| Selective non-catalytic reduction is a technology which has been widely used in utility boilers. However, this technology has inherent defects such as narrow reaction temperature window and causing secondary pollutants emission. During the denitration process of NOxOUT, a certain amount of N2O will be produced. N2O has a strong greenhouse effect and can lead to depletion of the ozone layer. Many researchers have paid attention to the aspect of how to inhibit N2O emission. Considerable N2O generates in the combustion process of fluidized bed and it also has a certain significance to study the emission performance of N2O in NOxOUT process.First, a basic experiment has been performed to study the effects of temperature, normalized stoichiometric ratio (NSR), oxygen concentration and residence time on NOxOUT denitration and secondary pollutants (N2O and CO) emission. The results show that the optimal reaction temperature is about950℃and N2O emission reaches20ppm when NSR equal to1.5. The production windows of N2O and CO are similar to reaction temperature window and their emission has presented respective variation trend with different influence factors.In addition, this paper has studied the effects of additives including sodium carbonate, sodium acetate, sodium glutamate and ethanol on denitration features of NOxOUT. The four additives can all improve the denitration efficiency of low temperature side and broaden the temperature window in different degrees. Among these additives, sodium glutamate can broaden it to1.83times of the primary temperature window. The effect of additive amount on denitration efficiency and production of N2O and CO is not only related to the types of additives but also is closely related to reaction temperature.To the complex reaction process of NOxOUT, modeling and calculation have been earried out using Chemkin software. It aims to study the effects of some factors including factors mentioned above and moisture content on denitration features. The results of modeling and experiment accord with each other well. Through appending the reaction subset of sodium salt to the file of reaction mechanism, the effects of sodium carbonate and CO on denitration features can be understood using modeling and the function characteristics of them can be investigated base on the experiment results.Finally, the modeling is divided into three parts considering the existing of a certain amount of N2O in the flue gas of coal combustion in fluidized bed. First, the denitration feature of initial flue gas including N2O has been studied through modeling and calculation. Second, the effects of additives on denitration features of initial flue gas including N2O and simultaneously including N2O and CO have been analyzed through modeling. The results show that the existing of N2O has little effect on denitration efficiency and N2O emission in the range from800℃to900℃. Adding Sodium carbonate leads to lower denitration efficiency at the temperature of950℃, but the extent is less than5%. N2O emission can be remarkably reduced with30ppm Sodium carbonate. Adding CO can increase N2O emission and it is positively associated with CO concentration. Through modeling and analysis, it can offer theoretical guidance for SNCR process of fluidized bed in order to achieve the goal of high denitration efficiency and low N2O emission... |
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