CA1127984A - Method for the recovery of a volatile compound by fermentation of a carbohydrate material - Google Patents
Method for the recovery of a volatile compound by fermentation of a carbohydrate materialInfo
- Publication number
- CA1127984A CA1127984A CA320,866A CA320866A CA1127984A CA 1127984 A CA1127984 A CA 1127984A CA 320866 A CA320866 A CA 320866A CA 1127984 A CA1127984 A CA 1127984A
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- vessel
- fermentation
- liquid
- ethyl alcohol
- product
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E50/00—Technologies for the production of fuel of non-fossil origin
- Y02E50/10—Biofuels, e.g. bio-diesel
Abstract
A METHOD FOR THE RECOVERY OF A VOLATILE COMPOUND BY
FERMENTATION OF A CARBOHYDRATE MATERIAL
ABSTRACT OF THE DISCLOSURE
The method for recovery of a volatile organic compound such as alcohol from resulting fermentation of a carbohydrate material in a fermentor, wherein the improvement involves conveying a part of the fermentation liquid to a separate vessel, standing under vacuum and, there, removing the volatile compound in the form of a vapor. The bulk of the carbon dioxide produced during the fermentation is removed before the fermentation liquid is conveyed to the vacuum vessel.
The method may be performed on a batch basis or as a continuous single stage process or as a multi-stage process.
FERMENTATION OF A CARBOHYDRATE MATERIAL
ABSTRACT OF THE DISCLOSURE
The method for recovery of a volatile organic compound such as alcohol from resulting fermentation of a carbohydrate material in a fermentor, wherein the improvement involves conveying a part of the fermentation liquid to a separate vessel, standing under vacuum and, there, removing the volatile compound in the form of a vapor. The bulk of the carbon dioxide produced during the fermentation is removed before the fermentation liquid is conveyed to the vacuum vessel.
The method may be performed on a batch basis or as a continuous single stage process or as a multi-stage process.
Description
,~,27~
SPECIFICATION
This invention relates to a method for the recovery of a volatile organic compound by fermentation of a carbo-hydrate material in a fermentor, the gases formed during the fermentation being allowed to escape from the fermentor from the space above the liquid surface. In the fermentation process alcohol and other volatile organic compounds act on the yeast inhibiting the fermentation, with the result that the fermentation process will stop when a certain, relatively low, concentration of these compounds has been achieved in the fermenting liquid. In order to eliminate this drawback and to make possible the utilization of higher than normal concentrations of fermentable carbo-hydrates, with a higher yield of produce from the fermenta-tion, it has been suggested that the alcoholic fermentation and other fermentations be carried out under a reduced pressure, making possible a recovery of the formed volatile compounds in vapor form from the fermenting liquid or mash.
Preferably, the vaporization should be carried out at, or near the fermentation temperature. For an alcoholic fermentation, in which ethyl alcohol is the predominating volatile product of fermentation, reduced pressures between 20 and 50 mm. mercury absolute should be employed.
In alcoholic fermentations to produce ethyl alcohol, approximately 95.6 grams of carbon dioxide gas are produced for every 100 grams of ethyl alcohol formed.
Consequently, when the fermentor vessel is subjected to a reduced pressure, the carbon dioxide gas will constitute a high proportion of the total vapors and gases being removed. Since the carbon dioxide gas is not condensed at a later stage, it will be drawn into the equipment used for producing the necessary reduced pressure conditions. There-fore, an appreciable energy requirement is necessary to achieve and maintain the reduced pressure level.
~Z7~
When ethyl alcohol and water vapors are being condensed, the presence of the carbon dioxide gas will also have an adverse effect upon the condensing conditions.
In alcoholic fermentations, the heat of fermentation liberated is in the order of 287 kilocarlories per kilogram of ethyl alcohol formed. Under a reduced pressure at normal fermenting temperatures, the vapor-liquid equilbirium con-ditions for vaporizing an ethyl alcohol and water mixture will require an additonal heat input. This heat input will vary depending upon the concentration of ethyl alcohol and water in the fermenting liquid.
The normal method of introducing heat into a fer-mentor to achieve vaporizing conditions is with hot water inside coils immersed in the fermenting liquid. In order not to destroy the viability of the yeast, it is generally necessary not to allow the warm water temperature to exceed 40~ centig~rade. By employing sensible heat from a warm water supply, or any other warm media, to provide the heat input, only a small temperature difference is possible. This condition necessitates large volumes of warm heating media and subsequently a large surface area to achieve sufficient heat transfer rates.
