OCR Text |
Show a portion is retained in the reduced state as V203 or V20*. The physicochemi-cal behavior of the residual ash would depend upon the fluxing action of the vanadium oxides on the individual coal ash specie, which may contain alumina, silica, iron, calcium, and magnesium in varying proportions, depending on the heterogeneity of the coal ash. Ash fusion tests were performed on COMs as a first step in estimating their fireside deposition potential. COMs containing coal in various concentrations up to 50 percent at 10-percent increments, from the coals whose iron levels range from 7 to 24 percent (as listed in Table 8), were ashed and subjected to ASTM ash fusion tests under air and in a reducing environment. The results, summarized in Figure 16, indicate that the vanadium present has little effect on the melting temperatures of the coal ash for coal concentrations in excess of 10 percent.*° Since the differences in combustion rates may have a secondary influence on the behavior of fireside deposits via the retention of vanadium in the ash or elongation of the flame because of the slower combustion rates of the coal, COM with varying concentrations of coal for different rank coals (i.e., bituminous, subbituminous, and lignite) were subjected to thermal analysis using thermogravi-metric analysis (TGA). A comparison of the derivative function of a TGA thermogram, frequently referred to as a combustion profile, for a bituminous COM with other rank coal appears in Figure 17. The thermogram indicates the oil ignites and volatilizes at a very low temperature. The combustion of the char is delayed to a much higher temperature and proceeds in two steps. The second step in the 1-54 |