EP1888193A1

EP1888193A1 - Separation method

Info

Publication number: EP1888193A1
Application number: EP06722799A
Authority: EP
Inventors: Stephan Rüdiger BLUM
Original assignee: White Fox Technologies Ltd
Current assignee: White Fox Technologies Ltd
Priority date: 2005-04-20
Filing date: 2006-04-19
Publication date: 2008-02-20
Also published as: CA2605570A1; CN101163528A; JP2008536503A; RU2007142494A; WO2007095875A1; DE112006001685A5; US20080135396A1; BRPI0610023A2

Abstract

The invention relates to a separation method, in particular a method for distilling ethanol as a final product from a mash. According to said method, the feed stream is fed to a first distillation stage comprising at least one distillation column (stripper) and the distillate from said first distillation stage is fed to a second distillation column (rectifier). The feed stream is sub-divided into two streams (40, 41) and fed to two distillation columns (1, 2), in such a way that the rectifier (5) maintains a predefined energy balance.

Description

separation processes

Description:

The invention relates to a separation process, in particular a distillation of ethanol as a final product from a mash.

In a conventional process of distilling and dehydrating ethanol from a beer mash, having after fermentation about 10% ethanol, 85% water and 5% solids, this is fed preheated to a first distillation column. In the first

Distillation column, the mash is evaporated, whereby solid components can be removed as bottoms with water. A part of this bottom product is usually recycled to the distillation column after heating (reboiler).

The first vaporous distillate, still containing water, ethanol and fusel oil is, if necessary. via a collecting and mixing tank, fed to a second distillation column, which is designed as a rectification column. In this

Rectification carried a more extensive separation, in which the fuselages are discharged in a side stream. Of the water precipitated in the second distillation column as the bottom product, a small proportion is returned to the rectification column again after heating (reboiler) and otherwise also removed, so that it exudes from the production process. The distillate of the second distillation column, still containing water and ethanol, can be partially recycled to the first and second distillation column, if necessary. over the already mentioned collection tank. The predominant amount of the ethanol-water mixture constituting the second distillate of about 95% ethanol and 5% water undergoes a final dehydration to obtain as pure as possible a purity of 99 to 99.8% ethanol. This last dehydration occurs by means of molecular sieves, in which crystalline zeolites adsorb spongy H ₂ O molecules.

However, the zeolites of a molecular sieve are rapidly saturated in water. For a constant dehydration therefore water-saturated zeolites must be regenerated. As a result, molecular sieves are regularly used in pairs. It can then be provided by a first active molecular sieve high purity ethanol, which can also be used for the regeneration of a second, passive molecular sieve. In the regeneration of a passive molecular sieve, the ethanol used there can be recycled to a distillation column, this reflux can be about 30% of the obtained pure ethanol of the active molecular sieve. In this case, the constant change of the pressure load of the molecular sieves causes a dusty abrasion of the filling material. This burdens downstream plant stages, which must be completely replaced periodically. This is reflected adversely in investment and operating costs.

The dehydration of ethanol is an energy-intensive process. In particular, the evaporation of the mash in the first distillation column as well as the need for large amounts of reflux of the distillates cause considerable operating and investment costs. Also, a high degree of purity of about 90-95% ethanol of the ethanol-water mixture is necessary before treatment with molecular sieves, including apparatus technology and In terms of operating costs, the substance mixture must be rectified as close as possible to the acetropole point. As a result, a large number of separation stages and a high reflux are required in the rectification column.

It is known from PCT / DE2004 / 000867 to reduce the energy requirement of the rectification column by the measure that the molecular sieves are replaced by membrane filtration units, whereby the distillate of the rectification has only a concentration of 80 wt.% Ethanol supply. As a result of this measure, the required reflux is significantly lower than when using molecular sieves. However, the energetic design of the first distillation column, the stripper, remains unchanged. However, the total energy balance is not satisfactory, since the rectification is driven at a lower energy level and correspondingly at the rectification now only a small excess of energy is obtained, which can be fed to the first distillation column. For this reason, it must also be supplied with considerable energy from outside.

