DE102012020469A1 - Method for separating methane from methane-containing synthesis gas in separation unit, involves feeding capacitor with secondary portion of refrigerant of outlet temperature to intermediate temperature and cooling to lower temperature - Google Patents

Abstract

The method involves supplying an expander (X1) and the capacitor (E5) respectively with the compressed and cooled portions of the refrigerant from the refrigerant circuit. The expander is powered by a primary portion of the refrigerant. The expander is cooled to an intermediate temperature (TI) from a starting temperature (TA). The capacitor is fed with a secondary portion of the refrigerant of the outlet temperature to the intermediate temperature and then cooled to a lower temperature (TE). An independent claim is included for device for separating methane from methane-containing synthesis gas.

Description

The present invention relates to a method for the separation of methane from a methane-containing synthesis gas and a corresponding device.

State of the art

Synthesis gases, which are produced by known methods from coal, oil or natural gas, usually after removal of sour gas in addition to the desired components hydrogen and carbon monoxide and methane still with a typical proportion of 3 to 30 vol.% And smaller amounts of other components , These are, for example, each less than 1 vol.% Nitrogen, oxygen, argon, carbon dioxide and ethane. In particular, since methane is undesirable in the synthesis gas, it is usually separated.

The separation of methane from methane-containing synthesis gas can be carried out in a cryogenic separation plant. This can be operated with a refrigeration cycle in which a refrigerant, for example, multi-stage and under intermediate and aftercooling, is compressed. The compressed refrigerant may then be cooled in one or more heat exchangers. The compressed and cooled refrigerant is then released cold-performance.

A method and system for separating methane from methane-containing synthesis gas is for example US 2009/0205367 A1 known.

In particular, in cases in which liquid refrigerant or corresponding two-phase mixtures are required in corresponding plants, known processes prove to be inefficient because the production and / or handling of such mixtures, ie. H. their compression, cooling, relaxation and / or transmission, often associated with considerable effort.

The invention is therefore based on the object to show more efficient ways to methane separation from a methane-containing synthesis gas.

Disclosure of the invention

Against this background, the present invention proposes a method for the separation of methane from a methane-containing synthesis gas and a corresponding device with the features of the independent claims. Preferred embodiments are the subject of the respective dependent claims and the following description.

In the present application, substances and mixtures of substances in a plant or a process, for example, synthesis gas and refrigerants, referred to as "streams" and "fractions". A stream is usually routed as fluid in a conduit designed for this purpose. A fraction usually denotes a portion of the starting mixture separated from a starting mixture. A political group can generate a corresponding current at any time if it is managed accordingly. Conversely, for example, a stream can serve to provide a starting mixture from which a fraction can be separated.

A stream or fraction may be "rich" or "poor" in one or more of its contained components, with "rich" accounting for greater than 75%, 80%, 85%, 90%, 95%, 99%, 99.5% or 99.9% and "poor" for less than 25%, 20%, 15%, 10%, 5%, 1%, 0.5% or 0.1%, respectively a weight or volume basis, can stand.

Advantages of the invention

The invention can be used, for example, in a process for the separation of methane from a methane-containing synthesis gas, in which a methane-rich and carbon monoxide-containing bottom fraction is cryogenically separated from the synthesis gas in a first separation column and carbon monoxide is desorbed from the bottom fraction in a second separation column which has a condenser , A usable for this purpose cryogenic separation plant was developed by the applicant and is the subject of a parallel patent application. She is partly in the 1 illustrated and is explained in more detail in the accompanying figure description.

The methane-containing synthesis gas can initially be cooled by heat exchange in such a cryogenic separation plant. From the cooled methane-containing synthesis gas, a methane-rich and carbon monoxide-containing bottom fraction is cryogenically precipitated in the first separation column. The methane-rich and carbon monoxide-containing bottom fraction is transferred to the second separation column, in which the carbon monoxide is largely desorbed (stripped off) from the bottom fraction. Among other things, a low-carbon methane fraction and a carbon monoxide-rich overhead stream are obtained. The latter can be recycled as reflux into the first separation column.

