GB2141350A

GB2141350A - Evaporating a dissolved product and recovering a more volatile fraction of the solvent

Info

Publication number: GB2141350A
Application number: GB08411512A
Authority: GB
Inventors: Udo Werther
Original assignee: Wiegand Karlsruhe GmbH
Current assignee: GEA Wiegand GmbH
Priority date: 1983-05-06
Filing date: 1984-05-04
Publication date: 1984-12-19
Also published as: JPS59206001A; IT8467458A0; GB8411512D0; FR2545372A1; IT8467458A1; GB2141350B; SE8402362L; SE8402362D0; IT1179642B; DE3316661A1

Abstract

A process for evaporating or removing solvent from a product dissolved in a solvent with components of varying volatility and for recovering at least one fraction of the solvent enriched with at least one more volatile component by means of an evaporation plant which comprises at least two evaporation stages through which the product flows in parallel flow or in counterflow to the heating vapour and/or vapours of the product and at least two evaporators through which the dissolved product flows one after the other, not necessarily but preferably directly, in one evaporation stage, in which the at least two evaporators through which the product flows one after the other in the evaporation stage are heated in parallel with heating vapour and/or vapours of the product and in which the vapours containing a concentration of at least one more volatile component from the evaporator through which the product flows first in this evaporation stage are condensed within the evaporation plant in order to recover a current of liquid containing an enriched concentration of at least one more readily volatile component.

Description

SPECIFICATION Process for evaporating a dissolved product and for recovering a more volatile fraction of the solvent This invention relates to a process for evaporating or removing solvent from a product dissolved in a solvent having components of varying volatility, and for recovering a more volatile fraction of the solute.

In the evaporation of liquids from a mixture comprising at least one relatively non-volatile solvent (e.g. water), at least one relatively volatile solvent in a lower concentration than the relatively non-volatile solvent (e.g. alcohol) and dissolved solids, the more volatile solvent preferentially pas ses over in the vapours. Apart from the actual function of evaporation, namely to concentrate the solids, it is generally desirable also to try and separate the two types of solvent from each other as economically as possible so as to recover them in as pure form as possible. Evaporation can therefore be supplemented, for example, by the rectification of the distillate formed in the evaporator.However, it is also possible to solve the problem of separation and concentration by rectifying the entire quantity of liquid and subsequently concentrating the solids in the resulting solution which is virtually free from the more volatile solvent. The particular method used in individual cases depends essentially on the total energy and investment costs of evaporation and the further separation process. The following processes are known for working up the solutions in question: a) rectification of the entire quantity of liquid, in which this liquid is separated into a more volatile component which is as concentrated as possible (top product) and a less volatile component containing the solids (bottom product). The bottom product is then concentrated in, for example, what is usually a multi-stage evaporation plant.This may be heated by an independent heat source, by a heat pump (mechanical vapour compression) or else by vapours from the top of a rectifying column.

This process has the disadvantage that the total energy consumption is high, chiefly on account of the large quantity of liquid which has to be rectified.

The same applies to the investment costs.

b) Separation of the more volatile component from a solution which contains only small amounts of the more volatile component, in a directly heated evaporation stage with its own condensation, provided upstream of the actual multi-stage evaporation.

Here, in order to save vapour, only enough vapour is produced as is required to drive off the more volatile component to give the desired residual content from the product fed in. A quantity of heating energy must be used which corresponds approximately to the evaporation enthalpy-of the vapours produced. The heat content of these vapours cannot be used for further evaporation.

The type of evaporator used is selected in accordance with the particular conditions; if there is little risk of incrustation, a counterflow falling film evaporator is preferred.

c) Separation of ethanol from low-alcohol mashes in a multi-stage evaporation plant (e.g. with down draught or forced circulation evaporators), com bined with concentration of the mash. After one or a few stages, the mash is virtually free from alcohol.

The vapour condensate from these stages which contains alcohol is discharged separately and de composed in a rectifying plant which may be smaller and operated with less energy consumption than one for the total quantity of vapour condensate.

