OCR Text |
Show 12 of Cr and Ni was noted, which may have been attributed to stainless steel particles contaminating the system. These elements are fairly common in small quantities in many types of stainless steel. Possible sources of the stainless steel and resultant Ni and Cr contamination may have been the erosion of metal parts in the coal pulverizer or slight corrosion-erosion of PDTF parts, such as the gas quench probe, the multicyclone, or the steel lines leading from the quench probe to the multicyclone. There seemed to be a depletion of Hg, As, Cd, Se, and Ph, which may have been the result of ash loss, reaction of these species with PDTF parts, or at least possibly for Hg and Se, loss as a vapor through the impinger system. To avoid the effect of closure, the amount of trace metals collected in each stage of the multi cyclone and the fliter are reported as a percentage of the total amount of each trace metal collected. The assumption is made that the relative partitioning of the elements between coarse particulate, fme particulate, and vapor phase will be less affected than absolute concentrations by inhomogeneities in the feed coal and losses in the furnace and sampling system. Comparison of the average percentages of each element in the collection devices shows that a substantial portion, 4()O/0 or more of the total amount of the trace elements are recovered in the coarse ash of the first cyclone (Figures 3 and 4). The trace elements have remained with the larger ash particles, have recondensed, or have been captured on the ash. Cr, Ni (Figure 4), and, surprisingly, Hg (Figure 3) partition with the coarse ash with an average of more than 650/0 remaining in the >3-J.lm fraction of collected sample, with the balance appearing in the 1-3-J.lm fraction or the <O.4-J.lm filter fraction. Very little Cr and Ni pass through the filter into the impingers (Figure 4), which is probably an indication that they are nonvolatile species, such as refractory oxides. The behavior of Hg is more complex. Although much of the Hg is collected in the cyclones and filter, under certain test conditions up to 3()o/0 of the Hg is in a volatile form passing through the filter into the impingers. Pb partitions primarily in the 1-3-J.lm ash fraction and the <O.4-J..UIl filter, probably as a very fine oxide fume (Figure 4). Generally, little Pb passes through the filter into the impingers. Along with Hg, the trace |