EFFECT OF THE OCCURRENCE AND COMPOSITION OF IRON COMPOUNDS ON ASH FORMATION, COMPOSITION, AND SIZE IN PILOT-SCALE COMBUSTION OF PULVERIZED COAL AND COAL-WATER SLURRY FUELS

Two coals, Beulah (North Dakota) lignite and Elk Creek (West Virginia) high-volatile A bituminous, were burned in both pulverized coal and c oal-water slurry fuel forms to study the effect of the modes of occurr ence and composition of iron compounds in the coal on the particle siz e distribution and composition of ash. The slurry preparation process appeared to cause a significant reduction in the particle size distrib ution of pyrite in the lignite, relative to the pulverized coal. This in turn caused a change in the dominant mechanism of ash formation. In the Beulah pulverized coal, pyrite fragmentation is the major process , forming submicrometer- or micrometer-sized iron oxide particles. In the slurry, however, coalescence and agglomeration, facilitated by the fluxing action of iron incorporated into aluminosilicates, dominate a sh formation. This behavior could not have been predicted by relying s olely on elemental composition data without the supplementary informat ion on mineral matter particle size distribution in the fuels. The Elk Creek fuels provide a useful contrast. In this case both the composit ion and particle size distributions of the mineral matter in the two f uels are quite similar, and the same ash formation mechanism, coalesce nce, dominates in both cases. The principal cause of the differences i n ash particle size distribution is the formation of a coal particle a gglomerate during atomization of the Elk Creek slurry.