| OCR Text |
Show composition of the volatiles released when the samples were heated in vacuum to ~50oC for 12 to 15 minutes. The volatiles were trapped with liquid N2 and then analyzed by mass spectrometry. While the volatile matter of the parent coals was composed pr imar ily of H 2 S, CH .. , and C 2 and higher hydrocarbons, that of the MCL-treated samples consisted mainly of CO and C02. The calorific value of the MCL products is about 10% lower than the parent coals on a moisture- and ash-free basis. The higher moisture contents of the MCL products further lower the calor ific values of the products on an as-rece i ved bas is in compar ison with the parent coals. However, this is offset somewhat by their lower ash contents, resulting in a net reduction of approximately 5~ in the as-received calorific value of the Pittsburgh No. 8 product and 15~ for the Kentucky No. 11 product. Level 2 thermogravimetric studies were conducted by the Babcock & Wilcox Company (B&W) while the newly acquired PETC instrument was being installed in the Fundamental Combustion Research Laboratory. Burning and volatilerelease profiles of the MCL products and their parents are shown in Figures 1 and 2. Babcock & Wilcox concluded from their studies that in commercial practice, the MCL-treated fuels of this study may be more difficul t to igni te, but once they are igni ted, burn out should be similar to that of the parent coals. The dramatically increased surface area and porosity of the MCL products, as shown in Table 1, should enhance char burn out once the fuels are ignited. For a given boiler, the degree of slagging and fouling that will occur is governed by its design and operation, and by the characteristics of the fuel being fired. The interdependence of these factors makes it difficul t to quantitatively predict the extent of ash deposition throughout a boiler. The ash deposition propensity of a coal can be assessed in general terms by established relationships between various fuel properties and actual field or test performance. The most widely used slagging and fouling correlations are based on the coal ash content, ash chemistry, and ash melting behavior [2 J . Although the ash content of the MCL products has been greatly reduced, enough ash remains to pose potential deposi tion problems in oil- and gasdesigned boilers. The approach taken at this point in the evaluation to determine the slagging and fouling behavior of the advanced clean-coal products was to consider all of the available predictive indices [2-12J. While many of these indices have shown good correlations wi th actual field performance for the coals in the limited data bases for which they were developed, their general application to a wide range of coals has resulted in ser ious misrepresen ta t ions of ash depos i t ion propens i ty . Also, such an approach is likely to (and does) yield contradictory indications of fuel performance. Such a naive approach, i.e., considering all available predicti ve indices, however, is usually the only means available, given I imi ted resources, to predict the ash deposition propensity of new fuels. As shown in Table 1, the composi tion of the ash in the MCL products is dramatically different from that of the parent coals. Tables 3 and 4 show the resul ts of var ious slagging and fouling parameters applied to the four samples. All of the samples are classified as having bi tuminous-type ash |
