08-06-2013, 04:54 PM
Techno-economic analysis of Bio-alcohol production in the EU: a short summary for decision-makers
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TECHNICAL FUNDAMENTALS
WHAT IS BIO-ALCOHOL?
Today bio-alcohol is probably the most used non-fossil alternative transport fuel in the
World. Brazil’s decision to produce fuel alcohol from sugar cane, and the use of bio-alcohol in
USA as an octane enhancer of gasoline, among other reasons have made transportation bioalcohol
a relatively well-developed industry.
Fermenting and distilling sugar crops, starch crops that have been converted into simple
sugars or processing cellulose bio-mass can produce bio-alcohols. These bio-alcohols are mainly
bio-ethanol and bio-methanol.
Bio-ethanol can be produced from any biological feedstock that contains appreciable amount of
sugar or material that can be converted into sugar such as starch or cellulose. To date, the most
widely used raw materials for bio-ethanol are sugar-cane (Brazil), maize (USA), sugar-beet and
wheat (European Union). Cellulose materials such as straw, maize stalks and wood, are
expected to be used widely as processing technology is developed. Bio-ethanol is mainly
converted into bio-ETBE or used mixed with gasoline and diesel.
Bio-ETBE (ethyl-tertio-butyl-ether) is an additive to enhance the octane rating of petrol as a
replacement of the fossil MTBE (replacing lead and benzene in unleaded petrol) and to reduce
emissions. It is produced by combining bio-ethanol and isobutylene. European countries have
opted for ETBE to petrol blends, whereas it is not used in Brazil and the USA.
BIO-ETHANOL/ETBE PRODUCTION
Bio-ethanol is produced from fermentation of sugar by enzymes produced from specific
varieties of yeast. The most abundant sugars in agricultural crops are sucrose and glucose (the
latter usually obtained from starch). Ligno-cellulose materials such as straw, maize stalks and
wood are potential sources of sugars.
The technology for production of industrial ethanol has improved considerably, but the
underlying principles remain the same: extraction of fermentable carbohydrate from feedstock,
followed by fermentation and recovery of ethanol in a three-stage distillation. The organisms and
enzymes for carbohydrate conversion and glucose fermentation on a commercial scale are
readily available.
The most energy intensive part of the process, fermentation and recovery of ethanol, is
the same for all raw materials. Where the individual processes differ, it is in the extraction and
preparation of fermentable carbohydrates. In the case of starch, the conversion to sugar is
derived from enzymatic hydrolysis, which is a cheap, simple and effective process. Lignocellulose
materials are made up from cellulose components (essentially long chains of sugars
and protected by lignin). An extensive process is required for the extraction and fermentation of
carbohydrates. Enzymes required for these processes are currently too expensive for commercial
use.
PRODUCTION OF RAW BIOMASS FOR BIO-ETHANOL
In the European Union the most widely used feedstock for production of bio-ethanol are
wheat and sugar beet. Given that their bio-ethanol production process is already available, in this
paper wheat and sugar beet will be considered as reference crops for the economic analysis,
comparing their results to the straw based bio-ethanol production.
The attainable crop yields are estimated on the basis of national and European statistics.
For wheat, three alternative crop yield levels are examined: average yield for the EU (7t/ha), high
yield (9 t/ha), and average yield for Mediterranean climate conditions and CEECs countries (3.5
t/ha).
In the case of sugar beet, two crop yield levels are considered: average yield level for the
EU (66 t/ha) and high yield level (78 t/ha).
Substantial reductions in bio-ethanol production costs may be achieved by replacing
cereals or sugar beet with less expensive ligno-cellulose based feedstock3. This feedstock can be
categorised as agricultural waste, forest residue and various energy crops. The agricultural
waste, available for bio-ethanol conversion, includes crop residues such as wheat straw, corns
stove and rice straw. The forestry waste includes under-utilized wood and logging residues;
rough, rotten and salvable dead wood and excess sapling and small trees.
BIO-ETHANOL / ETBE CHARACTERISTICS AND ENGINE PERFORMANCE
Compared to the conventional fossil fuels and especially – gasoline, bio-ethanol and bio-
ETBE show several strong points.
First of all, after phasing out the lead from gasoline as an agent for increasing the octane
rating, refineries started to add oxygenates to gasoline for this purpose – alcohol and ethers
(benzene, xylene, toluene, etc.), the latter however being rather toxic. In this context, with an
average octane rating of about 110, bio-ethanol represents an excellent, non-toxic octane
enhancer. The fact that bio-ethanol is a little bit heavier than gasoline – the average density of
bio-ethanol is 790-800 kg per 1000 litres, as compared to 720-780 kg per 1000 litres for gasoline
– does not prevent its successful blending into gasoline. Bio-ETBE in low-concentration (up to 15
%) blends is also used as an alternative [especially to methyl-tertiary-butyl-ether, (MTBE)]
oxygenated agent into gasoline for increasing the octane rating. These properties offer the
opportunity to blend bio-ethanol or bio-ETBE with lower-octane (so called “sub-octane”) gasoline.
ENERGY BALANCE
When analysing the overall energy balance of bio-ethanol (the so called “Life-Cycle”),
different literature sources are giving a great diversity of data and conclusions. This is due to the
fact that the energy balances heavily depend on the feedstock used, the extent of utilisation of
by-products and other specifics, etc. However, it may be affirmed as a broad conclusion that the
overall energy balance of bio-ethanol is definitely positive. It means that bio-ethanol generates
more energy than it uses during its production, as it is shown in Table 3.
BIO-ETHANOL AND ENVIRONMENT
Apart from diversity of fuel supply, the application of bio-ethanol (in comparison with
fossil fuels and especially – with gasoline) provides also environmental benefits in terms of
decreased greenhouse and other polluting emissions. The quantification of those environmental
benefits usually is performed basis the so-called “Well-To-Wheel” (WTW) approach, i.e.
measuring the aggregate net emissions over the whole production-consumption chain. On the
other hand, the WTW emission results may fluctuate significantly on case-by-case basis,
depending on the production pathways and the use of by-products. Therefore, the emission
benefits from utilisation of bio-ethanol herein are given on a tail-pipe (except CO2 where a WTW
view is essential) measurement basis.