市政污泥CO2气化中氮素的反应路径及NOx前驱体削减机制研究

Due to rapid urbanization, significant increase in the generation of sewage sludge (SS) from wastewater treatment plants has resulted in a substantial shortfall in the capability of SS treatment and disposal. Gasification could achieve clean energy conversion and remarkable volume reduction through an environmentally friendly re-utilization technique, however, energy-intensive sludge dewatering and excessive emissions of NOx precursors resulting from high moisture and nitrogen contents in SS have posed great barriers to the application for gasification of SS. Hence, in this study, hydrothermal treatment with calcium oxide conditioner (HT/CaO) will be applied to achieve simultaneous energy-efficient sludge dewatering and source reduction of nitrogen in SS. Subsequently, CO2 gasification of the SS derived hydrochar will be conducted to control nitrogen transformation and further reduce emissions of NOx precursors, thereby producing syngas fuel with high quality. The objectives of this study are to (i) elucidate effect of different HT/CaO parameters on reactivity, reaction kinetics, and releasing profile of nitrogen species during CO2 gasification; (ii) identify effects of different HT/CaO parameters and CO2 gasification conditions on the gasification performance, nitrogen transformation pathways, and formation mechanism of NOx precursors; and (iii) propose theoretical foundation and key strategy to manipulate the reduction of NOx precursors by optimizing the HT/CaO parameters and CO2 gasification condition, and constructing corresponding reaction kinetics model. Therefore, this research would provide theoretical and technical guidance for reduction of energy consumption and pollutants emissions during thermochemical conversion of combustible solid wastes with high moisture and nitrogen content for energy recovery, which plays a vital role in mitigating the imperative demand for disposal and resource utilization of municipal solid wastes.

快速城镇化使市政污泥产量剧增，造成巨大的处置能力缺口。气化作为清洁的能源化技术能极大程度实现污泥无害化和减量化，而高含水率、高含氮市政污泥深度脱水的高耗能及NOx前驱体的超标排放制约了污泥气化技术的发展。本项目采用水热/CaO调理实现低能耗深度脱水和源头减氮，通过研究污泥调理形成的水热炭在CO2气化过程中的反应活性及反应动力学，明晰气化反应时含氮气体的释放特征；阐明不同调理参数及气化条件对气化效果、氮素的反应路径、NOx前驱体形成的作用机理；明确NOx前驱体削减的调控机制，构建最优CO2气化过程的反应动力学模型。该项目的研究成果有助于揭示污泥CO2气化中NOx前驱体削减调控的反应理论，为高含水率、高含氮的市政污泥能源化过程中的污染物减排提供技术支撑，对城镇可燃固体废弃物处置与资源化具有重要意义。

快速城镇化使市政污泥产量剧增，造成巨大的处置能力缺口。气化作为清洁的能源化技术能极大程度实现污泥无害化和减量化，而高含水率、高含氮市政污泥深度脱水的高耗能及NOx前驱体的超标排放制约了污泥气化技术的发展。本项目采用水热/CaO调理实现低能耗深度脱水和源头减氮，通过研究污泥调理形成的水热炭在CO2气化过程中的反应活性及反应动力学，明确了气化反应时含氮气体的释放特征；阐明不同调理参数及气化条件对气化效果、氮素的反应路径、NOx前驱体形成的作用机理；明确了NOx前驱体削减的调控机制，构建最优CO2气化过程的反应动力学模型。当将污泥转化成水热炭（HC）并将其作为气化原料时，焦油的产量从10.9%减少到6.8%，并将合成气的热值从14.1 MJ/Nm3提高到了15.7MJ/Nm3；水热处理增加了HC中非活性的季氮的含量。并且添加CaO可以促进氮的去除，在较低的水热温度下增加HC中吡咯氮和季氮的含量，这对降低NOx前驱体的产率有很大的影响。此外，由于CO2对焦油分解和Boudouard反应的催化作用，气化过程中引入CO2可以显着降低焦油产量，并提高碳转化率和合成气产量。纯CO2气氛可以最大限度地提高气体产量，但并不利于NOx前驱体的削减，相反，20% CO2浓度可以显着降低NOx前驱体的总量，尤其是NH3，这与在CO2存在下NH3到N2的转化增强有关，尽管如此，它也产生少量的HCN，这与CO2促进焦油中含氮物质的热裂解有关。该项目的研究成果有助于揭示污泥CO2气化中NOx前驱体削减调控的反应理论，为高含水率、高含氮的市政污泥能源化过程中的污染物减排提供技术支撑，对城镇可燃固体废弃物处置与资源化具有重要意义。