EP1495274A1

EP1495274A1 - Method for extracting argon by low-temperature air separation

Info

Publication number: EP1495274A1
Application number: EP03722379A
Authority: EP
Inventors: Reinhard Glatthaar; Christian Kunz; Harald Ranke
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 2002-04-12
Filing date: 2003-04-01
Publication date: 2005-01-12
Also published as: CA2502706A1; JP2005527767A; AU2003229590A1; CN1646869A; RU2303211C2; RU2004133324A; KR20040101453A; US20060005574A1; WO2003087686A1

Abstract

The invention relates to a method for extracting argon by low-temperature air separation. To this end, the rectifying system (2, 4) comprises at least one air separation column (4) subdivided into a first and second partial section (6, 7) by a partition (5) extending in a longitudinal direction of the column. A fluid (3) containing oxygen and argon is introduced into the first partial section (6), and a flow (13) containing oxygen and argon and having an argon concentration ranging from 15 % to 50 % is withdrawn from the second partial section (7).

Description

description

Process for the production of argon by cryogenic air separation

The invention relates to a method for the production of argon by low-temperature separation of air in a rectification system which has three rectification sections arranged in series, the first and second and the second and third rectification sections being connected to one another on the gas and liquid side, and the second rectifying section has two sections, which are not connected to one another on the gas and liquid side and are flowed through in parallel, a fluid containing oxygen and argon being introduced into the first of the two sections and a stream containing oxygen and argon being withdrawn from the second of the two sections.

The boiling point of argon is between the boiling points of oxygen and nitrogen. In the classic low-temperature separation of air through two-stage rectification, the argon accumulates in a central area of the low-pressure column. To obtain argon, a gaseous fraction, which essentially consists of oxygen and argon, is usually removed from this area. This fraction, enriched with about 10% argon, is fed to the so-called crude argon column, in which a rectification separation of oxygen and argon is carried out. Argon can be drawn off at the top of the crude argon column and an essentially oxygen-containing liquid collects in its sump, which is then returned to the low-pressure column.

In practice, argon purities of over 95% are often required. In the known method, however, a stream containing only about 10% argon is fed to the crude argon column. In order to concentrate this to the desired high argon purities and to be able to draw off the desired amount of product from the top of the crude argon column, considerable amounts of steam have to be introduced into the crude argon column and rectified therein. The cross-section of the raw argon column must be chosen accordingly, which results in considerable investment costs. In particular from the field of hydrocarbon production, it is already known to use so-called dividing wall columns for the decomposition of ternary mixtures. In a dividing wall column, part of the column is divided into two sections by a wall arranged in the longitudinal direction of the column. Above and below the partition, the two sections are connected on the flow side. With a corresponding procedure, a three-component mixture introduced into the section on one side of the dividing wall can be broken down into three fractions in a single column. The component with the lowest boiling point can be at the top of the dividing wall column, the medium boiler on the side of the dividing wall opposite the feed and the high-boiling component

Component can be obtained from the swamp. In comparison to a column without a dividing wall, higher concentrations of the medium boiler can be achieved with the dividing wall column at the side draw.

Up to now, dividing wall columns have hardly been used in low-temperature air separation due to their more difficult control. EP 0638778 B1 describes a process for the low-temperature separation of air in a dividing wall column. The low pressure column is divided in a central area by a partition. Sump liquid is fed from the pressure column on one side of the partition, while the argon-containing fluid is drawn off on the other side of the partition. For better control of the process, a waste fluid is removed on the side of the partition wall on which the bottom liquid is introduced. The process parameters are selected so that the argon-containing fluid obtained has an argon concentration of at least 70%.

In the case of a product requirement in the range of 70% argon concentration, the number of theoretical plates in the crude argon column can be reduced with the method described in EP 0638 778 B1 and the overall height can thus be saved. However, if high argon concentrations of, for example, more than 95% are required, the advantages of concentrating the fluid drawn off from the low pressure column and fed to the crude argon column to values above 70% argon are becoming less and less. The reason for this is that in order to achieve high argon concentrations, the majority of the theoretical plates in the crude argon column are necessary to remove the last percentages of oxygen from the argon. That is, at high The initial concentration of the fluid introduced into the crude argon column plays a less important role in purity requirements.

The object of the present invention is therefore to demonstrate an improved process for the production of argon by low-temperature air separation.

This object is achieved according to the invention by a method of the type mentioned at the outset, the argon concentration in the stream taken from the second section being between 15% and 50%, preferably between 15% and 40%, particularly preferably between 20% and 35%.

The invention is based on the knowledge that, given the quantity and purity of the argon product, an increase in the initial concentration of argon in the stream introduced into the crude argon column leads to a reduction in the quantity of steam to be transferred. This is positive in that the cross-section of the crude argon column can be reduced accordingly and costs can be saved.

However, such an increase in the argon concentration in the side vent of the air separation column is associated with a more complicated design of the air separation column and more complex control. It should also be noted that the advantages of the argon concentration in the side vent from the air separation column become less and less with high product requirements, since, as described above, in this case the number of theoretical plates in the crude argon column depends essentially on the final concentration to be achieved and not on the Initial concentration depends.

Studies have now shown that the minimum amount of steam that has to be fed to the crude argon column for proper function initially decreases with increasing argon concentration, but remains the same from an argon concentration of 50%. This means that a further enrichment of argon in the side draw to values above 50% does not result in any further reduction in the amount of steam to be introduced into the crude argon column and thus no possibility of a further cross-sectional reduction of the crude argon column. There remains only the advantage of a higher argon concentration in the mixture fed to the crude argon column. However, since the number of theoretical plates in the crude argon column is essentially independent of the one with high demands on the argon purity Starting concentration is, a further increase in the argon concentration in the stream taken from the air separation column no longer makes sense. In the context of the present invention, this fact was examined in more detail and it was found that an argon concentration between 15% and 50% in the stream taken from the second subsection is particularly favorable.

