WO2014191213A1

WO2014191213A1 - Method for capturing carbon dioxide from a gas stream, in particular from a flue gas stream, and method for work-up of contaminated potassium sulphate

Info

Publication number: WO2014191213A1
Application number: PCT/EP2014/059943
Authority: WO
Inventors: Ansgar Kursawe; Markus Kinzl; Rüdiger Schneider; Ralph Joh
Original assignee: Siemens Aktiengesellschaft
Priority date: 2013-05-28
Filing date: 2014-05-15
Publication date: 2014-12-04

Abstract

The invention relates to a method for capturing carbon dioxide from a gas stream, in particular from a flue gas stream, according to which method the gas stream is brought into contact with a scrubbing medium in an absorber (5) of a capturing device (7), capturing carbon dioxide contained in the gas stream, the scrubbing medium loaded with carbon dioxide is fed to a desorber (9) of the capturing device (7) to release the carbon dioxide, the scrubbing medium that has been freed of carbon dioxide is fed to a work-up stage (13), in which sulphur oxides contained in the scrubbing medium are precipitated out as potassium sulphate, and the potassium sulphate precipitated out is fed to a separation unit (23), in which the potassium sulphate is separated from the scrubbing medium, in order to obtain purified potassium sulphate. The potassium sulphate precipitated out is at the same time subjected to a scrubbing process in the separation unit (23). The invention furthermore relates to a method for work-up of contaminated potassium sulphate, according to which method the contaminated potassium sulphate is separated from the scrubbing medium by means of a separation unit (23) and at the same time subjected to a scrubbing process in the separation unit (23) in order to obtain purified potassium sulphate.

Description

description

Process for separating carbon dioxide from a gas stream, in particular from a flue gas stream, and process for the treatment of contaminated potassium sulfate

The invention relates to a method for separating carbon dioxide from a gas stream, in particular from a flue gas stream. Furthermore, the invention relates to a method for the treatment of contaminated potassium sulfate.

Against the background of climatic changes, it is a global goal to reduce the emission of pollutants into the atmosphere. This applies in particular to the emission of carbon dioxide (C0 ₂ ), which accumulates in the atmosphere, hindering the heat radiation of the earth and thus as a greenhouse effect leads to an increase in the Earth's surface temperature. Especially with fossil-fired power plants for the production of electrical energy, the combustion of a fossil fuel produces a carbon dioxide-containing flue gas. To avoid or reduce carbon dioxide emissions into the atmosphere, the carbon dioxide must be separated from the flue gas. Correspondingly, suitable measures are being discussed, especially in the case of existing fossil-fired power plants, in order to separate the resulting carbon dioxide from the exhaust gas after combustion (C0 ₂ post-combustion capture).

As a technical realization, the flue gas after combustion is brought into contact with a suitable washing medium, with gaseous carbon dioxide contained in the flue gas being dissolved in the washing medium or being absorbed in a chemical sense. The exhaust gas freed of carbon dioxide is finally released into the atmosphere. The loaded with carbon dioxide wash medium can be regenerated by desorption of the absorbed carbon dioxide and again for the absorption of Carbon dioxide can be used from the flue gas. Common washing media are based on primary, secondary or tertiary amines and show good selectivity and high capacity for carbon dioxide.

In addition to carbon dioxide, which can be effectively removed from the flue gas by means of the amine-containing wash media, pollutants such as solid particles, sulfur oxides (S0 _X ) and nitrogen oxides (N0 _X ) are also introduced into the C0 ₂ separation process by the flue gas. Accordingly, the washing medium must be prepared after the separation of the carbon dioxide. For this purpose, the washing medium is cleaned, for example in the context of a so-called SO _x recycling process of interfering sulfur oxides. In the SO _x recycling process, sulfur oxides are usually precipitated in the washing medium by lowering the temperature and changing the concentration in the washing medium as potassium sulfate (K ₂ S0 ₄ ). The potassium balance is compensated by adding potassium hydroxide (KOH). The potassium sulphate obtained through the SO _x recycling process can be used as a fertilizer component, for the production of building materials such as plasterboard, as well as in specialty chemicals. However, the requirements for the purity of the potassium sulfate are correspondingly high.

