Note: Descriptions are shown in the official language in which they were submitted.
V00~2CA
FERMENTATION PROCESS AND APPARATUS
This invention relates to an improved process and apparatus for
separating multiphase mixtures internally in a fermenter. More
specifically the invention relates to a process and apparatus wherein
three phase systems from a biological conversion process are subjected
inside of the fermenter to a centrifuge action resulting in three
distinct streams.
Backgrolmd of the Invention
Biological prccesses have been used for centuries, for
instance, in the production of beer and wine. Recently, single cell
protein processes have become a field of significant research among the
biological processes. Whereas broadly speaking biological processes
include all operations involving reactions between living materials and
non living materials, in the present specification and claims a more
limited definition of a biological process is used. Here a biological
process is intended to refer to processes involving microorganism
fermentation in a fluid environment. Such microorganisms may be, e.g.
bacteria or yeasts, and such fluid environments include foam
environments.
One well known biological process to which this invention is
applicable is a fermentation process for the production of single cell
protein. A presently preferred example for such a process is described
in U.S. Patents 3,642,578 and 3,982,998. Generally, in a single cell
protein fermentation process an aerobic fermentation involving a
microorganism and a nutrient fluid is carried out in the presence of free
oxygen supplied for instance by the injection of air. In a fermenter
generally the nutrient fluid together with the microorganism are
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subjected to gas injection. A foam is formed in the upper portion of the
fermenter whereas the lower portion of the fermenter gener~lly contains a
liquid. The foam formed :is broken in a foam breaker and from this foaM
breaker gas is removed whereas the fluid remains in the fermenter.
From the bottom of the fermenter a microorganism containing
fluid is usually withdrawn, subjected to a solid/liquid separation step,
e.g., in a wash centrifuge and the recovered washed microorganism mass is
thereafter dried to obtain the final product. The fluid removed during
such a solid/liquid separation step contains still valuable ingredients
and is therefore generally sterilized and thereafter returned to the
fermenter. In the prior art procedures, the sterilization of this
recycle liquid is necessary to avoid any contamination of the recycled
stream. The fluid introduced into the fermen-ter has -to be absolutely
free of contaminating materials, such as contaminating organisms, in most
biological process, since the smallest contamination with living
organisms in the fermenter can destroy the entire reaction and result in
undesired products, and a plant shut down and thus increased costs.
Therefore, it has been proposed in the art to sterilize all recycled
streams. This practice is today followed throughout the industry.
The Invention
It is one object of this inven-tion to provide a new
fermentation process and apparatus for allowing simpler and more
efficient recovery of -the material to produce from the fermentation zone
as compared to known processes.
Another object of this invention is to provide a fermentation
process and apparatus with which cells from a fermentation process can be
recovered in a concentrated stream.
A yet further object of -this invention is to provide a
fermentation process and apparatus in which a liquid s-tream essentially
free of cell material can be recovered directly from the fermenter.
These and other objects, advantages, details, features and
embodiments of this invention will become apparent to those skilled in
the art from the following description, the appended claims and the
drawing in which
Figure 1 shows schematically and in cross section an apparatus
for carrying out the process of this invention.
In accordance with this invention a fermentation process is
provided which comprises passing a multiphase mixture to be defined into
a centrifuge cylinder and subjecting it to a rapid spinning movement
inside of such a centrifuge cylinder to generate two fluids, namely a
firs-t fluid being rich in cells and second fluid being depleted of cells
and comprising liquid and gas. The separation into an outermost cell
rich area and inner cell depleted f:Luid area occurs inside of the
centrifugal cylinder and inside of the fermenter. The efficiency of the
separation depends upon the specific operating conditions and ma-terials
involved.
Preferably, the process of this invention uses a continuous
scraping operation in which the first area of material which is in
contac-t with the centrifuge cylinder and which is radically outermost
layer is scraped from the wall and moved in axial direction mechanically
toward a discharge means. This enables the use of a stronger centrifugal
action and thereby a higher enrichment of cellular material in -the
outermost layer of cell rich fluid which without such scraping action
would build up on the centrifuge walls.
The multiphase mixture referred to frequently is a foam. The
multiphase mixture always comprises a gas phase, a liquid and a cell
phase. In single cell protein ~SCP~ fermentation procedures the product
to be withdrawn from the fermentation operation is the phase that is
depleted of liquid and rich in cells. In other biological processes the
product may be the liquid product and thus may be the liquid phase
depleted in cells. An example for the latter would be alcohol producing
fermentation.
The process of -this invention is applicable to aerobic systems,
i.e., systems in which 2 is added to the fermenter, as well as to
anaerobic systems, in which, e.g., N2 or no gas at all is added; in the
latter environment the cells during fermentation produce gas, such as C02
in an alcohol fermentation for the production of ethanol.
In a preferred embodiment of this invention, either -the cell
rich fluid or the cell depleted liquid is recycled to the fermentation.
