EP4647700A1

EP4647700A1 - Method and apparatus for producing air products

Info

Publication number: EP4647700A1
Application number: EP24020150.9A
Authority: EP
Inventors: Christian Kunz; Kathrin Hummel; Christian Hermann
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 2024-05-08
Filing date: 2024-05-14
Publication date: 2025-11-12

Abstract

A method and an apparatus for producing air products comprising the steps of providing a feed mixture (201) comprising krypton, xenon and oxygen, introducing the feed mixture (201) into a first rectification column (121), withdrawing a first fraction (202) depleted in oxygen and enriched in krypton and xenon relative to the feed mixture (201) and a second fraction (203) enriched in oxygen and depleted in krypton and xenon relative to the feed mixture (1) from the first rectification column (121), introducing a third fraction (204) derived from the second fraction (203) into a second rectification column (125) and withdrawing a high-purity oxygen fraction (O) from the second rectification column (125).

Description

The present invention relates to a method and to an apparatus for producing air products, particularly including a krypton/xenon mixture and oxygen.

Field of the invention

The production of air products in liquid or gaseous state by cryogenic separation of air in air separation units is well known and described, for example, in H.-W. Häring (ed.), Industrial Gases Processing, Wiley-VCH, 3006, especially section 2.2.5, "Cryogenic Rectification". Unless expressly defined otherwise, the terms used below have the meanings customary in the technical literature.
The noble gases krypton and xenon, which are contained in atmospheric air at concentrations of about 1 ppm and 0.09 ppm, can be obtained by processing considerable amounts of air in air separation units. The boiling temperatures of krypton and xenon are well above the boiling temperatures of nitrogen and oxygen. Krypton and xenon therefore accumulate in liquid oxygen along with hydrocarbons in the commonly used rectification column arrangements. The task of producing krypton and/or xenon products includes an enrichment to obtain a krypton/xenon mixture and separating said mixture as further explained below.
It is an object of the present invention to improve the processing of mixtures particularly including a krypton/xenon mixture and oxygen, particularly to provide additional or improved air products. The feed mixture may also contain argon and/or hydrocarbons.

