Early evolution of coal nitrogen in opposed flow combustion configurations.

Persistent Link:
http://hdl.handle.net/10150/185308
Title:
Early evolution of coal nitrogen in opposed flow combustion configurations.
Author:
Ghani, Muhammad Usman.
Issue Date:
1990
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:
A laminar opposed flow, pulverized coal combustion configuration was used to explore the early evolution of light gaseous nitrogenous and hydrocarbon species into the bulk gas phase. Two coals of different ranks were considered. Effects of pyrolysis environment, particle size and heating rates were investigated. Concentration profiles of HCN, NH₃, NO, CH₄, C₂H₂, C₂H₄ and C₂H₆ were measured, under both oxidizing and reducing environments, for three particle sizes, and at high heating rates provided by the hot flue gases of a CO/O₂/Ar flame. Net rates of formation into the bulk gas phase were calculated from the experimental data after correcting for diffusion and convection effects, and were then related to particle time-temperature histories. Experimental data show that HCN precedes NH₃ and NO for both coals. It is the first light gaseous product of coal nitrogen evolution entering into the bulk gas phase. For low rank coals, either only a small amount of tar nitrogen is released or its subsequent oxidation to light gaseous products is slow. For high rank coals secondary reactions of tars are rapid and lead to substantial levels of nitrogenous species. Nature of nitrogenous species evolving into the bulk gas phase was found to be independent of particle size. Lower heating rates favor increased yields of ammonia. Evolution of hydrocarbon species from high rank coals occurs via low molecular weight species, whereas low rank coals yield high molecular weight species. Evolution of hydrocarbon species was found to be independent of particle size and heating rates. Evolution of hydrogen occurs during late stages of devolatilization indicating that it is a product of secondary pyrolysis reactions. A simple kinetic model is proposed to relate rates of formation of nitrogenous species to coal devolatilization kinetics. The latter are similar for three experiments, with fine particles, involving two coals and can be described by a single rate constant given by 63.8 exp (-5220/RT). Bituminous coal (fines), under oxidizing conditions, shows substantially higher rates, possibly due to energy feedback mechanisms in the vicinity of the particles. Literature values, which originated from solid phase measurements, underpredict the quantities of total XN entering the post flame zone by substantial amounts. Our value, which was derived from gas phase species measurements, yields a better prediction of total nitrogenous species entering the post flame zone, and can be incorporated in engineering models aiming at optimizing of pollutant emissions.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Engineering.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Chemical Engineering; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Wendt, Jost O.L.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleEarly evolution of coal nitrogen in opposed flow combustion configurations.en_US
dc.creatorGhani, Muhammad Usman.en_US
dc.contributor.authorGhani, Muhammad Usman.en_US
dc.date.issued1990en_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.abstractA laminar opposed flow, pulverized coal combustion configuration was used to explore the early evolution of light gaseous nitrogenous and hydrocarbon species into the bulk gas phase. Two coals of different ranks were considered. Effects of pyrolysis environment, particle size and heating rates were investigated. Concentration profiles of HCN, NH₃, NO, CH₄, C₂H₂, C₂H₄ and C₂H₆ were measured, under both oxidizing and reducing environments, for three particle sizes, and at high heating rates provided by the hot flue gases of a CO/O₂/Ar flame. Net rates of formation into the bulk gas phase were calculated from the experimental data after correcting for diffusion and convection effects, and were then related to particle time-temperature histories. Experimental data show that HCN precedes NH₃ and NO for both coals. It is the first light gaseous product of coal nitrogen evolution entering into the bulk gas phase. For low rank coals, either only a small amount of tar nitrogen is released or its subsequent oxidation to light gaseous products is slow. For high rank coals secondary reactions of tars are rapid and lead to substantial levels of nitrogenous species. Nature of nitrogenous species evolving into the bulk gas phase was found to be independent of particle size. Lower heating rates favor increased yields of ammonia. Evolution of hydrocarbon species from high rank coals occurs via low molecular weight species, whereas low rank coals yield high molecular weight species. Evolution of hydrocarbon species was found to be independent of particle size and heating rates. Evolution of hydrogen occurs during late stages of devolatilization indicating that it is a product of secondary pyrolysis reactions. A simple kinetic model is proposed to relate rates of formation of nitrogenous species to coal devolatilization kinetics. The latter are similar for three experiments, with fine particles, involving two coals and can be described by a single rate constant given by 63.8 exp (-5220/RT). Bituminous coal (fines), under oxidizing conditions, shows substantially higher rates, possibly due to energy feedback mechanisms in the vicinity of the particles. Literature values, which originated from solid phase measurements, underpredict the quantities of total XN entering the post flame zone by substantial amounts. Our value, which was derived from gas phase species measurements, yields a better prediction of total nitrogenous species entering the post flame zone, and can be incorporated in engineering models aiming at optimizing of pollutant emissions.en_US
dc.description.notep. 106, p. 107, p. 108 are missing from paper original and microfilm version.-
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectEngineering.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineChemical Engineeringen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorWendt, Jost O.L.en_US
dc.contributor.committeememberPeterson, Thomas W.en_US
dc.contributor.committeememberShadman, Farhangen_US
dc.contributor.committeememberPerkins, Henry C.en_US
dc.contributor.committeememberRamohalli, Kumar N.R.en_US
dc.identifier.proquest9114056en_US
dc.identifier.oclc710839322en_US
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