返回
类型 基础研究 预答辩日期 2017-12-20
开始(开题)日期 2016-03-01 论文结束日期 2017-11-01
地点 动力楼420 论文选题来源 973、863项目     论文字数 7.5 (万字)
题目 燃煤PM2.5在水汽条件下的核化长大特性研究
主题词 PM2.5,水汽相变,核化,长大,烟气回流
摘要 燃煤PM2.5是大气颗粒物污染的主要来源之一,而常规的除尘器对于PM2.5的捕集效率极低,尤其是针对0.1-1 μm之间的粒径段的细颗粒。大量的燃煤细颗粒进入大气中不仅给国民经济的发展造成损失,而且会对人体健康带来伤害,因此实现对燃煤PM2.5的有效捕集成为当前急需解决的问题。水汽相变促进细颗粒物的长大并脱除是一项非常具有应用前景的预处理技术,尤其是与燃煤电站排放的高热高湿烟气结合具有明显的适用性,因此燃煤PM2.5在水汽条件下的核化凝结长大特性的研究具有重要的应用价值。 本文首先分析了不同燃煤电厂细颗粒的化学组成,对细颗粒的润湿性能进行了表征,讨论了燃煤电厂细颗粒润湿性与其典型成分之间的关系,并分析了残炭对细颗粒润湿性能的影响。通过在水中添加Tween20润湿剂对电厂细颗粒表面的润湿性能进行了改善,结果发现,原始润湿性越差的细颗粒,添加润湿剂后润湿性能的改善越明显,另外,随着润湿剂浓度的增加,不同颗粒表面的接触角最终仍存在一定的差异。 为了对水汽在细颗粒表面的核化凝结进行可视化研究,制备了超疏水/细颗粒表面,成功实现了水汽在细颗粒表面的可控核化凝结。实验考察了水汽在单个SiO2细颗粒和多个SiO2细颗粒表面的核化凝结过程,结果发现,水汽在单个细颗粒表面的核化凝结模型与Fletcher模型基本一致,晶胚首先出现在颗粒表面的某一点;水汽在多个细颗粒表面的核化凝结则是从颗粒的交界面开始;初步确定了细颗粒在水汽条件下的核化模型。 为了避免使用不确定的动力常数K_c,基于蒸汽直接扩散和颗粒表面吸附水分扩散两种作用机制,研究了液滴在单个燃煤细颗粒表面的长大动力学,结果表明,液滴的长大与颗粒粒径、蒸汽过饱和度、蒸汽温度、液滴粒径和燃煤细颗粒表面润湿性都有关系,利用动力学模型预测了液滴在实际燃煤细颗粒表面的长大速率。 搭建了直接测量细颗粒长大后粒径分布的实验平台,在平台上研究了3个不同燃煤电厂细颗粒和1个生物质电厂细颗粒在水汽条件下的长大特性及其影响因素的作用规律。结果表明,由于颗粒粒径、化学组分及表面润湿性能的差异,不同源细颗粒表现出了不同的长大特性;过饱和度是影响细颗粒长大的最重要影响因素;颗粒数量浓度的增加会加剧颗粒之间的水汽竞争作用,从而降低生长管中的过饱和水平,并最终对细颗粒的长大效果产生不利影响;停留时间的增加有利于细颗粒的长大。当生长管中的最大过饱和度达到1.324时,燃煤细颗粒和生物质细颗粒长大后的平均粒径都可以达到2 ?m以上。 添加润湿剂能够强化细颗粒的长大效果,尤其能够促进小粒径段细颗粒的长大;颗粒的润湿性能和初始粒径对颗粒在润湿剂作用下的长大有一定的影响,粒径越大,润湿性能越好的细颗粒,长大后的效果越好。颗粒长大后的平均粒径随着润湿剂浓度的增加而增大,但是对于小粒径段占比高的细颗粒,当润湿剂浓度的增加到一定量时,添加润湿剂虽然会增大颗粒的长大后的平均直径,却会抑制其促进小粒径段细颗粒的长大效果。 提出了一种新的烟气回流耦合水汽相变促进细颗粒长大的技术,实验研究了该技术对SiO2细颗粒的长大促进作用。与原生长管中的长大效果对比,发现该技术即使在低过饱和水平下也能够高效地促进细颗粒的长大。烟气回流位置、回流比例、过饱和度和颗粒数量浓度对该技术效果均有影响,在最佳的实验条件下,原始平均粒径为0.130 ?m的细颗粒长大后的平均粒径可达到6.156 ?m。
英文题目 CHARACTERISTICS OF COAL-FIRED PM2.5 NUCLEATION AND GROWTH UNDER SUPERSATURATED WATER VAPOR
英文主题词 PM2.5,phase transition of water vapor,nucleation,growth,gas circulation
英文摘要 PM2.5 emitted from coal combustion is one of the major source of air particle pollution, however, the traditional dust removal equipment is far less efficient for these particles colletion, especially for the fine particles range from 0.1-1μm. A great amount of coal-fired fine particles enter into ambient air which not only makes great loss for national economic development but also causes damage for human health. Therefore, it has become an urgent problem to collect the coal-fired fine particles with high efficiency. Vapor condensation is one of the most promising pretreatments for particle enlargment and subsequent removal, especially for the high temperature and humidity of the flue gas, hence, study of the characteristics of nucleation and condensational growth of coal-fired fine particles has important applied value. Firstly, this paper have investigated the chemical composition and the wettability of coal-fired fine particles, then the relationship between wettability and typical chemical compositon of coal-fired fine particles was discussed, also, the effect of carbon residue on particle wettability was analyzed. In order to improve the wettability of coal-fired fine particles, surfactant Tween 20 was applied and the contact angle was reduced successfully. For the sake of direct visualization of the process of vapor nucleation and condensation on fine particle’s surface, the superhydrophobicity/particle was made to realize the spatial control in the vapor nucleation and condensation on fine particle’s surface. Vapor condensation on single particle and a few particles’ surface were experimentally studied, and the nucleation model of vapor nucleation on particle’s surface was confirmed, the results showed that the vapor condensation on single particle’s surface was seem like it proposed by Fletcher, the embryo appeared at some point of particle’s surface randomly; nevertheless, the embryo was always appeared at the interface of particles when vapor condensation on serval few particles’ surface; the fine particle nucleation