DE4206923A1 - METHOD AND DEVICE FOR DISASSEMBLING A GAS MIXTURE - Google Patents

Abstract

This process serves for separating a gas mixture (4), in particular air, a product (21; 23), in particular nitrogen, enriched with lower-boiling components, being obtained. A lower-boiling fraction (18, 19) from the upper region of a rectifier column (7) is at least partially condensed in a condenser/evaporator (11) in indirect heat exchange with an evaporating higher-boiling fraction (8). The higher-boiling fraction (8) is, before the indirect heat exchange, supplied with a further fraction (24) which has a lower proportion of higher-boiling components than the higher-boiling fraction (8). <IMAGE>

Description

The invention relates to a method for decomposing a gas mixture, especially of air, in which a low-boiling component enriched product, especially nitrogen, is obtained, one lower boiling fraction from the top of a rectification column in a condenser-evaporator in indirect heat exchange with one evaporating heavy-boiling fraction at least partially condensed is, and an apparatus for performing this method.

Such a method is known from EP-A-02 41 817. For extraction Nitrogen is used to turn cold purified air into a rectification column an oxygen-enriched swamp fraction and into a nitrogen-rich one Head product disassembled. The bottom fraction is placed in a condenser evaporator passed and evaporated there against condensing nitrogen.

The invention has for its object the method of the beginning to make the type mentioned economically more economical, in particular through Improvement of the heat exchange process on the condenser-evaporator.

This problem is solved in that the heavy-boiling fraction another fraction is fed to the indirect heat exchange, the has a lower proportion of higher-boiling components than that heavy-boiling fraction.

A mixture of fractions of different compositions means Obviously a disadvantage at first, as it has already done so Separation work is lost again. However, within the scope of the invention surprisingly found that this disadvantage is caused by another, advantageous effect of adding low-boiling fractions in the heavier boiling fraction is predominated, especially in the case of particularly high ones Heat conversion at the condenser evaporator.

On the one hand, the throughput on the evaporation side of the condenser Ver alternatively or in addition to an increased throughput of the heavy-boiling fraction by feeding in a lower-boiling fraction Fraction will be increased. A particularly high throughput of heavy boilers Fraction means an additional load on the rectification column, since liquid condenses at the top of the column and passes back through the column the soils or other mass transfer elements (e.g. packing or orderly packs) flows down to subsequently boil Fraction can be removed. The as an additional refrigerant The other fraction used must be in contrast to the heavier-boiling one Fraction is not initially condensed at the top of the column and by practical the entire column can be led. If one takes the Ver Mixing the heavy-boiling fraction with the other, with higher-boiling Components poorer fraction in purchase, this fraction can in principle can be removed from any point in the process without loading the column.  

On the other hand, due to the increase in the low-boiling components, Vapor pressure of the boiling fraction on the evaporation side of the condensate gate evaporator (at constant evaporation temperature). In exploitation This effect can be the pressure of the heavy boiling fraction and in the As a result, the entire process pressure is lowered and therefore accordingly Compaction energy can be saved. It works especially when there is an increased need for cold the feeding of low-boiling components also energetically unfavorable tendency to increase the temperature difference during heat transfer opposite.

The feeding of the additional fraction brings in an additional advantage Gaseous form according to a further development of the inventive idea. The height Proportion of gas bubbles on the evaporation side of the condenser-evaporator draws a strongly turbulent flow and thus an improved one Heat transfer after itself.

Any fluid that is above the Removal of the heavy-boiling fraction from the rectification column becomes. However, two special variants have proven to be particularly cheap proven.

In a first preferred variant, the further fraction is replaced by a Partial stream of the lower-boiling fraction formed. This usually represents represents the top fraction of the rectification column, so it has a maximum proportion on low-boiling components. The effect of steam described above pressure reduction on the evaporation side of the condenser-evaporator with it the highest. This procedure can be compared to a procedure without feeding low-boiling components into the evaporation chamber the achievable amount of liquid product can be increased without further Actions are required.

