水磁化对燃煤PM2.5在过饱和水汽环境中长大的影响及其机制

Making coal-burning PM2.5 efficiently enlarging is a difficult problem for the pretreatment technology of dust removal by vapor phase change under low degree of supersaturation. For solving this problem, applicants present a new technique that is vapor phase change coupled with magnetic field, according to the wettability of the particles that is one of the key factor determining the particle enlargement and the decrease of surface tension under the magnetic field. In this technique the influence of magnetic field on water property is the key of determining the process. Here the researches will be done around two key scientific issues: the law and mechanism of water magnetization impact on the enlargement of particles. Through experiment and theoretical analysis, the law and related factors of water magnetization effect will be studied from two main aspects reflecting the growing process of the particles: the particle nucleation and the characteristics of particle enlargement, including the critical supersaturation, the characteristics of embryo formation and the rate of embryo growing for the nucleation of the particles in the supersaturated environment formed by magnetic water; the effect of water magnetization on the characteristics of particle enlargement. For understanding the mechanism, the researches will be carried out by combining experimental and numerical methods: the change rule of water properties after magnetization and relevant conditions; the influence of the magnetic field on the property of vapor and the characteristics of particle enlargement under the environment of magnetized vapor; the characteristics of supersaturation environment constructed by magnetized water. This project will broaden the application of the water magnetization and lay a foundation for the theoretical establishment of coal-burning PM2.5 enlargement by vapor phase change under the action of magnetic field.

解决低过饱和度下燃煤PM2.5的有效增长是水汽相变除尘预处理技术的难点。申请者根据影响颗粒长大的关键条件之一颗粒润湿性和水磁化下表面张力降低，提出了水汽相变与磁场耦合，以促进颗粒在低过饱和度下的长大效果。项目针对磁场影响的根本——水性质，围绕两个关键科学问题水磁化对颗粒长大影响的规律和影响机制展开研究。通过实验和理论分析，从反映颗粒长大过程的两个主要方面颗粒核化和长大特性，研究水磁化对颗粒长大影响规律以及影响水磁化作用的相关因素：研究水磁化下颗粒核化的临界过饱和度和晶胚的形成特征及生长速率；研究水磁化对细颗粒长大特性的影响。通过实验与数值计算，研究水磁化后性质的变化规律及其相关条件，研究磁场对水汽性质的影响以及磁化水汽下颗粒长大的特性，研究磁化水形成的过饱和场的特征，以揭示水磁化影响的机制。本项目研究将拓宽水磁化应用的领域，并为燃煤PM2.5在磁场作用下水汽相变凝结长大的理论建立奠定基础。

为解决低过饱和水平下细颗粒物的有效长大问题，本项目提出利用磁化水来强化细颗粒的生长性能，并围绕水磁化对颗粒长大影响的规律和机制展开了研究。 .（1）利用流动云室研究了高浓度多分散颗粒群的临界过饱和度。结果表明，添加磁场可使颗粒群激活所需的临界过饱和度降低0.57%。研究结果能为水磁化过饱和水汽环境的构建提供理论依据。.（2）采用ESEM平台研究了晶胚的形成特征和生长速率以及表面形貌和颗粒成分对核化过程的影响，确定了不同颗粒空间分布下的核化模型。研究结果加深了对水蒸气在细颗粒表面非均相成核过程的理解和认识。.（3）采用生长管实验平台研究了磁化水和磁化润湿剂对细颗粒长大特性的影响。结果表明，磁化水能够有效地促进细颗粒的长大效果；润湿剂磁化后可改善其作用性能。.（4）以四种典型燃煤成分颗粒为对象，在生长管实验平台上研究了主要工艺参数对细颗粒物在过饱和水汽环境中凝结长大的影响，并根据理论计算了水磁化后颗粒长大的成核速率和临界饱和度。研究结果证明了采用磁化水强化细颗粒生长性能的可行性。.（5）测量了不同性质水在不同磁场强度和磁化时间下的表面张力以及与四种典型燃煤成分颗粒之间的接触角，并基于Zisman理论计算了颗粒在磁化水作用下的临界表面张力。这为分析磁化水的影响提供了基础数据。.（6）通过将磁场与过饱和水汽环境直接耦合研究了磁场对细颗粒长大的影响。实验结果表明，在加入强度为61.1 mT的磁场后，长大颗粒群中亚微米级颗粒的数量减少，而粒径大于2.1 m的颗粒数量增加。总的来说，加入磁场后，长大颗粒的算术平均直径能增加0.32%-6.89%。.（7）研究了不同强度的磁场对水扩散性能的影响。结果表明，当磁场强度从0 mT升至136.1 mT时，水的蒸发速率提高了35.3%。磁场的影响与蒸发环境的温度和气氛有关升。研究结果为解释磁场的作用机理提供了理论依据。