可凝結性微粒產生器之研發

Abstract

美國環保署公告的可凝結性微粒(Condensable particulate matter, CPM)採樣方法有兩種，分別為乾式衝擊瓶法(Method202)及稀釋法(EPA CTM-039)，許多研究發現乾式衝擊瓶法易與煙氣內可溶性氣體(例如SO2)反應，導致採樣結果高估；稀釋法被認為能更準確地量測CPM排放量，因為它們較能模擬大氣中顆粒形成的過程。然而，CPM量測方法可能受到煙氣特性、採樣程序和樣品回收效率的影響。為了比較兩種方法，需一可控且穩定的CPM產生源。然而，一般煙囪中CPM不僅不穩定且無法預測，煙道內CPM的含量可能會受到煙道溫度、濕度或燃料物質的影響。因此，本研究的目的是設計一CPM產生器，可以穩定的產生已知成分、濃度的CPM。透過此CPM產生器比較乾式衝擊瓶法和稀釋法，評估影響CPM測量的因素，以提高CPM量測方法的準確性。 本研究分別使用兩種方式產生CPM：蒸發型、氣化型。蒸發型為透過載流氣體吹拂過加熱液體之表面，攜出蒸氣之方式產生CPM，其缺點為無法準確預估所產生之CPM蒸汽，且長期使用產生器尚有物質氧化之問題。氣化型則透過將液體注入稀釋氣體中並加熱至沸點之方式產生CPM，產生系統使用一段時間後，加熱棒表面有物質加熱氣化成蒸氣殘留之不純物、氧化物導致加熱棒表面特性改變，進而使產生系統不穩定。綜合上述優缺點設計一改良式蒸發型CPM產生器，透過注射泵將溶液注入超音波霧化器將液體霧化成更小的液滴，透過這個方式來增加加熱蒸發之速率。此外，硬脂酸微粒相較於石蠟更能提供穩定的微粒產生。整個產生及採樣系統在未加熱之狀態下，載流氣體為10 L/min、溶液推進速度為0.1 ml/min時，微粒損失低於1%。此實驗系統可透過調整加熱溫度控制FPM及CPM之產生比率，而此系統在溶液濃度為1.5 mg/ml、推進速度為0.1 ml/min，載流氣體為10 L/min、加熱溫度為255oC下，最高可產生97%的CPM。CPM採樣部分，第二段屏蔽流為5 L/min下有最低之損失量(20%)，未來研究可透過管道淋洗的方式，增加CPM的回收率。

There are two condensable particulate matter sampling methods announced by the US Environmental Protection Agency, which are the dry impinger method (Method202) and the dilution method (EPA CTM-039). Many studies have found that the dry impinger method would over estimate CPM concentration because of the soluble gas (SO2) in stack. Dilution method was thought have more accurately represent CPM emissions because they are more simulate the natural physicochemical processes of particulate formation in the atmosphere. However, CPM measurement methods may be affected by flue gas characteristics, sampling procedures and sample recovery efficiency. In order to compared two methods, we should have a controllable, stable CPM generating source. But general CPM amount in stack is unpredictable and unstable and its sampling amount may affect by flue gas temperature, humidity or material of the fuel in stack. Therefore, the aim of this study is design a CPM generator which can produce known composition, concentration and long-term stability CPM. Through this CPM generator to compare condensation and dilution CPM methods measurement amount and evaluate the factors affecting CPM measurements to improve the accuracy of the CPM methods. This study uses two methods to generate CPM such as evaporation and vaporization. The evaporative type generates CPM by blowing the carrier gas over the surface of the heated liquid and carrying out steam. However, it is impossible to accurately estimate the CPM steam, and there is still a problem of material oxidation if using the generator for a long time. The vaporization type generates CPM by injecting liquid on heating rod which reached the boiling point and use carrier gas to carry out steam. After the generation system is used for a period of time, the surface of the heating rod is heated and vaporized into impurities and oxides remaining in the vapor, which causes the surface characteristics of the heating rod to change. Make the production system unstable. Based on the above advantages and disadvantages, an improved evaporative CPM generator is designed. The solution is injected into the ultrasonic atomizer through a syringe pump to atomize the liquid into smaller droplets. This method increases the rate of evaporation. In addition, stearic acid particles provide more stable particle production than paraffin wax. When the entire generation and sampling system is unheated, the carrier gas is 10 L/min and the feeding rate is 0.1 ml/min, the particle loss is less than 1%. This experimental system can control the generation ratio of FPM and CPM by adjusting the heating temperature. As solution concentration is 1.5 mg/ml, feeding rate is 0.1 ml/min, carrier gas is 10 L/min, and heating temperature is 255oC , can produce up to 97% CPM. As the CPM sampling methods, the second shields flow has the lowest loss (20%) at 5 L/min. In the future, people can increase the recovery ratio of CPM by rinsing the whole sampling train.