71. Partitioning Behavior of Arsenic in an Ultra-Supercritical Coal-Fired Power Plant Equipped with APCDs for Ultra-Low Emission

To study the partitioning behavior of arsenic (As) in an ultra-supercritical coal-fired power plant equipped with air pollution control devices (APCDs) for ultra-low emission, the US EPA Method 29 was used to simultaneously sample flue gas before and after selective catalytic reduction (SCR), electrostatic precipitator (ESP), and wet flue gas desulfurization (WFGD). The solid and liquid samples including feed coal, bottom ash, ESP ash, limestone slurry, flush water, WFGD gypsum and wastewater were simultaneously collected in step with flue gas sampling. The mass distribution of As was obtained based on mass balance calculation. Results indicate that the mass balance rate of As is in the range of 78.40–117.68\(\%\), which is acceptable. At the outlet of air-preheater, particulate-bound As is the dominant species in the flue gas, which accounts for over 98\(\%\). Most of As were migrated to ESP ash and bottom ash, accounting for 95.19% and 4.28\(\%\), respectively. Both As⁵⁺ and As³⁺ existed in the feed coal and bottom ash, while As⁵⁺ was found to be the major form in the ESP ash, WFGD gypsum and wastewater. The removal efficiency of As by ESP and WFGD is 99.3–99.4\(\%\), while that by ESP is 99.87–99.90\(\%\) and that by WFGD is 26.32–46.77\(\%\). The new APCD (mercury absorption device) can oxidize As³⁺ to As⁵⁺ in the flue gas, but somewhat increase the emission concentration of As. As tends to enrich in ESP ash (relative enrichment index \(=\) 1.28) but dilute in bottom ash (relative enrichment index \(=\) 0.23).