OCR Text |
Show configuration. Before presenting the results in detail, it should be noted that just as the Chinese "X" coal was found difficult to burn, the CWM formulated from this coal was also very difficult to burn. With the watercooled burner section, the nX" coal CWM could only be stabilized with 1-2 percent natural gas assist (on a Btu basis). Flame stabilization without natural gas assist was possible using a conventional diffuser; however, the combustion efficiency was reduced. All other CWM's exhibited a burner turndown of at least two to one before encountering flame stabilization problems. A comparison of the combustion efficiency of the CWM's to that of the parent coal is shown in Figures 9, 10 and 11 for the Elk Creek, Chinese "O", and Chinese "X" coals, respectively. The Elk Creek coal exhibited comparable combustion efficiencies for both pulverized firing and firing as a CWM with combustion efficiencies greater than 98 percent at excess air levels greater than 3 percent. The bimodal CWM made from the Elk Creek coal exhibited a slightly lower combustion efficiency. The Chinese "O" coal CWM showed comparable combustion efficiency at an excess oxygen setting of 2.5 percent (98 percent) but exhibited a decrease in combustion efficiency as the excess air setting was increased (Figure 10). The results for the Chinese "X" coal are shown in Figure 11. While the combustion efficiency of the "XM parent coal was about 94 percent, the combustion efficiency of the CWM made from this coal was on the order of 91 percent. The combustion efficiency of this "X" coal CWM dropped dramatically as the excess oxygen was increased above 4 percent. The results shown in Figure 11 were obtained with 1-2 percent natural gas assist (Btu basis). The NO emissions for the CWM's are shown in Figure 12. In parallel with the results of the combustion efficiency tests, the NO emissions are comparable for the Elk Creek CWM and the Chinese "0" coal CWM with levels on the order of 400 - 500 ppm. The Chinese "X" coal exhibited substantially lower NOx levels as did the micronized and Elk Creek slurry. The N0X levels from the bimodal CWM was moderately lower than the utility grind CWM. Reducing the firing rate increased the combustion efficiency for the CWMs. This effect was modest for the CWM's formulated from the high volatile 24 KVB72-P327 D1 94 |