An object of the present invention is to provide a method of the type mentioned which permits the utilization
SPECIFICATION
This invention relates to a method for the recovery of a volatile organic compound by fermentation of a carbo-hydrate material in a fermentor, the gases formed during the fermentation being allowed to escape from the fermentor from the space above the liquid surface. In the fermentation process alcohol and other volatile organic compounds act on the yeast inhibiting the fermentation, with the result that the fermentation process will stop when a certain, relatively low, concentration of these compounds has been achieved in the fermenting liquid. In order to eliminate this drawback and to make possible the utilization of higher than normal concentrations of fermentable carbo-hydrates, with a higher yield of produce from the fermenta-tion, it has been suggested that the alcoholic fermentation and other fermentations be carried out under a reduced pressure, making possible a recovery of the formed volatile compounds in vapor form from the fermenting liquid or mash.
Preferably, the vaporization should be carried out at, or near the fermentation temperature. For an alcoholic fermentation, in which ethyl alcohol is the predominating volatile product of fermentation, reduced pressures between 20 and 50 mm. mercury absolute should be employed.
In alcoholic fermentations to produce ethyl alcohol, approximately 95.6 grams of carbon dioxide gas are produced for every 100 grams of ethyl alcohol formed.
Consequently, when the fermentor vessel is subjected to a reduced pressure, the carbon dioxide gas will constitute a high proportion of the total vapors and gases being removed. Since the carbon dioxide gas is not condensed at a later stage, it will be drawn into the equipment used for producing the necessary reduced pressure conditions. There-fore, an appreciable energy requirement is necessary to achieve and maintain the reduced pressure level.
~Z7~
When ethyl alcohol and water vapors are being condensed, the presence of the carbon dioxide gas will also have an adverse effect upon the condensing conditions.
In alcoholic fermentations, the heat of fermentation liberated is in the order of 287 kilocarlories per kilogram of ethyl alcohol formed. Under a reduced pressure at normal fermenting temperatures, the vapor-liquid equilbirium con-ditions for vaporizing an ethyl alcohol and water mixture will require an additonal heat input. This heat input will vary depending upon the concentration of ethyl alcohol and water in the fermenting liquid.
The normal method of introducing heat into a fer-mentor to achieve vaporizing conditions is with hot water inside coils immersed in the fermenting liquid. In order not to destroy the viability of the yeast, it is generally necessary not to allow the warm water temperature to exceed 40~ centig~rade. By employing sensible heat from a warm water supply, or any other warm media, to provide the heat input, only a small temperature difference is possible. This condition necessitates large volumes of warm heating media and subsequently a large surface area to achieve sufficient heat transfer rates.
An object of the present invention is to provide a method of the type mentioned which permits the utilization
2~ of a substrate with a relatively high concentration of fermentable carbohydrates, and which is not impaired by such drawbacks as are characteristic in the prior art, i.e., a high energy consumption for maintaining a low pressure in the fermentor, that is requisite when using a heating medium with a relatively low temperature, relatively large size equipment requisite because of the large heat transfer surface required, and relatively long residence time of the fermenta-tion material in the apparatus. According to the present l~Z7984 invention, the method is characterized in that part of the fermentation liquid which is conveyed from the fermentor to a separate vessel, standing under vacuum (herein referred to as a separate vacuum vessel) wherein the organic compound formed is removed in the form of a vapor under reduced pressure at or near the fermentation temperature.
According to the present invention, the bulk of the carbon dioxide gas formed during fermentation is allowed to escape from the fermentor vessel in the normal way from the gas space above the surface of the liquid. Since only the fermentation liquid itself is to be subjected to a reduced pressure, the fermentation liquid is transported from the fermentor to a separate vessel wherein the organic compounds formed are removed in the form of vapor under a reduced pressure at or near the fermentation temperature. Part of the gases, like carbon dioxide, contained in the fermentation liquid as absorbed gases, are also conveyed with the fermentation liquid to the separate vessel where these gases are desorbed under vacuum.
Because most of the carbon dioxide gas was removed prior to subjecting the fermenting liquid to a reduced pressure in the separate vessel, it is possible for the equipment for condensing the vapors back to a liquid to be smaller in surface area due to an improvement in the heat transfer condensing film conditions. Also, the dew point for the mixed vapors and gases will be elevated in temperature by the absence of a large proportion of the carbon dioxide gases.
At the same time, the size of the equipment for producing and maintaining the required reduced pressure level will be much smaller, together with the energy consumption for operation.
~g With the present invention, by the use of a separate vessel for the evaporation of vapors and gases from the liquid under a reduced pressure it is possible to achieve a constant head level at the liquid-vapor interface by using overflow weirs or downcomer pipes. Also, by transporting the liquid continuously from the fermentor vessel to this vapor disengaging vessel and retur~ng the residual liquid back -again to the fermentor (or another vessel), the residence time in the separate vessel can be short. In consequence, the depth for the heating surface media within the liquid can be suitable and optimum. Also, as the boiling point of the liquid is a function of its composition, surface pressure and liquid depth, the form of heating need not be from a sensible heat source.
