| OCR Text |
Show Unfortunately, most of the energy available in atomization fluid is not used in breaking up the fuel. As little as less than one percent of this energy is used for droplet formation. A quick calculation of the energy required to atomize a fuel is given by: E . = a x (change in fuel surface area) (5-2) atomization 6 Thus to atomize a fuel having a surface tension of 30 dynes/cm2 and a specific gravity of 1.085, the required energy to produce a 20 micron fuel droplet is 3.56 x 10 3 (BTU/lb fuel). Comparison of this quantity to the quantities actually used in this experiment shows several orders-of- raagnitude above the theoretical quantity required for small droplet sizes and high combustion efficiency. However, when compared with utility and industrial- scale burning of residual fuels, the amount of atomizing fluid used in our experiments is not excessive. Fuel-to-atomization fluid flowrate ratios typically vary between 1:1 to 5:1 or higher for most efficient boiler operations. Some atomizers are capable of efficiently atomizing fluids up to 1300 cp, but most handle fuels easily to 50 cp. The successful operation of both the Franklin and Modified North American nozzles with air atomization prove that properly optimized burner nozzles can be developed for highly viscous fuels (on the order of 850 cp exhibited by our slurry fuel at 250°F preheat temperature). However, higher than normal air or steam consumption is also required for these high viscosity fuels. For PETCOM, preheat temperatures as high as 350°F may be required to achieve low atomizing fluid flowrates. In order to more clearly define the effect of nozzle performance on the slurry fuel combustion efficiency, mean droplet diameters for the test conditions were calculated. Several empirical correlations for twin-fluid atomizers were considered (Refs. 9, 10, 11, 12, 13) and the correlation of Wigg (Ref. 9) was found to best correlate our test data. Wigg's corrleation is: 19-22 |
