DE10061908A1 - Device for low temperature decomposition of air, for recovery of nitrogen, oxygen and argon, comprises two-stage rectifier column comprising high pressure column - Google Patents

Abstract

Device for low temperature decomposition of air to recover nitrogen, oxygen and argon comprises a two-stage rectifier column comprising a high pressure column (1) and a low pressure column (3) which are thermally connected together using a condenser (2). Device for low temperature decomposition of air to recover nitrogen, oxygen and argon comprises a two-stage rectifier column comprising a high pressure column (1) and a low pressure column (3) which are thermally connected together using a condenser (2). The columns are connected to a heat exchange network, a crude argon column (10) and a liquefied air column (17) via lines including measuring, controlling, regulating and conveying devices. An Independent claim is also included for a process for the low temperature decomposition of air to recover nitrogen, oxygen and argon using a rectifier system consisting of a pressure column and a low pressure column thermally connected using a main condenser, a crude argon column, and a liquefied air column.

Description

The invention relates to a method and a device for low temperature separation of air to obtain nitrogen, oxygen and argon, according to the features of the preamble of claims 1 and 14.

In the known air separation plants with internal compression, the Air rectified products from the rectification system at least partially as Liquids drawn off using conveyors, such as cryo- Pumping, pumped to the desired final pressure and then in one with the heat exchanger network connected to the rectification system in counterflow compressed air to gaseous products, preferably to pressure nitrogen or Pressurized oxygen, evaporated.

The air separation plants designed with an internal compression circuit have the fundamental disadvantage that depending on the from the Rectification system as a liquid withdrawn product quantities partially Liquefaction of the process air used is accompanied by the amount in the pressure column of the rectification system reduces the amount of rectified air, which leads to The consequence is that the separation effort and thus the structural effort in the the rectification columns connected to the pressure column and / or the product exploit and in particular reduce the argon yield.

From US 5 715 706 a method is known in which the oxygen-rich Bottom product of the pressure column in an additional column, the RL flash column rectified and additionally low-oxygen return liquid is obtained, whereby the deterioration associated with the internal compression Return ratios are at least partially reversed can. This is done by compressing (cleaned) carbon dioxide and water and cooled air in a pressure column using conventional Rectifiers under a pressure of about 5.3 bar in an oxygen-rich Fraction and a gaseous stream of nitrogen rectified. The resulting one gaseous nitrogen stream is at least partially condensed and as a return for uses the pressure and low pressure column. The oxygenated one Bottom liquid of the pressure column is in a with or without rectifiers, a bottom evaporator and a top condenser equipped RL flash column relaxed and the steam generated during the relaxation in the RL flash  Column under one between that of the pressure column and that of the low pressure column rectified operating pressure. In the RL-Flash column is marked with gaseous nitrogen from the bottom column evaporation additionally low-oxygen steam is generated. At which no rectifiers having the RL flash column only becomes the sump liquid throttled a two-phase mixture, which is then in the Low pressure column is further disassembled.

In addition, the throttled sump liquid or, alternatively, in one finds advantageous embodiment of US 5 715 706, liquid side trigger from the Low pressure column, as a condensation medium for that at the head of the RL flash column arranged capacitor use, by means of which the in the RL flash column rising vapor medium is at least partially condensed. The condensate is fed back into the RL flash column and low pressure column as a return and / or withdrawn as a liquid product from the liquid air column.

The disadvantage of this method known from US 5 715 706 is that the raw argon capacitor must be dimensioned significantly larger, since the Oxygen concentration of the raw oxygen increases and thus the am Crude argon condenser available temperature difference for the Heat exchange is reduced if that instead of the bottom product of the pressure column Bottom product of the RL flash column for cooling the crude argon condenser Is used. In addition, the achievable yield of additional Return is limited by the fact that only a relatively small proportion of the gaseous Compressed nitrogen from the pressure column for heating the bottom evaporator of the RL Flash column can be used without the buoyancy flow to the lower sections of the low pressure column is reduced so much that the Nitrogen content in the argon side gas rises so much that the crude argon condenser can no longer be operated.

The invention is therefore based on the object of a method and a device to create the type mentioned, by means of which an inexpensive Oxygen and nitrogen production with high product yields, especially at connected argon rectification.

This object is achieved by a method and a device with the features solved by claims 1 and 14.

Further developments of the invention are the subclaims 2 to 13 and 15 to 20 remove.  

According to the invention, a heat exchanger network (all of the in the Coldbox involved in cooling the incoming and outgoing process streams Heat exchangers, such as high heat exchangers, subcoolers and LOX Evaporator) pre-cooled process air in a first partial flow predominantly vaporous process air directly and in a second partial flow to the pressure level throttled the pressure column as predominantly liquid process air with the from the Throttling resulting steam flow at least partially into the pressure column fed.

The remaining portion of liquid process air not supplied to the pressure column is transferred to the Pressure level of the liquid air column throttled as a liquid and vapor Partial air flow into the liquid air column and as a liquid return to the low pressure column fed.

Those with rectifiers in the form of differently arranged conventional floors and / or ordered packings or packing and thermally by means of a main condenser with the low pressure column Coupled pressure column fed process air is under a pressure of usually 4 to 6 bar in an oxygen-rich liquid bottom product and in one nitrogen-rich vaporous top fraction disassembled.

The nitrogen product present at the top of the pressure column with a Residual oxygen content of up to less than 1 ppm is at least partially considered vapor and / or liquid product withdrawn from the rectification column.

The vaporous top product rectified in the pressure column is by means of the main condenser through indirect heat exchange with evaporating acid Substance-rich liquid bottom fraction of the low pressure column at least partially condensed and the condensate obtained at least partially as a return of Pressure column fed.

The oxygen-rich liquid bottom product of the pressure column becomes at least partially as a cooling medium in the condenser of the crude argon column and / or as a return in the Low pressure column fed.

The media fed into the low pressure column are under a pressure of usually 1.1 to 1.6 bar by means of rectifiers in the form of differently arranged conventional floors and / or ordered Packs or packing in a nitrogen-rich vaporous overhead product and broken down into an oxygen-rich liquid sump product.  