Against this technical background, the object of the invention is to provide a separation process by means of which the economic efficiency, in particular in the dehydrogenation of ethanol from a mash, is markedly improved.

To solve this technical problem is in a separation process, in particular in the distillation of ethanol from a mash in which an inlet of a first distillation stage with a distillation column, a stripper, and the distillate of the first distillation stage of a second distillation column, a rectification, is supplied gem. of claim 1, that the feed divided into two streams is fed to two distillation columns in such a way that the rectification column complies with a predetermined energy balance.

The separation method according to the invention has a number of advantages. Previously, the energetic concept of a distillation plant was determined by the design of the stripper, so according to the invention the first distillation stage is operated according to the energetic specifications of the rectification column, which can thus be operated optimally. It thus determines the energy balance of the rectification column essentially that of the first distillation stage.

In a first variant of the method, it may be thought that the feed is merely separated into two streams, so that both streams have similar energetic and / or chemical potentials, which streams are then fed to a respective distillation column. Also, most of the volume flow of the two streams will move in the same order of magnitude, each about half, but it may be appropriate in individual cases, depending on the configuration of the first and second distillation stage to specify the volume flows differently.

Different volume flows may occur in such a simple splitting of the feed, when a first stream is fed to a stripper and a second stream to a rectification column. Is then still envisaged that a bottom product of the rectification than in

Process flow back distillation column is returned to a stripper as a front, improves the energy balance per liter of end product over conventional methods already by about 40%. If the feed is split equally into two streams and two strippers are provided in the first distillation stage, a stream is alternatively fed to each stripper, wherein then preferably the volume flows of the two streams are also about the same size. Is then still thought in a preferred embodiment, that a bottom product of a preferably operated at high pressure first stripper is fed to a preferably subjected to a lower pressure second stripper and further in that the distillate of the rectification in a

Membrane filtration device is cleaned, the energy balance improves by more than 60%

In a further embodiment of the method according to the invention can be thought of it, by separation devices such

Sieves, filters, membranes, centrifuges or the like to achieve an increased concentration in one of the feeds. In such a separation into two liquid phases of substantially the same energy level is in a preferred variant of the method according to the invention the

Retentate, for example, a membrane separator in a stream of a stripper and the permeate are fed in a stream of a rectification column.

When using a separating device, a separation into a low-solids or even solids-free stream and into a stream subjected to solids is regularly carried out

If there is a separation of an inlet into two streams, one of which has a liquid phase and the other is at an elevated temperature and / or in particular in a vaporous phase, then this stream with the elevated temperature becomes, in particular, a retentate, for example, a membrane separation device Stripper preferably supplied at the top and is with the distillate of this stripper to the rectification. The feed of the stream of lower temperature then takes place as permeate, for example, in a lower region of the stripping column.

In a further development of the method described above, a vapor phase generating separation device may be provided as an evaporator, in particular by a relaxation of a vapor phase generating or as a distillation column whose distillate is then present with the distillate of a stripper to the rectification and their bottom product to the stripper next a further stream of the feed is still supplied.

Regularly, it is contemplated that the power requirement for the operation of the first distillation stage from the surplus energy incurred in the operation of the rectification and the heat recovery from a final product is completely covered. This will be the

Separation method according to the invention used in an optimal manner, since the operation of the first distillation stage is completely determined by the rectification and the heat recovery from a final product.

The distillation columns are preferably run at different operating pressures, in particular with those which allow optimal heat recovery. This ensures the lowest possible heat loss.

In addition, it is thereby possible that three distillation columns can be operated in a cascade connection. Assuming that the rectification column is operated at a highest energy level, a stripper is formed by the surplus energy arising in this case driven a medium energy level. With its excess energy, the second stripper is then preferably operated at a lower energy level.

In order to keep the energy level of the stripper operated at medium level as high as possible, it is preferably provided that the heat recovered from the heat recovery from the final product is fed into the reboiler circuit of the operated at a medium energy level distillation column.