When a partial current of condensate enriched with a more volatile component is removed from a multi-stage plant, the economy of the total process which can be achieved depends on the total number of stages or total evaporating power of the evaporat ing plant in relation to the number of stages or evaporating power required to evaporate the more volatile component. If, for example, one third of the total quantity of condensate with enriched, more volatile componenthas to be removed and the evaporation plant is constructed in six stages, this quantity of condensate must be removed separately from the vapours of the first two stages at the product end in order to achieve optimum economy.

It becomes unfavourable if the evaporation plant is constructed in four stages. Then, more than one third of the total quantity of condensate would have to be taken and worked up and it would be impossible to achieve optimum economy.

The situation is even less favourable when the quantity of condensate to be removed is 1/10 and the plant has two stages, such as might be found in mechanical vapour compression, even if the outputs are considerable.

In evaporation plants with mechanical vapour compression which are being increasingly installed in order to save energy, with a single-stage arrangement it is naturally impossible to remove a condensate enriched with a more volatile component.

Two-stage plants would require about half the total quantity of condensate to be worked up, even though it would be sufficient to work up perhaps ten percent of the total quantity of condensate in order to enrich the more volatile component. The quantity of condensate removed and, in inverse ratio thereto, the content of more volatile component therein is, however, critical to the energy and investment costs of the subsequent rectifier plant or separating apparatus with a similar action, perhaps based on the membrane separation technique.

There is therefore a need to provide a process for evaporating a product dissolved in a solvent having components of varying volatility, in which at least one fraction of the solvent is recovered enriched with at least one more volatile component, and in which the solution can be thickened as economically as possible and wherein only the smallest possible portion of condensate with the highest possible content of more volatile component need be removed, whilst the more volatile component is substantially eliminated from the remaining condensate and the concentrated solution. This small portion of condensate can then subsequently be separated with relatively little expenditure on energy. In this way, the energy cons#umption for the entire process, consisting of the evaporation and rectification or the like is kept particularly low.

We have now been able to devise a process which achieves many of the. above requirements,- and according to the invention we--provide a process for evaporating or removing solvent from a product dissolved in a solvent with components of varying volatility and for recovering at least one fraction of the solvent enriched with at least one more volatile component by means of an evaporation plant which comprises at least two evaporation stages through which the product flows in parallel flow or in counterflow to the heating vapour and/or vapours of the product and at least two evaporators through which the dissolved product flows sequentially not necessarily but preferably directly, in one evaporation stage, wherein the at least two evaporators through which the product flows sequentially in the evaporation stage are heated in parallel with heating vapour and/or vapours of the product and the vapours containing a concentration of at least one - more volatile component from the evaporator through which the product first flows in this evaporation stageare condensed within the evaporation plant in order to recover a current of liquid containing an enriched concentration of at least one morereadily volatile component.

The vapours of the first evaporator through which the mixture flows contain a high proportion of the or each more volatile component and therefore, after its heat content has been used in the evaporation plant by condensation, it can be further separated or used directly with relatively little expenditure on energy.

Advantageous embodiments of the invention are explained hereinafter by means.of examples, which refer to the accompanying drawings.

In the drawings: Figures 1 to 10 diagrammatically showevaporation plants or parts thereof which are particularly suitable for performing the process according to the inv#ention with its particular advantage#s.

The evaporation plant shown in Figure 1 has two evaporation stages I and II which are arranged one behind the other in terms of the product and each consist of two evaporators la, Ib and Ila, lIb arranged one behind the other in terms of the product.

The product which is to be evaporated is fed into the evaporator Ia-through the duct 2, then passed via the ducts 4, 6,8 through the evaporators lb, lla and lIb and discharged as a concentrate from the vapor ator lIb through the duct 10.

The evaporators la, Ib are heated by means of product vapours from evaporator I I b, which are discharged via the duct 12, compressed in a compressor 14 and passed through the ducts 16, 20- parallel to the heating chambers of the evaporators la and ib. The vapour condensate is discharged from the heating chambers of the evaporators la, Ib via the ducts 22, 24, conveyed through a common duct 26 to the heating chamber of the evaporator llb and from there discharged through the duct 28.

The productvapours from evaporator la are used to heat the evaporator Ila via the duct 30. The condensate of these vapours is discharged through the duct 32. The product vapours-from the evaporator Ib are used to heat the evaporator lIb via the duct 34.

The product vapours from the evaporator Ia are conveyed to the duct 12 via the duct 36.