Should a pure nitrogen product with one in the low pressure column Residual oxygen content of 0.5 to 10 ppm will be generated, so some separation stages below the tap for the pure nitrogen a gaseous with up to 2 vol .-% Withdrawn oxygen-contaminated gaseous nitrogen product.

The bottom liquid evaporated at least partially by means of the main condenser rises in the low pressure column and is countercurrent with trickling liquid rectified.

To obtain raw argon, the middle area of the low pressure column, the so-called argon belly, an argon-rich argon-oxygen side gas deducted and in the rectifier in the form of different arranged ordered packings and / or packing and top capacitor equipped raw argon column and fed under an operating pressure that only is slightly below the operating pressure of the low pressure column, in a gaseous Raw argon product and broken down into an oxygen-rich liquid sump product.

The gaseous low-oxygen crude argon present at the top of the crude argon column product with a maximum of 6 vol .-% residual oxygen is replaced by indirect Heat exchange with liquid process medium, such as with Bottom liquid of the pressure column, at least partly to liquid raw argon condensed and at least partially as a return of the crude argon column fed. At least part of the top product is either vaporized Product directly in front of the head or as a liquid product from the raw argon condenser deducted or possibly after further treatment steps, such as Heating up to ambient temperature of the gaseous crude argon product, Compression to approx. 4 to 6 bar, catalytic conversion of the in crude argon remaining residual oxygen, with the help of added hydrogen Water vapor, recooling to ambient temperature, adsorptive separation of the in the reaction with hydrogen generated water vapor in one Molecular sieve, re-cooling the oxygen-free crude argon in counterflow with the extracted from the raw argon column, a pure argon column for Extraction of nitrogen-free pure argon product supplied.

The one with rectifiers in the form of differently arranged ordered packings and / or packing, top condenser and Sumpfver Pure argon column equipped with steamer is fed under a raw argon Operating pressure from 1.1 to 5 bar to a large extent oxygen and Low nitrogen liquid sump product, part of which is a pure argon product  less than 1 ppm residual oxygen content and residual nitrogen content from the Deducted pure argon column and the part remaining in the pure argon column Maintaining rectification in the bottom evaporator is evaporated to one rectified nitrogen-rich top product.

The sump liquid rectified in the pure argon column is removed using a Gaseous process medium operated bottom evaporator at least partially evaporates and the vaporous nitrogen-rich in the pure argon column Top product by means of sump liquid injected from the liquid air column condensed.

The non-condensable gaseous inert part of the nitrogen-rich top product the pure argon column is blown off into the system environment as a purge gas.

The one that occurs on the coolant side during operation of the crude argon condenser Steam is fed into the low pressure column.

The vaporous and fed into the liquid air column in the manner described above liquid process air is under a pressure that is between the operating pressure of the Pressure and the low pressure column and which is when using liquid air Cooling medium at approx. 2.3 to 2.6 bar, by means of both the upper and arranged below the feed point, as conventional floors and / or orderly packs or packing formed rectifiers in one gaseous low-oxygen head product and in an oxygen-rich Swamp liquid disassembled.

The sump liquid rectified in the liquid air column is in one Bottom evaporator partially evaporated to below the feed point liquefied air to enable rectification and thereby the Oxygen content of the bottom liquid and thus the yield of the top product increase.

The latent heat of an is advantageous for heating the bottom evaporator predominantly gaseous process medium and / or the sensitive heat of one liquid extracted from the process.

As a heating medium for at least partially evaporating in the liquid air column present bottom liquid finds a current decoupled from the process, such as for example bottom liquid of the pressure column, a vaporous side gas stream or top product stream of the pressure column and particularly preferably a vaporous one  Side deduction of the raw argon column use, which individually or in combination a bottom evaporator of the liquid air column can be fed.

The can also be used to evaporate sump liquid in the liquid air column Feed material itself, i.e. pressurized, cryogenic gaseous process air can be used by referring to the pressure levels of the Liquid air column is passed through the bottom evaporator of the liquid air column and there by releasing the sensitive heat contained in the gas stream generated for the liquid air column.

That in the liquefaction of the vaporous top product in the condenser Liquid air column at least partially liquefied process medium is used as return in the pressure and low pressure column fed or as a liquid nitrogen product deducted.

In a further advantageous embodiment of the invention, the Extracted partial flow of process air from the heat exchanger network, which after the Throttling to the pressure level of the compressed air or liquid air column in predominantly is in liquid form, throttled and directly as predominantly liquid process air and completely fed into the pressure column and liquid from the pressure column Side deductions as a coolant for the condenser and as a feed for the liquid air column and as a return for the low pressure column.

If strong steam development is to be expected during throttling, then it turned out to be favorable to process air before throttling in a swamp the evaporator arranged by indirect heat exchange with to pre-cool evaporating bottom liquid of the pressure column.

Furthermore, it has proven to be advantageous to use all of the air to be liquefied Feed directly into the liquid air column and liquid at the feed point Side deductions to provide liquid air both as a cooling medium to operate the Condenser of the liquid air column as well as a return liquid for the Subtract low pressure column, if for apparatus reasons on a previous feeding of the liquid air flow into the pressure column is dispensed with shall be.

In a further advantageous embodiment of the invention, the entire is made of withdrawn from the heat exchanger network and predominantly after throttling liquid air flow in a operated at the operating pressure of the liquid air column Separation tank that connects directly to the liquid air column via a gas line  connected, relaxed into it. The separator container becomes the one at Throttling generated steam and part of the liquid air as feed streams in the liquid air column is fed in, another part of the liquid air is called Cooling medium passed to the condenser of the liquid air column and the remaining part the liquid air as the return liquid into both the low pressure and the Pressure column fed. Because the container is at a sufficient height in the Coldbox is arranged, it is possible to remove liquid from the separation tank solely by using the geodetic height difference in the pressure column feed. This arrangement has proven to be particularly advantageous if Larger quantities of process air are liquefied and / or with throttling high steam is to be expected.

The invention further relates to a device according to the features of Claims 14 to 20.

