OCR Text |
Show 2. The reduction furnace was operated under reducing conditions while still firing natural gas to heat up the oxidation furnace. 3. The fuel was switched from natural gas to number 2 fuel oil, a fuel similar to diesel. 4. Recycle flue gas was added to the combustion air being introduced across the burner. The two streams were adjusted to give an oxygen content of 10-12%. 5. Visual observation through the various sight ports indicated that very little soot was being formed at these conditions. 6. The firing rate was reduced from about 2 million Btu/hr to about 0.5 million Btu/hr during this run to maintain the burner pressure drop below 10 inches of water. Estimated conditions in the reducing furnace were 90 to 95% of stoichiometric air. After stable combustion was achieved, a sample run was made to measure the soot produced in the reducing furnace. 7. Data were recorded, as summarized in Table 1, over a one-hour period. RESULTS AND DISCUSSION Radian recognized at the outset that this testing program posed several significant challenges to stable combustion. Primary among these was maintaining stable combustion with a low oxygen combustion air source simulating a diesel exhaust stream. Stable combustion would be further complicated by the fact that the afterburner would be fired under "reducing conditions," especially since achieving stable combustion with low oxygen concentrations is difficult even under oxidizing conditions. We knew that preheating the low oxygen stream, to simulate the temperature of diesel exhaust, would enhance the combustion characteristics. Diesel exhaust typically ranges from 700 to SOooF, and as such would increase the stability of the combustion in the afterburner. The temperature of the simulated exhaust gas stream used in the testing, however, was limited to a maximum of 400 to 500°F by the recycle fan's -4- |