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类型 基础研究 预答辩日期 2018-05-18
开始(开题)日期 2016-01-19 论文结束日期 2018-03-15
地点 热能所1楼会议室 论文选题来源 973、863项目     论文字数 8.6 (万字)
题目 基于脱硫废水烟道蒸发的燃煤烟气PM2.5/SO3/Hg协同脱除研究
主题词 脱硫废水蒸发,协同脱除,PM2.5/SO3/Hg,密度泛函理论
摘要 燃煤烟气粉尘、SO2、NOx排放控制已达到较高水平,但对于PM2.5、SO3、Hg的控制相对滞后。单独设立处理单元控制PM2.5、SO3、Hg占用空间且成本大。燃煤锅炉采用湿法烟气脱硫(WFGD)系统脱除SO2过程中产生脱硫废水,其中烟道蒸发技术是一种具有良好应用前景的脱硫废水零排放处理技术。为此,本文提出在脱硫废水烟道蒸发过程中协同增强现有污染物处理设备脱除PM2.5、SO3、Hg。从宏观脱除性能和微观脱除机理两个尺度,以脱硫废水烟道蒸发技术为基础,结合化学和湍流团聚技术,增强电除尘脱除PM2.5;结合碱性吸收剂喷射脱除SO3技术,增强SO3的脱除;利用脱硫废水中的氯离子促进Hg0的氧化和脱除;最后采用量子化学密度泛函理论揭示PM2.5、SO3、Hg的脱除机理。实现脱硫废水零排放的同时协同增强PM2.5/SO3/Hg脱除,达到“以废治废”的目的。 首先基于液滴传热传质方程,建立液滴烟道蒸发数学模型,分析液滴蒸发过程中热量、质量传递规律,得到液滴蒸发过程中粒径随时间变化规律。针对典型300 MW燃煤机组烟道参数,利用建立的数学模型计算不同粒径的液滴在不同烟气温度下的蒸发时间。研究发现:平均粒径为40 μm的液滴在150 ℃和350 ℃温度下的蒸发时间分别为0.44 s和0.15 s。利用搭建的燃煤热态试验平台,采用荧光示踪可视化方法,研究液滴在实际烟道中蒸发特性;结果表明:烟气温度与液滴粒径对液滴蒸发时间的影响与模型计算结果相同,烟气中颗粒物浓度对液滴烟道蒸发影响较小。 基于燃煤热态试验平台,研究了脱硫废水蒸发所导致的烟气温湿度变化对电除尘脱除PM2.5性能的影响。在此基础上,开展了脱硫废水烟道蒸发促进PM2.5脱除的试验研究,分析了脱硫废水蒸发前后烟气中细颗粒物的物性变化特性,以及增强电除尘脱除PM2.5的规律。此外,结合化学和湍流团聚技术,研究了单独化学团聚以及化学耦合湍流团聚增强电除尘脱除PM2.5的规律。结果表明:脱硫废水烟道蒸发能够提高电除尘的击穿电压,有利于细颗粒物的荷电,提高电除尘器的除尘效率;脱硫废水蒸发促进细颗粒物团聚长大,蒸发过程中析出物质能够降低飞灰比电阻,典型工况下PM2.5脱除效率可提高15%左右,且脱硫废水蒸发量越多,脱除效率提高越明显;脱硫废水中添加化学团聚剂细颗粒物数浓度峰值粒径增大,化学团聚剂卷曲的柔性分子链吸附固体颗粒物形成大的凝聚体,0.1-1 μm粒径段的颗粒数量脱除效率可提高20%-30%;化学团聚耦合湍流团聚可进一步提高烟气中细颗粒数浓度峰值粒径,团聚效果依次为化学团聚耦合湍流团聚>化学团聚>湍流团聚。烟气流速增大、烟气中细颗粒浓度提高有利于团聚发生。典型工况下,湍流团聚、化学团聚、两种技术耦合可使电除尘数量脱除效率分别提高10%-20%、20%-30%、40%-50%左右。 在此基础上,开展了脱硫废水中添加碱性吸收剂脱除SO3及不同氯离子浓度脱硫废水蒸发对烟气中Hg形态分布的影响,分析了SO3二元成核机理。结果表明:实际燃煤烟气中,SO3以二元成核快速形成硫酸蒸汽,烟气湿度和SO3浓度越大,烟气酸露点温度越高;当烟温降至酸露点以下时,烟气中H2SO4凝结吸附在飞灰表面,凝结吸附量符合Weber-Morris经验公式,内部扩散是影响H2SO4雾滴在飞灰上的冷凝吸附速率的主要因素;脱硫废水中添加碱性吸收剂,SO3脱除效率依次为NaOH>Na2CO3>NaHCO3,增加碱性吸收剂添加量、脱硫废水喷入量以及降低雾化液滴粒径均有利于SO3脱除效率的提高。n(Na/S)为2时,三种碱性吸收剂SO3脱除效率均大于70%。脱硫废水在SCR和ESP前蒸发均可降低WFGD出口烟气中Hg浓度,SCR前蒸发脱硫废水可显著提高SCR对Hg0的氧化效率;ESP前蒸发脱硫废水,ESP中Hg0的氧化率可提高15%左右;WFGD中Hg2+的脱除效率可达80%以上。 基于上述宏观试验结果,采用量子化学密度泛函理论探讨了PM2.5、SO3、Hg的协同脱除机理,以SiO2作为模拟粉尘颗粒,分析了化学团聚剂与SiO2吸附絮凝过程中的振动频率、反应能、自然键轨道;建立了SO3与化学团聚剂、SiO2共存体系,分析了SO3均相成核的过渡态(TS)以及化学团聚剂、SiO2吸附SO3的过程;最后建立V2O5和Hg模型,研究了V2O5对Hg0的氧化机理。结果表明:化学团聚剂通过与SiO2形成的氢键(O-H…O)吸附SiO2,分子链越长的团聚剂分子,对SiO2的吸附能越高,促进了烟气中细颗粒物团聚;SO3、H2O、团聚剂、SiO2共存体系中,SO3首先与H2O结合形成H2SO4,化学团聚剂和SiO2均能吸附SO3,化学团聚剂吸附效果优于SiO2;V2O5分子中不同位置上的氧原子对Hg0均有氧化作用,氯离子可增强V2O5对Hg0的氧化,并生成中间产物HgCl,最终转化为HgCl2。
英文题目 STUDY ON THE SIMULTANEOUS REMOVAL OF PM2.5, SO3 AND HG FROM COAL-FIRE FLUE GAS BY WFGD WASTEWATER EVAPORATION
英文主题词 Desulfurization wastewater evaporation, Collaborative removal,PM2.5/SO3/Hg,DFT
