Transformation Mechanisms of NO_x into N_2O and Its Depression in Coal Combustion and De-NO_x Process

一氧化二氮（N_2O）作为燃煤产生的环境污染物之一，一直受到人们的关注。本文从实验和理论两方面探讨了湍流煤粉燃烧（高温燃烧）和鼓泡流化床燃烧（低温燃烧）中N_2O的生成/破坏特性。煤粉湍流燃烧时，挥发分燃烧区N_2O浓度升高。温度梯度越温和，最大N_2O浓度越高。最后，在炉膛出口，N_2O达到相当低的值。NH_3非催化选择性还原NO对N_2O生成/破坏的影响取决于提供NH_3的燃烧气氛。在鼓泡流化床煤燃烧过程中，N_2O浓度随温度的降低和燃烧化学计量量的增加而增加。不同煤种N_2O…More浓度的差异可以用随挥发物演化的含氮物种的差异来解释。发现HCN比NH_3对N_2O的形成贡献更大。当煤颗粒直接供给床面时，N_2O主要在燃烧室干舷形成。另一方面，在底部进料实验中，N_2O在空气分布器上方迅速形成。在几种颗粒床分解N_2O的实验中，炭、CaO和氧化的不锈钢颗粒对N_2O的分解有催化作用。在炭燃烧实验中，N_2O的生成趋势特征与挥发分燃烧的趋势相似。从单粒煤燃烧数值模型来看，N_2O主要在挥发性燃烧过程中产生。NCO、NH和N_2反应生成N_2O。另一方面，H自由基成为还原N_2O的重要物质之一。该模型能较好地解释实验结果。少

Nitrous oxide (N_2O) has been arrested the attention as one of environmental pollutants produced from coal combustion. In this study, characteristics of N_2O formation/destruction in both turbulent pulverized coal combustion (high temperature combustion) and bubbling fluidized bed coal combustion (low temperature combustion) are discussed experimentally and theoretically.In case of turbulent pulverized coal combustion, during the volatile matter combustion region, N_2O concentration increases. The maximum N_2O concentration becomes higher, if the temperature gradient gets gentler. Finally, at the exit of furnace, N_2O reaches quite low value. The influence of non-catalytic selective reduction (NCSR) of NO by NH_3 injection on N_2O formation/destruction depends on the combustion atmosphere where NH_3 is supplied.In the bubbling fluidized bed coal combustion, N_2O concentration increases with decreasing temperature and with increasing the combustion stoichiometry. The difference of N_2O … More concentration due to coal types can be explained by the difference of N-contained species evolved together with the volatile matter. HCN is found to contribute more to N_2O formation than NH_3. In case that the coal particles are directly supplied onto the bed surface, N_2O is mainly formed in the freeboard of combustor. In case of bottom feed experiments, on the other hand, N_2O is rapidly formed just above the air distributor. In the experiments of N_2O decomposition through the beds of several kinds of particles, char, CaO and oxidized stainless steel particles can catalytically contribute to the N_2O decomposition. In the char combustion experiments, the tendency of N_2O formation characteristics is similar to that of the combustion of volatile matter.From the numerical model for single coal particle combustion, N_2O is mainly produced during the volatile combustion. The reactions by way of NCO, NH and N_2 contribute to N_2O formation. On the other hand, H radical becomes one of the important species for N_2O reduction. The modeling could explain well the experimental results. Less