The low-temperature separation of air according to the invention for the production of nitrogen, oxygen and argon has the following significant advantages over the known prior art:
According to the invention, a rectification-untreated liquid air stream is used in the liquid air column, which has a higher nitrogen content than the bottom liquid of the pressure column used up to now in accordance with US Pat. No. 5,715,706, whereby a higher yield of nitrogen with the same oxygen content of the bottom liquid in the liquid air column and RL flash column and the resulting additional column return results in a performance optimization of the liquid air column.

The invention can be used particularly advantageously when liquid products, preferably liquid oxygen or nitrogen, from the rectification columns of the Rectification system to be deducted to only liquid products generate or to counter the liquid products with compressed air evaporate (internal compression systems and liquid systems with integrated Air liquefier).

That which also occurs in the known methods for air separation under pressure standing, cryogenic air, which due to the throttling to the pressure level of the various rectification columns would be at least partially liquefied conventional process control as return liquid in the pressure or Low pressure column and would feed the reflux conditions in this Only slightly improve the columns.  

The inventive pre-separation of the liquefied air in the Liquid air column creates a low-oxygen overhead product that is above the Feed point for the liquid air in the low pressure column as additional return can be fed, whereby the with the inventive method achievable argon yield improved by 5 to 10%.

Another significant advantage of being supplied with liquid air according to the invention Liquid air column is that in the low pressure column is a pure gaseous Nitrogen product can be generated without having to do so in the pressure column accordingly to have to produce low-oxygen washing liquid.

The fact that the production of the pure nitrogen product in the Low pressure column required return liquid in front of the head of the liquid air column is deducted, the pressure column with up to 15 to 20 separation stages less provided and accordingly reduces the overall height of the cold box and thus the Plant costs can be significantly reduced.

A procedure in which - in contrast to US 5 715 706 - for cooling the top condenser of the liquid air column rectified untreated liquefied process air or a liquid side vent the liquid air column, which is taken from the feed point of the liquid air column is used. For this purpose, the liquefied process air or the liquid Side drain of the liquid air column directly or after further pre-cooling on the Pressure level of the low pressure column throttled and the top condenser Liquid air column supplied.

The operation of the top condenser with liquefied air ensures that the Operating pressure of the liquid air column only about 1 bar above that of the low pressure column lies, whereby in comparison to the pressure column the separation effort, d. H. the number of Separation stages reduced by up to 10 and / or the required return flow rate reduced and the nitrogen yield in the liquid air column is increased accordingly.

The pressure-reduced operation of the liquid air column advantageously results in a Variety of, optimally adapted to the specific rectification system Integration options for the liquid air column.

Furthermore, it has proven to be particularly favorable in addition to the known heating of the bottom evaporator of the liquid air column vapor Top product of the pressure column, also the sensitive heat from the bottom product of the Pressure column and / or one withdrawn from the heat exchanger network, under  Standing pressure and throttling to the pressure level of the pressure or Liquid air column to use liquefied, cryogenic partial air flow.

For this purpose, the heat extracted from the system process is extracted using the Bottom evaporator coupled into the liquid air column in such a way that the Oxygen concentration in the bottom liquid of the liquid air column between 45 and Is 70 percent. In this way, sales in the liquid air column and thus the yield of low-oxygen overhead product in the liquid air column, especially in comparison to the pressure column, so increased that for the upper one Section of the low pressure column up to 12% more return is available.

The fact that a vaporous side stream with an oxygen content of 30 to 90% is drawn off from the crude argon column and at least partially liquefied in the sump heater of the liquid air column by indirect heat exchange and fed back into the crude argon column, the following significant advantages can be achieved:

• - Reduction of irreversibility in air separation due to the low Temperature differences of those used in the method according to the invention Heating and cooling media;
• - Variability in terms of plant costs, energy use and product yields due to the optimal temperature gradient in the sump heating Liquid air column enables raw argon column tapping;
• - Reduction of the system costs for the cold box and for the rectification column Reduction of rectification facilities and other internals as well Reducing the cross-section of the crude argon column above the side gas vent;
• - Reduction of the system costs by using a top capacitor smaller dimension in the raw argon column.

It can contain between 7 and 12% of the steam rising in the crude argon column can be used as heating medium for the sump heating of the liquid air column, without that the argon yield with the same number of theoretical plates in the Raw argon column drops by more than 0.5%.

According to the invention, not only is the yield of low-oxygen overhead product in the Liquid air column increases, but also the irreversibility in the Raw argon column reduced.  

Another significant advantage of the invention is that a liquid Side draw or part of the bottom product of the liquid air column for cooling the Head capacitor of the pure argon column can be used. Because of the engagement of the side draw or bottom product of the liquid air column as condensation medium in the pure argon column can do this with conventional process control used for this purpose liquid head product of the pressure column and instead used as additional return liquid in the low pressure column be, whereby the argon yield increases again and / or the Number of separation stages in the low pressure column can be reduced.

In addition, due to the additional in the pure argon condenser Separation of the process pressure into the low pressure column from the liquid product column fed sump product a further reduction in Separation effort and thus an optimization of the separation process in the Low pressure column possible.

In a further preferred embodiment of the invention, the liquefied All or part of the air is initially fed into the pressure column and out of the Pressure column in the form of liquid side deductions as an insert medium for the Liquid air column, as well as a condensation medium for the top condenser Liquid air column related and the remaining portion of the liquid air as Return liquid fed into the low pressure column.

A procedure in which the liquefied air precedes has proven particularly useful the relaxation and division into the pressure, low pressure and liquid air column passed through an evaporator arranged in the sump of the pressure column and there is pre-cooled by indirect heat exchange, which increases the irreversibility of the Reduce throttling process and by the incomplete theoretical Separating sump evaporator, the yield of top product in the Pressure column is increased.

In a further advantageous embodiment of the air separation according to the invention becomes the liquid air column of the rectification system at the greatest possible height in the Coldbox arranged separator tank upstream. In the same Operating pressure like the separating tank working the liquid air column is the cryogenic liquid air stream under pressure relaxes. The one at the Steam generated in the separating tank is released with a Partial flow of the air liquefied during throttling into the downstream Liquid air column fed.  

