FIELD OF THE INVENTION:
The present invention, in general, relates to a process and an apparatus for producing alcohol by fermentation.
In particular, the invention relates to a process and an apparatus for the production of alcohol by continuous fermentation of raw material, wherein the portable water is utilized for alcohol production and yeast is obtained in active state and therefore could be reused after one cycle.
BACKGROUND OF THE INVENTION:
It is well known that alcohol can be obtained by fermentation of molasses by employing certain microbes like yeast capable of carrying out fermentation process.
Traditionally, batch processes were employed for the commercial-scale production of alcohol. The drawback of such a mode was that it accounted for high capital cost and high energy consumption. The batch process required complex control and were time consuming. Also it did not provide uniform production of the desired product and could only be employed for small industrial units. This resulted in development of continuous fermentation employing multi-stage processes wherein the fermentation steps are separated and therefore the effect of the catalyst on the yeast and maintenance of the anaerobic metabolism of yeast could be separately handled.
In recent years, there has been a considerable interest in the production of alcohol through the continuous fermentation process. In the process of continuous fermentation, initial stages include reproduction of micro-organisms in oxygen rich environment which then produce alcohol anaerobically. The residual raw material is then quantitatively converted to obtain a high alcohol concentration. It is advantageous to use continuous fermentation process for the reason that it provides uniform alcohol production, has simpler control and avoids cleaning and start-up phases. The concept of continuous basis of fermentation comprises

supplying the raw material at a steady rate into the apparatus and withdrawing the fermented product from a different part of the apparatus at the same rate. The speed at which the unfermented liquid is fed must be equilibrated with the rate of propagation of yeast cells and fermentation. For continuous fermentation of alcohol it is necessary to make available, adequate supply of raw material to the microorganisms and maintain the favorable fermentation conditions. The state of art comprises processes in which the process is carried out in one stage or in several stages. The continuous process for production of alcohol utilizes plurality of fermentation vessels connected in series and transferring the raw product from one vessel to another. It is well known that fermentation temperature and yeast concentration affect the speed of fermentation. The continuous production thus reduces the amount of time spent for alcohol production as compared to the batch process where the filling and emptying of the fermentation vessels is required. However, continuous fermentation cannot be continued indefinitely since the raw material eventually becomes poisoned thus carrying out different reactions like acid fermentation. Therefore cleaning of the vessels is necessary to restart the alcohol fermentation process. Also a steady rate of flow is required to be maintained throughout the apparatus since there is a danger of contamination which could result in loss of alcohol yield. These processes, being divided into stages, involve much time, labour, floor space, vessel volume and power and also with continuous method it has not been possible to control the biochemical and physical processes in the maturing process. In conventional ethanol fermentation processes, increase in ethanol concentration to 8-12% cause an inhibitory effect on the fermentation since the activity of yeast is hindered or even demolished at this level of ethanol concentration. Therefore the fermentation process must be interrupted to remove ethanol when concentration exceeds the limit. But this is an inefficient and a very costly operation and highlights the major technical problem in ethanol production that is

presented by inhibition of fermentation due to the increase in ethanol concentration.
In order to overcome the high ethanol concentration problem, selection of ethanol-tolerant yeast strains or lower fermentation temperatures has been utilized in current industrial processes.
EXISTING KNOWLEDGE:
The following Patents disclose several methods of fermentation for production of
alcohol.
The continuous fermentation method for alcohol/ethanol production has been
disclosed in various patents such as US 4419448, US 4383040, US 4385118, US
4376163, US 4886751, GB 1170873, GB 1087307 and the like.
Published German patent application DE-OS No. 1,642,693 discloses a continuous alcohol fermentation process and apparatus wherein the continuous flow of mash into and product out of the apparatus is maintained through fermentation vessels of the augmented series that can be individually taken out of operation. The said apparatus and its operation is very complex which amounts to increase in total cost
The methods of production as disclosed in the prior art are time consuming. Also the equipment employed is costly thus making the process expensive. Besides, the water consumption in the prior art is high and spent wash obtained is not as concentrated as desired.
Thus, a simple and economic, high alcohol yielding continuous fermentation process for the production of alcohol is required.