The cryogenic separation plant comprises a refrigerant circuit with a refrigerant, for example nitrogen. In this, the refrigerant is compressed, for example, multi-stage and intermediate and after-cooling of a low outlet pressure to a high final pressure. The compressed refrigerant is then cooled from the initial temperature in a first heat exchanger, which is also used to cool the methane-containing synthesis gas, to a lower intermediate temperature.

A first portion of the cooled to the intermediate temperature refrigerant is cooled directly in a second heat exchanger, which is also used to cool the methane-containing synthesis gas to an even lower final temperature. A second portion of the cooled to the intermediate temperature refrigerant, however, is not cooled to the final temperature but fed to a bottom reboiler and a side evaporator of the second separation column. Again, the refrigerant cools to some extent. The two parts of the refrigerant are then reunited. As a result, a refrigerant flow is obtained whose temperature is composed of the contributions of the two shares.

The refrigerant flow is then expanded in an expander cold and work and fed into a condenser of the second separation column. The capacitor is designed, for example, as a top condenser. The refrigerant partially condenses during relaxation. The resulting due to the relaxation pressure is referred to in the context of this application as feed pressure.

The condenser of the second separation column, which is used for cooling a head side of the second separation column withdrawn fluid is thus cooled by a compressed and cooled refrigerant flow is expanded to a feed pressure and fed into the condenser, whereby the refrigerant flow cools. As a result, the refrigerant flow is at least partially liquefied. Another compressed and cooled refrigerant flow is used to operate an expander. In the expander, the refrigerant flow is released in a cold-working and working capacity.

The partially condensed refrigerant can be heated after removal from the condenser and completely evaporated. It has hereafter back to its output pressure and its initial temperature and can again, as explained, be compressed to the final pressure. The refrigerant circuit is closed.

For cooling the condenser, a certain amount of liquid of the refrigerant depressurized to the feed pressure is required because the condenser for cooling a top fraction from the second second separating column has a submerged heat exchanger which must be covered by liquid during operation. However, this liquid content of the refrigerant, which is present at the output of the expander used deteriorates its efficiency. In addition, the maximum usable output pressure of the refrigerant is limited in the described method, because inter alia due to the increasing liquid content in the relaxed to the feed pressure refrigerant in the line to the condenser causes a pressure loss. Therefore, a relatively large amount of cycle energy is required to compress the refrigerant to its final pressure. The required compressors are correspondingly expensive.

In more general terms, it is a method for separating methane from a methane-containing synthesis gas in a cryogenic separation plant having a refrigerant circuit with at least one expander and at least one separation column with a condenser, wherein the at least one expander and the capacitor each with compressed and cooled portions of a refrigerant can be fed from the refrigerant circuit

According to the invention it is now provided to feed the expander with a first portion of the refrigerant, which was cooled from an initial temperature to an intermediate temperature, and to feed the capacitor with a second portion of the refrigerant, the first from the initial temperature also to the intermediate temperature and then on was cooled to a lower final temperature. The first portion and the second portion are preferably cooled as a common refrigerant flow to the intermediate temperature.

In contrast to a plant, as has been explained above, so that the capacitor used, which requires a certain liquid content of a refrigerant fed, not fed via the expander but, for example, via an expansion valve provided for this purpose. The expander, for its part, is also operated differently from the operation of a previously described system, by contrast with a proportion of the refrigerant which has not previously been cooled to the final temperature and is therefore warmer.

Advantageously, as mentioned, for feeding the second portion of the refrigerant into the condenser, an expansion valve is used with which the second portion of the refrigerant is expanded to a feed pressure and thereby at least partially liquefied. In contrast to an expander, an expansion valve can also be easily used to provide partially liquefied refrigerant flows. The still existing expander, however, can work completely with gaseous streams. The efficiency increases as a result.

Advantageously, at least one first heat exchanger and for further cooling of the second portion of the refrigerant from the intermediate temperature to the final temperature, a second heat exchanger is used for cooling the first and the second portion of the refrigerant from the starting temperature to the intermediate temperature. These are preferably plate heat exchangers, each of which can cool or heat a plurality of fluids, so that the expenditure on equipment is reduced and heat losses can be reduced. When cooling the first and second portion to the intermediate temperature can, as explained below, still be involved in other heat exchangers.

