OCR Text |
Show combustion air, using fuels ranging from refinery gas down to vacuum residual heavy oil. The mean temperature of the products of combustion in the firebox of these pipe-stills is around 1500°F and it is a highly radiant heat transfer area. Unfortunately, the significance of fuel bound nitrogen in the oil was neither appreciated nor measured at the time of these tests, but it is thought to have been fairly low in most cases. When firing gas, all types of burners, at all operating conditions were in the 50 to 80 ppm of NOx range, no results using combustion air preheat are available. The lower end of the range relates to the lower excess air levels. When firing refinery fuel oils, the toroidal combustors gave results of 80 to 100 ppm NOx, other forced draft burners, 125 to 180 ppm# natural draft burners, 105 to 200 ppm. Two results taken more recently using combustion air preheat at approx. 450°F with toroidal combustors gave 200 to 250 ppm NOx. Under similar conditions to those described above, stack solids emissions results were obtained. Unfortunately, neither fuel oil ash content nor atomization details are available in most cases and both will affect stack solids. Firing oil in all cases, the toroidal combustors gave 0.030 to 0.015 Ibs./MM BTU from 10 to 30 percent excess air. Other forced draft burners gave 0.10 to 0.06 Ibs./MM BTU from 10 to 30 percent excess air. No representative results available for natural draft burners. Very recently, field NOx measurements were completed on a secondary oil recovery steam generator retrofitted with a toroidal combustor. The heat release is just over 60 MM BTU/hr. at 10 to 15 percent excess ambient air, firing into a watertubed firebox just over 8 feet inside diameter by 40 feet long. The fuel oil was a heavy oil 13/12 |