| OCR Text |
Show - 13 - Marked differences were noted in the sticking coefficients measured for each of the size and gravity fractions of the medium-cleaned Pittsburgh #8 coal. The lowest sticking coefficients were observed for the 1.4 float fraction for all size fractions. The sticking coefficients measured for the whole coal fell between that obtained for the 1.4 float and the 1.4x1.8 sized fraction with the exception of the >75-micrometer size fraction. In general, the sticking coefficients were found to increase with increasing gravity fractions. In addition, the sticking coeffic ient was found in increase with increasing size. However, the 1.8x2.5 specific gravity fraction exhibited, in most cases, higher sticking coefficients than that obtained for the 2.5 sink. The sticking coefficients for the sized fractions of the 1.8x2.5 gravity cut decreased with increasing size. This trend was the opposite of that obtained for the other size and gravity fractions. The difference can be attributed to the high level of calcium found in the 1.8x2.5 gravity fraction. The calcium acts as flux that lowers the melting behavior of ashes and can result in increased ash deposit growth rates and increases in deposit strength. Comparison of the compositions, distribution of phases and the microstructure of the deposits produced in the CE combustor and the drop-tube furnace reveal some similarities and differences. The composition of the deposits were similar. The only difference was the higher level of iron and lower aluminum and silicon found in the drop-tube deposit as compared to the CE deposit. The deposit formed in the CE combustor was more melted and fused than the one produced in the drop-tube furnace. This is due to the higher temperatures found in the the CE combustor and the length of time the deposit was in the furnace at elevated temperatures. The distribution of phases determined with the SEMPC technique illustrates the effect of temperature differences on the deposits. The deposit formed in the CE combustor contained an abundance of unclassifiable phases. These phases are a result of a high degree of interaction of inorganic constituents. In addition, the drop-tube furnace deposit contained a greater quantity of derived materials such as montmorillonite and iron oxides that had not been assimilated into the melt phase. In general, the distribution of phases found in the drop-tube furnace deposits is consistent with those found in the CE combustor. REFERENCES 1. Borio, R.W. and R.R. Narcisco, Jr., "The Use of Gravity Fractionation Techniques for Assessing Slagging and Fouling Potential of Coal Ash," ASME Winter Annual Meeting, December 10-15, 1978. 2. Jones, M.L. and S.A. Benson, "An Overview of Fouling and Slagging with Western Coals," Proceedings of the EPRI-sponsored conference on The Effects of Coal Quality on Power Plants, Atlanta, GA, Oct. 1987. 3. Abbott, M.F., and L.G. Austin, "A study of slag deposit initiation in a drop-tube type furnace," in Mineral Matter and Ash in Coal, Vorres, K. S. (Ed.), ACS Symposium Series No. 301, Washington, DC, p. 325 (1986). 4. Benson, S.A. and L.G. Austin, IIStudy of Slag Deposit Initiation Using a Laboratory-Scale Furnace,1I Presented at the Conference on Mineral Matter and Ash Deposition From Coal, Engineering Foundation, Santa Barbara, CA, Feb. 1988. |
