DE102016014921A1 - Method and device for reducing material losses in sour gas scrubbing - Google Patents

Abstract

The invention relates to a process for gas scrubbing in which a first (1) and a lower carbon monoxide content than the first having second synthesis crude gas (7) at elevated pressure in each case a separate laundry (A1, A2) for the separation of carbon dioxide and / or sulfur components be subjected to, wherein in each of the washes a separated substances laden detergent stream (6, 12) obtained from which a co-absorbed substances containing gas phase (21, 16) is separated to with one of the synthesis gas to be washed (7) unite. Characteristic here is that one of one of the loaded detergent streams (12) separated gas phase (16) is used as stripping gas to separate co-absorbed substances from the other loaded detergent stream (6) by stripping.

Description

The invention relates to a method for gas scrubbing in which a first and a lower carbon monoxide content than the first having the second synthesis crude at elevated pressure in each case a separate wash for the separation of carbon dioxide and / or sulfur components is subjected, wherein in each of the washes with a separated Substances laden detergent stream is obtained, is separated from the co-absorbed substances containing gas phase in order to combine them with one of the syngas to be washed synthesis gases.

Furthermore, the invention relates to a device for carrying out the method according to the invention.

Gas scrubbing is used to scrub certain components from a gas mixture with the aid of a detergent and thereby produce a product gas. It exploits the property of liquids to absorb gaseous substances and to keep them chemically or physically bound in solution. How well a gas is absorbed by a liquid is expressed by the solubility coefficient: the better the gas dissolves in the liquid, the greater its solubility coefficient. The solubility coefficient increases i.Allg. with falling temperature and increasing pressure.

The washed-out gas components are removed after the wash from the liquid used as a detergent, whereby the detergent is regenerated. While the leached gas components are either disposed of or put to commercial use, the regenerated detergent is normally used again in the scrubbing of the gas mixture.

A method for gas scrubbing of the generic type is described for example in the patent application DE102012016643 disclosed. Here, a the raw materials hydrogen and carbon monoxide and the acid gases carbon dioxide, hydrogen sulfide and Kohlenoxidsulfid containing synthesis gas is divided into a first and a second partial stream, the first partial stream - possibly after a drying step - is fed directly as the first synthesis gas of a first wash, while the Carbon monoxide contained in the second partial stream is converted by water gas shift with water to hydrogen and carbon dioxide before the gas mixture thus obtained is fed as a second, geshiftetes or converted Syntheserohgas a parallel operated second wash. The shifted synthesis gas has a higher hydrogen and a lower carbon monoxide partial pressure than the first, unshifted synthesis gas. While a fuel gas containing carbon dioxide for a gas turbine is obtained in the first scrubbing by desulfurization from the unenhifted synthesis gas, carbon dioxide and sulfur components are selectively separated in the second scrubbing from the scrubbed synthesis gas to obtain raw hydrogen.

In the laundry, each of the synthesis raw gases is brought into contact with a respective detergent, with respect to which the sour gas components have a solubility coefficient several orders of magnitude higher than hydrogen and carbon monoxide. Therefore, although acid gases are primarily washed out by the particular detergent, it also inevitably dissolves small amounts of hydrogen and carbon monoxide from the synthesis gas. To avoid that reduced by this, called co-absorption process, the yield of carbon monoxide and / or hydrogen, the laden detergent washes are supercooled and relaxed in a first regeneration each in a separate separator to an intermediate pressure before they be further regenerated to separate the leached sour gases at lower pressure. Among the temperature and pressure conditions prevailing after relaxation, the co-absorbed substances are largely converted into the gas phase, while the acid gases washed out of the synthesis gas gases remain largely dissolved in the expanded detergent, but nevertheless form a large part of the gas phases called flash gases. The flash gases withdrawn from the separators are subsequently compressed, recycled and usually combined with the second, shifted synthesis crude gas to be washed.

By lowering the intermediate pressure level, the amount of flash gas generated in a separator increases, and with it, the yield of hydrogen and carbon monoxide of the gas scrubber. In addition, it becomes easier to comply with environmental standards, in particular with regard to carbon monoxide, because less of the valuable hydrogen and carbon monoxide can reach the atmosphere with the acid gas fractions obtained in the further regeneration of the loaded detergent. However, these advantages are also faced with significant disadvantages.