Summary of the invention

Against this background, the present invention provides a method and an apparatus for producing air products, particularly including a krypton/xenon mixture and oxygen, comprising the features of the independent claims. Embodiments are subject of the dependent claims and of the explanations that follow hereinbelow.
A method for producing air products comprising the steps of providing a feed mixture comprising in particular 1 to 10 ppm by volume krypton, 0.1 to 1 ppm by volume xenon, and 99 to 99.9 % by volume oxygen is proposed. The feed mixture or a part thereof is subjected to a rectification (first rectification column) providing a first fraction depleted in oxygen and enriched in krypton and xenon relative to the feed mixture and a second fraction enriched in oxygen and depleted in krypton and xenon relative to the feed mixture.
The first fraction and the second fraction are preferably withdrawn in liquid form from a first rectification column used in the rectification, the feed mixture or the part thereof subjected to the rectification is preferably introduced with a proportion of liquid of 90% or more, particularly of 95% or more or 99% or more, particularly in an essentially liquid form, into the rectification column. A total feed to the rectification column is made up to at least 90%, particularly of at least 95% or 99%, particularly essentially completely, by the feed mixture or the part thereof subjected to the first rectification.
A third fraction is derived from the second fraction, in the simplest case by taking a portion or all of the second fraction; in other cases it may have a composition and/or an aggregate state (liquid/gaseous) slightly differing from the second fraction. The third fraction is introduced into a second rectification column from which a high-purity oxygen fraction is withdrawn.
In many cases, the second fraction is in liquid state; in special cases, it may be in gaseous state. The third fraction is in liquid state in all of the embodiments shown here.
In contrast to conventional methods for processing feed mixtures of the type considered here, the inventive method allows recovering the oxygen from the feed mixture, which is otherwise reject, - and it allows the recovery of a particularly high-purity oxygen product as the high-purity oxygen fraction. It may be withdrawn in liquid form to be easily stored if there is no oxygen gas consumer close to the unit.
The second fraction may be withdrawn from the top of the first rectification column. It may be withdrawn in gaseous form but in most cases, it is preferred to withdraw the second fraction may be from the top of the first rectification column in liquid state.
The second third fraction is introduced into the second rectification column as a liquid, in particular at the top of the second rectification column.
The lower part of the first rectification column may be electrically heated. In principle, it can be heated alternatively or additionally by indirect heat exchange with a heating medium, e.g. in a bottom reboiler.
It is advantageous to withdraw the high-purity oxygen fraction from the second rectification column in liquid form.
The liquid feed mixture (1) is preferably provided using a liquid withdrawn from a cryogenic storage tank, wherein the liquid withdrawn from the cryogenic storage tank is at least in part made up by a liquid produced in one or more air separation units and stored in the cryogenic storage tank. The system of the invention may either be operated close to one or more air separation units, or it may be operated in remote from any air separation unit. In both cases, it may make sense to transport the liquid used as feed for the first rectification column of the invention from one or more air separation units to another air separation unit od to the remote unit.
Preferably, the first rectification column has a head condenser, cooled particularly by using liquid nitrogen. The liquid nitrogen is evaporated in indirect heat exchange with top gas from the first rectification column. The gaseous nitrogen produced thereby can be used as a heating medium in another heat exchanger of the system and/or led into a neighbouring air separation unit, if applicable. The liquid nitrogen may be taken from a liquid tank or from a neighbouring air separation or nitrogen liquefaction unit.
The head condenser (122) may be arranged at the top of the second rectification column as it is conventional. Alternatively, in the invention, it may be arranged at the top of the second rectification column. In this case the second fraction is withdrawn in gaseous form from the top of the first rectification column, e.g. as the total amount of top gas available. It is introduced into the liquefaction space of the head condenser. The liquid nitrogen produced there is split into a first portion and a second portion, the first portion being introduced as reflux to the first rectification column, the second portion making up the third fraction and being introduced into the second rectification column.
In another embodiment, the second rectification column has separate head condenser. Both head condensers are then preferably arranged at the top of the respective columns. The third fraction may still enter the second column in liquid form.
In addition or alternatively to an electrical heating, , the second rectification column may have a bottom reboiler heated by a condensing gas. The condensing gas may be all or a portion of the fees fraction. The fraction condensed in the bottom reboiler of the second column may be used as a cooling medium for the head condenser of the second column. The resulting gaseous fraction may then be introduced as the feed fraction into the first rectification column.
The method of the invention may comprise a third rectification, the second fraction (203) being introduced into a third rectification column (129) and the third fraction (204) derived from the second fraction being withdrawn from the third column (129). The third column may have a head condenser. The third rectification causes a slight modification of the composition of the third fraction relative to the second fraction by removing methane. There not many theoretical trays necessary. The third rectification column preferably comprises just 1 to 10 practical trays, preferably 2 to 5 trays.
In an embodiment of the present invention, the liquid feed mixture comprises 4 to 7 or 5 to 6 ppm by volume krypton, 0.2 to 0.6 or 0.3 to 0.5 ppm by volume xenon, and 99.5 to 99.8 % by volume oxygen. Embodiments of the present invention may therefore be used for treating liquid oxygen withdrawn from the sump of a low-pressure column of an air separation unit as generally known from the prior art.
According to an embodiment of the present invention, the liquid withdrawn from the cryogenic storage tank comprises one or more hydrocarbons and providing the liquid feed mixture comprises removing at least a part of the hydrocarbons from the liquid withdrawn from the cryogenic storage tank. Removal of hydrocarbons may be performed as known in the prior art, e.g. by a demethanizer unit, which typically consists of a catalysator, a heat recuperator, an electrical heater, and a dryer station (molecular sieve) with a precooling heat exchanger.
An apparatus for producing air products is also provided, the apparatus being adapted to perform the steps of the method as described above. As to further details and advantages of such an apparatus, reference is made to the explanations above in connection with the method according to the present invention and its embodiments. Particularly, such an apparatus provided according to the present invention may comprise means adapted to perform a method according to any of the embodiments of the present invention.

Brief description of the Figures

Embodiments of the invention will now be described, by way of example only, with reference to accompanying drawings, in which:

Figure 1 illustrates a conventional unit for processing of a mixture containing krypton, xenon and oxygen in a configuration.
Figure 2 illustrates a unit for processing of a mixture containing krypton, xenon and oxygen in a configuration usable according to an embodiment of the present invention.
Figure 3 illustrates a unit for processing of a mixture containing krypton, xenon and oxygen in a configuration usable according to an embodiment of the present invention.
Figure 4 illustrates a unit for processing of a mixture containing krypton, xenon and oxygen in a configuration usable according to an embodiment of the present invention.
Figure 5 illustrates a unit for processing of a mixture containing krypton, xenon and oxygen in a configuration usable according to an embodiment of the present invention.