model was identified preliminarily. In order to avoid using the uncertain kinetic constants, K_c, growth kinetics of droplet fomed on single coal-fired fine particle was studied based on these two mechanism: direct addition of water molecules from the vapor and surface diffusion of adsorbed water molecules on the particle. The results showed that particle diameter, vapor supersaturation, temperature, droplet radius and particle’s surface wettability have effect on droplet growth, the growth rate of droplet formed on different coal-fired fine particles’ surface was predicted with this kinetic model. The experimental platform was set up for direct measurement of particle size after its growth, the characteristics and the effects on the three coal-fired fine particles and a biomass-fired fine particles growth under supersaturated water vapor were researched. The results showed that the particle initial size and wettability have an effect on particle growth, supersaturation was the most important effect on its growth, particle number increase would worse the vapor competition among particles which would lead to a decline of supersaturation level in the growth tube, and then have a negative effect on the particle enlargement; however, residence time increase have a positive effect on its growth. The average diameter of all the fine particles emitted from power plant boiler could be enlarged above 2 ?m when the maximum supersaturation reached 1.324. The surfactant was added into the hot water and it could highly improve the particle enlargement, especially for the small range particles, the wettability and initial particle size have an effect on the average diameter of particle size after growth. The average diameter of particles after growth increased with the increase of surfactant addition, however, for the particles with great amount small particles, the increase of wet agent addition could increase the final average diameter, but decrease the enlarment performance of small particles. A new technique of gas circulation coupled with vapor condensation was proposed, and the effect on paritlce enlargement of this technique was experimentally studied. Comparing with the particle growth in the original growth tube, this technique could highly improve the particle enlargement even under low supersaturated environment. The circulation point, proportion, supersaturation and particle concentration had an effect on this technique, under the optium condition, the average diamemer of particles could reach from 0.130 to 6.156 ?m.
学术讨论
主办单位时间地点报告人报告主题
清华大学 2015年7月 清华大学 徐俊超 水汽相变促进细颗粒长大的实验方法
浙江大学 2015年8月 浙江大学 徐俊超 课题4——东南大学研究进展汇总
华中科技大学 2015年9月 华中科技大学 徐俊超 水汽在燃煤细颗粒表面长大的动力学研究
浙江大学 2015年11月 浙江大学 徐俊超 香烟细颗粒在过饱和水汽中核化凝 结长大的实验研究
长沙理工大学 2016年9月 长沙理工大学 张军教授 细颗粒核化凝结长大研究
课题组 2016年10月 东南大学 徐俊超 年度计划及进展
东南大学 2016年10月 东南大学 徐俊超 回流混合促进细颗粒长大的实验研究
华北电力大学 2015年10月 华北电力大学 徐俊超 亚微米细颗粒长大特性的直接测量研究
     
学术会议
会议名称时间地点本人报告本人报告题目
5th Sino-Australia Symposium on Advanced Coal Utilization Technology 2015年12月 华中科技大学 Characteristics of vapor condensation on coal-fired fine particles
2nd International conference on advances on clean energy research 2017年4月 柏林 Heterogeneous condensation on fine particles of water vapor in a moderated growth tube
     
代表作
论文名称
Characteristics of vapor condensation on coal-fired fine particles
细颗粒长大特性的直接测量
生物质燃烧源PM2.5在水汽条件下长大特性研究
Heterogeneous condensation of water vapor on particles at high concentration
Heterogeneous condensation on fine particles of water vapor in a moderated growth tube
Heterogeneous condensation coupled with partial gas circulation for fine particles abatement
 
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
袁竹林 正高 教授 博导 东南大学
何小民 正高 教授 博导 南京航天航空大学
杨宏旻 正高 教授 博导 南京师范大学
钟兆平 正高 教授 博导 东南大学
肖军 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