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Show Pulverized coal samples were extracted from the PC-laden stream after the mill (before the filterhouse) according to the ASME PTC 4.2 procedure. Particle size distributions of the as-fired samples were checked by screening the collected sample, every time that coal was pulverized. Typical size distributions are listed in Table 2. Table 2. Typical PC Size Distribution Mesh Designation and Size Fine PC Standard PC Screen # (~m) % Smaller % Smaller 16 (1190) 100.0 100.0 30 (595) 100.0 99.95 50 (297) 99.9 99.4 100 (149) 96.7 92.0 200 (74) 80.8 70.9 Baseline XCL PC Burner Thermal Load, Coal Fineness, and Burner Stoichiometry Effects - Major results at different stoichiometries, and full and part load operation are illustrated in Figure 3. Increasing the excess air converted more fuel-N to NOx, and decreased CO formation and UBCL. Increasing the coal fineness improved the char oxidation substantially and increased the NOx emissions. At full load and 17% excess air, average NOx, CO, and UBCL values were 296 PPMV (0.43 lb N02IMBtu), 93 PPMV, and 0.37%, respectively with the standard size PC (70% through 200 mesh screen). Corresponding values for the finer PC (80% through 200 mesh screen) were 330 PPMV (0.46 lb NO/MBtu), 57 PPMV, and 0.06%. Relative to full load conditions, part load operation at a fixed burner stoichiometry generated lower NOx and higher UBCL due to the cooler furnace environment. In commercial units where excess air and primary air-to-fuel ratio are normally increased with decreasing thermal load, UBCL is reduced except at very low loads. Burner Stoichiometry and Fuel Effects - Coal rank and stoichiometry effects at full load are shown in Figure 4. The NOx and UBCL results for each coal reflect optimum burner settings and spin vane orientation for the secondary air flow. General trends for UBCL, and NOx and CO emissions are similar to those discussed earlier. As expected, NOx levels increase with increasing fuel-N and decreasing volatile matter contents. High volatile coal flames gave off intense soot radiation from the evolving volatile matter, while the lower volatile coal flames appeared more translucent and visually shorter. All flames were stable and attached at the . 7 |