Neither fluid has to be sterilized because the recycling is done within a
sterile environment. For ins-tance, in a fermentation operation to
produce alcohol or gum, the cell rich fluid is recycled and these
recycled organisms are reused to produce more of the desired product.
Therefore it is possible to operate in a very efficient manner despite
the Eact -that, e.g., the alcohol concentration in the withdrawn cell
depleted fluid is kept low at say 6-8 vol. % for highest cell activity.
The same reasoning is true in case liquid products other than ethanol are
produced that are inhibi-tory to organism growth, such as butanol,
acetone, isopropanol, etc.
A further variation of the process is the removal of the l:iquid
products in the stream of cell depleted fluid under vacuum. This
operation enhances the burs-ting of gas bubbles in the foam; fur-thermore,
some solvents and/or product fluids may be partially or completely
evaporated under -the low pressure to facilitate their recovery or
separation from the cells entrained in the cell depleted fluid.
More specifically, -the process of this invention comprises
subjecting a mixture of a growth medium and a microorganism to a
fermentation in a fermenter. In this fermenter, a three phase mixture of
gas, liquid and cells is generated. This three phase mixture is
separated inside of the fermenter into a fluid comprising a gas phase and
a liquid phase depleted of cells and into a cell rich phase depleted of
liquid. This separa-tion is done in a cen-trifuge cylinder arranged within
the fermentex. In the process of this invention, the liquid depleted
cell phase is in contact with the internal cylindrical surface of the
centrifuge cylinder. At least a por-tion of the fluid phase and/or the
cell rich phase is withdrawn from the fermenter.
In accordance with a second embodiment of this invention, an
apparatus for carrying out a fermentation process as described is
provided. This appara-tus comprises a housing with inlet and outlet
conduits. A centrifuge is arranged within the housing and this
centrifuge comprises a centrifuge cylinder having an inner surface
arranged and designed for receiving fluid material in a substantially
tangential movement on this inner cylindrical surface. A conduit for
receiving and conveying fluid comprising a liquid product depleted of
fermentation cells, and a cell product conduit for receiving and
conveying cell rich fluid product depleted of liquid from -the centrifuge
cylinder described are associated with the centrifuge. The apparatus is
provided with means for subjecting a multiphase material comprising gas
phase, a liquid phase, and a cell phase to a rapid movement having a
substantial tangential component with respect to the inner cylindrical
surface of the centrif-lge. This rapid movement inside of the centrifuge
cylinder causes the generation of the two fluicls and their separa-tion.
To allow the use of the apparatus wi-th a high centrifuge
efficiency, there is preferably prov:ided a scraper arranged within the
centrifuge which is designed and arranged in the centrifuge cylinder for
coaxial rotat:ion with respect -to this inner cylindrical surface and for
advancing cell rich material along the inner cylindrical surface -toward
-the cell product conduit. This scraper may have essentially helical
structure. The rotation of such a scraper causes the ma-terial in contac-t
with -the scraper to be advanced in axial direction. Basically, the
centrifuge and scraper may be a known device such as a Sharples
centrifuge; the arrangemen-t of the centrifuge inside of the fermenter in
accordance with this invention may, however, requi.re certain
modifications.
Process and apparatus of this invention can be used in
connection with fermentation processes of various kinds. The gas phase
frequently is an oxygen supplying phase but can also be a phase free of
any free oxygen. An example for a process wherein the gas phase is an
oxygen supp:Lying phase would be an aerobic single cell protein
fermentation process. Such a process is the presen-tly preferred
application of the invention. Another example for the application of the
process and apparatus of this inven-tion is a process wherein the cells
themselves produce CO2 which causes foaming. Other operations may be
anaerobic systems in which nitrogen or no gas at all are injected. As
mentioned above, the actual product of the process may be the cells but
may also be the liquid phase. Alcohol and water soluble gums would be
examples of products recovered from the liquid phase of a fermentation
process.
The invention will be still further understood from the
following description of the drawing:
Figure l is a cross sec-tional view of a fermentation apparatus
l in accordance with this invention. The fermentation apparatus l
comprises a housing 2 of essentially cylindrical shape which at the -top
portion is covered with a lid section 3. At the lower end of -the
cylindrical section 2 the housing is closed with a bottom section 4.
In-to the housing 2 feed material can be introduced via conduit
10 from a supply 11 by means of a pump 12. Inside of the housing 2 a
turbine 5 is arranged connected to a hollow shaft 6. This hollow shaft 6
is supported in bearings 7 and 8 and arranged for high speed rotation. A
motor drive unit 9 for rotating the hollow shaft 6 and the turbine 5 is
operatively connected thereto.
For the in-troduction of air into the turbine a chamber 13 is
attached to the bottom sec-tion 4 of the housing. Passages 14 are
provided in the hollow shaft 6. Air introduced into the chamber 13 via
line 16 therefor can pass through the hollow shaft 6 into the turbine 5
and leave the turbine 5 in the interior of the housing generating small
bubbles and creating the aeration of the fermentation mass inside of the
housing 2.