OBJECTS OF THE INVENTION:
Accordingly, the objects of the present invention are as follows:
The primary object of the present invention is to provide an improved process for alcohol production, characterized in that the process continuously converts fermentable substrate into alcohol, thereby continuously producing usable alcohol.
Another object of the present invention is to provide a novel fermentation system, primarily characterized for continuous conversion of fermentable substrate into alcohol, thereby continuously producing usable alcohol.
Another object of the present invention is to provide a novel fermentation system for production of alcohol, characterized by reduced water input, thereby significantly decreasing the water consumption.
Still another object of the present invention is to provide a novel fermentation system for alcohol fermentation, which is designed in way that it utilizes portable water thus avoiding specific water treatment plants
Another object of the present invention is to provide a novel fermentation system for production of alcohol characterized in that a reduced amount of spent wash with higher concentration is obtained from the distillation step.
Still another object of the present invention is to provide an improved process for alcohol fermentation, characterized in that the yeast employed in the process is returned in active state to the fermenter.

Yet another object of the present invention is to optimize the process in the best interest of the economics of the process in terms of low cost of equipment and labor.
A further object of the present invention is to provide a novel fermentation system for production of alcohol which is less time consuming and energy saving process
SUMMARY OF THE INVENTION:
In accordance with the primary aspect of the present invention there is provided a process for continuous fermentation, in which fermentable substrate selected from the group consisting of molasses, cane juice, beet juice and mixtures thereof and water is fed continuously into the fermentation vessel that contains substantially homogeneously distributed yeast. The initial fermentation takes place to obtain a threshold concentration of alcohol. The reaction mixture thus obtained is centrifuged in centrifuge separators to separate yeast cream from the fermenting liquid, from wherein the fermenting liquid is continuously passed to a Yeast settling tank and yeast enriched liquid withdrawn from the lower part of separators is returned to the fermentation zone. The yeast free liquid is withdrawn from the upper part of the yeast settling tank and passed to a set of distillation columns to obtain alcohol vapor which are being condensed. A spent wash obtained in the distillation column is recycled back to the fermenter and a part is discharged where phase separation is performed by removing volatiles and alcohol vapor thus obtained.
According to a another important aspect of the present invention, there is provided a novel fermentation system for continuous fermentation comprising a series of fermentation vessels and means for conducting the raw material continuously into said vessels and out of said vessels to a Series of Centrifuge separators and means

for conducting the yeast enriched liquid back from bottom of separators to the fermentation vessels and for conducting the fermenting liquid from the Separators to the Yeast settling tank, there being provided means to direct yeast-free liquid from the top of the settling tank to distillation columns. There is also provided a means for transferring a part of spent wash from distillation step to the fermentation vessels.
The novel characteristic features of the invention are set forth in particular in the appended claims. Both the construction features and mode of operation of the improved fermentation system of the invention, along with its additional features and advantages, will be best understood by following detailed description of invention together with certain specific embodiments with reference to the accompanying drawing.
BRIEF DESCRIPTION OF DRAWINGS:
The invention will now be described with reference to accompanying drawing.
Fig. 1 illustrates arrangement for continuous preparation of alcohol in accordance
with the Present invention
Fig. 2 illustrates arrangement for preparation of alcohol in accordance with prior
art.
DETAILED DESCRIPTION OF THE INVENTION:
In accordance with the primary aspect of the present invention there is provided an improved method and an apparatus for the continuous alcohol production. In pursuance of the aforesaid objects and others, one critical aspect of the present invention resides in a method of producing alcohol by fermentation of a continuously supplied fermentable substrate selected from the group consisting of molasses, cane juice, beet juice and mixtures thereof containing yeast and other nutrients which comprises briefly the steps of continuously feeding fermentable

substrate and water into the fermentation vessel containing yeast, transferring the reaction mixture to centrifuge separators. The yeast free liquid is passed to a set of distillation columns to obtain alcohol vapor which is passes to condenser to obtain alcohol vapor.
A particular advantage of this approach is that the yeast enriched liquid withdrawn from the lower part of separators is recycled back to the fermentation zone. Another advantage of the invention is that a part of the spent wash obtained is recycled back to the fermenter.
The apparatus for performing the method of the present invention advantageously includes a plurality of fermentation vessels; means for transferring the reaction mixture through the fermentation vessels, including conduit means connecting the fermentation vessels in series, means for conducting the raw material continuously into said vessels and out of said vessels to the Series of Centrifuge separators and a means for conducting the fermenting liquid from the Separators to the Yeast settling tank, there being provided means to direct yeast-free liquid from the top of the settling tank to distillation columns.
Advantageously, the arrangement further includes a means for transferring a part of spent wash from distillation step to the fermentation vessels conducting the yeast enriched liquid back from bottom of separators to the fermentation vessels. According to the present invention, there is provided a continuous process for the production of alcohol, in which the fermentation vessel containing substantially homogeneously distributed yeast and maintained at a fixed temperature, is fed with molasses and water at a particular TDS and viscosity. The reaction mixture is allowed to stand in the fermentation vessel for a fixed time till the concentration of alcohol attains the desired threshold concentration of about 8%. The samples are constantly drawn to check the alcohol concentration achieved. When a threshold concentration of alcohol is achieved, the reaction mixture is allowed to leave the fermentation vessel and pumped into centrifuge separator with the flow rate of 112 m3/hr and centrifuged at 6000 rpm to separate the stream of fermentation liquid

