煤粉在O_(2)/N_(2)和O_(2)/CO_(2)富氧分级燃烧中的氮元素迁移路径研究

Study on the migration path of nitrogen in coal during O_(2)/N_(2)and O_(2)/CO_(2)oxygen enriched combustion

空气分级燃烧在煤粉燃烧初期形成的还原性气氛是抑制燃料型NO_(x)的生成的主要因素,富氧分级燃烧能扩大煤粉燃烧初期还原性区域、延长煤粉在还原性气氛中的停留时间,对不同气氛下煤中氮元素在富氧燃烧过程的迁移路径进行研究,可为抑制焦炭NO_(x)的生成及提升煤粉燃烧效率提供支撑。通过高温滴管炉实验平台,研究O_(2)/N_(2)和O_(2)/CO_(2)富氧分级燃烧条件下过量氧气系数和氧气体积分数对煤粉燃烧过程中固定碳、挥发分、C、H、O、N、S元素的释放及煤中氮迁移转化的影响。实验结果表明:当二次风氧气体积分数为40%时,O_(2)/N_(2)、O_(2)/CO_(2)气氛下的煤中挥发分、固定碳、N、H、O、S的释放率均随二次风过量氧气系数的增加而增加,煤中的挥发分和H元素在煤粉燃烧初期基本完全释放,煤中N、O、S元素的释放与C元素的释放有很强的正相关性。燃烧过程中煤中释放的氮主要转化成N_(2),少量向NH_(3)、HCN和NO_(x)转化,且N_(2)>>NH_(3)>>HCN,N_(2)的转化率随二次风过量氧气系数的升高呈先升高后降低的趋势,NH_(3)、HCN转化率随二次风过量氧气系数的升高不断降低,二次风过量氧气系数较低时,烟气中并未检测到NO_(x)排放。二次风过量氧气系数为1时,O_(2)/N_(2)、O_(2)/CO_(2)气氛的NO转化率分别为29.9%、28.1%。当二次风过量氧气系数为0.5时,O_(2)/N_(2)和O_(2)/CO_(2)气氛中煤中各组分释放率均随二次风氧气体积分数的增加而增加,煤中释放的氮主要向N_(2)转化,N_(2)的转化率随二次风氧气体积分数的升高而增大,NH_(3)和HCN的转化率均随二次风过量氧气系数的增加而减小。高浓度CO_(2)能促进焦炭气化反应,导致O_(2)/CO_(2)气氛中各组分的释放率较高,且N_(2)转化率也相对较高。

The reducing atmosphere formed by air staged combustion in the early stage of coal combustion is the main factor that suppresses the generation of fuel type NO_(x).Oxygen rich staged combustion can expand the reducing area in the early stage of coal combustion,extend the residence time of coal in the reducing atmosphere.Research on the migration pathways of nitrogen in coal during the oxygen-rich combustion process under different atmospheres can provide support for suppressing the formation of NO_(x)in coke and enhancing the combustion efficiency of coal.The effects of excess oxygen coefficient and oxygen concentration on the release of fixed carbon,volatile matter,C,H,O,N and S elements and the migration and transformation of nitrogen in coal during pulverized coal combustion were studied under two kinds of oxygen enriched staged combustion conditions(O_(2)/N_(2)and O_(2)/CO_(2)),using a high temperature dropper furnace experimental platform.The experimental results show that when the oxygen concentration of secondary air is 40%,the release rates of volatile matter,fixed carbon,N,H,O and S in coal under O_(2)/N_(2)and O_(2)/CO_(2)atmospheres increase with the increase of excess oxygen coefficient of secondary air.The volatile matter and H element in coal are completely released in the early stage of pulverized coal combustion,and the release of N,O and S elements in coal has a strong positive correlation with the release of C element.During the combustion process,the nitrogen released from coal is mainly converted into N_(2),and a small amount is converted to NH_(3),HCN and NO_(x),and N_(2)>>NH_(3)>>HCN.The conversion rate of N_(2)increases first and then decreases with the increase of excess oxygen coefficient of secondary air.The conversion rates of NH_(3)and HCN decrease with the increase of excess oxygen coefficient of secondary air.When the excess oxygen coefficient of secondary air is low,no NO_(x)emission is detected in flue gas.When the excess oxygen coefficient of secondary air is 1,the NO conversion rates of O_(2)/N_(2)and O_(2)/CO_(2)atmosphere are 29.9%and 28.1%,respectively.When the excess oxygen coefficient of secondary air is 0.5,the release rates of each component in coal in O_(2)/N_(2)and O_(2)/CO_(2)atmospheres increase with the increase of oxygen concentration of secondary air.The nitrogen released from coal is mainly converted to N_(2).The conversion rate of N_(2)increases with the increase of oxygen concentration of secondary air,and the conversion rates of NH_(3)and HCN decrease with the increase of excess oxygen coefficient of secondary air.High concentration of CO_(2)can promote coke gasification reaction,resulting in higher release rate of components in O_(2)/CO_(2)atmosphere,and relatively high N_(2)conversion rate.