Combustion conditions and feed coals regulating the Fe- and Ti-containing nanoparticles in various coal fly ash

Quantitative characteristics and sizes of nanoparticles (NPs) in coal fly ash (CFA) produced in coal-fired power plants as a function of coal type and plant design will help reveal the NP emission likelihood and their environmental implications. However, little is known about how combustion conditions and types of coal regulate the NP abundance in CFAs. In this study, based on single particle (SP)-ICP-MS technology, particle number concentrations (PNCs) and sizes of Fe- and Ti-containing NPs in CFAs were determined for samples collected from power plants of different designs and burning different types of coal. The PNCs of Fe- and Ti-containing NPs in all CFAs measured were in the range of 1.3 × 10⁷ - 3.4 × 10⁸ and 6.8 × 10⁶ - 2.2 × 10⁸ particles/mg, with the average particle sizes of 111 nm and 87 nm, respectively. The highest Fe-NP PNCs likely relate to the highest contents of Fe and pyrite in the feed coal. In addition, high TOC in CFAs are associated with metal-containing NPs, resulting in elevated abundances of these NPs with relatively large sizes. Moreover, elevated PNCs of NPs were found in CFAs produced by coal-fired power plants burning low-rank coals and with small installed capacity (especially those under 100-MW units). Compared to cyclone filters, ESPs and FFs with higher removal efficiency typically retain more Fe-/Ti- containing NPs with smaller sizes. Based on a structural equation (SE) model, raw coal properties (coal rank and Fe/Ti content), boiler types, and efficiency of particulate emission control devices likely indirectly affect PNCs of Fe- and Ti-containing NPs by influencing TOC contents and their corresponding metal concentrations of CFAs. This study provides the first analytic and comprehensive information concerning the direct and indirect regulating factors on NPs in various CFAs.