順流式旋轉填充床對細懸浮微粒去除之效能評估

21世紀是人類與空污的戰爭，尤以細懸浮微粒(PM2.5)為甚。許多研究已指出以逆流式旋轉填充床為主的超重力技術對去除細懸浮微粒具有較佳的效果，但較少研究著重於順流式旋轉填充床。本篇研究重點即在於調查超重力技術應用於細懸浮微粒的去除效能，將順流式旋轉填充床作為研究核心。首先應用計算流體力學(CFD)對順流式旋轉填充床內的流場模式進行分析，結合普遍常用的動量、質量、能量等統御方程式和紊流模型以評估流場速度及靜壓分布變化，其結果將作為輔助設置操作條件；接著於實驗室中以發電機為模擬之PM2.5產生源，評估順流式旋轉填充床於不同操作條件(超重力因子、液氣比)下對細懸浮微粒的去除效果，並推導出細懸浮微粒去除效率的相關性；同時為順流式旋轉填充床發展一套細懸浮微粒的去除效率模式，以填充材、液膜、液滴為三參數，找出各參數所對應的主導因子，再對實驗結果進行指數曲線擬合；最後以中油公司林園石化廠的煙囪(P070)作為假想的排放情境，與其他常用的除塵設備相比，對順流式旋轉填充床進行估算其環境成本會計以評估其用於去除細懸浮微粒下的經濟效益。 CFD結果發現隨轉速提升，順流式旋轉填充床之進液量雖能更有效地被離心力所分散至填充材區，但也有部分進液量被旋轉之填充材區所阻擋而反彈至空腔區；而在填充材區外圍的靜壓通常來的較大，這是由於液體進入填充材區後由離心力所推動造成的結果，這也意味著在一定轉速下，靜壓較大區域被認為主要是細懸浮微粒的去除區域。實驗結果則發現隨轉速增加，去除效率也隨之提升；相同地，液氣比的提升也對去除效率具有正面影響。故順流式旋轉填充床在高轉速(1500 rpm)、高液氣比(L/G= 1.5)的操作條件下具有最大的PM2.5去除效率(99.75%)，並且所對應出口氣體之PM2.5濃度為33.7 μg/m3，而藉由多重線性回歸模式所得之相關性結果則顯示液氣比對去除效率的影響較超重力因子大。整體去除效率模式的結果則顯示順流式旋轉填充床中的去除效率以填充材為主、液膜為次、液滴則為輔。在操作條件為40 lpm的廢氣量、30 lpm的液體量下，使用微孔均勻沉降衝擊器(MOUDI)量測藉由順流式旋轉填充床處理後廢氣中不同粒徑的微粒質量濃度，而這將用於模式建立過程中常係數項的推導。填充材主導效率的機制中，以孔隙率、軸高、填充材厚度及液氣比為主導因子進行模式擬合。液膜主導效率的機制，以微粒粒徑與液膜厚度的比值影響為最，而這也是參考截留機制所建立的參數，同樣進行模式擬合；而液滴主導效率的機制中，則以布朗擴散作用較不明顯，截留作用較慣性衝擊所佔的影響較大，這也間接說明順流式旋轉填充床中的液滴主要以截留的方式來去除細懸浮微粒。環境成本會計的估算結果顯示了每年所需的操作維護費用以文丘里濕式除塵器較高，而順流式旋轉填充床則具有相對較低的花費；以潛在效益而言，由於袋濾式集塵器及靜電集塵器去除細顆粒的效率較好，故具有較高的效益；若以淨現值而言，靜電集塵器與順流式旋轉填充床於假想排放情境下作為除塵設備是相當具有經濟可行性的。然而，值得注意的是，順流式旋轉填充床同時具有去除氣狀污染物的能力，因此其有可發展的潛力作為未來主要的空污防制設備。

