Partitioning behavior of Pb in particulate matter emitted from circulating fluidized bed coal-fired power plant

Abstract

Inhalable fine particulate matter (PM), which is rich in Pb and other pollutants from coal-fired power plants, can cause air pollution and severe health problems. To facilitate the development of efficient techniques for controlling fine particulate Pb emissions, in this study, various types of size-resolved fine PM (<10.0 μm) were collected from the outlets of fabric filter units (FFs) at an industrial circulating fluidized bed (CFB) power plant to assess the distribution and partitioning behavior of Pb. The results showed that the mass particle size distribution (PSD) of the collected fine PM followed unimodal distribution, peaking at 5.8–4.7 μm, which might be caused by the fragmentation of limestone additives and new-formed CaSO4. However, the mass PSD of Pb for size-fractionated PM displayed different distribution pattern. Two peaks were observed in the size ranges of 5.8–4.7 μm and 1.1–0.7 μm. The mechanism of Pb enrichment in the supermicron particles was mainly controlled by the surface adsorption reaction, which could be explained by 1/dp dependence and be improved using excess active CaO produced by the injected limestone. For submicron particles, gas-film transfer or heterogenous condensation (mass transfer) might represent the deposition mechanism. Besides Pb enrichment, it was found that the submicron particles (<0.7 μm) mainly consisted of Si-rich and Si–Al phases. The emission of those fine SiO2-bearing particles should be limited as they can be inhaled and can damage the respiratory system.