| OCR Text |
Show fuel nitrogen to N0X is shown in Figure 17. The first stage was operated at three levels of theoretical air (50, 60, and 70 percent) while the overall theoretical air was varied from 60 to 150 percent. With 50 percent first stage air, the oxidizable nitrogen levels ( EXN=HCN+NH3+N0) were relatively insensitive to the overall air with a weak minimum below 30 percent conversion around 100 percent theoretical air. When the primary was operated at a more optimum condition (60-70 percent theoretical air) the E XN decreased to below 10 percent. Other studies of fuel nitrogen conversion show that the level attainable is strongly dependent on the catalyst as well as the operating conditions. Low thermal N0X coupled with minimum fuel nitrogen conversions make catalytic combustion an attractive technique where very low emissions are required. Development of improved catalyst and auxiliary system components is in progress. These components will be integrated into several prototype systems for laboratory evaluation of the performance of catalytic combustion in various applications. Homogeneous Reduction. The homogeneous non-catalytic selective reduction of N0X with NH3 occurs in the presence of oxygen at temperatures around 1300K. The temperature window can be lowered by the addition of hydrogen. This technique is a proprietary process that has been evaluated in oil- and gas-fired systems both in the laboratory and in field operating boilers. N0X reductions from 40 to 60 percent have been reported for practical systems. The EPA has conducted an analysis of the potential applicability of the process as a supplement to combustion modification in coal-fired boilers. The system requires a manifold for injection of N^/^/carrier streams into the boiler volume at the appropriate temperature window (normally in the superheater region). Laboratory tests have shown 40-60 percent reduction in a coal-fired system using practical NH3 levels. The main problem areas are (a) achieving uniform injection; (b) maintaining the injection in the proper temperature window during load swings; (c) ammonium sulfate deposition on convective surfaces; and (d) significant capital and operating costs. The technique appears to be a potentially useful supplement to combustion modification in Air Quality Control Regions where very stringent control may be required. 3-47 47 |
