煤粉高温空气分级燃烧中N2O生成及转化对NO还原影响的机理研究

The furnace overall air-staged combustion technology can greatly reduce NOx emission from pulverized coal combustion. However, the mechanism experiments show that there is a phenomenon of NO second rise after NO deep reduction, which has become a strong stumbling block to achieve ultra-low NOx emission. Previous char nitrogen oxidation mechanism can not give a reasonable explanation for it. Additionally, it was found that NO reduction process would be accompanied by a large number of N2O generation and disappeared after the addition of burnout air. Many studies have been devoted to the mechanisms of N2O formation and decomposition, but all limited to the low temperature (≤1000℃) reactions in fluidized beds. These studies show that generation and decomposition of N2O is inseparable from NO. So, it is possible to speculate that NO high temperature reduction inevitably has complex nitrogen transport and conversion mechanisms concerning N2O, which may be closely related to NO second rise. Because various characteristics including reaction atmosphere and char particles properties are more sensitive to N2O at high temperature, it is of great theoretical and practical value to study the mechanisms of interaction and the mutual conversion between N2O generation and NO reduction in pulverized coal combustion at high temperature (>1000℃). A high temperature fixed bed with precise controllable atmosphere and a down-fired flame combustion furnace will be employed to investigate the paths, conditions and limits of the mutual conversion between NO and N2O under various high temperature and complex combustion atmospheres. The influence mechanisms of atmosphere, temperature, char particles and other controllable factors on the mutual conversion of species containing nitrogen, such as NO, N2O and char nitrogen, will be established to elucidate the underlying mechanism of NO second rise. Correspondingly, the theory and method for eliminating NO second rise are expected be obtained.

炉内整体空气分级燃烧技术能大幅降低燃煤NOx排放量，但实验发现NO深度还原后燃尽阶段会二次跃升，成为实现超低NOx排放的瓶颈，先前的焦炭氮氧化机理对此无法合理地解释；同时发现NO还原时伴随大量N2O生成，且在燃尽风送入后消失。国内外对N2O生成分解有较多研究，揭示了其与NO密不可分。但研究都限于较低温度（≤1000℃）的流化床中，然也可借此推测NO高温还原和N2O存在相互转化等复杂的氮迁移机制，进而与NO二次跃升密切关联。因高温下反应气氛、颗粒等特性对N2O更为敏感，研究煤粉高温燃烧中（>1000℃）N2O生成与NO还原作用关系有重要理论与实用价值。项目拟借助精确可控气氛的高温固定床和下行燃烧炉，研究高温复杂燃烧气氛下NO和N2O相互转化的途径、条件及限度，建立气氛、温度、焦炭颗粒等可控因素对NO、N2O、焦炭氮等含氮物质相互转化的影响机制，揭示NO二次跃升的内在机理和相应抑制理论及方法。

燃烧过程中氮氧化物生成排放问题一直是国内外众多学者长期以来致力于研究的问题，N2O是燃烧过程中特定条件下生成的氮氧化物的形式产物，由于其特殊性一直视为是循环流化床锅炉中的特有产物，在煤粉锅炉燃烧中却被忽略。但是近年来本团队对煤粉高温空气分级燃烧的研究过程中却发现了还原区存在较多N2O生成，以及NO的二次跃升现象，基于此，本文通过可控燃烧环境温度的一维下行燃烧炉和高温固定床反应器等平台深入地研究了煤粉高温空气分级燃烧过程中N2O的生成分解机制和其对NO二次跃升影响的机理。. 本研究首次系统地探索了煤粉高温空气分级燃烧条件下N2O在还原区的生成和NO在燃尽区二次跃升现象，揭示了煤粉空气分级燃烧条件下N2O生成的机制和过渡区NO二次跃升的现象本质。探究了煤粉空气分级燃烧的高温微氧还原区中NO真实还原与隐匿效应的机制。得到了还原区中各种烟气气氛、煤焦单一或联合作用对在微氧高温区间中NO还原及N2O、HCN或NH3和其它含氮中间产物的还原转化影响规律，及还原区复杂热力气氛条件下的NO及N2O等含氮产物相互转化的促进和抑制机理。并基于N2O和NO之间的相互生成转化关系，优化了均相反应动力学模型，建立了N2O和NO生成转化的煤粉单颗粒燃烧模型和基于煤粉空气分级燃烧的NO和N2O多相流反应生成模型，准确地预测了N2O的生成以及其和NO之间的转化关系。. 研究成果对广泛的工业领域燃烧过程中NOx的生成与控制研究具有重要意义，为进一步降低空气分级燃烧过程NOx新技术提供了研究思路和理论支持。