World Energy Outlook 2006

ethanol yields and lowering unit costs. 10 Conversion efficiencies of 60% to
70% may ultimately be possible, yielding greenhouse-gas emission reductions
of 90% or more compared with gasoline, assuming all the process energy is
provided by the lignin component in the feedstock that cannot be converted to
ethanol (Hamelinck et al., 2004).
Succesful ligno-cellulosic ethanol technology would open the door to a much
wider array of potential cellulosic feedstocks, including dedicated cellulosic
crops, such as grasses and fast-growing trees. In North America, attention is
being given to corn stover and switchgrass. In Europe, attention is focused on
food-processing waste, miscanthus grass and short-rotation woody biomass. In
Brazil, sugar cane stalks (bagasse) are already used to provide heat and electrical
process energy for ethanol conversion, once the sugar is removed, but are not
actually processed into ethanol itself. Much of the sugar-cane crop is still left in
the field and burned. Advanced ligno-cellulosic conversion processes would
allow the full use of the biomass available in the cane. Other forms of cellulosic
feedstock could be grown on poorer quality soils than those currently used to
grow crops for conventional ethanol production, requiring less fertilizer and
water. Production costs could be considerably lower than for the cereal and
seed crops currently used in Europe and the United States (Table 14.5)
For the production of ethanol from ligno-cellulosic feedstocks to become
commercially viable, significant technological challenges still need to be
overcome. Today, there is virtually no commercial production of ethanol from
cellulosic biomass, but there is substantial research going on in this area in IEA
countries, particularly the United States, Canada and Sweden. A key objective
is to produce a fermented broth with a higher concentration of ethanol, in
order to reduce the energy needs of the distillation process to fuel grade.
A commercial scale plant is under construction in the United States and others
are planned in Europe. The unit production cost is expected to be almost
$1 per litre of gasoline equivalent, based on a biomass feedstock price of
$3.60/GJ (Hamelinck et al., 2005). Significantly lower costs are believed to be
achievable in the next one or two decades, through optimised pre-treatment,
higher ethanol concentrations before distillation, enhanced enzymes and
improved separation techniques. Integration of biomass gasification and
combined-cycle technology to improve the efficiency of use of the unused
portion of lignin to power the process may also help lower costs and reduce
greenhouse-gas emissions. Scaling up production facilities and better logistics
10. The financial cost of biomass from perennial crops such as trees and grasses is around $2/GJ
(assuming each tonne of biomass contains 19 GJ) in many world regions, including Eastern Europe
and the United States. It is lower in Latin America and sub-Saharan Africa. In temperate regions, the
cost of producing cereals and seeds for ethanol production is typically five to ten times higher.
Chapter 14 - The Outlook for Biofuels
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