Inorganic submicron aerosol formation during petroleum coke and residual oil coke combustion.

摘要

Submicron aerosols formed during combustion of four petroleum cokes containing vanadium (0.46 {dollar}pm{dollar} 0.06 or 1.68 {dollar}pm{dollar} 0.09 wt%) or nickel (0.33 or 0.99 {dollar}pm{dollar} 0.15 wt%) and residual oil cokes collected from two oil-fired electric utility boilers were studied in a laboratory furnace in order to elucidate the processes controlling conversion of the metal species to submicron particles during combustion of residual fuel oils.; No mechanism other than vaporization, nucleation, and recondensation of metal species was found to be responsible for the formation of inorganic submicron particles. The processes contributing to particle formation and growth were analyzed using classical nucleation theory. Conversion of VO{dollar}sb2{dollar} vapor to particles was initiated by homogeneous nucleation, in the absence of other particles from the petroleum cokes which would serve as nucleation sites. The mean particle size of the submicron aerosols was proportional to the aerosol volume concentration raised to powers of 0.36 and 0.43 at gas temperatures of 1700 and 1800 K, respectively, showing that Brownian coagulation was the dominant mechanism for particle growth.; The yield of submicron oxide vanadium aerosols was influenced by coke properties and combustion conditions, including gas temperature, oxygen mole fraction, coke particle size, and vanadium concentration. The yield of submicron particles increased with increase in gas temperature for the vanadium-doped petroleum cokes. The yield was higher at the higher vanadium concentration (1.62 wt%). The yield of submicron particles versus oxygen mole fraction exhibited a minimum at an oxygen mole fraction near 0.05 when burning the coke containing the lower vanadium concentration (0.51 wt%) at the nominal gas temperature of 1700 K.; Nickel species in petroleum coke were found to be much less vaporizable than vanadium. The amounts of submicron particles formed while burning nickel-doped petroleum cokes (0.33 and 1.14 wt% Ni) having sizes of 38-45 {dollar}mu{dollar}m were in most cases similar to the yields of submicron particles approximately from the petroleum coke containing no additive. Transformation of nickel to submicron particles was greater when burning the petroleum cokes containing 0.88 and 0.84 wt% nickel and having larger particle sizes (53-63 and 90-106 {dollar}mu{dollar}m, respectively).; The residual oil cokes from utility boilers contained a high concentration of inorganic matter (approximately 40 wt% ash content on the dry basis) including Si, Al, Fe, V, Ni, Mg, Ca, Na, and K compounds, but the level of submicron particulate formed was observed to be substantially lower than from the pitch-derived coke having similar vanadium content. Addition of magnesium oxide particles to the pitch coke was found to suppress the vaporization of vanadium species during combustion, possibly by formation of less volatile Mg-V-O compounds.