In a fermentor vessel where the liquid contents have a specific gravity of about 1.150, a 5 centigrade rise in boiling point would represent a liquid depth of about 14 cm. Boiling of the liquid throughout this depth could occur without the fermentative capacity of the yeast being seriously altered.
If the boiling time is of short duration, such as 30 seconds, boiling temperatures of up to 50 centigrade are permissible without the yeast's fermentative ability being seriously impaired, once the temperature of the yeast is 2S returned to its normal fermenting temperature range.
High heat transfer rates can he achieved by the use of condensing steam as the heat source; or some other form of heat input, preferably with a condensing character-istice can be used. In order to prevent scaling and/or yeast degradation at the outside wall of the heat transfer surface media, low pressure steam is recommended at a temperature not exceeding 75C. However, depending upon the `1~
overall heat transfer coefficient and the nature of the liquid being evaporated, higher steam temperatures may be used.
In one preferred embodiment, fermentation liquid is transported continuously to the separate vacuum vessel and is returned to the fermentor and/or a second fermentor, or is discharged from the system.
Alternatively, the fermention can be carried out batchwise.
In this context, "fermentor" means, either one single fermentor tank, or a plurality of fermentor tanks, coupled in series.
A tubular fermentor reactor for "plug-flow"
operation can be used as well.
In said embodiment of the method, part of the fermenting liquid is withdrawn close below the liquid surface in the fermentor and is transported to the separate vacuum vessel, in order that the fermentation liquid fed to the separate vessel shall contain only the absorbed gases which are formed by fermentation in the fermentor and in the fermenting liquid during transport.
In another embodiment, part of the fermenting liquid is hydraulically removed from the fermentor by intimate contact with an inert gas, or a gas less soluble than those gases formed by fermentation and absorbed in the fermenting liquid, said inert or less soluble gas being separated from the transported part of the fermenting liquid before this is exposed to a reduced pressure in the separate vessel.
Suitably, the apparatus for carrying out the method according to the invention is designed in order that the difference in elevations of the liquid surface in the fermentor and in the separate vessel is slightly greater than the barometric height of the liquid needed to balance ~m~4 the reduced pressure in the separate vessel and the pressure in the fermentor.
Thus the liquid surface is kept on a relatively constant level by the utilization of overflow weirs or down-comer pipes, through which the fermenting liquid flows down,after the vapor of organic compound has been removed.
In production of ethyl alcohol, the pressure in the separate vessel is suitably maintained at 20 to 50 mm. of mercury absolute.
The usage in the separate vessel of a heating wall, in contact with low pressure steam with a condensing temperature comprised between 40 and 75 centigrade, is advantageous.
The residence time of the fermenting liquid in the separate vessel should not, suitably, be longer than 60 seconds, and the temperature at the contact with the heating surface at its lowest point should not be higher than 55C.
In one preferred embodiment of the method according to the invention, the fermentation is carried out in order than an ethanol concentration is maintained in the part of the lqiuid or liquid mixture that is transported to the separate vessel, at 1.0 to 8.0 grams ethanol/100 mls.
Other objects and advantages of the invention will appear as the invention is described in connection with the accompanying drawings.
In the drawings, FIGURE 1 is a schematic view of apparatus for carrying out the invention~
FIGURE 2 is a similar view of an alternative part of the apparatus shown in Figure 1.
The apparatus in Figure 1 comprises two process stages, coupled in series, each of them provided with a llZ7~4 fermentor vessel, Al and A2, respectively, and with separate evaporators Cl and C2, standing under vacuum.
Each fermentor vessel is connected, via a pump, Bl and B2, respectively, and pipe such as F-l to its evaporator. In this case evaporators Cl and C2 are designed as hairpin evaporators for low pressure or vacuum steam, condensing on the inside of the tubes. Evaporators Cl and C2 are placed on such an elevation above the fermentor vessels, that the difference in elevations of the liquid surface in the fermentor and in the separate vessel (as shown by the broken line) is slightly greater than the needed barometric height of the liquid; in this case the difference is 10 meters.
The evaporators are provided with overflow weirs 20, in order to maintain the liquid head level constant.
