高效率文氏洗滌器之測試研究

Abstract

本研究利用高溫飽和蒸氣混合常溫廢氣，使廢氣中之次微米微粒與水蒸氣混合增長，再以文氏洗滌器去除增長之微粒，研究中所測試的微粒分別為氯化鈉、二氧化矽及油酸三種。利用異相核凝的原理，提高洗滌器之去除效率，並考量系統壓降，期望能在低壓降下達高去除效率的目的。 測試去除細微粒用的高效率文氏洗滌器系統，此系統由於廢氣與蒸氣混合的方式不同而分為系統一及系統二。系統一之設計為廢氣與蒸氣先混和後，廢氣推動蒸氣進入文氏洗滌器；系統二之設計則是將廢氣由文氏管上方之左側引入，蒸氣由文氏管上方之右端入流，廢氣與蒸氣在文氏管上端混合後再一起進入文氏洗滌器。實驗中操作條件為廢氣氣流量Q=200、250及300 lpm，液體-氣體混合比L/G=1.5、2及2.5 l/m3。由實驗結果可知，傳統的文氏洗滌器在氣流量低、壓力降低的情況下，去除效率差，而高效率文氏洗滌器的去除效率已有改善。其中系統二因廢氣與蒸氣混合較好，去除效率較系統一大幅提昇。 以氣流量Q=200 lpm，L/G=2.5 l/m3為例，粒徑大於100nm以上，傳統文氏洗滌器氯化鈉微粒的去除效率為20∼40%，在高效率文氏洗滌器系統一所測得的去除效率約為40∼50％之間，而由高效率文氏洗滌器所測得的去除效率提高為80∼85％。對二氧化矽微粒而言，傳統的文氏洗滌器、高效率文氏洗滌器系統一及系統二之去除效率分別為小於40％、20∼40％及65∼85％之間。油酸微粒傳統的文氏洗滌器、高效率文氏洗滌器系統一及系統二之效率分別為40％、50％及80％。 研究發現實驗中壁面損失及混合不均會造成混合後之蒸氣壓較理論值低。若前者為後者之0.465倍時，理論收集效率始能與實驗值吻合。本實驗以(Calvert1972)所提之效率理論式推估高效率文氏洗滌器之去除效率，並與實驗值比較。以氣流量Q=300 lpm，L/G=2.5 l/m3的操作條件為例，氯化鈉微粒在粒徑為50∼500nm之間之收集效率理論值約為95∼100%之間，而實驗的去除效率則介於90∼100%。粒徑大於100 nm以上的二氧化矽微粒效率理論值約為80∼90%，而實驗值也是介於此範圍;至於油酸的理論值為60∼80%，而實驗值為80∼95%。 將來若能進一步改善廢氣與蒸氣混合情形，及克服壁面損失(wall loss)，預期將能在低壓降的操作條件下達到更高的去除效率。

An efficient new venturi scrubber uses high temperature (100℃)and saturated stream to mix with normal temperature exhaust gas (30℃), allowing the submicron particles to grow to bigger particles by heterogeneous nucleation. This research used different kinds of test aerosols：NaCl、SiO2 and Olecid acid, and made use of heterogeneous nucleation theory to improve the removal efficiency of the venturi scrubber. It was expected that high efficiency could be achieved at low pressure drop. Depending on the mixing method of fuel gas and steam, two different highly efficient venturi scrubber systems were used：system 1 and system 2. Prior to entering the venturi scrubber, fuel gas flew into the steam generator and mixed with it in system 1. In system 2, fuel gas coming from the tube at the left side of the venturi scrubber mixed with steam coming from the tube at the right side of the venturi scrubber on top of the venturi scrubber. In the test, the gas flow rates were 200、250 and 300 lpm, and the liguid-to-gas rates were 1.5、2 and 2.5 l/m3. The results showed that removal efficiency of the traditional venturi scrubber was low at low gas flowrate and pressure drop. The removal efficiency of the venturi scrubbing system was improved. In particulate, due to better mixing of the gas and steam of the system 2, its particles removal efficiency was much higher than the system 1. For example, at the gas flow rate of 200 lpm, the liquid-to gas ratio of 2.5 l/m3, and particles diameter larger than 100nm, the efficiency of the traditional venturi scrubber was between 20~40%, the efficiency in the system 1 was 40~50%, and the efficiency was increased to 80~85%. For SiO2 particles, the efficiency of the traditional venturi scrubber is less than 40%. In comparison, the efficiency of the system 1 and system 2 of the new venturi scrubber were 20~40% and 65~85%, respectively. For Olecid acid particles, the efficiency of the traditional venturi scrubber was 40%, while the efficiency of system 1 and system 2 of the new venturi scrubber was improved to 50% and 80%, respectively. This study here found that the stream wall loss and the uneven mixing of steam and gas resulted in lower saturation ratio than the theoretical values. If the experimental saturation ratio is 0.465 times to the theoretical values, the theoretical efficiency will be much close to the experimental data. For example, when the mixing ratio was 0.091, the gas flow rate was 200 lpm and the liquid-to-gas ratio was 2.5 l/m3, the theoretical efficiency of the NaCl particles would be greater than 95%, and the experimental efficiency was 90~100% for particulate diameter ranging from 50~500nm. When the diameter of SiO2 particles was above 100nm, theoretical efficiency was between 80~90% and the experimental efficiency is in the same range. The theoretical efficiency of Olecid acid particles was 60~80%, and the experimental efficiency was between 80~95%. The theoretical values appear to be in good agreement with the experimental data. If we could further improve the mixing of exhaust gas and steam and decrease steam wall loss, it is expected that the system would achieve even higher efficiency at lower pressure drop than the current new venturi scrubber system.