DE102007035619A1 - Process and apparatus for recovering argon by cryogenic separation of air - Google Patents

Abstract

The method and apparatus are for recovering argon by cryogenic separation of air. Spare air (1) is compressed (3) and introduced into a distillation column system for nitrogen-oxygen separation (13, 14). An argon-containing stream (72) is taken from the distillation column system for nitrogen-oxygen separation. The argon-containing stream (72) is fed to a crude argon column (25). The crude argon column (25) has a top condenser (24) in which a top gas from the crude argon column (25) is at least partially condensed. At least a portion of the condensate obtained is applied as reflux liquid to the crude argon column (25). The crude argon column (25) or the top condenser (24) is taken from a crude argon stream (76, 176, 276a, 276b). The crude argon stream (76, 176, 276a, 276b) is fed to a pure argon column (20). The pure argon column (20) is removed from a pure argon product stream (81). The top condenser (24) of the crude argon column (25) is designed as a reflux condenser and top gas of the crude argon column is introduced into the return passages of the reflux condenser.

Description

The The invention relates to a method according to the preamble of claim 1

For example, methods and apparatus for cryogenic decomposition of air are off Hausen / Linde, Tiefftemperaturtechnik, 2nd edition 1985, chapter 4 (pages 281 to 337) known. The distillation column system for nitrogen-oxygen separation of the invention may be formed as a single column system for nitrogen-oxygen separation, as a two-column system (for example as a classic Linde double column system), or as a three or more column system. In addition to the columns for nitrogen-oxygen separation and for the production of argon, further steps for obtaining other air components may be provided in the method, in particular further noble gases.

The "crude argon column" in the sense of the claim is used for argon-oxygen separation. The crude argon column may be formed by a one-piece column or by a two- or multi-part column, as in EP 628777 B1 is described. The "pure argon column" is used for argon-nitrogen separation. The "crude argon stream" has a higher argon concentration than the "argon-containing stream". The "pure argon product stream" has a higher argon concentration than crude argon stream and is preferably withdrawn from the bottom of the pure argon column, for example from its bottom.

Processes for argon recovery of the type mentioned are, for example DE 2325422 A . EP 171711 A2 . EP 377117 B2 (= US 5019145 ) DE 4030749 A1 . EP 628777 B1 (= US 5426946 ) EP 669508 A1 (= US 5592833 ) EP 669509 B1 (= US 5590544 ) EP 942246 A2 . EP 1103772 A1 . DE 19609490 (= US 5669237 ) 8th . EP 1243882 A1 (= US 2002178747 A1 ) and EP 1243881 A1 (= US 2002189281 A1 ) is known, both conventional condenser used as the top condenser of the crude argon column, are conducted in gas to be condensed and condensed liquid in the liquefaction passages in cocurrent.

Of the Invention is based on the object, a method of the initially specify type and a corresponding device, the are economically particularly favorable to operate by an increased product yield, a higher product purity, have lower operating costs and / or lower investment costs.

These Task is solved in that the top condenser of Rohargonsäule formed as a reflux condenser is and top gas of the crude argon column in the return passages the flyback capacitor is initiated.

Under "Reflux condenser" (also called dephlegmator) is understood here a heat exchanger, the return passages having. These return passages are steamed from below (here: Overhead gas of the crude argon column). This condenses when ascending in the return passages at least partially. The return passages are designed so that the condensed liquid is not entrained, but flows down. By the counterflow of vapor and liquid Rectification takes place in the return passages. The condensate that exits at the lower end is at low volatility Components enriched, the steam exiting overhead at more volatile.

There are various types of flyback capacitors known. The heat exchanger block (or even a plurality of heat exchanger blocks) may be arranged inside a pressure vessel, as described, for example, in US Pat EP 1189000 A2 is shown, or the heat exchanger block is completed on all sides by headers, see for example US 6128920 , Alternatively, the reflux condenser may be installed in the top of a separation column (here: the crude argon column) with the return passages in communication with the top of the separation column at its lower end, see German patent application 102006037058 and corresponding applications. The one or more heat exchanger blocks of the reflux condenser are preferably designed as a plate heat exchanger, in particular as a brazed aluminum plate heat exchanger.

spatial Terms like "top", "bottom", "side", etc. refer to here always on the orientation of the flyback capacitor in the intended operation.