So decreases with falling intermediate pressure on the one hand in the return of the flash gas in the second synthesis gas to be overcome pressure difference and on the other hand, the proportion of acid gases in the flash gas, so that the increased yield of hydrogen and carbon monoxide with a disproportionate increase in the power of the Flash gas feedback used compressor has to be bought. In addition, since the amount of detergent required in gas washes is directly proportional to the amount of gas to be treated, the detergent requirement also increases more than proportionally with the yield. In addition, to achieve the required yields and / or compliance with environmental standards, the pressure level must be lowered so far that additional pumps are needed to raise the pressure of the loaded detergent to a sufficiently high level for further regeneration.

The object of the present invention is therefore to specify a method and a device of the generic type with which it is possible, without the disadvantages of the prior art, to increase the yield of valuable substances and / or to comply with environmental standards.

This object is achieved procedurally according to the invention that a separated from one of the loaded detergent streams gas phase is used as the stripping gas to separate co-absorbed substances from the other loaded detergent stream by stripping.

Prerequisite for the applicability of the method according to the invention is that at least one of the co-absorbed substances in the gas phase used as stripping gas is present at a lower partial pressure than in the detergent stream to be treated by stripping, since only under this condition carbon monoxide and / or hydrogen from the loaded Detergent in the stripping gas - and thus in the gas phase - passes.

Preferably, the gas phase used as stripping gas is recovered from the loaded detergent stream by relaxation. The laden detergent stream to be treated by stripping is expediently likewise expanded prior to stripping, as a result of which a first part of the co-absorbed substances dissolved in it already passes into the gas phase. Especially when the stripping gas is under sufficiently high pressure and does not need to be compressed for its use, it may be useful not to relax the detergent stream to be treated prior to stripping and to transfer co-absorbed substances by stripping into the gas phase alone.

Compared to the prior art, in which the co-absorbed substances comprising gas phases are obtained only by relaxation of the loaded detergent streams can be achieved by the inventive stripping at the same final pressures higher yields of carbon monoxide or hydrogen or compliance with environmental standards. On the other hand, the loaded, to be treated by stripping detergent stream must be less deeply relaxed to recover the recyclables contained in it with the same yield.

Preferably, at least one acid gas species is present in the stripping gas used according to the invention with a partial pressure, as a result of which sour gas of this type is stripped off less effectively from the laden detergent than carbon monoxide or hydrogen. Particularly preferably, the partial pressure of at least one Sauerergasart in the stripping gas is higher than in the loaded, to be treated by stripping detergent stream so that sour gas of this kind is dissolved by the loaded detergent and separated from the stripping gas. As a result, the ratio of recyclable materials to acid gases shifts in favor of recyclables, so that compared to the prior art with the same recycling value less gas with correspondingly lower compressor performance must be attributed to one of the synthesis gas to be washed, the laundry therefore less detergent is needed.

A variant of the method according to the invention provides that in the scrubbing of the second synthesis gas, carbon dioxide and sulfur components are selectively separated, wherein a sulfur-free, loaded with carbon dioxide and a charged both with sulfur components, as well as with carbon dioxide detergent flow, from which by relaxation to an intermediate pressure two gas phases are obtained. Due to the higher carbon monoxide content of the first syngas, laden laundry detergent may have a higher carbon monoxide partial pressure than any of the gaseous phases obtained by expansion from the detergent streams laden in the scrubbing of the second syngas, which are therefore basically both suitable as stripping gas for separation be used by carbon monoxide from the loaded in the scrubbing of the first synthesis raw gas detergent. Preferably, however, the gaseous phase obtained from the sulfur-free, carbon dioxide-laden detergent stream is used for this purpose. A sole or additional use of the gas phase from the detergent stream loaded with both sulfur components and carbon dioxide may be expedient if the detergent stream to be treated by stripping likewise contains sulfur components which are removed anyway during its further regeneration.

If the two synthesis gas gases are supplied to their respective washes at different pressures, it makes sense to return the gas phases obtained by relaxation to the intermediate pressure and by stripping from the loaded detergent streams into the synthesis gas, which is at the lower pressure. However, a return to the other higher-pressure synthesis gas should not be ruled out.

The process according to the invention can be used with particular preference when the two synthesis gas gases are obtained from a synthesis gas containing hydrogen, carbon monoxide and carbon dioxide and sulfur components, which is divided into two partial streams, one of which is the first without further treatment or after partial conversion Synthesis raw gas forms, while the second synthesis gas from the other partial flow is formed by complete conversion in a water gas shift, which is why it has a lower pressure than the first. In this case, the gas phases separated from the laden detergent streams and comprising co-absorbed substances are preferably recycled to the second synthesis crude.

