660MW燃煤机组汞迁移转化特性研究

Research on migration and transformation characteristics of mercury in 660MW coal-fired unit

燃煤电厂是我国汞排放的主要源头。为表征燃煤电厂中汞的脱除性能,以某660 MW燃煤机组为例,系统研究了500 MW和600 MW工况下,汞在选择性催化还原脱硝装置(SCR)、静电除尘器(ESP)、湿法脱硫(FGD)以及湿式除尘器(WESP)等设施中的迁移特性。结果表明,各测试位置的汞质量平衡率分别为72.01%~90.05%、79.14%~96.36%,验证了测试准确性;烟气汞是主要的排放形式,其次为排灰、石膏,脱硫废水和炉渣排放占比很小;脱硝催化剂促进单质汞向氧化汞和颗粒汞的转化率超过40%,但对总汞减排不明显;ESP可以去除全部颗粒态汞,但因对单质汞和氧化汞的脱除率较低,总汞脱除率最高仅为33.73%;600 MW工况下因浆液中HSO_(3)^(-)还原氧化汞作用更强,导致单质汞浓度增加更明显,FGD和WESP对氧化汞的累计脱除率达91%以上。沿程环保设施对总汞的脱除效率高于59%,SCR下游设施对单质汞和氧化汞的协同脱除率最低分别为6.16%、94.12%,表明SCR对单质汞的氧化是降低汞排放的关键。机组排放的烟气总汞质量浓度最高为3.66μg/m^(3),小于国家排放标准。

Coal-fired power plants is the main source for mercury emission.In order to characterize the removal characteristics of mercury,a 660 MW coal-fired unit was taken as an example.The migration and transformation characteristics of mercury in selective catalytic reduction equipment(SCR),electrostatic precipitator(ESP),flue gas desulfurization(FGD)and wet electrostatic precipitator(WESP)was systematically studied under 500 MW and 600 MW.The results show that the mercury mass balance rate in test locations are 72.01%-90.05%and 79.14%-96.36%respectively,which verify the accuracy of test results.Flue gas mercury is the main discharge form,followed by ash and gypsum.The proportions of mercury emission from FGD waste water and slag account for a small proportion.The conversion rate elemental mercury to oxidized mercury and particulate mercury by SCR catalysts is beyond 40%,but the total mercury reduction is insignificant,and higher ammonia consumption can reduce the conversion rate.ESP can remove all particulate mercury,but the total mercury removal efficiency is less than 33.73%because of lower removal of elemental and oxidized mercury.Because reduction effect of HSO_(3)^(-) is stronger for oxidized mercury to element,the elemental mercury concentration increases more obviously under 600 MW condition.And the cumulative removal efficiency of oxidized mercury by FGD and WESP reaches over 91%.Total mercury reduction by all the environmental protection facilities is more than 59%.However,collaborative lowest removal efficiency of elemental and oxidized mercury are 6.16%and 94.12%by downstream facilities of SCR,which indicate that mercury oxidation by SCR is the key to reducing mercury emission.Finally,the total mercury concentration in exhaust gas is less than 3.66μg/m^(3),which is below the national emission standard.