Thus, advantageously, the methane-containing synthesis gas is cooled before being fed into the first separation column in the first and then in the second heat exchanger. Both the cooling and heat requirements of the second separation column and the cold required for cooling the methane-containing synthesis gas can thus be operated from a common refrigeration cycle. Preferably, the expansion refrigeration released in the illustrated expander and optionally the expansion refrigeration released in one or more further expanders are used to cool the methane-containing synthesis gas. A synthesis gas product obtained from the methane-containing synthesis gas by separation of methane can also be passed through the heat exchangers in countercurrent to the methane-containing synthesis gas.

With particular advantage, at least one further heat exchanger is used in the process in which a fluid removed at a defined removal height of the at least one separation column is heated. In this case, a further heat exchanger may be formed, for example, as a so-called bottom reboiler, wherein in the bottom reboiler, a fluid withdrawn from the bottom of the second separation column may be heated and optionally evaporated. Furthermore, a further heat exchanger may be provided in the form of a so-called side evaporator. In this, a withdrawn, for example, in a separating bottom fluid heated and optionally evaporated. By using appropriate heat exchangers, the separation efficiency increases in the second separation column.

Advantageously, at least a portion of the first and second portions of the refrigerant cooled in the first heat exchanger may be further cooled in the at least one further heat exchanger. In other words, the refrigerant of the refrigerant circuit is used for heating the fluid withdrawn in the at least one defined removal height of the second separation column, for example in a bottom reboiler. In this way, its temperature can be lowered and the cold released during the heating of the fluid removed in the at least one defined removal height of the second separation column can be used efficiently.

In the at least one further heat exchanger, alternatively or additionally, the methane-containing synthesis gas which has been cooled in the first heat exchanger can be further cooled and, at the same time, the fluid removed from the second separation column can be heated. This reduces the energy required to cool the methane-containing synthesis gas.

It may also be advantageous to heat at least a portion of the carbon monoxide-containing bottoms fraction deposited in the first separation column in such a process in the second heat exchanger. As a result, it is possible to dispense with an otherwise required further heat exchanger (bottom reboiler and / or side evaporator).

In a corresponding method, advantageously, the first portion of the refrigerant is expelled in the expander working and / or cold-performing and then fed cold side into the second heat exchanger. As mentioned, an expansion cooling generated in the expander can be used efficiently. Because the expander is only operated with gas, it works with higher efficiency.

Particular advantages arise when a portion of the separated in the first separation column rich methane and carbon monoxide sump fraction is heated in the second heat exchanger and fed to the second separation column in a defined feed height. This makes it possible to dispense with a conventionally required side evaporator. The function of the side evaporator is fulfilled by the second heat exchanger, which reduces the expenditure on equipment and reduces heat losses.

Advantageously, the first or second portion of the refrigerant to a pressure of 50 to 100 bar, in particular 60 to 90 bar, compressed and / or to a feed pressure (PC) of 8 to 20 bar, in particular 10 to 15 bar relaxed and / or to an intermediate temperature (TI) of -120 to -170 ° C, in particular -130 to -160 ° C and / or to a final temperature (TE) of -140 to -180 ° C, in particular -150 to -170 ° C, cooled.

Advantageously, in a corresponding method, 80% and / or 20% of the refrigerant is used as the first portion. The respective shares can be, for example, each adjust for refrigeration demand in the condenser and / or the second heat exchanger.

Advantageously, the refrigerant is compressed with a main compressor and at least one secondary compressor from the outlet pressure to the final pressure. The expander, which, as explained, is supplied with the first portion of the refrigerant, which has been cooled from an initial temperature to an intermediate temperature, is coupled to a secondary compressor. If only one secondary compressor is provided, the coupling takes place with this, with more than one secondary compressor, however, with the after-compressor, which delivers the final pressure (ie to the last after-compressor in a compressor chain). The expander is mechanically coupled to this booster and drives it. This allows a particularly effective operation, in particular, depending on the amount of methane to be separated and thus the required cold only one expander or a second expander, which is then mechanically coupled to a further booster, is required.

