WO2014135322A1

WO2014135322A1 - Method for separating carbon dioxide from a gas stream, and method for reprocessing potassium sulfate contaminated with nitrosamines

Info

Publication number: WO2014135322A1
Application number: PCT/EP2014/052101
Authority: WO
Inventors: Ansgar Kursawe; Markus Kinzl; Ralph Joh; Jürgen Maisch; Rüdiger Schneider
Original assignee: Siemens Aktiengesellschaft
Priority date: 2013-03-05
Filing date: 2014-02-04
Publication date: 2014-09-12
Also published as: DE102013203720A1

Abstract

The invention relates to a method for separating carbon dioxide from a gas stream, in particular from a flue gas stream, wherein in a separating device (3), the gas stream is brought into contact with a washing medium (5) while separating carbon dioxide contained in the gas stream. After separating the carbon dioxide, the used washing medium (5) is conveyed to a treatment stage (7) for reprocessing the washing medium (5), and sulfur oxides contained in the washing medium (5) are precipitated in the treatment stage (7) as potassium sulfate. The precipitated potassium sulfate is freed of impurities by subsequent heating to temperatures between 200 ⁰C and 600 ⁰C. The invention further relates to a method for reprocessing potassium sulfate contaminated with nitrosamines, wherein the contaminated potassium sulfate is heated to temperatures between 200 ⁰C and 600 ⁰C to obtain purified potassium sulfate with decomposition of the nitrosamines.

Description

description

METHOD FOR REMOVING CARBON DIOXIDE FROM A GAS STREAM AND METHOD FOR THE RECYCLING OF NITROSAMINE-INGREDIENED CALIUM SULFATE

The invention relates to a method for separating carbon dioxide from a flue gas, in particular from a flue gas stream. Furthermore, the invention relates to a process for the treatment of contaminated with nitrosamines 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 leads to an increase in the Earth's surface temperature as a greenhouse effect.

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 is brought into contact with a suitable washing medium after combustion, whereby gaseous carbon dioxide contained in the flue gas is dissolved in the washing medium or absorbed in the chemical sense. The exhaust gas freed of carbon dioxide is finally released into the atmosphere. That with carbon dioxide loaded scrubbing medium can be regenerated by desorption of the absorbed carbon dioxide and used again for the absorption of carbon dioxide 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.

After the separation of the carbon dioxide from the washing medium, this is usually processed in a recycling stage of the separator. Here, the washing medium is cleaned as part of the reclamation (Reclaiming) of sulfur oxides. In this so-called

SO _x recycling process, the sulfur oxides are usually precipitated by lowering the temperature and concentration changes in the washing medium as potassium sulfate (K ₂ S0 ₄ ). The potassium balance is compensated by adding potassium hydroxide (KOH). Potassium sulfate can be used as a fertilizer ingredient, to make building materials such as gypsum board, as well as in specialty chemicals. However, the requirements for the purity of the potassium sulfate are correspondingly high.

For example, 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 as part of the reprocessing process. The permitted residual moisture, ie the proportion of water and undesirable impurities in the potassium sulfate, depends both on the respective re-use and on the recycler. Particularly stringent requirements are set for use as a specialty or in high-quality fertilizers. Here, the values for the permitted residual moisture are sometimes in the range below 0.5% by weight.

To th to warranty broad applicability of the potassium sulphate, this must therefore be treated on the SO _x -Reclaiming process addition. In previous treatment processes, for example, the residual moisture content of potassium sulfate in the solid-liquid separation with the aid of a centrifuge is so reduced as much as possible. 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 can lead to problems when using amines and amino acid salts, since the residual moisture in the potassium sulfate may contain portions of the amine or amino acid salt solution in the form of nitrosamines. Nitrosamines can be formed by reaction of NO _x and the amines or amino acids contained in the washing solution or in the washing medium. Since nitrosamines (N-nitroso compounds) are suspected of being carcinogenic, their removal or at least a reduction in concentration is essential with regard to the potential for exploitation of potassium sulphate.

