析。结果表明：正脉冲电晕放电过程中产生的高能电子能够有效地轰击粉尘颗粒表面,甚至穿透颗粒,从而改变了粉尘颗粒原有的孔隙结构,能有效地降解垃圾焚烧炉排放粉尘中的PAHs和二恶英等有害有机污染物。目前燃煤电厂广泛应用的湿法烟气脱硫装置,利用石灰/石灰石溶液洗涤烟气,只能对SO2进行有效控制,但是不能脱除烟气中的NO和Hg0。基于以上的研究基础,如果能够采用脉冲电晕放电将烟气中的NO,SO2, Hg0氧化成为高价态易溶于水的状态,就可以采用碱液吸收实现一塔多脱。本文采用脉冲电晕放电结合碱液吸收对烟气中SO2、NO和Hg0进行协同脱除实验,并且针对脉冲电晕放电脱硫脱硝脱汞化学动力学过程进行了研究。实验结果表明：脉冲放电电凝并结合碱液吸收能够很好地协同脱除烟气多种污染物,在实验优化工况下,对PM1、SO2、NO和Hg0的协同脱除效率可以分别达到90%、97%、50%和50%以上本文推导了直流电场中的荷电场强和收尘场强计算公式,在电场荷电前提下建立了半经验公式对脉冲电晕放电颗粒荷电进行计算。根据理论分析编写程序计算了双极性荷电颗粒的电凝并系数和电凝并效率,结果显示在实验工况不考虑凝并区收尘的情况下,颗粒越小,其电凝并效率越高；对于超细颗粒,其颗粒数量浓度有了一定的下降,电凝并效率可以达到20-30%左右。利用Fluent软件模拟了不同粒径段荷电颗粒在直流收尘电场中的运动轨迹,结果表明颗粒在外加直流电场力作用下向收尘极板基本作直线偏移运动,颗粒粒径越大,其驱进速度越大,偏移越明显。直观地确定不同粒径颗粒的除尘效率,并且跟实验结果进行了对比分析,两者吻合较好。更多还原

【Abstract】 Particulate matter(PM), SOx, NOx, Hg, PAHs and dioxins emitted from coal-fired power plants are becoming one of the most important sources of air pollution in China. Pulsed corona discharge electrostatic agglomeration is an effective method to remove fine particles, which has good particle charging and agglomeration effects. It has also good oxidation effect of SO2, NO and Hg0 to solvable components; meanwhile, the decomposition of PAHs and dioxins in fly ashes can be also achieved. When combined with conventional lye absorption technology, it is possible to simultaneous remove fine particles, SO2, NOx, Hg0, PAHs and dioxins, which reduces the cost of flue gas cleaning. This thesis focuses on the research of flue gas multi-pollutants control, and detailed experimental and theoretical investigations were carried out on flue gas multi-pollutants control enhanced by pulsed corona discharge electrostatics agglomeration combined with lye absorption.An isokinetical particle sampling system was built and experimental study on the characteristics of particulate matter emitted from a 440t/h circulating fluidized bed(CFB) coal-fired boiler. Cascade impactor was employed to sample the particles at both electrostatic precipitator(ESP) inlet and outlet. The particle size distribution and dust resitivity were measured and the influences of coal composition, boiler load, Ca/S and oxygen concentration on the characteristics of PM emissions during coal combustion were investigated. Also the experimental study on porous structure of variously sized fly ash particles was made under different combustion conditions.The experimental set up of pulsed corona discharge electrostatic agglomeration was built and the influences of pulse peak voltage, pulse frequency, residence time and initial particle concentration on the particle charging, agglomeration and collection were discussed. The results indicate that particles were biopolarly charged during the pulsed corona discharge. Diffusion charging is the dominant charging mechanism for particles with diameter<0.2μm, which are positively charged; while field charging is the dominant charging mechanism for particles with diameter>0.2μm, which are negatively charged. The particle collection efficiency curve under pulsed corona discharge electrostatic agglomeration is of "V" shape, which has the lowest collection efficiency of particles with diameter near 0.2μm.Experimental and theoretical study on decomposition of PAHs and dioxins in fly ashes by pulsed corona discharge was also made. The results indicate high energy electrons produced in positive pulsed corona discharge could collide with particles and change the pore structure, which results in PAHs and dioxins decomposition.Wet flue gas desulfurization(WFGD) is widely used in coal-fired power plants. WFGD utilizes lime/limestone solution as absorbent, which removes SO2 effectively, however, NO and Hg0 in flue gas are insoluble to be removed. Based on the research above, pulsed corona discharge was able to oxidize NO, SO2 and Hg0 in flue gas to solvable components, then flue gas multi-pollutants removal can be achieved with WFGD. So pulsed corona discharge combined with lye absorption was proposed to experimentally investigate the simultaneous removal of NO, SO2 and Hg0 in flue gas; meanwhile the chemical reaction dynamics of multi-pollutants during pulsed corona discharge were discussed. The results show good simultaneous removal efficiencies up to 90%,95%,50% and 50% can be achieved for PM1, SO2, NO and Hg0, respectively.The charging and collection electric field intensity in DC were put forward and particle electric charging calculation under pulsed corona discharge was made by a semi-experiential formula. Program was used to calculate the electrostatic agglomeration coefficient and efficiency of bipolar-charged particles. The results indicate that without the consideration of particle collection in agglomeration area, the electrostatic efficiency increases with descreasing particle size. For ultra-fine particles, the number concentration was decreased by 20～30% through electrostatic agglomeration. Fluent software was employed to simulate particle track in DC electric field. The particles were forced to move toward linearly to collection plates by electric field force and particles with larger diameter move faster. The collection efficiency of different particle size was obtained and compared with our experimental results, which agree well with each other.更多还原