One Return condenser not only allows one Heat exchange, but also a mass transfer between the rising gas in the return passages and there down-flowing liquid, similar like the corrugated packs of a mass transfer column. This release effect can be described as HETP value (Height Equivalent to one Theoretical Plate = height of a theoretical soil). Of the HETP value of the capacitor is in the range of 300 to 600 mm. Thus, for example, acts a 1.5 m high return capacitor about like up to five theoretical plates. However, it works At the top of the crude argon column this effect does not occur the argon-oxygen separation, that is the use the reflux condenser saves no mass transfer elements (practical soils, ordered packing or disordered packing) in the crude argon column.

Therefore, a reflux condenser has been used in argon recovery only when in the column, which is connected directly to the distillation column system for nitrogen-oxygen separation, no crude argon, but pure argon is recovered (see US 5133790 ). In this case, both the argon-oxygen separation and the argon-nitrogen separation are made in a single argon column and a separate pure argon column for argon-nitrogen separation is expressly not provided. The upper area of the argon column is off US 5133790 is not used for argon-oxygen separation (as in the crude argon column of the invention), but for argon nitrogen separation, which is carried out in the process of the type mentioned almost exclusively in the pure argon column.

So far So no reason was seen in procedures that have their own pure argon column for argon nitrogen separation, a part of the argon-nitrogen separation into the crude argon column or its top condenser because there are no floors in the columns to save.

in the However, within the scope of the invention, it has been found that the insert such a reflux condenser at the top of the crude argon column has a further advantage. Such capacitors are regular designed as a condenser-evaporator. Against that on the Condensing side (return passages) condensing Top gas thus becomes a cooling fluid on the evaporation side evaporated. The heat exchanger block is conventional arranged in a bath. Because of the hydrostatic pressure increases the temperature in the evaporation passages from top to bottom.

Due to the separating effect of the reflux condenser at the top of the crude argon column, the gas flowing upwards in the return passages becomes increasingly nitrogen-rich and is the coldest at the top of the condenser because of the increased nitrogen content (see 4 ). Thus, the temperature profile in the return passages adapts to those of the evaporation passages. In this way, the return condenser creates a natural tendency for a driving temperature gradient which remains almost constant over the entire block height. In the conventional crude argon capacitor, however, the driving temperature gradient in the lower capacitor area is always much smaller than in the upper area. This weakens the contribution of the heating surface located in the lower part of the condenser to the total heat exchange. In the method according to the invention, however, the temperature difference between evaporation and liquefaction passages is almost constant. Thus, the exchange losses can be reduced and thus operating costs can be saved, or the exchange area is reduced accordingly and thus reduces the investment costs.

In order to increase product purity and / or product yield. At constant or less greatly increased separation effect can be the number of theoretical plates in the crude argon column be reduced; This will reduce the investment costs of the plant reduced.

It is particularly advantageous when in the inventive Process the crude argon stream from the top of the return passages is deducted. The gas after flowing through remaining fraction has a particularly high argon concentration and their oxygen content is particularly low. Although contains the crude argon stream thus also relatively much nitrogen; this one can but without much effort in the pure argon column be separated.

In Another embodiment of the invention will become apparent from the upper area the crude argon column and from the return passages no residual gas stream withdrawn. Preferably, from the upper area including the return passages next to the Rohargonstrom no further electricity withdrawn at all. For example, the crude argon column will be next to the crude argon stream just another stream withdrawn into the distillation column system returned to the nitrogen-oxygen separation (for Example in the low-pressure column of a two-column system, from which the argon-containing stream is subtracted).

It is also favorable if the crude argon stream of the crude argon column or the top condenser taken in gaseous form and upstream his introduction to the pure argon column in an additional capacitor at least partially, for example, completely condensed becomes. As a result, the Rohargonstrom can at least partially, for example completely introduced into the pure argon column in liquid form become. This booster capacitor and the following measures can also be used in processes in which the top condenser is not designed as a reflux condenser is.

Preferably are the top condenser and the additional condenser designed as a condenser-evaporator, wherein both evaporation passages with the same cooling fluid be fed. The cooling fluid is in the evaporation passages partially evaporated, whereby the thermosiphon effect liquid entrained and returned to the liquid bath becomes. As the cooling fluid, for example, oxygen-enriched Liquid from the distillation column system for Nitrogen-oxygen separation, for example from the bottom of the high-pressure column a two-pillar system.

