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Title:
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Co-production of bio-ethanol, electricity and heat from biomass residues
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Author(s):
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Reith, J.H.; Uil, H. den; Veen, H. van; Laat, W.T.A.M. de; Niessen, J.J.; Jong, E. de; Elbersen, H.W.; Weusthuis, R.; Dijken, J.P. van; Raamsdonk, L.
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Published by:
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Publication date:
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ECN
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1-7-2002
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ECN report number:
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Document type:
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ECN-RX--02-030
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Conference Paper
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Number of pages:
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Full text:
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22
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Download PDF
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Presented at: 12th European Conference and Technology Exhibition on Biomass for Energy, Industry and Climate Protection, Amsterdam, The Netherlands, 17-21 juni 2002.
Abstract:
The use of lignocellulosic biomass residues as a feedstock offers goodperspectives for large scale production of fuel ethanol at competitive
costs. An evaluation was performed to assess the international status
of lignocellulose-to-bioethanol technology and the economical and ecological
system performance, to identify R&D approaches for further development.
Deriving fermentable sugars from the hemicellulose and cellulose fractions
of lignocellulosic materials via suitable pretreatment and enzymatic
cellulose hydrolysis is a critical R&D issue. Further development of
pretreatment via mild, low temperature alkaline extraction or weak acid
hydrolysis using CO2 dissolved in pressurized hot water (?carbonic acid
process?) shows good perspectives. Enzymatic cellulose hydrolysis with
the currently available industrial cellulases accounts for 36-45% of
ethanol production costs. At least a 10-fold increase of cellulase cost-effectivenes
is required. Despite substantial R&D efforts, no suitable fermentation
system is currently available for the fermentation of pentoses (mainly
xylose) from the hemicellulose fraction. Several strains of anaerobic,
thermophilic bacteria are able to convert all (hemi)cellulose components
into ethanol. Follow-up R&D will focus on isolation of suitable strain(s)
from this group. The system evaluation shows a 40-55% energetic efficiency
(LHV basis) for conversion of lignocellulosic feedstocks to ethanol.
Thermal conversion of non-fermentable residues (mainly lignin) in a
Biomass-Integrated-Gasifier/Combined Cycle (BIG/CC) system can provide
the total steam and electricity requirement for the production process
and an electricity surplus for export to the grid, giving a total system
efficiency of 56-68%. Water consumption in the process (28-54 liter
water/liter ethanol) is much higher than in current ethanol production
(10-15 l/l ethanol). The large amount of process water (used in the
pretreatment and cellulose hydrolysis sections), necessitates concentration
of the sugar solutions by evaporation to obtain an industrially acceptable
final ethanol concentration in the fermentation broth (>8.5 vol%). Follow-up
R&D will focus on reduction of water use, internal water recycling and
energy integration of the evaporation step with the ethanol purification
section. The estimated production costs of bio-ethanol from 3 types
of (ligno)cellulosic residues are 0.75-0.99 ?/l (34-45 ?/GJ), which
is considerably higher than the current costs of fuel ethanol from corn
starch (0.34 ?/l; 16.2 ?/GJ) and gasoline (7.3 ?/GJ). A sensitivity
analysis shows that cellulase costs will have to be reduced with at
least a factor 10 and capital costs need to be reduced by 30% to reach
ethanol production costs competitive with ethanol from starch crops.
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