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Yeast selection vs. investment levels
for Ethanol production plants.
by Luis R. Calzadilla, Contactos Mundiales Ltda.
In reference to Ethanol production I would like to mention some ideas about
the issue of ethanol production plants and investment.
Firstly let us remember that ethanol is produced by yeasts and there are
many strains with quite different attributes. For the lowest cost plant
one has to select the best Saccharomyces Cerevisae yeast for the purpose
in mind and, then, design the plant around the selected organism's
attributes.
If you are looking forward to produce ethanol fuel, then you would want
to use a yeast strain that:
- Can ferment the available sugars at the highest possible speed.
If a yeast can completely ferment a batch in 8 hours, then the plant capital
costs will be lower per unit of ethanol produced as compared to a yeast that
can only manage to ferment one batch per day. The same holds true for the
capital costs of pumps, piping, controls, space, etc. Most yeasts can only
produce one batch per day. The HS /LE Yeast and Process can produce 3
batches per day.
- Performs under high osmotic pressures.
Most yeasts can only ferment in very diluted molasses, around 18 or 20 Brix.
If you have a yeast that can perform in a 35 Brix substrate, then you can
put twice as much sugar into the fermenter and produce twice the ethanol with
every batch. Again, here is a lower plant capital cost, since you can save
on fermenter size and the associated gears. The HS / LE Yeast and Process
can ferment molasses solutions of 35 Brix.
(At this point your productivity per fermenter is six fold as compared to
the commonplace yeast)
- Separates quickly from the substrate at the end of each fermentation
cycle.
Recycling the yeast after each batch saves in propagation costs, therefore
it is advisable to reuse the yeast cells for as many cycles as possible.
Recycling common yeast calls for the use of expensive centrifuges which
add to the plant capital costs. However, if you use a flocculent yeast,
then you do not need to buy (and support) any centrifuge, thus lowering further
your plant capital costs. The HS / LE Yeast and Process do not require
the installation of any centrifuge, because the yeast is of a highly
flocculent type.
- Produces a low volume of highly concentrated effluent (vinasse or dunder).
Ethanol plants that use common yeasts produce around 12 to 14 liters vinasse
per liter of ethanol and require high capital costs for the effluent disposal
processes. The HS /LE Yeast and Process generates only between 4-7 liters vinasse
per liter ethanol, thus lowering the plant capital costs associated with the
effluent treatment process.
- Is tolerant to high ethanol concentration.
Some common yeasts can not tolerate high ethanol concentrations and thus
can only produce wines low in ethanol. Plants designed for low ethanol
concentrations (ie: 6% v/v) have to provide more thermal energy per liter
of ethanol than plants designed to process higher concentrations (ie: 12%).
A higher steam supply demands the use of larger boilers, therefore
increasing the plant capital costs. The HS /LE Yeast and Process can deliver ethanol
concentrations in the range of 12 % v/v, and this require lower capital
costs.
When you add up the capital cost reductions made possible by the use of
a yeast that embodies the above traits, then the capital costs can be
reduced by around 45%, with a significant production cost savings that results
from reduced depreciation, lower maintenance costs, lower casualty
insurance, lower energy costs, lower effluent treatment expenses, smaller plant
size and lower labor costs.
The astronomical capital costs for ethanol plants that use sugar cane
molasses or glucose from starch must be revised in the presence of the HS / LE
Yeast & Process.
Luis R. Calzadilla
Contactos Mundiales Ltda.
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