Reduced pressure is supplied by vacuum apparatus G
which in this instance is a mechanical unit employing exhauste~s and ring pumps. Mixed vapors from evaporators Cl and C2 pass throught pipes 14 to "vacuum"-condenser D, where the mixture is condensed and is conveyed to an atmospheric receiver E via a barometric seal leg. This product is pumped out by pump F
under level control LC for further rectification. The sealing liquid of the vacuum apparatus should be returned for substrate dilution, as it will contain most of the uncondensed ethyl alcohol that passes through the condenser D.
Control of the steam for each evaporator Cl and C2, is an individual temperature controller TC, which senses the li~uid temperature and controls the steam to each evaporator.
The tubes 21 are provided with baffles 23 for the liquid flow along their length to the overflow of the weir 20. The steam condensate is discharged to and through a cooler and a ring pump, system H, by pipes 11', 11", in order to maintain the proper temperature of the steam condensing in the tubes.
~Z7g~
The liquid may be withdrawn from fermentors Al and A2, which are at or slightly below atmospheric pressure, by a suction swing arm 10 through which liquid is withdrawn close below the liquid surface to pump Bl and B2, respectively.
Alternatively, the equipment shown in Figure 2 may be used.
Since air has a much lower solubility in water and water solutions than carbon dioxide gas, the displacement of carbon dioxide gas by air in the liquid will be an advantage in improving the dew point for the vapors being condensed at a later stage under reduced pressure and in reducing the size and the energy requirements at the reduced pressure producing equipment.
It is known that liquids can be transported by means of a compressed gas by the system generally called an air left, when compressed air is employed. Also, it is known that stripping or negative gas absorption can be carried out by bringing a liquid containing a dissolved gas into contact with an inert or less soluble gas in order to remove the dis-solved gas fromthe liquid.
In Figure 2 we have shown an air lift system with excess gas and foam removal returning back to the fermentor, together with any recirculated liquid not being taken into the suction of pump P. As there shown, compressed air from a foot piece jet 16 is delivered to a lift pipe J immersed in the fermentor vessel K and lifts the liquid to chamber L located externally of the fermentor. This chamber L is fitted with an agitator 17 rotating at an optimum speed sufficient to assist the disengagement of entrained gas from the liquid. Gases, foam and any surplus liquid overflow through pipe M back to the fermentor vessel K above the operating liquid level. At the same time, the optimum oxygen tension in the fermenting substrate can be achieved by regulating the air flow to the 1~79B4 lift pipe J in order that an excess of liquid returns to the fermentor vessel in whi_h air is absorbed.
Liquid under gravity head flows through pipe O to pump P, from which it is transported to the separate vessel Cl under a reduced pressure, as illustrated in Figure 1.
In a plant of the type shown in Figure 1, comprising two fermentor and two evaporator stages, coupled in series, improved operation economy is possible compared with a ~lant, consisting of one single fermentor stage. A relatively high substrate concentration may be employed in the flow, fed to fermentor vessel Al, while the second stage with fermentor vessel A2 is utilized for recovering residual alcohol through a final fermentation. By using a circulating flow, the flow through the evaporator can be greater than the flow between the fermentor vessels, excess of liquid being returned to its original fermentor vessel. Generally, this excess flow will be in the order of up to 90% of the liquid circulating in the evaporative loop. Hence, there will be little chance of fermentable sugars bypassing the fermentors and being discharged in the final fermentor effluent.
Should too much water be evaporated with the ethyl alcohol vapor and the solids concentrations increase too much in the fermentor vessel, diluent water can be added to establish optimum fluidity.
As an example of operational data for the new process, it may be mentioned, that in a two stage plant as shown in Figure 1 when fermenting molasses, a reduced pressure of 32 mm. mercury absolute in evaporators Cl and C2, and low pressure steam, condensing at 75C. are used for the evaporation. The depth of the overflow weir is set at 275 mrn.
and the height of the tube bundle allows a 25 mTn. cover of liquid at the liquid-vapor interface.
Atmospheric pressure is prevailing in fermentor Al, _g_ 1~4 and the yeast concentration is 40 grams pressed yeast per liter of liquid. The liquid is at a specific gravity of 1.130, containing 5 grams ethyl alcohol per 100 milliliters and having a 4.9 pH. Carbon dioxide, that is evolved during the fermentation is prmitted to be discharged from the upper part of fermentor vessel Al.
The flow rate through evaporator Cl in this case is set so that one gram of ethyl alcohol per 100 milliliters is removed by evaporation from the liquid. For an evaporation rate of 100 kilograms per hour of ethyl alcohol, this would equate to a pumping rate for pump Bl of 10 cubic meters of liquid per hour.
Hence, pump Bl is only required to overcome friction losses and a small static head of approximately 1.2 meters of liquid.
