CA1333367C

CA1333367C - Process and apparatus for the production of ethanol from sugar-containing raw materials

Info

Publication number: CA1333367C
Application number: CA000530526A
Authority: CA
Inventors: Friedrich Gutschireiter
Original assignee: Vogelbusch GmbH
Current assignee: Vogelbusch GmbH
Priority date: 1986-03-10
Filing date: 1987-02-25
Publication date: 1994-12-06
Anticipated expiration: 2011-12-06
Also published as: EP0237520A2; EP0237520A3; DE3768104D1; ES2023221B3; EP0237520B1; AT395983B; ATA61186A

Abstract

A process for the production of ethanol from sugar-containing raw materials by extraction of the raw materials by means of an aqueous medium, fermentation of the saccharide-containing fermentable extract and distillative processing of the resulting ethanol-containing fermentation liquid. At least part of the water-enriched stillage incurring as a residue at the distillative processing of the fermentation liquid is recycled for extraction in counterflow to the raw materials. In a plant for carrying out the process, the extraction apparatus includes a series of vessels being under atmospheric pressure and connected with its each other, in whose interior a partition wall not reaching as far as to the bottom of the vessel is each provided.

Description

The invention relates to a process for the production of ethanol from sugar-containing raw materials by extraction of the raw materials by means of an aqueous medium, fermentation of the saccharide-containing fermentable extract and distillative processing of the resulting ethanol-containing fermentation liquid, as well G pparat~l~
as to an ~rrang- -~t for carrying out the process.
As sugar-containing raw materials, sugar cane, sugar millet or sugar beets, for instance, may be used.
With processes of this type, the soluble substances including saccharose and other sugars at first are washed out from the raw materials by extraction (incorrectly also called "diffusion").
For the extraction of comminuted sugar cane, elongate screw conveyors that are slightly inclined with respect to the horizontal line have been used so far. The cane pieces are bottom-charged and are brought into contact with water supplied on the upper end of the screw conveyor. The extract (juice) is drawn from the lower end of the 20 conveyor.
According to another known technique, the comminuted raw materials are charged onto a conveying belt provided with fine apertures and are sprayed with sharp liquid jets of high pressure from nozzles located thereabove. The extract formed is collected in a trough.
The apparatus and energy expenditures involved in the extraction stage are high with the known techniques.
The sugar-containing extract - optionally after cooling - is fermented in a fermenting station comprising one or more fermentors upon addition of suitable microorganisms, e.g., Saccharomyces strains.
The resulting fermentation-product (primarily ethanol) containing fermentation liquid is conducted to one or several distillation and rectification columns, from which there are extracted substantially ethanol as the top product and what is called stillage as the sump product.
The stillage, which contains non-fermentable constituents of the raw materials, residues of the microorganisms used and salts, has constituted a topical waste disposal problem to a constantly increasing extent. Vaporization of the stillage to dry solids that are storable at least to a limited extent, as had been realized in some places, hardly is of interest any longer because of the high energy costs involved.
The invention has as its object to eliminate the described difficulties and disadvantages connected with known processes for the production of ethanol from vegetable raw materials and to provide a process and a particularly reliable apparatus for carrying out the process, which does not require a complex device and in which the incurring amounts of waste products to be transferred outwards as well as the energy demand may be kept comparatively low without having to put up with losses in yield.
In accordance with the invention, at least part of the water-enriched stillage incurring as a residue at the distillative processing of fermentation liquid is recycled for extraction in counterflow to the raw materials.

1333~7 More precisely, the present invention provides a process for the production of ethanol from sugar-containing raw materials which comprises extracting the raw materials with an aqueous medium so as to obtain an extract containing fermentable saccharides, fermenting the extract so as to obtain an ethanol-containing fermentation liquid, processing the ethanol-containing fermentation liquid by distillation with a water-enriched stillage incurring as residue, and recycling at least part of the water-enriched stillage in counterflow to the raw materials for extraction.