It is also advantageous if the top condenser and the additional capacitor formed as a liquid bath evaporator and in the same Liquid bath are arranged. Because the additional capacitor regularly a lower height than that Has top condenser, the additional capacitor can still with a lower end temperature can be operated as the temperature is at the lower end of the top condenser.

If the Rohargonstrom is given up in the liquid state to the head of the pure argon column, this can be used as reflux liquid and can be dispensed with a top condenser of the pure argon column. This is in itself US 5970743 and US Pat. No. 6574988 B1 known. In combination with the reflux condenser, however, results in an increased argon yield.

It is also advantageous if a residual gas stream is withdrawn from the head of the pure argon column or from the upper region of the return passages and mixed with the feed air, in particular before its compression. This recycling of the residual gas from the head of the pure argon column or the crude argon column can also be used with advantage in argon recovery processes without reflux condenser at the top of the crude argon column. In contrast to discarding the residual gas, the argon contained in it is returned to the process. The argon yield increases accordingly. In principle, a separate recompressor can be used, but more favorable is the feed into the unpressurized feed air upstream of the air compressor, in particular more favorable than the direct return of the residual gas in the distillation column system for nitrogen-oxygen separation, as in US 5133790 is proposed.

The The invention also relates to a device according to claim 9th

The Invention and further details of the invention are hereinafter Based on schematically illustrated in the drawings embodiments explained in more detail. Hereby show:

1 A first embodiment of the method according to the invention without additional capacitor,

2 a second embodiment with additional capacitor,

3 the crude argon column and the pure argon column of a third embodiment,

4 the temperature and concentration profile in a crude argon column overhead condenser, which is designed according to the invention as a reflux condenser,

5 a schematic longitudinal section through a return passage of a special design of a reflux condenser and

6 Another special design of the reflux condenser with a longitudinal section through a return passage.

each other wear corresponding components or process steps in the drawings, the same reference numerals.

In the process of 1 becomes atmospheric air 1 is about a filter 2 from an air compressor 3 sucked and there compressed to an absolute pressure of 5.0 to 7.0 bar, preferably about 5.5 bar and is then in a direct contact cooler 4 in direct heat exchange with cooling water 5 . 6 cooled, the one ( 5 ) from an evaporative cooler 7 comes to one another, 6 ) is supplied from an external source. The compressed and cooled air 8th is in a cleaning device 9 cleaned having a pair of containers filled with adsorbent material, preferably molecular sieve. The purified air 10 is in a main heat exchanger system 11a . 11b . 11c cooled to about dew point. The cold air 12 gets into the high pressure column 13 introduced a distillation column system for nitrogen-oxygen separation, which also has a low pressure column 14 having. High-pressure column 13 and low pressure column 14 are designed as classic Linde double column and have a main capacitor 15 in heat exchanging connection. The operating pressures - at the top - are 4.5 to 6.5 bar, preferably about 5.0 bar in the high pressure column and 1.2 to 1.7 bar, preferably about 1.3 bar in the low pressure column.

Liquid crude oxygen 16 is from the bottom of the high pressure column 13 subtracted, in a subcooling countercurrent 17 undercooled and to a part 19 in a sump evaporator 21 the pure argon column 20 further cooled. Another part 22 can at the bottom evaporator 21 be led past. Subsequently, a part flows 23 in the evaporation space of a top condenser 24 a crude argon column 25 , another part in the evaporation space of a top condenser 27 the pure argon column 20 , The in the head condensers 24 . 27 evaporated crude oxygen 28 . 29 will be over line 30 the low pressure column 14 supplied at a first intermediate point. The liquid remaining proportion 31 from the top condenser 24 the crude argon column 25 also becomes the first intermediate point of the low-pressure column 14 guided. The liquid remaining proportion 32 from the top condenser 27 the pure argon column 20 is at a second intermediate point of the low pressure column 14 abandoned, which is above the first Intermediate point lies.