It is therefore a first object of the invention to provide a method which makes potassium sulfate obtained in a carbon dioxide removal process accessible by the effective removal of impurities for wide use. A second object of the invention is to provide a process which makes it possible to obtain potassium sulfate with improved product quality compared with conventional processes. 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 a separation device with separation of carbon dioxide contained in the gas stream, after the separation of the Carbon dioxide, the used washing medium of a treatment stage for the reprocessing of the washing medium is supplied, and in the

Washing medium contained sulfur oxides in the treatment stage fe be precipitated as potassium sulfate. The precipitated potassium sulfate is then freed of impurities by subsequent heating to temperatures between 200 ° C and 600 ° C.

The invention takes account of the fact that potassium sulphate, previously obtained in the context of a carbon dioxide deposition process, can not sufficiently fulfill 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 potassium sulphate is the presence of nitrosamines. Although the concentration of nitrosamines in potassium sulphate can be reduced by displacement washing with water, the proportion of nitrosamines remaining in the potassium sulphate is still high after such a work-up step too high to use the recovered potassium sulfate, for example in the fertilizer sector or in specialty chemicals. A further reduction of the nitrosamine concentration as a prerequisite for the widest possible applicability of the potassium sulfate would be achievable only when using a larger amount of washing water. As the amount of wash water increases, however, more and more potassium sulfate dissolves and is thus returned together with the wash solution to the process plant, that is to say into the separator for carbon dioxide. The efficiency of

Reclaiming process drops accordingly. As a result, the amount of wash water that can be used and thus also the nitrosamine depletion are limited by displacement washing.

In view of the problem described above, the invention recognizes that the desired reduction in the concentration of impurities, and in particular of nitrosamines, can be achieved if the precipitated potassium sulfate is subjected to an additional work-up step. For this purpose, by a subsequent precipitation of the contaminated potassium sulfate subsequent heating to temperatures _.

Between 200 ° C and 600 ° C impurities removed from the precipitated potassium sulfate, or the precipitated potassium sulfate is freed of these undesirable impurities.

In particular, the potassium sulfate is precipitated or crystallized by a reduction in temperature, by changes in concentration and / or by adding potassium hydroxide solution.

At a drying temperature in a range between 200 ° C and 600 ° C unwanted impurities can be removed from the potassium sulfate and at the same time its use as a reusable recyclable material can be ensured due to the high temperature resistance of potassium sulfate. By heating and the associated removal of undesirable impurities, the product quality of the potassium sulfate is improved to the extent that it meets the high demands on the purity required for further utilization or use.

In contrast to the previously common treatment or cleaning process can be such by the

Reclaiming process subsequent high-temperature drying the requirements for quality improvement of potassium sulfate can be met in just one step. In other words, in addition to the expulsion of water to obtain purified potassium sulfate in particular the decomposition of undesirable impurities can be achieved. The precipitation of the potassium sulfate from the washing medium is carried out in a treatment stage, which serves to reprocess the washing medium of the targeted Störstoffausschleusung and the recovery of usable products from the flue gas. For this purpose, the treatment stage expediently comprises a number of reclaiming, which are preferably fluidically connected to the carbon dioxide separation device. Thus, after the separation of the carbon dioxide from the washing medium in a reclaimer of the regeneration stage disturbing Sulfur oxides are precipitated by the addition of potassium hydroxide solution (KOH) as potassium sulfate and also removed from the washing medium. The high-temperature drying of the precipitated potassium sulfate is preferably carried out subsequent to a separator for carbon dioxide, for which purpose it is expediently coupled to the corresponding separation device. For example, the drying can be carried out in a corresponding drying device, which is connected to the processing stage of the separating device. For example, during the reprocessing of the washing medium, precipitated potassium sulfate can be treated on site and without further transport steps.

In principle, of course, it is also possible to have the drying of the contaminated potassium sulfate carried out by an external service provider as a wage drying in a local drying device.