The vapours in the duct 30 contain a high proportion of more volatile components, and the same therefore is true of the condensate which is discharged through the duct 32. The quantity of this condensate may, in some instances, be only 1/10 of the total evaporator output.

The condensate discharged through the duct 28 contains relatively few readily volatile components.

The condensate discharged through the duct 32 may be worked up still further, e.g. in a rectifying apparatus, orused directly.

Figure 2 shows a three-stage evaporation plant.

There is no need for a detailed description as the same reference numerals have been used as in Figure 1.

The vapours from evaporator la enriched with more volatile components are conveyed through the duct 40 to the first evaporator lla of evaporation stage II to heat it and are discharged through the duct 42 in condensed form.

The evaporation plant shown in Figure 3 compris es-three evaporation stages. Thefirstevaporation stage I consists of an evaporator. The product vapours from this evaporator, which contain even more volatile components, are passed through the duct 50 and used to heat the two evaporators Ila, lIb of evaporation stage II which are mounted one behind the other at the product end. The vapours from evaporator Ila, which also contain even more highly volatile components, are passed through the duct 52 and used to heat the first evaporator llia of the third evaporation stage Ill. The condensate containing the more volatile components is dis charged through the duct 54.The heating vapour condensates discharged from evaporator stages lIe and llb via the ducts 56, 58 also contain more volatile components. Accordingly, the vapour condensate discharged via the duct 60 from the evaporator Illb is relatively very poor in highly volatile components.

According to Figure 2 or Figure 3, it is also possible to use four or more evaporation stages. Any two successive stages are provided with at least two evaporators. The arrangement is such that the desired quantity of vapour condensate with more volatile components is obtained, as accurately as possible.

In the evaporation plants shown in Figures 1 to 3, the product and the heating medium flowthrough the evaporation stages in the same direction. These are therefore parallelflow arrangements. Figure 4 shows an example having a counterflow arrange ment (conceivably, there could also be partial coun terfiow arrangements).

The evaporation plant shown in Figure 4 comprises a first evaporation stage I with the evaporators la and Ib arranged one behind the other in terms of the product and an evaporation stage II with only one evaporator-which is mounted behind evaporation stage I in terms of the product.

The product is fed into the evaporator through the duct 70, then conveyed from the evaporator la to the evaporator lb via the duct 72, from the evaporator lb to the evaporator of the evaporation stage II via the duct 74 and from there discharged as a concentrate through the duct 76. The evaporator of the evaporation stage II is heated via a compressor 78 which is supplied, on the one hand, via the duct 80 with fresh vapour and, on the other hand, via the duct 82 with some of the product vapour from the evaporator of evaporation stage II. Heating is effected via the duct 83. The condensate from the vapours and heating vapour is discharged through the duct 87. The evaporator of evaporation stage II may also, however, be heated purely with heating vapour.The heating vapour is fed into the heating chamber of the evaporator of evaporation stage II via the duct 89 which is shown by broken lines.

The product vapours from the evaporator of evaporation stage II are passed through the ducts 84, 86 and 88 to heat the evaporators la and Ib in parallel.

The product vapours from evaporator la are discharged through the duct 90, condensed in a condenser I and discharged as a condensate through the duct 92. This condensate contains the more volatile components. The condenser I is cooled by means of a coolant which is fed into the condenser through the duct 94 and discharged from the condenser through the duct 96.

The heat medium condensates from the evaporators la and lb are discharged through the ducts 98, 100 and, combined, are fed through the duct 102 to a condenser 11. The product vapours from evaporator lb reach the condenser II through the duct 104 and are there condensed. The combined condensate which does not contain any high proportion of more volatile components is discharged through the duct 105.

The condenser II is cooled, like condenser I, with a coolant which is fed in via the duct 106 and discharged by means of the duct 108.

In the embodiment shown in Figure 5, the product flows in series through the evaporators la, Ib, Illa, II and Illb. It is fed into the evaporator la through the duct 120 and discharged as a concentrate from the evaporator Illb through the duct 122. The evaporators la and lb are heated in parallel with the product vapours from the evaporators Illa and Illb via a compressor 124.

The product vapours from evaporator la are used to heat the evaporator Illa. The condensate discharged from the heating chamber is discharged through the duct 126 and contains a concentration of more volatile components.