The device according to the invention is set up for carrying out the method explained for the separation of methane from a methane-containing synthesis gas and has corresponding means. It benefits from the advantages explained above in the same way so that reference can be made to them.

A basic idea of the invention can be seen altogether in giving up the refrigerant stream, which has been expanded in the expansion valve, directly to the condenser of the second separating column. The capacitor is therefore not supplied via the expander with cold, but directly through the outlet flow of a throttle valve.

A further basic idea of the invention can be seen in dividing the refrigerant stream upstream of the expander, wherein a first gaseous partial stream is supplied to the expander and a second gaseous partial stream is cooled and expanded in a throttle valve and fed as low-pressure refrigerant into the condenser of the second separation column.

It is particularly advantageous according to the invention that the expander is operated such that an outlet flow of the expander is gaseous. The expander thus has a high efficiency. Preferably, the expander can be operated such that the outlet is approximately in the range of the dew point of the refrigerant. In addition, can be in this way increase the suction pressure of the compressor of the refrigerant circuit, which also leads to an improvement in the efficiency of the process.

The invention will be further elucidated below with reference to the accompanying figures which show inter alia preferred embodiments of the invention.

Brief description of the drawings

1 shows a plant for the separation of methane from a methane-containing synthesis gas according to the prior art in a schematic representation.

2 shows a plant for the separation of methane from a methane-containing synthesis gas according to an embodiment of the invention in a schematic representation.

3 shows a plant for the separation of methane from a methane-containing synthesis gas according to an embodiment of the invention in a schematic representation.

4 shows a plant for the separation of methane from a methane-containing synthesis gas according to an embodiment of the invention in a schematic representation.

In the figures, the same or corresponding elements are provided with identical reference numerals. The in terms of the 1 The statements made in terms of pressures, temperatures, compositions and the like also apply to those in the 2 to 4 illustrated embodiments of the invention, unless otherwise specified therein.

Detailed description of the drawings

1 shows a system not according to the invention for the separation of methane from a methane-containing synthesis gas. The plant is in total with 100 designated.

The attachment 100 has a first separation column S1 and a second separation column S2. The first separation column S1 and the second separation column S2 are operated at different pressures. The pressure difference is for example 5 to 30 bar, in particular 10 to 20 bar. The pressure of the second separation column S2, in order to ensure a density difference between gas and liquid phase of at least 240 kg / m ³ , in particular at least 270 kg / m ³ , be limited to 25 to 30 bar.

A methane-containing synthesis gas SYN is in a first heat exchanger E1 to a temperature of for example -60 to -110 ° C, in particular -80 to -95 ° C, and in a second heat exchanger E2 to a temperature of for example -120 to -170 ° C. , in particular -130 to -160 ° C, cooled and the first separation column S1 fed in a defined feed height. In the first separation column S1, methane can be washed out of the methane-containing synthesis gas SYN by means of a carbon monoxide-rich reflux pumped by a pump L1. In this way a low-methane head fraction and a methane-rich and carbon monoxide-containing bottom fraction are obtained.

The carbon monoxide-containing bottoms fraction is deposited at the bottom of the first separation column S1. The low-methane overhead fraction is withdrawn from the top of the first separation column S1, heated in the heat exchangers E2 and E1 and depleted to a residual methane content of, for example, 0.01 to 1.00 vol.%, In particular 0.1 to 0.5 vol.% Synthesis gas product PRO delivered.

The methane-rich and carbon monoxide-containing bottoms fraction from the first separation column S1 is expanded via a valve V3 to the pressure of the second separation column S2 and, again in a defined feed height, fed into the same. The second separation column S2 is operated as a so-called carbon monoxide stripper. For this purpose, a third and a fourth heat exchanger E3 and E4 are provided, which are operated as a bottom reboiler (third heat exchanger E3) on the one hand and as a side evaporator (fourth heat exchanger E4) on the other hand and heated with a refrigerant. The second separation column S2 also has a condenser E5, which is designed, for example, as a top condenser and in which vapors ascending in the second separation column S2 can be condensed out.

