Life Cycle Energy Balance And Ghg Emissions Of Cassava-based Fuel Ethanol In Guangxi

The Chinese government currently faces great challenges in national energy security, as well as in the mitigation of the effects of global warming. Therefore, the choice of reasonable strategies to achieve both objectives above is crucial. Among all the strategies, the development of biofuel is considered as one of the most attractive options because of its renewability and carbon neutrality. In China, cassava is the most preferred non-grain feedstock for bioethanol development.Many life cycle analyses have been conducted on the energy balance and GHG emissions of cassava-based fuel ethanol (CFE) in the existing literatures, while cassava planting modes have been overlooked in most previous studies, in which most crucial parameters are based on foreign mature models. Thus, five scenarios related to cassava planting modes have been selected to evaluate the lifecycle energy balance and GHG emissions of the CFE system based on local data. In addition, potential technological modes, which may achieve energy conservation and emission mitigation, have been screened for further comparative scenarios analysis.Results show that five CFE scenarios all show positive net energy values (NEV),3.47-4.75MJ/L, and25.8%-34.1%GHG emissions savings compared with the conventional gasoline. Ethanol conversion is found to have the biggest energy input and the highest GHG emissions among all scenarios examined, followed by cassava planting and logistics because of the huge coal consumption. Using cassava stems as fuel for coal replacement have been simulated and results show that about60.6% GHG emission can be saved compared with using coal as fuel scenario. What’s more, if dry chips instead of fresh roots were used during logistics,1.58MJ/L ethanol can be saved, causing7.8%-8.8%GHG emissions reductions compared with those of the fresh-roots logistics scenarios.The planting modes had significant impacts on their energy and GHG performance. The intensive planting modes (high-intensity of fertilizer use and machinery harvest) generally show poorer performance than the extensive ones, primarily because of the intensive energy consumption and GHG emissions during nitrogen fertilizer production, the N2O emission of nitrogen fertilizer use, and higher yield loss rate caused by machinery harvest.Uncertainties stemmed from the selection of parameters could vary GHG emissions. In this paper, agricultural parameters and industrial process data, which are of high uncertain and may have significant impacts on the life cycle GHG emissions, have been obtained from our survey and interview in Guangxi, and a Monte Carlo simulation has also been performed to reduce the uncertainties.The mean values of the GHG emission of CFE in five scenarios are29.2-37.6g CO2-eq/MJ ethanol (using dry stems as processing fuel) and69.1-77.6g CO2-eq/MJ ethanol (using coal as processing fuel), which are all lower than the conventional gasoline GHG emission. What’more, if a40％GHG reduction target was set, the probability that GHG emissions of CFE (using coal as fuel) would meet the GHG reduction target was only0.6%-6.8%, whereas the probability that GHG emissions of CFE (using dry cassava stems as fuel) would meet the GHG reduction target reached97.8%-99.8%.Finally, this study has chosen three cases from China, Thailand and Vietnam for a comparative analysis. Combined with results in this paper, policy implications of CFE development as well as the research prospects are thoroughly explored.