Investigation of the mechanism of fly-ash formation in coal-fired utility borders. Quarterly report, February 1--April 30, 1978

Technical Report · Thu Jun 01 04:00:00 EDT 1978

DOI:https://doi.org/10.2172/6557937· OSTI ID:6557937

Ulrich, G. D.

The submicron fraction of coal fly-ash, though comprising a minor fraction of the total mass, has become increasingly recognized as a health hazard and a possible link in irreversible boiler fouling. An outgrowth of continuing research on submicron particle behavior, this document describes efforts to predict the composition and morphology of condensation ash. A model based on a process of metal oxide vaporization from a burning char particle, diffusion and recondensation has been constructed and employed. A submicron particle concentration equaling five percent by weight of the fly-ash from a cyclone-fired boiler is predicted. Because of lower combustion temperatures in pulverized-fuel-fired boilers, less than one tenth of one percent of the total fly-ash is attributed to vapor transport. Enrichment of silicon and iron is predicted in the submicron fraction. This is verified experimentally for silicon but not for iron. Experimental examination reveals aggregates containing primary particles, of about 60 nm in diameter. Particles of this size are evidence that the submicron ash precipitates in the combustion zone of the boiler to grow by coagulation for several seconds before quenching.

• Research Organization: New Hampshire Univ., Durham (USA). Dept. of Chemical Engineering
• OSTI ID: 6557937
• Report Number(s): FE-2205-11
• Country of Publication: United States
• Language: English

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20 FOSSIL-FUELED POWER PLANTS
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AEROSOL WASTES
AGGLOMERATION
BOILERS
CARBONACEOUS MATERIALS
CHARS
CHEMICAL REACTION KINETICS
CHEMICAL REACTION YIELD
CHEMICAL REACTIONS
COAL
COMBUSTION
ELECTRON MICROSCOPY
ELEMENTS
ENERGY SOURCES
ENRICHMENT
FLUIDS
FLY ASH
FOSSIL FUELS
FOULING
FUELS
GASES
IRON
KINETICS
MATHEMATICAL MODELS
METALS
MICROSCOPY
OXIDATION
PARTICLE SIZE
PYROLYSIS PRODUCTS
REACTION KINETICS
SEMIMETALS
SILICON
SIZE
THERMOCHEMICAL PROCESSES
TRANSITION ELEMENTS
VAPORS
WASTES
YIELDS