OCR Text |
Show of the minor and trace constituents, the melting temperature of the ash may vary from about 2200 to 2800°F. All the coal-bearing species are expected to reach the maximum furnace temperatures because of their intimate contact with the combustibles in the coal. Three other species may exist-one containing pure aluminosilicate compounds; one consisting of pure pyrites; and the third, a blend of the two. All these species should reach a maximum temperature somewhat lower than the flame temperature because of the flow of heat from the flame to the particles. The actual temperature will depend upon particle size and physical location within the combustor. The pure aluminosilicate compounds have a specific gravity between 2.0 and 2.8, depending upon composition, and melting temperatures between 2200 and 2800°F, depending upon the concentration of minor elements. The blended specie of pyritic and nonpyritic ash has a specific gravity ranging between 2.0 and slightly less than 5.0, depending upon the percentage of pyrites present. Melting temperatures may range between 1900 and 2800°F, again depending upon the percentage of pyrites present. The heavier particulate will have the lower melting temperatures until the pyrites exceed 50 percent by weight concentration. A further increase in pyrite concentration will increase this weight and the melting temperature of the oxidized ash. The specie consisting of pure pyrites has a specific gravity of about 5.0. Its melting temperature depends upon the degree of sulfur reduction and iron oxidation. Melts as low as 1112°F have been detected during the early stages of desulfurization.3z Figure 10 is a thermogram illustrating the formation of a melt under reducing conditions. Figure 11 is scanning electron photomicrographs (SEMs) of specimens heated in a 1-38 |