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Show (and similar high volatile fuels). Carbon combustion efficiency and NO emissions were comparable to Run No. 1 and Run No. 2. The carbon monoxide and total hydrocarbon emissions, however, were luwer than in the previous runs as a result of the higher excess air used in these runs. 5.3.3 Test Series No. 3: Runs No. 5 and No. 6 The objective of this test series was to examine the effects of gas residence time and fluidization quality on such combustion characteristics as freeboard combustion and carbon combustion efficiency. To achieve longer gas residence time and better fluidization quality, Greer limestone beds were used and were operated at low fluidization velocities. Results of these two runs are also given in Table 4. As can be seen, carbon combustion efficiency increased from 94 percent to 97 percent. Comparison of ultimate analyses of the fines collected by the primary and secondary cyclones from this test series with the previous test series also indicates a drop in carbon content from a high of 57 percent and 71 percent to a low of 16 percent and 7.5 percent, respectively (Table 5). The recorded temperature distribution, as illustrated in Figure 5, shows that freeboard combustion did not take place. As expected, no sulfur dioxide emission was detected throughout the test series since, unlike Runs 3 and 4, the fresh limestone in the bed did not reach its saturation state during the 4 to 5 hours it was in use. In order to investigate the effects of the gas residence time and fluidization quality on sulfur retention, either a sulfated spent bed material must be used or the bed must be allowed to reach its equilibrium state. Due to the time limitations on this experiment, no test was conducted to investigate these specific effects. 5.4 Conclusions and Recommendations Based on these experimental results, the following conclusions with respect to fluidized-bed combustion of scrap tire materials may be drawn from the preliminary tests: o Ninety-seven percent carbon combustion efficiency can be achieved without the recycling of fines. o Carbon combustion efficiency and freeboard combustion phenomena are strongly dependent upon gas residence time and quality of fluidization. o Sulfur dioxide emissions were measured between 1200 ppm (1.82 lb S02/ 106 Btu input) when no sorbent was added, to a low of 500 ppm (0.91 lb S02/106 Btu input) as Greer limestone was added to the bed at a Ca/S molar feed ratio of 2.9. 11-27 |