Note: Descriptions are shown in the official language in which they were submitted.
~3235a
The invention relates to a method of continuously re-
covering fermentation products, in particular ethanol, from
fermented mash, wherein the mash from a fermentation plant
that possibly includes a raw material processing, possibly
after separation and return of a microorganism culture into
the fermentation plant - is supplied to a distilling unit,
distillery 510ps to a large extent freed from fermentation
products are drawn off from the bottom part of the di-
stilling unit and partially returned into the raw material
processing and fermentation stages.
U.S.patent No. 2,440,925 discloses a method of pro-
ducing alcohol, in which mash present in a fermentation
vessel is fermented with yeast, a part of the fermented
mash liquid is continuously drawn off, distilled under a
reduced pressure, and the distillery slops freed from alco-
hol are returned to the fermentation vessel so as to keep
low the alcohol content of the mash and thus not damage the
yeast. However, from time to time the production process
must be interrupted in order to let off mash enriched with
unusable substances from the fermentation vessel.
In zymotechnological plants the disposal of the dis-
tillery slops constitutes a problem of increasing impor-
tance. At present, one of the most common methods is the
concentration of the distillery slops and their use as
fodder or as fuel - e.g., for the production of vapor.
For reducing the amounts of distillery slops incurring
and for decreasing the amount of process water required for
diluting the mash, lt is known to recycle alcoholic mash
liquid having varying contents of ethanol or distillery
slops from the distillation to the raw material processi.ng
358
and/or to fermentation. The raw material processing may,
e.g., consist in hydrolyzing and saccharifying starch. Also
a possible separation and outward transfer of suspended
solids with the help of separating devices such as screen
bends, sedimentation vessels and centrifuges, as well as
the separation oE yeast from alcoholic mash and return of
yeast into the fermentation stage are known.
Thus, European Patent No. 0 011 334 relates to a pro-
cess for the continuous production of ethanol, wherein a
partial stream of the fermented mash is continuously re-
moved, the yeast cells are separated from the mash by means
of a centrifuge and are returned into the fermentation and
the mash is returned to the fermentation after a complete
or partial removal of the alcohol in a vacuum evaporator.
According to Canadian patent No. 1,110,986, a flow from the
fermentation is separated by centrifugation into a yeast
concentrate and yeast-free flow, the yeast concentrate is
returned to fermentation, and the yeast-free flow is
distilled. The residual flow having a low ethanol content
resulting from the distillation is partially returned to
fermentation as a substrate flow freed from solids after
having been ut1lized for the preparation of a raw material
flow.
Also according to Canadian patent No. 1,147,678 a
yeast concentrate is separated from the fermentation liquid
and returned to fermentation; the ethanol-containing liquid
that is free from yeast is first fed into a simple evapora-
tor and, there, is separated into a vapor flow rich in
0 ethanol and a bottom flow. The larger portion of the liquid
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bottom flow is returned to fermentation, and the residual
portion is supp]ied to a stripping unit, from which the top
product rich in ethanol gets into a distilling unit to-
gether with the vapor flow from the evaporator rich in
ethanol.
From Canadian patent No. 1,140,872 it is known, for
the production of ethanol by fermentation of a carbohy-
drate-containing substrate, to first supply the fermenta-
tion broth to a simple vacuum evaporator, to return the
liquid yeast-containing bottom flow from the evaporator
partially to the fermentation, and to separate the remain-
der into a yeast concentrate flow that is also returned to
the fermentation, as well as into a flow free from yeast
which is supplied to a stripping unit. The vapor flow rich
in ethanol from the vaccum evaporator is further worked up
in a rectifying column, the vapor flow rich in ethanol from
the stripping unit may be supplied to the evaporator.