英文摘要 Dust, SO2 and NOX emission control technologies have reached a higher level for coal-fired flue gas, but the PM2.5, SO3 and Hg control technologies are relatively lagged. Separate processing units for control PM2.5, SO3 and Hg take up space and have high cost. The wet flue gas desulfurization (WFGD) system was used to remove SO2 for coal-fired boiler flue gas, the desulfurization wastewater was produced in the process of desulfurization. Evaporation treatment technology is a good application prospect in the numerous technologies. And for this, a novel technology was proposed to enhance air pollutant control devices (APCDs) removal of PM2.5, SO3 and Hg during desulfurization wastewater evaporation in the flue. Then, the paper gone on to study the macroscopic removal performance and micro removal mechanism, respectively. Based on the basis of desulphurization wastewater evaporation technology and combined with chemical and turbulent agglomeration technology, the electrostatic precipitator (ESP) removal PM2.5 was strengthened. Combining the technology of alkaline absorbent spray removing SO3, the removal efficiency of SO3 was enhanced in APCDs. By using chlorine ion, the oxidation and removal of Hg0 in desulfurization wastewater were promoted. At last, the removal mechanism of PM2.5, SO3 and Hg were studied by using the density functional theory (DFT). This technology realized desulfurization wastewater zero discharge and collaborative removal of PM2.5, SO3 and Hg, which achieved the aim of waste control by waste. Based on heat and mass transfer equations of droplet, the mathematical model of droplet flue vaporization was established. The law of heat and mass transfer in the process of the droplet evaporation was obtained, and the variation of droplet diameter with time was also obtained. Aiming at the parameters of a typical 300 MW flue, the model was used to calculate the evaporation law of the droplets with different diameters and different temperature changes. The results showed that the evaporation time for the droplet with the diameter of 40 μm were 0.44 s and 0.15 s, respectively for 150 ℃ and 350 ℃. Based on the established the coal-fired thermal experimental platform, the characteristics of droplet evaporation in actual flue were studied by the visualization method of fluorescent tracer. The results indicated that the influence of temperatures and diameters on the droplet evaporation time were in good agreement with the calculated results in the model. The particle concentration had little effect on the droplet evaporation time. Based on the coal-fired thermal system, the ESP removal of PM2.5 was investigated experimentally with different flue gas temperature and humidity caused by desulfurization wastewater evaporation. Also, the law of strengthen ESP removal of PM2.5 was discussed, and physical property change of fine particles in flue gas were analyzed in the wastewater evaporation process. In addition, the