| 摘要: | 化石燃料短缺及空氣污染問題驅使科學家積極投入潔淨能源的研發工作。氫氣/合成氣可使用於引擎或燃料電池，使汙染氣體的排放量減至最少，為降低環境衝擊之永續能源選項之一，但是在應用於機動車輛及燃料電池時，存在貯存及基礎設施缺乏的問題。碳氫化合物重組產氫為解決此一問題的可行途徑，因此開發具有省能、精巧、可快速啟動之重組器是相當重要的。本研究探討甲烷、乙醇重組技術以及其可能的應用如固態氧化物燃料電池(SOFC)。本文分為三個部份，包括甲烷重組、乙醇重組及重組器應用於機車時之操作策略。 第一個部份為重組甲烷產氫，包括電漿輔助觸媒重組及觸媒重組兩種方式。電漿輔助觸媒重組之顆粒狀鎳觸媒置於電漿區後方，採用部分氧化法，重組過程沒有外加熱源，觸媒床溫度是由反應本身放出之熱量所維持的。測試結果達到氫氣產率89.9%及甲烷轉化率90.2%良好重組效果，其產氫耗能僅有1.21 MJ/kg-H2。若是以此重組器與燃料電池結合發電，其發電效率將比一般天然氣發電高出約20%。此外，熱力學模擬計算的結果與實驗結果相互吻合，顯示此一電漿輔助觸媒系統已達到理想的熱效率。觸媒重組，則是利用SOFC的高溫排氣廢熱，以Pt觸媒，採自熱重組反應，可以提供濃度將近80%的可燃氣體(H2 + CO，乾基)予SOFC。經1000小時以上長期測試，觸媒仍相當穩定。 第二個部份為商業規模的乙醇重組系統，以自熱重組法藉觸媒作用將乙醇重組產生富氫氣體。此重組系統首先測試四種貴金屬觸媒7天的性能表現，評估後，挑選Pt-Pd-Rh/?-Al2O3及Rh/?-Al2O3-CeO2-ZrO2進行26天的長期測試。前者在測試初期顯示出極佳的活性，乙醇轉化率達到97%。但是其活性隨著測試時間增加，有明顯的下降，5天後下降幅度趨緩，第26天測試結束時，乙醇轉化率僅剩約50%。Rh/?-Al2O3-CeO2-ZrO2的高活性則可維持約14天後逐漸降低至第26天的85%。 最後一個部份，我們設計一個電漿輔助觸媒重組器，將其安裝於機車引擎前。此車載型重組器可將甲烷重組轉化為富氫氣體，並與汽油混合為複合燃料後導入引擎。此重組器針對機車冷車啟動、低負載及巡航三種狀況發展各自最佳的操作模式。在冷車啟動階段，藉由電漿的作用，可以使觸媒床溫度在14秒內由室溫約25oC提升到500oC以上。在巡航模式，其目標是達到最大的熱值產出，而在低負載模式，其策略則是以省能為考量。重組器的電漿消耗32.4W的電能，但是可提高重組產物2 ~ 16%的熱值。低負載時，引擎結合重組器以複合燃料測試的結果，排氣中的CO及HC濃度可以分別降低42%及21%，引擎馬力提高14%，而油耗反而降低33%。且經實驗證實，引擎在低負載運轉時，重組器的電漿可以關閉以減低耗能，又不會過於降低重組器的效果，可以滿足引擎運轉需求。總而言之，電漿在冷車啟動模式扮演相當重要的角色，於巡航模式則是扮演次要的角色，至於在低負載模式，其影響則相當輕微。 本研究已成功開發甲烷電漿輔助觸媒重組器及觸媒重組器，可分別使用於機車引擎及SOFC，未來若能推廣應用，可改善能源利用效率、CO2排放及空氣品質，對環境品質有相當的助益。 The scarcity of fossil fuels and the problems of air pollution draw researchers to search more efficient and clearer energy sources. Syngas/hydrogen may become a vital energy for sustained power consumption with reduced impact on the environment. It can be used in engines or fuel cells with minimal emissions of pollutant gases. But certain problems such as syngas/hydrogen storage and infrastructure.exist for vehicles and fuel cells application The conversion of hydrocarbon to hydrogen is a potential source of hydrogen production and supply to fuel cell and hybrid vehicles. Therefore, a reformer designing to generate syngas on board with the characters of energy-saving, compactness, fast start-up and rapid response is particularly important and essential. This study demonstrates methane and ethanol reforming technologies as well as their possible applications. There are three parts in this study, i.e. methane reforming, ethanol reforming and operating strategy for motorcycle. The first part demonstrates an economic reforming process that combines arc plasma with catalyst in series for hydrogen production. Hydrogen was generated by means of partial oxidation of methane. Granular Ni catalysts were packed in the post plasma zone. No extra-energy was needed to sustain the temperature of catalyst bed; the elevated temperature was maintained both by the hot gases from plasma region and by the heat of reforming reaction itself. A promising energy efficiency of 1.21 MJ/kg-H2, being together with high hydrogen yield (89.9%) and high methane conversion (90.2%), was experimentally achieved. The energy efficiency is estimated 20% higher compared with a gas turbine system