Inside of the housing 2 a concentrating centrifuge 27 is
arranged. This centrifuge comprises a cylindrical housing 30 coaxially
arranged inside of said housing 2 providing an annular space 28 between
the centrifuge housing 30 and centrifuge tube 25. In this annular space
28 fluid flows from holes 70 in the top 25a of the tube 25 toward the
weir 25b and out of housing 2 through outlet 45. Inside of the
centrifuge tube 25 a helically shaped rotor element 32 on a coaxial
hollow rotor 53 is provided. This hollow rotor 53 is attached to a shaft
20 33 which is supported for rotation by means of bearings 34 and 35 ~a-t the
lower end~. A motor drive uni-t 36 is operatively connected with the
shaft 33 at-tached to the rotor 53 for rapid rotation of helical element
32 within the centrifuge tube 25.
Centrifuge tube 25 is also rotatable within the housing 30 by
means of hollow shaft 60 which is concentric with shaft 33 of the rotor
53. Hollow shaft 60 is mounted for rotation on bearings 61 and 62.
Hollow shaft 60 and shaft 33 are both connected for rotation in the same
direction but at different speeds of rotation through gear box 63 and
motor drive uni-t 36. Hollow rotor 53 extends through the top 25a of
30 centrifuge -tube 25 and housing 30 to frustoconical member 31 which is
rotatable with hollow rotor 53 through bearings 62 and 64. Foam and/or
liquid entering frustoconical member 31 progresses downward through
hollow rotor 53 and out through holes 65 for separation or concentration
during the rotation of the hollow rotor and centrifuge tube 25. For
example, with this hollow rotor 53 and the helical rotor element 32
operating at 4000 rpm and centrifuge tube 25 opera-ting at 5000 rpm the
fluid or foam from holes 65 containing OrganiSDIS would be separated as
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the liquid and gas phases move upward and discharge ou-t of centrifuge
tube 25 through holes 70 into annular space 28. The liquid is collected
on the weir 25b and passes out of the housing 2 through outlet 45. The
weir 25b is attached -to the inside wall of housing 30 on one edge and
spaced from the outside of centrifuge tube 25 a sufficient distance to
allow rotation. The cell rich fluicl phase or paste would then move
downward along the beach 66 of centrifuge tube 25 and out through holes
85 collecting on the sloping bot-tom 86 of the housing 30. This cell rich
fluid may leave the fermenter through outlet 43. Tubing 44 through the
housing tube can be utilized for recycling the liquid phase from outlet
45 or the cell rich phase from outlet 43 as desired; the valves or
control mechanisms used in such a recycle have been omitted rom the
drawing. It is a particular advantage of this invention -that a recycle
of either cell rich paste or of cell depleted liquid is possible while
these products are still in the sterile environment.
To illustrate the invention more specifically, the following is
a possible operation and exemplification of the invention not intended to
limit the scope thereof unduly.
A yeas-t which produces a product, i.e., extra cellular
metabolite, is cultured in medium with nutrients adequate to support the
population desired. The product, which can ei-ther be inhibitory at
higher concentration, for example alcohol or solvents, or reu-tilized
~i.e., amino acids such as lysine~ should be withdrawn continually from
the fermenter. Taking a case of alcohol production, -the yeast, S.
cervesiae, is grown on molasses with adequate minerals, phosphate,
magnesium, etc. Once the cell density is reached that is desired, the
centrifuge is turned on. The foam caused by C02 production which
contains a higher concentration of cells is passed continually through
the centrifuge. The cells are returned to the fermenter in the form of
the cell rich paste from the centrifuge while the effluent contains
alcohol to a concentration of 5-8%. The alcohol can be stripped from -the
liquid cell depleted effluent stream and the liquid phase can be recycled
or otherwise disposed of. In most cases, it would be refortified with
more molasses for another pass. This keeps the alcohol concentration
down to a level where the yeast is most active; -the yeast slows down as
alcohol level bLIilds up and fermentation stops at about 10-12% alcohol
concentration. The return of the cells to the fermenter builds up a
higher cell density so the fermenter rate of alcohol production
increases.
Should the process be designed to produce single cell protein,
the process involves growing the cells to high densities, -then removing
the cells while recirculating the supernatant. For example, Pichia
pastoris can be grown to leve]s oE 120 grams per li-ter, on methanol being
fed a-t a concentration of 40/0, but the alcohol concentration in the
fermenter is maintained at 0-0.05%. The temperature would be 30C and
the pH at 3.5 with ~13 being supplied ~or pH adjustment and nitrogen
conten-t. The recycled medium is refortified with phosphate, magnesiwm
and trace minerals as needed. The retention time in the fermenter can be
about 8-10 hrs. In this case, -the supernatant could contain an
extracellular product such as lysine, methionine, and -tryptophan which
could be removed by an extractive technique and recovered as a marke-table
product prior to the return of the supernatant to fermenter.
~ easonable variation and modification which will become
apparent to those skilled in the art can be made in this invention
without departing from the spirit and scope thereof.