In a second favorable variant of the method according to the invention the further fraction through a partial flow of the gas mixture to be separated educated. The amount of fluid fed into the evaporation space is thus not led through the rectification column. By a corresponding Reduced load on the column can be dimensioned more cost-effectively will. Already performed for the extraction of low-boiling product Separation work is not lost.

Instead of a mixture of heavy boiling and another fraction upstream of the condenser-evaporator it may be convenient to continue Feed fraction to the evaporation side of the condenser-evaporator. The Mixing of the two fractions then takes place in the evaporation room itself instead of. Especially with gaseous feed of the other fraction, the above the described improvement in heat transfer is used particularly efficiently will.

It has proven to be particularly advantageous if the further Fraction and / or the heavier boiling fraction in the lower part of the Evaporation side of the condenser-evaporator are introduced. A corresponding device and its mode of operation are in DE-A-28 35 355 described. This allows a particularly favorable vapor pressure and achieve further improved heat transfer.  

Similarly, the other fraction and the heavier boiling Fraction first mixed and then the evaporation side of the Condenser-evaporator are supplied.

The method according to the invention offers further advantages if the vaporized heavier-boiling fraction downstream of the condenser-evaporator in indirect heat exchange with gas mixture to be dismantled and is then relaxed while working. The relaxation can for example in a relaxation machine, a so-called residual gas bine done. In this case, the additional feed Fraction according to the invention, the throughput at the turbine - and thus its Cooling capacity - can be increased without the rectification column in addition strain. In addition, the particularly high vapor pressure on the evaporation side of the condenser evaporator to increase the pressure ratio at the Residual gas turbine and thus to further improve refrigeration be exploited.

A modification of the invention also relates to a disassembly method a gas mixture, especially air, in which a low-boiling Component-enriched product, in particular nitrogen, is obtained, with a lower-boiling fraction from the upper part of a Rectification column in a condenser-evaporator in indirect heat exchange with a vaporizing heavy-boiling fraction at least is partially condensed. In addition, with this procedure the evaporated heavy boiling fraction downstream of the condenser evaporator heated in indirect heat exchange with the gas mixture to be separated and then relaxed while working.

This modified form of the invention is also based on the object to make this process economically more economical, in particular at high cooling demand.

This problem is solved in that the heavy-boiling fraction a further fraction is fed downstream of the condenser-evaporator which has a lower proportion of higher-boiling components than the heavy-boiling fraction.

Similar to the first-mentioned variant of the invention, as the heavier boiling fraction another fraction of different composition fed without this having to be passed through the column. Hereby the throughput during work relaxation can be increased without that this would burden the column. Here, too, can be achieved Advantage the disadvantage of the loss of separation work in the mixing weigh out.

The further fraction ( 25 a) can be fed to the heavy-boiling fraction at least partially between the condenser-evaporator and heating ( 5 ) against gas to be broken down and / or at least partially between heating ( 5 ) against gas to be broken down and work-related relaxation ( 14 ).

Again, the further fraction from the lower-boiling fraction from Head of the rectification column or from a gas mixture to be separated (gaseous Nitrogen or feed air when used in the Air separation) exist. Because of the particularly simple implementation is here the use of the gas mixture to be broken down as the further fraction very cheap.

Analogous to the variants of the invention explained further above, it is also possible for the modification of the procedure the heavier boiling fraction in the lower Area of the evaporation side of the condenser / evaporator introduced be, as described in DE-A-28 35 355 in detail.

The method according to the invention shows particularly large in all variants Advantages if at least part of the condenser evaporator condensed more volatile fraction as a liquid product, in the case of Air separation, i.e. liquid nitrogen, is obtained.

In addition to the method described so far, the invention relates to a Device according to claims 17 to 21.

The following is the invention and further details of the invention explained in more detail using exemplary embodiments, which in the drawings are shown schematically. The methods shown are for extraction of nitrogen from air; however, the invention is readily applicable to the Disassembly of other two-substance mixtures transferable.

