EFFECT OF THE OCCURRENCE AND COMPOSITION OF SILICATE AND ALUMINOSILICATE COMPOUNDS ON ASH FORMATION IN PILOT-SCALE COMBUSTION OF PULVERIZEDCOAL AND COAL-WATER SLURRY FUELS

Beulah (North Dakota) lignite and Elk Creek (West Virginia) high-volat ile A bituminous coal were burned in both pulverized coal and coal-wat er slurry fuel forms to study the effect of the modes of occurrence an d composition of aluminosilicates and silicates on the particle size d istribution and composition of ash. The dominant mechanism for ash for mation in the Beulah pulverized coal was fragmentation of mineral part icles, such as quartz and pyrite, during combustion. By contrast, the main mechanism for determining the Beulah CWSF ash particle size distr ibution was coalescence and agglomeration of inherent aluminosilicates and silicates during combustion. The particle size distribution of th e inorganic phases formed during combustion of the Elk Creek fuels is slightly coarser than the original mineral matter, due to coalescence of inherent aluminosilicates and silicates during combustion. The slur ry ash is slightly coarser than the pulverized coal ash as a result of the larger agglomerate formed on atomization of the Elk Creek slurry. The larger slurry agglomerate increases the number of mineral particl es in proximity to one another and increases the time required for cha r burnout. In turn, the increased char burnout time increases the time interval during which mineral particles can coalesce, as evident by c hanges in the particle size distribution and composition of silicates and aluminosilicates. The result is enhanced coalescence and agglomera tion of the mineral particles in the Elk Creek slurry compared to the pulverized coal. The results emphasize the importance of determining t he size distribution and occurrence of inorganics in a fuel and the ef fect of changing either of these two parameters for a particular miner al group as a result of fuel form.