Finally, Canadian Patent No. 1,138,798 deals with a
method of a similar kind with integrated raw material
processing, in which the fermenting broth is separated into
a returned yeast concentrate flow and a flow free from
yeast, at least a part of the flow free from yeast is
separated in a simple evaporator into a vapor flow rich in
ethanol and a liquid bottom flow, the latter is at least
partially again returned to fermentation and the vapor flow
rich in ethanol is guided to a fractionation unit. The
polysaccharide-containing raw material is - preferably pre-
hydrolyzed - introduced into the evaporator and there en-
zymatically further hydrolyzed. With the liquid bottom
flow the dis30 integrated raw materials get to the fermen-
32;358
tation, wherein also enzymes may be added to the fermentor.
If, according to the known methods, only partly de-
alcolholized mash is recycled, due to the amount of alcohol
ie~ in circulation there results a corresponding increase
in the liquid volumes in the fermentation and in possible
separating devices. However, larger dimensioned apparatuses
cause higher investment costs and consume more energy when
operated.
If, however, mash de-alcoholized as far as possible
(distillery slops) is recycled which has the same content
of dry substances as the distillery slops to be derived
from the process, relatively large amounts of distillery
slops will still be incurred, since the amount of distill-
ery slops capable of being recycled in most substrates is
limited by a maximum dry substance concentration in the
fermentation plant. Despite this, in each case it is more
favorable for reasons of process technology to provide as
low a portion of unfermentable dry substance as possible in
the mash to be fermented.
The invention aims at overcoming the disadvantages and
difficulties still connected with the known methods and to
provide an energy-saving method requiring simple apparatus,
with which distillery slops of a higher concentration are
incurred in a reduced amount and the amount of process
water required comparatively may be kept very low without
having to put up with a substantial inhibition of the
course of fermentation due to a too pronounced enrichment
of fermenta~ion products or unusable substances.
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24242-410
Thus the present invention provides a method of
continuously recovering fermentation products, such as ethanol,
from a fermented mash, including supplying the mash from a
fermentation plant to a distilling unit having a lower region and
a bottom part, distilling the mash in the distilling unit thereby
separating the mash into fermentation products and distillery
slops, drawing off the distlllery slops largely freed from
fermentation products from the bottom part of the distilling unit,
partlally returning the distillery slops into the fermen~ation
plant, forming a further partial flow of the distillery slops
drawn off from the distilling unit, supplying the further partial
flow of distillery slops to an indirectly heated evaporator stage
so as to concentrate the distillery slops therein and form vapors,
feeding the vapors formed in the evaporator stage directly into
the lower region of the distilling unit and discharging the
concentrated distillery slops formed in the evaporator stage.
The invention further relates to a method of
continuously recovering fermentation products from a fermented
mash, comprising the steps of supplying the mash from a processing
~0 unit including a fermentation plant and a raw material processing
plant to a distilling unit having a lo~er region and a bottom
part, distilling the mash in the distilling unit thereby
separating the mash into fermentation products and distillery
slops, the distillery slops having substances suspended therein,
drawing off the distillery slops largely freed from fermentation
products from the bottom part of the distilling unit, separating
and discharging the substances suspended in the distillery slops,
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lX~323~
24242-410
partially returning the distlllery slops freecl from the suspended
substances into the fermentation plant, separating a micro-
organism culture from the mash coming from the fermentation plant
and returning ~he micro-oryanism culture into the fermentation
plant prior to supplying the mash to the distilling unit, and
forming a further partial flow of the distillery slops drawn off
from the distilling unit, supplying the further partial flow o~
dlstillery slops to an indirectly heated evaporator stage so as to
concentrate the distillery slops therein and form vapors, feeding
the vapors formed in the evaporator stage directly into the lower
region of the distilling unit and discharginy the concentrated
distillery slops formed in the evaporated stage, the distillery
slops largely freed from fermentakion products and drawn off from
the bottom part of the distilling unit being partially returned to
at least one of the raw materlal processing plant and the
fermentation plant.
The single figure of the drawings accompanying the
speciflcation is a schematic view of a fermentation plant suitable
for carrying out the process of the invention.
