Size Distribution of Fine Particles from Coal Combustion

Abstract

Measurements of the particle size distribution at the outlets of six coal-fired utility boilers showed a peak at a particle diameter near 0.1 micrometer. This submicrometer mode appears to be a general feature of coal combustion that results from a volatilization-condensation process in the boiler. At the boilers tested, the submicrometer mode contained 0.2 to 2.2 percent of the total fly ash mass. The importance of this mode is greater than its small quantity suggests because particles in the submicrometer size range are often much more difficult to collect with conventional particulate control devices than larger particles. Thus, the submicrometer mode may significantly influence the design and selection of future power plant emission controls. The particle mass in the submicrometer mode was correlated with the nitric oxide concentration in the flue gas. This correlation suggests that control of nitric oxide by modification of the combustion conditions may reduce the generation and emission of submicrometer particles.

Combustion Aerosols: Factors Governing Their Size and Composition and Implications to Human Health

“…• Particles entering the APCD are essentially bimodal in terms of mass, with on the order of 1% of the ash consisting of submicrometer particles and the larger residual ash falling into the 1-20 µm range. 54,63,180,182 • Particles in the 0.1-0.3 µm range have the highest penetration through APCD compared with both larger and smaller particles, 63,78,179,180 so the 0.1-1 µm particles form a larger fraction of the mass distribution leaving the APCD than they do in the uncontrolled combustion emissions. 63 • The submicrometer ash is enriched in volatile elements relative to the larger particles.…”

“…54,63,180,182 • Particles in the 0.1-0.3 µm range have the highest penetration through APCD compared with both larger and smaller particles, 63,78,179,180 so the 0.1-1 µm particles form a larger fraction of the mass distribution leaving the APCD than they do in the uncontrolled combustion emissions. 63 • The submicrometer ash is enriched in volatile elements relative to the larger particles. 148,152 The concentration of the trace elements within the submicrometer and supramicrometer ash fraction increases with decreasing particle size.…”

“…63,78,88,148,152,179,180 Additional efforts have focused on the effectiveness of APCDs in removing these potentially toxic substances. 63,78,179,180 These studies provide the following information: Figure 12. Normalized differential particle mass distributions measured in the stack for a sample of coal-fired power plants using different burner and gas-cleaning technologies.…”

“…The suboxides and metals will diffuse through the particle boundary layer into the bulk gas where they are oxidized and condense to produce the submicron aerosols. The vaporization rate is strongly temperature-dependent 55,[62][63][64] so that the amount of submicron aerosol will vary with combustion conditions. The vaporization of elements is complicated by their interaction with the minerals in the coal.…”

Toxic substances form coal combustion--a co prehemsice assessment

“…Many investigators have measured two distinct modes in the submicron ash, ultrafine 48,49 and intermediate. The ultrafine mode is primarily derived from vaporization and condensation of inorganics during the combustion process.…”