In the bottom of the second separation column S2, a low-carbon methane fraction having a concentration of, for example, from 0.01 to 1.00% by volume, in particular from 0.1 to 0.5% by volume, of carbon monoxide can thereby be obtained. This can be performed, for example, through the heat exchanger E2. It can be delivered in the form of a methane product LNG either as a boiling or supercooled liquid or as a gas at any pressure. For example, a pressure in the range of 1 to 100 bar is selected. A division of the methane product LNG into several parallel product streams with different release states, such. As liquid, boiling, supercooled and / or gaseous, is also possible.

A gaseous overhead fraction of the second separation column S2 is recompressed in a recompressor C4 to the pressure of the first separation column S1 and admixed with the feed stream SYN to the first separation column S1.

A liquid, carbon monoxide-rich overhead stream is withdrawn from the top bottom of the second separation column S2, pumped in the mentioned pump L1 to the pressure of the first separation column S1 and fed to the first separation column S1 as a carbon monoxide-rich reflux. This is used to wash out the methane in the first separation column S1.

For cooling or heating the second separation column S2, d. H. for the operation of the third heat exchanger E3, the fourth heat exchanger E4 and the condenser E5, a preferably closed refrigerant circuit is provided.

This comprises a preferably multi-stage main compressor C1 with intercoolers E6, E7 and E8 and a first and a second booster (booster) C2 and C3 with an aftercooler E9. In the main compressor C1 and the secondary compressors C2 and C3, a gaseous refrigerant, for example, technically pure, dry nitrogen, from an initial pressure PA of, for example, 5 to 20 bar, in particular 8 to 15 bar via corresponding intermediate pressures to a final pressure PE, for example 50 to 100 bar, in particular 60 to 90 bar, are compressed. According to the definition made here, the outlet pressure PA is located on the suction side of the main compressor C1, the final pressure PE on the pressure side of the after-compressor C3, as illustrated by dashed lines in the figure.

The first after-compressor C2 and the second after-compressor C3 can each be driven via expander X2 and X1, which are also operated with the refrigerant. The refrigerant is expanded in the expander X2 and X1 each working and cold-performing, the freeing cold respectively for the operation of the first and second heat exchangers E1 and E2 and the released mechanical power to operate the first and second booster C2 and C3 is used. The expanders X1 and X2 are referred to hereinafter as "warm" and "cold" expanders X2 and X1, respectively, according to the temperatures of the optionally expanded refrigerant therein, the warm expander X2 being the first after-compressor C2 and the first expander the second after-compressor C3 is assigned.

If the methane-rich product is to be released in gaseous form and thus less cold is required, the warm expander X2 and thus the first secondary compressor C2 can be omitted. This applies in particular when the feed stream E has less than 10% by volume, in particular less than 7% by volume, of methane. Under these conditions, the cooling demand in the first heat exchanger E1 can be economically covered even without the cold from the warm expander X2.

If a warm expander X2 is present, a "warm" portion of the refrigerant can be in this on a pressure of for example 5 to 20 bar, in particular 8 to 15 bar, cold and work to be relaxed. The expanded refrigerant stream can then be further warmed in the first heat exchanger E1 and then fed to the main compressor C1 again.

If no warm expander X2 is present, the entire refrigerant, otherwise the portion not expanded in the warm expander X2, first in the first heat exchanger E1 from an outlet temperature TA to a temperature of for example -60 to -110 ° C, in particular -80 to -95 ° C, cooled.

A larger proportion, for example 40 to 90%, in particular 75 to 85%, of the refrigerant from the first heat exchanger E1 is then branched off to the third and fourth heat exchangers E3 and E4 and fed there for boil-up of the sump or for side evaporation of fluids the second separation column S2 used. In this case, a further cooling of this portion to a temperature of for example -90 to -130 ° C, in particular -105 to -120 ° C.

A smaller proportion, for example 5 to 25%, of the refrigerant from the first heat exchanger E1, on the other hand, continues to a lower final temperature TE of, for example, -120 to -170 ° C. following the cooling in the first heat exchanger E1 in the second heat exchanger E2. in particular -130 to -160 ° C, cooled.

The two parts of the refrigerant are then reunited and expanded together in the cold expander X1. The cooled to the final temperature TE portion of the refrigerant is guided via a valve V2.

