Laboratory-Scale Ash Deposition Studies of a Size- and Gravity-Fractionated Coal

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- 7 - TABLE 2 (CONTINUED) 2.5 sink 2.5 sink 2.5 sink <44 ~m 44-75 ~m >75 ~m Ash 70.81 66.14 65.85 SiD 36.5 29.8 31.4 A1 263 12.6 13.2 12.4 F~6°3 45.2 52.1 51.7 T1 2 0.9 0.7 0.8 P205 0.0 0.0 _ 7 - 0.0 CaD 1.6 1.4 1.3 MgO 0.3 1.2 0.0 ~a6° 0.0 0.0 0.0 1.4 1.3 1.3 s63 1.4 1.4 1. 1 Deposits were formed by employing the drop-tube furnace system at selected timed intervals for each of the size and gravity fractions. The deposits were weighed and plots of deposit weight versus time were generated. Sticking coefficients were determined for each of the size and gravity fractions from the deposit weight versus time curve. The sticking coefficients are plotted versus time for the sized gravity fractions as shown in Figures 3-5. Figure 3 illustrates the trends obtained for the <44 micrometer size cut of the specific gravity fractions. The 1.4 float and 1.4x1.8 specific gravity fractions had a relatively even rate of growth as compared to the whole coal and the 1.8x2.5 and the 2.5 sink fractions. The sticking coefficients for the 1.4 float size fractions were less than those obtained for the whole coal except for the >75-micrometer size cut. The 1.4x1.8 fraction had a higher initial coefficient than the whole coal but the whole coal had a much more accelerated rate of growth. The sticking coefficient for the 1.8x2.5 gravity fraction showed a rapidly accelerated rate of growth that approaches one. This deposit had evidence of a molten captive surface forming on the leading edge of the deposit. One of the significant compositional differences obtained for the 1.8x2.5 gravity fraction as compared to the others was the higher level of calcium present. The calcium will act as an effective flux that will lower the melting point of the ash which results in the formation of a low-melting point captive- surface. The ash sticking coefficients for the 44- to 75-micrometer size fraction of the various specific gravity fractions are illustrated in Figure 4. The trends obtained for the 44- to 75-micrometer size fraction is similar to the <44-micrometer size fraction. The sticking coefficients for the whole coal falls between the 1.4 float and the 1.4xl.8 gravity fractions. The 1.8x2.5 gravity fraction had -the highest sticking coefficient, and this is due to the higher level of calcium found in this fraction using the same rational-stated above.