Embodiments of the invention

Krypton and xenon production based on cryogenic air separation may be performed in three sub-units or steps which are often referred to as C1, C2 and C3. The C1 unit or step is typically a part of, or performed in, an air separation unit as described at the outset and it produces so-called crude krypton/xenon which has comparatively low concentrations of krypton and xenon and contains about 99.3% oxygen. Crude krypton/xenon from several air separation units may be collected and transported to the C2 unit or step, in which a purification is performed, mainly by removing the oxygen. The product of the C2 unit or step is essentially a krypton/xenon mixture with traces of impurities. The removed oxygen is conventionally used as a gaseous oxygen product at low pressure. From several C2 units or steps, the krypton/xenon mixture may be passed on to a C3 unit or step to produce pure krypton and xenon. The designation of units or steps as C1, C2, C3 is not limiting and the present invention can be used with other arrangements of apparatus units or method steps.
Figure 1 illustrates a conventional unit 100 for processing of a mixture containing krypton, xenon and oxygen in a configuration usable in an embodiment of the present invention. In the Figures, components with comparable or identical function are indicated with like reference numerals. A repeated explanation is omitted for reasons of conciseness only. Explanations relating to apparatus or plant units or components thereof likewise relate to corresponding method steps and vice versa.
Unit 100 may be a conventional C2 unit as referred to above. Unit 200 may comprise a tank 101 which may be filled by a truck with crude krypton/xenon from several C1 units, as indicated with C1 in Figure 1. The crude krypton/xenon from tank 101 may be flashed into a separation vessel 102 from which a flash gas may be vented to the atmosphere A or be reliquefied and fed back to the tank. A liquid from separation vessel 102 may be pumped using a pump 101, partly buffered in a buffer vessel 104, and passed through a heat exchanger 105 operated with water W or steam or ambient air, before optionally being combined with further fluids from tanks or gas cylinders 106 and 107, such as an externally provided product of a C2 unit from a tank 106, a gas from a gas balloon of a C3 unit from tank 107, or gas from a gaseous oxygen header 108 of a further C2 unit. These fluids generally comprise oxygen, krypton and xenon and less than 1 ppm nitrogen. Units 102 to 105 may be provided in plurality and may each process a part of the crude krypton/xenon.
The crude krypton/xenon may thereafter be processed in a catalytic demethanization unit 110 which includes a counterstream heat exchanger 111, an (electric) heater 112, a catalyst bed 113, a cooler 114 operated with water W, a condenser vessel 115 for removing a condensate C, and a pair of adsorber vessels 116 which may comprise e.g. a molsieve material as adsorbent adapted to be regenerated using a regeneration gas R, such as gaseous nitrogen, and waste oxygen (which is produced as described below) heated in an (electric) heater 117. In catalyst bed 113, trace hydrocarbons contained in the crude krypton/xenon heated in counterstream heat exchanger 111 and the (electric) heater 112 may be converted to carbon dioxide and water. Water produced thereby (and additionally water present before, as the case may be) may be condensed in condenser vessel 115 to form condensate C, and a remainder of water and other components may be removed in the adsorber vessels 116. Adsorber vessels 116 may essentially be operated like a so-called pre-purification unit (PPU) of an air separation unit as disclosed in the technical literature cited above.
The purified crude krypton/xenon is passed through a further counterstream heat exchanger 118 to a rectification unit 120 which, in the non-inventive example illustrated in Figure 1, comprises a single rectification column 121 with a head condenser 122 and reboilers 123 which may be operated electrically. Head condenser 122 is cooled with liquid nitrogen N which is evaporated in an evaporation space of head condenser 122 and thereafter e.g. vented to the atmosphere A (as illustrated with the stream withdrawn to the left from the head condenser 122). A sump stream from rectification column 121 may be passed on to a C3 unit or step, as indicated with C3, or may be stored in a cylinder bundle 124 or passed on to a storage balloon (not shown).
In the example illustrated in Figure 1, uncondensed head gas from rectification column 121 is vented to the atmosphere A as waste oxygen (with or without being passed through further counterstream heat exchanger 118) or partly used as regeneration gas to regenerate the adsorber vessels 116, as discussed before. A fraction (202) depleted in oxygen and enriched in krypton and xenon relative to the feed mixture (201) is withdrawn from the bottom of column 121 and sent to further steps C3 for krypton and xenon separation. The portion 203 of the top gas is called a second fraction (202 depleted in krypton and xenon relative to the feed mixture (1) and thereby further enriched in oxygen. Such fraction could be used as valuable product in prior art methods. In the current embodiment, it is not used, as the flow was only a minor amount
With C2 units or steps growing in size, the oxygen removed from crude krypton/xenon, e.g. in a rectification column 121 such as shown in Figure 1, can be further processed and utilized for additional products. Higher quality liquid oxygen products with increasing purity grades are for example so-called medical liquid oxygen, high purity liquid oxygen or ultra-high purity liquid oxygen (MedLOX, HiLOX or UHPLOX). As discussed, in a C2 unit or step, such as the one shown in Figure 1, hydrocarbons are removed as well. The catalytic conversion unit or step 110 as discussed in connection with Figure 1 may be used for this purpose. Such a unit or step 110 may also be referred to as a demethanizer unit or step. Be it noted that such a demethanizer unit or step generally is not comparable to a demethanizer unit or step as used in other apparatus such as a petrochemical unit or a steam cracker, the latter operating on the basis of a cryogenic removal of methane and lighter components. Downstream the catalytic conversion unit or step, carbon dioxide and water, which may at least in part be formed by said catalytic conversion, and components such as nitrous oxide may be removed in a molsieve station.
