生物柴油对能源和环境影响分析

Effect of biodiesel on the environment and energy

生物柴油是从植物或动物脂肪酸通过酯化反应而得到 ,由于生物柴油无毒 ,可生物降解和可以再生 ,因此受到越来越多人的关注。生物柴油的性质和普通柴油非常相似 ,它能直接被用到发动机上而不需要改动发动机的结构。该文基于美国能源部对生物柴油的统计数据 ,利用生命循环分析法 ,对生物柴油从生产到消耗的生命循环中的能量消耗和产出、循环中的排放以及生物柴油汽车尾气排放等方面进行了分析。生命循环开始于普通柴油或生物柴油生产的原料提取 ,结束于成品油在发动机上的使用。只有分析生命循环中的所有过程 ,才能确定它对自然环境总量的影响。例如研究温室效应就要对整个生命循环中 CO2 的排放进行分析。该文利用生命循环分析法分析了在生产生物柴油或柴油生命循环过程中的能量平衡、温室气体排放及对气体和固体污染物排放 ,提供了生物柴油生产过程和在发动机上使用的详细数据。分析结果表明∶生物柴油循环的石化能效比大大提高 ,大约是柴油的 4倍 ;生物柴油循环中 CO2 排放大大降低 ,大约降低了 78.4% ;发动机排气管有害物质的排放中 ,除 NOx 排放增加 8.89%外 ,CO、HC、PM等有害物质的排放大大降低 (分别降低了 46%、3 7%和 68% )。

Biodiesel is a fuel, which can be produced by the chemical process of reacting vegetable oils or animal fats (transesterification). Biodiesel is receiving increasing attention as an alternative, non toxic, biodegradable and renewable diesel fuel. Many studies have shown that the properties of biodiesel are very close to that of diesel fuel. Therefore, biodiesel can be used in diesel engine with little or no engine modification. Based on the statistical data of DOE (the U.S. Department of Energy), the whole picture of biodiesel, which includes energy consumption and yield, emissions and tailpipe emissions were analyzed by the method called 'life cycle analysis'. The life cycles begin with the extraction of all raw materials to make petroleum diesel and biodiesel, and end with using the fuels in an engine. Examining global issues, such as CO 2 emissions, requires a comprehensive life cycle analysis. The biodiesel energy balance, its effect on greenhouse gas emissions, and on the regulated gas emissions and solid waste pollutants were investigated in each step needed to make biodiesel and diesel fuel. This paper provides an overview of biodiesel production and biodiesel consumption in the engine. It includes data on energy and emissions for petroleum diesel and biodiesel. It concludes that fossil energy ratio of biodiesel is four times that of petroleum diesel; biodiesel reduces net CO 2 emissions by 78.45% compared to petroleum diesel in the life cycle. On the other hand, the tailpipe emissions of biodiesel such as CO, HC and PM are 46%, 37% and 68% lower than that of petroleum diesel, respectively, except the  NO x, which is 8.89% higher than petroleum diesel.