The individual shows:

Fig. 1 shows an air separation process according to the invention with the addition of nitrogen in the evaporation side of the condenser-evaporator

Fig. 2 shows a similar method with the addition of air

Fig. 3 shows a more modified method with a residual gas turbine and the supply of air upstream of the turbine

Fig. 4 shows a modification of the method of Fig. 3 with feeding from below into the condenser-evaporator

The method features common to the exemplary embodiments are first described. Air drawn in via line 1 is compressed in compressor 1 to a pressure of 6 to 14, preferably 7 to 10 bar, and treated in a cleaning device 3 , for example switchable molecular sieve absorbers. The air freed of impurities flows via line 4 to a heat exchanger 5 , in which it is cooled in countercurrent to product flows from approximately ambient temperature to 278 to 293 K, preferably 281 to 288 K. The cold air is fed via line 6 into a rectification column 7 , the working pressure of which is 6 to 14, preferably 7 to 10 bar.

From the rectification column 7 , a bottoms fraction 8 enriched with heavy-boiling constituents (here oxygen) is removed in liquid form, subcooled in countercurrent 9 , expanded in an expansion valve 10 to 5 to 2 bar, preferably 4 to 2 bar and finally introduced into a condenser-evaporator 11 . The condenser-evaporator 11 is shown in the drawings as an independent component. Deviating from this, it could also be integrated into the rectification column 7 , for example.

The fraction evaporated in the condenser-evaporator 11 is drawn off via line 12 and heated in the heat exchangers 9 and 5 . The residual gas fraction 13 , heated to an average temperature of 140 to 115, preferably 130 to 115 K, is expanded in a pressure-reducing turbine 14 to a pressure of 1.5 to 1.1, preferably 1.3 to 1.2 bar, via line 15 led to the heat exchanger 5 and leaves it at about ambient temperature via line 16 . The heated residual gas fraction can be used to regenerate the cleaning device 3 , as indicated by line 17 in the drawings. The invention can also be implemented in the method of FIGS. 1 and 2 without this work-relieving relaxation. In this case, the evaporation in the condenser-evaporator 11 can also be carried out under a lower pressure.

At the top of the rectification column 7 , nitrogen 18 is taken out in gaseous form as a more volatile fraction, is passed via line 19 to the condenser-evaporator 11 and there is at least partially, preferably completely, condensed in indirect heat exchange with the evaporating bottom fraction. The condensate is partly fed via line 20 as a return to the rectifying column 7 and partly removed as a liquid product (line 21 ).

Another part of the gaseous nitrogen 18 led out of the rectification column 7 is passed via line 22 to the heat exchanger 5 , warmed there to about ambient temperature and withdrawn as a gaseous product enriched with more volatile components ( 23 ).

In the method of Fig. 1 is fed via line 24, a part of the gaseous, not required as product nitrogen from the top of rectification column 7, which is a further fraction having a lower content of higher-boiling components than the higher-boiling fraction 8 from the bottom of rectification column 7 , in the relaxed expansion valve 10 bottoms fraction 8 fed. The mixture is introduced into the evaporation side of the condenser-evaporator 11 and occurs there in indirect heat exchange with another part 19 of the gaseous nitrogen from the rectification column 7 .

Instead of introducing the mixture into the condenser-evaporator 11 , a separate introduction of the relaxed bottom fraction and further fraction 24 into the evaporation space of the condenser-evaporator 11 is also possible.

In principle, the bottom fraction and the further fraction can be fed to the condenser-evaporator 11 at any point; however, preferably both fractions - together or separately - are fed in at the bottom of the condenser-evaporator 11 . Details of such a method and the corresponding device are described in DE-A-28 35 355. This aspect of the method according to the invention brings about not only the enrichment of the evaporating fraction of lower-boiling components, but also a noticeably improved heat transfer at the condenser-evaporator 11 .