The product vapours of the evaporator Ib are used to heat the evaporator II and the product vapours from the latter are used to heat evaporator Illb.

The heating medium condensates from evaporators la, Ib, II and Illb are combined and discharged through the duct 128; they contain only a relatively small proportion of volatile components.

In an evaporation plant as shown in Figure 5, the product may be conveyed, for example, along the route la, Ib, II, Illa, Illb or la, II, Illb, Illa, Ib as well.

In the apparatus shown in Figure 6, the product vapours from evaporator la are conveyed through a duct 140 through a preheaterforthe product fed into the evaporator la and from there are discharged in the form of a condensate through the duct 142. The condensate contains the more volatile components, considerably concentrated, and the product is fed into the preheater via the duct 144 and flows from the preheater into the evaporator la via the duct 146.

The heating medium condensates from the eva porators la, Ib and II are combined and discharged via the duct 148. They contain relatively small amounts of more volatile components. The concentrate is discharged from the product chamber of the evaporator II via the duct 150.

In the embodiment of the apparatus shown in Figure 7, the evaporators la and Ib have a common heating chamber 160 which is fed with condensed product vapours from the evaporators Ila and llb.

The product from the evaporators la and Ib flows in chambers 162, 164 which are hermetically separated from each other. Ducts 166, 168 from separating chambers 170, 172 for the productvapours lead into these chambers 162,164. The feed chambers 174, 176 for the two evaporators are hermetically separated from one another.

The product is fed in through the duct 178 and then passes from the evaporator la into the evapor -ator lb through the duct 180 and from the evaporator Ib via the duct 182 into the evaporators Ila and llb of evaporation stage II which are arranged parallel in terms of the product. The product feed chamber 184 is common to these two evaporators Ila and llb, like the product collecting chamber 186. The concentrate is discharged via the duct 188. The evaporator Ila is heated via the duct 190 with the vapours from the evaporator la which contain the more volatile components. The evaporator lIb is heated via the duct 192 with the product vapours from evaporatorlb.

The parallel heating of the evaporators la and Ib is effected using the product vapours from the evaporators Ia and llb via the duct 194 in which there is a compressor 196. The duct 194 leads away from a vapour precipitation chamber 198 which is common to both evaporators Ila and llb. This precipitation chamber 198 is also connected to the product collecting chamber 186 via a line 200.

The condensate of the vapour used to heat the evaporator Ila, said condensate containing the more volatile components, is discharged through the duct 202. The condensate of the heating-vapour from the evaporation stage I (evaporators la and Ib) is fed into the heating chamber of the evaporator llb via the duct 204, then combined with the condensate of the heating vapour supplied through the duct 192 and discharged through the duct 206. The condensate contains relatively few volatile components.

The embodiment shown in Figure 7 is characterised by a particularly compact construction, low investment costs, ease of insulation and low heat loss.

The evaporation plant shown in Figure 8 is a counterflow plant corresponding to Figure 4. The condensers I and II are combined to form a structural unit, like the evaporators la and Ib. The evaporators la and lb are combined as in Figure 7. The product is supplied via the duct 220 whilst the concentrate of the product is discharged via the duct 224.

The evaporator of the evaporation stage Ills heated via the duct 226. The condensate is dis- charged via the duct 228.

The condensers I and il are separated from each other only by a wall 230. Coolant is fed into them through a duct 232 and this coolant is discharged through a duct 234. The condensate, containing a concentration of more volatile components, is dis charged from the condenser l via the duct 236.

Condensate containing relatively few volatile com ponents is discharged through the duct 238.

The plant shown in Figure 8 has the same essential advantages as the plant shown in Figure 7.

Figure 9 shows a particular embodiment of an evaporator la wherein the product chamber is subdi vided into at least two chambers.

The product is fed into the first product chamber of the evaporator la via the duct 260 and then into the neighbouring chamber via the duct 262.

All the chambers comprise a common-heating chamber to which a heating medium is supplied through the duct 264. The condensate of the heating medium is discharged through the duct 266. The vapour discharged from the product collecting chambers 268 and 276 contains a higher concentra tion of more volatile components, compared with an evaporator la which is not subdivided into several product chambers.

