| A naturally occurring sorbent, kaolinite, is injected into a down-flow pilot scale combustor burning natural gas, doped with a surrogate metal containing waste (usually lead acetate). When sorbent is not introduced, lead vaporized in the flame ultimately forms a unimodal particle size distribution centered at approximately 0.1 {dollar}mu{dollar}m., often referred to as fume. The injection of sorbent prevents the formation of this fine particulate, by reactively scavenging the lead as vapor above its dewpoint temperature. The approximately 1 {dollar}mu{dollar}m lead alumina-silicate particles formed capture nearly 100% of the lead, yet yield very low water soluble lead mass fractions. Thus, lead is chemically fixed in particles that are approximately an order of magnitude larger in size than the lead aerosol fume. Consequently, air pollution control systems can capture these particles relatively efficiently, and the metal's isolation from the environment is ensured when subsequently disposed of in a landfill.; Chlorine is a commonly occurring halogen in many incinerable waste streams. With increasing Cl/Pb ratio, the mass fraction of lead captured decreases. At a chlorine gas injection rate resulting in a Cl/Pb ratio of 2/1, 10/1, and 17/1, the obtained mass fraction of lead captured was 79.7%, 44.0%, and 37.8%. The uncaptured lead remained in the gas phase as the relatively volatile PbCl{dollar}sb2,{dollar} which formed a water soluble fume upon temperature quench in the sampling probe. These results indicate that sorbent injection could be less effective at metal capture for incinerable waste streams with both chloride and metal fractions.; A multi-component aerosol simulations package (MAEROS) is utilized to model the temporal evolution of a lead aerosol particle size distribution in the combustor. Base case simulations model the Pb-O{dollar}sb2{dollar} system, and accounts for homogeneous nucleation, physical condensation, and coagulation. These simulations match the data fairly well under conditions which promote self nucleation (i.e. steep temperature profiles). The MAEROS model is also utilized to simulate the Pb-O{dollar}sb2{dollar}-sorbent and Pb-O{dollar}sb2{dollar}-Cl{dollar}sb2{dollar}-sorbent systems in an attempt to elucidate the lead capture mechanisms. Also, the model-fitted intrinsic reaction rates are much greater than the rates obtained from the lead/sorbent bench scale experiments from the literature. |