關鍵字

細懸浮微粒；順流式旋轉填充床；計算流體力學；細懸浮微粒去除效率模式；環境成本會計

並列摘要

The war between human beings and air pollution is in the 21st century, especially fine particulate matters (PM2.5). Much work has been done on studying that the counter-current flow rotating packed bed has a positive effect on fine particles removal, but little has considered the co-current flow rotating packed bed. This research investigates the performance of fine particles removal via high-gravity technology, carried out in a co-current flow rotating packed bed which was the core of this research. Computational fluid dynamics (CFD) was applied to analyze the flow field characteristics in the co-current flow rotating packed bed. The commonly used momentum, mass, energy equations, and turbulence models were combined to evaluate the variation of flow field velocity and static pressure distribution. The result would be used as an aid to set the operating conditions. Then, a generator was used as the simulated PM2.5 source in the laboratory, and the removal efficiency of fine particles using the co-current flow rotating packed bed under different operating conditions (high-gravity factor, liquid-to-gas ratio) was determined. In addition, the correlation of removal efficiency of fine particles was derived by the multiple linear regression. At the same time, a set of removal efficiency model of fine particles was developed for the co-current flow rotating packed bed. Taking packing, liquid film and droplets as three parameters, the dominant factors corresponding to each parameter were found out, and then the experimental results were fitted by the exponential curve. Finally, taking the chimney (P070) of Linyuan Petrochemical Plant of CPC Corporation as the hypothetical emission scenario, compared with other commonly used dedusting equipment, the environmental cost accounting of co-current flow rotating packed bed was estimated to evaluate its economic benefit in removing fine particles. The results of CFD showed that with the increase of rotating speed, although the liquid inflow rate of co-current flow rotating packed bed could be more effectively dispersed to the packing zone by centrifugal force, some was blocked by the rotating packing zone and rebounded to the cavity zone. The static pressure around the packing zone was usually larger, which is caused by the centrifugal force after the liquid entered the packing zone. This also meant that at a certain speed, the larger static pressure area was considered to be mainly the area of fine particles removal. The experimental results show that the removal efficiency increased with the increase of rotating speed, and the increase of liquid-to-gas ratio also had a positive impact on the removal efficiency. Therefore, the co-current flow rotating packed bed had the highest PM2.5 removal efficiency (99.75%) at high rotating speed (1500 rpm) and high liquid-to-gas ratio (L/G= 1.5), and the corresponding PM2.5 concentration of the outlet gas was 33.7 μg/m3. The correlation results obtained by the multiple linear regression model show that the effect of the liquid-to-gas ratio on removal efficiency was greater than that of high-gravity factor. The results of the overall removal efficiency model show that the removal efficiency of the co-current flow rotating packed bed was mainly packing, liquid film was secondary, and liquid droplets were supplementary. Under the operating conditions of waste gas flow rate at 40 L/min and liquid flow rate at 30 L/min, the mass concentration of particles with different particle sizes in the waste gas treated by the co-current flow RPB was measured by the micro-orifice uniform deposition impactor (MOUDI), and this would be used to derive the constant coefficients in the process of model development. The mechanism of packing-dominated Efficiency was model fitting with the dominant factors of porosity, axis height, packing thickness, and liquid-to-gas ratio; the ratio of particle size to liquid film thickness had the greatest effect on the mechanism of film-dominated Efficiency. This was also the parameter established by reference to the interception mechanism, and the model fitting was also carried out. In the mechanism of droplet-dominated Efficiency, the Brownian diffusion effect was less obvious and the interception effect was greater than that of inertial impaction, which indirectly indicated that the droplets in the co-current flow RPB mainly remove fine particles by interception. The estimated results of environmental cost accounting show that the annual operation and maintenance costs of venturi scrubber were higher than that of co-current flow RPB; in terms of potential benefits, the baghouse and electrostatic precipitator had higher efficiency in removing fine particles; in terms of net present value, the electrostatic precipitator and co-current flow RPB were economically feasible as dedusting equipment in the scenario of hypothetical emission. However, it is noteworthy that the co-current flow RPB has the ability to remove gaseous pollutants at the same time, so it has the potential to develop as the main air pollution control equipment in the future.

並列關鍵字

fine particle ； co-current flow rotating packed bed (RPB) ； computational fluid dynamics (CFD) ； removal-efficiency model of fine particles ； environmental cost accounting

參考文獻

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順流式旋轉填充床對細懸浮微粒去除之效能評估

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