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Show SECTION 5.0 CONCLUSIONS Based on the results from this test program, the following specific conclusions can be made: • Fine atomization can be achieved at a low air to fuel ratio when a CWM is formulated to optimize its rheology. Mass median diameters of the CWM's varied from 35 to 45 microns depending on the formulation: water produced a mass mean drop size of 25 microns for comparable atomization conditions. The coal particle size (MMD -40 microns) appears to be the factor limiting drop size distribution. Stable combustion of the CWM's was attained with a burner turndown of at least 2:1 (1.5 - 3 x 106 Btu/hr). Nitric oxide levels from the CWM and parent coal combustion were of the same level indicating that CWM combustion stability was not attained with an abnormally intense flame. • Combustion characteristics of the CWM's were found to be dependent on the coal type and formulation. The CWM's made from the higher volatile coals (Elk Creek and Chinese "O" coal) exhibited combustion characteristics comparable to pulverized coal firing with combustion efficiencies greater than 98 percent for nominal combustion conditions. The CWM made from the lower volatile coal (Chinese "X" coal) exhibited a combustion efficiency substantially below pulverized firing (approximately 4 percentage points, 91.5 percent compared to 95.5 percent). . The bimodal CWM was more difficult to burn than the unimodal CWM in terms of flame stability and slightly lower combustion efficiency. This behavior is thought to be a result of the PSD which influences the high shear rheology and hence atomization quality. • Ash particle size distribution results were inconclusive. A cascade impactor showed a larger particle size distribution with the CWM than with the parent coal fired in a pulverized form. This suggests agglomeration of the particles. However, analyses by a L&N particle size analyzer yielded identical, small particle size distributions for the coal and CWM ash. This indicates a weak agglomeration at worst if not an artifact. It is uncertain whether the agglomeration occurs in the combustion region, convective section of the boiler, or within the sampling device. ACKNOWLEDGMENTS The following people made important contributions to this research program: Dr. K. DuriSwamy, Dr. S. Tsai, and Dr. H. VonSchonfeldt of ORC, and Dr. M. Mansour and Mr. G. Shiomoto of KVB. 32 KVB72-P327 D1 94 |