It is advantageous to maintain a reasonably high ethanol content in the liquid before and after evaporation in order that the alcohol to water ratio in the distillate is maintained at a reasonable level. Should an excess of water be removed with the ethyl alcohol, a higher heat load is necessary for evaporation.
Depending upon the alcohol contents in the fermentors and the removal rates of ethyl alcohol in the evaporators, alcohol concentrations up to 30~ by weight can be expected in the product.
As the spirit is pure, there will be no problems with deposits on trays and in the evaporators, in further rectification.
A~ the end of the fermentation, when the alcohol concentration level starts to sink in the fermenting liquid, it will be necessary to remove more water vapor with the ethyl alcohol vapor in order to maximize the alcohol yield.
~Z~4 In this instance, a continuous fermentation and evaporation system in cascade flow is envisaged. Only two stages are shown in Figure 1, but more stages may be used.
The residence time for ~he liquid through evaporator Cl is set to be less than 30 seconds. The overflowing liquid is recirculated by passing down through another barometric leg to a seal chamber 12, where it overflows to next fermentor vessel A2, the excess being recirculated to fermentor Al.
Where molasses is used in fermentation at a high initial concentration, the effluent will be rich in solids, possibly at four or five times the solids contents found in normal molasses distillery effluents. Hence the effluent has an economic value if it is to be further evaporated to a syrup or used for other purposes, such as a liquid fertilizer.
According to the present invention, the bulk of the carbon dioxide gas formed during fermentation is allowed to escape from the fermentor vessel in the normal way from the gas space above the surface of the liquid. Since only the fermentation liquid itself is to be subjected to a reduced pressure, the fermentation liquid is transported from the fermentor to a separate vessel wherein the organic compounds formed are removed in the form of vapor under a reduced pressure at or near the fermentation temperature. Part of the gases, like carbon dioxide, contained in the fermentation liquid as absorbed gases, are also conveyed with the fermentation liquid to the separate vessel where these gases are desorbed under vacuum.
Because most of the carbon dioxide gas was removed prior to subjecting the fermenting liquid to a reduced pressure in the separate vessel, it is possible for the equipment for condensing the vapors back to a liquid to be smaller in surface area due to an improvement in the heat transfer condensing film conditions. Also, the dew point for the mixed vapors and gases will be elevated in temperature by the absence of a large proportion of the carbon dioxide gases.
At the same time, the size of the equipment for producing and maintaining the required reduced pressure level will be much smaller, together with the energy consumption for operation.
~g With the present invention, by the use of a separate vessel for the evaporation of vapors and gases from the liquid under a reduced pressure it is possible to achieve a constant head level at the liquid-vapor interface by using overflow weirs or downcomer pipes. Also, by transporting the liquid continuously from the fermentor vessel to this vapor disengaging vessel and retur~ng the residual liquid back -again to the fermentor (or another vessel), the residence time in the separate vessel can be short. In consequence, the depth for the heating surface media within the liquid can be suitable and optimum. Also, as the boiling point of the liquid is a function of its composition, surface pressure and liquid depth, the form of heating need not be from a sensible heat source.
In a fermentor vessel where the liquid contents have a specific gravity of about 1.150, a 5 centigrade rise in boiling point would represent a liquid depth of about 14 cm. Boiling of the liquid throughout this depth could occur without the fermentative capacity of the yeast being seriously altered.
If the boiling time is of short duration, such as 30 seconds, boiling temperatures of up to 50 centigrade are permissible without the yeast's fermentative ability being seriously impaired, once the temperature of the yeast is 2S returned to its normal fermenting temperature range.
High heat transfer rates can he achieved by the use of condensing steam as the heat source; or some other form of heat input, preferably with a condensing character-istice can be used. In order to prevent scaling and/or yeast degradation at the outside wall of the heat transfer surface media, low pressure steam is recommended at a temperature not exceeding 75C. However, depending upon the `1~
overall heat transfer coefficient and the nature of the liquid being evaporated, higher steam temperatures may be used.
In one preferred embodiment, fermentation liquid is transported continuously to the separate vacuum vessel and is returned to the fermentor and/or a second fermentor, or is discharged from the system.
Alternatively, the fermention can be carried out batchwise.
In this context, "fermentor" means, either one single fermentor tank, or a plurality of fermentor tanks, coupled in series.
A tubular fermentor reactor for "plug-flow"
operation can be used as well.
In said embodiment of the method, part of the fermenting liquid is withdrawn close below the liquid surface in the fermentor and is transported to the separate vacuum vessel, in order that the fermentation liquid fed to the separate vessel shall contain only the absorbed gases which are formed by fermentation in the fermentor and in the fermenting liquid during transport.