Thus, applications of potassium sulfate in the fertilizer sector, but also in chemistry and in the building materials industry require at least partial drying and purification of the crude product obtained in the course of the reprocessing process. The permitted residual moisture in potassium sulfate, ie the proportion of water and impurities, depends both on the respective re-use and on the recycler. Particularly stringent requirements are made for use as a special chemical or in high-quality fertilizers. Here, the values for the permitted residual moisture are sometimes in the range below 0.5% by weight. In order to ensure a wide applicability of the potassium sulfate, this must be further treated beyond the actual SO _x recycling process. In previous processing processes, for example, the residual moisture of potassium sulfate in the solid-liquid separation is reduced as far as possible with the aid of a centrifuge. However, the contaminated crude product may have a residual moisture of up to 10 wt .-% even after this treatment. This residual moisture contains not only water but also parts of the

Washing medium, which is obtained in the crystallization of potassium sulfate as the mother liquor. This is lost to the deposition process, so that the capacity of the washing medium due to the loss of the active component, so the amino acid salt decreases.

Furthermore, problems can result in the use of amine-containing wash media, since the residual moisture in the potassium sulfate portions of the amine or amino acid salt solution may contain in the form of presumably lent carcinogenic nitrosamines by reaction of nitrogen oxides contained in the flue gas and the amines or amino acids contained in the wash medium arise. These hazardous substances, as well as any solids contained, reduce the possible applications or the selling prices of the potassium sulphate obtained enormously. Thus, with regard to the utilization possibilities, a separation or at least a reduction of the potassium sulfate contaminating mother liquor is desirable. It is therefore a first object of the invention to provide a method which makes available as part of a deposition process for carbon dioxide won potassium sulfate by the effective removal of impurities and with recovery of adhering mother liquor of a wide use.

A second object of the invention is to provide a process which permits the recovery of potassium sulfate with regeneration. Winning of adhering mother liquor with a comparison with common methods improved product quality allows.

The first object of the invention is achieved by a method for separating carbon dioxide from a gas stream, in particular from a flue gas stream, in which the gas stream is brought into contact with a washing medium in an absorber of a separation device under deposition of carbon dioxide contained in the gas stream, which with Carbon dioxide laden scrubbing medium is fed to a desorber of the separator for releasing the carbon dioxide, the scrubbing medium freed from carbon dioxide is fed to a treatment stage, in which sulfur oxides contained in the scrubbing medium are precipitated as potassium sulfate, and the precipitated potassium sulfate to obtain purified potassium sulfate a separation unit is supplied, in which the potassium sulfate is separated from the washing medium. In this case, the precipitated potassium sulfate in the separation unit is also subjected to a washing process.

The invention takes account of the fact that potassium sulphate, previously obtained in the context of a carbon dioxide deposition process, can not sufficiently meet the sometimes stringent requirements for further use due to impurities contained therein. One of the most important criteria in the evaluation of the quality of the potassium sulfate in this case represent impurities by the washing medium or adhering to the precipitate mother liquor, as well as impurities caused by nitrosamines formed in the washing medium.

Although the concentration of the impurities contained in the potassium sulfate can be reduced following the precipitation of the solid by a solid-liquid separation. The remaining in the potassium sulfate content of impurities and mother liquor - especially in the interstices and pores of the solid - but after such a work-up step is not sufficiently low to the recovered Potassium sulfate for a wide range of applications to make accessible.

Other treatment options, such as the use of filters to remove impurities or to remove adhering mother liquor are less efficient or associated with increased equipment complexity.

In view of the problem described above, the invention recognizes that the desired removal of adhering mother liquor and thus a reduction of impurities contained in the potassium sulfate can be achieved if the potassium sulfate precipitated in a separation unit is subjected to an additional work-up step. For this purpose, the potassium sulfate precipitated from the washing medium is separated from the washing medium by means of a separating unit and at the same time subjected to a washing process in the separating unit.

The known work-up step of the solid-liquid separation for the removal of adhering mother liquor and the impurities contained is supplemented by an additional treatment step, namely the washing of the potassium sulfate. The separation of the precipitated potassium sulfate as well as the washing process take place at the same time in a common separation unit. The separation unit thus offers the possibility to implement the desired purification and treatment of the potassium sulfate in only one system component.

In other words, an additional processing step for the potassium sulfate - the washing process - in an already used plant component - the separation unit - are integrated. Thus, the purification of the potassium sulfate by the integration of the washing process in the SO _x recycling process can be implemented cost-saving without the use of additional equipment necessary. The potassium sulfate obtained by means of the process can be used as valuable material and, thanks to the combined work-up steps, is also suitable for use fertilizer, to which it was previously inaccessible due to the purity requirements.

