防塵濾罐過濾品質探討

Abstract

研究就過濾品質觀點，探討職業衛生常見之防塵濾罐影響因素，研究透過單一纖維理論模擬計算濾材表面風速、濾材靜電密度、濾材纖維直徑、填充密度、厚度、濾材積重、濾材不均勻度等對濾材過濾品質、穿透率、與最易穿透粒徑之影響。研究也設計實驗，測試防塵濾罐常採用之摺疊方式對過濾品質之影響。 研究各項濾材影響因素帶入單一纖維理論，計算各項過濾幾制，求得不同微粒粒徑下之濾材性質，每次計算只更改一個變項，評估各項因素對濾材性質之影響。研究發現影響濾材過濾品質最大影響因素為過濾風速，要增加濾材過濾品質應該降低濾材表面風速及填充密度，而應該增加及濾材靜電密度及濾材纖維直徑。濾材穿透率隨著過濾風速及纖維直徑增加而增加，而隨著填充密度、厚度、靜電密度增加而降低，此影響趨勢與濾材過濾品質部份不相同，若不考慮通氣阻力，濾材製造商可降低纖維直徑及增加填充密度，來達到濾材低穿透率，但所增加之通氣阻力，使得濾材過濾品質下降。研究也發現，最易穿透粒徑(MPS)也會受到這些因素之影響，現階段各國測試規範都是設定特定粒徑微粒進行測試，就模擬中最易穿透粒徑變化情形來看，特定微粒粒徑測試結果並不能代表所有粒徑微粒之捕集效率。規劃未來呼吸防護具防塵濾罐測試規範時，應該更慎選測試微粒粒徑，也應該考慮未來可能發展之低濾材表面風速與高靜電密度濾材，如何進行測試與負載及儲存之管理，另也應考慮設定更嚴格的通氣阻力要求，讓呼吸防護具廠商更重視濾材過濾品質。 對於摺疊濾材研究採用單一一摺之摺疊濾材進行實際穿透率及通氣阻力量測，研究透過浸泡異丙醇方式及挑選相同通氣阻力之方式，降低濾材本身(含靜電密度)之的差異。實際測試結果顯示，通氣阻力量測部份證實與文獻之趨勢符合，摺疊濾材之穿透率及過濾品質與測試微粒粒徑及摺疊數都有關係，就現有研究對於過濾品質考慮之最佳摺疊數，約較最低通氣阻力之最佳摺疊數增加每公分0.5摺。研究中推測摺疊濾材中濾材表面風速並不均勻分布，因此造成摺疊濾材穿透率降低，特別是高摺疊數濾材。 研究已掌握濾材品質之各項影響因素之影響趨勢，可供防塵濾罐測試規範修訂之方向，也可提供濾材生產廠商努力方向之參考，但對於實際之影響係數與生產技術，則須更多實驗設計才能更精確掌握實際影響因素，例如濾材表面風速降低與濾材靜電密度增加是否有一定限制，而對於應用於防塵濾罐上，是否有其使用上限制與管理之要求，而防塵濾罐測試規範如何研擬，以及濾材廠商如何設計生產更高品質之防塵濾罐，都需更多研究或更多測試數據補強。

The filter quality of dust cartridge depends both on the collection efficiency of the filter material and the pressure drop across the filter, and is affected by the face velocity, fiber diameter, packing density, filter thickness, charge density, and homogeneous of the filter. The study used theoretical model to examine the filtration factors effect the penetration and filter quality. The study also used the experiment to measure the collection efficiency and the pressure drop of pleated dust cartridge. The study used theoretical model to measure the penetration and filter quality on each aerosol sizes depend on one filtration factors. The results showed the filter quality effects more significant with face velocity than the other mechanisms, the filter quality increase with face velocity decrease and charge density increase. The penetration increases with face velocity, fiber diameter increase, and packing density, thickness, charge density decrease. The most penetrating size increases with face velocity, fiber diameter increase, and packing density, thickness, charge density decrease. But for filter with no charge, the most penetrating size increases with face velocity decrease and doesn’t effect by thickness. The study of pleat filter fabricated six sizes of filter holders to hold just one pleat of filter, simulating six different pleat counts, ranging from 0.5 to 3.33 pleats per centimeter. The possible electrostatic charges on the filter were removed by dipped in isopropyl alcohol (IPA), and the air velocity is fixed at 100 centimeter per second. Liquid dicotylphthalate (DOP) particles generated by a constant output atomizer were used as challenge aerosols to minimize particle loading effects. A scanning mobility particle sizer (SMPS) was used to measure the challenge aerosol number concentrations and size distributions upstream and downstream of the pleated filter. The pressure drop across the filter was monitored by using a calibrated pressure transducer. The results showed that the performance of pleated filters depend on not only the size of particle but also the pleat count of the pleated filter. Based on filter quality factor, the Optimal pleat count (OPC) is always higher than that based on pressure drop by about 0.5 pleats per centimeter. From the aspect of filter quality factor, this study suggests that the respirator manufacturers should add about 0.5 pleats per centimeter to the OPC derived from the generalized correlation curve for pleated filter design based on minimum pressure drop.