Study on the NO_x formation and decomposition mechanism at high temperatures

为了抑制燃煤过程中NO_x和N_2O的排放，必须抑制半焦氮中NO_x和N_2O的生成。研究了纯碳和气相NO生成HCN的机理。结果表明，NO被捕获在焦炭表面，由此形成的表面氮物种被转化为HCN和N_2。氢气量是决定HCN生成行为的重要因素。在氧气存在的情况下，氢化氢的生成是在600℃左右的较低温度区进行的。这是因为表面氮络合物在碳-氧反应过程中被激活。用专门设计的脉冲式反应器研究了1000-1300℃高温区氮气和氮氧化物的生成行为。再次证实了表面氮物种与气态NO之间的反应是生成N_2的主要反应。产物气中的N_2/NO比随着焦炭转化率的增加而降低。这表明了焦炭含量对N_2生成的重要性。引入O2后的温度升高也会影响N_2/NO比。这是第一次在1300℃这样的高温下进行无碳反应的基础性研究，所获得的信息对理解煤粉燃烧系统中NOx的生成是有用的。

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.