Study On The Effect Of Fly Ash And Additives On The Removal Of NO And N₂O

Nitrogen oxide is an important part of the polluting gases in Coal-fired power plants. Selective non-catalytic reduction?SNCR? is a system used for the reduction of NO with NH₃. It is simple, low cost, suitable for low concentration of nitrogen oxides, and can easily compatible with other denitrification technologies, or may not meet the increasingly stringent emission standards. Compared to other combustion condition, SNCR technology has a good application prospect in fluidized bed boiler system due to its lower production of NO_X. It is found that denitrification efficiency is still low by SNCR in fluidized bed boiler and the difference is great, the influence on the reduction of N₂O in SNCR is not clear. Researchs found that sodium salt and oxidation can increase the NO_X reduction ratio in SNCR process, but these studies did not take the actual situation of the flue gas into account adequately. In order to provide a reference for the development of SNCR technology to enhance the reduction of both N₂O and NO, the influence of fly ash and additives on SNCR process and N₂O decomposition is studied in the actual flue gas environment.First, this paper studied the effect on the oxidation of NH₃ by fly ash and additives. It turns out that the fly ash and additives both can enhance the reaction activity of NH₃. Additives in the reactor can produce a large number of OH active groups, the active metal oxides in fly ash, such as CaO and Fe₂O₃, make NH₃ more active by reducing the activation of NH₃ oxidation reaction.Then, experiments on the influence of additives and fly ash in SNCR process show that, at low temperature?less than 800??, additives promote NH₃ and OH reaction by producing a lot of OH, the NO_X reduction ratio increased, and make the optimum denitration temperature lower. Fly ash can reduce NH₃ reaction activity, denitrification rate improved. With the increase of temperature, the NH₃ and O₂ reaction rate is gradually accelerated, therefore, the fly ash has a significant inhibitory effect on the denitrification at high-temperature stage?above 900 ??. Experiments about the effect of oxygen concentration on the denitrification efficiency show that appropriate oxygen is necessary, denitrification rate is promoted as oxygen concentration increased from 2% to 6% when the temperature is less than 900?, but above 900?, the situation is reverse.Finally, this paper studies the effects on the thermal decomposition of N₂O by fly ash and additive. The results show that fly ash and can promote thermal decomposition of N₂O within the range of experimental temperature. H and OH groups produced by additives play an important role in the thermal decomposition of N₂O while fly ash may reduce activation energy of N₂O decomposition. Besides, fly ash behaved catalytic effect for the reactions of N₂O reduction with NH₃, so the conversion rate of N₂O was obviously increased at lower temperature.The results also show that the increase of O₂ concentration is harmful to the transformation of N₂O.Overall, the study shows that fly ash has great effect on the removal of NO, N₂O and N₂O thermal catalytic decomposition?with NH₃?, and the concentration of N₂O and NO decreased in low temperature. So, the simultaneous removal of NO and N₂O can be achieved when there is reasonable use of fly ash and additives in the appropriate temperature.