The heat recovered from the final product can be significantly increased if the concentration of the final product in a feed is at least 20%. It is then possible to significantly reduce the energy input of the overall system in relation to the amount of final product obtained. Such an increase, for example, of an ethanol content of about 10% in one feed can be achieved by a corresponding fermentation technique. Alternatively, upstream processes are possible, for example, that the feed to a previously explained

Membrane separation process has an increased proportion of the final product. As a result of these measures, the proportion of the end product in the entire system increases significantly. These measures further lead to a significantly increased output of the end product and thus also to an increased heat recovery, which can then be reintroduced into the process.

According to conventional methods, the distillate of

Rectifying be purified in molecular sieves or preferably in a membrane separation process in a filtration device. In particular, it can then be further provided that a regenerate of this a rectification in the Process flow subsequent filter device is fed into a stripper again.

The separation method according to the invention is explained in more detail with reference to the drawing, in which only schematically process flows are shown. In the drawing shows:

1: three distillation columns and a final purification by means of molecular sieves,

2 shows an arrangement of three distillation columns and a final purification by means of a membrane separation process,

Fig. 3: a further arrangement of three

Distillation columns,

Fig. 4: variants of a feed of a Renegats a

Filtration device of a final cleaning,

5 shows an arrangement of two distillation columns,

6 shows a variant of the splitting of an inlet in two distillation columns,

7 shows a splitting of the feed into preferably a liquid and a vapor phase,

8 shows a variant of the splitting into a liquid phase and a vapor phase,

Fig. 9: a splitting into a liquid and a vapor phase by means of a distillation column and 10: a variant of this.

In FIG. 1, two strippers 1, 2 connected in parallel form a first distillation stage for a separation process, for example for the distillation of ethanol from a beer mash whose inflow 3, comprising about 11.5% ethanol, divided into two streams 40, 41 is more similar chemical and energetic potentials the two strippers 1,2 is fed in equal parts. The distillate 4 of the two strippers 1,2 is fed together to a rectification column 5.

Their distillate 6 is purified by molecular sieves 7 and discharged as, for example, high-purity methanol of a purity of 99.6% as product stream 8.

According to the invention, the rectification column 5 is driven to the highest energy level. For example, approx. 18,000 kW of primary energy 9 are fed in, indicated by the heat exchanger in the reboiler cycle of the rectification column 5. An excess of energy of about 9,800 kW is present, which is indicated via a heat exchanger 10 in the return 12 of the rectification column 5 Part is fed into the stripper 2, so that it can be driven at a medium energy level. Required for the operation of the stripper 2, however, are only about 8,500 kW, so that about 1,300 kW unused can be discharged from the circulation, indicated by the heat exchanger 11 in the return 12th

The stripper 1 is operated with the excess energy of the stripper 2, for which approximately 6,500 kW are required with a surplus of about 6,900 kW of the stripper 2, so that here again about 400 kW of excess energy can be discharged. A portion of the excess energy can be used for the regeneration and operation of the molecular sieves 7. However, since in the molecular sieves 7 supplied distillate 6 of, for example, a purity of ethanol of 93% also an energy of about 8,200 kW is included, although to a part, about 3000 kW, for example. By feeding the regenerate 13 of the molecular sieves 7 or the like is used for the operation of the rectification 5, remain in the product stream 8 ultimately still about 5.200 kW, due to the operation of the molecular sieves 7, largely cyclically to 5,000 kW as unused heat can be withdrawn from the system, indicated by the heat exchanger 14.

If the distillate is ethanol, a production rate of 19.57 l / h can be achieved with 1.58 kg steam / 1 ethanol in this calculation example.

To ensure the cascade of energy transfer from one distillation column to the next, the distillation columns are driven 1,2,5 with graduated, different pressures. As a result, an optimal operation of the distillation columns 1,2 and 5 is possible with an optimal energy transfer.