In contrast to the method just described, in the variant of FIG. 2 not part of the top product, but part of the cleaned cold air, that is to say the gas mixture to be broken down, is fed via a line 24 ′ to the relaxed bottom fraction before evaporation in the condenser. Evaporator 11 fed.

FIGS. 3 and 4 show another way to increase the throughput of the expansion turbine 14 at a correspondingly high cooling demand. Here, cold, purified air is fed to the vaporized bottom fraction 12 upstream of the turbine 14 . This can be realized via one of the lines 25 a or 25 b upstream or downstream of the heat exchanger 5 ; A combined use of the two lines 25 a, 25 b is also possible.

In FIG. 3, in a departure from the previous exemplary embodiments, the relaxed bottom fraction is fed into the evaporation space of the condenser-evaporator 11 in a conventional manner, while in the process of FIG. 4 a feed from below is again provided according to DE-A-28 35 355.

Claims (21)

1. A process for the separation of a gas mixture ( 4 ), in particular air, in which a product ( 21 ; 23 ), in particular nitrogen, enriched in lower-boiling components is obtained, a lower-boiling fraction ( 18 , 19 ) from the upper region of a rectification column ( 7 ) is condensed at least partially in a condenser-evaporator ( 11 ) in indirect heat exchange with an evaporating heavy-boiling fraction ( 8 ), characterized in that the heavy-boiling fraction ( 8 ) has a further fraction ( 24 ; 24 ′) before the indirect heat exchange. is supplied, which has a lower proportion of higher-boiling components than the heavy-boiling fraction ( 8 ). 2. The method according to claim 1, characterized in that the further fraction ( 24 ; 24 ') of the heavy-boiling fraction is supplied in the gaseous state. 3. The method according to claim 1 or 2, characterized in that the further fraction is formed by a partial stream ( 24 ) of the lower-boiling fraction ( 18 ). 4. The method according to claim 1 or 2, characterized in that the further fraction is formed by a partial stream ( 24 ') of the gas mixture to be broken down. 5. The method according to any one of claims 1 to 4, characterized in that the further fraction ( 24 ; 24 ') of the evaporation side of the condenser-evaporator ( 11 ) is supplied. 6. The method according to claim 5, characterized in that the further fraction ( 24 ; 24 ') in the lower region of the evaporation side of the condenser-evaporator ( 11 ) is introduced. 7. The method according to any one of claims 1 to 6, characterized in that the high-boiling fraction ( 8 ) is introduced into the lower region of the evaporation side of the condenser-evaporator ( 11 ). 8. The method according to any one of claims 1 to 7, characterized in that the further fraction ( 24 ; 24 ') and the heavy-boiling fraction ( 8 ) are mixed and then the evaporation side of the condenser-Ver evaporator ( 11 ) are supplied. 9. The method according to any one of claims 1 to 8, characterized in that the evaporated heavy-boiling fraction ( 12 ) downstream of the condenser-evaporator ( 11 ) in indirect heat exchange ( 5 ) with the gas mixture ( 4 ) to be dismantled and then relaxed to perform work (14 ) becomes. 10. A process for the separation of a gas mixture ( 4 ), in particular air, in which a product ( 21 ; 23 ), in particular nitrogen, enriched in low-boiling components is obtained, a low-boiling fraction ( 18 ) from the upper region of a rectification column ( 7 ) is at least partially condensed in a condenser-evaporator ( 11 ) in indirect heat exchange with an evaporating heavy-boiling fraction ( 8 ) and the evaporated heavy-boiling fraction ( 12 ) downstream of the condenser-evaporator ( 11 ) in indirect heat exchange ( 5 ) with to be dismantled The gas mixture ( 4 ) is warmed up and then expanded to perform work ( 14 ), characterized in that a further fraction ( 25 a, 25 b), which has a lower proportion of higher-boiling components, is fed to the heavy-boiling fraction ( 12 ) downstream of the condenser-evaporator than the heavier boiling faction. 