| OCR Text |
Show magnitude higher than for high level enrichment. This demonstrates that oxygen-fuel can produce less NOx than air-fuel under the proper conditions. INDUSTRIAL EXPERIENCE One of the problems with comparing field test data is that the operating conditions are usually very different. For instance, furnace air infiltration, burner type, furnace wall temperature profiles, and amount of nitrogen in the natural gas can all vary. Therefore, the applications will be discussed in general terms to show the effects of oxygen on NOx emissions. Two examples in different industries confirm that low level oxygen enrichment can increase NOx. In a waste-to-energy facility using a waterwall combustor, 2% enrichment of the combustion air increased NOx by 25%. In a container glass furnace, 2% enrichment increased NOx emissions over 50%. Since the glass furnace operates at much higher temperatures than the waterwall combustor, the NOx emissions were more adversely affected for the same level of enrichment. Most combustion systems are run with some level of excess air to ensure complete combustion and minimize CO emissions. In the glass furnace, a second trial showed that NOx emissions could actually be reduced 15% using 2% 02 enrichment by lowering the excess air from 3% to 1.5% without affecting the CO emissions. An application in the metals industry demonstrated that low NOx can be achieved by using oxygen instead of air for combustion. In a small, well-sealed forge furnace using an oxygen-fuel burner, NOx emissions were almost identical to the low levels measured ln the lab (shown in Figures 9 and 10). In a different glass application, NOx was reduced by almost 80% after the air-fuel system was replaced by oxygen-fuel. CONCLUSIONS The theoretical, laboratory, and field data all showed that NOx increases using low level oxygen enrichment when furnace air infiltration was excluded. One application showed that NOx could be reduced with low level enrichment if less excess air could be used while maintaining acceptable CO emissions. The data also showed that NOx emissions could be dramatically reduced by replacing air with pure oxygen. This is a significant conclusion since the combustion community previously expected NOx to increase due to the high flame temperatures. Therefore NOx reduction can be added to the many other benefits of oxygen. Oxygen-fuel combustion provides an attractive, low-cost, alternative to other currently available NOx control techniques. 1990 AFRC Symposium -9- October 1990 |
