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Liquid Transportation Fuels from Coal and Biomass: Technological Status, Costs, and Environmental Impacts
COAL AND BIOMASS SUPPLY
The United States has at least 20 years’ worth of coal reserves in active mines and probably sufficient resources to meet the nation’s needs for well over 100 years at current rates of consumption. In contrast, biomass can be produced continuously over a long term if managed sustainably, but the amount that can be produced in a given period is limited by the natural resources required to support biomass production. Given that production of corn requires large amounts of fertilizer and that corn grain is also an important source of food and feed, the panel regards corn-grain ethanol as a transition to cellulosic biofuels or other biomass-based liquid hydrocarbon fuels, such as biobutanol and algal biodiesel. Cellulosic biomass—obtained from dedicated fuel crops, agricultural and forestry residues, and municipal solid wastes—could potentially be sustainably produced at about 400 million dry tons per year with today’s technology and agricultural practices and with minimal adverse impacts on U.S. food and fiber production or on the environment. A key assumption underlying that estimate is that dedicated fuel crops will be grown on idle agricultural land in the U.S. Department of Agriculture’s Conservation Reserve Program. By 2020, the amount of sustainably produced biomass could reach 550 million dry tons per year.
Ensuring a sustainable biomass supply requires that the resource base be assessed systematically to address multiple environmental, public, and private sector concerns simultaneously. Producers will probably need additional incentives to grow biofeedstocks so as to avoid direct and indirect competition with the food supply and also to avoid land-use practices that add substantially to net greenhouse gas emissions. Appropriate incentives can encourage sustainable approaches to the production of lignocellulosic biomass.
Technology for biochemical conversion of the starch in grains to ethanol has been deployed commercially. Although grain-based ethanol has been important for initiating public awareness and the development of industrial infrastructure for fuel ethanol, cellulosic ethanol and other advanced cellulosic biofuels have much greater potential for reducing U.S. oil use and greenhouse gas emissions without