處理酸性廢氣的高效率多平板洗滌塔

Abstract

濕式洗滌設備為目前普遍應用於處理高科技產業製程廢氣的一項傳統技術，但傳統式洗滌塔對於HF、HCl、NH3等酸鹼氣體的去除效果不佳，無法達到法規規定的95 %去除效率，且廢氣中污染氣體濃度愈低時去除效率愈差，使洗滌塔在低廢氣濃度時無法有效的去除廢氣。為了改善傳統濕式洗滌塔效率不佳的問題，本研究依吸收理論設計了一個高效率多平板的濕式洗滌系統(PPWS, Parallel Plate Wet Scrubber)，其內部以多平行平板取代傳統式填充塔的填充料，並於平板表面塗敷奈米TiO2凝膠以增加潤濕性，使氣體通過吸收性良好及接觸面積(327 m2/m3)大的平板表面，進而在低壓損下增加其去除效率。 本研究以HCl、HNO3及CH3COOH三種酸性氣體混合成低濃度(< 2 ppm)的模擬廢氣來進行PPWS去除效率的測試，其中洗滌液的pH值均控制在7以上。結果顯示，當測試風量為1.62 CMM、氣體於平板間的滯留時間(gas retention time in the multi-parallel plate, Tg)為0.5秒、液氣比(liquid to gas ratio, L/G)為18.5 L/m3時，HCl、HNO3及CH3COOH氣體的去除效率分別為99.51±0.48 %、99.13±0.87 %及99.15±0.46 %；當測試風量增為8.1 CMM、Tg降至0.1秒及L/G降至3.7 L/m3時，上述的去除效率則分別降至98.34 ± 1.62、97.42 ± 2.08及94.94 ± 3.48 %。 因此在滯留時間0.1 sec條件，液氣比為3.7 L/m3時，多平板洗滌塔對低濃度HCl 、HNO3、CH3COOH氣體之去除效率均可達法規所規定的95 %以上。

Wet scrubbing system is widely used in high-tech industries to remove the exhaust gases. However, traditional wet scrubber has poor removal efficiency toward acid-bases gas such as HF, HCl and NH3, etc., especially for those in low concentration and thus fails to meet emission standard promulgated by Taiwan EPA. In this study, a high removal efficiency parallel plate wet scrubber (PPWS) was designed to meet this problem. In the PPWD, traditional packing material was replaced by the multi-parallel plate. The plates were coated with nano-TiO2 gel to enhance its wettability. That will let exhaust passing through the plates with large contact surface area (327 m2/m3) and well absorbency, and further increase its removal efficiency in low pressure drop condition. Simulated exhaust gases (< 2 ppm) in low concentration mixed with HCl, HNO3 and CH3COOH were used for testing the removal efficiency of the PPWS. Results show that when the gas flowrate is 1.62 CCM, gas retention time in the multi-parallel plate (Tg) is 0.5 s and the liquid/gas ratio (L/G) is 18.5 L/m3, the removal efficiency of the PPWS toward HCl, HNO3 and CH3COOH are 99.51 ± 0.48 , 99.13 ± 0.87 and 99.15 ± 0.46 %, respectively, while the gas flowrate is increased to 8.1 CCM, the Tg is decreased to 0.1 s and the L/G is decreased to 3.7 L/m3, the corresponding removal efficiency are decreased to 98.34 ± 1.62, 97.42 ± 2.08 and 94.94 ± 3.48 %, respectively. That is, the removal efficiencies of the PPWS toward the HCl and HNO3 are able to meet the emission standard when the Tg and L/G are 0.1 s and 3.7 L/m3, respectively, while for the CH3COOH, the Tg must be extended to 0.5 s allowing its removal efficiency to achieve the emission standard.