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Title:
Co-production of bio-ethanol, electricity and heat from biomass residues
 
Author(s):
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.
 
Published by: Publication date:
ECN 1-7-2002
 
ECN report number: Document type:
ECN-RX--02-030 Conference Paper
 
Number of pages: Full text:
22 Download PDF  (397kB)

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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