into a yeast enriched liquid and a yeast-free liquid. The yeast enriched liquid withdrawn from the lower part of separators is returned to the fermentation zone. The supernatant liquid is continuously passed to a Yeast settling tank. The yeast free liquid leaves from the upper part of the yeast settling tank to a set of distillation columns to obtain alcohol vapor. A Spent wash obtained in the distillation column is recycled back to the fermenter and a part is discharged where phase separation is performed by removing volatiles and alcohol vapor thus obtained are then condensed to final concentration. The process in accordance with the invention is made fully continuous to obtain and maintain a desired rate of fermentation for the production of alcohol with the advantage of reusing the yeast in live state.
The apparatus, in accordance with the present invention consists of the
following parts:
The fermentation vessels-
The fermentation vessels are designed to operate continuously with a height and diameter of about 9meter and 10.4 meter respectively. The feed inlet is positioned at the top of the vessel and the reaction mixture outlet is positioned at bottom of the vessel.
According to the present invention, yeast added to the fermenter is about 10 to 12% by weight and molasses and water feed is maintained at TDS of 28%.The yeast concentration is maintained throughout the fermentation vessel at 350 to 400 X 106 cell/ml. The Brix value is maintained at 24 to 26. The room temperature is maintained at about 31 to 32 degree C. It is desirable to maintain a level of viability of yeast to at least about 96 percent and preferably, at least about 90 percent and an alcohol level (by weight) of from about 6.5 percent to about 6.6 percent, and preferably from about 6.3 percent to about 6.5 percent, in fermentation vessel. To maintain uniform temperature, removal of heat from the fermentation zone is necessary, which is ensured by providing cooling water

through PHE. According to the present invention the water input in alcohol fermentation on molasses has been considerably reduced compared with the water input used in the prior art. The said reduction in the water consumption has been realized by high DS in fermenter. Moreover, the water input that is used is in the fermenter is Raw water with Hardness of about 60 to 200. Centrifuge Separators
It is also advantageous to separate a stream of fermentation liquid into a yeast enriched liquid and a yeast-free liquid by centrifugal separation. It is also desirable to separate impurities like dead yeast cells and other solid impurities form the liquid stream which can be realized using the aforesaid separators. Yeast settling tank
The apparatus may comprise a means to move liquid from the Separators to the settling tank, means to remaining yeast-enriched liquid containing sludge from the bottom of the settling tank to the decanter, means to lead off yeast-free liquid from the top of the settling tank. At decanter sludge has been removed and drawn into sludge drying bed & sludge free liquid sent to wash holding tank. Distillation Columns:
The set of distillation columns under vacuum employ a thin film heat exchanger. The said columns are maintained at a temperature of about 80 to 85 degree C. The spent wash obtained having brix of 17 to 18 is collected at the first distillation column. Here, in accordance with the invention, the advantage is that the spent wash can be reused. The second distillation column is employed for phase separation of volatiles like aldehydes etc. In the third distillation column, in accordance with the invention, refining the alcohol containing vapour to desired concentration and quality is realized to obtain an alcohol vapour of about 95 to 96 % (v/v) concentration.
In accordance with the present invention, in order to maintain the alcohol productivity of the yeast, the fermenter system is suitably dimensioned so that the

