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Show development, and as a comparison to the laboratory-generated fly ash samples. The C K sample was run-of-plant material obtained from a fly ash recycling broker. Details on the plant configuration and combustion conditions at the time the ash was produced are not available. Quantitative Soot and Char Separation A gravity separation procedure was developed to determine the relative amounts of soot and coal char in a fly ash sample. The goal was to develop a method to quantify the soot as a component of the total unburned carbon in the fly ash produced from a range of fuels and combustion conditions. This separation method was based on observations made while preparing electron microscopy samples. Ultrasonic agitation dispersed the large soot aggregates into clusters of only a few primary particles, but the char particles remained intact. Suspensions of low bulk density ash samples that contained dispersed soot remained opaque for days, while suspensions of char particles settled in less than an hour. The quantitative soot separation method consisted of placing a weighed sample of ash in a test tube, suspending the ash in ethyl alcohol, settling, decanting, and repeating the process with fresh ethyl alcohol in a countercurrent fashion, as shown in Figure 1. The products of the separation are then evaporated to dryness, weighed, and analyzed for carbon. The carbon found in the final supernatant fraction was assumed to be soot and the carbon in the bottom fraction of the separation was assumed to be char. These assumptions were confirmed by examining the particle morphology of the two fractions using a scanning electron microscope. The quantitative separation was validated by analyzing synthetic ash mixtures containing weighed amounts of known materials. The effect of interacting components was tested by making the ash mixtures from real combustion products rather than reagent surrogates. The char-rich material used for the validation was produced during a previous char combustion study by burning Pittsburgh #8 coal in the 30 K W furnace. [18] This char was collected by extracting the combustion products through a port 0.5 m from the burner and rapidly cooling the particles by air dilution Char and Soot 5 September 4, 1998 |