Modeling the formation and size distribution of fly ash
A set of mathematical models has been developed to predict the size distribution of fly ash particles formed in pulverized coal combustion. The large particle mode of the size distribution, typically centered about 10 to 20 ..mu..m, is predicted by a simple breakup model that is based on the complete coalescence of molten mineral inclusions within fragments of the devolatilized coal char. The ultrafine particle mode, that is typically centered about 0.1 to 0.2 ..mu..m, is modeled in terms of ash volatilization, nucleation, and coagulation. Silica and alumina are reduced to volatile suboxides through reactions at the char surface. The volatile suboxides are transported from the char surface where they are oxidized back to the stable oxides in the bulk gas, and then nucleated in accordance with homogeneous nucleation theory. The ultrafine nuclei coagulate in accordance with Brownian coagulation theory. The predicted particle size spectra have been compared to measured size distributions from a pilot-scale combustor and a full-scale utility boiler. Considering the disproportionate loss of coarse particles in the pilot-scale unit, the agreement between the predicted and measured size distributions was considered reasonably good. Both the predicted ultrafine and large particle modes agreed reasonably well with the measured particle size distribution for the full scale boiler. The validated computer models were used to study the effect of changes in the coal ash content, coal particle size, and the combustion flame temperature.
- Research Organization:
- Alabama Univ., Birmingham (USA)
- OSTI ID:
- 6358478
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
010800 -- Coal
Lignite
& Peat-- Waste Management
014000* -- Coal
Lignite
& Peat-- Combustion
AEROSOL WASTES
ASH CONTENT
ASHES
BOILERS
CARBONACEOUS MATERIALS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COAL
COMBUSTION
COMBUSTION KINETICS
COMBUSTORS
DISTRIBUTION
ENERGY SOURCES
FLY ASH
FOSSIL FUELS
FUELS
KINETICS
MATERIALS
MATHEMATICAL MODELS
OXIDATION
PARTICLE SIZE
REACTION KINETICS
RESIDUES
SIZE
SYNTHESIS
THERMOCHEMICAL PROCESSES
WASTES