基于实测的超低排放燃煤电厂砷、硒、铅迁移与排放特性

Investigation on migrations and fates of arsenic, selenium and lead in ultra-low emission coal-fired power plants based on field measurement

  • 摘要: 选择煤粉炉(PC)和循环流化床(CFB)超低排放燃煤电厂开展实测研究,同步采集烟气净化装置(APCDs)前后烟气样品进行分析;并同时采集分析入炉煤、飞灰、底渣、省煤器(LTE)灰、脱硫浆液和湿式电除尘器(WESP)废水等样品,以揭示砷(As)、硒(Se)和铅(Pb)迁移与排放特性。结果表明:两家电厂APCDs对烟气中As、Se和Pb的总协同脱除率达到96%,净烟气中污染物浓度低,分别为0.13~0.49、1.05~2.15和0.86~3.19 μg/m3;不同APCDs的协同脱除率存在较大差异,其中布袋除尘器(FF)最高(99.56%~99.74%),静电除尘器(ESP)次之(85.61%~98.44%),湿法烟气脱硫(WFGD)的脱除率波动较大,WESP脱除率为11.61%~55.08%。燃煤中As、Se和Pb大部分迁移到飞灰中,占比为74.38%~95.24%;CFB底渣占比为3.51%~24.08%;LTE灰占比为5.85%~12.11%;脱硫浆液中均低于6%;WESP废水和出口烟气中占比最低,分别为0.68%和0.62%。相对于煤粉炉,循环流化床电厂底渣中As和Pb富集性更高;而对于Se,则燃烧方式无明显影响,但其在净烟气中占比高于As和Pb。

     

    Abstract: Extensive field tests were performed in ultra-low emission coal-fired power plants (ULE CFPPs), respectively installed with pulverized coal (PC) and circulating fluidized bed (CFB) boilers to investigate the migrations and fates of heavy metals such as arsenic (As), selenium (Se), and lead (Pb). Flue gas was simultaneously sampled at the inlet and outlet of each air pollution control devices (APCDs) and subsequently analyzed. Meanwhile, the samples of feed coal, fly ash, bottom ash, low-temperature economizer (LTE) ash, wet flue gas desulfurization (WFGD) slurry, and wet electrostatic precipitator (WESP) wastewater were collected for analyses. The results showed that the total synergistic removal efficiencies for As, Se, and Pb by APCDs in the two selected ULE CFPPs were all higher than 96%. The concentrations of pollutants in the clean flue gas were low, with As, Se, and Pb being 0.13-0.49, 1.05-2.15 and 0.86-3.19 μg/m3, respectively. Significant discrepancies were found in APCDs performance for heavy metal removal. The removal efficiency of fabric filter (FF) for As, Se, and Pb was the highest (99.56%-99.74%), followed by electrostatic precipitator (ESP) (85.61%-98.44%), while WFGD had a large fluctuation in the removal efficiency. WESP efficiency varied in the range of 11.61%-55.08%. The majority of As, Se, and Pb (74.38%-95.24%) were found in fly ash for the tested power plants. 3.51%-24.08% of these heavy metals remained in the bottom ash for CFB boiler. For PC boiler, 5.85%-12.11% of the metals were in LTE ash. They were below 6% in WFGD slurry. Around 0.68% and 0.62% of the metals were found in WESP drainage and outlet flue gas. More As and Pb were enriched in the bottom ash for CFB boiler in comparison with PC boiler. In terms of Se, no obvious effect of combustion modes was observed since it had relatively higher volatility. Its proportion in the clean flue gas was much higher than As and Pb for the two tested power plants.

     

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