考量可用能之生命週期評估─以臺灣生質酒精為例

Abstract

能源安全為當今世界面臨的重大危機之一。一方面，根據預測化石燃料於未來五十年間既會耗盡；此外，全球暖化的議題日益受到重視。而由於生質燃料被視為具有環境效益的替代燃料，因此推廣生質燃料的使用，被視為因應能源危機以及減緩氣候變遷的策略之一。然而近期亦有研究指出，生質燃料除有排擠糧食作物的隱憂外，而因其能源效率，因其整體環境衝擊是否會較傳統燃料為低，仍為令人存疑之處。鑑於以上論點，本研究結合外部能分析以及生命週期評估兩方法，分析以甘蔗轉化之生質酒精的能源效率以及環境衝擊，並比較台灣自產酒精以及從巴西進口生質酒精兩情境之總體能源效率與環境衝擊。 外部能分析結果顯示，在種植甘蔗階段，台灣的能源效率較巴西為佳。然而於甘蔗轉成酒精的工業製程方面，台灣的轉化技術的總能源耗用量，卻為巴西的一點五倍。而生命週期評估的分析結果指出，兩種情境中，甘蔗轉化為酒精的製程均為主要的污染熱點。由於轉化過程需使用柴油、瓦斯以及石灰石，這些原物料的製造階段，是整個生質酒精生命週期中，導致人體健康、資源耗用以及全球暖化的主因。 根據本研究的分析，台灣若要以自產甘蔗為原料的生質酒精為生質燃料的推廣政策的方向，當務之急為改善轉化製程的能資源耗用量，方能使該類生質燃料，具有較佳的環境效益。

Energy security is an urgent issue to be considered. The world fossil fuel is expected to be exploited in 50 years. Global warming issue is also consequent issue to be recognized. To mitigate these issues, biofuel was assessed its energy efficiency and its environmental performance. Thus to mitigate these issues, this study investigates the two bioethanol promotion strategies to compare and evaluate its environmental performance by life cycle assessment and exergy analysis. Exergy analysis conducted to consider the actual work of thermodynamics for biofuel. The result showed Taiwan has a strong possibility to improve resource management by self producing sugarcane however not producing ethanol. Industrial production of ethanol in Taiwan had shown that the ineffective performance than the Brazilian ethanol production about 1.5 point times of the impact. Importing ethanol from Brazil could sequestrate carbon dioxide (CO2) emission however in the overall emission to the earth is more significant in considering of long transportation. In the bioethanol production, environmental impact from ethanol production stage contributed significant impact in the both two scenarios assessed in this study. Use of fossil energy like diesel, gas and lime strongly impacted health risk to human, and resulting high non-renewable resource consumption and global warming. This study therefore can recommend to Taiwanese policy makers to improve industrial production of ethanol in Taiwan in considering of self production of bioethanol from sugarcane.