Urea-SCR催化器热失活特性数值仿真
发布时间：2018-12-25 12:07
【摘要】：随着我国排放法规日趋严格,NOx排放限值不断降低。柴油机仅依靠机内净化技术已不能满足NOx排放要求,因此有必要采取机外控制措施。SCR技术是控制柴油机NOx排放的有效手段。法规要求SCR催化器的耐久性里程不得少于16万公里。针对法规要求,本文对SCR催化器的热失活特性展开数值研究。基于反应动力学基本理论,结合NH3-SCR反应机理、反应速率模型、传热传质模型和储放氨模型,建立了SCR催化器单孔道反应动力学模型。采用Fluent耦合Chemkin的技术路线,对孔道内的多相催化反应过程进行模拟,得到NO浓度场和温度场的分布规律,并进行SCR催化器性能台架试验,试验结果表明转化效率的仿真值与试验值一致性较好,验证了单孔道反应动力学模型。分析SCR催化器的老化形式,并从催化剂颗粒直径和反应速率变化的角度对催化剂热失活特性进行研究。基于反应动力学模型,考虑SCR催化剂相对活性的降低,建立SCR催化器热失活动力学模型。根据快速老化循环,采用单孔道模型进行催化器热失活过程的数值模拟,得出催化器热失活前后孔道内的NO浓度场以及温度场的分布规律,得出不同热失活阶段后催化剂相对活性、NO转化效率以及催化器起燃特性的变化规律。为了研究催化剂相对活性沿载体径向的变化情况,建立SCR催化器二维流动模型,模拟载体入口处的温度变化,并以载体不同径向处的温度为单孔道的初始条件计算催化剂的平均粒径和相对活性变化。最后利用Matlab软件计算出不同热失活阶段后催化剂平均颗粒直径沿载体轴向截面的分布情况,得出载体的中心和前端热失活最为严重。通过研究SCR催化剂老化机理,本文建立了SCR催化器老化的数值仿真方法,得出催化剂相对活性、NO转化效率、起燃特性以及颗粒平均直径等老化特性参数的变化规律。
[Abstract]:With the increasingly stringent emission regulations in China, the emission limit of NOx is decreasing. Diesel engine can not meet the requirements of NOx emission only by means of in-engine purification technology, so it is necessary to take external control measures. SCR technology is an effective means to control diesel engine NOx emissions. The regulations require that the durability mileage of SCR catalytic converters shall not be less than 160000 km. The thermal deactivation characteristics of SCR catalytic converters are studied numerically. Based on the basic theory of reaction kinetics, combined with the reaction mechanism of NH3-SCR, reaction rate model, heat and mass transfer model and ammonia storage model, the kinetic model of single pore channel reaction of SCR catalytic converter was established. The multiphase catalytic reaction process in the pore channel was simulated by Fluent coupled Chemkin technique, the distribution of NO concentration field and temperature field was obtained, and the performance of SCR catalytic converter was tested by bench test. The experimental results show that the simulation value of conversion efficiency is in good agreement with the experimental value, and the kinetic model of single-pore channel reaction is verified. The aging forms of SCR catalytic converters were analyzed, and the characteristics of thermal deactivation of the catalysts were studied from the point of view of the change of catalyst particle diameter and reaction rate. Based on the kinetic model of the reaction, considering the decrease of the relative activity of SCR catalyst, the kinetic model of thermal deactivation of SCR catalyst was established. According to the rapid aging cycle, the single pore model is used to simulate the thermal inactivation process of catalytic converter. The distribution of NO concentration field and temperature field in the channel before and after thermal deactivation of catalytic converter are obtained. The relative activity of catalyst, the conversion efficiency of NO and the characteristics of ignition of catalyst were obtained after different thermal deactivation stages. In order to study the variation of the relative activity of the catalyst along the radial direction of the carrier, a two-dimensional flow model of SCR catalyst was established to simulate the temperature change at the inlet of the carrier. The average particle size and the relative activity of the catalyst were calculated by using the temperature at different radial points as the initial condition of the single channel. Finally, the distribution of the average particle diameter along the axial section of the carrier was calculated by using Matlab software. The results show that the center and front end of the support are the most serious thermal deactivation. Based on the study of aging mechanism of SCR catalyst, a numerical simulation method for aging of SCR catalyst was established, and the change rules of aging characteristic parameters such as relative activity of catalyst, conversion efficiency of NO, ignition characteristics and average particle diameter were obtained.
【学位授予单位】：武汉理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X734.2
本文编号：2391091
[Abstract]:With the increasingly stringent emission regulations in China, the emission limit of NOx is decreasing. Diesel engine can not meet the requirements of NOx emission only by means of in-engine purification technology, so it is necessary to take external control measures. SCR technology is an effective means to control diesel engine NOx emissions. The regulations require that the durability mileage of SCR catalytic converters shall not be less than 160000 km. The thermal deactivation characteristics of SCR catalytic converters are studied numerically. Based on the basic theory of reaction kinetics, combined with the reaction mechanism of NH3-SCR, reaction rate model, heat and mass transfer model and ammonia storage model, the kinetic model of single pore channel reaction of SCR catalytic converter was established. The multiphase catalytic reaction process in the pore channel was simulated by Fluent coupled Chemkin technique, the distribution of NO concentration field and temperature field was obtained, and the performance of SCR catalytic converter was tested by bench test. The experimental results show that the simulation value of conversion efficiency is in good agreement with the experimental value, and the kinetic model of single-pore channel reaction is verified. The aging forms of SCR catalytic converters were analyzed, and the characteristics of thermal deactivation of the catalysts were studied from the point of view of the change of catalyst particle diameter and reaction rate. Based on the kinetic model of the reaction, considering the decrease of the relative activity of SCR catalyst, the kinetic model of thermal deactivation of SCR catalyst was established. According to the rapid aging cycle, the single pore model is used to simulate the thermal inactivation process of catalytic converter. The distribution of NO concentration field and temperature field in the channel before and after thermal deactivation of catalytic converter are obtained. The relative activity of catalyst, the conversion efficiency of NO and the characteristics of ignition of catalyst were obtained after different thermal deactivation stages. In order to study the variation of the relative activity of the catalyst along the radial direction of the carrier, a two-dimensional flow model of SCR catalyst was established to simulate the temperature change at the inlet of the carrier. The average particle size and the relative activity of the catalyst were calculated by using the temperature at different radial points as the initial condition of the single channel. Finally, the distribution of the average particle diameter along the axial section of the carrier was calculated by using Matlab software. The results show that the center and front end of the support are the most serious thermal deactivation. Based on the study of aging mechanism of SCR catalyst, a numerical simulation method for aging of SCR catalyst was established, and the change rules of aging characteristic parameters such as relative activity of catalyst, conversion efficiency of NO, ignition characteristics and average particle diameter were obtained.
【学位授予单位】：武汉理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X734.2
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