It has proven to be advantageous to use additionally cooled liquid air as a cooling medium to relax the top condenser of the liquid air column. Not in the Liquid air column and as a cooling medium for the top condenser of the liquid air column Required liquid air is fed into the pressure and low pressure column.

Because with the liquid air column an additional source of return liquid for the Low pressure column is present, a pure one in the low pressure column Nitrogen product with a residual oxygen content of 0.5 to 10 ppm are generated, without producing a correspondingly pure return liquid in the pressure column must be, which in the pressure column fewer separation stages to produce a Top product with residual oxygen contents of 0.5 to 2% by volume are required, without the argon and oxygen yield in the low pressure column thereof being negative being affected.

The invention is described below with reference to preferred embodiments explained in more detail.

Show it:

Figure 1 is a schematic representation of a method for air separation according to the invention with a liquid air column used for air pre-rectification with raw argon extraction.

Figure 2 is a schematic representation of the method of the invention for air separation with an inserted for Luftvorrektifizierung liquid air column crude argon.

Figure 3 is a schematic representation of the method of the invention for air separation with an existing separator and from the liquid air column Luftvorrektifizierung with raw and clean argon recovery.

Fig. 4 is a graph of the irreversibilities in the crude argon column with deductions a vaporous partial stream;

In a rectification system shown schematically in Fig. 1 with a rectification column consisting of pressure and low pressure columns 1 , 3 with common main condenser 2 , which is connected to a crude argon and liquid air column 10 , 17 , the entire process air before it is fed into one of the The entirety of all heat exchangers arranged in the cold box, such as the main heat exchanger, freezer and / or other separate heat exchanger existing heat exchanger network to a slightly higher pressure level than that of the pressure column 1 , which usually moves between 4 and 6 bar, compresses and to ambient temperature levels of disturbing Minor components such as water vapor and carbon dioxide, cleaned. A partial flow of the air pre-cleaned in this way, the proportion of which in the total air depends on the amount of liquid or internally compressed gaseous products, is, before being fed into the heat exchanger network, to a pressure which is based on the required pressure level of the internally compressed product flows to be removed from the system and is usually between 10 and 80 bar, post-compressed. The compressed and cleaned process air available at the pressure level of the pressure column 1 is cooled in the heat exchanger network to near its dew point and as a predominantly vaporous first partial stream 4 via a line 63 directly below rectification devices 47 into which by means of the main condenser 2 with the low-pressure column 3 thermally coupled pressure column 1 is fed.

The conveyed to the higher pressure level second partial flow 5 of the process air is also cooled in the heat exchanger network and relaxed in a line 64 with throttle 45 to the pressure level of the pressure column and as a liquid air partial stream 5 b together with the resulting in the relaxation in the throttle 45 vaporous air partial stream 5 c fed into the pressure column 1 via a line 65 above the lower rectification devices 47 . In this context, the term throttle means any device suitable for reducing the pressure, such as a fitting with moving parts, but also a simple cross-sectional tapering of the line. The below the lower Rektifiziereinrichtungen 47 fed into the equipped with Rektifiziereinrichtungen 47 in the form of differently arranged conventional trays and / or structured packings or random packings pressure column 1 predominantly vaporous process air 4 is liquid together with the fed in the lower area above the lower Rektifiziereinrichtungen 47 of the pressure column 1 Air partial stream 5 b and the vaporous air partial stream 5 c are broken down into an oxygen-rich liquid bottom product 6 and into an oxygen-poor vaporous nitrogen product 7 with a residual oxygen content of usually 0.5-10 ppm. The obtained at the top of the pressure column 1 vaporous nitrogen product is partly removed as a vapor pressure nitrogen product 7 a via a line 40 and the remaining in the pressure column 1 product fraction in the condenser 2 is condensed by indirect heat exchange with thereby evaporating liquid bottom product 8 of the low pressure column. 3 The condensate produced in this way is distributed via a line 9 as reflux liquid to the pressure and low-pressure column 1, 3, or as a liquid nitrogen product 7 b via a line 41 with a residual oxygen content of 0.5 to 10 ppm subtracted. The operating pressure of the pressure column 1, which is typically coupled from the condenser 2 to the operating pressure of the low-pressure column 3, from 1.2 to 1.6 bar, is between 4 and 6 bar. The sump liquid 6 rectified in the pressure column 1 is fed through a line 48 equipped with a throttle 48 a as a return into the low pressure column 3 and via a further line 49 provided with a throttle 49 a as a cooling liquid in the working at the same operating pressure as the low pressure column 3 , generally designed as a thermosiphon top condenser 11 of the crude argon column 10 relaxed. The liquid and gaseous streams fed into the low-pressure column 3 equipped with rectifying devices 50 in the form of differently arranged conventional trays and / or ordered packings or packing elements are operated with the help of the oxygen-rich liquid bottom product 8 evaporating in the bottom at an operating pressure of usually 1.2 to 1. 6 bar into a low-oxygen vaporous nitrogen product 12 with a residual oxygen content of 0.2 to 10 ppm and into the oxygen-rich liquid bottom product 8 with an oxygen content of at least 99.5% by volume.

To simultaneously both a pure nitrogen product 12 and a pure oxygen product 8 a, b via line 43, to be able to pull out of the low pressure column 3 42, in the upper portion of the low pressure column 3 is also contaminated with oxygen vaporous nitrogen stream 12 a with an oxygen content of 0 , 1 to 2% deducted.

