Kinetic modeling of nitric oxide removal from exhaust gases by Selective Non-Catalytic Reduction

Abstract

Selective Non-Catalytic Reduction is one of the most promising techniques for the removal of oxides of nitrogen from combustion exhaust gases. These techniques are based on the injection of certain compounds, such as cyanuric acid and ammonia, into hot exhaust gases. The oldest and most well researched is the thermal DeNOx process where ammonia is injected as an additive to remove nitric oxide from the exhaust. The most recent technique, the RAPRENOx process involves the use of cyanuric acid as an additive. The thermal DeNOx process was studied using the detailed chemical mechanism developed at Sandia National Laboratories. For the RAPRENOx process, a chemical mechanism has been developed to match the available experimental data. The influence of physical effects on the RAPRENOx process were also evaluated. The modeling results from the calculations compare favorably with experimental data collected for a wide range of exhaust gas compositions and operating conditions. The modeling results for increased pressure predict a wider temperature range at which significant nitric oxide can be removed and also in the case of RAPRENOx process the levels of N20 (a by-product in the case of the RAPRENOx process) are significantly lower. The accounting of mixing effects, non uniform temperature profile into the modeling the process does not help the overall modeling effort. The process of NO removal is best explained as a process controlled by gas phase chemistry. The uncertainty with regard to the cyanuric acid decomposition into isocyanic acid has to experimentally studied along with high pressure results.