desired alcohol production can be achieved at the end of the operation period as well when the alcohol productivity of the yeast is the lowest. In accordance with the invention, the advantage achieved is that the highly concentrated spent wash is obtained in a quantity which is quite manageable. In accordance with the present invention, the improved fermentation system avoids the more frequent starting up and emptying of the fermenter, cost for propagating new yeast for each start up, and fermenter environment giving lower average ethanol productivity.
The invention is now further illustrated with reference to the accompanied drawing, which shows a flow sheet of a preferred embodiment of the invention. In the drawing, numerals refer to the following:
The flow lines refer to the continuous circuit. The fermenters 10, 12 and 14 are connected in series. The substrate (molasses + water) is fed through inlet LI to Fermenter (10). The reaction mixture passes to Fermenter (12) through flow line L2 and then to Fermenter (14) through flow line L3.The reaction mixture is passed from Fermenter (14) to series of centrifuge separators 16, 18 and 20 through flow lines SI, S2, S3 respectively. The yeast enriched liquid is transferred from the bottom of separators (16, 18, 20) to Separator cream tank (22) through flow line S4 and from there it is re-circulated to the Fermenters (10, 12, 14) through flow line Rl. The yeast free liquid obtained from the top of separators (16,18,20) is passed to the Yeast settling tank (24) through flow line Yl. The fermentation stream obtained from the Yeast settling tank (24) is passed to the distillation columns (28, 30 and 32) through flow line Y2. The steam flow is passed to the distillation columns (28, 30 and 32). From the distillation column (32), an alcohol enriched vapor stream is discharged and condensed through condenser (34) to obtain alcohol.

Following examples illustrate the invention, but are not intended to limit the scope of the present invention.
EXAMPLE 1:
An apparatus as shown diagrammatically in Fig. 1 was used for the fermentation of molasses for continuous production of alcohol using Yeast with accession number 3360.
A fermenter with a total liquid capacity of 50 m3/hr was charged with prepropagated yeast culture of yeast species Schizosaccharomyces pombe at the flow rate of 50m3/hr. A fermentation liquid containing 18 MT/hr of molasses and 23m3/hr of portable water with brix 36 to 40 was fed to the said fermenters giving a mean residence time of about 24 hr. for initialization. The air flow in the fermenter is maintained in the range of 600nm3/hr to 1000 nrn3/hr.The fermentation temperature was thermostatically controlled at 31 to 32 degree C and preferably at a level of about 32 degree C. The pH of each fermentation vessel is similarly regulated and could range from about 4.2 to about 4.5 and preferably from about 4.3 to 4.4. Room temperature is maintained at about 31 to 32 degree C. he mixture was then passed to second fermenter and then to third fermenter of same liquid capacity as that of first and was allowed to stand till the fermented liquid containing 6.6 by weight alcohol was obtained.
The filled fermenter was connected to Centrifuge separator as described above. Fermented liquid with 8% v/v alcohol concentration was pumped to centrifuge separators at the flow rate of 112 m3/hr and centrifuged at the rpm of 6000 to separate yeast cream from the fermenting liquid. The alcohol enriched liquid (yeast free liquid) with a brix of 10 to 12 was passed to yeast settling tank and from there it was pumped to set of distillation columns maintained at a temperature of about 70 to 80 degree C to obtain alcohol vapor. The spent wash with brix of 14 obtained from distillation was partly sent to columns to obtain a spent wash of about 35 brix. The remaining part of the spent wash was recycled

back to the fermenter at flow rate o 30-35 m3/hr. The recirculation ratio of spent wash and yeast liquid was controlled so that steady-state was maintained in the system.
The phase separation was performed to remove volatiles and further refine alcohol vapour. The alcohol vapor thus obtained was passed through condenser to obtain alcohol vapor which was then concentrated to final concentration of 95 to 96%. The data below represent a typical material balance for an alcohol fermentation process which is capable of producing about 6.5 weight percent alcohol. Please refer Table 1(a), Table 1(b), Table 1(c) and Table 1(d)
Table 1(a): Yeast Activation Tank (YAT)


Table 1(b): Fermenter No: 1


Table 1(c): Fermenter No: 2


Table 1(d): Fermenter No: 3 and Weak beer recycle

EXAMPLE 2-Comparison between Prior art and Present Invention
An apparatus for continuous fermentation for the production of alcohol as shown diagrammatically in Fig. 1 representing the present invention and another apparatus for continuous fermentation for the production of alcohol as shown diagrammatically in Fig.2 representing the prior art has been compared for alcohol productivity, cell vitality etc. Please refer to Table 2(a), Table 2(b) and Table 2(c)

for the results of prior art which have been compared with results of present invention. (Please refer Table 1(a), Table 1(b), Table 1(c) and Table 1(d))
Table 2(a); Prior Art for Yeast Activation Tank (YAT)

ANALYSIS OF RESULTS:
(a) Comparison of results for YAT: (Refer Table 1(a) and Table 2(a))
The total number of days for which fermentation was conducted were 22 days
both for prior art and present invention.
Fed Substrate:
Total molasses for prior art = 0.7 M3/hr
Total molasses for present invention = 0.8 M3/hr

