燃煤电厂颗粒物中硫酸根与硝酸根离子的转化规律

Conversion Characterizations of Sulfate Ion and Nitrate Ion in Particulate Matter from Coal-fired Power Plants

燃煤电厂排放的颗粒物可以分为可凝结颗粒物(condensable particle matter,CPM)和可过滤颗粒物(filterable particle matter,FPM).通过分析7个超低排燃煤电厂的湿法脱硫(wet flue gas desulfurization,WFGD)进出口和湿电除尘(wet electrostatic precipitator,WESP)出口烟气中CPM和FPM的SO_(4)^(2-)和NO_(3)^(-)浓度,揭示了这2种典型水溶性离子在烟道内的变化规律与转化特征.结果表明在WFGD前后,CPM中的SO_(4)^(2-)和NO_(3)^(-)浓度呈降低趋势,其降低率范围分别为43.12%~86.84%和17.99%~91.58%,而FPM中SO_(4)^(2-)和NO_(3)^(-)浓度呈增大趋势.在WESP前后,CPM中SO_(4)^(2-)和NO_(3)^(-)浓度呈增大趋势,增长率范围分别为21.05%~424.65%和13.51%~298.37%,而FPM中SO_(4)^(2-)和NO_(3)^(-)浓度呈减小趋势.在WFGD中,随着烟气温度降低和湿度增加,部分CPM会通过冷凝和团聚作用进一步转化为FPM;在WESP中,由于烟气一直处于低温、高湿的条件,烟气中存在的SO_(2)与NO_(2)会结合水蒸气发生氧化还原反应,进而经过协同作用促进CPM中SO_(4)^(2-)和NO_(3)^(-)的生成.

The particulate matter emitted from coal-fired power plants includes condensable particulate matter(CPM)and filterable particulate matter(FPM).By analyzing the concentration of SO_(4)^(2-)and NO_(3)^(-)components of CPM and FPM in the inlet/outlet of wet flue gas desulfurization(WFGD)and the outlet of wet electrostatic precipitator(WESP)from 7 ultra-low emission coal-fired power plants,the variation laws and transformation characteristics were investigated.The results showed that the concentration of SO_(4)^(2-)and NO_(3)^(-)of CPM decreased after WFGD,with reduction rates of 43.12%-86.84%and 17.99%-91.58%,respectively,which were different from the conversion trend of FPM.The concentrations of SO_(4)^(2-)and NO_(3)^(-)of CPM increased after WESP,with reduction rates of 21.05%-424.65%and 13.51%-298.37%,respectively,which were also different from that of FPM.In the WFGD system,CPM could be transformed into FPM due via condensation and aggregation under the decreasing temperature and increasing of humidity of the flue gas.In the WESP system,SO_(2)and NO_(2)in the flue gas combine with water vapor in a redox reaction,which promotes the generation of SO_(4)^(2-)and NO_(3)^(-)in CPM through synergistic action.