NOx formation and reduction mechanisms in staged O2/CO2 combustion
NOx formation and reduction mechanisms in staged O2/CO2 combustion
复制标题
DOI：
10.1016/j.combustflame.2010.11.006
复制
发表时间：
2011-07
影响因子：
4.4
通讯作者：
Hirotatsu Watanabe;J. Yamamoto;K. Okazaki
中科院分区：
文献类型：
--
作者：
Hirotatsu Watanabe;J. Yamamoto;K. Okazaki
研究了O2/CO2分级燃烧和空气燃烧中NOx的生成和还原机理。在蜂窝上方形成了掺入NH3的平坦甲烷火焰，并对其NOx生成特性进行了研究。此外，还测量了OH~+分布的化学发光，并用CHEMKIN-PRO研究了NOx还原的详细机理。总体而言，NOx转化率随着一次O2/CH4比的降低而降低，而在O2存在下容易转化为NOx的NH3和HCN迅速增加。因此，分级燃烧存在一个合适的一次O2/CH4比。实验表明，在O2/CO2燃烧中，给出最小固定氮化合物的一次O2/CH4比低于空气燃烧。在适当的分级燃烧条件下，O2/CO2燃烧的NOx转化率比空气燃烧低40%。这可能是由于O2/CO2燃烧中CO2浓度较高所致。实验和数值模拟结果表明，在O2/CO2燃烧过程中，通过CO_2+H-→CO+OH生成了丰富的OH自由基。由于甲烷火焰中存在大量氢源，OH自由基通过H2+OH→H+H2O和O2+H→OH+O生成H和O自由基。富油区生成的O和OH自由基促进了NH3和HCN的氧化。NH3和HCN氧化生成的NOx，由于氧化发生在NOx还原效果较高的富油区，因此转化为N2。实际上，在分级燃烧中，富油区NH3和HCN的氧化优先于二次喷氧前残留的NH3和HCN。在O2/CO2燃烧中，分段燃烧可以显著降低NOx排放。
The purpose of this study was to investigate the NOxformation and reduction mechanisms in staged O2/CO2combustion and in air combustion. A flat CH4flame doped with NH3for fuel-N was formed over the honeycomb, and NOxformation characteristics were investigated. In addition, chemiluminescence of OH*distribution was measured, and CHEMKIN-PRO was used to investigate the detailed NOxreduction mechanism. In general, the NOxconversion ratio decreases with decreasing primary O2/CH4ratio, whereas NH3and HCN, which are easily converted to NOxin the presence of O2, increases rapidly. Therefore, a suitable primary O2/CH4ratio exists in the staged combustion. Our experiments showed the primary O2/CH4ratio, which gave the minimum fixed nitrogen compounds in O2/CO2combustion, was lower than in air combustion. The NOxconversion ratio in O2/CO2combustion was lower than in air combustion by 40% in suitable staged combustion. This could be explained by high CO2concentrations in the O2/CO2combustion. It was shown that abundant OH radicals were formed in O2/CO2combustion through the CO2+H→CO+OH, experimentally and numerically. OH radicals produced H and O radicals through H2+OH→H+H2O and O2+H→OH+O, because a mass of hydrogen source exists in the CH4flame. O and OH radicals formed in the fuel-rich region enhanced the oxidation of NH3and HCN. NOxformed by the oxidation of NH3and HCN was converted to N2because the oxidation occurred in the fuel-rich region where the NOxreduction effect was high. In fact, the oxidation of NH3and HCN in the fuel-rich region was preferable to remaining NH3and HCN before secondary O2injection in the staged combustion. A significant reduction in NOxemission could be achieved by staged combustion in O2/CO2combustion.