In the method of Figure 2, the molecular sieves with far-reaching consequences are replaced by a

Membrane Filtriervorrichtung 15. For their operation, it requires only one distillate 16 of the rectification column 17 of a purity, for example, in ethanol of 80%. As a result, it requires only a feed of a primary energy of only about 10,500 kW. Corresponding less energy rich is the return 18, are provided by the only about 1860 kW for the operation of the stripper 19. Accordingly, the distillate 16 has an energy content of about 8,600 kW. The However, both strippers 19, 20 are essentially to be operated in accordance with the specifications of the preceding exemplary embodiment.

As a result of the permeate 21 of the membrane filtration device 15 remaining in the process, approximately 3,000 kW are again made available for the operation of the rectification column 17. Thus remain in the product stream 22 about 5,600 kW, of which about 5,000 kW in an advantageous manner continuously, indicated via a heat exchanger 23, 19 can still be used for the operation of the stripper. There remains at the made defaults a gap of about 1,660 kW, which are externally, indicated by the heat exchanger 24, are fed. Nevertheless, with 1.07 kg of steam, one liter of ethanol is produced at a product flow 22 of about 19.6 l / h.

In the method explained with reference to FIG. 3, the feed 25 contains a proportion of the end product, for example ethanol, at a level of 20%. As a result, the amount of distillate 26 of the two strippers 27, 28 will be significantly increased, with slightly increased energy requirements and equal working pressures. In order to be able to process the increased amount of distillate, the rectification column 29 is acted upon at unchanged pressure with a primary energy 30 of about 14,500 kW, of which in the return 31 about 2,500 kW for the operation of the stripper 28 are available.

The distillate 32 supplied to a membrane filtration device 33 has an energy content of about 12,500 kW in the case of, for example, an ethanol content of 80%. Through an infeed of the

Permeats 34 flow to the rectification column 29 thereof about 4,700 kW. This leaves about 7,800 kW in the product stream 35, which, indicated by the heat exchanger 36, can be fed into the reboiler circuit 37 for the operation of the stripper 28, the here an energy requirement of Approximately 9,700 kW has an excess of 8,300 kW for the operation of the stripper 27, which requires only about 8,050 kW. Thus, enough energy is provided for the energetically cascaded strippers 27, 28, 29. In addition, the product stream 35 increases significantly to 30.46 l / h. This with an energy input of 0.83 kg of steam per liter of ethanol produced.

On the basis of Figures 4 to 10 simplified variants are further explained.

Figure 4 shows two strippers 42,43, which are acted upon by two similar streams 44,45 of an inlet 46. The distillate 47 of the two strippers 42, 43 is fed to a rectification column 48 and its distillate 39 to a filtration device 49.

A renewed feed of a regenerate 50 of the filter 49, in particular again a membrane filtration device is carried out in this embodiment not in the rectification column 48, but in one of the stripper 42,43, indicated by dashed lines in the drawing.

If appropriate, both strippers 42, 43 can also be charged with the regenerate 50.

In the exemplary embodiment according to FIG. 4, the streams 44, 45 of the same chemical and energetic potential are introduced by way of example in an upper region of the columns of the strippers 42, 43, and the distillate 47 of the strippers 42, 43 is introduced approximately in the center of the rectification column 48.

In the embodiment according to FIG. 5 with only one stripper 51 and one rectification column 52, the two streams 53, 54 are fed into the stripper 51 and the rectification column 52. In such a case, the volume flows of the two streams 53, 54 also differ significantly from each other.

The bottom product 55 of the rectification column 52 is from the

Process not discharged, but fed here in the stripper 51.

FIG. 6 shows the division of an inlet 56 into two streams 57, 58 by a separating device 59. The

Separator 59, formed for example by sieves, filters, membranes, centrifuges or the like, provides on the one hand for a significant increase in the proportion of the final product, for example. Ethanol, in the stream 57, which is supplied to a stripper 60.

On the other hand, in addition to an increased concentration of the end product, this stream 57 will usually only have a low solids content or even be solids-free.

