Mechanistic study of sorbent injection for vanadium emission control in combustion systems

Mechanistic study of sorbent injection for vanadium emission control in combustion systems was conducted experimentally and theoretically. Potential sorbent material for chemisorption was determined by thermodynamic equilibrium analysis. The computer code, STANJAN, was used to implement the calculations. Ca-, Na- and Mg-based sorbents were evaluated for a wide range of combustion temperatures. The strong affinity between vanadium and these sorbents was identified which implies the great potential of these sorbents to chemically adsorb vanadium. Sulfur was found to strongly impair the performance of these sorbents at lower temperatures (<1000K) due to the formation of sorbent sulfates that depleted the available sorbents in the system.; Bimodal lognormal model was applied to investigate the impact of inter-coagulation rate on the size distributions of fine-mode aerosols. Fine mode particle removal time was found to strongly depend on the number concentration of coarse mode particles but independent on the number concentration of fine mode particles. A 60% increase of geometric standard deviation of fine mode particles significantly increased the dimensionless removal time. Fine mode particles ultimately approached monodisperse when the dominant mechanism was inter-coagulation. Meanwhile, coarse mode particles approached the asymptotic shape because intra-coagulation was the dominant mechanism. On a constant mass, monodisperse and 1 mum mean diameter are the optimal condition for coarse particles to effectively remove fine particles through inter-coagulation.; Aerosol reactor was applied for a mechanistic study of sorbent injection. Condensation was found to be the preferred mechanism for sorbent injection based on experimental results. CaCO3 sorbent which has strong chemical affinity with vanadium and silica sorbent which has no chemical affinity but high surface area successfully reduced vanadium submicron particle formation. Vanadium was highly concentrated where surface area was high. Surface hydrolysis enhanced physical adsorption while gas phase hydrolysis reduced the efficiency of sorbent technique by forming nano particles.; Bimodal lognormal modeling based on the experimental condition showed that condensation was a very effective means to scavenge vanadium oxide vapor. A high number concentration of fine particles by instant nucleation reduced inter-coagulation rate and quickly scavenged vanadium oxide vapor. Therefore, enhancing condensation while suppressing nucleation was shown to be critical to successful removal of vanadium compound.