燃煤发电机组超低排放改造前后汞排放规律对比研究

Comparative Study on the Characteristics of Mercury Emission from Coal-Fired Plants before and after Ultra-Low Emission Retrofitting

采用安大略法(Ontario hydro method,OHM)对2台超低排放改造机组排放的烟气汞进行了采样检测,并将测试数据与改造前的测试数据进行了对比分析。试验结果表明:2台机组排口总汞浓度分别为2.31、4.22μg/m^3,远低于国内现行标准。汞排放因子由改造前的1.76和3.13 g/TJ下降为0.83和2.17 g/TJ,降幅分别为52.84%和30.67%。改造后SCR+DESP+WFGD+WESP组合环保设施的总汞脱除效率分别为87.91%、82.27%,相较于改造前SCR+DESP+WFGD的组合效率69.57%、65.61%,效率绝对值分别提升了18.34、16.66个百分点。研究表明:改造提高了SCR对单质汞的氧化率,强化了WFGD对氧化汞和颗粒汞的捕集能力,新增设的WESP表现出对氧化汞和单质汞的协同脱除能力。另外,提高SCR流场均匀性、加强催化剂维护、抑制WFGD中氧化汞的再还原等能有效保障现有环保设施协同脱汞能力。

In this paper,with the aid of Ontario Hydro Method(OHM),the mercury emissions from the two units with ultra-low emission retrofit are sampled and tested,then the testing data are compared and analyzed with those before the retrofitting.The testing results show that the mercury emission concentrations from the two units are 2.31 and 4.22μg/m3 respectively,far below the limit value in the current domestic national standard.The mercury emission factors are reduced from 1.76 and 3.13 g/TJ to 0.83 and 2.17 g/TJ correspondingly,52.84% and 30.67% of decrease.And the total mercury removal efficiencies of the retrofitted air pollution control devices with the combination of SCR+DESP+WFGD+WESP are 87.91% and 82.27%,respectively,18.34% and 16.66% of increase compared with the efficiency of 69.57% and 65.61% of the combination of SCR+DESP+WFGD before the retrofit.These data indicate that the ultra-low emission retrofit has improved the oxidation rate of SCR to elemental mercury,and enhanced the capability of WFGD to capture mercury oxide and particulate mercury.Besides,the newly added WESP also displays a synergistic removal capability of both mercury oxide and elemental mercury.Furthermore,by improving the uniformity of SCR flow field,strengthening the maintenance of catalyst and inhibiting the reduction of mercury oxide in WFGD,the synergistic mercury removal capacity can be effectively guaranteed for the present air pollution control devices.