law of strengthen ESP removal of PM2.5 was discussed by coupled with chemical and turbulent agglomeration technology. The results showed that the ESP breakdown voltage raised with desulfurization wastewater evaporation, which was beneficial to charged particles and the improvement of dust efficiency. Desulphurization wastewater evaporation promoted particles agglomeration, besides, the fly ash resistivity was reduced. The PM2.5 concentration at ESP outlet decreased by about 15% under typical conditions, the removal efficiency of PM2.5 increased with increasing amount of evaporation. With the addition of agglomerants, the peak diameter of particle was increased in the flue gas, particles were bonded together by chemical agglomeration agent to form larger aggregates, and the number removal efficiencies of particles from 0.1 μm to 1.0 μm were increased by 20%-30%. The diameter of particle further increased by chemical coupled turbulence agglomeration technology, agglomeration efficiency was the highest by chemical coupled turbulence agglomeration technology, and agglomeration efficiency was the lowest by turbulence agglomeration technology, the increase of velocity and particle concentration were good to strengthen particles agglomeration. The ESP removal efficiency increased by 10% to 20% with turbulence agglomeration technology under typical conditions, and the removal efficiency increased by 20% to 30% with turbulence agglomeration, the removal efficiency increased by 40% to 50% with chemical coupled turbulence agglomeration technology. The removal characteristics of SO3 and Hg by desulfurization wastewater evaporation were investigated experimentally based on the coal-fired thermal system. The SO3 binary nucleation mechanism was analyzed. The experimental results showed that SO3 formed sulfuric was fast by binary nucleation in actual coal-fired flue gas, the flue gas acid dew point temperature increased with the improvement of humidity and SO3 concentration. When the temperature dropped the acid dewpoint, H2SO4 condensed and adsorbed on the surface of fly, the adsorption capacity followed the empirical formula of Weber-Morris. Furthermore, SO3 condensation on the ?y ash was mainly controlled by internal diffusion. When added alkaline absorbents (NaOH, Na2CO3, NaHCO3) to desulfurization wastewater, the removal efficiency of SO3 followed by NaOH > Na2CO3 > NaHCO3, the removal efficiency of SO3 increased with increasing amount of evaporation and alkaline absorbents, moreover, smaller atomized droplet was beneficial to improve the SO3 removal efficiency. When the n(Na/S) was 2, the SO3 removal efficiency was greater than 70% for three kinds of alkaline absorbents. The Hg