| 摘要: | 大氣中的揮發性有機化合物 (Volatile organic compounds, VOCs)
中高達70%可歸類為非甲烷總碳氫化合物 (Non-methane
hydrocarbons, NMHC)，而其中又以固定排放源的石化產業鏈作為最
大貢獻者，這些工業廢氣經管道或逸散排放至大氣中將造成空氣污染，
長期排放也會對工廠附近的居民造成健康危害，為此本研究透過建立
一套完整的監測系統，即時掌握管道排放濃度。
本研究以符合標準方法(NIEA A723.75B)的逆吹層析原理自製自
動化非甲烷總碳氫化合物分析儀，NMHC 的計算方式是由總碳氫化
合物 (Total hydrocarbons, THC) 經換算成單位碳濃度後扣除甲烷
(Methane)得到。此方法相較於普遍使用的觸媒法，藉由儀器的樣品捕
集和逆吹技術可大幅增加層析管柱的使用壽命。儀器開發完成後須在
實驗室內建立相關品保品管規範，包含了：丙烷回收率修正為79.6%，
施打50ppm甲烷標準氣體進行6重複測試時，THC側的精密度(RSD)
和準確度(Bias) 分別為0.59%和 -1.86%；CH4側的精密度(RSD) 和準
確度(Bias)分別為0.84 和 - 2.20%，儀器的偵測極限 (Method detection
limit, MDL) 測試結果THC側及 CH4側皆為0.05ppm，為了模擬監測
高含水量(%)的排放管道環境，採用加濕甲烷、丙烷和民生氣體施打
入儀器中，其感度分別為95.60%~102.00%、77.02%~79.08%和
79.89%~82.26%。除此之外，由於不同物種在火焰離子化偵測器
(Flame ionization detector, FID) 中的感度存在差異，導致經換算成單
位甲烷濃度時，將造成檢量線斜率不一致的結果，因此本研究提出一個校正方式，將丙烷的碳感度 (Carbon response, CR) 經感度因子修正
後，從3修正為2.58，能有助於將甲烷和丙烷的THC檢量線斜率統
一，避免在實場監測中造成濃度誤差。
為了驗證儀器在排放管道監測時是否和實驗室內一樣具高可靠
性，因此進行了15場次不同製程排放管道的實場監測，並且藉由離
線式氣相層析質譜儀 (Gas Chromatography/Mass Spectrometry,
GC/MS) 針對排放管道排放源 NMHC 進行物種層析分離分析，補強
了總碳氫分析儀無法得知個別成分之特性。
研究最後針對標準方法內品保規範的誤差原因設計實驗進行探
究，透過變異數計算分析將影響品保查核誤差最大的因子，也就是
FID 的點火氣源流量控制設備加以改善，以提高監測數據的可信度，
以利儀器進行長期連續監測。;Among the volatile organic compounds (VOCs) in the atmosphere, up
to 70% can be classified as non-methane hydrocarbons (NMHCs). The
petrochemical industry chain being the largest contributor among
stationary emission sources. These industrial exhaust gases are discharged
into the atmosphere via pipelines. These might cause air pollution and
health risks to residents near the factories. Therefore, it is necessary to
design and test an analyzer that can monitor the flue gas from of stack
emissions in real-time.
This study follows the standard method (NIEA A723.75B) and
develops an automated non-methane hydrocarbons analyzer using the back
flush chromatographic method. The calculation of NMHC is derived by
subtracting methane (CH4) from total hydrocarbons (THC). Compared to
the commonly used catalytic method, the sample collection and back flush
techniques significantly extend the lifespan of the chromatographic column.
After the instrument development, relevant quality assurance and quality
control standards need to be established in the laboratory. Propane recovery
was adjusted to 79.6%. When performing 6 repeated tests using 50 ppm
methane standard gas, the precision (RSD) and accuracy (Bias) for THC
were 0.59% and -1.86%, respectively; for CH4, the precision (RSD) and
accuracy (Bias) were 0.84% and -2.20%, respectively. The MDL test
results showed that both the THC and CH4 path were 0.05 ppm. To simulate the environment of emission conditions from smokestacks pipelines with
high moisture content (%), humidified methane, propane, and livelihood
gas were injected into the analyzer. The sensitivity for humidified methane,
propane, and livelihood gas ranged from 95.60% to 102.00%, 77.02% to
79.08%, and 79.89% to 82.26%, respectively. Additionally, due to the
varyed sensitivities of individual NMHC species in the Flame Ionization
Detector (FID), when converting them to unit methane concentration, this
can lead to inconsistent calibration curve slopes. Therefore, this study
proposes a correction method where the carbon response (CR) of propane
is adjusted from 3 to 2.58. This adjustment helps unify the slopes of the
THC calibration curves between different species, and improve accuracyin
field monitoring.
To verify its high reliability during the monitoring of smokestacks,
fifteen field test were conducted on different smokestacks with varied
chemical processes. Offline GC/MS was used to perform speciation of
NMHC, compensating for the inability to identify specific compounds
individually.
Lastly, investigation of the major sources of error in measurements
were made. Via variance calculations, it was found that the flow rate
instability for the hydrogen and air streams to FID was the most significant
source of error. |
