A Statistical Investigation on Particle to Particle Variation of Fly Ash Using SEM-AIA-EDAX Technique.

Abstract

Due to the particle to particle variation of coal mineral properties and random coalescence of mineral particles during coal burnout, fly ash particle properties change from particle to particle. The variations of particle properties (e.g. SiO2 content, viscosity) can be mathematically described by random variables. Since bulk analysis of fly ash gives only the mean values of chosen random variables, it is considered insufficient to describe the fly ash behavior either in boiler slagging/fouling or in different concrete structures. SEM-AIA-EDAX technique was used to supply raw data for estimating the distribution functions of particle size and chemical compounds in Texas lignite minerals and fly ash and Eagle Butte fly ash. To determine the volume based size distributions of these samples from their area-based size distributions, Abelian transformation was used. To estimate the distribution functions of CaO and SiO2 contents of the samples, particle area fractions were used. The confidence limits were also calculated for the estimated parameters. By determining the distribution functions of particle viscosity and chemical composition, it was shown that in the case of Texas lignite the coal burnout does not cause significant changes in the mineral matter properties. It was observed that the properties of fly ash depended solely on the mineral matter properties. However, in the Eagle Butte case the coal burnout has a major effect on the fly ash size distribution and its chemical composition.

Combustion Aerosols: Factors Governing Their Size and Composition and Implications to Human Health

“…109,115 If such information is not available, an approximate distribution can be obtained by assuming that the minerals are randomly distributed between coal particles. [116][117][118][119] The ash particles will have a particle-to-particle variation in composition that will reflect the variation in the mineral content of the individual coal particles from which they are produced. This is illustrated in Figures 6 and 7, which show the Al, Si, and Fe distributions both in the parent coal minerals and in the resulting fly ash, respectively.…”

Transformations of inorganic coal constituents in combustion systems

“…The studies of mineral matter transformztion during coal combustion are motivated by concern with fouling and slagging in utility boilers. Previous studies have shown that many factors control the final ash particle size and composition distributions: mineral content, mineral distribution among pulverized coal particles (Charon et al, 1990;Barta et al, 1989), coal particle size distribution (psd) (Holve, 1980, char structure and burnout mechanism (Monroe, 1989;Wibberley and Wall, 1980, viscosity and surface tension of ash particles. This paper will provide additional evidence, experimental and computational, to support recent experimental and simulation studies (Helble and Sarofim, 1990; Kang, et al 1988) showing that the fragmentation of char induced by macmpores can influence the final ash psd.…”

Advanced combustor design concept to control NOx and air toxics

“…An extensive series of experimental studies, largely by Sarofim's group at MIT (Sarofim, Howard et al 1977;Neville, Quann et al 1981;Haynes, Neville et al 1982;Neville and Sarofim 1982;Quann, Neville et al 1982;Quann and Sarofim 1982;Kang, Helble et al 1988;Helble and Sarofim 1989;Barta, Vámos et al 1990;Barta, Toqan et al 1992), lead to a general consensus of the fly ash formation mechanism. A large particle mode is formed from the residual ash from individual coal particles and the size distribution is determined by competition between coagulation and fragmentation mechanisms.…”