OCR Text |
Show (ash) deposition in the burner block, slight misalignment of the nozzle, or some air leakages through the sampling opening may have affected the flame. Gas Analysis The oxygen concentration on the furnace axis along the furnace length is plotted in Figure 17 to show some differences in aerodynamic patterns in the furnace when firing different coal particle sizes. The carbon dioxide readings on the furnace axis (Figure 18) also indicate differences in aerodynamics for different coal particle sizes in the region close to the burner wall. The profiles of carbon monoxide concentrations along the furnace axis (Figure 19) indicate a large reduction in the flame length for the smaller particles. Although Trials 1 and 2 show a sharp reduction in CO concentrations downstream, the visual and measured flame lengths in Trial 3 (the coarsest coal) show carbon monoxide over 1000 ppm far beyond its visual and measured flame length. The nitrogen oxides concentrations measured along the furnace axis (Figure 20) do not illustrate any change of concentration with the size of the coal particle burned. Fly Ash Analysis Samples of solid material were collected along the furnace axis for Trials 1, 2, and 3 and were then analyzed for carbon and hydrogen. The solid samplings were not performed isokinetically so the particle size could have had an effect on the results, and the absolute values for unburned carbon may be low. However, because coarser coals produce larger ash particles, the possible error in the analysis would be greater with the coarser coal sampling. Figure 21 is a plot of the percent of unburned carbon .ilong the furnace axis against the distance from the burner for Trials 1, 2, 3, and 5. The plot indicates more rapid combustion for fine-ground coal and the reduction in the flame length for smaller particle sizes similar to the visual flame length and carbon monoxide measurements. Trial 5 at 700 kW (2.4 million Btu/hr) firing rate showed some increase in unburned 27 |