Beside ethanol, also other distillable fermentation
products, such as butanol and acetone, may be obtained as the top
products of a distilling unit. Bu~anol and possibly acetone are
formed in the anaerobic fermentation wlth, e.g., Clostridium
butylicum or acetobutylicum ~rom glucose-containing substrates.
For ethanolic fermenta~ion yeasts are commonly
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used as micro-organisms.
The separation of the micro-organism culture from the
fermented mash may already take place prior to feeding the
fermentation-product-containing mash into the distilling unit -
e.g., by centrifugation. If the pressure is not sufficient while
working in the distilling unit, so that temperatures of more -than
approximately 40C are reached during distillation, which
temperatures are already detrimental to the micro-organisms, it
is of course preferable in many cases that the micro-organisms
are separated beforehand.
According to a preferred embodiment of the method
according to the invention, substances suspended in the drawn off
distillery slops are separated. Only the distillery slops freed
from suspended solids are divided, partially returned into the
raw material processing and/or the fermentation stages, and a
different partial flow is led into -the evaporator stage.
The invention further provides a method of continuously
recovering fermentation products, such as ethanol, from a
ermented mash, including supplying said mash from a fermentation
plant to a distilling unit having a lower region and a bottom
part, distilling said mash in said distilling unit thereby
separating said mash into fermentation products and distlllery
slops, drawing off said distillery slops largely freed from
fermentation products from the bottom part of said d~isti]ling
unit, partially returning said distillery slops into said
fermentation plan~t, comprising separating a micro-organism
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- 5~ - 24242-410
culture from said mash coming from said fermentation plant and
returning said micro-organism culture into said fermentation
plant prior to supplying said mash to said distilling unit, and
forming a further parti.al flow of said distillery slops drawn off
from said distilling unit, supplying said further partial flow of
distillery slops to an indirectly heated evaporator stage so as
to concentrate said distillery slops therein and form vapors,
feeding said vapors formed in said evaporator stage directly into
the lower region of said distilling unit and discharging said
concentrated distillery slops formed in said evaporated stage,
said fermentation plant further including a raw material
processing plant wherein said distillery slops largely freed from
fermentation products and drawn off from said bottom part of said
distilling unit are partially returned to at least one of said
raw material processing plant and said fermentation plant.
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3~13
In case of a distilling unit operated under a suffi-
cient vacuum, the micro-organism culture may also be sepa-
rated from the drawn-off distillery slops - e.g., by means
of centrifugal separators - and may again be added to the
fermentation stage.
If the distilling unit is opera-ted under a slight
vacuum only, under normal or overpressure, suitably the
thermal content of the distillery slops drawn off from the
distillation unit is partly transferred to the mash sup-
plied to the distilling unit via one or more heat exchan-
gers. The heat transfer to the mash coming from the fermen-
tation plant in this case is particularly effected before
the separation of suspended substances from the distillery
slops, i.e., immediately after the drawing off of the
distillery slops from the distilling unit (separating
column) so as to avoid disturbances connected with the
boiling behavior of the distillery slops - e.g~, during a
separation by decantation - as well as thermal losses
during a possible intermediate storing. For an even better
utilization of the energy, it is of additional advantage
also to pre-heat the partial flow of the distillery slops
freed from suspended substances and to be led into the
evaporator stage, by means of the total amount of the
distillery slops immediately drawn off from the distilling
unit, a part of the thermal content of the distillery slops
still containing suspended substances at first being
transferred to this partial flow and subse~uently to the
mash supplied to the distilling unit.
If a sufficiently low pressure is adjusted in the
0 distilling unit, a cooling of the total amount of the drawn
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~ ~X358
off distillery slops is not necessary, and preferably only
that part of the distillery slops returned to the raw
material processing and/or to the fermentation stages is
used for pre-heating the mash. The pre-heating of the mash
may additionally or exclusively be also carried out with
any other media incurred in the plant.
A preferred embodiment of the invention will be ex-
plained in the following in more detail by way of a process
diagram.
