300 MW燃煤电厂ESP和WFGD对烟气汞的脱除特性

采用燃煤电厂汞形态浓度取样测试OHM标准方法,对一座300 MW燃煤电厂静电除尘器(ESP)和湿法脱硫装置(WFGD)前后烟气进行了等速取样.使用美国Leeman Labs Hydra AA全自动汞分析仪检测烟气中的汞形态浓度.采集了固体样品,包括入炉煤、底渣、ESP电场灰、脱硫剂石灰石、脱硫产物石膏等,使用意大利Milestone公司生产的DMA80全自动汞分析仪检测固体样品中的汞浓度.计算锅炉系统的汞质量平衡,获得了ESP和WFGD前后烟气的汞形态浓度和分布规律,分析讨论了影响烟气汞形态转化的各种影响因素.结果表明,燃煤烟气中气态单质汞Hg⁰和气态氧化汞Hg²⁺占到总汞量的95%.煤渣中的汞可忽略不计;ESP对颗粒态汞Hg^p的脱除效率达到95%以上,但是对Hg⁰和Hg²⁺脱除率不高.ESP对烟气总汞Hg^T脱除效率为12.77%~17.38%;WFGD对Hg²⁺的脱除率达到79.93%~90.53%,但是对Hg⁰没有脱除效果,其含量不仅没有下降反而有少量上升,说明有部分Hg²⁺在WFGD中被还原成Hg⁰.WFGD对Hg^T脱除效率为9.68%~29.36%;该电厂现有污染控制设备ESP+WFGD可以脱除全部的Hg^p和大部分Hg²⁺,但是由于部分Hg²⁺的还原使得Hg^T的脱除效率在25.38%~38.38%.综合来看,该燃煤电厂的污染物控制设备在进行除尘和脱硫的同时,对汞的脱除率并不高,与燃煤中的氯含量较低有关.

Mercury removal by ESP and WFGD in a 300 MW coal-fired power plant

The Ontario Hydro Method (OHM) was used to sample and analyze the mercury concentration in flue gas before and after ESP and WFGD in a 300 MW power plant. Mercury content in coal, bottom slag, fly ash of ESP, adsorbent (limestone) and desulfurization product (gypsum) was detected by DMA80. Mercury mass balance was calculated based on the online measurements through the boiler system. Factors affecting the distribution, transformation and removal of mercury in flue gas were discussed. The results show that the gaseous mercury (Hg⁰ and Hg²⁺) in flue gas accounts for about 95% of total mercury, while mercury in the bottom ash can be neglected. More than 95% of Hg^p and a little gaseous phase mercury (Hg⁰ and Hg²⁺)were removed by ESP. The efficiencies to remove total mercury by ESP range from 12.77% to 17.38%. A removal efficiency for Hg²⁺(g) reaches up to 79.93%~90.53% by WFGD, however, the content of Hg⁰ after WFGD increases because part of oxidized mercury is reduced to elemental mercury during WFGD. The efficiencies to remove total mercury by WFGD range from 9.68% to 29.36%. ESP and WFGD can remove all of the Hg^p and a majority of Hg²⁺ with a total mercury removal efficiency of 25.38%~38.38%. In general, the demercuration in the conventional devices of ESP and WFGD is not high, which perhaps is owing to the lower concentration of Cl in feed coal.