关键词: 城市污泥, 慢速热解, 氰化氢, 氨

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