The rectified in the low pressure column 3 liquid oxygen product 8 a can be withdrawn via a line 43 and the vaporous oxygen product 8 b present in the low pressure column 3 via a line 42 from the low pressure column 3 for further use. The remaining portion of bottom liquid 8 remaining in the low-pressure column 3 is evaporated in order to maintain the rectification by indirect heat exchange in the condenser 2 , which is usually designed as a thermosiphon, in special cases also as a downflow evaporator. From the low-pressure column 3 the so-called argon abdomen, a an amount corresponding to about 30% of the ascending from the condenser 2 amount of steam argon-oxygen mixture 13 is in the central column portion is subtracted with an argon content of usually 8 to 12 vol .-%, and via a line 13 a fed into the raw argon column 10 . The gaseous argon-oxygen mixture that is fed into the crude argon column 10 equipped with rectifiers 51 in the form of differently arranged trays and / or ordered packings or packing elements is rectified into an oxygen-rich liquid bottom product 15 and into an oxygen-poor vaporous crude argon product 14 . The crude argon product 14 is withdrawn as a vaporous or liquid crude argon product 14 a, b with a residual oxygen content of 0.2 to 5% by volume via a line 33 a, 33 b from the crude argon column 10 for further use. The vaporous crude argon stream not drawn off as a product in front of the top of the crude argon column 10 is condensed in the condenser 11 , which is usually designed as a thermosiphon, by indirect heat exchange with cooling medium which evaporates, usually bottom liquid 6 of the pressure column 1 , and is fed back into the crude argon column 10 as a return. The steam generated in the condenser 11 during condensation on the coolant side is fed in via a line 53 in the central section of the low-pressure column 3 . The oxygen-rich liquid bottom product 15 rectified in the crude argon column 10 is fed back into the low-pressure column 3 via a line 62 . From the lower section of the crude argon column 10 , between 7 and 15% of the steam rising in the crude argon side is removed as side gas with an oxygen content of 20 to 90% by volume and fed via line 20 to a sump evaporator 21 of the liquid air column 17 , in which the side gas is condensed by indirect heat exchange with evaporating bottom liquid and is fed back into crude argon column 10 as a return liquid via line 52 . The part of the liquid air stream 5 b of the process air which is not fed directly into the pressure column 1 is expanded and relaxed by means of a throttle 46 a arranged in a line 46 to the operating pressure of the liquid air column 17 , which is between the operating pressure of the pressure and low pressure columns 1 , 3 at least partially as a liquid partial air flow 5 d together with the vaporous partial air flow 5 e generated during the expansion, into which the liquid air column 17 equipped with rectifying devices 54 in the form of differently arranged conventional trays and / or ordered packings or packing elements. The partial air streams 5 d, e fed into the liquid air column 17 are rectified by means of the rectifying devices 54 into a low-oxygen vaporous nitrogen product 18 with a residual oxygen content of 0.5 to 10 ppm and into an oxygen-rich liquid bottom product 19 . The liquid bottom product 19 rectified in the liquid air column 17 has an oxygen content of 40 to 70% by volume.

The fed into the liquid air column 17 liquid air partial stream 5 is d tapped in a predominant part in the level of its feed point of the liquid air column 17 again and fed via a line 23 with throttle 55 in an overhead condenser 22 of the liquid air column 17th The liquid air which is not fed into the top condenser 22 of the liquid air column 17 is expanded as a liquid partial air flow 5 f via a line 16 by means of a throttle 56 into the area of the upper rectifying devices 50 of the low pressure column 3 .

The coolant-side operating pressure of the condenser 22, which is usually designed as a thermosiphon, is only slightly above the operating pressure of the low-pressure column 3 , so that the vapor formed during the evaporation of the liquid air can be fed into the low-pressure column 3 via a line 25 .

By operating the top condenser 22 with the liquid air supplied via line 23 as the cooling medium and having only an oxygen content of 15 to 23 vol.%, The liquid bath of the top condenser 22 is in a temperature range of approx. 87 to 89 K, so that the liquid air column 17 can be operated at an operating pressure of 2.2 to 2.6 bar.

The accumulating in the liquid air column 17 in front head oxygen-poor vaporous nitrogen product 18 as a gaseous oxygen free top product 18 c from the liquid air column 17 drawn off and / or condensed by indirect heat exchange in top condenser 22 with thereby evaporating liquid air and partially fed as reflux liquid back into the liquid air column 17 , The condensate 18 b which is not fed as return liquid into the liquid air column 17 is fed via a line 24 by means of a throttle 57 as an additional return above the rectifying devices 50 into the low-pressure column 3 .

The portion of oxygen-rich liquid bottom product 19 not evaporated in a bottom evaporator 21 of the liquid air column 17 is fed to the low pressure column 3 via a line 58 .

In contrast to the embodiment shown in Fig. 1 embodiment of the invention, a rectification system is shown in Fig. 2, in which, although also a pure nitrogen product is withdrawn 12 ppm with a residual oxygen content of 0.5 to 10 in the low pressure column 1, but in which the return liquid 18 b required for this is drawn off exclusively from the liquid air column 17 .

In the pressure column 1, no pressurized nitrogen product is produced any longer and this reduces the number of separation stages and a peeled off before head a liquid nitrogen stream 9 via the line 9 with a residual oxygen content of 0.5 to 3 vol .-% and fed as reflux liquid into the low-pressure column 3 ,

In addition, in the rectification system according to the invention shown in FIG. 2, the second partial air flow 5 cooled from the heat exchanger network and under a pressure of 10 to 80 bar is not throttled to the pressure level of the pressure column as shown in FIG. 1, but before the pressure drop in the Throttle 46 a by means of a line 66 to the bottom evaporator 21 and pre-cooled by indirect heat exchange with evaporating bottom liquid and then passed via line 46 to the throttle 46 a and relaxed to the pressure level of the liquid air column 17 . The liquefied air 5 d, together with the vapor stream 5 e formed during the expansion, is completely fed into the liquid fluid column 17 . A partial flow of the liquefied air is withdrawn from a side outlet of the liquid air column 17 and used as a cooling liquid for the condenser 22 and as a return liquid for the low pressure column 3 .

