Partitioning of Hazardous Trace Elements among Air Pollution Control Devices in Ultra-Low-Emission Coal-Fired Power Plants

Abstract

In this work, the partitioning of hazardous trace elements among air pollution control devices in five ultra-low-emission coal-fired power plants was investigated. Results showed that most of the trace elements were enriched in fly ash at 58.0–93.3% (Hg), 75.2–95.3% (As), 78.2–94.9% (Cd), 79.4–96.6% (Se), 73.8–89.2% (Cr), and 86.5–99.5% (Pb). A low-low temperature electrostatic precipitator (LLT-ESP) and electric fabric filter (EFF) greatly increased the relative enrichment factors of Hg, As, and Se in fly ash up to 0.78–1.23, 0.85–1.04, and 0.83–0.99, respectively. In the wet flue gas desulfurization (WFGD) system, the concentrations of trace elements in fine fractions were much higher than those in coarse fractions. Large amounts of Hg (2.17–168 μg/kg), Se (21.3–357 μg/kg), and Cd (44.1–839 μg/kg) in wastewater needed special treatment to satisfy the discharge standard. The wet electrostatic precipitator (WESP) system removed hazardous trace elements mainly by capturing fine particles in the flue gas, and a small amount of hazardous trace elements (0.2–26%) were retained in the washing water. The concentrations of Hg in the fine particulates captured by WESP were 16.8–60.1 times of those in the fly ash, which could reach up to 17.5 mg/kg. The application of selective catalytic reduction + LLT-ESP/EFF + WFGD + WESP could effectively control the emission of hazardous trace elements in coal-fired power plants.