The precipitation of the potassium sulfate preceding separation of the carbon dioxide from the gas stream takes place in the separator by means of a washing medium by a common absorption-desorption process. For this purpose, the flue gas stream is expediently brought into contact with the washing medium within an absorber of the separating device, where it is absorbed or reversibly bound. The purified flue gas is discharged from the absorber, whereas the loaded scrubbing medium for separating C0 _{2 is passed} under temperature elevation in a desorber of the separator. In the desorber, the carbon dioxide is thermally desorbed and the used washing medium is fed to the processing stage for recycling. Here, the washing medium is treated in such a way that it can be used again for the absorption of carbon dioxide from the flue gas.

In an advantageous embodiment of the invention, an amino acid salt is used as the washing medium. Here is one aqueous amino acid salt solution appropriate. Amino acid salts show good selectivity and high capacity for carbon dioxide. In the use of an amino acid salt as the absorption medium, it has been found advantageous to use an amino acid salt having a carbon substituent selected from the group consisting of hydrogen, an alkyl, a hydroxyalkyl and an aminoalkyl. More preferably, an amino acid salt is used which has a nitrogen substituent selected from the group consisting of hydrogen, an alkyl, a hydroxyalkyl and a haloalkyl. Again, a single amino acid salt such as a potassium salt of glycine or other amino acids may be employed. Also, mixtures of different amino acid salts can be used as the absorbent. More preferably, the amino acid salt is a salt of a metal, especially an alkali metal.

More preferably, by heating the contaminated potassium sulfate, substantially nitrosamines contained in the potassium sulfate are decomposed to yield purified potassium sulfate. The decomposed nitrosamines can be expelled from the potassium sulfate and the correspondingly purified potassium sulfate are fed to another use. Conveniently, the contaminated potassium sulfate is heated for a period of 2 to 200 minutes. During this period, the essential component of the nitrosamines contained in the potassium sulfate decomposes, so that they can be almost completely expelled from the potassium sulfate.

Of course, longer times for heating the potassium sulfate are possible, wherein the duration of the thermal treatment is particularly dependent on the drying temperature. Advantageously, the contaminated potassium sulfate is heated in a contact dryer. A contact dryer is a high-temperature dryer in which the substance to be dried is heated by contact with a heating surface and the moisture is driven out. For this purpose, the substance can either be permanently in contact with the heating surface or be rearranged in the dryer. In the present case, the use of a contact dryer in addition to the expulsion of the water in particular the decomposition of undesirable impurities contained in the potassium sulfate is achieved.

More preferably, the contaminated potassium sulfate is heated in a flotation dryer, in which also sufficiently high temperatures for expelling residual water and for removing unwanted impurities from the potassium sulfate can be adjusted.

In principle, of course, all dryers are suitable for removing the impurities from the potassium sulfate, which allow adjustment of temperatures above 200 ° C. For example, a fluidized-bed dryer, a rotary-tube dryer or a mixer-dryer can also be used.

The second object of the invention is achieved by a process for the treatment of contaminated with nitrosamines potassium sulfate, in which the contaminated potassium sulfate is heated to recover purified potassium sulfate with decomposition of nitrosamines to temperatures between 200 ° C and 600 ° C.

Through this process, potassium sulphate contaminated with nitrosamines is treated to meet the stringent requirements, in particular for further use in fertilizers, components or specialty chemicals.

The process for the treatment of nitrosamine-contaminated potassium sulfate, which is separate from the carbon dioxide removal process, is considered to be inventive in its own right.

The high-temperature drying of the contaminated potassium sulfate at temperatures above 200 ° C, for example, at to be carried out by an external service provider as wages drying. Alternatively, it can also be coupled to a process plant, such as in particular a separator for carbon dioxide.

In order to achieve complete decomposition of the nitrosamines obtained in potassium sulfate, the contaminated potassium sulfate is preferably heated for a period of 2 minutes to 200 minutes.

Conveniently, the contaminated potassium sulfate is heated in a contact dryer. More preferably, the contaminated potassium sulfate is heated in a flotation dryer. Further advantageous embodiments of the method for

Preparation of potassium sulfate contaminated with nitrosamines results from the subclaims directed to the process of separating carbon dioxide from a gas stream. The advantages mentioned for this purpose can be correspondingly transferred accordingly.

