A mechanistic study of vanadium-sorbent surface interaction at high temperature

A mechanistic study of vanadium-sorbent interaction at high temperature was conducted to investigate the underlying mechanisms of sorbent injection for controlling vanadium emissions from combustion systems. Both calcium- and silica-based sorbents successfully reduced the formation of vanadium submicron particles. The capture of vanadium was found to correlate well with sorbent surface area, demonstrating that the dominant mechanism was condensation. Bimodal lognormal modeling based on the experimental conditions verified that condensation on injected sorbents was a very effective means of scavenging vanadium vapor. However, if vanadium vapor quickly nucleated (e.g., through gas phase hydrolysis in the studied system) to form a large number of ultrafine particles, their much larger specific surface area overshadowed that of the sorbent particles and scavenged the rest of the vanadium vapor. Using the residence times employed in this study, intra-coagulation of and condensation onto these ultrafine vanadium particles was not an effective means of growing the particles to the supermicrometer range. Such a scenario decreased the effectiveness of the sorbent technique. Consequently, enhancing direct vanadium condensation onto sorbent particles and suppressing vanadium nucleation is critical to successful reduction of vanadium emissions from combustion sources.