- 學位論文
利用引擎排氣廢熱之乙醇重組器研製及產氫特性研究
Fabrication and study of ethanol reformer with engine exhaust heat recycling on hydrogen production
摘要
本研究自行設計一組小型重組器，利用生質燃料-乙醇，進行重組產氫。而本重組器欲裝置於機車排氣管內，並利用排氣管之高溫廢熱提供重組所需之熱能。而重組產出之富氫氣體可供作機車引擎為輔助燃料，以期降低廢氣污染，並改善引擎燃燒效率。並分別以A組觸媒與B組觸媒中的短型觸媒(Short)以及長型觸媒(Long)，在各操作條件下進行自發熱重組實驗。本重組器搭配使用乙醇進料流率、H2O/EtOH比、O2/EtOH比，並以溫控箱控制不同操作溫度，模擬排氣管環境溫度，進行自發熱重組產氫。 實驗結果發現，在乙醇進料流率6mL/min時，在各操作條件下，不論A-Short與B-Short短型觸媒均可得到最高熱效率，其範圍分別為56.6~60.4%之間與 45.4~48.5%之間；隨著O2/EtOH比越高，搭配適當的H2O/EtOH比，有助於氫氣和一氧化碳的產率提升。A-Short觸媒當重組溫度達到680℃左右時，氫氣與一氧化碳的最高產率分別為61.4%和41.9%左右；而在B-Short觸媒部分，在重組溫度位於720℃左右時，氫氣與一氧化碳的最高產率分別為59.4%和26.7%左右。 然後在A-Long與B-Long長型觸媒方面，可以發現在整體乙醇轉化效率、氫氣產率以及熱效率皆有提升的現象，但以A-Long觸媒表現最為明顯，乙醇轉化效率提升了3~5%左右，而氫氣產率提升了1~4%左右，熱效率方面則提升約3~4%左右。另外，在系統的反應過程中，可以發現A-Long與B-Long觸媒，由於空間速度的減少，使得燃料通過觸媒的滯留時間較久，重組的效能越佳，所以整體的H2/(CO+CO2)比值有明顯提升的現象。而富氫氣體要導入內燃機引擎必須要有較適當的助燃以及阻燃的比例，就以A-Short觸媒以及A-Long觸媒之助阻比分別為0.4~1之間與0.37~1.1之間；而B觸媒則分別介於0.15~0.68之間及0.32~0.8之間。當助阻比範圍越廣時，可依內燃機引擎不同的負荷情況，導入適當的富氫氣體，進而改善熱效率以及排氣污染。但也必須注意觸媒在重組過程中的反應溫度，以防過高的溫度造成觸媒本體的燒結及損壞。
並列摘要
This study was to develop a small reformer for hydrogen production from bio-fuel, i.e. ethanol. The reformer will be installed in the motorcycle exhaust pipe for recycling the exhaust heat for reforming. Hydrogen-rich gas was produced and will be used as the supplementary fuel of the engine for the improvement of thermal efficiency and exhaust emissions. Autothermal reforming was performed on the short and long models of A and B catalysts under the parameters of ethanol flow rate, H2O/EtOH ratio and O2/EtOH ratio with various temperatures to simulate the exhaust stream for hydrogen production. The experimental results of the short models of catalysts were shown as follows. No matter what the A-Short catalyst or B-Short catalyst is, the best thermal efficiency could be obtained under the ethanol flow rate of 6 mL/min. They were 56.6~60.4% and 45.4~48.5% respectively. With higher O2/EtOH ratio and suitable H2O/EtOH ratio, better hydrogen and carbon monoxide of yield were achieved. As reforming temperature reached 680℃ for A-Short catalyst, the best hydrogen yield of 61.4% and carbon monoxide yield of 41.9% were obtained; and as reforming temperature reached 720℃ for the B-Short catalyst, the best hydrogen yield of 59.4% and carbon monoxide yield of 26.7% were obtained. For the long models of A-Long and B-Long catalysts, the experimental results were shown as follows. It could be found that better ethanol conversion efficiency, hydrogen yield and thermal efficiency were obtained. The improvement of ethanol conversion efficiency was about 3~5%, hydrogen yield 1~4% and thermal efficiency 3~4% for A-Long catalyst. Higher H2/(CO+CO2) mole ratio was obtained by the long models of A-Long and B-Long catalysts due to the longer residence time. The hydrogen-rich gas was produced and would be used as the supplementary fuel of the engine. The suitable A/I ratio is needed. For the A catalyst of short and long models, the A/I ratios were between 0.4~1and between 0.37~1.1, respectively. For B catalyst, the A/I ratio were in the range of 0.15~0.68 and 0.32~0.8 respectively. Wider range of A/I ratio can meet the requirement of engine operation for the improvement of thermal efficiency and exhaust emissions. However, the reaction temperature should be monitored, because high temperature would cause the sintering and damage of the catalyst.