The refrigerant is partially liquefied by the expansion in the expander X1, wherein after the relaxation, a proportion of, for example, 1 to 30 wt.%, In particular 5 to 25 wt.%, Of the refrigerant is in liquid form. The inlet temperature of the refrigerant into the cold expander X1 can be adjusted, for example, by the amount and the temperature to the final temperature TE cooled portion of the refrigerant to obtain the desired liquid content after the expansion in the cold expander X1. The pressure after relaxation is referred to in this application as "feed pressure".

The partially liquefied refrigerant is supplied to the condenser E5 at a feed pressure PC thereby obtained. In the condenser E5 at least a portion of the liquid fraction is evaporated. Subsequently, the refrigerant, which may now have a liquid content of, for example, 0 to 20%, in particular 0 to 10%, withdrawn on the one hand via a liquid line with a valve V4 and on the other hand via a gas line separated from the head of the condenser E5, in the heat exchangers E2 and E1, if necessary, completely evaporated and optionally superheated, and then fed back to the main compressor C1.

For a sufficient cooling in the condenser E5 a certain liquid content of the refrigerant is required. The refrigerant must therefore be biphasic at the outlet of the cold expander X1. As explained, this degrades the efficiency of the cold expander X1. In the illustrated arrangement, moreover, the maximum pressure that can be used as the output pressure PA is limited by the evaporation pressure of the refrigerant required in E5.

In 2 is a plant for the separation of methane from a methane-containing synthesis gas according to an embodiment of the invention shown schematically and in total with 10 designated. The attachment 10 has the essential components of the above-mentioned plant 100 on.

In contrast to the plant 100 , in which the condenser E5 of the second separation column S2 is fed via the cold expander X1, is in the system 10 For this purpose, a relaxation valve V1 is provided. Notwithstanding the operation of the system 100 will be in the plant 10 the cold expander X1 is operated with a proportion of the refrigerant which has not previously passed through the heat exchanger E2 and is therefore warmer.

As before with reference to the attachment 100 is explained, the entire refrigerant or the part that has not been relaxed in the possibly present warm expander X2, is first cooled in the first heat exchanger E1.

Subsequently, a proportion of the refrigerant, for example, 50 to 97%, diverted and, as explained above, be performed by the third and the fourth heat exchanger E3 and E4. This is done, as mentioned, a corresponding cooling. After reconnecting with a residue not passed through the third and fourth heat exchangers E3 and E4, the refrigerant has an intermediate temperature TI resulting from the cooling in the first heat exchanger E1 on the one hand and the partial further cooling in the heat exchangers E3 and E4 on the other results. As explained, the refrigerant in the first heat exchanger E1 is cooled to a temperature of, for example, -60 to -120 ° C, especially -90 to -110 ° C. In the third and the fourth heat exchangers E3 and E4, a further cooling of a correspondingly branched portion takes place on one Temperature of, for example, -80 to -130 ° C, especially -100 to -120 ° C. Thus, the intermediate temperature TI between these temperatures, but in any case higher than the final temperature TE, which is achieved in the second heat exchanger with, for example, -140 to -180 ° C, especially -150 to -170 ° C.

The refrigerant with the intermediate temperature TI is now again divided into a first and a second portion. A first portion, for example 60 to 95% of the refrigerant, is supplied to the cold expander X1. Due to the higher intermediate temperature TI of the refrigerant supplied to the cold expander X1 compared to the system 100 used final temperature TE is carried out in the cold expander X1 no liquefaction. The cold expander X1 can therefore work more efficiently.

By contrast, the second portion, ie the remainder, is then cooled directly from said intermediate temperature TI to the end temperature TE explained several times, as mentioned, for example, -140 to -180 ° C., in particular -150 to -170 ° C. Via a relaxation valve V1, this second portion of the refrigerant is expanded to a feed pressure PC and fed into the condenser E5. As a result, the refrigerant is partially or completely liquefied.

