【摘要】：隨著我國(guó)排放法規(guī)日趨嚴(yán)格,NOx排放限值不斷降低。柴油機(jī)僅依靠機(jī)內(nèi)凈化技術(shù)已不能滿足NOx排放要求,因此有必要采取機(jī)外控制措施。SCR技術(shù)是控制柴油機(jī)NOx排放的有效手段。法規(guī)要求SCR催化器的耐久性里程不得少于16萬(wàn)公里。針對(duì)法規(guī)要求,本文對(duì)SCR催化器的熱失活特性展開數(shù)值研究。基于反應(yīng)動(dòng)力學(xué)基本理論,結(jié)合NH3-SCR反應(yīng)機(jī)理、反應(yīng)速率模型、傳熱傳質(zhì)模型和儲(chǔ)放氨模型,建立了SCR催化器單孔道反應(yīng)動(dòng)力學(xué)模型。采用Fluent耦合Chemkin的技術(shù)路線,對(duì)孔道內(nèi)的多相催化反應(yīng)過(guò)程進(jìn)行模擬,得到NO濃度場(chǎng)和溫度場(chǎng)的分布規(guī)律,并進(jìn)行SCR催化器性能臺(tái)架試驗(yàn),試驗(yàn)結(jié)果表明轉(zhuǎn)化效率的仿真值與試驗(yàn)值一致性較好,驗(yàn)證了單孔道反應(yīng)動(dòng)力學(xué)模型。分析SCR催化器的老化形式,并從催化劑顆粒直徑和反應(yīng)速率變化的角度對(duì)催化劑熱失活特性進(jìn)行研究。基于反應(yīng)動(dòng)力學(xué)模型,考慮SCR催化劑相對(duì)活性的降低,建立SCR催化器熱失活動(dòng)力學(xué)模型。根據(jù)快速老化循環(huán),采用單孔道模型進(jìn)行催化器熱失活過(guò)程的數(shù)值模擬,得出催化器熱失活前后孔道內(nèi)的NO濃度場(chǎng)以及溫度場(chǎng)的分布規(guī)律,得出不同熱失活階段后催化劑相對(duì)活性、NO轉(zhuǎn)化效率以及催化器起燃特性的變化規(guī)律。為了研究催化劑相對(duì)活性沿載體徑向的變化情況,建立SCR催化器二維流動(dòng)模型,模擬載體入口處的溫度變化,并以載體不同徑向處的溫度為單孔道的初始條件計(jì)算催化劑的平均粒徑和相對(duì)活性變化。最后利用Matlab軟件計(jì)算出不同熱失活階段后催化劑平均顆粒直徑沿載體軸向截面的分布情況,得出載體的中心和前端熱失活最為嚴(yán)重。通過(guò)研究SCR催化劑老化機(jī)理,本文建立了SCR催化器老化的數(shù)值仿真方法,得出催化劑相對(duì)活性、NO轉(zhuǎn)化效率、起燃特性以及顆粒平均直徑等老化特性參數(shù)的變化規(guī)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.
【學(xué)位授予單位】：武漢理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：X734.2

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本文編號(hào)：2391091