In another embodiment, part of the fermenting liquid is hydraulically removed from the fermentor by intimate contact with an inert gas, or a gas less soluble than those gases formed by fermentation and absorbed in the fermenting liquid, said inert or less soluble gas being separated from the transported part of the fermenting liquid before this is exposed to a reduced pressure in the separate vessel.
Suitably, the apparatus for carrying out the method according to the invention is designed in order that the difference in elevations of the liquid surface in the fermentor and in the separate vessel is slightly greater than the barometric height of the liquid needed to balance ~m~4 the reduced pressure in the separate vessel and the pressure in the fermentor.
Thus the liquid surface is kept on a relatively constant level by the utilization of overflow weirs or down-comer pipes, through which the fermenting liquid flows down,after the vapor of organic compound has been removed.
In production of ethyl alcohol, the pressure in the separate vessel is suitably maintained at 20 to 50 mm. of mercury absolute.
The usage in the separate vessel of a heating wall, in contact with low pressure steam with a condensing temperature comprised between 40 and 75 centigrade, is advantageous.
The residence time of the fermenting liquid in the separate vessel should not, suitably, be longer than 60 seconds, and the temperature at the contact with the heating surface at its lowest point should not be higher than 55C.
In one preferred embodiment of the method according to the invention, the fermentation is carried out in order than an ethanol concentration is maintained in the part of the lqiuid or liquid mixture that is transported to the separate vessel, at 1.0 to 8.0 grams ethanol/100 mls.
Other objects and advantages of the invention will appear as the invention is described in connection with the accompanying drawings.
In the drawings, FIGURE 1 is a schematic view of apparatus for carrying out the invention~
FIGURE 2 is a similar view of an alternative part of the apparatus shown in Figure 1.
The apparatus in Figure 1 comprises two process stages, coupled in series, each of them provided with a llZ7~4 fermentor vessel, Al and A2, respectively, and with separate evaporators Cl and C2, standing under vacuum.
Each fermentor vessel is connected, via a pump, Bl and B2, respectively, and pipe such as F-l to its evaporator. In this case evaporators Cl and C2 are designed as hairpin evaporators for low pressure or vacuum steam, condensing on the inside of the tubes. Evaporators Cl and C2 are placed on such an elevation above the fermentor vessels, that the difference in elevations of the liquid surface in the fermentor and in the separate vessel (as shown by the broken line) is slightly greater than the needed barometric height of the liquid; in this case the difference is 10 meters.
The evaporators are provided with overflow weirs 20, in order to maintain the liquid head level constant.
Reduced pressure is supplied by vacuum apparatus G
which in this instance is a mechanical unit employing exhauste~s and ring pumps. Mixed vapors from evaporators Cl and C2 pass throught pipes 14 to "vacuum"-condenser D, where the mixture is condensed and is conveyed to an atmospheric receiver E via a barometric seal leg. This product is pumped out by pump F
under level control LC for further rectification. The sealing liquid of the vacuum apparatus should be returned for substrate dilution, as it will contain most of the uncondensed ethyl alcohol that passes through the condenser D.
Control of the steam for each evaporator Cl and C2, is an individual temperature controller TC, which senses the li~uid temperature and controls the steam to each evaporator.
The tubes 21 are provided with baffles 23 for the liquid flow along their length to the overflow of the weir 20. The steam condensate is discharged to and through a cooler and a ring pump, system H, by pipes 11', 11", in order to maintain the proper temperature of the steam condensing in the tubes.
~Z7g~
The liquid may be withdrawn from fermentors Al and A2, which are at or slightly below atmospheric pressure, by a suction swing arm 10 through which liquid is withdrawn close below the liquid surface to pump Bl and B2, respectively.
Alternatively, the equipment shown in Figure 2 may be used.
Since air has a much lower solubility in water and water solutions than carbon dioxide gas, the displacement of carbon dioxide gas by air in the liquid will be an advantage in improving the dew point for the vapors being condensed at a later stage under reduced pressure and in reducing the size and the energy requirements at the reduced pressure producing equipment.
It is known that liquids can be transported by means of a compressed gas by the system generally called an air left, when compressed air is employed. Also, it is known that stripping or negative gas absorption can be carried out by bringing a liquid containing a dissolved gas into contact with an inert or less soluble gas in order to remove the dis-solved gas fromthe liquid.
In Figure 2 we have shown an air lift system with excess gas and foam removal returning back to the fermentor, together with any recirculated liquid not being taken into the suction of pump P. As there shown, compressed air from a foot piece jet 16 is delivered to a lift pipe J immersed in the fermentor vessel K and lifts the liquid to chamber L located externally of the fermentor. This chamber L is fitted with an agitator 17 rotating at an optimum speed sufficient to assist the disengagement of entrained gas from the liquid. Gases, foam and any surplus liquid overflow through pipe M back to the fermentor vessel K above the operating liquid level. At the same time, the optimum oxygen tension in the fermenting substrate can be achieved by regulating the air flow to the 1~79B4 lift pipe J in order that an excess of liquid returns to the fermentor vessel in whi_h air is absorbed.
