| OCR Text |
Show INTRODUCTION Slagging of utility steam generator furnaces by ash in Eastern bituminous coals is generally attributed to the fluxing action of the iron found in pyrites on the acidic constituents comprising the major portion of the remaining coal impurities (i.e.,Al203, Si02,etc). On occasion, different coals with identical ash composition have been known to produce decidedly different slagging conditions in boilers of identical design, operated in the same mode. Variations in composition of the slag when compared to the coal ash have led some investigators to believe fly ash is being selectively deposited on the furnace wall according to its gravity, composition, physicochemical properties upon being heated, and local flow patterns. 2'3 The implication is that coal ash is heterogeneous in nature, and each particle behaves independently as it is introduced into the furnace. During pulverization the coal and ash are reduced in size and subdivided into many different size and gravity fractions with different coal composition and ash chemistry. The final composition of the individual species will depend to a large extent on the original distribution and orientation of mineral matter in the coal. Slagging is caused by the individual species with the lowest melting temperature and greatest potential for attaching themselves to the furnace wall. If during pulverization the composition of individual species is altered such that a portion of the ash has a higher melting temperature than the composite ash sample, and the remaining portion of the particulate has a lower melting temperature than the composite ash sample, then slagging of the furnace may occur unexpectedly for coals identified as nonslagging on the basis of a composite analysis. An investigation of the impact of minerals in coal and their juxtaposition with regard to other mineral matter and carbonaceous material comprising coal on furnace slagging and convective pass fouling is underway. The presence of minerals in coal is characterized by conventional analysis of the elements in size and gravity fractionated, pulverized coal samples at gravities of 1.30, 1.80, and 2.85. Select samples are also low-temperature ashed and examined for mineral COIIUMU. The pulverized coal is fired in an 100 lb/h laboratory combustor for evaluation of slagging and fouling potential. Deposits are analyzed in detail for chemical composition, particle size and surface morphology, and the physicochemical properties which may influence deposit formation. Although the program is directed at pyritic-rich Eastern bituminous coals, comparisons are made 2 |
