科研之友
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摘要
Global biofuels production grew rapidly from 2007 to 2012, led by the United States and Brazil, the world's two largest fuel-ethanol-producing systems. In this paper we provide insights into the characteristics of mature Brazilian sugarcane and maturing US dry mill corn ethanol industries. Both systems continue to improve as measured by life cycle data such as total renewable energy produced per unit of fossil energy consumed [renewable energy ratio (RER)]. Sugarcane self-benchmarking systems showed RER values of 7.0 in 2002 to 9.4 in 2009 as the industry started to switch to mechanized harvesting. The average US RER improved from 1.1 to 1.7 from 2000 to 2010. RERs of 4.4 to 5.5 are observed in corn ethanol plants employing natural gas or corn stover combined heat and power. Ethanol systems configured to produce ethanol and electricity had similar net energy balances (a ratio of net energy produced to energy contained in the fuel). One measure of greenhouse gas (GHG) emissions reductions (biomass use efficiency) compares the effectiveness of displacing carbon from combustion of fossil fuels with renewable carbon. Advanced corn ethanol systems reach higher GHG emission reduction levels compared to sugarcane ethanol by displacing coal-based electricity. Sugarcane systems achieve double the GHG emissions reductions per unit of harvested land relative to corn ethanol because sugarcane and corn are grown as perennial and annual crops in tropical and temperate climatic zones, respectively. Carbon dioxide capture and storage systems could offer additional GHG emission reductions for both corn and sugarcane ethanol systems.
- 出版日期2014-3