Total water input for prior art = 7 M3/hr
Total water input for present invention = 7.5 M3/hr
Results:
Average vitality for prior art= 92%
Average vitality for present invention= 98%
Average cell count for prior art=300
Average cell count for present invention= 450
Total RS for prior art= 0.8
Total RS for present invention= 0.5
Total alcohol formed for prior art= 4.0%
Total alcohol formed for present invention^ 4.9%
Therefore, the alcohol formed is more and RS formed is less in present invention
when compared to prior art. Also, the average cell count and vitality for present
invention is also higher as compared to prior art.
Table 2(b): Prior Art for Fermenter No.l



(b) Comparison of results for Fermenter No. 1: (Refer Table Kb) and Table 2(b))
The total number of days for which fermentation was conducted were 22 days
both for prior art and present invention.
Fed Substrate:
Total molasses for prior art = 6.5M3/hr
Total molasses for present invention = 6.8 M3/hr
Total water input for prior art = 24 M3/hr
Total water input for present invention = 14 M3/hr
Results:
Average vitality for prior art= 80%
Average vitality for present invention= 92%
Average cell count for prior art=198
Average cell count for present invention=350
Total RS for prior art= 1.74%
Total RS for present invention= 1.4%.
Total alcohol formed for prior art= 6.4%
Total alcohol formed for present invention= 7.1%
Therefore, the alcohol formed is more and RS formed is less in present invention
when compared to prior art. Also, the average cell count and vitality for present

invention is also higher as compared to prior art. Moreover, the water consumption is reduced in present invention as compared to the prior art
Table 2(c): Prior Art for Fermenter No.2 and Weak beer recycle

(c) Comparison of results for Fermenter No. 2 and weak beer recycle:
(Refer Table 1(c), Table 1(d) and Table 2(c))
The total number of days for which fermentation was conducted were 22 days
both for prior art and present invention.

Fed Substrate:
Total molasses for prior art = 2.4 M3/hr
Total molasses for present invention (Fermenter 2) = 2.9 M3/hr
Total molasses for present invention (Fermenter 3) = 0.5 M3/hr
Total water input for prior art = 5M3/hr
Total water input for present invention (Fermenter 2) = 1.2M3/hr
Total water input for present invention (Fermenter 3) =nil
Results:
Total RS for prior art=2%
Total RS for present invention for Fermenter 2=T .7% and for Fermenter 3=1.8%
Total alcohol formed for prior art= 6.7%
Total alcohol formed in present invention for F2= 7.75% and for F3= 8.15%.
Vinasse recycle for Fermenter 1 and Fermenter 2:
F1 for prior art= 2m3/hr
F1 for present invention= 9m3/hr
F2 for prior art= 0
F2 for present invention:=4m3/hr
Therefore, the alcohol formed in present invention is much higher and RS is less
as compared to prior art. Moreover, the water consumption is much reduced in
present invention as compared to the prior art. It is nil for third fermenter. The
vinasse recycle is also much higher in present invention as compared to prior art.
Technical advancement
The process for the continuous fermentation for the production of alcohol in accordance with the present invention has several advantages such as:

a) The process utilizes portable water thus avoiding the employment of special water treatment plants
b) The process reduces the water consumption to about 600 to 800 M3/day
c) Energy saved in accordance with the process of invention is about 2 to 3tons /hr of steam.
d) The process is speedy being continuous
e) The spent wash that is produced is in manageable quantity but with higher concentration.
f) The equipment being employed for the invention is cheaper.
While considerable emphasis has been placed herein on the various components of the preferred embodiment, it will be appreciated that many alterations can be made and that many modifications can be made in the preferred embodiment without departing from the principles of the invention. These and other changes in the preferred embodiment as well as other embodiments of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

WE CLAIM:
1. A process for continuous production of alcohol comprising:
a) continuously feeding a fermentable substrate and water to the fermenter zone continuously being charged with yeast for fermenting said substrate to alcohol, wherein the reaction mixture is allowed to stand till the fermentation liquor attains a threshold alcohol concentration;
b) continuously passing the fermentation liquor to separator for continuously separating the said fermentation liquor into a yeast-enriched stream and a yeast-free stream,
c) continuously recirculating said yeast-enriched stream to the fermentation zone to maintain yeast concentration and continuously passing the yeast-free stream to the yeast settling tank to obtain a fermented liquid
d) continuously passing the said fermented liquid to distillation columns to obtain an alcohol vapour and a spent wash;
e) continuously feeding the said alcohol enriched vapour to the condenser to obtain an alcohol vapour condensate; and
f) continuously and simultaneously recirculating a part of spent wash to the fermentation zone.

