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標題: | 靜電集塵器集塵效率的數值模擬 Numerical Study of the Collection Efficiency of an Electrostatic Precipitator |
作者: | Jui-Hung Ma 馬瑞鴻 |
指導教授: | 李雨(U Lei) |
關鍵字: | 靜電集塵器,單向耦合,二維數值模擬,微粒運動軌跡,集塵效率, Electrostatic precipitator,One-way coupling,Two-dimensional numerical analysis,Particle trajectories,Particle collection efficiency, |
出版年 : | 2020 |
學位: | 碩士 |
摘要: | 靜電集塵器是控制流體中懸浮微粒排放的一項主要設備,其藉由電暈放電使微粒帶電後,再利用靜電吸引將帶電微粒自氣流中抽離並收集於集塵板上。集塵效率就是“收集到的微粒”與“進入到集塵器的微粒”的比率,其與微粒的運動軌跡有直接關連;因此了解微粒的運動有助設計優化的集塵器。但微粒的運動受集塵器內紊流場及電場影響、並不易進行實驗,故本文以數值方法進行分析。因為粒子屬稀薄懸浮狀態、且帶電粒子所產生的電場遠小於放電極電壓所產生者,所以在流場、電場及微粒運動三項物理現象中,我們假設微粒運動不影響電場和流場、及流場不影響電場。在此等單向耦合的前提下,我們以COMSOL Multiphysics軟體建立靜電集塵器內二維數值模型,去分析集塵器內平均紊流流場、電場、電暈放電及微粒充電、和微粒運動軌跡,並進而計算集塵效率。電位分佈及集塵效率的模擬結果經與文獻中的實驗數據驗證無誤後,我們進行了工作電壓、出口煙氣流速、微粒粒徑、放電極直徑等參數分析,並研究了交錯電棒佈放效應、及進口側風效應。就所模擬的集塵器單元(一公尺長度)而言,在固定幾何參數下,隨著工作電壓的增高、煙氣流速的下降、及放電極直徑的減少,各粒徑微粒的集塵效率均會上升;但在正常工作電壓(35 – 55 kV)、出口煙氣流速(0.5 – 2 m/s)、及放電極直徑(1 – 3 mm)下,介於0.01µm至1µm的微粒,其集塵效率均未達100%,而以約0.1µm微粒的集塵效率最差。然而計算結果也顯示,採用“交錯放電極佈放方式、及加入進口側風”(稱之為改良設計)均有助提升0.01µm至1µm微粒的集塵效果。以電廠為例,如要將排氣中的所有微粒在集塵器出口處降至低於其在進口處的0.01%,需要串連37個原設計的“集塵器單元”才可達成;但如採用改良設計,則只需17個集塵器單元。 Electrostatic precipitator is a key device for removing suspended particles from a fluid stream; particles were charged through corona discharge, and then removed from the gas stream through the electrostatic Coulomb force. The collection efficiency, the ratio of “the numbers of the particles collected” to “the numbers of the inlet particles”, is strongly related to the particle trajectories; and the understanding of the particle motion is crucial for designing a better precipitator. However, the particle motion depends on the turbulent flow field and electric field, it cannot be assessed easily through experiment, and thus will be studied numerically in this thesis. As the particles are dilute suspended, and the electric field associated with the charged particles is much less than that associated with the imposed high voltage at the discharged electrodes, it is assumed that the particle motion has no effect on both the flow and electric fields, and the flow field has no effect on the electric field. Under such a one-way coupling assumption, we built up a two-dimensional model for the physics inside the electrostatic precipitator via the aid of the commercial software “COMSOL Multiphysics”, and apply it to study the turbulent flow field, the electric field, the corona discharge and the particle charging, the particle motion, and finally the collection efficiency. After the validation of the calculation through comparing with the existing experimental data for both the electric potential and the collection efficiency in the literature, we performed a detailed parametric study, including working voltage, inlet gas speed, particle diameter, discharged electrode diameter, staggered arrangement of discharged electrodes, and inlet side wind effect. For a given electrostatic precipitator unit (1 m in length) with given geometry, the collection efficiency increases as the working voltage increases, as the inlet gas speed decreases, and as the discharged electrode diameter decreases. The collection efficiency cannot reach 100% for particles between 0.01 – 1 µm, and is worst around 0.1 µm, for normal working voltages (35 – 55 kV), inlet gas speeds (0.5 – 2 m/s) and discharged electrode diameter (1 – 3 mm). However, the collection efficiency can be improved for those particles using staggered arrangement of discharged electrodes and imposing an inlet side wind (called the modified design). For a typical electrostatic precipitator in power plant, if the particle concentration at the exit is required to be less than 0.01% of that at the inlet, 37 electrostatic precipitator units in serial are required for the original design, but only 17 units are needed for the modified design |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/17777 |
DOI: | 10.6342/NTU202003375 |
全文授權: | 未授權 |
顯示於系所單位: | 應用力學研究所 |
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