with methane as the fuel. In addition, thermodynamic analysis for partial oxidation of methane was conducted. Experimental data agreed well with the thermodynamic results, indicating that high thermal efficiency can be achieved with the plasma-assisted catalysis process. Methane was also reformed by Pt catalyst in this study. Autothermal reaction was adopted and preheated reactants by recovering the waste heat of high temperature flue gas exhausted form SOFC. The concentration of combustible gas (H2 + CO, dry base) was as high as 80% in the reformate. Catalyst performance was very stable during the 1000-hr durability test. The second part shows a commercial-scale ethanol reforming system, which converts ethanol into hydrogen-rich gases, via autothermal reaction mechanism. In this study, four kinds of noble metal catalyst were extensively investigated with the ethanol reforming system. Two of the four catalysts, Pt-Pd-Rh/?-Al2O3 and Rh/?-Al2O3-CeO2-ZrO2, had been conducted in a 26-day long-time test. The Pt-Pd-Rh/?-Al2O3 catalyst showed high catalytic activity and achieved an ethanol conversion of 97% in the early stage; but deactivated with reaction time and finally achieved a conversion of only 50% at 26th day. The Rh/?-Al2O3-CeO2-ZrO2 catalyst achieved and maintained high ethanol conversion for the first 14 days, then gradually decreased and achieved a conversion efficiency of 85% at 26th day. In the last part, we designed a compact plasma-assisted catalysis (PAC) reformer as an onboard device for motorcycle. This PAC reformer was used to convert methane into a hydrogen-rich gas which then mixed with gasoline to fuel motorcycle engine. Performance of the PAC reformer for motorcycle operated in the cold start, low load and normal cruising periods were evaluated experimentally. In the cold start period, with the assistance of plasma the catalyst-bed temperature could rise from 25oC to > 500oC in 14 s. In the normal operation mode, the goal is to achieve either a high power output in the cruising mode or a low energy consumption in the idle mode. At 32.4 W power consumption of plasma, the total thermal power of reformates increased by 2% to 16% at given conditions. Idle engine test showed that the PAC reformer not only reduced CO and HC emission by 42% and 21%, respectively, but also enhanced the engine performance, e.g. the brake power increased by 14% and the gasoline consumption by 33%. This study confirmed that in the low load mode, the plasma can be turned off without sacrificing the PAC’s performance. In brief, the plasma plays a great role in the cold start, be minor in the cruising mode, and trivial in the low load mode. This study has successfully developed a methane plasma-assisted catalysis reformer and a methane catalyst reformer for motrocycle engine and SOFC, respectively. They could improve the energy utility efficiency, CO2 emission and air quality if these reformer could be applied in the future. This is beneficial to the environment. |