The oxygen removed from the krypton/xenon mixture may essentially comprise the same impurities as the gas directly downstream the catalytic conversion or an adsorptive purification, such as in adsorber vessels 116. For the production of medical liquid oxygen, often specific regulations in regard of types of material for gaskets and cleanliness must be considered. Argon is generally the main impurity. The highest purity levels are used in the electronic industry where ultra-high purity liquid oxygen must generally comprise less than 50 ppb of argon and less than 10 ppb total hydrocarbons, for example.
Figure 2 shows an embodiment of the invention using a second rectification column 125 in addition to with a reboiler 126, as illustrated for a unit 200 which otherwise essentially corresponds to unit 100 shown in Figure 1.
In unit 200, liquefied head gas from first rectification column 121 is taken as second and third fractions (203, 204) and introduced into the top of an additional second rectification column 125. The rectification in this additional rectification column 125 mainly strips argon from said reflux. An amount of liquid nitrogen N, which is used as a coolant in head condenser 122 as mentioned, must be increased in such a setup in order to condense gaseous oxygen to produce the feed for the additional rectification column 125. The reboiler 126 can be driven electrically. In the second rectification (125), argon is stripped from the reflux made up by the third fraction 204. The liquid nitrogen coolant must be increased over prior art to condense waste GOX to produce the feed for the column.
Using the setup shown in Figure 2 for unit 200, a high-purity liquid oxygen product O is withdrawn as valuable product from the bottom of the second rectification column 125.
For larger product flows and higher purities of the oxygen product, the additional rectification column 125 may require more theoretical trays and so more packing height may have to be implemented in additional beds. For this the head condenser 122 can be shifted from rectification column 121 to the top of the additional rectification column 125, such a setup being illustrated in Figure 3 showing a corresponding unit 300. The pressure in the condenser vessel of the head condenser 122 can be lowered in such a setup in order to allow pressurized liquid nitrogen to overcome the elevation as for reflux the static height is gained to enter column 121.
The operation pressure in rectification column 121 is in the range of 3 bar (abs.) whereas the pressure in the demethanizing unit 110 is about 10 bar (abs.). The pressure is typically reduced upstream a coldbox in which the rectification unit 120 is arranged. However, the relatively high pressure can be used for thermal integration of the condenser/reboiler for either rectification column 121 or additional rectification column 125, as illustrated in Figure 4 for a unit 400 where an (additional) reboiler of additional rectification column is indicated 127 and a second head condenser of second rectification column 125 is indicated 128.
To condense gaseous oxygen against liquid oxygen, a pressure difference of higher than 2 bar is generally required. The pressure difference is also used to lift the liquid to the head condenser 128. A purge flow of the head condenser 128 is not shown in the flow diagram for reasons of conciseness.
The higher the amount of high-purity oxygen O produced, the more the flow ratio at the further counterstream heat exchanger 118 drifts away from the ideal ratio of 1. For compensation, gaseous nitrogen from head condenser 122 can be added to the waste gas passed through the heat exchanger. In case the waste gas is utilized as low pressure gaseous oxygen, such as illustrated in Figure 5 for product L in a unit 500, an additional passage in the counterstream heat exchanger 118 may be provided and gaseous nitrogen may be routed separately.
In the case the limit for total hydrocarbon impurity in the high- purity oxygen O requires further removal of methane a third column 129 being operated as trap tray column 129 can be added, as also shown in Figure 5. The cooling of the trap tray column 129 can be done either thermally integrated or also with use of pressurized liquid nitrogen. The cooling method depends on the amount of the high-purity oxygen O.
The minimum modification to produce higher quality LOX is an additional column with a reboiler. The rectification is this column strips Argon from the reflux (Fig 2). The LIN coolant must be increased to condense waste GOX to produce the feed for the column. The reboiler can be driven electrically.
Even if some features were shown in Figures 2, 3, 4 and 5 or units 200, 300, 400 and 500 specifically for one unit 200, 300, 400 and 500, they can likewise be used in other embodiments or units as required or if useful or advantageous.
The various embodiments described herein are presented only to assist in understanding and teaching the claimed features. These embodiments are provided as a representative sample of embodiments only and are not exhaustive and/or exclusive. It is to be understood that advantages, embodiments, examples, functions, features, structures, and/or other aspects described herein are not to be considered limitations on the scope of the invention as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised, and modifications may be made without departing from the scope of the claimed invention. Various embodiments of the invention may suitably comprise, consist of, or consist essentially of, appropriate combinations of the disclosed elements, components, features, parts, steps, means, etc., other than those specifically described herein. In addition, this disclosure may include other inventions not presently claimed, but which may be claimed in future.

