Study on the NO_x formation and decomposition mechanism at high temperatures

为了抑制煤燃烧过程中NO_x和N_2O的排放，必须抑制煤焦氮生成NO_x和N_2O。研究了纯碳与气相NO反应生成HCN的机理。结果表明，NO被捕获在炭表面上，由此形成的表面氮物质被转化为HCN和N2。实验还发现，氢的量是决定HCN生成行为的重要因素。在O_2存在下，HCN的生成发生在较低的温度区，如600 ℃。采用脉冲式反应器研究了1000-1300 ℃高温下N2和NO的生成行为。再次证实了表面氮物种与气态NO之间的反应是N_2生成的主要反应。产物气中N_2/NO比值随半焦转化率的增加而降低。这表明了焦炭量对N_2生成的重要性。通入O_2后温度的升高也会影响N_2/NO比。这是首次对1300 ℃高温下NO-碳反应进行的基础性研究，所获得的信息对了解煤粉燃烧系统中NO_x的生成具有重要意义。

In order to suppress the NO_x and N_2O emissions during coal combustion, it is necessary to suppress the formatione of NO_x and N_2O from char nitrogen. The mechanism of HCN formation from pure carbon and gas-phase NO was studied. It was clarified that NO is captured on the char surface and the surface nitrogen species thus formed is converted to HCN and N2. It was also found that the amount of hydrogen is an important factor to determine the HCN formation behavior. In the presence of O_2, HCN formation takes place in a lower temperature region like 600 ℃. This is because the surface nitrogen complexes are activated during the carbon-O_2 reaction.N_2 and NO formation behaviors at a high temperature region between 1000-1300 ℃ were investigated using a specially designed pulse-type reactor. Again it was confirmed that the reaction between the surface nitrogen species with gaseous NO is the main reaction for N_2 formation. N_2/NO ratio in the product gas decreased with increasing char conversion. This indicates the importance of the amount of char for N_2 formation. The temperature increase upon the introduction of O_2 also affects the N_2/NO ratio. This is the first fundamental study on the NO-carbon reaction at a high temperature like 1300 ℃, and the information obtained is useful to understand the NO_x formation in a pulverized fuel combustion system.