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-lowemission 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.

Emission Characteristics of Hazardous Atmospheric Pollutants from Ultra-low Emission Coal-fired Industrial Boilers in China

“…The #5 unit was equipped with SNCR, while the #6 and #9 units were equipped with hybrid SNCR-SCR, which is usually equipped in coal-fired industrial boilers to meet the NOx emission limit. Like the #1-4 units, the combination of low-NO x burner technology (LNB) and SNCR is usually applied in CFB boilers, because of the calcium poisoning of de-NO x catalysts on SCR and the space limit after furnace (Shang et al, 2013;Wang et al, 2017;Zheng et al, 2017). Meanwhile, in order to adapt to the low-temperature flue gas emitted from coalfired industrial boilers, the oxidation denitrification (OD) technology using NaClO 2 or O 3 as the oxidant and sorbent to remove NO x , has been used in recent years (Chien and Chu, 2000), such as the #7 and #8 units in this study.…”

“…The mass balance method is calculated by normalizing the concentration of each trace element for the entire process. It is widely used to investigate the EFs and removal efficiency for trace elements (Zhang et al, 2016;Zheng et al, 2017;Wu et al, 2018). In this study, based on the inlet and outlet concentration of trace elements for APCDs, the EFs and removal efficiency of trace elements were calculated by Eqs.…”

“…(5). Generally, REFs presented the partitioning of trace elements after coal combustion and a high REF means a strong enrichment capacity for the trace element in the ash (Bhattacharyya et al, 2009;Zheng et al, 2017):…”

“…Several studies have conducted on emission level and removal efficiency of hazardous air pollutants from ULE and non-ULE coal-fired power plants (Zhang et al, 2008;Zheng et al, 2017). Wu et al (2018Wu et al ( , 2020 established an integrated emission factors (EFs) database of size-fractioned particulate matter (PM) for typical ULE technical routes installed in coal-fired power plant.…”

An Investigation of SO3 Control Routes in Ultra-low Emission Coal-fired Power Plants

“…Regarding the WESP, the transformation can be considered when there is sufficient space at the tail of the boiler and it also requires the control of PM 2.5 , Hg and other pollutants (Zheng et al, 2017;Yang et al, 2019). Recent studies indicate that the SO 3 removal efficiency of WESP can be effectively improved by reducing gas velocity, increasing corona power and optimizing the electrode when burning high-sulfur coal .…”