Fig. 3 shows an inventive rectification system, in contrast to that shown in Fig. 1 rectification part of the bottom product 19 is fed to the Flüssigluifsäule 17 via a line 59 as a cooling medium in a capacitor 31 a equipped with conventional Rektifiziereinrichtungen 39 pure argon column 32 wherein, wherein the coolant side operating pressure of usually designed as thermosiphon pure argon condenser is 31 only so slightly above the operating pressure of the low pressure column 3, that the evaporating bottom liquid employed can be fed 19 together with the vapor stream from the crude argon condenser 11 returned to the low pressure column. 3 For this purpose, a liquid oxygen-free crude argon product 14 b is fed into the pure argon column 32 via line 33 b, which is rectified into a nitrogen-free and oxygen-free bottom product 34 and a nitrogen-rich top product 35 . The top product 35 is withdrawn as a gaseous inert stream 38 via a line 29 provided with a throttle 38 a and blown off into the environment. Via a further line 69 , the steam formed on the coolant side of the condenser 31 is fed into the low-pressure column 3 at the level of the rectifying devices 50 . In order to generate the buoyant gas required for the rectification, bottom liquid 34 is evaporated by indirect heat exchange in a sump heater 37 with condensing vaporous nitrogen 7 a, which is fed in from the pressure column 1 via a pipeline 36 . The unevaporated portion of bottom liquid 34 is drawn off as a liquid product via a line 68 and the liquid nitrogen condensed during the condensation in the bottom evaporator 37 is fed back into the pressure column 1 via a line 44 .

The further difference between the rectification system shown in FIG. 3 and the rectification system of FIG. 1 is that the second partial air flow 5 drawn off from the heat exchanger network is directly and completely expanded into a separating container 27 via a line 67 provided with a throttle 67 a , the operating pressure of which is only slightly above that of the liquid air column 17 so that the entire steam 5 e produced during the throttling can be fed directly from the separating container 27 into the liquid air column 17 via a line 28 . The separating container 27 is arranged so far up in the cold box that part of the liquid air 5 d can be fed into the pressure column 1 via the line 59 due to the geodetic height difference. In addition, at least a further part of the liquid partial air stream 5 d is drawn off from the separating container 27 via the line 59 and fed into the liquid air column 17 . The removal of cooling medium for the condenser 22 of the liquid air column 17 and of return liquid 5 f takes place, as already shown in FIG. 1, as a side discharge from the liquid air column 17 , but alternatively could also take place directly from the separating container 27 .

FIG. 4 shows a graphic representation of the irreversibilities in the crude argon column 10 when operated with and without side condenser 11 . For this purpose, the individual floors are plotted on the ordinate and the exergy loss on the abscissa as a measure of the irreversibility on each floor. It can be seen that the area under the curve for the exergy loss of the crude argon column 10 with side draw is significantly smaller than the curve for a crude argon column 10 without side draw.

Reference numeral lineup

1

pressure column

2

main condenser

3

Low-pressure column

4

first partial flow of process air (mainly vapor)

5

second partial flow of process air (10 to 80 bar)

5

a predominantly liquid air flow (from

5

)

5

b Liquid partial air flow

5

c partial vapor air flow

5

d partial liquid air flow

5

e partial vapor air flow

5

f liquid partial air flow

6

oxygen-rich liquid sump product (

1

)

7

low-oxygen vaporous nitrogen product (

1

)

7

a nitrogen product drawn off in vapor form (

1

)

7

b liquid nitrogen product (

1

)

8th

oxygen-rich liquid sump product (

3

)

8th

a vaporized oxygen product (

3

)

8th

b Oxygen product drawn off in liquid form (

3

)

9

Liquid line (condensate from

7

)

9

a liquid nitrogen flow

10

crude argon

11

Capacitor (

10

)

12

low oxygen vaporous nitrogen product
12a. , , gaseous nitrogen product contaminated with oxygen

13

gaseous argon-rich argon-oxygen mixture

13

a gas pipe (

13

)

14

low-oxygen vaporous crude argon product (

10

)

14

a crude argon product drawn off in vapor form

14

b raw argon product

10

)

15

oxygen-rich liquid sump product (

10

)

16

Liquid line (

5

f)

17

Liquid air column

18

Gaseous low-oxygen overhead product (

17

)

18

a nitrogen product drawn off as a liquid (

17

)

18

b liquid to the low pressure column (

1

) nitrogen product withdrawn (

17

)

18

c oxygen-depleted overhead product (

17

)

19

Liquid oxygen-rich bottom product (

17

)

20

gaseous side trigger (

10-21

)

21

Sump evaporator (

17

)

22

Head capacitor (

17

)

23

Liquid line (

17-22

)

24

Liquid line (

17-3

)

25

Steam flow (

22-3

)

26

-

27

separating vessel

28

Gas pipe (

27-17

)

29

Gas pipe (

32

-Surroundings)

30

-

31

Head capacitor (

32

)

32

Pure argon column

33

a gas pipe (

14

a)

33

b liquid line (

14

b)

34

Swamp product (

32

)

35

Header product (

32

)

36

Gas pipe (

1-32

)

37

Sump evaporator (

32

)

38

Withdrawn gaseous inert stream (

32

)

38

a choke (

38

)

39

Rectification equipment (

32

)

40

Gas pipe (

7

a)

41

Liquid line (

7

b)

42

Gas pipe (

8th

b)

43

Liquid line (

8th

a)

44

Liquid line (

32-1

)

45

Throttle (

5

)

46

Liquid line (

5

b)

46

a choke (in

46

)

47

Rectification equipment (

1

)

48

Liquid line (

6

)

48

a choke (in

48

)

49

Liquid line (

6

)

49

a choke (in

49

)

50

Rectification equipment (

3

)

51

Rectification equipment (

10

)

52

Liquid line (

17-10

)

53

Steam pipe (

10-3

)

54

Rectification equipment (

17

)

55

Throttle (

23

)

56

Throttle (

16

)

57

Throttle (in

24

)

58

Liquid line (

17-3

)

59

Liquid line (

17-31

)

59

a choke (

59

)

60

Liquid line (

27-17

)

61

-

62

Liquid line (

15

)

63

Liquid line (

4

)

64

Liquid line (

5

a, b,

65

Liquid line (

5

a, b, c)

66

Liquid line (

5

)

67

Liquid line (

5

)

67

a choke (in

67

)

68

Liquid line (

34

)

69

Gas pipe (

34-3

)

Claims (20)