The inventive method can be carried out both with physically and chemically acting detergents. Examples of such detergents include ethanol, dimethyl polyethylene glycol ether (DMPEGE), N-methyl pyrrolidone (NMP), amines and their derivatives (eg methyldiethanolamine (MDEA), monoethanolamine (MEA) and diethanolamine (DEA)) and mixtures of these detergents , With particular preference, however, cryogenic methanol is used as a detergent.

Furthermore, the invention relates to a device for gas scrubbing with a first and a second washing device in which separated from each other two synthesis gases at elevated pressure of a laundry for the separation of carbon dioxide and / or sulfur components subjected and with separated substances separated in the laundry detergent streams can be obtained, and Facilities for separating co-absorbed substances from the loaded detergent streams during the wash and converting them into the gas phase.

According to the invention, the stated object is achieved in that it comprises a stripping device in which a gas phase separated from one of the loaded detergent streams can be used as stripping gas in order to separate co-absorbed substances from the other loaded detergent stream by stripping.

Conveniently, the device according to the invention comprises a relaxation device, such as a throttle body with downstream separator, via which the gas phase to be used as stripping gas can be separated from the loaded detergent stream.

The stripping device is preferably designed as a column, in its lower part the stripping gas and at its head to be treated by stripping detergent stream can be fed.

At least one of the washing devices can have two washing sections, by means of which carbon dioxide and sulfur components can be separated substantially selectively from one of the synthesis raw gases, whereby a sulfur-free, carbon dioxide-laden and a both with sulfur components, as well as charged with carbon dioxide detergent stream incurred. The device for producing the gas phase to be used as stripping gas is preferably connected to this washing device such that the stripping gas can be obtained from the sulfur-free, carbon dioxide-laden detergent stream without sulfur.

In the following, the invention is based on a in the 1 schematically illustrated embodiment.

The 1 shows a section of a gas scrubber according to the invention, in which a geshiftetes and an unshifted synthesis crude are washed simultaneously in two parallel operated washing devices.

Via wire 1 is a ungeschiftetes first synthesis gas, which also contains carbon dioxide and sulfur components in addition to hydrogen and carbon monoxide, in the heat exchanger E1 cooled down before it over line 2 the first washing device designed as an absorber column A1 is abandoned in its lower part. In the first washing device A1 , which is typically operated at pressures between 20 and 80 bar, flows the cooled first synthesis gas 2 upwards and is in intensive contact with uncharged methanol detergent 3 brought at the top of the first washing device A1 is supplied in a required for the separation of the sulfur components minimum amount. Since in addition to the sulfur components and carbon dioxide is inevitably absorbed by the detergent, this results in a largely sulfur-free gas mixture with reduced carbon dioxide content, via line 4 from the head of the first washing device A1 withdrawn and after warming up against the first synthesis crude to be cooled 1 via wire 5 For example, a gas turbine (not shown) is supplied as fuel. In the bottom of the first washing device A1 becomes methanol detergent 6 deducted, which was loaded in the laundry mainly with sulfur components and carbon dioxide, but in addition also contains the co-absorbed recyclables carbon monoxide and hydrogen.

A second, shifted synthesis gas 7 that is opposite to the first syngas 1 indicates a much lower carbon monoxide and a significantly higher carbon dioxide content is in the heat exchanger E2 cooled down before it over line 9 the second, also designed as an absorber column washing device A2 can be abandoned in its lower part. The second washing device A2 , which is typically operated at a pressure between 15 and 75 bar, has a lower S1 and an upper wash section S2 on, passing through a chimney floor K are separated from each other. The cold synthesis gas 9 is in the second washing device A2 directed upwards and brought into intensive contact with methanol detergent, the unladen via line 10 from the regeneration section R fed and after cooling against partially regenerated methanol detergent 11 in the heat exchanger E3 in the washing section S2 is initiated. Over the lines 12 and 13 and the control element b is already pre-loaded with carbon dioxide methanol detergent from the fireplace floor K in the washing section S1 continued, where it mainly absorbs sulfur components from the syngas, before being loaded with carbon dioxide and sulfur components from the sump space of the second washing device A2 deducted and via wire 14 is forwarded. From the head of the second washing device A2 can be a largely hydrogen gas 8th be deducted after heating against the second synthesis gas 7 as raw hydrogen 15 For example, a PSA (not shown) is supplied for further purification.

