| 摘要: | 「氫」雖然不屬於初級能源，但被視為是最有潛力用以替代化石燃料的能源載體。氫在自然界中是最普遍的元素，主要以水的形式化合存在，而且氫與氧燃燒或藉由燃料電池將化學能轉換成電能，反應後生成物為水，因此是極佳的潔淨能源。然而，儲存和運送氫氣一直是從理想面前進到實際應用面上的技術瓶頸之一。由於氫的密度很小，所以高壓儲氫法需要外加壓縮功耗費在儲存氫氣，再加上高壓環境的安全顧慮，使得儲存容器必須使用特製厚重的材料才可行。而氫氣的液化需要達到攝氏零下252 度，因此液化儲存時就需耗費大量的能量，並且保存環境需要有很好的隔熱設備來維持低溫。相形之下，利用金屬氫化物來儲氫則具有體積儲氫密度高、不需要高壓容器或隔熱裝置、安全性高，無爆炸疑慮、可獲得高純度的氫氣等優點，因此被世界各國列為氫氣儲存技術開發重點項目之一。金屬氫化物儲放氫反應速率與系統的溫度及壓力息息相關，由於合金吸氫時放熱，必須將熱量傳遞至儲氫容器外界，而合金放氫為吸熱反應必須由外界供給熱量，因此儲氫裝置不僅是吸放氫反應器，也必需是一個熱交換器。加以用氫端對於氫氣的供應速率有一定的要求，整個系統的熱傳效率必須優質化，才能滿足用氫運作與需求。因此，一套金屬氫化物儲氫容器之設計，就使用上而言，除了合金吸放氫特性、儲氫容量、操作溫度和壓力為基本考量外，尚需注意影響合金吸放氫速率之罐體熱傳特性。目前國內已開發且商業化之儲氫合金罐，多採取試誤法進行罐體設計，並非最佳設計方案，更由於沒有精確的熱傳分析，致使合金罐內部溫度分佈不均，影響合金充放氫速率。本計畫擬對儲氫合金罐體熱傳特性進行詳實的理論與實驗探討，希冀透過此研究建立儲氫合金罐體熱傳設計與分析的實驗測試平台與電腦輔助工程工具，以實際應用於儲氫容器的研製。計畫內容包含三部分，預計三年完成。第一年將進行儲氫合金罐體實驗測試平台的建立，整合儲氫合金材料與儲氫容器實驗以測試儲氫合金於儲氫容器之吸氫與放氫的反應速率及吸放氫效能。第二年進行電腦輔助工程儲氫合金吸放氫氣熱流模型及分析程式的建立，用以詳實評估氫氣吸放時的熱流行為，降低儲氫合金罐設計試誤的成本。待建立儲氫合金吸放氫實驗測試與電腦模擬平台後，第三年將進行新型熱傳增強儲氫罐體的設計開發，罐體內部亦將進行分隔單元的構裝以解決儲氫合金因循環吸、放氫過程粉碎化，致使金屬產生緻密堆積，降低吸放氫效率的問題。其後再以實驗方式確認儲氫容器的設計，與電腦模擬比對進行參數探討，如此將可建立一套完整的儲氫容器的設計法則。本計畫希冀經由對儲氫合金罐之熱傳相關問題進行深入探討，理論與實驗的相互印證，提高對合金吸放氫機制與熱流特性的理解與掌握，開發有效之儲氫合金罐設計分析技術，並歸納出最佳化設計方案，以提升國內儲氫合金容器在市場上的競爭力及附加價值。Hydrogen is the most abundant element on Earth, present principally as chemical compounds of H2O in water and some as liquid or gaseous hydrocarbons. Hydrogen, as an ideal energy carrier, is regarded to be a promising replacement for fossil fuels in the future, and also a clean fuel once produced, which yields only water when burnt with oxygen in combustion chambers or fuel cells. In order to develop hydrogen energy, hydrogen production, transmission and usage must attain sufficient efficiency. For transmission, hydrogen stored as metal hydrides is a potent candidate for its advantages in safe and reliability and being able to offer high energy density compared to the conventional ways of high pressure gas and liquefaction. In a practical point of view of using metal hydrides for hydrogen storage, heat transfer issues cannot be ignored as metal hydriding/dehydriding inevitably involves exothermic/endothermic reactions. In the absorption case, an increase in temperature due to the exothermic reaction can raise the equilibrium pressure so high that the hydriding may be ceased. On the other hand, a temperature decrease in the endothermic desorption reaction can bring the equilibrium pressure too low for the dehydriding to proceed. Therefore, reducing thermal resistance of the storage vessels becomes crucial to the success of the metal hydride hydrogen vessel design. This proposal will address the key technical challenges in the design of metal hydride hydrogen storage vessels. The whole plan is divided into three major parts and will be completed in three years. The first part includes setting up an experiment system for assessing the performance of the canister design. Hydrogen charging and releasing rates as well as heat transfer efficacy will be investigated with the experiment system. As the second part of the research plan, a mathematical model will be set for describing the thermal fluid behavior in the metal hydride hydrogen storage vessels. Based on the mathematical work, a computer-aided-engineering (CAE) scheme will be established too, which is aimed to facilitate the design and analysis of novel reactors, saving experimental efforts as before by traditional trial-and-error methods. Results of simulation will be compared with the experiments to correct the modeling details. Following the previous two works, the third part of the research plan is to set up a comprehensive design and analysis protocol that combines mathematical modeling, computational simulation and experimental verification as to interpret the entire processes of hydrogen absorption/desorption in storage vessels. By completion of the research period in three years, it is expected that a novel hydrogen storage reactor based on metal hydrides will be designed and made in house to fulfill the perspective hydrogen usage in fuel cells. The research results will be of important contribution to the advances of hydrogen storage technology, specifically helping improve heat transfer enhancement of metal hydride reactors. 研究期間：10008 ~ 10107 |