~- - 2a -13~3~ 7 ._ With the process according to the invention, one may, eli~4te, thus, ~ totally wiLI.~ut the supply of fresh process water into the extraction stage.
A major portion of non-fermentable dry substance (TS) is recycled to extraction together with the stillage and, thus, gets enriched in the system.
The condition of equilibrium has been reached when the total amount of TS transferred out of the process together with, for instance, bagasse and hydrocyclone slurry equals 10 that amount of non-fermentable TS which is supplied with the raw materials (for instance, sugar cane in case bagasse is obtained as pressing residue) plus residual amounts of fermentable monosaccharides not utilized in fermentation, which are transformed into non-fermentable TS in the course of distillative processing and optional vaporization procedures.
According to a preferred embodiment, the total amount of incurring stillage is reduced by vaporization and the reduced amount, as a whole, is recycled into extraction.
In this manner, the residues that constitute a load on the environment practically completely pass into the pressing residues that remain after extraction of the sugar-containing raw materials. These residues are eliminated by combustion, the inorganic portion (salts) will remain in the ashes and may be dumped therewith or may be recovered. Depending on the raw materials used, the energy released during combustion will suffice for the complete or at least partial coverage of the thermal demand of the process.
If lower mrarcaL~gl~me~t costs have priority over 1333~67 environmental problems - i.e., with small plants -, it is also possible to recycle into extraction only that fraction of incurring stillage which is actually required there.
Vaporization is omitted and the excess of stillage is let off. In this manner, it is still the major portion of environmental load substances that gets into the pressing residues.
The thin juice pressed off after extraction likewisely may be recycled for extraction in a known manner.
Suitably, the sugar-containing raw materials are guided through extraction upon dilution with the two- to ' ~ ~ four-time ~ of aqueous medium.
This measure offers the advantage that the mixture of raw materials and aqueous medium is ready for pumping such that no complex mechanical conveying means, which are otherwise usual, are necessary in the extraction stage.
Advantageously, the mixture of raw materials and aqueous medium present during extraction is heated under pressure to a temperature of above 100 C, in particular to 20 a temperature of between 105 and 150 C, and subsequently is rapidly released to atmospheric pressure.
As a result of such treatment, disintegration of the raw materials by breaking the cell structure is obtained, the ingredients of the cells, thus, being accessible to a better and larger extent.
In respect of sugar cane, a disintegration method has already been suggested, with which, however, the pre-comminuted stock per se, i.e., yet without aqueous extraction medium, is pressurized mechanically and then is 30 suddenly released.