Gaseous nitrogen 33 from the head of the high pressure column 13 becomes a first part 34 to cold end of the main heat exchanger 11a passed there, warmed to about ambient temperature and then into a pressure product stream 36 (GAN I) and a circulation stream 37 divided up. The circulation stream 37 is in a cycle compressor 38 with aftercooler 39 compressed to a pressure of 25 to 60 bar, preferably about 35 bar and in the main heat exchanger 11a cooled. A part 40 of the high pressure nitrogen is removed at an intermediate temperature from the main heat exchanger and in an expansion turbine 41 working at about high-pressure column pressure work. The relaxed circulation stream 42 gets cold again 34 Mixed pressure product stream. Any existing liquid is previously separated ( 43 ) and via wire 44 on the head of the low-pressure column 14 given up. Another part 61 of high-pressure nitrogen goes to the cold end of the main heat exchanger 11a guided and then on the high pressure column 13 given up.

The remaining gaseous head nitrogen 45 the high pressure column 13 will be in the main capacitor 15 at least partially condensed. The generated liquid nitrogen 46 becomes a part 47 the high pressure column 13 abandoned as return. Another part 48 . 49 is after subcooling in the subcooling countercurrent 17 to the head of the low-pressure column 14 directed. There can be a part 50 are withdrawn as liquid nitrogen product (LIN).

Immediately above the bottom of the low pressure column 14 becomes gaseous oxygen 51 removed, in the main heat exchanger 11a warmed up and over wire 52 withdrawn as a non-pressurized gaseous product (GOX III). A liquid oxygen stream 53 from the bottom of the low-pressure column 14 is in the subcooling countercurrent 17 undercooled and over wire 54 a liquid tank (LOX) are supplied. At least a portion of the liquid oxygen is via line 55 removed from the tank, in a pump 56 brought to the required product pressure, for example 6 to 60 bar, preferably about 31 bar, and in the main heat exchanger 11a evaporated to high pressure nitrogen (or pseudo-vaporized at supercritical pressure) and warmed to ambient temperature and finally via line 57 withdrawn as gaseous high pressure product (GOX I). A part 58 the high pressure liquid is via a throttle valve 59 relaxed to an intermediate pressure of, for example, 6 to 25 bar, preferably about 15 bar and evaporated under this lower pressure and via line 60 withdrawn as gaseous medium pressure product (GOX II).

Gaseous nitrogen 62 . 63 . 64 from the top of the low-pressure column 14 and gaseous impurity nitrogen 65 . 66 . 67 from an intermediate point of the low-pressure column 14 are each in the subcooling countercurrent 17 undercooled, in the main heat exchanger blocks 11c respectively 11b warmed up and over wire 68 - if necessary after heating 69 - As a regeneration gas for the cleaning device 9 used, via wire 70 the evaporative cooler 70 supplied and / or via line 71 blown off directly into the atmosphere.

At a third intermediate point, which is arranged below the first intermediate point, the low-pressure column 14 an argon-containing stream 72 taken and the crude argon column 25 fed directly above the sump. The crude argon column 25 is in this example made in one piece. bottoms liquid 73 the crude argon column is pumped 74 and direction 75 returned to the low pressure column.

The top condenser 24 the crude argon column 25 is inventively designed as a reflux condenser. Gas from the head of the crude argon column 25 flows down into the return passages and is partially condensed there. The condensate generated in this case flows in countercurrent to the rising gas in the return passages down and is in the crude argon column 25 used as a liquid reflux. On the evaporation side is the top condenser 24 designed as a bath condenser. The cooling fluid, here by liquid raw oxygen 23 is formed, flows down through one or more lateral openings in the evaporation passages and is partially evaporated there. Liquid is entrained by the thermosiphon effect, exits along with the vaporized portion at the top of the evaporation passages, and is returned to the liquid bath.

From the upper end of the return passages is a Rohargonstrom via a side header 76 taken in gaseous form and the pure argon column 20 forwarded to an intermediate body. The top condenser of the pure argon column 20 is conventionally carried out in the example on the liquefaction side, that is, the head gas 77 the pure argon column 20 flows from top to bottom through the liquefaction passages. (Alternatively, also the top condenser 27 the pure argon column 20 and / or the main capacitor 15 be designed as reflux condensers.) From the top condenser 27 becomes a residual gas flow 78 subtracted and blown off in the example in the atmosphere. Alternatively, it can have its own blower in the distillation column system for nitrogen-oxygen separation or in front of the air compressor 3 to be led back.

