基于空化热点效应的船舶尾气脱硝机理研究

With the the increasingly serious situation of ship exhaust gas pollution control, it has become an important development direction to investigate integrated wet methods for removal of NOx and SOx from ship exhaust gas. However, nitric oxide (NO), accounting for more than 90% of nitrogen oxides (NOx), is difficult to be removed by alkali scrubbing alone. This is one the of critical issues for integrated treatment technology for ship exhaust gas. Therefore, based on our preliminary research, we have firstly proposed to apply the "hot spot" effect with ultra-high temperature and ultra-high pressure induced by liquid cavitation to achieve the reduction of NO under high temperature and the oxidation of NO under high pressure. In this project, the RRKM theory, the transition state theory and the canonical variational transition state theory will be used to calculate the reaction pathways, which will clarify the NO reaction pathways, rate constant, intermediate and final products under transnormal temperature and pressure. End-products of NO cavitation reactions will be determined using spectroscopic and mass spectrometric analysis, and ion chromatography analysis. By comparing theoretical calculation with experimental results, the NO removal pathways under cavitation condition will be clarified, and the removal mechanisms of NO will be revealed. On the above basis, the influence of reactor parameters and reaction conditions on cavitation denitrification will be experimently investigated using ship exhaust gas. This project will have profound theoretical guidance to the realization of integrated treatment technology for ship exhaust gas.

船舶尾气污染控制的形势日益严峻，研究环境友好型湿法脱硫脱硝技术，实现船舶尾气的一体化处理成为重要发展方向。然而氮氧化物（NOx）中占比90%以上的一氧化氮（NO）难以碱洗脱除，是船舶尾气一体化处理的关键。因此本项目在前期工作基础上，拟利用液体空化引起的超高温、超高压的“热点效应”处理NO，实现高温条件下CO对NO的还原和高压条件下O2对NO的氧化。本项目利用RRKM理论、过渡态理论和变分过渡态理论，进行化学反应路径计算，明确超常规温度、压力下的NO反应路径、速率常数、中间产物、终产物等信息；通过光谱和质谱实验分析、反应溶液成分测定等方法确定NO空化反应的终产物。对比理论计算和实验结果，明确空化脱除NO的反应路径，揭示空化脱除NO的机理。在此基础上，进行船舶尾气空化脱硝实验，确定反应器参数和反应条件对空化脱硝的影响规律。本项目的研究对船舶尾气一体化处理技术的实现具有重要的理论价值。

船舶尾气脱硝是当今业界未解的难题。针对一体化船舶尾气处理需求，本项目提出了水力空化强化脱硝的新方法。项目主要开展了水力空化强化纯水脱硝的机理研究，水力空化强化ClO2脱硝的机理研究以及水力空化强化NO2去除的机理研究三方面内容。项目取得的主要成果包括：（1）揭示空化热点效应在纯水空化脱硝时的作用机制。水力空化虽然可以产生高温高压的热点，并引起强烈微射流，但由于•OH生命周期短，NO难溶于水，水力空化产生的•OH不能有效和NO接触氧化。此成果对研究水力空化强化难溶气相物质的化学反应具借鉴作用。（2）阐明水力空化强化ClO2脱硝的机理。在空化热点效应的强化下，气液接触面积得到几十倍扩展，加上微射流的强烈扰动，气液传质得到加强；而化学反应形式从单纯的气液界面反应扩展到气液界面和气相反应，从而有效提高了化学反应速率，降低了ClO2的使用浓度。水力空化条件下ClO2高效将NO氧化为NO2，而空化产生的•OH则强化去除NO2，提高了脱硝率。此成果对理解水力空化协同氧化剂脱硝具有重要指导意义。（3）阐明了水力空化强化去除NO2的机理。•OH可有效将NO2和HNO2氧化为HNO3，从而减少溶液中NO2因溶解饱和而造成的逸出。水力空化条件下NaClO2、Na2S2O8、H2O2、NaClO、ClO2等对NO2吸收性能影响较小。NaClO2、ClO2对NO2的氧化能力较弱，NaClO2溶液中ClO2的逸出可裹挟出NO2，导致NO2剩余浓度增大。此成果对解决传统湿法脱硝过程中NO2生成量过多的问题具有指导意义。