Transformation mechanism of nitrogen of municipal sewage sludge in the slow pyrolysis process

doi:10.16085/j.issn.1000-6613.2016.01.041

Abstract

Abstract: The TG-MS technique was used to analyze the slow pyrolysis characteristics of municipal sewage sludge and the transformation mechanism of gaseous nitrogen compounds in the pyrolysis process. The dynamic change of functional groups on the surface of solid residual coke in sludge pyrolysis process was detected by an in-situ infrared spectrometer. Results showed that the pyrolysis process of primary sludge has been finished before 500℃ whereas due to the addition of mineral salts there is a relatively large weightlessness peak around 700℃ in the secondary sludge pyrolysis process. The generations of both HCN and NH₃ in secondary sludge pyrolysis process are less than those of primary sludge. It means that release of HCN and NH₃ is restrained on account of the addition of mineral substances. Whereas the added gives rise to the promoting of HNCO above 400℃. Cyclic amide materials, nitrogenous heterocyclic compounds and nitrile materials can be produced from the thermal decomposition of protein and those compounds are eventually converted to HCN, which is the main source of HCN in the pyrolysis process. When the temperature is below 400℃, NH₃ is mainly derived from the decomposition of ammonium salt and the conversion from HCN, while the thermal decomposition of protein contributes slightly to the generation of NH₃. When the temperature is above 400℃, NH₃ has not been detected. It means that the secondary reactions of volatile have minor impact on the formation of NH₃ in this temperature range. In the range of 300-480℃, a large number of oxygen free radicals is produced from thermal decomposition of lignin, this leads to the conversion of HCN into N₂O and the conversion of HNCO into NO.

Key words: municipal sewage sludge, slow pyrolysis, hydrogen cyanide, ammonia

摘要： 利用热重-质谱联用(TG-MS)技术研究城市污泥慢速热解特性及含氮气体产物的生成规律,同时利用原位红外光谱仪实时检测固体表面官能团的变化。研究结果表明:初沉污泥在500℃之前热解已基本完成,二沉污泥由于添加了矿物质盐类,在700℃左右仍有一个较大的失重峰;二沉污泥热解过程HCN和NH₃总生成量均小于初沉污泥,即二沉污泥所加矿物质抑制了HCN和NH₃释放;但温度大于400℃时所加矿物质对HNCO生成具有一定促进作用;污泥中蛋白质热分解会产生环酰胺类物质、含氮杂环化合物和腈类物质,并最终转化为HCN,这是污泥热解过程中HCN的主要来源;400℃以下NH₃主要来自铵盐分解和HCN转化,蛋白质热分解对于NH₃生成贡献很小;400℃以上基本检测不到NH₃生成,即较高温度下挥发分二次反应对NH₃生成几乎没有影响;300~480℃,污泥中木质素裂解产生了大量含氧自由基,促使HCN转化为N₂O,HNCO则最终转化成了NO。

关键词: 城市污泥, 慢速热解, 氰化氢, 氨

CLC Number:

GUO Mingshan, JIN Jing, LIN Yuyu, WANG Yongzhen, HOU Fengxiao. Transformation mechanism of nitrogen of municipal sewage sludge in the slow pyrolysis process[J]. Chemical Industry and Engineering Progree, 2016, 35(01): 302-307.

郭明山, 金晶, 林郁郁, 王永贞, 侯封校. 城市污泥慢速热解过程中氮的转化规律[J]. 化工进展, 2016, 35(01): 302-307.

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