DE10000017A1 - Process for recovery of krypton and/or xenon comprises removing oxygen-enriched fraction from the pressure column at an intermediate point - Google Patents

Abstract

The oxygen-enriched fraction (13) of the pressure column is removed from an intermediate point and has a theoretical or practical base (15) arranged above the point at which compressed pre-purified air (5) is injected into the column. The krypton- and xenon-containing fraction (116) is removed from the column below the intermediate point. Process for recovery of krypton and/or xenon comprises: introducing compressed prepurified air into the rectification system for nitrogen-oxygen, the system having a pressure column (6) and a low pressure column (7) or a pressure column with head condenser; introducing a part of the compressed pre-purified air into the pressure column; removing an oxygen-enriched fraction from the column and feeding into the low pressure column and/or head condenser of the single column; removing a krypton- and xenon-containing fraction from the rectification system for nitrogen-oxygen separation and feeding into the above or middle region of an exchange column (102); feeding an inert gas to the lower or middle region of the exchange column; and removing a krypton- and/or xenon-enriched mixture (117) from the lower region of the exchange column. The oxygen-enriched fraction (13) of the pressure column is removed from an intermediate point and has a theoretical or practical base (15) arranged above the point at which compressed pre-purified air (5) is injected into the column. The krypton- and xenon-containing fraction (116) is removed from the column below the intermediate point. An Independent claim is also included for an apparatus for carrying out the low temperature decomposition of air.

Description

The invention relates to a method for obtaining krypton and / or xenon by Cryogenic decomposition of air according to the preamble of claim 1 The process is a krypton- and xenon-containing fraction, which from a Rectification system for nitrogen-oxygen separation, in an exchange column in brought direct countercurrent with an inert gas to the bottom of this column a mixture enriched with krypton and / or xenon and low in oxygen produce.

Such a process is, for example, from Streich, Daimer, extraction of Noble gases in air and ammonia plants, Linde reports from technology and Wissenschaft, 37/1975, 10-14, from DE 11 22 088 B, US 4401448 or EP 218741 A known. In these processes, argon or nitrogen is used as the inert gas. The Krypton and xenon enriched mixture, which the exchange column as a bottom product leaves, not only shows an increased content of this relatively low volatility Components, but is also practically free of oxygen. Further Methods and devices for krypton and / or xenon extraction are from the German patent application 198 23 526 and the corresponding one international patent application PCT / EP99 / 03079 and from German Patent application 198 55 487 and the corresponding patent applications in other countries (e.g. European patent application 99102628) are known.

Air separators in the narrower sense with at least two separation columns are, for example, out Hausen / Linde, low-temperature technology, 2nd edition 1985, chapter 4 (pages 284 to 340) known. The rectification system for nitrogen-oxygen separation can be act a two-column system that only one pressure column and one Has low pressure column, or around a multi-column system with other separation columns for nitrogen-oxygen separation. In Hausen / Linde there are several examples of Two-column systems shown (page 284, Figure 4.3. And various examples in the Sections 4.5.1 and 4.5.2). The method according to the invention and the corresponding one If necessary, the device can be used outside the rectification system for nitrogen  Oxygen separation additional separation columns for the extraction of further Have air components, such as noble gases such as argon, helium, neon. The Exchange column can further columns to separate the krypton and / or xenon-enriched mixture and / or for further purification of the krypton and / or xenon product. The invention is also based on a Rectification system for. Nitrogen-oxygen separation applicable as One column system is formed and a single column with a top capacitor having.

From the unpublished patent application DE 198 52 020 the same Applicant and from the corresponding international application PCT / EP99 / 05678 a method is known in which a krypton and xenon containing Mixture from the pressure column first of all cleaning - one Concentration-changing measure - is subjected before it enters a Exchange column is initiated.

The invention has for its object with a method of the beginning mentioned type or a corresponding device Krypton and / or To separate xenon in a particularly economical way.

This object is achieved in that the oxygen-enriched fraction which is in the Low pressure column (or in the top condenser of the single column) is initiated, the pressure column is removed at an intermediate point which at least one theoretical or practical floor above the spot is arranged on the compressed and pre-cleaned feed air of the pressure column is fed, and that the krypton- and xenon-containing fraction at least one theoretical or practical ground below this intermediate point from the Pressure column is removed.

