木薯燃料乙醇的碳效应分析

出于能源安全的考虑及对温室气体减排的关注,世界各国近些年大力发展生物液体燃料,我国政府提倡以木薯等非粮作物为原料生产燃料乙醇。一直以来科学家们对生物液体燃料的碳效应争论激烈,争论的焦点在于原料种植对土壤碳库的影响及不同技术条件下副产品利用的评估。论文通过建立碳平衡分析模型,将原料种植对土壤碳库影响及副产品利用的替代效应纳入研究体系,评估了我国木薯燃料乙醇生产各个环节的碳排放,研究结果显示:木薯原料种植环节碳排放主要来自氮肥的使用及对土壤碳库的破坏;木薯燃料乙醇加工转化环节碳排放主要来自蒸馏和脱水过程能源消耗,改进加工转化技术对减少此环节碳排放至关重要;木薯燃料乙醇运输及储存过程碳排放较小。在现有生产技术条件下,生产单位质量(1 kg)木薯燃料乙醇平均碳排放为0.647 kg。以汽油的碳排放为参照,在目前技术水平条件下,我国木薯燃料乙醇碳排放呈现负效益;采用较为先进的双酶法中温喷射液化-大罐浓醪间歇发酵-多塔多耦合差压精馏和分子筛变压脱水技术,则其碳排放为汽油的90%;倘若能避免对土壤碳库的破坏,则这一比例下降到64%。因此,为了促进我国木薯燃料乙醇的发展,减少木薯燃料乙醇生产的碳排放,首先应该引导农民合理施肥,利用边际土地种植木薯,不转换林地、草地等土地类型的利用方式,减少对土壤碳库的破坏;此外,要开发高效节能的燃料乙醇转化技术并加强对副产品的二次利用。

Study on Carbon Balance of Cassava-Based Fuel Ethanol

Considering the energy security and greenhouse gas emissions, many governments have been developing bio-liquid fuel industry in recent years. Chinese government also advocates to develop fuel ethanol industry with non-food crops such as cassava. However, scientists have been debating heatedly on carbon emission of bio-liquid fuels. The focuses are the destruction of soil carbon pool during cassava plantation and the use of by-product during processing in different technical conditions. This paper builds the carbon balance analysis model, then, assesses the carbon emission of cassava fuel ethanol in its life cycle. The results show the carbon emission of cassava fuel ethanol per kilogram in its life cycle is 0.457 kg and 0.647 kg respectively in the new and old technical conditions. Carbon emission mainly comes from the use of nitrogen fertilizer, the destruction of soil carbon pool and the fossil energy input of cassava processing, the three parts are 9%, 29% and 50% of total emission respectively in the new technical condition. Taking gasoline as a reference, in old technical condition, the carbon emission of cassava fuel ethanol is negative benefit. But in new technical condition, the carbon emission of cassava fuel ethanol is 90% of gasoline carbon emission. This percentage will drop to 64% if the destruction of the soil carbon pool was avoided. Therefore, in order to promote the development of China’s cassava fuel ethanol, first, farmers should be guided to apply fertilizer properly, grow cassava on marginal land, not convert woodland, grassland and other types of land use patterns. In addition, we should exploit efficient fuel ethanol conversion technologies and strengthen the use of by-product meanwhile.