以綠色二甲醚作為能源載體之國際再生能源供應鏈研究

Abstract

在全球暖化與低碳能源轉型的背景下，如何將再生能源從資源豐富國透過長距離海運輸送至能源需求國，已成為未來能源系統的重要議題。氫氣雖被視為具潛力的低碳能源載體，但其體積能量密度較低，且大規模運輸通常需仰賴高壓儲存或低溫液化，使整體儲存與運輸成本偏高。因此，將再生能源轉換為化學能源載體，成為長距離能源運輸的一項替代方案。本研究以綠色二甲醚作為能源載體，先透過 Aspen Plus 建立二甲醚合成、二甲醚蒸氣重組、氫氣與二氧化碳分離，以及二氧化碳液化等程序模型，再結合經濟評估與碳排分析，並將各程序整合為跨國再生能源供應鏈，以評估其整體表現。

在出口國，以卡達為例，再生電力首先透過固態氧化物電解槽轉換為綠氫，並與二氧化碳反應合成二甲醚。二甲醚合成所釋放的反應熱可進一步回收，用於產生電解進料所需之蒸汽，以提升系統熱整合效果。在進口國，以台灣為例，運輸後的二甲醚經蒸氣重組產生氫氣，並利用固態氧化物燃料電池可回收之廢熱供應吸熱重組反應所需熱量。重組後產生的二氧化碳經捕獲與液化後回送至出口國，而純化後的氫氣則供應燃料電池發電。

模擬結果顯示，當出口國輸入 44.99 MWhₑ/t-H₂ 的再生電力時，經過電解水產氫、二甲醚合成、運輸、二甲醚重組、分離與燃料電池發電後，進口國可輸出 14.29 MWhₑ/t-H₂ 的電力至當地電網，對應的往返能源轉換效率為 31.8%。在出口國再生電力成本為 USD 30/MWhₑ 的條件下，進口國之供電成本為 USD 271.8/MWhₑ，約為出口國再生電力成本的 9.1 倍。整體而言，本研究量化了低碳二甲醚供應鏈之技術與經濟表現，並提供未來與甲醇、氨及其他化學能源載體進行比較之基準。

Global warming and the transition toward low-carbon energy systems have increased the need for long-distance renewable energy transport by shipping. Although hydrogen is a promising low-carbon energy carrier, its low volumetric energy density and the need for high-pressure storage or low-temperature liquefaction make large-scale transport costly and challenging. This study establishes an international renewable energy supply chain using green dimethyl ether (DME) as the energy carrier, including DME synthesis, DME steam reforming, H₂/CO₂ separation, and CO₂ liquefaction.

In the exporting country, renewable electricity is converted to green hydrogen via SOEC electrolysis, and the hydrogen reacts with CO₂ to synthesize DME. The heat released from DME synthesis is recovered to generate steam for the electrolysis feed, improving thermal integration. In the importing country, transported DME is steam reformed to produce hydrogen, while recoverable SOFC waste heat is used to support the endothermic reforming process. The captured CO₂ is liquefied and returned to the exporting country.

The proposed DME-based supply chain achieves a round-trip efficiency of 31.8%, converting 44.99 MWhₑ/t-H₂ into 14.29 MWhₑ/t-H₂ of delivered electricity. At a renewable electricity cost of USD 30/MWhₑ, the delivered electricity cost is USD 271.8/MWhₑ. Overall, this study provides quantified efficiency and cost benchmarks for future comparison with methanol, ammonia, and other energy carriers.