The mass transfer section between the point of the feed air supply (usually at the bottom of the pressure column) and the removal of the oxygen-enriched fraction enables a largely complete washing out of the less volatile impurities, in particular N ₂ O, from the feed air into the bottom of the pressure column. It is formed either by at least one practical shelf or by a packing section with a separating effect from at least one theoretical shelf. There are preferably 1 to 10, most preferably 3 to 5 theoretical or practical trays between the air supply or pressure column sump on the one hand and the point of withdrawal of the oxygen-enriched liquid on the other. (If only practical floors are used as mass transfer elements in this section, the information in practical plate numbers applies; if packing, packing or combinations of different types of material exchange elements are used, the data in theoretical plate numbers are to be used.)

With such a mass transfer section between the air supply and the removal of the oxygen-enriched fraction, the most important less volatile impurities can be retained almost completely from the oxygen-enriched fraction. The oxygen-enriched fraction contains, for example, less than 1 ppb N ₂ O (molar concentration less than 10 ^-9 ), preferably the molar N ₂ O concentration is 10 ^-12 or less.

In the procedure according to the invention, in addition to its usual function for krypton / xenon extraction, the exchange column can also be used to discharge less volatile impurities such as N ₂ O from the rectification system for nitrogen-oxygen separation (the air separator in the narrower sense). The less volatile impurities are washed into the sump of the exchange column and leave the exchange column with the mixture enriched with krypton and / or xenon. In this way, reintroduction into the air separator in the narrower sense is avoided without the need for additional apparatus parts.

The krypton and / or xenon-containing mixture is usually at the bottom of the Exchange column and withdrawn in the liquid state. Leave with the head throttle Oxygen, inert gas and optionally other components such as methane Exchange column.

In the simplest case, the exchange column of the invention is made with a single one Mass transfer section realized without heating and cooling, at the head of which krypton- and xenon-containing fraction is liquid. Immediately above that The inert gas which is enriched with krypton and / or xenon can be fed to the bottom  Mixture is formed by the bottom liquid. The latter contains both here Krypton as well as Xenon in significant amounts. The krypton and xenon Liquid can be temporarily stored or a further process step to Example of another column, for separation into raw krypton and raw xenon be forwarded.

In addition, the exchange column can have another mass transfer section above the task of the krypton- and xenon-containing fraction and / or another Have mass transfer section below the feed of the inert gas.

In the context of the method according to the invention, the pressure column can be implemented as a single container. Alternatively, different sections can be enclosed by separate containers. For example, the mass transfer section, which is used to wash out N ₂ O, can be constructed separately from the rest of the pressure column.

The introduction of the oxygen-enriched fraction from the pressure column into the Low pressure column can in the invention directly or indirectly, for example via an intermediate evaporator. The oxygen-enriched fraction can, for example, initially in the Head condenser of a crude argon column passed and there partially or completely be evaporated.

In addition to the fraction from the pressure column, another krypton and xenon-containing fraction withdrawn from the low pressure column and into the exchange column be initiated. The two krypton and xenon-containing fractions are preferably fed into the exchange column at the same point. Through the Additional discharge from the low pressure column can reduce the yield of krypton and / or xenon can be further increased. Alternatively or additionally, too liquid containing krypton and / or xenon from other sources on the Exchange column are abandoned, for example from a liquid tank and / or from another air separation plant, which otherwise would not work with the Rectification system for nitrogen-oxygen separation is connected.  

Preferably at least a portion of the top vapor from the exchange column is injected into the Rectification system initiated for nitrogen-oxygen separation. In this way go both the inert gas (for example nitrogen) and that in the krypton and xenon-containing fraction does not lose oxygen, but can be used as Products are won.

A crude krypton fraction can be obtained from the middle area of the exchange column subtracted from. In this case, the exchange column has at least two Mass transfer sections, with the upper (above the raw krypton deduction) the serves the classic function of an exchange column and the lower one (below the raw Krypton deduction) acts like a raw krypton / raw xenon column. That at the swamp withdrawn "krypton and / or xenon-containing" mixture in this case is already the Raw xenon product that only contains less volatile components must be cleaned. This aspect of the invention is also with an exchange column sensible, which is fed exclusively from the low pressure column.

