Condensation Behavior of Heavy Metals during Oxy-fuel Combustion: Deposition, Species Distribution, and Their Particle Characteristics

This study aimed to characterize the condensation behavior of two heavy metals, namely, Pb and Zn, during oxy-fuel combustion and to clarify and compare the differences in their behavior during oxy-fuel versus air-fired combustion. A lab-scale rotary quartz reactor with a multi-stage cooling zone was used to analyze the deposition content and species distribution of the condensed Pb and Zn vapors at different temperature ranges and/or points and to observe their particle characteristics in the simulated oxy-fuel flue gas (OFFG), air-fired flue gas (AFFG), oxy-fuel flue gas without steam (OFFGWS), and air-fired flue gas without steam (AFFGWS). The deposition content of the condensed Pb and Zn vapors in the AFFG was consistently higher than that of OFFG in the cooling zone from 800 to 100 °C. Moreover, the steam content had an obvious influence on the deposition content. The condensed Pb and Zn vapors were mostly deposited in the sulfates in OFFG at 600–300 °C, instead of in the chlorides in AFFG. The average diameter of particles that contain Pb and Zn increased as the temperature decreased, and their shape factor in both AFFG and AFFGWS was higher than that in OFFG and OFFGWS.