concentration at WFGD outlet decreased by desulfurization wastewater evaporation before SCR and ESP, the Hg0 oxidation ef?ciency was increased significantly when wastewater evaporated before SCR. The ESP removal efficiency of HgT increased by about 15% with wastewater evaporated before ESP, the WFGD removal efficiency of Hg2+ reached more than 80%, respectively. Based on the above experimental results, the collaborative removal mechanism of PM2.5, SO3, Hg were studied by DFT, SiO2 was as dust particles in simulation calculation. Vibrational frequencies, free energy, natural bond orbital (NBO) were calculated to reveal the interaction between chemical agents and SiO2. the reasonable calculation model was established, which contained SO3, chemical agent, SiO2. And the interactions between SO3, H2SO4, SiO2, chemical agent were explored. Finally, the oxidation process and mechanism of Hg0 on V2O5 were analyzed by establishing the Hg0 and V2O5 model. In the results, the chemical agent molecule and SiO2 were integrated by hydrogen bonds (OH?O). The longer molecular chain molecules, the higher free energy between chemical agent molecule and SiO2, which was benefitted to particle agglomeration. In SO3, H2O, chemical agent, SiO2 coexisting system, SO3 combined with H2O formed H2SO4 first, and chemical agent and SiO2 showed the adsorption ability of SO3, however, adsorption ability of chemical agent for SO3 was better than SiO2. The oxygen in V2O5 showed oxidation ability to Hg0, more importantly, the chloride ion strengthened Hg0 oxidation on the V2O5, and generated the intermediate (HgCl), further generated HgCl2.
学术讨论
主办单位时间地点报告人报告主题
东南大学能环学院 2015.5.15 热能所一楼会议室 胡斌 化学团聚及脱汞研究
东南大学能环学院 2015.9.7 热能所一楼会议室 胡斌 湍流和化学团聚研究
东南大学能环学院 2015.11.25 热能所一楼会议室 常倩云 液滴强化条件下颗粒双极性电凝并模式实验研究
东南大学能环学院 2016.11.20 热能所一楼会议室 吴昊 应用水汽相变增强WFGD系统脱除细颗粒物及SO3酸雾的研究
东南大学能环学院 2016.12.25 礼西309 胡斌 学期科研进展
东南大学能环学院 2017.5.15 礼西309 胡斌 脱硫废水蒸发实验方案及结果
东南大学能环学院 2017.6.2 礼西309 申奥 湍流团聚装置优化
东南大学能环学院 2017.6.2 礼西309 夏亚磊 旋转机械弯曲转子振动特性及减振技术研究
     
学术会议
会议名称时间地点本人报告本人报告题目
国际电除尘会议 2016.9.19 波兰 化学团聚增强电除尘脱除PM2.5
973中期讨论交流会 2016.10.16 南京 增强电除尘脱除PM2.5试验研究
     
代表作
论文名称
Improving the electrostatic precipitation removal efficiency by desulfurization wastewater evaporati
SO3 reduction in the flue gas by adding a chemical agent
PM2.5 and SO3 collaborative removal in electrostatic precipitator
Experimental and DFT studies of PM2.5 removal by chemical agglomeration
脱硫废水蒸发脱除PM2.5试验研究
低低温电除尘协同脱除细颗粒与SO3实验研究
化学团聚促进电除尘脱除烟气中PM2.5和SO3
脱硫废水蒸发增强电除尘脱除PM2.5和SO3实验研究
烟气温湿度对电除尘脱除细颗粒的影响
 
答辩委员会组成信息
姓名职称导师类别工作单位是否主席备注
陈晓平 正高 教授 博导 东南大学
盛昌栋 正高 教授 博导 东南大学
薛建明 正高 教授级高级工程师 硕导 国电环境保护研究院
杨宏旻 正高 教授 硕导 南京师范大学
袁竹林 正高 教授 博导 东南大学
      
答辩秘书信息
姓名职称工作单位备注
王沛 其他 讲师 东南大学