In this case in particular, it is expedient if the replacement column has a Has bottom evaporator, in which at least a part of its bottom liquid is evaporated.

Alternatively or additionally, the exchange column can have a top condenser, in which at least part of their head vapor is liquefied. In this case, a additional mass transfer section above the feed of the krypton and xenon-containing fraction installed. These measures can increase the yield Krypton and / or Xenon can be further increased.

The invention and further details of the invention are described below of embodiments shown schematically in the drawings explained. Here show:

Fig. 1 shows an embodiment of the invention, at a glance,

Fig. 2 shows the exchange column of the embodiment in detail and

Fig. 3 shows an exchange column of another embodiment of the invention.

The drawing of Fig. 1 shows a double column system for nitrogen-oxygen separation. Compressed feed air 1 is fed to a preliminary cleaning 2 and is preferably subjected to adsorption there. Water vapor and CO _{2 are} almost completely removed from the compressed feed air; In contrast, about 20 to 50% of N ₂ O is let through by a conventional molecular sieve. The pre-cleaned feed air 3 is cooled in a main heat exchanger 4 in indirect heat exchange against decomposition products and completely fed via line 5 to the pressure column 6 of the rectification system. The rectification system for nitrogen-oxygen separation also includes a low-pressure column 7 which is connected via a condenser evaporator, the main condenser 8 with the pressure column 6 in heat exchange relationship. At the top of the pressure column 6 , pressure nitrogen 9 is generated, which is partially or completely fed to the main condenser 8 and is condensed there at least partially, preferably completely or essentially completely. A portion 11 of the nitrogen 10 liquefied in the main condenser 8 is fed as return to the pressure column 6 . At least a part 12 of the remaining condensate is led to the upper area of a low pressure column 7 . On the evaporation side of the main condenser 8 , bottom liquid of the low-pressure column evaporates. The steam generated rises in the low pressure column in counterflow to the return liquid. (In the exemplary embodiment of the drawing, the main capacitor 8 is located directly in the sump of the low-pressure column; alternatively, it can be arranged outside the double column.)

An oxygen-enriched fraction 13 in liquid form is removed from the pressure column 6 and fed to the low-pressure column 7 at an intermediate point as a further insert fraction ( 14 ). The oxygen-enriched fraction 13 is withdrawn from an intermediate point which is arranged above a mass transfer section 15 , which corresponds to three theoretical plates in the example. It is therefore free of less volatile impurities such as xenon, C ₂ H ₄ , N ₂ O and C ₃ H ₈ . This means that no N ₂ O can get into the low-pressure column 7 and lead to malfunctions in the main condenser 8 .

The less volatile constituents are drawn off from the bottom of the pressure column 6 with a fraction 116 containing krypton and / or xenone and, in the liquid state, are fed to an exchange column 102, which is only indicated here. The desired krypton and / or xenon enriched mixture 117 on the one hand and a top gas 118 on the other hand are removed from the exchange column. The latter is fed into the pressure column 6 . Alternatively, the top gas 118 of the exchange column can also be supplied in whole or in part to the low pressure column 7 .

In the exemplary embodiment, the entire feed air is fed into the pressure column 6 via the line 5 ; in particular, no feed air reaches the low pressure column 7 without pre-disassembly (for example via a turbine).

The mass transfer section 15 below the removal of the oxygen-enriched fraction 13 can be formed by any known mass transfer element, for example by packing or any type of mass transfer tray; sieve trays or, with a very small amount of rinsing fraction, bell and / or chimney trays are preferably used.

In the example, the oxygen product is withdrawn in gaseous form from the low-pressure column 7 via line 21 , heated in the main heat exchanger 4 and discharged as a product via line 22 . The fume cupboard is located some theoretical or practical trays above the bottom of the low pressure column in order to keep less volatile components such as krypton and / or xenon out of the oxygen product. These less volatile components are drawn off from the bottom liquid of the low-pressure column with a further fraction 24 containing krypton and xenon and are also led to the exchange column 102 . Alternatively or in addition to this method, oxygen can be withdrawn via line 23 as a liquid product which is free of less volatile components and / or as a gaseous product via line 25 . (The heating of the product to be drawn off via line 25 and the supercooling of the oxygen-enriched fraction 13 are not shown in the drawing.)