The disintegration to be carried out according to the invention in an advantageous manner has been integrated in the extraction and, thus, more appropriately adapted to the process course. Moreover, a further elevated disintegration degree is attained thereby.
The exhaust vapors forming during release of the extraction mixture preferably are used to preheat this mixture and/or vaporize the extract.
The present invention also provides an apparatus particularly suitable for carrying out the process mentioned above. The apparatus comprises an extraction means, a fermenting station and a distillation device and, in accordance with the invention, is characterized in that:
- (a) the extraction means is comprised of X~ a series of ., vessels operable under atmospheric pressure, each having a bottom and a partition wall not reaching as far as the bottom of the vessel and a means for charging the first vessel of the series of vessels with comminuted sugar-containing raw materials, (b) a means is provided for feeding the stillage from the distillation device into the last vessel of the series of vessels, seen in the conveying direction of the raw materials, (c) the bottom portion of each vessel is connected with the consecutive vessel via an extraction mixture conduit including a thick matter pump, 1333~7 (d) a conduit equipped with a thick matter pump leads from the bottom portion of the last vessel of the series of vessels to an extract (juice) separating means, (e) the vessels are connected with each other by an overflow conduit, a descending liquid level of the extraction - 5a -_ 13333~7 mixture contained in the vessels being provided from the last to the first vessel of the series of vessels, and . C~) f an extract (juice) discharge conduit leading to the fermenting station is connected to the first vessel.
Preferably, a preheater, a pressure tank and a pressure release tank are consecutively incorporated in the extraction mixture conduit after the thick matter pump between the first and the second vessels of the vessel series, seen in the conveying direction of the raw 10 materials.
It is particularly advantageous to connect the bottom portion of the pressure tank with the pressure release tank disposed at an elevated level via an ascending pipe and to connect the steam room of the pressure release tank with the preheater via an exhaust vapor conduit. In case the pressure adjusting in the pressure tank in dependence on the height and internal diameter of the ascending pipe is not sufficient, a reducing valve may additionally be provided in front of the entry of the ascending pipe into 20 the pressure release tank.
Fast flowing of the mixture of raw materials and extraction medium through the ascending pipe, where a pressure gradient adjusts, will result in a particularly thorough disintegration of the raw materials.
According to a further preferred embodiment of the arrangement according to the invention, at least one heat exchanger, a vacuum evaporator and a cooler are consecutively arranged in the extract (juice) discharge conduit.
The invention will now be explained in more detail by way of examples with reference to the drawings, wherein:
Fig. 1 illustrates part of an ~a..gr ~nt according to the invention;
Fig. 2 is a diagram of an embodiment of the process according to the invention with quantity flows;
Fig. 3 illustrates the extraction stage according to Fig. 2 in more detail;
Fig. 4 illustrates another embodiment of the process according to the invention including the pertaining 10 quantity flows; and Fig. 5 is a more detailed illustration of the counterflow extraction with the superposed liquid recirculatory system according to Fig. 4.
In Fig. 1, sugar-containin~ raw materials at first get over an inclined feeding table~into a comminuting means 2.
If sugar cane is used, the comminuting means 2, for instance, is a cutting machine in which the sugar cane is cut to pieces of about 2 cm length. The comminuted raw materials fall into the first vessel 3a, which is charged 20 through an overflow conduit 4 with extract (juice) from the second vessel 3b. In the example illustrated, a total of four extraction vessels 3a, 3b, 3c and 3d are connected in series, the overflow conduits 4, 5 and 6 being disposed in slightly offset heights in a manner that a descending liquid level of the extraction mixture contained in the vessels from the last to the first vessel 3a of the vessel series results.
It is, of course, also possible to arrange the vessels 3a, 3b, 3c and 3d themselves at slightly different levels 30 and to attach the overflow conduits to each vessel at the 13~3~7 same height. The extract or juice, thus, flows in the direction of the arrows from vessel 3d to vessel 3a. From the bottom portion of the vessel 3a, the extraction mixture with the comminuted raw materials is conveyed, by means of a thick matter pump 7, through an extraction mixture conduit 8 via a preheater 9 into a pressure tank 10, and there is brought to an elevated temperature (with sugar cane suitably to 110 to 120 C) by direct steam from steam conduit 11. Through the ascending pipe 12, the extraction 10 mixture subsequently reaches the pressure release tank 13.
Closely in front of the entry of the ascending pipe 12 into the pressure release tank 13, a reducing valve 14 is provided with the embodiment illustrated. In the pressure relea~e tank 13, the mixture is released to approximately atmospheric pressure. The thermal content of the exhaust vapors forming is used to preheat the extraction mixture as well as, if desired, to preheat the extract (juice) from container 3a, provided the extract is to be concentrated by expansion vaporization. To this end, the steam room of the 20 release tank 13, via an exhaust vapor conduit 15, at first is connected with the preheater 9, whose discharge 16 is connected to a heat exchanger 17 to preheat the extract.
From the release tank 13, the extraction mixture (the socalled pulp), through conduit 18, reaches the vessel 3b, from whose bottom portion it is extracted through the extraction mixture conduit l9 containing a thick matter pump 20 and is supplied to the next vessel 3c.

In the same manner, conveyance is continued into the -1 ` V ss ..L~ 3~d through an extraction mixture conduit 21 30 including a thick matter pump 22. From the bottom portion of the last vessel 3d of the vessel series, the pulp is supplied through a conduit 24 equipped with a thick matter pump 23 to an extract (juice) separating means - to a screen type worm extruder 25 in the present case. The pressed off thin juice, as it is called, through a juice conduit 26, flows back into one of vessels 3b or 3c or even into both vessels, the residues from pressing, for instance, bagasses, falling into the dosing means of a residue combustion boiler 27 in the embodiment illustrated.
A supply conduit 28 for stillage coming from a distillation apparatus (not illustrated) enters into the last vessel 3d of the series of vessels.
The vessels 3a, 3b, 3c and 3d are each equipped with a partition wall 29a, 29b, 29c and Z9d deeply immersing into the liquid in order to avoid a short circuit flow and to enforce an intensive contact of the extraction medium (stillage and thin juice) guided in counterflow to the extraction mixture or pulp. A portion of the extract, i.e., of the juice enriched with sugar substances and non-fermentable substances, is extracted from the first vessel3a through an extract discharge conduit 31 via a strainer basket 30 and is supplied to the heat exchanger 17, from which the extract gets into a second heat exchanger 32, in which latter its temperature is raised further.
Via a control valve 33, the extract is guided on into a vacuum evaporator 34. The steam room of the vacuum evaporator 34 is connected to a vacuum pump 36 via a condenser 35. The concentrated extract is supplied to a fermenting station (not illustrated) through conduit 38 by means of a pump 37. Since the concentrated extract incurs at a temperature of about 50 C, it may be cooled to a temperature suited for fermentation in a cooler 39.
Some of the required measuring and controlling means inclusive of the pertaining electric lines have been entered in Fig. 1 in broken lines.
If an adequately low amount of stillage is fed into the last vessel 3d, the expansion vaporization described in connection with the embodiment of Fig. 1 may be omitted.
Example 1:
To produce 10,000 kg ethanol, 186,744 kg of comminuted sugar cane having a content of 72.8 % water and 12.65 %
fibers are used as sugar-containing raw material. In the process diagram illustrated in Fig. 2, all the numerical values refer to amounts in kilogram. Since the fibers substantially run through the process without influencing the quantity balance, all the concentration data in the following are based on the liquid portion exclusive of fibers. The following abbreviations are used in Figs. 2 and 3:
TS: dry substance TS: dry substance, with the portion of fermentable sugars having been converted to monosaccharides W : water F : fibers Z : fermentable monosaccharides A : ethanol aA: other alcohols Pressure heating of the mixture present at the extraction to disintegrate the raw materials is effected with 2,000 kg of steam.

