Study on the Effects of Iron and Arsenic on Particle Formation in a Diffusion Flame

摘要

Iron pentacarbonyl and cacodylic acid(C_2H_7AsO_2) were added to a co-centric diffusion burner flame burning in a co-flowing stream of air. The basic fuel was a mixture of acetylene and ethylene. Liquid iron pentacarbonyl was vaporized by passing ethylene through it and was loaded into the flame. Cacodylic acid(C_2H_7AsO_2) was dissolved in a waterbed and was novelized by using a Venturi nozzle and Ar gas. The novelized arsenic compound was introduced into the diffusion dryer to get rid of water and it was introduced into the flame. Samples of aerosols and gaseous species were collected within the flames and also above the flames with filters and sampling bottle, and soot volume fraction through the flame was calculated with laser light extinction measurements. Aerosol was collected isokinetically also in the Inhalation chamber to measure particle concentration and size distribution. Laser extinction measurement showed that iron(Fe) gave an effect on soot formation process due to nucli and soot particle oxidation reactions, but arsenic did not make any role in soot particle oxidation reaction. FE-SEM of the aerosol sample showed that soot particle size for the iron doped flame was relatively smaller than one of non-iron doped flame, however one for the arsenic flame was even bigger than that of the pure hydrocarbon flame. Equilibrium products and temperature of stoichiometric mixture fraction were calculated with STANJAN Code for the iron and arsenic doped flames. The iron oxide of FeO(g) was found from mixture fraction of 0.1 and remained a dominant iron species between the reaction zone and near the fuel lean side. Fe_2O_3 started to appear near reaction and remained a dominant iron oxidized form through out the fuel lean side of the flame. The stoichiometric mixture fraction for the arsenic flame was 0.209. Elemental arsenic was found to be the dominant equilibrium form of arsenic in the fuel-rich part of the flame, either as atomic arsenic or as the allotrope As4.