OCR Text |
Show - 11 - The stick i ng coefficients obtained for the >75-micrometer fractions of Pittsburgh #8 are illustrated in Figure 5. All of these fractions had sticking coefficients greater than the whole coal. The 1.4 float fraction showed an even rate of growth, while the others exhibited a more accelerated rate of growth. Size was found to have an effect on the ash sticking coefficients in some cases. The results of the 1.4 float indicate a higher sticking coefficient for the <75-micrometer fraction as compared to the <44-micrometer fraction. The 44- to 75-micrometer fraction had a lower sticking coefficient than the <44-micrometer fraction. The sticking coefficients for the sized fractions of 1.4xl.8 specific gravity cut increased with increasing size. The greatest sticking coefficient was exhibited by the >75-micrometer size fraction. The ash sticking coefficient for the 1.8x2.5 gravity fraction exhibited a decrease in sticking coefficient with increasing size. This is probably due to the high level of calcium found in the <44-micrometer size fraction as compared to the >75-micrometer. The calcium level in the <44-micrometer sized fraction was 9.0 as compared to 6.5 in the >75-micrometer sized fraction. The sticking coefficients f or the sized 2.5 sink fractions were nearly the same, although there was a sl i ght decrease in the sticking coefficient for the >75-micrometer size fraction as compared to the other two size cuts. A deposit produced in the drop-tube furnace from the whole, medium cleaned Pittsburgh #8 coal was compared to a deposit removed from a waterwall panel in the radiant section of the CE pilot-scale combustor. The conditions of the drop tu be furnace were adjusted in order to mimic the conditions of deposition at the point where panel P3 exists. The conditions in the droptube furnace were 1550 °C (2822 °F) combustion temperature, residence time of approximately 0.6 to 0.7 seconds, and a gas temperature at the constrictor of 1440 °C (2624 nF) . The conditions in the CE combustor were as follows: 2900 °F flame temperature, residence time of 0.5 seconds at panel P3, and gas temperature of 2720 °F at panel P3. The temperatures obtained for the droptube furnace were slightly lower than those observed in the CE combustor. The composition of deposits produced in the drop-tube furnace and the CE furnace are summarized in Table 3. In general, the compositions of the deposits are s i milar. The drop-tube furnace deposit contains a higher level of Fe203 than the CE deposit. In addition, the levels of A1 203 and Si02 are lower for the drop-tube furnace deposits. The distribution of phases determined by the SEMPC technique for the CE deposit and the drop-tube furnace deposit are listed in Table 4. The CE deposit contains more unclassifiable phases than those found in the drop-tube furnace deposit. In addition, the CE pilot-scale deposit contains fayalite (Fe2Si04) and hercynite (FeA1 204) phases. These species are products of crystallization from a melt. The presence of these components indicate that the CE deposit was exposed to high temperatures, resulting in the assimilation or absorption into a molten phase. The drop-tube furnace deposit contains higher levels of montmorillonite-derived, kaolinite-derived, quartz, and iron oxides than the pilot-scale deposit. These results indicate that the components have not been significantly altered as a result of exposure to higher temperatures. Backscattered electron images of polished cross sections of deposits formed in the CE combustor and the drop-tube furnace are shown in Figure 6. |