2. The process as claimed in claim 1, wherein the fermentable substrate is selected from the group consisting of molasses, cane juice, beet juice and mixtures thereof.
3. The process as claimed in claim 1, wherein fermentation zone is a plurality of fermentation vessels, wherein the said vessels are arranged in series.
4. The process as claimed in claim 1, wherein the fermentation substrate is introduced to the first fermentation vessel and all or part of the fermentation

liquid is continuously passed from first fermentation vessel to second fermentation vessel and then to third fermentation vessel.
5. The process as claimed in claim 1, wherein the yeast is recirculated to the fermenter in active state to maintain the yeast concentration in the fermenter.
6. The process as claimed in claim 1, wherein fermentation zone introducing part or all of the first, substantially yeast-free aqueous ethanol stream into the second fermentation vessel.
7. The process as claimed in claim 1, wherein the spent wash is recirculated at the flow arte of 30-35 m3/hr.
8. The process as claimed in claim 1, wherein the yeast is initially charged to the fermenter at a flow rate of 10 m3/hr.
9. The process as claimed in claim 3, wherein the temperature inside the fermenter is maintained in the range of about 32 to 34.
10. The process as claimed in claim 1, wherein the distillation is carried out at the temperature range of about 82 to 72°C.
11. The process as claimed in claim 1 wherein the yeast concentration in the first fermentation vessel and/or second fermentation vessel and/or third fermentation vessel-is maintained at from about 12 to about 15 weight percent of the fermentation medium therein.

12. The process as claimed in claim 1, wherein the viability of the yeast cells in the first fermentation vessel is maintained at a level of at least about 90 percent.
13. The process as claimed in claim 1, wherein the viability of the yeast cells in the second fermentation vessel is maintained at a level of at least about 80 percent.
14. The process as claimed in claim 1, wherein the viability of the yeast cells in the third fermentation vessel is maintained at a level of at least about 70 percent.
15. The process as claimed in claim 1, wherein the yeast species used for the fermentation is Schizosaccharomyces Pombe.
16. The process as claimed in claim 1, wherein the water used is portable water.
17. The process as claimed in claim 1, wherein the input of water is controlled by recycling of vinasse from the distillation column.
18. The process as claimed in claim 1, characterized in that the average brix of the fermentable substrate in the fermenter is maintained at about to 22 to 26.
19. The process as claimed in claim 1, wherein the fermentation in the fermentation zone is carried out until alcohol concentration of about 6.4 to about 6.5 weight percent of the fermentation medium is attained.

20. The process as claimed in claim 1, wherein the alcohol vapour condensate obtained has a final alcohol concentration of 95 to 96.
21. The process as claimed in claim 1, wherein the spent wash solution obtained has a brix of 35 to 38.
22. An arrangement for producing alcohol by continuous fermentation of a continuously supplied fermentable substrate containing yeast, comprising:
a plurality of fermentation vessels arranged in series (with equal volumetric capacity); a conduit means connecting the fermentation vessels in series, means for conducting the fermentable substrate continuously into said vessels and out of said vessels; means for transferring the fermentable substrate through the fermentation vessels to the series of separators; a means for conducting the fermented liquid from the said Separators to the Yeast settling tank, there being provided a means to direct yeast-free liquid from the top of the settling tank to series of distillation columns and a means to conduct the alcohol vapor to condenser.
23. The arrangement for producing alcohol by continuous fermentation as claimed in claim 22, wherein the separators are plurality of centrifuge separators arranged in series.
24. The arrangement for producing alcohol by continuous fermentation as claimed in claim 22, wherein the fermentation vessel is a set of atleast three fermentation vessels arranged in series.
25. The arrangement for producing alcohol by continuous fermentation as claimed in claim 22 further includes a means for recirculating a part of spent wash from said distillation columns to the fermentation vessels and

means for recirculating the yeast enriched liquid back from bottom of separators to the fermentation vessels.
26. The arrangement as claimed in claim 22, wherein the distillation columns are provided with thin film heat exchanger.
27. The arrangement for carrying out the process as claimed in any of the preceding claims, substantially as herein described with reference to the accompanying drawing.