富N生物质原料气化过程NOx前驱物生成特性及规律

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

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,NH_3-N为主要NO_x前驱物并伴随一定量的HCNN,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℃,NH_3-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,CO_2主要影响HCN-N,起一定抑制作用,H_2O主要影响NH_3-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。

Based on gasification of 4N-rich biomass（SBS,RS,CS and MDF） in a horizontal tubular quartz reactor,formation characteristics of NOx precursors were investigated with the help of chemical absorptionspectrophotometry 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 NOx precursor species mainly produced during devolatilization stage.Each operational factor would alter the yield of each NOx 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 NOx precursors for MDF reaches up to 74.7% which is higher than that for other strawbiomass by15%.On the other hand,gasification conditions would influence the reaction routes relevant to NOx 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 CO-2 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 NOx precursors could be changed by employing different ratio of gasifying agents.