11. The method according to claim 10, characterized in that the further fraction ( 25 a) of the heavy-boiling fraction ( 12 ) is at least partially supplied between the condenser-evaporator ( 11 ) and heating ( 5 ) against gas to be separated. 12. The method according to claim 10 or 11, characterized in that the further fraction ( 25 b) of the heavy-boiling fraction ( 12 ) is at least partially supplied between heating ( 5 ) against gas to be broken down and work-relieving relaxation ( 14 ). 13. The method according to any one of claims 10 to 12, characterized in that that the further fraction by a partial flow of low-boiling Fraction is formed. 14. The method according to any one of claims 10 to 12, characterized in that the further fraction ( 25 a, 25 b) is formed by a partial stream of the gas mixture ( 4 ) to be broken down. 15. The method according to any one of claims 10 to 14, characterized in that the high-boiling fraction ( 8 ) is introduced into the lower region of the evaporation side of the condenser / evaporator ( 11 ). 16. The method according to any one of claims 1 to 15, characterized in that at least part of the more volatile fraction condensed in the condenser-evaporator ( 11 ) is obtained as a liquid product ( 21 ). 17. Device for carrying out the method according to one of claims 1 to 3 with a feed line ( 6 ) for gas mixture to be separated, which leads into a rectification column ( 7 ), a bottom fraction line ( 8 ) which emerges from the lower region of the rectification column ( 7 ) leads to the evaporation side of a condenser-evaporator ( 11 ), a residual gas line ( 12 ) for discharging gas from the evaporation side of the condenser-evaporator ( 11 ), a top gas line ( 19 ) which leads gas from the upper region of the rectification column ( 7 ) to the liquefaction side of the condenser-evaporator ( 11 ), and a product line ( 18 , 22 ) which is connected to the upper region of the rectification column ( 7 ), characterized by a further line ( 18 , 24 ) which is located at a point above the connection of the Bottom fraction line ( 8 ) is connected to the rectification column ( 7 ) and to the evaporation side of the condenser-evaporator ( 11 ). 18. An apparatus for performing the method according to claim 4 with a feed line ( 6 ) for gas mixture to be separated, which leads into a rectification column ( 7 ), a bottom fraction line ( 8 ) which leads from the lower region of the rectification column ( 7 ) to the evaporation side of a condenser Evaporator ( 11 ) leads, a residual gas line ( 12 ) for discharging gas from the evaporation side of the condenser-evaporator ( 11 ), a top gas line ( 19 ), the gas from the upper region of the rectification column ( 7 ) to the liquefaction side of the condenser-evaporator ( 11 ) leads, and a product line ( 18 , 22 ), which is connected to the upper region of the rectification column ( 7 ), characterized by a further line ( 18 , 24 ), which leads from the feed line ( 6 ) to the evaporation side of the condenser. Evaporator ( 11 ) leads. 19. The apparatus according to claim 17 or 18, characterized in that the residual gas line ( 12 ) leads to an expansion machine ( 14 ). 20. Device for carrying out the method according to one of claims 10 to 15 with a feed line ( 6 ) for gas mixture to be separated, which leads into a rectification column ( 7 ), a bottom fraction line ( 8 ), which comes from the lower region of the rectification column ( 7 ) leads to the evaporation side of a condenser-evaporator ( 11 ), a residual gas line ( 12 ), which is connected to the evaporation side of the condenser-evaporator ( 11 ) and to an expansion machine ( 14 ), a top gas line ( 19 ), the gas from the upper area the rectification column ( 7 ) leads to the liquefaction side of the condenser-evaporator ( 11 ), and a product line ( 18 , 22 ) which is connected to the upper region of the rectification column ( 7 ), characterized by a further line ( 25 a, 25 b ) that leads from the feed line ( 6 ) to the residual gas line ( 12 ). 21. Device according to one of claims 17 to 20, characterized by a liquid product line ( 21 ) for discharging liquid from the liquefaction side of the condenser-evaporator ( 11 ).