A nitrogen-containing fraction 19 is drawn off as a gaseous nitrogen product or residual gas above the head of the low-pressure column 7 and heated in the main heat exchanger 4 . The heated nitrogen-containing fraction 20 can be used in part as a regeneration gas for the pre-cleaning 2 .

Process cold is obtained in the exemplary embodiment by means of work-relieving expansion of an intermediate fraction 30 which is withdrawn in gaseous form from the pressure column 6 in the amount of the deduction of the oxygen-enriched fraction 13 or higher. It is heated in countercurrent to feed air 3 in the main heat exchanger 4 , compressed in a compressor 32, for example from 5 bar to 7 bar, and fed to the main heat exchanger 4 again after cooling 33 (line 34 ). The compressed air is removed from the main heat exchanger (line 35 ) at an intermediate temperature and fed to a relaxation machine 36 . Downstream of the work-relieving expansion 36 to 1.2 bar, it is fed via line 37 to the low-pressure column 7 at an intermediate point. In the specific example, both the removal from the pressure column 6 and the feed into the low-pressure column 7 are located at those intermediate points at which the oxygen-rich fraction 13 , 14 is also drawn off or introduced. At least a part of the energy required for the compression of the heated gas fraction 31 is formed by the mechanical energy generated during the relaxation 36 ; For this purpose, the expansion machine 36 and the compressor 32 are preferably coupled mechanically. In certain cases, the compression 32 can be omitted; then it is sufficient to heat the gas fraction 30 only up to a medium temperature and then to supply it to the work-relieving relaxation 36 directly via line 35 .

Fig. 2 shows the circuit of the exchange column 102 in detail. Bottom liquid of the pressure column 6 as a fraction containing krypton and xenon is fed in via line 116 below a first mass transfer section 241 as a liquid. In addition, an inert gas 240 is blown into the exchange column 102 between a second mass transfer section 242 and a third mass transfer section 243 . In the example, gaseous nitrogen from the top of the pressure column 6 is used as the inert gas. (Alternatively or additionally, nitrogen from an external source can be used, for example from an atmospheric evaporator or a water bath evaporator, which is fed from a liquid tank.) Via line 118 , a first part of the top gas of the exchange column 102 is fed into the pressure column, above the mass transfer section 15 . The krypton and / or xenon-enriched mixture 117 is drawn off in liquid form and, if appropriate, fed to one or more further separation steps. The exchange column 102 also has a top condenser 244 and a bottom evaporator 245 , which are operated by indirect heat exchange with suitable media such as air, one or more process gases from the rectification system for nitrogen-oxygen separation or another air gas. The first mass transfer section 241 of the exchange column 102 has, for example, 3 to 15, preferably 5 to 10 practical or theoretical trays, the second mass transfer section 242, for example, 12 to 26, preferably 15 to 20 practical or theoretical trays, and the third mass transfer section 243, for example 5 to 20, preferably 8 to 13 practical or theoretical floors.

Another example of an exchange column 302 , which is used in a method and a device according to the invention, is shown in FIG. 3. It is constructed largely analogously to FIG. 2 and in this respect bears the same reference symbols. There is an additional liquid discharge for a raw krypton fraction 346 between the first and third mass transfer sections 241 , 243 . The "krypton and / or xenon enriched fraction" 317 hardly contains any krypton here and represents a crude xenon product. The two crude products 346 and 317 are preferably further processed in a pure krypton column or in a pure xenon column worked up.

In the drawing, the discharge for the crude krypton fraction 346 is designed as a liquid discharge and is arranged immediately above the third mass transfer section 243 . In many cases, however, it is cheaper to withdraw the crude krypton fraction in gaseous form from an intermediate point of the second mass transfer section 242 .

The krypton- and xenon-containing fraction which is at least in part from the pressure column of the air separation plant in the narrower sense, can at Fig. 3, analogous to Fig. 2 can be fed via a line 116 directly into the exchange column 302nd As an alternative or in addition, however, buffering of liquid 351 containing krypton and xenon, which at least partially comes from the pressure column, is possible in a tank 349 . In this case, the krypton- and xenon-containing feed fraction is introduced into the exchange column by means of a pump 348 via a line 347 . Alternatively or additionally, liquid 350 containing krypton and / or xenon can be filled into the tank 349 from other systems and processed in the exchange column 302 . The liquid can be transported, for example, from a neighboring air separator via a pipeline or by means of a tanker from more distant locations.

