| OCR Text |
Show ~~nc~e there is effectively no change in the inlet or boundary conditions on the flame between fuese fuels (for any given excess air), we conclude that these differences are attributable to differences in flame chemistry and/or transport properties between the fuels. One possible explanation for the differences observed is partial premixing in the lifted flame jets coupled with enhanced flammability limits due to hydrogen. Another is local differential diffusion between the hydrogen, methane, and propane in the fuel. 2 BTEX Emission Results of the BTEX measurements at the furnace exit are shown in Figs. 7-11. Table V lists the numerical values. In reviewing these results it should be borne in -mind that our detection limit, at a SIN of 1 is approximately 0.5 ppbv for each species. As such, even though values are shown which are below this limit, they should not be interpreted as having significance past the fact that a discernible peak was obtained by virtue of an -unusually quiet baseline in the vicinity of the peak. Stated another way: Any value listed below 0.5 ppbv can only be quantitatively interpreted as being < 0.5 ppbv, but with a discernible amount of the species -present. Similarly, non-detects, shown in the figures as squares with no height, can only be quantitatively interpreted as conditions for which the emission was < 0.5 ppbv. Beginning with benzene in Fig. 7 and proceeding through each of the species, it is apparent that none of the fuels produces benzene, toluene, ethylbenzene, or xylene emissions in excess of 3 ppbv in the normal operating range of excess air (10-50%). In fact, most of the species are ~!~ie ~-11 non-detects in this region, with the exception of toluene which is present in the 0.2 to 3 ppbv range and increases slightly with fuel hydrogen and propane contents. These results differ significantly from unpublished (proprietary) data from operating refmery units which are reported to be in the range from 10 to 150 ppbv. For this reason, and to investigate the effects that locally rich conditions (rich eddies) might have on emissions, the range of excess air investigated was extended to stoichiometric (0% excess air) and substoichiometric (negative excess air) conditions. - 9- |
