| 摘要: | 本研究目的為針對製程中產生之有機氣體成分，開發氣相層析自動線上系統，並運用於：一、煙道氣體；二、生質氣體。
而為瞭解成分的必要性，故層析系統採恆溫(isothermal)且搭配逆吹(back-flush)概念之設計，使管柱能夠在分析時間時完成淨化，而不須高溫烘烤，進而大幅降低分析時間與電力消耗，且兼具長期量測與穩定之特性，以期對前述的兩項議題分別建立適宜系統，並應用於線上(on-line)分析。
實驗系統以二位十孔閥作為主體，串聯適宜的管柱組合與偵測器，輔以層析條件，並對不同分析目的進行系統微調，則可達到對不同的分析目標物進行量測。管柱為自製之填充管柱，填充不同的靜相材料，即可應用於不同的分析目標物。
有別於目前頒布之標準方法，使用吸附管捕捉非甲烷碳氫(NMHCs)以量測甲烷與總碳氫，本研究希冀利用層析概念，使用管柱分離以完成量測；本研究完成「逆吹」與「分流」兩套系統，由於應用於環境端時，逆吹系統之非甲烷總碳氫之峰形過於增寬，而使其精確度表現較為差強人意，故在此選用分流系統與商業化儀器進行平行比對。比對之結果發現，兩者趨勢極為相似，另外，當高濃度非甲烷碳氫欲經由觸媒轉化時，觸媒將無法一次完全轉化，而造成貫流效應，但層析法則是利用逆吹概念將非甲烷碳氫排除於系統外，故將不會影響量測結果。
生質氣體部分，使用實驗室先前建立之系統，對炭化產氣樣品進行離線(off-line)實測，即發現不同時間點產氣濃度將有一趨勢變化，而隨著炭化溫度的提升，產氣濃度(C1~C4)亦隨之上升，最大濃度出現之時間點亦相對往前。同時，亦對新的靜相材料進行測試，藉由不同的管柱組合，可將分析時間縮短至4分鐘內，有助於數據點的密集度，之後將此系統應用於生質物炭化試驗之線上(on-line)分析，可發現其產氣趨勢與離線實驗極為相似，證明此系統可實際應用於線上分析。
This study developed two gas chromatographic (GC) systems: one is to monitor the chemical composition of stack gas from factories, and the other is to analyze the composition of biogas from biomass torrefaction. Both methods have a common ground
that is they both measure methane and non-methane hydrocarbons (NMHCs). However, the first method only separates NMHCs as a group from methane, whereas the second method performs elaborate separation of more than 10 gases.
To allow long-term operation with minimal downtime and maintenance, both GC systems adopted isothermal and back-flush design, involving a 10-port, 2-position switching valve and several column sets with each set consisting of a pre-column and analytical column kept at a constant oven temperature.
Two methods were tested for the first application
they are back-flush and split methods. Because the back-flush method caused the undesired peak tailing with the NMHC peak, the split design was adopted and tested by inter-comparing with the catalytic method which is widely used for the EPA air quality monitoring stations. Although both readings were very similar, the catalytic instrument was found to be susceptible to incomplete catalytic removal of NMHCs resulting in systematic bias, especially when ambient air contained high levels of NMHCs. By contrast, this problem can be fully avoided by our GC method.
In the application of biogas analysis, a GC system with the similar back-flush isothermal concept was built to separate more than 10 species, i.e., N2, O2, CO, CO2, CH4 and C2-C4 NMHCs, for each injection. The system was first tested in the off-line mode, and later adapted to a biomass torrefaction chamber for on-line monitoring gas composition. Both the off-line and on-line results appeared to be very similar, proving that the GC system can perform on-line analysis as planned. Basing on the instantaneous chemical compositional information provided by the on-line GC, the process parameters for a given type of biomass can be optimized accordingly. |
