一個濕式靜電旋風集塵器模組的測試研究

Abstract

傳統旋風集塵器對於次微米以下之微粒收集效率不高，乾式旋風靜電集塵器可靠離心力來去除氣 動直徑在5-10 m 以上的微粒，而5-10 m 以下的微粒則靠靜電力去除，可改進傳統旋風器之缺點。 但是乾式旋風靜電集塵器會有粉塵微粒累積於旋風器壁面及放電電極時導致收集效率降低的問題，除 非有敲擊的機構設計，否則無法長期操作。本計劃擬設計並製造一個濕式靜電旋風集塵器的模組，旋 風器圓柱部分的內徑為40cm，其放電電極是由數個裝在中空電極棒的圓盤所組成，各圓盤電極的最外 緣呈尖銳狀（尖端的直徑約為100μm）且與旋風器壁面均保持同一距離，用於電暈放電及微粒充電及 靜電移除之用。另外利用旋風器入口噴入細水滴(梭特直徑約為50~200 m)以增加水滴的電場充電 量，水滴受離心力及靜電力的作用，將會徑向飄移至旋風器壁面形成水膜，並可連續清洗旋風器壁面 累積的粉塵至下方的漏斗中，在飄移過程中水滴也會與微粒接觸而增加微粒的去除效果。為了解決圓 盤電極粉塵累積問題，在靠圓盤電極周圍的中空電極棒上設計了小槽孔，可以利用脈衝氣流對圓盤放 電尖端做定期的粉塵清除。預期本研究設計的濕式靜電旋風集塵器，可解決一般乾式靜電旋風集塵器 在處理高濃度粉塵時因粉塵累積造成效率降低的問題。 在研究期程內，我們會先完成一個濕式靜電旋風集塵器的模組設計及製造，氣體處理流量為 200~1000 L/min，接著再完成實驗室的低濃度氣膠及高濃度碳煙的長期去除效率測試，探討設計參數 與操作條件對收集效率的影響，並完成高科技業的一個細微粒排氣的模廠測試。預計本研究完成之 後，可以大幅提升合作廠商在空污防制設備的競爭能力。

The submicron particle collection efficiency of traditional cyclones is not high. Dry-type electrocyclones have the advantage that particles greater than 5-10 m in aerodynamic diameter can be removed by centrifugal force while those smaller than 5-10 m can be removed by electrostatic force. However, the collection efficiency will drop when dust particles accumulate on the wall of the cyclone and the discharge electrodes. Therefore, it can't operate continuously unless the design incorporates the rapping mechanism. This project intends to design and make a pilot-scale electrocyclone with the inner diameter of 40 cm in the cylindrical part. The discharge electrodes consist of several circular discs installed on the hollow electric rod for particle charging and removal. The discs have sharp edges (diameter at the edge: 100 m) at the rim whose distances to the cyclone wall are kept the same. Fine water mist with the Sauter diameter of 50 to 200 m is sprayed in the cyclone inlet and the droplets acquire charges by field charging mechanism. The water droplets will be drifted in the radial direction to the cyclone wall by both electrostatic and centrifugal forces forming uniform water film which cleans the accumulated dust on the wall continuously into the hopper down below. During the drifting process, particles are contacted with water droplets and the removal efficiency of particles is therefore enhanced. To remove dust particles accumulated on the discharge discs, there is a small slot on the central rod near each disc which allows the use of pulse-jet air to clean the tips of the discs continuously. It is expected that the present wet electrocyclone is able to resolve dust accumulation problem which leads to the reduction of collection efficiency in traditional dry-type electrocyclones. During the project period, a pilot-scale wet electocyclone will be designed and manufactured with the gas flow rate of 200~1000 L/min. Then the short-term and long-term collection efficiency tests for low concentration aerosols and high concentration soot particles, respectively, will be conducted to investigate the influence of design parameters and operating conditions. Finally the field pilot test will be conducted in an exhaust gas containing fine particles in the high-tech industry. It is expected the competitiveness of the cooperating company for the air pollution control devices will be greatly enhanced after the completion of the project.