非热等离子体脱除湿法烟气脱硫排气氮氧化物和雾粒的研究

In china, the apllication of wet electrostatic precipitation is widely being promoted because the air pollution problems, such as acid mist and gypsum rain from wet flue gas desulfurization, can be thoroughly solved by the advanced pollution control technology. Theoretically, high efficient removal of NOx and fine droplets from the exhaust of the wet flue gas desulfurization is possible by modifying the wet electrostatic precipitator and introducing oxidative non-thermal plasma into the precipitator. Being concerned with the problem of high efficient oxidization of NO by non-thermal plasma and absorption of NOx by the fine droplets and electrode cleaning solution, the introduction behavior of non-thermal plasma into the humid atmosphere, motion behavior of the droplets under the joint action of electrostatic force and inertial force, physical and chemical process about NO oxidation/removal from the exhaust of typical wet flue desulfurization, removal efficiencies of NOx and droplets as well as energy consumption will be investigated, based on a two-stage non-thermal plasma reactor energized by a positive high voltage power supply. The aims of the project are to define the relationship between NO oxidation/removal and applied voltage, electrode configuration, compositions of the exhaust and electrode cleaning solution, to optimize the electrode configurations of non-thermal plasma reactor, to determine the key factors, major active species and rate control steps affecting NO oxidation/removal and energy consumption, to clarify NO oxidation/removal mechanisms, finally, to lay the foundation of technology research & development of removal of NOx and fine droplets from the exhaust of wet flue gas desulfurization by non-thermal plasma.

湿式静电除雾能够从根本上解决湿法烟气脱硫带来的酸雾和石膏雨污染问题，是我国鼓励发展的先进污染控制技术。从理论上分析，通过湿式静电除雾系统的改造，引入强氧化性非热等离子体，可望实现湿法烟气脱硫气雾环境中氮氧化物和雾粒的高效脱除。本项目针对如何实现NO高效氧化，继而又被雾粒和电极清洗液高效脱除的问题，采用由正直流高压供电的双区式非热等离子体反应器，研究非热等离子体注入气雾行为、雾粒在电场和气流惯性作用下的运动行为、典型湿法烟气脱硫排气环境中NO氧化及其脱除所涉及的物理化学过程、氮氧化物和雾粒脱除效率，以及能量消耗。旨在明确供电电压、电极配置、气雾和清洗液构成与NO氧化及其脱除的关系；优化等离子体反应器电极配置；确定影响NO氧化及其脱除效率、能量消耗的关键因素、主要活性组分和控制步骤；阐明NO氧化及其脱除的机制。为非热等离子体脱除湿法烟气脱硫排气氮氧化物和雾粒技术研发奠定基础。

湿式静电除雾能够从根本上解决湿法烟气脱硫带来的酸雾和石膏雨污染问题，因而被广泛应用。从理论上分析，通过湿式静电除雾系统的改造，引入强氧化性非热等离子体，可望实现湿法烟气脱硫气雾环境中氮氧化物和雾粒的高效脱除。本项目基于在双区式非热等离子体反应器中，NO先被非热等离子体氧化继而被雾粒吸收，再在电风作用下碰撞电极清洗液（液膜）而被吸收脱除的思路，开展了烟气组分、气雾构成、电极结构、供电电压和液膜组成对NO氧化和NOx脱除的影响及其作用机制的研究。结果表明，引入气雾使放电电压升高、电流降低、O3浓度减小。增大烟气中O2浓度，有利于强氧化性活性物质形成，促进NO氧化及吸收脱除。增大SO2浓度，可促进气雾对NOx的吸收脱除，其被归因为SO2吸收导致溶解态SO32-形成，继而促进NO2还原。尽管理论上分析CO2能与高能电子碰撞，从而形成O原子，但是，对NO氧化的贡献作用有限，反而因其强电负性附着大量电子而降低O3生成量，降低NO氧化效率。偏碱性Na2SO3气雾对NO的氧化及NOx的脱除促进作用明显优于中性或酸性气雾。随着供电电压升高，NO氧化继而被脱除的效率升高。电极表面液膜的存在可在单纯气雾的基础上，进一步提高NOx脱除效率。实验条件下，基于正直流和负直流高压放电的非热等离子体反应器，其NOx脱除能量效率分别可达到2.5 g/kWh和8~9 g/kWh。采用IC、GC、FTIR等检测手段，分析了得到吸收产物的构成。在此基础上，提出了气雾环境中，NO被非热等离子体氧化继而被吸收脱除的机制为，NO被等离子体产生的强氧化性物质氧化至NO2，而后被作为吸收剂的气雾吸收，吸收后的气雾在放电区域与大量的电子碰撞被荷电，在电场力的作用下向接地极移动，从而被捕集。本研究不仅验证了非热等离子体氧化，继而脱除气雾中NO的可行性，也对类似复杂气雾环境中多污染物的协同处理具有重要参考价值。