In addition to a separation into two streams 57,58 with liquid phases and with substantially the same energy potentials, a division acc. Fig. 7 by means of a suitably designed separating device 61 in a first current 62 with respect to a second current 64 increased

Temperature and / or in particular present in the vapor phase present at the head of a stripper 64 and pending with the distillate at the rectification column 65. The introduction of the second stream 64 takes place in a lower region of the stripper 63.

Suitably designed separating devices 61 may be, for example, evaporators and, in particular, strippers 85, for example, shown in FIG. 9. Figure 8 shows a variant in which an inlet 66 is divided into two similar streams 67,68. The stream 68 is fed directly to a stripper 86.

The other stream 67 is again divided by a separating device 69 into two further streams 70, 71, of which the stream 70 present in particular in the vapor phase is supplied again to the stripper 86 on the top side and is present with the distillate at the rectification column 87. The stream 71 can still be supplied to the stripper 86 and thus remain within the process.

In FIG. 9, as compared with FIG. 8, a stripper 85 is provided as the separating device. While the distillate 72 of the stripper 85 of elevated temperature, in particular vapor phase, a stripper 73 is fed to the top and is present with the distillate at the rectification column 88, a feed of the bottom product 74 of the stripper 85 in the stripper 73rd

The stripper 73 is further supplied with a further, branched stream 75 of the feed still.

Conveniently, in the process according to FIG. 9, the distillation column 65 is driven at a higher pressure than the stripper 73.

FIG. 10 shows how two strippers 79, 80 are acted upon by an inlet 76, divided into two identical streams 77, 78. Their distillate 81 is, for example, summarized as shown, fed to a further distillation column 82. Its bottom product 83 is then introduced into a rectification column 84.

Claims

Claims:

A separation process, in particular a distillation process of ethanol as a final product from a mash, in which an inlet of a first distillation stage with at least one distillation column (stripper) and the distillate of the first distillation stage of a second distillation column (rectification) is fed, characterized in that the Feed divided into two streams (40,41) two distillation columns (1,2) is fed so that the rectification column (5) complies with a predetermined energy balance.

2. Separation method according to claim 1, characterized in that the two streams (40, 41) have similar energetic and / or chemical potentials.

3. Separation method according to one or more of the preceding claims, characterized in that a stream (57) has an increased concentration of the final product.

4. Separation process according to one or more of the preceding claims, characterized in that a stream (57) is a low-solids or solids-free stream.

5. Separation method according to one or more of the preceding claims, characterized in that a stream (62) has an elevated temperature and / or is present as a vapor phase.

6. Separation method according to one or more of the preceding claims, characterized in that a first stream (53) is fed to a stripper (51) and a second stream (54) to a rectification column (52).

7. Separation process according to one or more of claims 1 to 5, characterized in that the two streams

(40,41) two strippers (1,2) are supplied.

8. Separation process according to one or more of the preceding claims, characterized in that a bottom product (55) of a rear in the process sequence

Distillation column (52) is returned to a front.

9. Separation method according to one or more of the preceding claims, characterized in that a regenerate

(50) of a rectification column (48) subsequent filter device (49) in a stripper (42; 43) is fed.

10. Separation process according to one or more of the preceding claims, characterized in that the bottom product (74) of a first stripper (65) is fed to a second stripper (73).

11. Separation method according to one or more of the preceding claims, characterized in that the first stripper (65) is driven at a higher pressure than the second stripper (73).

12. Separation process according to one or more of the preceding claims, characterized in that three distillation columns (1,2,5) are operated in a cascade connection.

13. Separation process according to one or more of the preceding claims, characterized in that the heat recovered from the heat recovery from the end product (35) is fed into the reboiler circuit (37) operated at a medium energy level distillation column (28).

14. Separation method according to claim 1, characterized in that the power requirement for the operation of the first distillation stage from the in the operation of the

Rectifying column (29) resulting excess energy and the heat recovery from a final product (35) is completely covered.