Before the vapours leave the evaporatorthrough the duct 270 to heat the evaporator: lla, for example, in Figure 1 or 2, theyflowthrougha precipitation chamber 272 which empties into the first product collecting chamber via the duct 274.

The product collecting chambers 268 and 276 are separated from each other in such a way that the vapours from all the collecting chambers can pass into the common separator 272 whilst the product currents can be drawn off separately.

The product is discharged from the collecting chamber 276 via the duct 278 and fed into the evaporator Ib, for example, in Figure 1 or 2.

Due to the construction shown in Figure 9, a product is discharged through the duct 278 contain ing relatively tiny quantities of more volatile compo nents of the solvent. This may, for example, be led to evaporator Ib in Figure 1 or Figure 2. The vapour discharged through the duct 270 contains a very large proportion of more volatile components and may, for example be led to evaporator lla in Figure 1 or Figure 2.

The embodiment of the plant shown in Figure 10 corresponds to that of Figure 1, except that the evaporator la is provided with a stripping column 280 placed on top and is constructed as a counterf low falling film evaporator (downdraught evaporator with product and vapours flowing in countercur rent}. The product is passed as runback via the duct 282 into the uppermost stage of the stripping column. The product vapour produced in the evapor ator la eliminates quantities of the more volatile components in the solvent ofthe product fed through the duct 282 before the product is evapo rated in the evaporator la. As a result, the concentra tion of the more volatile components in the vapour discharged through the duct 284 is increased.

The condensate containing the predominantly more volatile components is dis#charged through the duct 286, the condensate containing r#elatively few volatile components is discharged through the duct 288 and the concentrate of the product is discharged through the duct 290.

Claims

1. A process for evaporating or removing solvent from a product dissolved in a solvent with components of varying volatility and for recovering at least one fraction of the solvent enriched with at least one more volatile component by means of an evaporation plant which comprises at least two evaporation stages through which the product flows in parallel flow or in counterflow to the heating vapour and/or vapours of the product and at least two evaporators through which the dissolved product flows sequentially in one evaporation stage, wherein the at least two evaporators through which the product flows sequentially in the evaporation stage are heated in parallel with heating vapour and/or vapours of the product and-the vapours containing a concentration of at least one more volatile component from the evaporator through which the product first flows in this evaporation stage are condensed within the evaporation plant in order to recover a current of liquid containing an enriched concentration of at least one more readily volatile component.

2. A process as claimed in claim 1, wherein the condensation is effected by using the heating vapour(s) to heat at least one evaporator in a subsequent evaporation stage (II in Figures 1, 2; Ill in Figures 3, 5; Il in Figures 7, 10) of the evaporation plant.

3. A process as claimed in claim 1, wherein the condensation is carried out in a condenser of the evaporation plant.

4. A process as claimed in claim 1, wherein the condensation is carried out by using the heating vapour(s) to heat a preheater for the product which is to be evaporated in the evaporation plant.

5. A process as claimed in any of claims 1 to 3 wherein the evaporation stage comprises at least two evaporators having a common heating chamber, and separate product chambers.

6. A process as claimed in any of claims 1, 2 or 5 wherein the subsequent evaporation stage comprises at least two evaporators which are arranged in compartments of a hermetically subdivided heating chamber.

7. A process as claimed in any of claims 1,3 or 5 wherein at least two condensers from different evaporation stages are combined in a single unit.

8. A process as claimed in either of claims 1 or 2 wherein the evaporator which supplies the vapour containing a concentration of at least one readily volatile component is constructed as a counterflowfalling film evaporator with a stripping column placed on top.

9. Aprocess as claimed in any one of the preceding claims, wherein the first evaporator through which the product flows is subdivided several times at the product end in order to increase its separating effect and accordingly comprises a plurality of product chambers which are separated from one another in such a way that the product is prevented from being mixed between the individual product chambers, whilst the vapours given off by the product from the various product chambers are able to mix.

10. A process as claimed in any one of the preceding claims, wherein the content of more volatile components in the solvent is small compared with its content of less volatile components.

11. A process as claimed in any one of the preceding claims, wherein the product dissolved in the solvent is a solid substance when undissolved.

12. A process substantially as hereinbefore described with reference to any of the accompanying drawings.

13. Each and every novel process, method, step and apparatus hereinbefore described.