OCR Text |
Show The tendency to stick will depend upon the target efficiency of the particles (the fraction of particles in the combustion gases that will impinge on the ceramic probe), the particle temperature, and the ash fusion temperature of the mineral matter. Since the micronized and pulverized coal samples were fired at the same LAF operating conditions, the difference in the deposition rates may be due to lower target efficiency of finer fly ash particles of micronized coal. The flue gas velocities are low in the LAF, compared to commercial-scale boilers. The effect of velocities on particles impacting on tubes will be investigated during BCTU testing, since the tests will be performed at the higher velocities of commercial-scale boilers. These results indicate that the micronized-coal fly ash particles may follow flow streams around the tightly spaced tubes of gas- and oil-fired boilers with less deposition than would occur firing the same coal ground to conventional pulverized-coal size. Similar trends were observed with Ohio and West Virginia coals. However, the results were significantly different. The deposition rate from Ohio micronized coal was less than Indiana micronized coal, and the deposition rate was negligible from West Virginia micronized coal. These differences could be the result of the differences in ash fusion temperatures. The probe deposit from the Indiana pulverized coal was comparable to that of the pulverized Ohio and West Virginia coals, even though the fly ash was finer. The reason for this behavior is not clear; however, it might be related to impingement of partially burned particles, lower ash fusion temperature, and the higher slagging index of Indiana coal. ..J 9-48 |