Selective non-catalytic reduction of nitrogen oxides by ammonia: Experiments and model calculations.

摘要

The DeNOx process (SNCR of NOx by NH3) was investigated experimentally and numerically. The experiments were conducted by using simulated exhaust gases in a well-defined laminar reactor facility over the temperature range from 850 K to 1350 K (Chapter 5). Established chemical kinetic programs were utilized for the model calculations, including sensitivity analysis to identify the reaction pathways (Chapter 6).; When the beta-ratio (the molar ratio of NH3 to NOx ) was greater than about 1.5, more than 80% of NOx could be removed (Chapter 7). The existing model for the experimental system was improved in two major ways. First, the radial velocity profile was included as opposed to the use of a constant velocity (plug flow). Second, the gas temperatures before and after the center region of the reactor were included. These two improvements resulted in closer agreements with the experiments than the calculations limited to only the major reacting zone (Chapter 8).; For the base conditions of 670-ppm NH3, 325-ppm NO, and 10-ppm of NO2, the NOx removals were determined as functions of the residence time (up to 1527.8/T sec) and the initial levels of O2 (up to 15.0%), CO (up to 1260 ppm), and H2O. The maximum NOx removals occurred at lower temperatures with the increase of the residence time, and the levels O2 and CO, while the effects of H2O (up to about 8%) were insignificant on the NO x removals. In general, the maximum NOx removals were above about 80% at around 1200 +/- 150 K for the current conditions (Chapter 9). The decrease of TDeNOx (the temperature for the maximum NOx removals) due to the increase of the residence time and the O2 levels could be related to simple exponential (logarithmic) functions, while the increase of CO resulted in the linear deductions of TDeNOx (Chapter 10).; Compared to the experiments, the predictions from the currently utilized DeNOx mechanisms showed significant discrepancies for TDeNOx and the formed concentrations of N2O at certain conditions (especially, for the given O2 levels). Possible weaknesses of the current mechanisms were suggested with the identified NO x removal pathways through sensitivity analysis (Chapter 11).