Vast emission of Fe- and Ti-containing nanoparticles from representative coal-fired power plants in China and environmental implications

Abstract

Coal combustion is considered an important source of atmospheric nanoparticles (NPs). However, the underlying information on the emission of NPs from coal-fired power plants (CFPPs) is still lacking. Along these lines, in this study, coal fly ashes (CFAs) were collected from different multi-stage particulate emission control devices (PECDs) in three representative CFPPs in China. The particle size and particle number concentration (PNC) of typical metal-containing NPs (Fe- and Ti-containing NPs) were analyzed by using the single-particle inductively coupled plasma mass (SP-ICP-MS) technology. By increasing the stage of PECDs, the mean particle sizes of NPs gradually declined and the PNCs of Fe- and Ti-containing NPs increased significantly. Specifically, the PNC of final-stage CFA was 3 - 8 times that of the first-stage CFA. A comparison of the electrostatic precipitators (ESPs), fabric filters (FFs), and electrostatic-fabric-integrated precipitators (EFIPs) showed that the state-of-the-art EFIPs exhibited a relatively good NP-removal efficiency with the highest PNCs. In addition, NP hourly emissions in all coal combustion by-products (CCPs) were further calculated in a typical CFPP. The total emissions of Fe- and Ti-containing NPs in all CCPs were 1.87 × 1018 and 1.57 × 1018 particles/h, respectively. NPs were mainly enriched in CFA trapped by PECDs (80% of total emissions). Although the mass of the CFA that escaped through the stack was extremely low, it contained the highest PNCs of Fe- and Ti-containing NPs of all CCPs, accounting for 3.41% and 1.67% of the corresponding total NP emissions. These NPs may also coexist with various toxic metals, such as Zn and Pb, and be released directly into the atmosphere, where they pose a potential risk to human health.