Liquid under gravity head flows through pipe O to pump P, from which it is transported to the separate vessel Cl under a reduced pressure, as illustrated in Figure 1.
In a plant of the type shown in Figure 1, comprising two fermentor and two evaporator stages, coupled in series, improved operation economy is possible compared with a ~lant, consisting of one single fermentor stage. A relatively high substrate concentration may be employed in the flow, fed to fermentor vessel Al, while the second stage with fermentor vessel A2 is utilized for recovering residual alcohol through a final fermentation. By using a circulating flow, the flow through the evaporator can be greater than the flow between the fermentor vessels, excess of liquid being returned to its original fermentor vessel. Generally, this excess flow will be in the order of up to 90% of the liquid circulating in the evaporative loop. Hence, there will be little chance of fermentable sugars bypassing the fermentors and being discharged in the final fermentor effluent.
Should too much water be evaporated with the ethyl alcohol vapor and the solids concentrations increase too much in the fermentor vessel, diluent water can be added to establish optimum fluidity.
As an example of operational data for the new process, it may be mentioned, that in a two stage plant as shown in Figure 1 when fermenting molasses, a reduced pressure of 32 mm. mercury absolute in evaporators Cl and C2, and low pressure steam, condensing at 75C. are used for the evaporation. The depth of the overflow weir is set at 275 mrn.
and the height of the tube bundle allows a 25 mTn. cover of liquid at the liquid-vapor interface.
Atmospheric pressure is prevailing in fermentor Al, _g_ 1~4 and the yeast concentration is 40 grams pressed yeast per liter of liquid. The liquid is at a specific gravity of 1.130, containing 5 grams ethyl alcohol per 100 milliliters and having a 4.9 pH. Carbon dioxide, that is evolved during the fermentation is prmitted to be discharged from the upper part of fermentor vessel Al.
The flow rate through evaporator Cl in this case is set so that one gram of ethyl alcohol per 100 milliliters is removed by evaporation from the liquid. For an evaporation rate of 100 kilograms per hour of ethyl alcohol, this would equate to a pumping rate for pump Bl of 10 cubic meters of liquid per hour.
Hence, pump Bl is only required to overcome friction losses and a small static head of approximately 1.2 meters of liquid.
It is advantageous to maintain a reasonably high ethanol content in the liquid before and after evaporation in order that the alcohol to water ratio in the distillate is maintained at a reasonable level. Should an excess of water be removed with the ethyl alcohol, a higher heat load is necessary for evaporation.
Depending upon the alcohol contents in the fermentors and the removal rates of ethyl alcohol in the evaporators, alcohol concentrations up to 30~ by weight can be expected in the product.
As the spirit is pure, there will be no problems with deposits on trays and in the evaporators, in further rectification.
A~ the end of the fermentation, when the alcohol concentration level starts to sink in the fermenting liquid, it will be necessary to remove more water vapor with the ethyl alcohol vapor in order to maximize the alcohol yield.
~Z~4 In this instance, a continuous fermentation and evaporation system in cascade flow is envisaged. Only two stages are shown in Figure 1, but more stages may be used.
The residence time for ~he liquid through evaporator Cl is set to be less than 30 seconds. The overflowing liquid is recirculated by passing down through another barometric leg to a seal chamber 12, where it overflows to next fermentor vessel A2, the excess being recirculated to fermentor Al.
Where molasses is used in fermentation at a high initial concentration, the effluent will be rich in solids, possibly at four or five times the solids contents found in normal molasses distillery effluents. Hence the effluent has an economic value if it is to be further evaporated to a syrup or used for other purposes, such as a liquid fertilizer.
Claims (9)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for recovering ethyl alcohol by fermentation of a carbohydrate material, comprising the steps of fermentation of the carbohydrate material in a first vessel to produce carbon dioxide gas and a liquid fermentation product including ethyl alcohol, separating the bulk of carbon dioxide gas produced by said fermentation from said first vessel and material, transporting said liquid fermentation product of said material including ethyl alcohol from said first vessel to a second vessel at a greater elevation than said first vessel, maintaining the ethyl alcohol concentration in said transported fermentation product at about 1.0 to 8.0 grams of ethyl alcohol per 100 ml., contacting the ethyl alcohol with a heat transfer surface in said second vessel at a temperature of about 40-75°C., maintaining a sub-atmospheric pressure of 20-50 mm. mercury absolute in said second vessel while removing said ethyl alcohol in the form of a vapor from said fermentation proauct in the second vessel, and maintaining the difference in elevation between the liquid surface in said first and second vessels greater than the barometric height of the liquid needed to balance the reduced pressure in said second vessel and the pressure in said first vessel, while maintaining the liquid surface in the second vessel at a relatively constant level.
