基于CFD模拟的臭氧低温氧化烧结烟气中NO过程分析

CFD simulation of low-temperature NO oxidation using ozone in sintering flue gas

以256 m2烧结机O3氧化烧结烟气中NO过程为研究对象,采用CFD数值模拟方法考察了含O3喷射气体与烧结烟气流动及NO低温氧化特性。通过与76步复杂反应机理的对比验证了11步简化机理的适用性,分析了反应温度、O3/NO摩尔比以及O3分布特性对NO氧化效率和不同价态NOx转化率的影响规律。通过对简单结构反应器的模拟结果表明:NO3稳定性较差,烟道内主要氧化产物为NO2与N2O5;随反应温度升高,NO氧化效率基本保持不变,NO2转化率提高且提升速率逐渐增大而N2O5呈相反规律;随O3/NO摩尔比增大,NO氧化效率提高但提升速率逐渐减小,NO2转化率先增大后在摩尔比高于1.25时开始减小,而各工况均产生N2O5且生成量逐渐增大,其原因为射流核心区可提供高O3/NO摩尔比条件;通过优化O3分布器结构改善O3与烟气接触与混合条件,O3与NO摩尔比为1.0、停留时间为0.87 s时NO氧化率可提高约12.8%,摩尔比为2.0、停留时间为1.73 s时N2O5转化率可提高约15.6%。

The flue gas from a 256 m2sintering machine was selected to explore the characteristics of NO oxidized by ozone at low temperature.The flow characteristics of O3injection gas and sintering flue gas and NO oxidation characteristics were investigated by CFD numerical simulation method.By compared with 76-step complex reaction mechanism,11-step simplified mechanism was verified to be reasonable for the above process.The effects of process conditions,including reaction temperature,O3/NO molar ratio and O3distribution,on the conversion rates of NOxwith different chemical valences were examined.The results from the simulation for the reactor,which is simple in structure,show that NO2and N2O5are the main oxidation products in the flue gas,whilst NO3is consumed due to its poor chemical stability.The oxidation efficiency of NO changes little with the increase of reaction temperature,the conversion rate of NO2increases and performs more significant change at higher temperature.However,the conversion rate of N2O5presents an opposite trend compared with that of NO2.With the raise of O3/NO molar ratio,the oxidation rate of NO increases slowly and that of NO2increases firstly and then decreases when the molar ratio higher than 1.25,while N2O5emerges in the condition even the O3/NO molar ratio less than 1.0 and the N2O5production increases gradually,resulting from a higher O3/NO ratio in the injection core regions.Furthermore,the structural optimization for the ozone distributor could improve the homogeneity of O3in the sintering flue gas.Afterwards the oxidation efficiency of NO increases by 12.8%approximately when the O3/NO molar ratio is 1.0 and the average residence time is 0.87 s,while the increase for N2O5conversion rate of about 15.6%was obtained when the O3/NO molar ratio is 2.0 and the average residence time is 1.73 s.