不同超低排放技术路线的燃煤电站汞脱除研究

Removing Mercury from Flue Gas of Coal-fired Power Plants by Different Ultra-low Emission Technical Routes

文章对使用不同超低排放技术路线的燃煤电站烟气污染物处理设施进出口进行汞形态和浓度的研究分析,研究发现:SCR脱硝过程前后,总汞(Hg^(T))以及颗粒态汞(Hg^(p))质量浓度变化不大,但可有效促进单质游离态汞(Hg^(0))向Hg^(2+)的转化,SCR过程可将烟气中Hg^(2+)的占比从4.3%~23.9%上升至15.5%~71.4%;除尘过程中,袋式除尘器通过对汞的捕集、氧化等作用促进汞的脱除,其效率可达97.1%以上;在低低温电除尘过程中,降低烟气温度,有利于烟气中的Hg^(0)向Hg^(2+)或Hg^(p)的转变,故而低低温电除尘器对总汞的脱除率可达95.9%;而静电除尘装置对汞的脱除效果有限,仅对Hg^(p)有较好的脱除效率;湿法脱硫对汞的脱除效率与脱硫系统入口汞形态分布有关;湿式电除尘器在汞入口浓度较低时,脱汞效果不明显。经超低排放改造后的燃煤电站烟气出口的汞排放浓度在0.076~0.26μg/m^(3),远低于当前我国燃煤电站的汞排放标准。

In situ experiments were carried out at three coal-fired power plants for investigating mercury in flue gas in terms of its speciation and concentration,which involved the testing performed to measure mercury before and after the flue-gas treatment facilities where different ultra-low emission technology routes were adopted.The experimental results showed that SCR(selective catalytic reduction)de-nitrification process scarcely affect the mass concentration of HgTand Hgp,but it can effectively promote the conversion of Hg^(0) to Hg^(2+);the proportion of Hg^(2+)in flue gas was increased from 4.3%~23.9%to 15.5%~71.4%by SCR process.The mercury removal efficiency of coal-fired power plant B installed FF is over 97.1%by collecting and oxidizing mercury.Reducing flue gas temperature was conducive to the transformation of Hg^(0) to Hg^(2+)or Hgpin flue gas promoting the removal of total mercury in the low-temperature electrostatic precipitation process,so the mercury removal efficiency could be as high as 95.9%.However,mercury removal by ESP(electro-static precipitator)was rather limited,while ESP was effective in capture of Hgp.On the other hand,mercury removal efficiency of WFGD(wet flue gas desulfurization)was related to the distribution of mercury species at the inlet of the desulfurization system,and as to the WESP(wet electro-static precipitator),when mercury concentration was low at its entrance,the effects of mercury removal was inappreciable.To sum up,mercury emission concentrations of the flue gas in coal-fired power plants after the ultra-low emission retrofit could decline to the range from 0.076 to 0.26μg/m3,far below the mercury emission concentration which is stipulated in the related national standard for coal-fired power plants.