Kemppainen Amber J, Shonnard David R
Department of Chemical Engineering, Michigan Technological University, Houghton, MI 49931, USA.
Biotechnol Prog. 2005 Jul-Aug;21(4):1075-84. doi: 10.1021/bp049548q.
This study compares life-cycle (cradle-to-gate) energy consumption and environmental impacts for producing ethanol via fermentation-based processes starting with two lignocellulosic feedstocks: virgin timber resources or recycled newsprint from an urban area. The life-cycle assessment in this study employed a novel combination of computer-aided tools. These tools include fermentation process simulation coupled with an impact assessment software tool for the manufacturing process life-cycle stage impacts. The process simulation file was provided by the National Renewable Energy Laboratory (NREL) and was modified slightly to accommodate these different feedstocks. For the premanufacturing process life-cycle stage impacts, such as the fuels and process chemicals used, transportation, and some preparatory steps (wood chipping, etc.), a life-cycle inventory database (the Boustead Model) coupled with an impact assessment software tool were used (the Environmental Fate and Risk Assessment Tool). The Newsprint process has a slightly lower overall composite environmental index (created from eight impact categories) compared to the Timber process. However, the Timber process consumes less electricity, produces fewer emissions in total, and has less of a human health impact. The amount of life-cycle fossil energy required to produce ethanol is 14% of the energy content of the product, making the overall efficiency 86%. Process improvement strategies were evaluated for both feedstock processes, including recycle of reactor vent air and heat integration. Heat integration has the greatest potential to reduce fossil-derived energy consumption, to an extent that fossil-derived energy over the life cycle is actually saved per unit of ethanol produced. These energy efficiency values are superior to those observed in conventional fossil-based transportation fuels.
本研究比较了以两种木质纤维素原料（原始木材资源或城市地区回收的新闻纸）为起始原料，通过基于发酵的工艺生产乙醇的生命周期（从摇篮到大门）能耗和环境影响。本研究中的生命周期评估采用了计算机辅助工具的新颖组合。这些工具包括发酵过程模拟以及用于制造过程生命周期阶段影响的影响评估软件工具。过程模拟文件由美国国家可再生能源实验室（NREL）提供，并进行了轻微修改以适应这些不同的原料。对于制造前过程生命周期阶段的影响，例如使用的燃料和工艺化学品、运输以及一些准备步骤（木材切碎等），使用了生命周期清单数据库（布思迪模型）以及一个影响评估软件工具（环境归宿和风险评估工具）。与木材工艺相比，新闻纸工艺的整体综合环境指数（由八个影响类别创建）略低。然而，木材工艺消耗的电力更少，总排放量更少，对人类健康的影响也更小。生产乙醇所需的生命周期化石能源量为产品能量含量的14%，整体效率为86%。对两种原料工艺的过程改进策略进行了评估，包括反应器排放空气的循环利用和热集成。热集成在降低化石能源消耗方面具有最大潜力，以至于每生产单位乙醇在生命周期内实际节省了化石能源。这些能源效率值优于传统化石基运输燃料中的观察值。
