Shuai Guo,Tiecheng Liu,Jicheng Hui,Deyong Che,Xingcan Li,Baizhong Sun,Shaohua Li
The addition of CaO has been used to reduce the harmful NO x precursors (NH 3 and HCN) generated by the pyrolysis of municipal sewage sludge . However, the underlying reduction mechanism remains unclear. To address this issue, we systematically investigated the effects of temperature and CaO addition on the generation of NH 3 and HCN during the pyrolysis of sludge protein and a model protein. With increasing temperature from 300 to 900 °C, the inhibitory effect of CaO on NH 3 emission was observed to fluctuate, maximizing at 400 °C. The inhibition was attributed to the reaction of CaO with nitrogen in the produced char to form CaC x N y , resulting in enhanced fixation of the char pyridines and nitriles. The nitriles exhibited high thermal stability and inertness to CaO. The increased nitrile content at high temperatures was attributed to the formation of the species from amines and N-containing heterocycles . The CaC x produced by the thermal decomposition of CaC x N y above 700 °C was found to increase P–N fixation and decrease NH 3 formation. The observed poor inhibitory effect of CaO on NO x precursor formation at 650 °C was attributed to the production of NH 3 via HCN hydrolysis. Because HCN directly reacted with CaO, the inhibition of HCN formation was highest at 650–900 °C, preventing the conversion of char nitriles into HCN.
Shuai Guo,Lidong Liu,Xin Guo,Tiecheng Liu,Xingcan Li,Guangyu Li
Municipal sewage sludge poses environmental and health risks, and thus, requires proper disposal using pyrolytic techniques. However, these techniques are hindered by the production of NH 3 and HCN (NO x precursors) by the sludge. Hence, a comprehensive understanding of NH 3 and HCN formation during sludge pyrolysis is required to minimize its NO x footprint. As sludge N mainly occurs in proteins forms, its transformations can be modeled using amino acids. Here, we aimed to the study the mechanism by which carbohydrates influence the formation of NO x precursors during sludge protein pyrolysis at different temperatures using glutamic acid , tyrosine, and histidine as protein models and cellulose and lignin as carbohydrate models. During pyrolysis, the release of NH 3 and HCN was promoted by high temperatures and inhibited by carbohydrates. Despite this inhibitory effect, the results suggested that the release of NH 3 should be considered for samples rich in aliphatic amino acids. For glutamic acid and tyrosine, NO x precursor formation was inhibited by N fixation in coke under the action of volatiles produced during carbohydrate pyrolysis. For glutamic acid, adding cellulose and lignin increased the coke-N content by 25.32% and 44.73% at 700 ℃. For histidine, this effect was ascribed to the ring-opening reactions induced by the free radical products of carbohydrate decomposition and the enhanced transfer of N-containing compounds to tar after ring-opening recombination. Further, heterocyclic-N within tar increased to 69.12% due to lignin-histidine interactions at 700 ℃. The results of this study can assist in regulating sludge protein pyrolysis intended for minimizing the production of NO x precursors.
危险品化学品经营许可证（带存储）