1. A process for the low-temperature separation of air to obtain nitrogen, oxygen and argon, in which in a rectification system with at least one pressure and low pressure column ( 1 , 3 ) thermally coupled to one another by means of the main condenser ( 2 ), with at least one crude argon column ( 10 ) and a two-stage rectification column connected to a liquid air column ( 17 ):

• a) compressed, pre-cleaned process air pre-cooled in a heat exchanger network in a first predominantly gaseous partial stream ( 4 ) directly into the pressure column ( 1 ) and in a second partial stream ( 5 ) after throttling ( 45 ) to the operating pressure of the pressure column ( 1 ) predominantly liquid Partial flow ( 5 a) at least partially as a liquid partial air flow ( 5 b) together with the gaseous partial air flow ( 5 c) formed during the throttling ( 45 ) into the pressure column ( 1 ) and a further part of the liquid partial air flow ( 5 b) after further throttling ( 46 a) to the operating pressure of the liquid fluid column ( 17 ) at least partially as a liquid and gaseous partial air flow ( 5 d, e) into the liquid air column ( 17 ) and out of the liquid air column ( 17 ) as a predominantly liquid partial air flow ( 5 f) after throttling ( 56 ) are fed into the low pressure column ( 3 );
• b) the process air ( 4 , 5 a, b, c) fed into the pressure column ( 1 ) is rectified by means of rectifiers ( 47 ) into an oxygen-rich liquid bottom product ( 6 ) and into an oxygen-poor vaporous nitrogen product ( 7 ), and this at the top of the pressure column ( 1 ) the present low-oxygen nitrogen product ( 7 ) is at least partially withdrawn as a gaseous and / or liquid product ( 40 , 41 );
• c) the vaporous nitrogen product ( 7 ) rectified in the pressure column ( 1 ) is at least partially condensed by means of the main condenser ( 2 ) in indirect heat exchange with the evaporating liquid liquid product ( 8 ) of the low-pressure column ( 3 ) which evaporates, and the condensate obtained during evaporation at least partially as return ( 9 ) is fed back into the pressure and low pressure column ( 1 , 3 );
• d) the oxygen-rich liquid bottom product ( 6 ) of the pressure column ( 1 ) is supplied as a cooling medium for a condenser ( 11 ) of the crude argon column ( 10 ) and / or as return liquid of the low pressure column ( 3 );
• e) from the low pressure column (rectified 3) media supplied the oxygen-rich liquid bottom product (8) and an oxygen-poor vaporous nitrogen product (12) and column from the bottom (8) of the low pressure (3) a vaporous and / or liquid oxygen product (8a , b) deducted;
• f) the rectified in the low-pressure column (3) by means Rektifiziereinrichtungen (50) the bottom product (8) at least partially vaporized in step 1 c) to Rektifikationsdampf for the low-pressure column (3) and is withdrawn as nitrogen product (12) before the head of the low-pressure column (3) ,
• g) a gaseous argon-rich argon-oxygen mixture is withdrawn ( 13 ) from the low-pressure column ( 3 ) and fed into the crude argon column ( 10 ) and in it by means of rectifiers ( 51 ) into a low-oxygen vaporous crude argon product ( 14 ) and into an oxygen-rich liquid Bottom product ( 15 ) is broken down;
• h) at the top of the crude argon column ( 10 ) present low-oxygen vaporous crude argon product ( 14 ) by indirect heat exchange with a liquid process medium, such as with liquid bottom product ( 6 ) of the pressure column ( 1 ), at least partially condensed and at least partially as a return of the crude argon column ( 10 ) is fed;
• i) the crude argon product ( 14 ) is at least partially withdrawn from the crude argon column ( 10 ) as a vaporous or liquid product ( 14 a, b) and / or at least partially fed into a pure argon column ( 32 ) for the production of oxygen-free and nitrogen-free pure argon product ( 34 ) become;
• j) from the air or partial air flow ( 5 d, e) equipped according to step 1 a) into the above and below the feed point with rectifying devices ( 54 ) and with one between that of the pressure and low pressure column ( 1 , 3 ) process air fed to the operating pressure operated liquid air column ( 17 ), an oxygen-poor vaporous top product ( 18 ) and an oxygen-rich liquid bottom product ( 19 ) are rectified;
• k) the oxygen-rich liquid sump product ( 19 ) rectified in the liquid air column ( 17 ) is partially evaporated by means of a sump evaporator ( 21 ) operated with a predominantly gaseous process medium by indirect heat exchange;
• l) the low-oxygen vaporous overhead product ( 18 ) present in the liquid air column ( 17 ) is at least partially liquefied by means of an overhead condenser ( 22 ) operated with a predominantly liquid process medium, and any condensate obtained is fed at least partially as return into the liquid air and low-pressure column ( 17 , 3 ) ;
• m) a vapor stream ( 25 ) which arises in the condenser ( 22 ) of the liquid air column ( 17 ) during the evaporation of the predominantly liquid process medium and at least some of the liquid bottom product ( 19 ) are fed into the low pressure column ( 3 ).

