富N生物质原料气化过程NOx前驱物生成特性及规律

基于水平管式反应器气化条件,结合化学吸收-分光光度法和X射线光电子能谱（XPS）分析,研究了四种富氮生物质（豆秆（SBS）、稻秆（RS）、玉米秆（CS）和中密度纤维板（MDF））气化过程NO_x前驱物生成特性及规律,对比考察了燃料特性（燃料N官能团、N含量）及气化条件（温度、气化介质）的影响。结果表明,NH₃-N为主要NO_x前驱物并伴随一定量的HCN-N,绝大部分形成于初次裂解和二次反应同时进行的挥发分析出阶段。各因素通过影响NO_x前驱物组分生成路径而改变其产率：燃料特性对产率的影响主要体现在N官能团（胺类-N（N-A）类型）稳定性方面,与N含量关系不大,因不稳定N-A在初次裂解中的关键作用,MDF总产率高达74.7%（质量分数）,比秸秆类平均总产率高出15%（质量分数）;温度和气化介质会影响二次反应中与NO_x前驱物相关的反应路径（特别是加氢氢化反应）,秸秆SBS气化,温度从800℃到1000℃,NH₃-N产率从38.9%（质量分数）增加至47.7%（质量分数）,HCN-N产率先增加后减少,峰值为18.3%（质量分数）,源于各反应路径受温度影响的平衡性;气化介质改变加氢氢化反应,CO₂主要影响HCN-N,起一定抑制作用,H₂O主要影响NH₃-N,起促进作用,因此,通过调节气化介质比例可一定程度改变NO_x前期物组分的选择性。

Formation characteristics of NOx precursors during gasification of N-rich biomass

Based on gasification of 4 N-rich biomass (SBS, RS, CS and MDF) in a horizontal tubular quartz reactor, formation characteristics of NO_x precursors were investigated with the help of chemical absorption-spectrophotometry and XPS methods. Effects of fuel's properties (nitrogen functionality and nitrogen content) and gasification conditions (temperature and gasifying agent) were discussed and compared. The results indicate that NH₃-N is the predominant NO_x precursor species mainly produced during devolatilization stage. Each operational factor would alter the yield of each NO_x precursor by affecting their formation pathways. On one hand, thermal stability of nitrogen functionality in fuels (N-A) is a much more important factor than nitrogen content among fuel's properties. Subsequently, due to the primary cracking of unstable N-A (polyamide), total yield of NO_x precursors for MDF reaches up to 74.7% which is higher than that for other straw biomass by 15%. On the other hand, gasification conditions would influence the reaction routes relevant to NO_x precursors during secondary reactions, especially for the hydrogenation reaction. As a consequence, during SBS gasification, when temperature rises from 800 to 1000℃, NH₃-N yield keeps a constant increase from 38.9% to 47.7% while HCN-N increases first and then decreases with a peak value of 18.3%, which may depend on the balance between reaction routes affected by temperature. As for gasifying agent, the presence of CO₂ would partly inhibit HCN-N yield while the introduction of H₂O would moderately promote NH₃-N yield, which is attributed that the hydrogenation reaction would be strongly affected by gasifying agent. Hence, it is concluded that the selectivity and partitioning of NO_x precursors could be changed by employing different ratio of gasifying agents.