有机废弃物在水热-热解耦合过程中NOx前驱物的释放机制研究

以城市污泥(SS)、中药药渣(HTW)和硅藻(DT)为对象,在水平管式反应器上对比研究了水热处理前后样品在热解过程中NO_x前驱物的生成特征,并结合热重(TGA)和X射线光电子能谱(XPS)表征分析了该耦合过程对NO_x前驱物的影响机制。结果表明,在240℃下进行水热预处理能直接或间接地影响样品燃料N在不同热解阶段时的转化路径,从而在整体层面上降低NO_x前驱物的释放量,例如当热解温度为900℃时,源于水热焦燃料N的NO_x前驱物为55.0%(SS_(240))、48.1%(HTW_(240))和51.2%(DT_(240)),比未经处理样品的NO_x前驱物释放量分别少9.5%(SS)、6.0%(HTW)和15.4%(DT),但若以原料燃料N为基准,源于水热焦的NO_x前驱物则比未经处理样品的NO_x前驱物释放量分别少90.1%(SS)、41.9%(HTW)和59.8%(DT),并且对NH_3的抑制效果高于HCN。进一步根据热失重曲线及其半焦N官能团的演变规律可以推测,水热预处理对NO_x前驱物的两条影响机制,即含N官能团的脱除(对于初次反应的NH_3释放)与含N官能团的稳定化(对于二次反应的HCN释放),可为废弃物的清洁利用提供理论参考。

Formation mechanism of NOx precursor during organic waste pyrolysis coupled with hydrothermal pretreatment

Taking the high moisture-containing sewage sludge (SS), herbal tea waste (HTW) and diatom (DT) as the feedstock, the characteristics of NO_x precursors during pyrolysis with or without hydrothermal pretreatment in a horizontal tubular reactor were compared. The formation mechanism of NO_x precursors in pyrolysis coupled with hydrothermal pretreatment was also investigated by means of TGA and XPS techniques. The results show that the hydrothermal pretreatment can affect the formation pathways related to NO_x precursors at different pyrolysis stages and reduce the release amount of NO_x precursor on the whole level. For example, when the pyrolysis temperature is 900 ℃, the NO_x precursor yield derived from the hydrothermal treated coke is 55.0% for SS₂₄₀, 48.1% for HTW₂₄₀ and 51.2% for DT₂₄₀, which is 9.5%, 6.0% and 15.4% less than that for SS, HTW and DT untreated sample, respectively. But if calculating based on the amount of N content in feedstock, the released NO_x precursor from the hydrothermal treated coke is 90.1%, 41.9% and 59.8% less than that for SS, HTW and DT untreated sample, respectively. The inhibition effect on NH₃ formation is higher than that on HCN formation. Meanwhile, two influencing pathways caused by hydrothermal pretreatment were further elaborated, i.e., the removal of N functionalities that leads to a decrease in NH₃ on the primary reaction and the stabilization of N functionalities that leads to a decrease in HCN on the secondary reaction.