2. The method of claim 1, in which said transporting step includes removing said fermentation product from said first vessel hydraulically by intimately contacting the product with a gas less soluble than the gases formed by said fermentation, and separating said less soluble gas from the fermentation product before it is exposed to reduce pressure in said second vessel.
3. The method of claim 1, in which said transported fermentation product is withdrawn from beneath the surface of said product in the first vessel, said transporting step including removing said product from the first vessel hydraulically by intimately contacting the product with a gas less soluble than the gases formed by said fermentation, and separating said less soluble gas from the fermentation product before it is exposed to reduce pressure in said second vessel.
4. A method as claimed in claim 1, wherein fermentation product is conveyed continuously to said first vessel, conveying said fermentation product continuously from said first vessel to said second vessel, and conveying back at least a portion of said fermentation product from said second vessel to said first vessel for reprocessing with the product added to said first vessel.
5. The method as claimed in claim 1 including the steps of conveying fermentation product from said second vessel to a further fermentation vessel, transporting said product to a second sub-atmospheric pressure vessel, maintaining a sub-atmospheric pressure in said second sub-atmospheric vessel while removing in the form of a vapor said ethyl alcohol from the fermentation product in said second sub-atmospheric vessel.
6. The method as claimed in claim 1, in which the fermentation product transported to the sub-atmospheric second vessel from the first vessel is withdrawn from beneath the surface of the fermentation product in said first vessel in order to make the fermenting liquid fed to the separate sub-atmospheric vessels contain only absorbed gases of fermentation.
7. The method as claimed in claim 1, in which the residence of the liquid in said sub-atmospheric second vessel is limited to about 60 seconds and the temperature in the second vessel is maintained at less than 55°C.
8. A method for recovering ethyl alcohol by fermentation of a carbohydrate material comprising the steps of adding said material continuously to a first vessel and there fermenting the material separating the bulk of carbon dioxide gas produced by said fermenting from said first vessel and material, continuously transporting a liquid fermentation product of said material including ethyl alcohol from said first vessel to a second vessel, maintaining the ethyl alcohol concentration in said transported fermentation product at about 1.0 to 8.0 grams of ethyl alcohol per 100 ml., contacting the transported product with a hot surface in said second vessel at a temperature of about 40-75°C., maintaining a sub-atmospheric pressure of 20-55 mm. mercury ab-solute in said second vessel while removing ethyl alcohol in the form of a vapor from said fermentation product in the second vessel, and returning only part of said residue to said first vessel for reprocessing with said material added to the first vessel.
9. The method of claim 8 comprising also the steps of continuously feeding another part of said residue to a third vessel and there subjecting said other part to further fermentation, continuously transporting a liquid fermentation product including ethyl alcohol from said third vessel to a fourth vessel and there contacting the product with a hot surface at a temperature of about 40-75°C., and maintaining a sub-atmospheric pressure of 20-55mm.
mercury absolute in said fourth vessel while separately removing ethyl alcohol vapors therefrom, the rate of return of said one part of said first vessel being substantially greater than the rate of feeding said other part to the third vessel.
mercury absolute in said fourth vessel while separately removing ethyl alcohol vapors therefrom, the rate of return of said one part of said first vessel being substantially greater than the rate of feeding said other part to the third vessel.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA320,866A CA1127984A (en) | 1979-02-05 | 1979-02-05 | Method for the recovery of a volatile compound by fermentation of a carbohydrate material |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA320,866A CA1127984A (en) | 1979-02-05 | 1979-02-05 | Method for the recovery of a volatile compound by fermentation of a carbohydrate material |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1127984A true CA1127984A (en) | 1982-07-20 |
Family
ID=4113463
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA320,866A Expired CA1127984A (en) | 1979-02-05 | 1979-02-05 | Method for the recovery of a volatile compound by fermentation of a carbohydrate material |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1127984A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2438617A (en) * | 2006-06-03 | 2007-12-05 | Edward Arthur Jackman | Continuous fermentation process for the production of ethyl alcohol |
-
1979
- 1979-02-05 CA CA320,866A patent/CA1127984A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2438617A (en) * | 2006-06-03 | 2007-12-05 | Edward Arthur Jackman | Continuous fermentation process for the production of ethyl alcohol |
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