Claims

A method for producing air products comprising the steps of
- providing a feed mixture (201) comprising krypton, xenon and oxygen,

- introducing the feed mixture (201) into a first rectification column (121)

- withdrawing a first fraction (202) depleted in oxygen and enriched in krypton and xenon relative to the feed mixture (201) and a second fraction (203) enriched in oxygen and depleted in krypton and xenon relative to the feed mixture (1) from the first rectification column (121),
characterized by

- introducing a third fraction (204) derived from the second fraction (203) into a second rectification column (125) and

- withdrawing a high-purity oxygen fraction (O) from the second rectification column (125).
The method according to claim 1, wherein the second fraction (203) is withdrawn from the top of the first rectification column (121).
The method according to claim 1, wherein the third fraction (204) is introduced into the second rectification column (125) as a liquid, in particular at the top of the second rectification column (125).
The method according to any of the preceding claims, the lower part of the first rectification column (121) being heated using electric energy (123).
The method according to any of the preceding claims, withdrawing the high-purity oxygen fraction (O) from the second rectification column (125) in liquid form.
The method according to any of the preceding claims, wherein the liquid feed mixture (1) is provided using a liquid withdrawn from a cryogenic storage tank (101), wherein the liquid withdrawn from the cryogenic storage tank (101) is at least in part made up by a liquid produced in one or more air separation units and stored in the cryogenic storage tank (101).
The method according to any of the preceding claims, the first rectification column (121) having a head condenser (122), cooled particularly by using liquid nitrogen (N).
The method according to claim 7, the head condenser (122) being arranged at the top of the second rectification column (125).
The method according to any of the preceding claims, the second rectification column (125) having a separate head condenser (128).
The method according to any of the preceding claims, the second rectification column (125) having a bottom reboiler (127) heated by a condensing gas.
The method according to claims 0 and 10, the condensate produced in the bottom reboiler being used as cooling medium for the head condenser.
The method according to claim 10 or 11, the feed mixture (201) being used as a condensing gas for the bottom reboiler (127) of the second rectification column (125).
The method according to any of the preceding claims, the second fraction (203) being introduced into a third rectification column (129) and the third fraction (204) derived from the second fraction being withdrawn from the third column (129).
The method according to claim 13, the third column having a top condenser (128).
An apparatus (10) for producing air products, the apparatus (10) being adapted to perform the steps of
- providing a feed mixture (201) comprising krypton, xenon and oxygen,

- introducing the feed mixture (201) into a first rectification column (121)

- withdrawing a first fraction (202) depleted in oxygen and enriched in krypton and xenon relative to the feed mixture (201) and a second fraction (203) enriched in oxygen and depleted in krypton and xenon relative to the feed mixture (1) from the first rectification column (121),
characterized by being adapted to perform the further steps of
- introducing a third fraction (204) derived from the second fraction (203) into a second rectification column (125) and

- withdrawing a high-purity oxygen fraction (O) from the second rectification column (125).