Combustion Characterisitcs of Occidental Coal-Oil Mixtures

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promotes higher viscosities which in turn must require higher fuel preheat temperatures. In the combustion tests, the fuel preheat te mperatures have been 238-245°F. At these temperatures, No. 6 fuel oil has viscosity of about 20 cp while that of 45 Wt% coke PETCOM has about 850 cp. Both air and steam were used to atomize No. 6 fuel oil and PETCOM. Tests were conducted with steam and air on both the Franklin (FRC) burner nozzle and the modified North American (NA) nozzle. In all the air atomizer tests, approximately one pound of air was used to atomize each pound of fuel. This ratio was significantly lower for steam: about 0.33 (lb. of steam/ lb. of fuel) with the FRC nozzle and about 0.55 with the NA nozzle. Fuel flow rates were constant, 44-50 lbs/hr in all the tests. Table 4-1 shows selected test data as being typical of the test results using air and steam atomization. The excess air level was approximately constant for these tests (between 11 and 15 percent) and typical of actual boiler operation. The air-atomized PETCOM test (number 2-45) shows heat transfer and combustion efficiencies that are comparable with that of No. 6 fuel oil. The steam-atomized PETCOM shows comparable heat-transfer efficiency, but a significant drop in combus­tion efficiency. Comparing air- atomized to steam-atomized PETCOM, it is apparent that the atomizing fluid/ fuel ratio is approximately four times lower for steam. The effect of lower steam flow rates on combus­tion performance will be discussed in the next section. Fuel injection velocities were approximately 2 ft/s, and atomization air velocities were maintained at 660 ft/s for the FRC nozzle and 440 ft/s for the NA nozzle. Steam injection velocities varied between 600 and 870 ft/s with the FRC nozzle and 470 ft/s with the NA nozzle. Combustion air varied between 1.5 percent and 50 percent in excess of stoichiometric air. Most of the tests were conducted at 10-20 percent excess air levels. Compared to the intense fireball of the No. 6 fuel oil flame, the PETCOM flame was smaller with a hazy flame surrounding its fireball. This secondary flame consisted of burning coke particles noticeable down to the middle of the furnace tube. Very few coke particles appeared at 19-13