2. The method according to claim 1, characterized in that for at least partially liquefying the low-oxygen vapor-shaped top product ( 18 ) of the liquid air column ( 17 ), a preferably cooled and throttled to the pressure level of the low-pressure column ( 3 ) subset of the liquid partial air flow ( 5 d) The steam ( 25 ) formed during the liquefaction of the top product ( 18 ) is fed into the low-pressure column ( 3 ). 3. The method according to claim 1 or 2, characterized in that the low-oxygen vaporous top product ( 18 ) of the liquid air column ( 17 ) as a liquid or gaseous nitrogen product ( 18 a, c) is withdrawn. 4. The method according to claim 1, characterized in that the oxygen-rich liquid sump product ( 6 ) of the pressure column ( 1 ) is used as the process medium for the partial evaporation of liquid bottom product ( 19 ) of the liquid air column ( 17 ), which is then used as a cooled liquid of the low pressure column ( 3 ) and / or the condenser ( 11 ) of the crude argon column ( 10 ) is supplied. 5. The method according to claim 1, characterized in that as a process medium for the partial evaporation of liquid sump product ( 19 ) of the liquid air column ( 17 ) from the crude argon column ( 10 ) into the liquid air column ( 17 ) fed gaseous side draw ( 20 ) is used, which is evaporated at least partially condensed as reflux ( 52 ) into the crude argon column ( 10 ) when the liquid bottom product ( 19 ) evaporates. 6. The method according to claim 1, characterized in that as a process medium for partial evaporation of the bottom liquid ( 19 ) of the liquid air column ( 17 ) from the pressure column ( 1 ) tapped side gas stream, preferably the top product ( 7 ) of the pressure column ( 1 ), is used which is at least partially condensed and fed back into the low pressure column ( 3 ) as a return liquid and / or as a cooling medium into the top condenser ( 11 ) of the crude argon column ( 10 ). 7. The method according to any one of claims 1 to 6, characterized in that at least one liquid side drain ( 23 ) of the liquid air column ( 17 ) as a cooling medium for the condenser ( 22 ) of the liquid air column ( 17 ) and / or as a return liquid in the pressure and / or low pressure column ( 1 , 3 ) is fed. 8. The method according to claim 1, characterized in that the predominantly liquid second partial stream ( 5 ) of the process air is at least partially fed as a heating medium into the sump evaporator ( 21 ) of the liquid air column ( 17 ), where it is pre-cooled by indirect heat exchange with evaporating bottom liquid ( 19 ), throttled ( 46 a) to the operating pressure of the liquid air column ( 17 ) and at least a partial flow of the liquefied air ( 5 d) is fed into the liquid air column ( 17 ) together with the steam ( 5 e) formed during the throttling. 9. The method according to claim 1, characterized in that the predominantly liquid second partial stream ( 5 ) of the process air directly into the pressure column ( 1 ) and from the pressure column ( 1 ) at least one liquid side drain ( 46 ) as a cooling liquid in the condenser ( 22 ) the liquid air column ( 17 ), as a feed into the liquid fluid column ( 17 ) and a further partial stream ( 5 f) is fed as a return into the low pressure column ( 3 ). 10. The method according to claim 1, characterized in that the second partial stream ( 5 ) of the process air in a bottom evaporator of the pressure column ( 1 ) cooled by evaporating bottom product ( 6 ) and throttled to the pressure level of the liquid air column ( 17 ) ( 46 a) as a liquid and vaporous partial air flow ( 5 d, e) are at least partially fed into the liquid air column ( 17 ) and from the liquid air column ( 17 ) into the low-pressure column ( 3 ) as a liquid partial air flow ( 5 f). 11. The method according to claim 1, characterized in that the predominantly liquid partial stream ( 5 ) relaxes directly into a separating container ( 27 ) upstream of the liquid air column ( 17 ) and the vapor produced during the expansion ( 5 e) together with at least one liquid partial air stream ( 5 b) is fed from the separating container ( 27 ) into the liquid air column ( 17 ). 12. The method according to claim 1, characterized in that a from the in the pure argon column ( 32 ) fed raw argon ( 14 a, b) by means of rectifiers ( 39 ) in the low-oxygen and low-nitrogen liquid and partially removable as liquid pure argon product removable bottom product ( 34 ) , partially evaporated by means of a bottom evaporator ( 37 ) operated from the pressure column ( 1 ) fed gaseous process medium ( 36 ) and the low argon vaporous overhead product ( 35 ) rectified from the crude argon ( 14 a, b) by means of a partial stream of the bottom product ( 19 ) from the bottom product ( 19 ) withdrawn liquid from the liquid air column ( 17 ) and the non-condensable gaseous inert portion of the top product is blown off into the system environment as a flush. 13. The method according to any one of claims 1 to 12, characterized in that the liquid air column ( 17 ) with an operating pressure between the pressure of the pressure and low pressure column ( 1 , 3 ), preferably with an operating pressure of less than 2.3 bar, is operated; 14. An apparatus for performing the method according to one of claims 1 to 13 with at least one two-stage rectification column, consisting of a pressure and low pressure column ( 1 , 3 ) with a common condenser ( 2 ), which with a heat exchanger network and at least one crude argon column ( 10 ) and at least one liquid air column ( 17 ) are connected by means of lines equipped with measuring, control and regulating and conveying devices. 15. The apparatus according to claim 14, characterized in that the liquid air column ( 17 ) equipped with lines ( 46 , 20 , 52 , 25 ) connected to the heat exchanger network and with rectifying devices ( 54 ), top condenser ( 22 ) and bottom evaporator ( 21 ) and product lines , 24 , 16 , 58 ) with the pressure, low pressure and crude argon column ( 1 , 3 , 10 ) is connected. 16. The apparatus according to claim 14 or 15, characterized in that the bottom evaporator ( 21 ) of the liquid air column ( 17 ) by means of lines ( 20 , 52 , 66 , 46 ) with the pressure and crude argon column ( 1 , 10 ) is connected. 17. The apparatus according to claim 14, characterized in that the equipped with rectifying devices ( 51 ), head condenser ( 11 ) and product lines raw argon column ( 10 ) by means of line ( 33 b) with a pure argon column ( 32 ) and by means of lines ( 13 a, 49 , 53 , 62 ) with the pressure, low pressure and liquid air column ( 1 , 3 , 17 ) is connected. 18. The apparatus according to claim 17, characterized in that the rectifier means ( 39 ) connected by means of line ( 33 b) with the crude argon column ( 10 ), a top condenser ( 31 ), a bottom evaporator ( 37 ) and a product line ( 38 ) having pure argon column ( 32 ) by means of lines (44, 365469) with the pressure, low pressure and liquid air column ( 1 , 3 , 17 ). 19. The apparatus according to claim 18, characterized in that the top condenser ( 31 ) of the pure argon column ( 32 ) by means of line ( 59 ) with the bottom of the liquid air column ( 17 ) is connected. 20. The apparatus according to claim 14, characterized in that a separator ( 27 ) by means of line ( 67 ) with the heat exchanger network and via lines ( 59 , 28 , 60 ,) is connected to the pressure and liquid air column ( 1 , 17 ).