In the following an embodiment of the invention will be explained with reference to a drawing. 1 shows a schematic device for carrying out a process for the treatment of potassium sulfate contaminated with nitrosamines from a carbon dioxide precipitation device. 1 shows a schematic device 1 for carrying out a process for the treatment of nitric acid contaminated potassium sulfate from a separator 3 for carbon dioxide. In a combustion of a fossil fuel incurred, loaded with carbon dioxide flue gas (RG) is the separator 3 is supplied. The flue gas is then removed in the separator 3 by an absorption-desorption Process by means of a washing medium 5 washed out of the flue gas. For this purpose fluidically connected absorbers and desorbers are used, which are not shown separately due to the schematic representation. The flue gas is brought into contact with the washing medium 5 within an absorber and absorbed or reversibly bound there. In the desorber, the carbon dioxide is desorbed from the loaded washing medium 5 by the supply of heat, expelled and can then be sent for storage or recycling.

The washing medium 5 is then subjected to a reconditioning process. In the context of the reclaiming process, the washing medium 5 is cleaned in a treatment stage 7 which is fluidically connected to the separation device 3, in particular by sulfur oxides. Here, the washing medium 5 in a not shown

Reclaimer potassium hydroxide added and the sulfur oxides as

Reclaimer raw product potassium sulfate precipitated. The purified washing medium is then fed to the separation device 3 for the renewed absorption of carbon dioxide from the flue gas via a return line 9.

Since the precipitated potassium sulfate after the treatment of the washing medium 5 still a high proportion of nitrosamines and

Contains water, the potassium sulfate is further processed in an adjoining the processing stage 7 drying device 11. The drying device 11 is designed as a contact dryer. In the contact dryer 11, the potassium sulfate is heated for at least 2 minutes to temperatures above 200 ° C and so both evaporates the water and in particular decomposes the contained nitrosamines. The potassium sulphate can thus be made available to a wide range of applications, in particular for use in specialty chemicals or as a fertilizer.

Of course, the drying of the potassium sulfate can be done in a separate step, not an Ab Sheath device for carbon dioxide downstream. In this case, contaminated potassium sulfate can be processed by a service provider in the form of a wage drying, regardless of its place of origin. Furthermore, all those dryers are suitable for drying the contaminated potassium sulfate, in which the desired temperatures for the decomposition of the impurities and in particular contained nitrosamines are adjustable.

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 is brought into contact with a washing medium (5) in a separating device (3) with separation of carbon dioxide contained in the gas stream,

after the separation of the carbon dioxide, the used washing medium (5) is fed to a treatment stage (7) for reprocessing the washing medium (5), and in the washing medium (5) contained sulfur oxides in the processing stage (7) are precipitated as potassium sulfate, wherein the precipitated potassium sulfate is freed from contamination by connecting the heating to temperatures between 200 ° C and 600 ° C.

2. The method according to claim 1, wherein as the washing medium (5) ei ne amino acid salt solution is used.

3. The method of claim 1 or 2, wherein zen by heating the contaminated potassium sulfate substantially contained nitrosamines are decomposed to obtain purified potassium sulfate.

A process according to any one of the preceding claims, wherein the contaminated potassium sulfate is heated for a period of from 2 minutes to 200 minutes.

A process according to any one of the preceding claims, wherein the contaminated potassium sulfate is heated in a contact dryer.

6. The method according to any one of the preceding claims, wherein the contaminated potassium sulfate in a flue dryer it is heated.

7. A process for the treatment of contaminated with nitrosamines potassium sulfate, in which the contaminated potassium sulfate for the recovery of purified potassium sulfate with decomposition of the nitrosamines to temperatures between 200 ° C and 600 ° C is heated.

The process of claim 7 wherein the contaminated potassium sulfate is heated for a period of from 2 minutes to 200 minutes.

9. The method of claim 7 or 8, wherein the contaminated potassium sulfate is heated in a contact dryer.

A process according to any one of claims 7 to 9, wherein the contaminated potassium sulfate is heated in a flue dryer.