Pulverized coal combustion: Flame attachment and nitrogen oxide emissions

Persistent Link:
http://hdl.handle.net/10150/289822
Title:
Pulverized coal combustion: Flame attachment and nitrogen oxide emissions
Author:
Ogden, Gregory E.
Issue Date:
2002
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
To fully utilize coal as a long-term energy source, pollution prevention technologies must be developed to mitigate the negative environmental and health impacts of coal combustion. NOₓ emissions are of particular concern due to their role in forming ground-level ozone, photochemical smog, fine particulates and acid rain. A systematic evaluation of near-flame aerodynamics was conducted to determine how burner operating parameters and oxygen partial pressure influence flame attachment and coal ignition, two properties essential for proper low NOₓ burner operation. A laboratory scale (17kW) 2m tall, 0.5m diameter electrically heated furnace and axial burner with adjustable secondary combustion air annuli and primary fuel jets were used in the study. Transport air oxygen partial pressure (PO₂), coal particle size distribution, primary and secondary jet velocity, and wall temperature were varied independently to determine the effect of each variable on flame attachment and NOₓ. NOₓ emissions from the furnace were similar to those from full-scale tangentially-fired boilers. The tendency for flame attachment increased with velocity ratio (Θ), wall temperature, PO₂, and coal fines. Θ's greater than 1 were required for stable combustion. Increasing Θ reduced flame standoff distances and NOₓ for always-detached flames. NOₓ increased with Θ for always-attached flames. Increasing PO₂ reduced NOₓ by up to 50% by promoting flame attachment. However both oxygen enrichment and increasing fines had little impact on NOₓ for always-attached and always-detached flames. Wall temperature and excess air in leakage were the dominant variables affecting NOₓ. Furnace exhaust oxygen levels increased when operating under a slight vacuum with corresponding increases in NOₓ. Emissions for detached flames increased with wall temperature 3 times faster than attached flames. Emissions data obtained from the furnace under slight positive furnace pressure increased linearly with wall temperature. A novel dual flame was produced at high Θ and reduced PO₂ consisting of one flame attached to the burner and one stabilized 18" below the burner. This configuration is similar to staged combustion but without separate over-fire air. Emissions from the dual flame were significantly below those observed from conventional Type-O attached and detached flames.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Engineering, Chemical.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Chemical and Environmental Engineering
Degree Grantor:
University of Arizona
Advisor:
Wendt, Jost O. L.

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titlePulverized coal combustion: Flame attachment and nitrogen oxide emissionsen_US
dc.creatorOgden, Gregory E.en_US
dc.contributor.authorOgden, Gregory E.en_US
dc.date.issued2002en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractTo fully utilize coal as a long-term energy source, pollution prevention technologies must be developed to mitigate the negative environmental and health impacts of coal combustion. NOₓ emissions are of particular concern due to their role in forming ground-level ozone, photochemical smog, fine particulates and acid rain. A systematic evaluation of near-flame aerodynamics was conducted to determine how burner operating parameters and oxygen partial pressure influence flame attachment and coal ignition, two properties essential for proper low NOₓ burner operation. A laboratory scale (17kW) 2m tall, 0.5m diameter electrically heated furnace and axial burner with adjustable secondary combustion air annuli and primary fuel jets were used in the study. Transport air oxygen partial pressure (PO₂), coal particle size distribution, primary and secondary jet velocity, and wall temperature were varied independently to determine the effect of each variable on flame attachment and NOₓ. NOₓ emissions from the furnace were similar to those from full-scale tangentially-fired boilers. The tendency for flame attachment increased with velocity ratio (Θ), wall temperature, PO₂, and coal fines. Θ's greater than 1 were required for stable combustion. Increasing Θ reduced flame standoff distances and NOₓ for always-detached flames. NOₓ increased with Θ for always-attached flames. Increasing PO₂ reduced NOₓ by up to 50% by promoting flame attachment. However both oxygen enrichment and increasing fines had little impact on NOₓ for always-attached and always-detached flames. Wall temperature and excess air in leakage were the dominant variables affecting NOₓ. Furnace exhaust oxygen levels increased when operating under a slight vacuum with corresponding increases in NOₓ. Emissions for detached flames increased with wall temperature 3 times faster than attached flames. Emissions data obtained from the furnace under slight positive furnace pressure increased linearly with wall temperature. A novel dual flame was produced at high Θ and reduced PO₂ consisting of one flame attached to the burner and one stabilized 18" below the burner. This configuration is similar to staged combustion but without separate over-fire air. Emissions from the dual flame were significantly below those observed from conventional Type-O attached and detached flames.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectEngineering, Chemical.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineChemical and Environmental Engineeringen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorWendt, Jost O. L.en_US
dc.identifier.proquest3060971en_US
dc.identifier.bibrecord.b43038475en_US
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