The one in the washing section S2 predominantly charged with carbon dioxide, but largely sulfur-free methanol stream 12 becomes after cooling in the heat exchanger E4 via the throttle body c in the expansion vessel D1 relaxed, while the methanol stream 14 in the two washing sections S1 and S2 was loaded with both carbon dioxide and sulfur components, via the throttle body d in the flash vessel D2 arrives. In the relaxation vessels D1 and D2 prevailing pressures, which is about one third of that in the second washing device A2 Not only the predominant part of the co-absorption from the second synthesis crude gas reaches the prevailing working pressure 7 Separated hydrogen and carbon monoxide, but also sour gas in the resulting gas phases, via the lines 16 and 17 subtracted from. The still loaded with sulfur components and carbon dioxide methanol flows 18 and 19 are introduced into the regeneration section R for further regeneration.

The gas phase 16 is the lower portion of the stripping column Z supplied to the head at the same time via the throttle body a loaded from the first washing device A1 withdrawn methanol detergents 6 is relaxed. The relaxation takes place at a pressure in which, although already a large part of the co-absorbed substances passes into the gas phase, but the acid gases remain largely completely dissolved. Due to the composition of the shifted second synthesis gas 7 indicates the gas phase 16 a lower carbon monoxide partial pressure than the methanol detergent 6 so that it acts as a stripping gas and additional carbon monoxide from the loaded methanol detergent 6 dissolves. The thus obtained, largely worthless methanol detergent 20 is used for further regeneration in the regeneration part R while the enriched with the separated recyclables stripping gas 21 from the stripping column Z subtracted, with the gas phase 17 from the second separator D2 to the material flow 21 united and through the compressor V before the second washing device A2 into the second synthesis gas 7 is returned.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102012016643 [0005]

Claims (9)

Process for gas scrubbing, in which a first (1) and a lower carbon monoxide content than the first comprising second synthesis crude (7) are each subjected at elevated pressure to a separate scrubber (A1, A2) for the removal of carbon dioxide and / or sulfur components, wherein in each of the washes, a loaded with separated substances detergent stream (6, 12) is obtained, from which a co-absorbed substances containing gas phase (21, 16) is separated, in order to unite with one of the laundry to be raw synthesis (7), characterized in that a gas phase (16) separated from one of the loaded detergent streams (12) is used as stripping gas in order to separate co-absorbed substances from the other loaded detergent stream (6) by stripping. Method according to Claim 1 , characterized in that as the stripping gas (16) a gas phase is used, in which carbon dioxide and / or at least one of the sulfur components is present at a higher partial pressure, as in the loaded, treated by stripping detergent stream (6). Method according to one of Claims 1 or 2 , characterized in that in the scrubbing of the second synthesis raw gas (7) carbon dioxide and sulfur components are selectively separated, wherein a sulfur-free, loaded with carbon dioxide (12) and a charged with both sulfur components, as well as with carbon dioxide detergent stream (14), from which by relaxation (c, d) to an intermediate pressure, a sulfur-free (16) and a sulfur component-containing gas phase (17) are obtained, of which one and / or the other is used as stripping gas. Method according to one of Claims 1 to 3 , characterized in that the first raw synthesis gas (1) is a non-converted or incompletely converted and in the second (7) is a fully converted raw synthesis gas. Apparatus for gas scrubbing with a first (A1) and a second scrubber (A2), in which two synthesis raw gases (1, 7) are subjected to scrubbing at elevated pressure to scrubbing carbon dioxide and / or sulfur components and loaded with substances separated during scrubbing Detergent streams (6, 12) can be obtained, as well as facilities (a, c) to separate in the laundry co-absorbed substances from the loaded detergent streams (6, 12) and into the gas phase (21, 16) to transfer, characterized in that it has a stripping device (Z) in which a gas phase (16) separated from one of the loaded detergent streams can be used as stripping gas in order to separate co-absorbed substances from the other loaded detergent stream (6) by stripping. Device after Claim 5 , characterized in that it comprises a relaxation device (c) via which the gas phase to be used as stripping gas (16) can be separated from the loaded detergent stream (12). Device according to one of Claims 5 or 6 , characterized in that the stripping device (Z) is designed as a column, in its lower part the stripping gas (16) and at its head the relaxed detergent stream (6) can be supplied. Device according to one of Claims 5 to 7 , characterized in that one of the washing devices (A2) has more than one washing section (S1, S2) by means of which carbon dioxide and sulfur components can be separated substantially selectively from one of the synthesis raw gases (7), wherein a sulfur-free, carbon dioxide-laden (12) and incurred with both sulfur components, as well as carbon dioxide laden detergent stream (14). Device after Claim 8 , characterized in that the device (c) for generating the gas phase (16) to be used as stripping gas is connected to the washing device (A2) having more than one washing section (S1, S2) in such a way that the stripping gas (16) does not contain sulfur sulfur-free, carbon dioxide-loaded detergent stream (6) is available.

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