An aqueous raw material flow 1 with vegetable, sugar,
starch and cellulose containing starting material, such as
cereals, sugar cane or molasses, at first reaches a pro-
cessing means 2, in which the raw materials are disinte-
grated, hydrolyzed, and, if necessary, purified. The sub-
strate obtained or mash 3 is guided into the fermentation
stage 4, where the fermentation takes place under the
action of micro-organisms.
A certain fraction of the fermented mash is contin-
uously drawn off and guided through duct 5 into a centri-
fugal separator 6. The separated micro-organism culture is
returned into the fermentation stage 4 vla duct 7, and the
fermentation-product-containing mash is pumped through a
regenerative heat exchanger 8 into the upper section of a
distilling unit 9. Su1tably, the distilling unit in most
cases comprises a single separating column from whose top a
vapor flow enriched with fermentation products is withdrawn
through duct 10, e.g. in order to be led to a rectifica-
tion.
If, e.g., very large amounts of fermented mash must be
0 worked up, the distilling unit may also consist of two or
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more distilling columns. The distillery slops that to a
large extent are freed from fermentation products are led
from the bottom part of the distilling unit 9 into a means
for separating suspended substances. In the embodiment
illustrated, a screen bend 11 is provided for the sepaxa-
tion.
The separated solids are withdrawn from the process as
indicated by arrow 12. A portion of the distillery slops
freed to a large extent from suspended substances by means
of the screen bend 11 is returned into the raw material
preparation means 2 and/or into the fermentation stage 4
via duct 13 while giving off heat in the heat exchanger 8
to the fermentation-product-containing mash. A further
partial flow of the distillery slops is led through duct
branch 14 into an indirectly heated evaporator stage 15.
The evaporator stage comprising one or more simple
evaporators each having one or only a few theoretical
separation stage(s) may, e.g., be heated with fresh vapor
or by heat exchange with any hot medium available in the
plant. The temperatures to be adjusted mainly depend on the
pressure conditions prevailing in the individual parts of
the plant. The vapors forming in the evaporator stage 15
and mainly consisting of water vapor, are supplied via~
supply duct 16 into the lower region of the distilling unit
9 for directly heating the same.
Due to the delivery of vapors, the distillery slops
finally leaving the evaporator stage 15 through discharge
17 are very concentrated as compar,ed to that part of the
distillery slops returned into the raw material processing
and fermentation stages through duct 13. The concentrated
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distillery slops from discharge 17 may in some instances be
used as fodder without further removal of water or, since
they are autothermic due to their high content of dry
substances, they may be burned directly.
With the method according to the invention, thus non-
fermentable substances as well as fermentation products
that are toxic for the micro-organisms in higher concen-
trations are continuously removed from the process in a
particularly energy-saving manner, and furthermore the
amount of distillery slops incurred is drastically reduced.
In the following table the advantages of the method
according to the invention are demonstrated by the example
of the ethanolic fermentation by comparing the material
flows of two known methods and of the method according to
the invention.
I relates to a known method in which the distilling
unit in the bottom part is indirectly heated, partly de-
alcoholized mash is returned into the raw material pro-
cessing and fermentation stages and distillery slops are
drawn off from the sump of the distilling unit.
II symbolizes a known method in which the heating of
the distilling unit is effected as in method I, yet largely
de-alcoholized mash tdistillery slops) from the sump of the
distilling unit is partly recycled.
III denotes the method according to the invention.
The composition of the fermented mash fed Erom the
fermentation plant was the same in all three cases. As
basis of reference the recovery of 100 kg of pure ethanol/h
was chosen, the ethanol content of the crude spirit drawn
off from th_ top of the distilling unit each being 40 % by
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mass.
As can be seen from the table, with the method of the
invention (III) the total amount of fermented mash to be
processed is lower by about 11 % as compared to method I.
The total amount of distillery slops of the method of
the invention is reduced by about 30 ~ - as compared to
method II - with a simultaneously higher content of dry
substance.
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