The solid-liquid separation particularly removes the mother liquor adhering to the surface of the potassium sulfate. By the solid-liquid separation preferably subsequent washing process of potassium sulfate in the separation unit at the same time contained in the pores and interstices of the solid mother liquor, the corresponding impurities as well as a possible residual portion of the washing medium. In particular, the concentrations of interfering minor components, such as amino acid salts, nitrosamines and heavy metals, can be reduced by a factor of 5-10 by the washing process. In the residual moisture of the potassium sulfate remaining after the washing process, no or only a negligible portion of undesired impurities are contained.

In an advantageous embodiment of the invention, the precipitated potassium sulfate is centrifuged in the separation unit in a separation zone. By means of a centrifuge, an effective separation of a large part of the mother liquor adhering to the solid can be achieved by centrifuging. In this case, preferably a continuously operating centrifuge is used. In such a centrifuge, the sample, so the contaminated potassium sulfate, the centrifuge is continuously fed while a rotor rotates at a predetermined speed. As the sample passes through the rotor, the separation of potassium sulfate from the mother liquor takes place

Centrifugation takes place. The potassium sulfate and the separated mother liquor can be removed separately from the centrifuge.

Alternatively, a so-called batch centrifuge can be used in which the separation of the washing medium from the potassium sulfate takes place batchwise. Here, a sample vessel filled with suspension is placed in a sample vessel in a rotor and after centrifuging the potassium sulfate taken separately in the sample vessel and the separated mother liquor.

The washing process preferably takes place as displacement washing in a washing zone within the separating unit. In the displacement laundry, an inserted detergent is pressed into a filter cake or on the surface of the filter cake. The detergent penetrates into the filter cake, whereby the existing in the interstices and the pores residual moisture, as in the present case the mother liquor with the impurities contained, is largely displaced. In this case, a large part of the adhering mother liquor is graft-like replaced by the detergent. By employing a displacement wash, in addition to the removal of adhering mother lye on the particle surface, effective removal of impurities contained in the pores and interstices of the potassium sulfate particles and adhering mother liquor can thus be achieved. The displaced mother liquor is then advantageously returned to the deposition process or to the corresponding carbon dioxide precipitator.

Preferably, the potassium sulfate flows from the separation zone of the separation unit into its washing zone. The washing zone is thus arranged in the flow direction behind the separation zone. Thus, by means of a solid-liquid separation in the separation zone, the mother liquor adhering to the particle surface can first be thrown off and finally the mother liquor remaining in the wash zone or the impurities contained can be removed from the interstices and the pores. In the preferred use of a continuous centrifuge thus enters in the separation unit by centrifuging pre-purified potassium sulfate in the washing zone, in which before the outlet of potassium sulfate further purification takes place. Preferably, the detergent used for the washing process is metered into the washing zone via a spray connection. The spray connection can in this case, for example, as a

Spray lance be formed and is suitably such arranged on the separation unit that allows accurate metering of the amount of detergent used in the washing zone of the separation unit. Preferably, a condensate stream discharged at the desorber serves as a source of the added detergent. Thus, detergent already contained in the process can continue to be used. Alternatively, the detergent can be added fresh. Conveniently, in this case, a detergent added to the corresponding amount of detergent at the desorber discharged again. Thus, detergent accumulation in the overall process can be avoided.

Preferably, water is used as the detergent. The secondary components present in the mother liquor can be effectively dissolved by water, while the solubility of potassium sulfate in water is negligible for the process.

Preferably, the detergent is used in a mass ratio of potassium sulfate between 0.5: 1 and 1: 1. At a mass ratio in said range, the water solubility of the potassium sulfate at the process temperature prevailing in the separation unit of preferably 10-15 ° C is less than 10 wt .-%.

At a mass ratio of 1: 1, ie if exactly as much detergent is used as there is to be purified potassium sulfate, then under idealized conditions during the washing process a maximum of one tenth of the potassium sulfate can dissolve in the detergent. At a mass ratio of 0.5: 1, the proportion of dissolving potassium sulfate is even only one twentieth. In the process, ie under real conditions, these proportions of dissolving potassium sulfate are even lower, since idealized conditions are achieved only in a complete equilibrium. However, a complete equilibrium setting requires a correspondingly long residence time of the sample in the washing zone, in particular when using a centrifuge for Carrying out the washing process is not given. Since the process takes place very quickly, the dissolution of the potassium sulfate will thus not take place until equilibrium is reached, so that the proportion of potassium sulfate dissolving in the detergent is much lower than assumed under idealized conditions.

