一個二階靜電集塵器的PM2.5油煙去除效率的實驗及理論研究

Abstract

二階靜電集塵器廣泛的應用於餐廳做為廢氣處理設備，但其去除效率及理論模式卻鮮少受到檢視與探討。有鑒於此，本研究將對一台額定風量為1000 CFM的市售靜電集塵器進行測試，測試項目包括：不同風量下(4 CMM~30.75 CMM)的PM2.5收集效率、臭氧副產物的濃度及PM2.5收集效率隨時間的變化，及建立二階靜電集塵器收集效率的理論模式。 實驗結果顯示，當風量從4 CMM上升至30.75 CMM時，油煙微粒的質量中間氣動直徑(MMAD, mass median aerodynamic diameter)會由0.44 µm降至0.2 µm，PM2.5收集效率則由96.3 %降為43.9 %。此結果顯示收集效率隨著風量上升而下降，與該廠商聲稱的適用風量1000 CFM(28.32 CMM)有很大的落差。另外，在10 CMM的風量下，使用高濃度油煙微粒對靜電集塵器進行長時間的效率測試，產生總油煙微粒質量濃度為1609.3 µg/m3、質量中間氣動直徑為0.5 µm，累積使用141小時後，PM2.5的收集效率由91%降至61%，而總負載微粒重量為 104.7克。 為了建立二階靜電集塵器的收集效率模式，本研究將二階靜電集塵器視為充電端與收集端的串聯，分別計算各粒徑的油煙微粒在充電端與收集端的收集效率，再計算出二階靜電集塵器的總體收集效率。計算的結果顯示，二階靜電集塵器的總體收集效率會隨風量的上升而下降。將模式計算的結果與實驗的實測值進行比對，結果顯示在測試風量範圍中，最大誤差皆不大於10%，與實測值相當吻合。

Two-stage electrostatic precipitators (ESPs) are commonly used in restaurants as exhaust gas treatment equipment, but only few studies have investigated the theoretical and experimental collection efficiency. A commercial two-stage ESP was tested in this study. Test items include: collection efficiency of fine particles at different flow rates, concentration of ozone by-products, and changes of collection efficiency of fine particles with time. When increasing the flow rate from 4 CMM to 30.75 CMM, the mass median aerodynamic diameter (MMAD) of generated oil fume decreased from 0.44 µm to 0.2 µm and PM2.5 collection efficiency also decreased from 96.3 % to 43.9 %. A long time exposure test also conducted at the flow rate of 10 CMM in this study, after 141 hours of exposure, 104.7g of particles were collected in ESP and the corresponding PM2.5 collection efficiency decreased from 91 % to 61 %. In order to build the collection efficiency model, two-stage ESPs are seen as a series connection of ionizing section and collector section, and the collection efficiency of each part are calculated separately. According to the model result, collection efficiency of the two-stage ESP is inversely proportional to the operating flow rate. The model was compared with experimental data. Result shows that model can fit experimental data quite well, error at all operating flow rate is less than 10 %.