基于木薯作为能源的分析

Keywords: Life cycle assessment; Ethanol fuel; Cassava; Life cycle inventory analysis
1. Introduction
Air emissions from automobiles have become one of the main polluted sources to the cities’ environment with the increasing of the amount of automobile. And it is also the main reason why the environment pollution becomes more and more serious for many metropolises in the world [1]. Many studies have shown that CO2 emissions from automobiles are about 14% of the total CO2 releases, CO and HC emissions are about 50e60%, and NOX and PM10 emissions are about 30% and 10e20%, respectively [2]. In China, among air emissions of metropolises, above 40%, 80%, 70% of the total NOX, CO and HC emissions, respectively, are due to automobiles [3].
R. Leng et al. / Journal of Cleaner Production 16 (2008) 374e384
375
Like other biomass fuel, ethanol fuel derived from cassava in China is also confronted with two controversial issues. One is whether ethanol fuel is environmental friendly, the other is that does it or doesn’t it produce positive net energy? As for the two issues, several studies were conducted in past decades. Cal Hodge [7] insisted that ethanol use in US gasoline should be banned, not expanded. Because the average ethanol life cycle energy balance indicated more energy is needed to make ethanol than ethanol gives back, and ethanol use increases NOX, VOC, and air toxics’ emissions relative to baseline gasoline. David Pimentel [8] argued that ethanol fuel based on corn degraded natural environment and contributed to water pollution and air pollution, and about 29% more energy is used to produce a gallon of ethanol than the energy in a gallon of ethanol. Chambers et al. [9] indicated that the energy efficiency is depended on many factors, such as energy-conserving farming practices, energy-conserving industrial technology, and crop residues. However, Hosein Shapouri et al. [10] concluded that corn ethanol was energy efficient as indicated by an energy output:input ratio of 1.34. Seungdo Kim [11,12] also concluded that the ethanol fuel from corn grain produced the positive energy. As for the US corn ethanol energy balance, in the latest literature, the Consensus of Farrell et al. [13] and von Blottnitz and Curran [14] is that US corn ethanol has a slightly positive energy balance.
China has been a net importer of petroleum since 1993. Imported oil currently accounts for about 25% [4] of China’s total domestic needs, and the amount will probably increase to
Journal of Cleaner Production 16 (2008) 374e384
/locate/jclepro
Life cnalysis of cassava-based Fuel ethanol in China
Cassava is a good feedstock to produce ethanol because it has high starch content and it is abundant in the southern provinces of China. Cassava is a starchy material. Starch contained is first liquefied so that dextrin and subsequently fermentable sugars can be obtained, and, after fermentation and distillation, ethanol of 95.6% w/w comes out, through dehydration, which is concentrated to 99.5% w/w. Thus cassava-based Fuel ethanol is produced, and it is usually denatured by small volume of gasoline or other materials added preventing people from drinking it.
more than 50% by the year 2015 due to the rapidly rising demand for oil by the flourishing economy [5,6].
The Chinese government is developing biomass ethanol as one of its transportation fuels for energy security and environmental improvement reasons. Two policies entitled as Denatured Fuel Ethanol and Ethanol Gasoline for Motor Vehicles have been executed in China since 2001, aiming at developing a sustainable energy resource, enhancing domestic energy security, and improving the domestic environment. Ethanol fuel is used by blending with gasoline to produce E10 (10% by volume Fuel ethanol added to gasoline) nowadays in China.
Received 30 July 2006; received in revised form 7 November 2006; accepted 10 December 2006 Available online 9 February 2007
Abstract
The Chinese government is developing biomass ethanol as one of its automobile fuels for energy security and environmental improvement reasons. The cassava is an alternative feedstock to produce this ethanol fuel. Its performance of environmental impacts and energy efficiency is the critical issue. Life cycle assessment has been used to identify and quantify the environment emissions, energy consumption and energy efficiency of the system throughout the life cycle. This study investigates the entire life cycle from cassava plantation, ethanol conversion, transport, Fuel ethanol blending and distribution to its end-use. Product system of cassava-based ethanol fuel is described and it is divided into six unit processes. The environmental impacts and energy consumption of each unit process are quantified and some of the potential effects are assessed. Ó 2006 Elsevier Ltd. All rights reserved.