Conveniently, precipitated potassium sulfate particles are separated in the crystallization step prior to entering the separation unit in a crystallizer of their particle size.

In other words, the crystallizer is part of the treatment stage. In the crystallizer, the necessary conditions for the separation by means of a separation unit and in particular by means of a centrifuge are created. By separating the salts crystallized from the washing medium according to their particle size, a suspension containing the number of coarse particles required for separation by means of a centrifuge can be made available in the crystallizer. Finally, the suspension is removed from the crystallizer and fed to the separation unit for removal of the mother liquor adhering to the potassium sulfate together with impurities.

It is advantageous if the separation unit is operated at temperatures in a range between 10 ° C and 15 ° C. In such a temperature range, the solubility of potassium sulfate in the detergent used is low, so that a high efficiency of the used SO _x reclaimer can be ensured in the context of the SO _x recycling process already described above. Furthermore, temperatures in a temperature range between 10 ° C and 15 ° C usually also prevail in a crystallizer upstream of the separation unit, which can be used as part of the treatment stage. Temperature control of the potassium sulphate suspension to be treated before it enters the separation unit can thus ideally be dispensed with. In a particularly advantageous embodiment, the detergent flows after passing through the washing zone in the separator for carbon dioxide. The amount of detergent that flows to the separating device from the washing zone, in this case is low based on the amount of detergent contained in the overall process. The dilution of the washing medium by the amount of detergent supplied to the process is thus negligible. The inflow of the detergent to the deposition process is preferably carried out with the mother liquor separated from the potassium sulfate. By recycling the mother liquor containing about 30 wt .-% amino acid salt, the loss of active component of the washing medium compared to a simple centrifuging can be significantly reduced. Since the detergent, based on the potassium sulfate, is preferably used in a mass ratio of between 0.5: 1 and 1: 1, the amount of detergent added, based on the amount of detergent present in the overall process, is negligibly small.

Furthermore, it is in principle possible, in addition to accumulating potassium sulfate, also to purify further by a corresponding process incurred by a deposition process by-products.

Expediently, the residual moisture remaining in the purified potassium sulfate is removed by drying following the washing process. In this case, the residual moisture, which after the displacement washing consists in particular of water, can be removed. The potassium sulfate obtained can finally be recycled.

The second object of the invention is achieved by a process for the treatment of contaminated potassium sulfate, in which the contaminated potassium sulfate separated to obtain purified potassium sulfate by means of a separation unit of a washing medium and is subjected to a washing process in the separation unit at the same time. This process treats contaminated potassium sulfate to meet stringent requirements, especially in the fertilizer sector and / or when used in structural and specialty chemicals.

The process for the treatment of contaminated potassium sulfate which is detached from the process for separating carbon dioxide from a gas stream is considered to be inventive in its own right.

In order to achieve effective separation of the potassium sulfate from the washing medium, the adhering mother liquor and the corresponding impurities, the precipitated potassium sulfate is preferably centrifuged in a separation zone of the separation unit.

It is particularly advantageous if the washing process takes place as displacement washing in a washing zone within the separation unit, since mother liquor can also be removed from the potassium sulfate by means of displacement washing in pores and interspaces.

Appropriately, a detergent is used for the washing process, which is metered via a spray connection in the separation unit.

Water is particularly suitable as washing agent, since water dissolves the impurities and secondary components contained in the washing medium and / or the mother liquor. The washed potassium sulphate, on the other hand, only dissolves in water to a limited extent, depending on the process temperature.

Preferably, the detergent is used in a mass ratio of potassium sulfate between 0.5: 1 and 1: 1, since in this area the proportion of the dissolving potassium sulfate is particularly low. Conveniently, the separation unit is operated at temperatures in a range between 10 ° C and 15 ° C, since at these temperatures, the solubility of the potassium sulfate in the detergent is particularly low.

