以選擇性摧化還原法去除氮氧化物之模式探討

Abstract

本研究藉由質量平衡法， 建立一能完整描述 SCR 反應器內的擴散 效應與壁面觸媒化學反應的數值模式， 並以文獻中不同形式之 SCR 觸媒 在不同條件下之實驗值，對模式中 NH3吸附常數 (KNH3) 及表面化學反應 常數 (Ks) 作分析， 並應用此觸媒特性參數預測 SCR 性能，結果驗證本 研究所發展之模式能正確預測 NO 的去除效率。再將此模式經敏感度分析 後，可知 SCR 方法中的溫度控制、NO 去除效率、反應器開口大小、流量 、表面反應速率常數對反應器大小的設計影響性較大， 而 NH3 的擴散性 、NO 進流濃度及 NH3 吸附常數的影響性則較小。 此外對 SCR 反應器， 可經由效率因子法完整的分析其控制因子，結果顯示 SCR反應器的控制因 子是由反應器的開口大小、壁面觸媒厚度、觸媒化學反應性及溫度共同決 定，而經由控制因子的判定，可提供 SCR 方法之改善方向。最後，再經 由流場與 NH3 擴散性的簡化， 求得二維模式之解析解， 以使 SCR 設計 模式有更廣的適用性。 This study developed a numerical model based on mass transfer theory todescribe the diffusional process and the surface catalytic chemical reactionlimitations in the SCR reactor. Experimental data of SCR performance employingdifferent types of catalysts were taken from the literature and analyzed fortheir NH3 adsorption constant and surface rate constant. The catalystscharacteristics are then used for the prediction of their SCR performance. Goodagreement is obtained between model results and experimental observations on theNO removals. Sensitivity analysis was performed and the temperature, NO removalefficiency, channel pitch, gas flow rate and surface rate constant are found tobe important parameters in the design of the SCR reactor. In addition, theeffective factors were used to analyze the relative importance of externaldiffusion, internal pore diffusion and chemical reaction. By varying the channelpitch, wall thickness, chemical reactive property of the catalyst and theoperation temp erature, the SCR performance can be improved. Finally, byassuming the flow pattern to be plug-flow and to neglect the NH3 diffusion, ananalytical solution was obtained for the two-dimensional model, therefore thedesign procedure can be simplified and the SCR design model has a widerapplicability.