13~33~ ~

With the process diagram, it is supposed that the above explained condition of equilibrium of substances supplied and discharged has been adjusted.
The total amount of stillage incurred is reduced by vaporization and the reduced amount, as a whole, is recycled for extraction (upon separation of the slurry in a hydrocyclone).
The procedures during extraction are illustrated in more detail in Fig. 3. Comminuted sugar cane having a liquid portion of about 163 t with about 15.2 % Z and about 2.16 % non-fermentable TS is guided in counterflow to 136 t stillage with about 17.8 % TS. The resulting products are about 261 t extract (juice) with about 9 % Z and 8.44 % TS
on the one hand, and sugar cane fiber residues (megasse) having a liquid portion of 205 t with about 3.4 % Z and about 14.2 % TS on the other hand. The megasse is pressed.
About 165 t pressed juice (thin juice) obtained are supplied to extraction. The remaining bagasse usually is burnt in a boiler for energy supply of the plant.
For a theoretical stage, it is supposed that upon intensive mixing in the stage the departing products have equal concentrations. Fig. 3 indicates that just three theoretical stages are required. Actually, more stages will, of course, be required, because the complete concentration equalization will not be entirely attained in practice.
The concentration of the extract with regard to Z and TS may be adjusted to be even higher.
The condensate (about 100 t W) coming from vaporization (cf. Fig. 2) is only slightly loaded, thus 1333~67 - `
constituting no waste disposal problem.
Example 2:
To produce 10 t ethanol, about 189 t comminuted sugar cane with 73 % water and 12.5 % fibers are used according to Fig. 4. The abbreviations used have the same meanings as in Figs. 2 and 3.
It is operated in a manner largely analogous to the flow sheet indicated in Fig. 2, with the difference that no vaporization takes place. Only is that portion of stillage recycled which is required for extraction. The remaining excess of stillage is transferred out of the process. In doing so, about 46 % of the substances detrimental to the environment still gets into the bagasse, only the remainder being removed with the excess stillage.
In order to render feasible a particularly simple and cheap design of the apparative equipment, the comminuted sugar cane is guided through extraction with a larger amount of aqueous medium, cf. Fig. 5 in this respect. To the amount of comminuted sugar cane fed, approximately three times the amount of thin juice from the press is admixed such that from stage 1 sugar cane pieces having a liquid portion of 620 tons as compared to 165 tons fed are supplied to stage 2. Accordingly, 583 tons of thin juice are separated before and within the press, which are guided in counterflow to the 620 tons of sugar cane pulp. In other words, to the 165 tons of sugar cane (exclusive of fibers) and 120 tons of stillage, which are guided in counterflow, about 500 tons of ~uice, which are conveyed through the extraction in circulation, are to be added.
The strongly diluted extraction mixture is particularly readily pumpable and capable of being processed in the arrangement illustrated in Fig. l most reliably and without the complex conveying means required so far.

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Claims

1. A process for the production of ethanol from a sugar-containing raw material using a system, which comprises:
extracting the raw material by a counterflow extraction with an aqueous medium so as to obtain an extract containing fermentable saccharide, fermenting the extract so as to obtain an ethanol-containing fermentation liquid, processing the ethanol-containing fermentation liquid by distillation so as to obtain ethanol and a water-enriched stillage as residue, recycling at least part of the water-enriched stillage in counterflow to the extraction stage, and withdrawing a solid residue resulting from the extraction stage out of the system.