Preferably, potassium sulfate particles contained in the washing medium are in a separator before entering the separation unit

Crystallizer separated according to their particle size. Of the

Crystallizer here is preferably part of a treatment stage used for the preparation of the potassium sulfate. From the crystallizer, a suspension is withdrawn which contains the number of coarse particles required for separation by means of a centrifuge. If the process for the treatment of contaminated potassium sulfate is part of a process for separating carbon dioxide from a gas stream, it is particularly advantageous if the detergent after passing through the washing zone in a separator for carbon dioxide, ie in the deposition process for carbon dioxide flows , The amount of detergent flowing to the separation device is minimal with respect to the overall process, so that no undesirable dilution of the washing medium is to be feared. For the final removal of remaining residual moisture in the purified potassium sulfate, this is expediently removed by a subsequent washing process drying. Further advantageous embodiments of the method for

Treatment of contaminated potassium sulfate results from the claims directed to the process for separating carbon dioxide from a gas stream. The advantages mentioned for the deposition process can be correspondingly transferred to the treatment process.

In the following an embodiment of the invention will be explained in more detail with reference to a drawing. Showing: 1 shows a schematic representation of a device for

Carrying out a process for the treatment of contaminated potassium sulfate as part of a separator for carbon dioxide.

1 shows a device 1 for carrying out a method for the treatment of contaminated potassium sulfate. In the present case, the process is part of a separation process for carbon dioxide from a flue gas stream.

In such a deposition process, a flue gas stream to be treated is introduced via a feed line 3 into an absorber 5 of a separation device 7. In the absorber 5, the carbon dioxide contained in the flue gas is brought into contact with a washing medium and absorbed therein. The released from C0 ₂ gas stream is released into the atmosphere. The scrubbing medium laden with carbon dioxide is then supplied to a desorber 9 which is connected to the absorber 5 in terms of flow. In the desorber 9, the carbon dioxide contained in the washing medium is released by increasing the temperature. The C0 ₂ - rich gas stream is recycled.

Since other acidic gases and in particular S0 _{X are introduced} into the deposition process via the flue gas in addition to the carbon dioxide, the scrubbing medium freed from carbon dioxide must be further processed after it leaves the desorber for its regeneration. For this purpose, the washing medium is fed via a feed line 11 to a treatment stage 13 before it can be returned to the absorber for re-absorption of carbon dioxide.

In the treatment stage 13, which is designed as SO _x recyclers, sulfur oxides contained in the washing medium by lowering the temperature and concentration changes in

Wash medium as potassium sulfate (K ₂ S0 ₄ ) precipitated. The separated in the treatment stage 13 washing medium is starting from the treatment stage 13 via a return line 15th returned to the deposition process or in the deposition device 7.

Since the potassium sulfate recovered by the SO _x recycling process in the treatment stage 13 is contaminated with adhering mother liquor, it must be cleaned before further use or recycling. This requires a separation of adhering mother liquor and impurities contained. In order to create the necessary conditions, the precipitated potassium sulfate is treated in a crystallizer 19, which is part of the treatment stage 13. The operating temperature of the crystallizer 19 is between 10 ° C and 15 ° C. In the crystallizer 19, a suspension with potassium sulfate particles with coarse particles necessary for the separation is produced. This suspension is then fed via a further supply line 21 to a separation unit 23.

In the present case, the separation unit 23 is designed as a continuously operating centrifuge into which the suspension flows continuously via the supply line 21. In a first separation zone 25 of the centrifuge 23, a large part of the washing medium is separated from the potassium sulfate by centrifuging. The pre-cleaned sample in the separation zone 25, ie the prepurified potassium sulfate, is then subjected to a washing process in a washing zone 27 adjoining the first separation zone 25. In this case, a displacement wash is used in which the detergent in the filter cake is pressed from potassium sulfate. The detergent penetrates into the filter cake, whereby the present in the interstices and the pores mother liquor and impurities are largely displaced. For this purpose, water is used as the detergent, which is metered into the washing zone 27 via a flushing connection 29. The amount of dosed water is in this case only half as large as the amount of potassium sulfate to be cleaned, so that less than one twentieth of the potassium sulfate in the water during washing.

The separation unit 23 is operated in a temperature range between 10 ° C and 15 ° C, since the water solubility of potassium sulfate in this range is sufficiently low to ensure a high Reclaimer efficiency. After separation in the centrifuge 23, ie after passing through the sample through the separation zone 25 and the washing zone 27, the purified potassium sulfate is fed via a feed line 31 to a utilization device 33.

