摘要：Since the United States began a programme to develop ethanol as a transportation fuel, its
use has increased from 175 million gallons in 1980 to 4.9 billion gallons in 2006. Virtually
all of the ethanol used for transportation has been produced from corn. During the period
of fuel ethanol growth, corn farming productivity has increased dramatically, and energy
use in ethanol plants has been reduced by almost by half. The majority of corn
ethanol plants are powered by natural gas. However, as natural gas prices have
skyrocketed over the last several years, efforts have been made to further reduce
the energy used in ethanol plants or to switch from natural gas to other fuels,
such as coal and wood chips. In this paper, we examine nine corn ethanol plant
types—categorized according to the type of process fuels employed, use of combined heat
and power, and production of wet distiller grains and solubles. We found that
these ethanol plant types can have distinctly different energy and greenhouse gas
emission effects on a full fuel-cycle basis. In particular, greenhouse gas emission
impacts can vary significantly—from a 3% increase if coal is the process fuel
to a 52% reduction if wood chips are used. Our results show that, in order to
achieve energy and greenhouse gas emission benefits, researchers need to closely
examine and differentiate among the types of plants used to produce corn ethanol
so that corn ethanol production would move towards a more sustainable path.
