| OCR Text |
Show 10 The axial centerline gaseous species concentration distributions in the two CVS flames with and without heat extraction are shown in Figures 9, 10, 11, 12. The two Op concentration profiles lie quite close to one another in Figure 9, except at positions close to the burner where combustion starts earlier in the flame with less heat extraction (No. 1) causing the Op concentration to decay more rapidly. The COp concentration profiles, shown in Figure 10 'mirror' the 0? concentration trends. The CO concentration (Figure 11) decays to a zero value within 1 - 1.5 m of the burner in both flames, with that in the flame with increased heat extraction (No. 2) perhaps being a little more persistent. Also shown in Figure 11 is the CO profile for a COM flame (Flame 4 of Table 5)t with behavior similar to that of CVS Flame 1. The axial NO concentration distributions are shown in Figure 12. Heat extraction has a noticeable effect on the NO concentration levels; the higher NO levels in Flame 1, compared with Flame 2, are due primarily to an increased rate of formation of 'thermal' NO resulting from the higher flame temperatures. Generally speaking, it has been found that conditions favoring flame stability and rapid ignition of CVS - intense fuel/air mixing, high air preheat, minimal heat extraction in the near field - also tend to increase NO emission. A selection of the best or 'optimal' CVS flame input conditions has to be based on a compromise in these conflicting requirements. Figures 13 and 14 show the total solids concentration and the percent carbon in the solids taken along the flame axis respectively. The distributions of combustible solids in the flame illustrate the good burn-out of the fuel corresponding to a coal conversion efficiency of better than 99^« Radial profiles of gas temperature (Figure 15) and of gaseous species concentrations (Op, COp, and NO , Figures 16, 17, and 18)are shown for Flame 2 for various axial stations. The conical spray distribution can be seen to have its effect upon the radial temperature profiles: the peak temperature is positioned off the flame axis up to an axial distance of 0.46 m, after which the radial temperature distribution becomes quite uniform. This trend is borne out also by the radial profiles of the gaseous species concentrations. Another example off-axis peaks occurs in Figure 19, which shows radial profiles of the solids concentrations and of their carbon content at an axial station 0.61 m from the burner, in this case for Flame 1. It should be noted that the radial profiles discussed cover only the so-called "near-field" of the flame, the flow region close to the burner. It can be assumed that at axial positions beyond approximately one meter from the burner the flame properties take on plug flow characteristics. Detailed Characterization of Particulate Matter in the Flame Figures 20 through 25 show scanning electron micrographs of solids sampled from coal-water slurry flames at a distance of just over one meter from the burner. The first three examples are obtained from Flame 1, and the remainder from Flame 2, which had higher heat extraction and thus lower flame temperatures. The photographs clearly show that individual coal particles agglomerate in the flames. The solids were extracted from the flame with a 'water quench' sampling probe in which a water spray was |