2. A process as set forth in claim 1, wherein the stillage is concentrated by vaporization of water contained therein and the concentrated stillage as a whole is recycled for extraction.

3. A process as set forth in claim 1, wherein the sugar-containing raw material is guided through the extraction stage in a condition diluted by two to four times the weight of the aqueous medium.

4. A process as set forth in claim 1, wherein an extraction mixture composed of the raw material and the aqueous medium is heated under pressure to a temperature of above 100°C and subsequently released quickly to atmospheric pressure.

5. A process as set forth in claim 4, wherein the extraction mixture is heated to a temperature between 105 and 150°C.

6. A process as set forth in claim 4, wherein an exhaust vapor formed when releasing the extraction mixture is used to preheat the extraction mixture.

7. A process as set forth in claim 4, wherein an exhaust vapor formed when releasing the extraction mixture is used to concentrate the extract before being subjected to the fermenta-tion.

8. An apparatus for producing ethanol from a sugar-containing raw material comprising:
an extraction means for extracting the raw material with an aqueous medium so as to obtain an extract containing a fermen-table saccharide, a fermenting station for fermenting the extract so as to obtain an ethanol-containing fermentation liquid, and a distillation device for processing the ethanol-containing fermentation liquid, with a water-enriched stillage incurring as residue, at least part of the stillage being recycled for extraction in counterflow to the raw material, wherein:
the extraction means is comprised of (i) a series of vessels under atmospheric pressure, each having a bottom portion and a partition wall therein not reaching the bottom portion and (ii) a means for charging a first vessel of the series of vessels with a comminuted sugar-containing raw material, a means is provided for feeding the stillage from the distillation device into a last vessel of the series of vessels, seen in the conveying direction of the raw materials, an extraction mixture conduit means, including thick matter pumping means, connects the bottom portion of each of the series of vessels with the consecutive vessel of the series of vessels, an extract separating means is provided and a further conduit means equipped with thick matter pumping means leads from the bottom portion of the last vessel of the series of vessels to the extract separating means, a series of overflow conduits is provided to connect the series of vessels, a descending liquid level of the extraction mixture contained in the vessels being provided from the last to the first vessels of the series of vessels, and an extract discharge conduit means is connected to the first vessel of the series of vessels, leading to the fermenting station.

9. An apparatus as set forth in claim 8, further comprising a preheater, a pressure tank and a pressure release tank consecutively incorporated in the extraction mixture conduit means between the first and the second vessels of the series of vessels following upon the thick matter pumping means, seen in the conveying direction of the raw materials.

10. An apparatus as set forth in claim 9, further comprising an ascending pipe adapted to connect the pressure tank in its bottom portion with the pressure release tank arranged at an elevated level and defining a steam room, and an exhaust vapor conduit means to connect the steam room of the pressure release tank with the preheater.

11. An apparatus as set forth in claim 8, further comprising at least one heat exchanger, a vacuum evaporator and a cooler consecutively arranged in the extract discharge conduit means.

12. A process for the production of ethanol from a comminuted fermentable saccharide-containing raw material using a system, which comprises:
extracting the raw material by a counterflow extraction with an aqueous medium using a series of extraction vessels, wherein an extraction mixture composed of the raw material and the aqueous medium from a bottom portion of each extraction vessel is conveyed to a subsequent extraction vessel in sequence, thereby obtaining an extract containing the fermentable saccharide, fermenting the extract so as to obtain an ethanol-containing fermentation liquid, processing the ethanol-containing fermentation liquid by distillation, thereby obtaining ethanol and a water-enriched stillage, recycling at least part of the water-enriched stillage in counterflow to at least one of the extraction vessels, and withdrawing a solid residue from a bottom portion of a last extraction vessel out of the system.

13. A process as set forth in claim 12, wherein the extraction mixture from the bottom portion of the last extraction vessel is separated into the solid residue and a thin juice; and the thin juice is recycled to at least one of the extraction vessels and the solid residue is withdrawn from the system.

14. A process as set forth in claim 13, wherein an overflow of the extraction mixture of each extraction vessel except for a first extraction vessel is returned to a preceding extraction vessel and the extract for the fermentation is taken from the first extraction vessel.

15. A process as set forth in claim 14, which further comprises:
heating the extraction mixture from the bottom portion of one of the extraction vessels to a temperature of above 100°C and not more than 150°C under pressure and subsequently releasing the pressure to atmospheric pressure before the extraction mixture is conveyed to a next extraction vessel.