OCR Text |
Show Measurements of Particle Speed --Een 2105 5 o L.&..L."-&..I....&...L.~~L..L.'-.I...I....Iu..&..I.II -1.0 0.0 1 .0 Radial Distance (m) Figure 15: Particle Speed vs Radial Distance at xID=8.75 (Test 1) -.!! -E Radial Distance (m) Figure 16: Particle Speed vs Radial Distance at xID=8.75 (Test 2) The measurements of particle speed reported in Figures 15 and 16 for the two tests can provide information on the fate of the micronized coal particles in the flow field. The measurements of gas temperature and velocity, discussed earlier, provided evidence for the existence of an IRZ on the bumerlboiler centerline, at xID=3.75, for the highly swirled, high combustion efficiency flame of Test 1. The amount of volatiles released in the IRZ depends on the residence time distribution of the coal particles in this zone. This in tum, is dependent upon the size and velocity of the coal particles, in addition to the flow type (I, II and ill). It was suggested earlier that in Test 1, as a result of the high degrees of swirl employed by the three combustion air streams, a large percentage of the micronized coal particles were entrained into the swirling air. This became evident by the maximum values of particle speed measured at the outside boundary of the flow field probed (Figure 15). At x!D=8.75, the speed of the particles on the center line of the boiler was 8.21 m1s and as the radial distance from the center line of the boiler toward the left side increased so did the speed of the particles, with values approaching a maximum of 13.21 m1s (Figure 15). It was also suggested t in Test 2, as a result of the lower swirl numbers utilized, a certain percentage of the par . ..:les penetrated the IRZ of the flame, before either being deflected to the side, or penetrating the IRZ completely. This became evident by the maximum value of particle speed (14.98 m1s) measured at xID=8.75, on the centerline of the boiler (Figure 16). As the radial distance from the center line of the boiler toward the left side was increased, values of particle speed decreased to 10.21 m1s and then increased closer to the boiler wall (Figure 16). The measurements of gas temperature, velocity and particle speed provide a body of evidence suggesting that the flow fields associated with Tests 1 and 2 were of Types II and III, respectively. In other words, the measurements indicated that a Type II flow associated with the high swirl number (2.1), produced a high combustion efficiency (98%) and high NOx emissions (700 ppm at 3% 02), while the Type III flow associated with the lower swirl number (1.9) produced a flame with high combustion efficiency (97%) and lower NOx emissions (380 ppm at 3% 0 2). |