Optionally, between the separating unit 23 and the utilization device 33, a drying unit can be interposed, which enables a final drying of the potassium sulfate to remove residual moisture still contained.

The water is fed after the washing of the potassium sulfate from the separation unit 23 via a feed line 35 into the C0 ₂ - deposition device 7. The feed takes place here together with the separated from the potassium sulfate in the washing process mother liquor, which is returned due to their high amino acid salt content back into the deposition process. A loss of active component can thus be reduced.

To feed the water into the deposition process, the feed line 35 in the present case opens into the return line 15, which returns the washing medium from the treatment stage 13 into the separation device 7. Thus, the feed of the water and the return of the separated mother liquor take place together due to the fluidic connection of the two lines 15, 35 in the deposition process.

Overall, can be obtained by the device 1 or by the feasible with this device method in an effective and cost effective manner potassium sulfate as a valuable material which is also suitable for special applications in the fertilizer sector, for the production of building materials such as plasterboard, as well as for use in specialty chemicals.

Claims

claims

1. A method for separating carbon dioxide from a gas stream, in particular from a flue gas stream, in which

- The gas stream in an absorber (5) of a separating device (7) is brought under deposition of carbon dioxide contained in the gas stream with a washing medium in contact, loaded with carbon dioxide washing medium a desorber (9) of the separator (7) for releasing the carbon dioxide is fed

the scrubbing medium freed from carbon dioxide is fed to a treatment stage (13) in which sulfur oxides contained in the scrubbing medium are precipitated as potassium sulfate, and the precipitated potassium sulfate is fed to a separating unit (23) for the purification of purified potassium sulfate, in which the potassium sulfate is separated from the scrubbing medium is, wherein the precipitated potassium sulfate in the separation unit (23) is also subjected to a washing process.

2. The method of claim 1, wherein the precipitated potassium sulfate is centrifuged in the separation unit (23) in a separation zone (25).

3. The method of claim 1 or 2, wherein the washing process in the form of a displacement laundry in a washing zone (27) within the separation unit (23).

4. The method according to any one of the preceding claims, wherein for the washing process, a detergent is used, which is metered via a spray connection (29) in the separation unit (23).

5. The method according to claim 4, wherein water is used as the detergent.

6. The method of claim 4 or 5, wherein the detergent is used in a mass ratio of potassium sulfate between 0.5: 1 and 1: 1.

7. The method according to any one of the preceding claims, wherein the separation unit (23) is operated at temperatures in a range between 10 ° C and 15 ° C.

8. The method according to any one of the preceding claims, wherein in the preparation stage (13) precipitated potassium sulfate particles prior to entry into the separation unit (23) in a crystallizer (19) are separated according to their particle size.

9. The method according to any one of claims 4 to 8, wherein the detergent after passing through the washing zone (27) flows into the separator (7) for carbon dioxide.

10. The method according to any one of the preceding claims, wherein remaining in the purified potassium sulfate residual moisture is removed by a subsequent washing process drying.

11. A process for the treatment of contaminated potassium sulfate, in which the contaminated potassium sulfate for recovering purified potassium sulfate by means of a separation unit (23) separated from a washing medium and in the separation unit (23) is simultaneously subjected to a washing process.

12. The method according to claim 11, wherein the precipitated potassium sulfate is centrifuged in a separation zone (25) of the separation unit (23).

13. The method of claim 11 or 12, wherein the washing process as displacement laundry in a washing zone (27) within the separation unit (23).

14. The method according to any one of claims 11 to 13, wherein for the washing process, a detergent is used, which is metered via a spray connection (29) in the separation unit (23).

15. The method according to claim 14, wherein water is used as the detergent.

16. The method of claim 14 or 15, wherein the detergent in a mass ratio to potassium sulfate between 0.5: 1 and

1: 1 is used.

17. The method according to any one of claims 11 to 16, wherein the separation unit (23) is operated at temperatures in a range between 10 ° C and 15 ° C.

18. The method according to any one of claims 11 to 17, wherein contained in the washing medium potassium sulfate particles before entering the separation unit (23) in a crystallizer (19) are separated according to their particle size.

19. The method according to any one of claims 14 to 18, wherein the detergent after passing through the washing zone (27) flows into a separator (7) for carbon dioxide.

20. The method according to any one of claims 11 to 19, wherein remaining in the purified potassium sulfate residual moisture is removed by a subsequent washing process drying.