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

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.