In other words, the demand for liquid refrigerant for the condenser C5 is covered by the expansion valve V1 and a refrigerant having the final temperature TE. The cold expander X1, on the other hand, is supplied with a refrigerant having a higher temperature TI, so that the refrigerant in the expander X1 does not liquefy. However, the released cooling and working power can still be used to operate the second heat exchanger E2 and the post-compressor C3.

Again, the refrigerant in the condenser E5 can be at least partially vaporized and then withdrawn via a liquid line with a valve V4 and a gas line separated from the head of the condenser E5 and combined with the first portion of the refrigerant expanded in the cold expander X1. The refrigerant is then passed through the heat exchanger E2 and E1 and then fed again on the suction side in the main compressor C1.

In addition to improving the efficiency of the cold expander X1 can in the plant 10 a significantly higher outlet pressure PA than in the system 100 can be used, which reduces the circulating energy to be applied. Overall, one offers in the plant 10 feasible process a clearer improvement in efficiency. In particular, a reduction of the required shaft power at the main compressor C1 in the range of about 10% to 20% can be achieved.

Furthermore, the gaseous overhead fraction of the second separation column S2 in the recompressor C4 can be recompressed to the pressure of the first separation column S1 and, after heating in E2 and E1, admixed with the low-methane product PRO. The admixture can also be made directly into the top product of the separation column S1.

In 3 is a plant for the separation of methane from a methane-containing synthesis gas according to an embodiment of the invention shown schematically and in total with 11 designated. The attachment 11 has up to the fourth heat exchanger E4, the essential components of the previously described system 100 on.

Instead of using a fourth heat exchanger E4 designed as a side evaporator, it is provided to lead a portion of the bottoms fraction rich in methane and carbon monoxide in the first separation column S1 via an expansion valve V5 and to heat it in the second heat exchanger E2. The fraction of the bottoms fraction which has been decompressed via the expansion valve V5 and heated in the second heat exchanger E2 is then fed into the second separation column S2 at a defined feed height, whereby heating takes place here. In this way, the function of the fourth heat exchanger E4 can be realized with less equipment expense, which saves costs.

In the plant 11 the intermediate temperature TI of the refrigerant thus results from the cooling in the first heat exchanger E1 and the further cooling of a corresponding proportion in the third heat exchanger E3.

Another plant for the separation of methane from a methane-containing synthesis gas according to an embodiment of the invention is in 4 shown schematically and in total with 12 designated. The attachment 12 has the essential components of the above-mentioned plant 11 on.

In the plant 12 However, the third heat exchanger operated as a bottom reboiler is not supplied with a refrigerant from the refrigerant circuit, but with at least a partial flow of the cooled in the first heat exchanger E1 methane-containing synthesis gas SYN. This is therefore performed here first via the first heat exchanger E1, then via the third heat exchanger E3 and then via the second heat exchanger E2. The attachment 12 This can be operated even more efficiently.

In the plant 12 The intermediate temperature TI of the refrigerant thus essentially results only from the cooling in the first heat exchanger E1.

A further advantageous embodiment of the method, which is not shown in the figures, however, relates to the heat exchangers E1 and / or E2. Advantageously, separate heat exchangers for methane LNG, methane-containing synthesis gas SYN and / or the product stream PRO on the one hand and the refrigerant streams on the other can also be provided here. This allows a more cost-effective implementation. This applies in particular to the heat exchanger E1, but may also be advantageous with respect to the heat exchanger E2. The illustrated heat exchangers E1 and / or E2 can therefore also be realized in the form of two or more structural units.

Although the present invention has been described with reference to equipment in which comparatively high pressure differences between the first separation column S1 and the second separation column S2 are used, this can also be used in processes and plants with lower pressure differences. Thus, plants can be operated accordingly, in which a methane-containing synthesis gas SYN between an entry into and an exit from the overall process, here defined respectively as inlet and outlet into and out of the first heat exchanger E1, only a pressure difference, in particular a pressure drop, in the range of 1 to 3 bar, for example from 1.5 to 2.5 bar, is subjected.

