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Show Type A slag represents the earliest stage of slag formation on cooled heat transfer surfaces in a zone of very high heat flux exposed to axial symmetric flow. This type of formation is analogous to the deposits which may accumulate on the water cooled furnace walls not subjected to direct flame impingement. Slag Type B represents an advanced stage of slag Type A formation on the fireside surfaces whose temperatures approach the ash-softening temperature of the coal. This type of slag deposit is analogous to slag formation on furnace walls already fouled by a layer of sintered deposit on hot refractory surfaces such as those found at the burner throat. Slag Type B is also an indication of the fluid characteristics of deposits formed in zones of excessively high heat release. Slag Type C is an intermediate stage of slagging where the flame temperatures are low. The heat flux is reduced, and the surface temperatures may be a few hundred degrees below the initial deformation temperature of the coal ash. Slag Type D is similar to Type C except for the flow regime. Instead of axial-symmetric flow, the flue gases make a 90-degree turn out of the furnace section and into the convective duct. The refractory surfaces, which are in line with the previous flow stream direction, are subjected to direct impingement by the heavier gravity, coarse particulates which depart from the main flow stream. The final type of slagging, (Type E), occurs in a zone where the flue gas temperature is lowest, the heat flux is governed primarily by convection, and direct impact of coarse particulates is promoted by much higher gas velocities. The Type A deposits formed on the slagging probes varied from a thin coating of dust for Kentucky No. 11, to large droplets of viscous ash for Upper Freeport, Indiana County coal, and rivulets of plastic slag for Lower Freeport, Cambria County coal. Figure 12 shows the degree of slagging on the lower slagging probes for each of the Ilring tests. In addition, the percent ash in coal, percent Fe?03 in ash, percent Fe203 in the 2.85 gravity fraction, and the ash-softening temperatures in a reducing gas are compared for each coal in Table 7. In general, the greatest degree of slagging occurred while firing fuels with the highest ash-softening temperature and the highest concentra 36 |