Combustion of Carbon Fines by Above-Bed Recycle in an Atmospheric Fluidized Bed Burner

摘要

Fluidized bed combustion studies have resulted in the development of a burner with 99.98% carbon utilization efficiency. This was made possible partly by use of a fines burning modeling technique that predicts burning efficiencies as a function of process parameters. A shrinking sphere reaction model was used in conjunction with empirical combustion kinetics data, actual particle size distribution, and gas environment variables such as temperature, pressure, and composition to determine required recycle rates for complete combustion. The fines burning model was verified on a 0.40-m (16-in.) diameter atmospheric burner operated at 1.1-m/s (3.6-ft/s) superficial velocity at 900 exp 0 C (1650 exp 0 F). During a 50-h test, burn rates of over 60 kg/h (130 lb/h) were attained. Carbon fines generation amounted to over 30% of the feed (which was sized to -5 mm (-3/16 in.) ring size), but the final carbon inventory was less than 0.5 kg (1 lb) upon completion of the test. Fines recycle rates during the test averaged 7 kg/min (15 lb/min); the fines combustion model had predicted a required recycle rate of 8 kg/min (17 lb/min). This close correlation lends a good measure of credibility to the techniques used in analyzing fine carbon combustion characteristics. This technique was also used to analyze coal fines combustion by recycle to the fluid bed. Reasonable recycle rates are predicted for lower bed fines injection. (ERA citation 05:000039)