Experiments on the reduction of nitric oxide from exhaust gases by selective non-catalytic reactions

Abstract

The use of ammonia in a selective non-catalytic process for the removal of nitric oxide (NO) from exhaust gases was studied. A quartz lined flow reactor system was constructed in order to examine the behavior of the process with 15% oxygen. The simulated exhaust gas contained varying amounts of N2, 02, H20, CO, and NO and the reactor conditions were varied with regard to temperature, residence time, and mixing. The results of these experiments show that the effect of oxygen concentration and NH3 to NO ratio are very different from what was previously seen for low levels of oxygen (I to 5%). Increasing the oxygen concentration results in a lower maximum reduction of NO at a lower temperature. Varying the NH3 to NO ratio was found to have a much more pronounced effect on the reduction process for high oxygen levels than it did for low oxygen levels. As the ratio was increased, the maximum reduction increased and the temperature for reduction decreased. The addition of CO caused a slight decrease in the amount of maximum NO removal but caused the process to take place at progressively lower temperatures. Water was found to reduce the amount of NO removed but did not cause a change in the temperature for maximum reduction Several different mixing schemes were studied to determine if the results would be affected by the effects of mixing. The results of these tests show that mixing was complete in all cases and therefore not a concern when analyzing the data. A wide variety of residence times were examined which ranged from 2.11 to 0.14 sec. at 1050 K. Decreasing the residence time resulted in a shift of the reduction process to progressively higher temperatures for both the point of initiation and the point of maximum reduction.