Partitioning and Emission Characteristics of Hg, Cr, Pb, and As among Air Pollution Control Devices in Chinese Coal-Fired Industrial Boilers

Toxic trace elements (TEs), such as Hg, Cr, As, and Pb, emitted from coal-fired industrial boilers (CFIBs) have gained considerable attention because of their harmful effects on environmental quality and human health. In this study, based on the field test data, Hg, Cr, Pb, and As emissions from six CFIBs in China were investigated. Solid samples including feed coal, bottom ash, fly ash, and gypsum, desulfurization wastewater samples, and stack flue gas samples were simultaneously collected for determining the internal partitioning behavior of TEs from these CFIBs. Results showed that Hg, Cr, Pb, and As concentrations in feed coal varied considerably, which were in the range of 0.02-0.22 mg/kg (Hg), 4.75-19.85 mg/kg (Cr), 4.85-35.00 mg/kg (Pb), and 0.50-9.35 mg/kg (As). The relative enrichment factors (REFs) of TEs in fly ash were all higher than those of the corresponding bottom ash, showing the stronger enrichment capacity of TEs in fly ash. TE concentrations from stack flue gas were in the range of 0.11-0.60 mu g/Nm(3) (Hg), 3.56-23.87 mu g/Nm(3) (Cr), 0.35-4.20 mu g/Nm(3) (Pb), and 0.63-5.17 mu g/Nm(3) (As). Current air pollution control devices (APCDs) have obviously positive effects on TE removal, with the integrated removal efficiencies of APCDs in the range of 80.97-98.86% (Hg), 85.82-99.45% (Cr), 98.13-99.99% (Pb), and 70.47-99.92% (As). TEs were mainly enriched in fly ash in the range of 55.22-96.67% (Hg), 56.97-85.76% (Cr), 41.68-91.99% (Pb), and 52.20-95.29% (As). These results could provide new insights into TE synergistic control in the CFIBs and assist policy making.