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

• US 2009/0205367 A1 [0004]

Claims (13)

Process for the separation of methane (LNG) from a methane-containing synthesis gas (SYN) in a cryogenic separation plant ( 10 ), which has a refrigerant circuit with at least one expander (X1) and at least one separation column (S2) with a condenser (E5), wherein the at least one expander (X1) and the condenser (E5) each with compressed and cooled portions of a refrigerant the refrigerant circuit are fed, characterized in that the at least one expander (X1) is fed with a first portion of the refrigerant which has been cooled from an initial temperature (TA) to an intermediate temperature (TI), and that the capacitor (E5) with a second portion of the refrigerant is fed, which was cooled from the initial temperature (TA) initially also to the intermediate temperature (TI) and then further to a lower end temperature (TE). The method of claim 1, wherein for feeding the second portion of the refrigerant in the condenser (E5), an expansion valve (V1) is used with which the second portion of the refrigerant to a feed pressure (PC) relaxed and thereby at least partially liquefied. The method of claim 1 or 2, wherein for cooling the first and the second portion of the refrigerant from the outlet temperature (TA) to the intermediate temperature (TI) at least a first heat exchanger (E1) and for further cooling of the second portion of the refrigerant from the intermediate temperature (TI) to the final temperature (TI) a second heat exchanger (E2) is used. Process according to Claim 3, in which the methane-containing synthesis gas (SYN) is present in the cryogenic separation plant ( 10 ) is also cooled at least in the first and then in the second heat exchanger (E1, E2). The method of claim 3 or 4, wherein at least one further heat exchanger (E3, E4) is used, in which a in a defined removal height of the at least one separation column (S2) removed fluid is heated. The method of claim 5, wherein in the at least one further heat exchanger (E3, E4) at least a portion of the first heat exchanger in the first (E1) cooled first and second portions of the refrigerant is further cooled. The method of claim 5 or 6, wherein in the at least one further heat exchanger (E3, E4) in the first heat exchanger (E1) cooled methane-containing synthesis gas (SYN) is further cooled. Method according to one of claims 3 to 7, wherein the first portion of the refrigerant in the expander (X1) working and / or cooling capacity relaxed and then cold side into the second heat exchanger (E2) is fed. Process according to one of claims 3 to 8, in which at least two separation columns (S1, S2) are used, wherein from the synthesis gas (SYN) in a first separation column (S1) a methane-rich and carbon monoxide-containing bottom fraction is cryogenically separated and from the bottom fraction in a second Separation column (S2) having the condenser (E5), carbon monoxide is at least partially desorbed, wherein at least a portion of the in the first separation column (S1) deposited methane rich and carbon monoxide sump fraction in the second heat exchanger (E2) heated and in a defined feed height in the second separation column (S2) is fed. Method according to one of claims 3 to 9, wherein the first or second portion of the refrigerant to a pressure of 50 to 100 bar, in particular 60 to 90 bar, compressed and / or to a feed pressure (PC) of 8 to 20 bar, in particular 10 to 15 bar relaxed and / or to an intermediate temperature (TI) of -120 to -170 ° C, in particular -130 to -160 ° C and / or to a final temperature (TE) of -140 to -180 ° C, especially -150 to -170 ° C, is cooled. A method according to any one of claims 2 to 10, wherein the first portion is 80% and / or the second portion is 20% of the refrigerant. Method according to one of the preceding claims, in which the refrigerant is compressed with a main compressor (C1) and at least two secondary compressors (C2, C3), wherein the expander (X1) is mechanically coupled to one of the at least two secondary compressors (C2, C3) and this drives. Contraption ( 10 . 11 . 12 ) arranged to carry out a process for the separation of methane (LNG) from a methane-containing synthesis gas (SYN) according to any one of the preceding claims and as a cryogenic separation plant ( 10 ), with at least one expander (X1) and at least one separation column (S2) with a condenser (E5), wherein the at least one expander (X1) and the condenser (E5) are arranged, each with compressed and cooled portions of a Refrigerant to be supplied from the refrigerant circuit, wherein means are provided which are adapted to the at least one expander (X1) with a first portion of the refrigerant, which has been cooled from an outlet temperature (TA) to an intermediate temperature (TI), and the condenser (E5) with a second portion of the refrigerant, the first of the initial temperature (TA) also to the intermediate temperature (TI ) and then further cooled to a lower final temperature (TE), to feed.

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