污泥燃烧过程氮迁移转化机理

Mechanistic study of nitrogen migration and transformation during sludge combustion process

焚烧是目前最有前景的污泥处理方法,但焚烧过程中会产生大量NO_(x)、SO_(x)等污染气体,增加了烟气脱硫脱硝负荷。关于煤、生物质等燃料燃烧过程氮氧化物排放机理的研究较多,但污泥氮元素的燃烧反应和污染排放研究较少。选取污泥中4种常见氨基酸模型化合物(甘氨酸、谷氨酸、苯丙氨酸和色氨酸),通过密度泛函理论DFT/B3LYP方法,采用6-31G基组进行化学计算。分析比较氨基酸的不同键长和Mulliken布居数,确定相对易断裂的键作为热解的引发键,反应路径的每一步都选择较弱的化学键断裂,逐步优化计算,直到分离出所有NO。对于甘氨酸,设计了3条氮迁移反应路径,对于谷氨酸,设计了5条氮迁移反应路径,对于苯丙氨酸,设计了2条氮迁移反应路径,对于色氨酸,则存在7条氮迁移路径。每条路径的生成物均为NO,比较计算得到的热力学参数,选择从外界吸热最少的路径为氨基酸最佳的反应路径。其中甘氨酸的最佳氮迁移路径需从外界吸收339.21 kJ/mol的热量,谷氨酸从外界吸收的热量为304.92 kJ/mol,苯丙氨酸从外界吸收324.27 kJ/mol的热量,色氨酸氮迁移的最佳反应路径无需从外界吸热。4种氨基酸的反应路径构建出污泥燃烧时含氮组分迁移和转化的多通道反应网络,明确污泥中典型含氮化合物的迁移和转化反应机理,为污泥资源化、无害化利用提供必要的基础数据和理论依据。

Incineration is the most promising method of sludge treatment at present.However,a large amount of NO_x,SO_(x) and other polluting gases are generated during the burning process,which increases the load on the flue gas desulphurization and denitrification.There are many studies on the mechanism of nitrogen oxide emissions during the combustion of fuels such as coal and biomass,but studies on the combustion reactions and pollution emissions of elemental nitrogen from sludge are rarely carried out.Four common amino acid model compounds(glycine,glutamic acid,phenylalanine and tryptophan) in sludge were selected and chemical calculations were conducted by the density functional theory DFT/B3LYP method with 6-31G basis groups.The different bond lengths and Mulliken Boujou numbers of the amino acids were analyzed and compared,using relatively easy to break bonds as initiating bonds for pyrolysis.Weaker chemical bonds were selected for breaking at each step of the reaction pathway,gradually optimizing the calculations until all the nitric oxide(NO) was isolated.Three nitrogen migration reaction paths were designed for glycine,and five nitrogen migration reaction paths were selected for glutamic acid,two nitrogen migration reaction paths were selected for phenylalanine,and with total of seven reaction paths were considered for tryptophan.The products of each path contain NO,and the path with the least thermal absorption from the outside world is chosen as the best reaction path for amino acids by comparing the calculated thermodynamic parameters.The best nitrogen migration path for glycine requires 339.21 kJ/mol of heat absorption from outside,304.92 kJ/mol of heat absorption from outside for glutamic acid,324.27 kJ/mol of heat absorption from outside for phenylalanine,and the best reaction path for tryptophan nitrogen migration does not require heat absorption from outside.A multi-channel reaction network for the migration and transformation of nitrogen-containing components during sludge combustion is constructed based on the reaction pathways of four amino acids,and the migration and transformation reaction mechanism of typical nitrogen-containing compounds in sludge are clarified,providing necessary basic data and theoretical basis for sludge recycling and harmless utilization.