| OCR Text |
Show Unfortunately, the ash-softening vs. percent-basic curve tells nothing about the quantity of each species present. To overcome this deficiency, the data was replotted on a fusibility bar graph reporting the percent weight of each species and its ash fusion temperature, as seen in Figures 6a through 6e. The size and gravity fraction of each species is identified by the legend and sequence in which it is reported. The fusibility diagrams indicate that most of the ash in the Kentucky No. 11 and the Illinois No. 6 coal is contained in the 1.30 float and 1.80 float fractions and, therefore, behaves like inherent ash. To a certain extent this may account for the homogeneity of the ash reported in the ash-softening vs. percent-basic curves. Some pure pyrite is released during pulverizing of the Illinois No. 6 coal. The quantity released, however, is very small. Substantial quantities of ash are released after pulverizing the two Pennsylvania coals. The quantity of ash reporting to the sink 2.85 gravity fraction was the greatest for the Upper Free-port, Indiana County, Pennsylvania, coal. Analysis of the individual size and gravity fractions unexpectedly revealed a wide variation in ash-softening temperature of the sink 2.85 gravity fraction, indicating the heaviest gravity fraction may be contaminated by some other heavy minerals rich in A1203, Si02, and CaO. Table 5 summarizes the chemistry of the sink 2.85 fractions. Characterization of the mineral content of the five coals, using size and gravity fractionation techniques applied to a pulverized sample, has revealed a decidedly different mineral orientation for each coal despite similarities in elemental composition of the composite ash analysis. The pyrites appear as finely-divided matter, uniformly dispersed through the coal in both the Illinois No. 6 and Kentucky No. 11 coals. A very small portion of pyrites is liberated as pure pyrites from the Illinois coal. Substantial quantities of mineral matter are liberated from the Kentucky No. 9, Upper Freeport, and Lower Freeport coals. There is a difference in the contamination level of the liberated pyrites bv clays and quartz. The impact of the differences in slagging and fouling potential due to the variation in occurrence of pyrites in the coal was evaluated in a laboratory combustor. 18 |
