應用垂直式光徑煙流分布預測石化工業區之排放量

Abstract

環保署對於來自固定性及非點源的揮發性有機化學物質的排放(例如：石油化學工業之製程)制定法律並收取費用。這個費用是依據排放量計算的結果收費，此收費所遵照的排放量計算標準是依據美國環保署所公告的AP-42方法(空氣汙染排放因子轉換)。這些排放因子是建立在許多假設結合一些可用資料所推估而得到的，且是依據美國的產業型態制定。美國環保署在2006年公布的Other Test Method 10中的垂直式光徑煙流分布方法，應用開徑式光徑積分的光學遙測技術，搭配多條不重疊的光徑，此方法有潛力成為取代現行排放量推估之方法。因為垂直式光徑煙流分布方法是根據特定的製程實際量測物質的濃度進而計算排放量，與存在許多假設的排放因子方法相比較具信賴性。此研究中利用開徑式傅立葉轉換光譜儀進行垂直式光徑煙流分布實驗。選擇四個石化工廠進行現場實驗。垂直式光徑煙流分布是一個二維的測量平面，此平面由三個光徑所組成。每場次實驗的光徑長度及反射鏡高度為配合目標製程去架設。收集濃度資料的同時也收集風向風速資料。為了驗證實驗的正確性，實驗進行中於製程中釋放已知排放量的SF6的追蹤氣體。在資料分析部分，將濃度資料、風速資料和分子量等做計算並積分已獲得各物質之排放量。重建結果使用CCFPIC between measured and predicted path integrated concentration (PIC)來判定。符合特定濃度趨勢(低測線濃度最高，中間測線次之，高空測線濃度最低)的資料重建結果之CCFPIC大部分都大於0.8。前兩場排放量計算結果十分接近真實的排放量，約低估20%。後兩場實驗結果雖低估非常嚴重，但也因此探討出許多會影響VRPM方法的重要因素：風向、tracer gas的擺放、測線長度相對於目標製程的長度、反射鏡的高度。

In Taiwan, VOCs emitted from fixed and fugitive pollution sources (such as various industrial processes in petrochemical industries) are being charged due to a regulation by the EPA. This fee is calculated based on the estimated emission rate of VOCs using the U.S. EPA’s Method AP-42 Compilation of Air Pollutant Emission Factors. However, these emission factors, which come from equations based on averages of available data, incorporate many assumptions and are not plant specific. The Vertical Radial Plume Mapping (VRPM) technique described in the Other Test Method 10 (OTM-10) of the U.S. EPA, which was released recently in 2006 and applies open-path path integrated – optical remote sensing (PI-ORS) system with multiple beam configurations, is a potential alternative to estimate the emission rates. Since the estimated emission rates from VRPM are calculated from measurement data at specific plants, rather than from assumed emission factors, these estimates should be more reliable. In this study, we evaluated the VRPM of OTM-10 in complicated petro-chemical industries. Open-Path Fourier Transform Infrared (OP-FTIR) spectroscopy was used to measure the emission rates in VRPM. Four factories in a petro-chemical industrial area were selected for field experiments. The VRPM configuration is a 2-D vertical plane. Length of beam paths and height of retroreflectors in the VRPM configuration were set up according to objective manufacturing process. The wind direction and wind speed were measured simultaneously. To verify the accuracy of experiment, we release the amount of the tracer gas of SF6 we know during manufacturing process. The amount of emission was obtained by integrating the data of concentration obtained from OP-FTIR measurement and reconstruction algorithm then multiplied by wind speed. Concordance Correlation Factor (CCFPIC) between measured and predicted path integrated concentration (PIC) was used to judge the fitting quality of the reconstruction results. PIC data which fit specific pattern (Among three beam paths the concentration of ground level is the highest, top level the lowest, middle level falls between the top level and ground level.) indicated that the CCFPIC were mostly higher than 0.8. In the first two field campaigns, the calculation result of the amount of emission is quite close to the true value, around 20% was underestimated. Although the last two field campaign provided a highly underestimated result, some important factors were derived: wind direction, arrangement of tracer gas, length of beam paths (compared with objective manufacturing process) and height of retrorelectors.