The bottoms liquid 79 the pure argon column 20 becomes a part 80 in the sump evaporator 21 evaporates and the steam generated thereby 81 is called ascending gas in the pure argon column 20 used. The remainder is called a liquid pure argon product stream 82 taken.

The embodiment of 2 gives way before all in the execution of the pure argon column 20 from 1 from. The pure argon column has no top condenser here. The crude argon stream 176 is here through part of the return passages of the top condenser 24 the crude argon column 25 formed and on the head of the pure argon column 20 given up. The head gas 177 the pure argon column 20 becomes the head of the crude argon column 25 recycled. The residual gas flow 178 is through the in the top condenser 24 uncondensed fraction of the top gas formed by crude argon column and pure argon column. It is taken from the top of the return passages via a side header and can be like the residual gas stream 78 of the 1 be treated.

3 shows only the crude argon column 25 and the pure argon column 20 , Otherwise, the procedure is identical to that of 1 and 2 , Similar to 2 Here is a first Rohargonstrom 276a liquid in the pure argon column 20 initiated. Deviating from 2 However, this introduction is not done on the head, but as in 1 at an intermediate point of the Reinargonsäule 20 , At this point is also a part 277 taken from the rising in the pure argon column gas and the head of the crude argon column 25 recycled.

The steam 276b from the head of the return passages of the top condenser 24 forms a second crude argon stream. This one is in an additional capacitor 227 , which is designed as a condenser-evaporator, at least partially condensed. The condensate 282 is given as reflux to the head of the pure argon column. The evaporation side of the additional capacitor 227 is like that of the top condenser 24 formed as liquid bath evaporator, wherein both are preferably arranged in the same liquid bath, the liquid raw oxygen 23 is fed.

In 4 On the one hand, the temperature profile is plotted against the height of the condenser block (left axis). Between the condensing in the return passages liquid whose temperature is approximately equal to the temperature in the evaporation passages (upper curve "condensation") and the counter-rising ascending evaporating gas (lower curve "evaporation") there is a temperature difference (MTD), the the height of the reflux condenser is almost constant.

To the another is also the nitrogen content of the rising in the block Gas shown. The reflux condenser has in the example a separation effect of five theoretical plates accepted. A theoretical bottom causes in the top condenser a Rohargonsäule a nitrogen accumulation in about the Factor 3 (K value of nitrogen in argon).

All described capacitors are preferably designed as soldered aluminum plate heat exchangers whose channels contain corrugated sheets, so-called fins. Within the return passages basically the same types of fins can be used. However, it may be beneficial in reflux condensers to use different Fintypen. An embodiment is in 5 shown. The return passages shown here are divided into four sections A to D, in which different types of fins are used. In the lower inlet region of the reflux condenser, the gas load and thus the flood tendency is greatest. At the top, the gas load is getting smaller. Therefore, in the lower region A, a fin with a small specific pressure loss and a relatively poor heat transfer is preferably selected. Towards the top, in the areas B, C and D fins are used, each with a greater pressure loss and better heat transfer. For example, the wavelength of the fins (Findichte) increases upward.

6 shows another method, the operation of the return passages of the reflux condenser 24 to be designed so that the generally decreasing gas load is compensated. This is via line 383 a part of the gas to be condensed on top of the return passages abandoned. This reduces the gas load in the lower zone. Since the amount of gas flowing to the head is only a subset of the amount of gas to be condensed, the necessary piping takes up less space and construction volume is saved.

In Another embodiment is the flyback capacitor configured on the evaporation side as a falling film evaporator, the means the cooling fluid to be vaporized is at the top abandoned and flows through in a film flow the evaporation passages down. Again, this results in a special favorable course of the evaporation and liquefaction temperatures over the height of the reflux condenser.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 628777 B1 [0003, 0004]
• - DE 2325422 A [0004]
• - EP 171711 A2 [0004]
• - EP 377117 B2 [0004]
• - US 5019145 [0004]
• - DE 4030749 A1 [0004]
• US 5426946 [0004]
• - EP 669508 A1 [0004]
• US 5592833 [0004]
• - EP 669509 B1 [0004]
• US 5590544 [0004]
• EP 942246 A2 [0004]
• - EP 1103772 A1 [0004]
• - DE 19609490 [0004]
• US 5669237 [0004]
• EP 1243882 A1 [0004]
• US 2002178747 A1 [0004]
• EP 1243881 A1 [0004]
• US 2002189281 A1 [0004]
• - EP 1189000 A2 [0008]
• - US 6128920 [0008]
• - DE 102006037058 [0008]
• US 5133790 [0011, 0011, 0022]
• US 5970743 [0021]
• US 6574988 B1 [0021]