Claims (7)

1. A method for obtaining krypton and / or xenon by low-temperature separation of air, in which

• - Compressed and pre-cleaned feed air ( 3 , 5 ) is introduced into a rectification system for nitrogen-oxygen separation, which has a pressure column ( 6 ) and a low pressure column ( 7 ) or a pressure column designed as a single column with a condenser, wherein
• - At least part of the compressed and pre-cleaned feed air is fed to the pressure column ( 6 ) ( 5 ),
• - An oxygen-enriched fraction ( 13 ) is removed from the pressure column ( 6 ) and the low-pressure column ( 7 ) or the top condenser of the individual column ( 14 ), and in which
• - A krypton- and xenon-containing fraction ( 116 , 351 , 347 ) is removed from the rectification system for nitrogen-oxygen separation and is introduced into the upper or middle area of an exchange column ( 102 , 302 ) without measures to change the concentration, wherein
• - An inert gas ( 240 ) is fed to the lower or middle area of the exchange column ( 102 , 302 ) and
• a krypton and / or xenon-enriched mixture ( 117 , 317 ) is drawn off from the lower region of the exchange column ( 102 , 302 ),
  characterized in that
• - The oxygen-enriched fraction ( 13 ) of the pressure column is removed at an intermediate point which is arranged at least one theoretical or practical base ( 15 ) above the point at which compressed and pre-cleaned feed air ( 5 ) is fed to the pressure column, and that the krypton and xenon-containing fraction ( 116 , 352 ) at least one theoretical or practical base ( 15 ) below this intermediate point is removed from the pressure column ( 6 ).

2. The method according to claim 1, characterized in that a further krypton- and xenon-containing fraction ( 24 ) is withdrawn from the low-pressure column ( 7 ) and introduced into the exchange column ( 102 , 302 ). 3. The method according to claim 1 or 2, characterized in that at least a part ( 118 ) of the top vapor of the exchange column ( 102 , 302 ) is introduced into the rectification system for nitrogen-oxygen separation. 4. The method according to any one of claims 1 to 3, characterized in that a crude krypton fraction ( 346 ) is withdrawn from the central region of the exchange column ( 302 ). 5. The method according to any one of claims 1 to 4, characterized in that at least part of the bottom liquid of the exchange column is evaporated in a bottom evaporator ( 245 ). 6. The method according to any one of claims 1 to 5, characterized in that at least part of the top vapor of the exchange column is liquefied in a top condenser ( 244 ). 7. Device for the low-temperature separation of air with a rectification system for nitrogen-oxygen separation, which has a pressure column ( 6 ) and a low-pressure column ( 7 ) or a pressure column designed as a single column with overhead condenser, with a feed air line ( 1 , 3 , 5 ) Introduction of compressed and pre-cleaned feed air into the pressure column ( 6 ), with a raw oxygen line ( 13 , 14 ) for an oxygen-enriched fraction, which is connected on the one hand to the pressure column ( 6 ) and on the other hand to the low pressure column ( 7 ) or to the top condenser of the single column , with an application line ( 116 , 351 , 347 ) for introducing a fraction containing krypton and xenon from the rectification system for nitrogen-oxygen separation without measures to change the concentration into the upper or middle area of an exchange column ( 102 , 302 ), with an inert gas line ( 240 ) with the lower or middle section of the Exchange column ( 102 , 302 ) is connected and with a product line ( 117 , 317 ) for removing a krypton and / or xenon-enriched mixture from the lower region of the exchange column ( 102 , 302 ), characterized by a mass transfer section ( 15 ) in the scope of at least one theoretical or practical base, which is arranged in the pressure column ( 6 ) between the raw oxygen line ( 13 ) and the feed air line and in that the feed line ( 116 , 351 , 347 ) has at least one theoretical or practical base ( 15 ) below the raw oxygen line ( 13 ) is connected to the pressure column ( 6 ).