NITROGEN OXIDESₓ ABATEMENT: THE EFFECT OF COOLING AND COMPOSITION ON STAGED PULVERIZED COAL COMBUSTION
AuthorBotsford, Charles Wesley
KeywordsCoal -- Combustion.
Combustion gases -- Composition.
Coal, Pulverized -- Combustion.
MetadataShow full item record
PublisherThe University of Arizona.
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.
Degree ProgramGraduate College
Degree GrantorUniversity of Arizona
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THE EFFECT OF COAL TYPE, RESIDENCE TIME AND COMBUSTION CONFIGURATION ON THE SUBMICRON AEROSOL COMPOSITION AND SIZE DISTRIBUTION FROM PULVERIZED COAL COMBUSTION (STAGED, FLYASH, SPECIES ENRICHMENT).Peterson, Tom; LINAK, WILLIAM PATRICK. (The University of Arizona., 1985)Pulverized samples of Utah bituminous, Beulah (North Dakota) low Na lignite, Beulah high Na lignite and Texas (San Miguel) lignite coals were burned at a rate of 2.5 kg/hr in a laboratory furnace under various (overall fuel lean) combustion conditions. Particle size distributions (PSD) and size segregated particle filter samples were taken at various positions within the convection section. Temperature and gas concentrations were measured throughout. The evolution of the submicron PSD within the convection section for the four coals was similar, although the location of the initial particle mode at the convection section inlet varied with coal type. While staged (.8/1.2) combustion of the Utah bituminous coal had a variable effect on the volume of submicron aerosol produced, staged combustion of two of the three lignites (Beulah low Na and Texas) caused a definite increase in the submicron aerosol volume. Vapor enhancement due to a localized reducing atmosphere, which would effect coals of higher ash volatility or higher inherent ash content, is thought to explain this behavior. Depressed combustion temperatures associated with the high moisture content of the Beulah high Na lignite are thought to offset the effects of staging. Increased combustion temperatures (through oxygen enrichment) caused staged volume increases for the Beulah high Na lignite. Combustion temperatures are a controlling factor even at more extreme staging conditions. Chemical analysis of the size segregated particle samples show the trace elements, As, Pb, Zn and the major elements, Na and K to be enriched in the submicron aerosol. Auger depth profiles show these small particles to be comprised of a core enriched in Fe, Si, Ca and Mg and surface layers enriched in Na and K. These results point to a mechanism of homogeneous nucleation of low vapor pressure species followed by successive layering of progressively more volatile species. Volatile species are enriched in the submicron aerosol due to the large surface areas provided. Modeling efforts show that while coagulation may be the dominant mechanism to describe the aerosol evolving within the convection section, it cannot be used solely to predict the PSD. Another mechanism, presumably surface area dependent growth (condensation) must be included.
Simplified kinetic models describing the fate of coal nitrogen under fuel-rich combustion conditionsWendt, Jost O. L.; Eftekharzadeh, Nooshin, 1965- (The University of Arizona., 1994)Twenty three sets of experimental data describing CO, CO₂, H₂, O₂, NO, NH₃, and HCN concentration profiles for fuel-rich pulverized coal combustion in plug flow configurations were correlated by a simple kinetic mechanism. A comprehensive mechanism covering the entire fuel-rich zone was formulated by combining models describing short and long time scale combustion. Short time scale phenomena (up to 0.6 seconds) including coal devolatilization were handled by developing global semi-empirical models based on fundamental concepts. Kinetic parameters for the proposed mechanism were estimated by using a non-linear regression technique. This model then allowed the prediction of major and nitrogenous species evolved in the early stages of combustion and yielded reasonable predictions of all these species concentrations. For the long time scale phenomena (up to 3 seconds) an existing model was used. Under most experimental conditions the extended model yielded good predictions of nitrogenous species from known process variables.