Cited non-patent literature

• - Hausen / Linde, Tiefftemperaturtechnik, 2nd edition 1985, chapter 4 (pages 281 to 337) [0002]

Claims (9)

Process for recovering argon by cryogenic separation of air, in which - feed air ( 1 ) ( 3 ) and in a distillation column system for nitrogen-oxygen separation ( 13 . 14 ), - the argon-containing stream of the distillation-column system for nitrogen-oxygen separation ( 72 ), - the argon-containing stream ( 72 ) of a crude argon column ( 25 ), - the crude argon column ( 25 ) a head capacitor ( 24 ), in which a top gas from the crude argon column ( 25 ) is at least partially condensed, and at least a portion of the condensate obtained as reflux liquid to the crude argon column ( 25 ), - the crude argon column ( 25 ) or the head capacitor ( 24 ) a crude argon stream ( 76 . 176 . 276a . 276b ), - the crude argon stream ( 76 . 176 . 276a . 276b ) of a pure argon column ( 20 ) and - the pure argon column ( 20 ) a pure argon product stream ( 81 ), characterized in that the top condenser ( 24 ) of the crude argon column ( 25 ) is formed as a reflux condenser and top gas of the crude argon column is introduced into the return passages of the reflux condenser. Method according to claim 1, characterized in that the crude argon stream ( 76 . 276b ) is withdrawn from the upper region of the return passages. Process according to claim 1 or 2, characterized in that from the upper region of the crude argon column ( 25 ) and from the return passages no residual gas stream is withdrawn. Method according to one of claims 1 to 3, characterized in that the Rohargonstrom ( 276b ) of the crude argon column or the top condenser ( 24 ) in gaseous form and upstream of its introduction ( 282 ) into the pure argon column ( 20 ) in an additional capacitor ( 227 ) is at least partially condensed. Method according to claim 4, characterized in that the head capacitor ( 24 ) and the additional capacitor ( 227 ) are formed as a condenser-evaporator, wherein both evaporation passages with the same cooling fluid ( 23 ) are fed. Method according to claim 5, characterized in that the head capacitor ( 24 ) and the additional capacitor ( 227 ) are formed as a liquid bath evaporator and are arranged in the same liquid bath. Method according to one of claims 1 to 6, characterized in that the Rohargonstrom ( 176 . 282 ) in the liquid state on the head of the pure argon column ( 20 ) is abandoned. Method according to one of claims 1 to 7, characterized in that from the head of the pure argon column ( 20 ) or from the upper region of the return passages, a residual gas stream ( 78 . 178 . 278 ) and the feed air, in particular before their compression ( 3 ) is mixed. Apparatus for recovering argon by cryogenic separation of air with - an air compressor ( 3 ) for the compression of feed air ( 1 ), - means for introducing the compressed feed air ( 8th . 10 . 12 ) in a distillation column system for nitrogen-oxygen separation ( 13 . 14 ), - means for taking an argon-containing stream ( 72 ) from the distillation column system for nitrogen-oxygen separation, - means for introducing the argon-containing stream ( 72 ) into a crude argon column ( 25 ), - the crude argon column ( 25 ) a head capacitor ( 24 ) for the at least partial condensation of a head gas from the crude argon column ( 25 ), Means for giving up at least part of the in the top condenser ( 24 ) recovered condensate as reflux liquid on the crude argon column ( 25 ), Means for extracting a crude argon stream ( 76 . 176 . 276a . 276b ) from the crude argon column ( 25 ) or the head capacitor ( 24 ), - means for introducing the crude argon stream ( 76 . 176 . 276a . 276b ) in a pure argon column ( 20 ), - means for withdrawing a pure argon product stream ( 81 ) from the pure argon column ( 20 ), characterized in that the head capacitor ( 24 ) of the crude argon column ( 25 ) is formed as a reflux condenser and has means for introducing head gas of the crude argon column into the return passages of the reflux condenser.