In practice, it has been found that a method in which a stream with an argon concentration between 15% and 40%, preferably between 20% and 35%, is drawn from the second subsection has particular advantages.

The invention is particularly advantageous when using a dividing wall column. In this case, the rectification system has at least one air separation column, which has three rectification sections arranged in series, each of which adjoining rectification sections are connected to one another on the gas and liquid side. The middle rectification section has a dividing wall which divides the rectification section into two sections. Within the second rectification section, gas and liquid exchange between the two sections is prevented by the partition. However, both sections are connected on the flow side to the rectification section above and below.

Instead of a dividing wall column, the division into two sections through which the flow is parallel can also be carried out by means of two columns arranged parallel to one another. Liquid is drawn off from a first air separation column at an intermediate point and fed to a second column. Gas is led out of the first air separation column at a second intermediate point and introduced into the second column. Gas and liquid formed at the top of the second column from the bottom of the second column are returned to the first air separation column, preferably at the two intermediate points. In this version, the two sections separated on the flow side are not realized by a partition, but by two columns connected in parallel.

The current withdrawn from the second section, depending on the design, either from the air separation column or from the second column, is preferably conducted into a crude argon column. The sump liquid obtained there, which essentially contains oxygen, is preferably in the second subsection returned, that is, in the section from which the argon-containing fraction is also removed.

The invention is preferably suitable for a rectification system which has a pressure column and a low-pressure column, the dividing wall being arranged in the low-pressure column, and an oxygen-enriched fluid, preferably bottom liquid, being introduced from the pressure column into the first section.

The advantages of the process according to the invention are particularly evident when argon with a high purity of more than 95%, preferably more than 98% and / or argon with an oxygen content of less than 100 ppm, preferably less than 10 ppm, is obtained in the crude argon column shall be. The invention is particularly advantageous when more than 100 theoretical trays, preferably between 150 and 200 theoretical trays, are used in the raw argon column. In these cases, the height of the raw argon column is determined by the number of theoretical plates required for the high final purity. The diameter of the crude argon column can, however, be significantly reduced compared to conventional processes without a dividing wall column.

Packings for rectification are preferably used in the air separation column. It is advantageous here if the packs are arranged in a plurality of areas, so-called beds, one above the other, the liquid to be rectified and / or the gas to be rectified being collected between two beds and redistributed to the next pack bed. Are other internals or devices for rectification in the

Air separation column used, it has also proven to be useful to provide collectors and / or distributors in the air separation column at certain intervals, so as to counteract distribution in the column.

The partition between the two divided areas in the air separation column preferably ends at the upper or lower end of a packing bed, or when using other column internals at the upper or lower end of the corresponding area, which is separated from the adjacent area by a collector / distributor. Since collectors / distributors are already arranged at these joints between two pillar areas, the partition must be used no additional collectors / distributors are provided. Only the collector / distributor located directly above the partition wall has to be converted in such a way that it distributes the liquid in the desired manner over the two sections separated from one another by the partition wall. The same applies if, instead of a dividing wall column, a second column arranged parallel to the first air separation column is used.

It has proven to be particularly advantageous to divide the air separation column, in particular the low-pressure column of a double-column system, into four areas, or when using packs in four packing beds, and to provide the partition at the level of the second and third areas.

In the first and the second subsection, mass transfer elements are preferably used, which bring about the same pressure drop for the rising gas.

The invention and further details of the invention are explained in more detail below with reference to exemplary embodiments shown in the drawings. Here show:

1 shows a device for carrying out the method according to the invention, FIG. 2 shows another embodiment according to the invention, FIG. 3 shows the specific amount of steam to be fed to the crude argon column as a function of its argon concentration and

Figure 4 shows the argon yield as a function of the argon concentration in the vapor supplied to the crude argon column.

FIG. 1 shows the rectification part of a low-temperature air separation plant with argon extraction. After appropriate cleaning and cooling, feed air 1 is introduced into the pressure column 2. The oxygen-enriched liquid accumulating in the sump of the pressure column 2 is transferred via line 3 into the low pressure column 4. The low pressure column 4 is designed as a dividing wall column. 4 packs are provided as rectification elements in the low-pressure column, which are arranged in a plurality of beds 19, 20, 21, 22 lying one above the other, each having a height of approximately 6 m. Collectors / distributors 23, 24, 25, 26, 27 are provided between each two beds for collecting and distributing the liquid flowing downward in the low-pressure column 4.

In a central region of the low-pressure column 4, a partition 5 is arranged such that the low-pressure column 4 is divided into two sections 6, 7. The partition 5 extends over the entire length of the two middle

Pack beds 20 and 21. A gas and liquid exchange between the two separated sections 6, 7 is not possible in this area.

The beds 19 and 22 below and above the separated sections 6, 7, on the other hand, extend over the entire cross-section of the low-pressure column 4, so that the gas or liquid flows ascending or flowing separately in the two sections 6, 7 are brought together again.

The low-pressure column 4 is fed into the divided subsection 6 via line 3 sump liquid from the pressure column 2. Turbine air can also be introduced into the low-pressure column 4 via line 12. At the top of the low-pressure column 4, gaseous product nitrogen can be obtained via line 8. Furthermore, a deduction 9 for impure nitrogen is provided above the divided sections 6, 7. Gaseous or liquid product oxygen can be removed from the sump of the low-pressure column 4 via the lines 10 and 11.

Packs with the same specific surfaces are installed in the two subsections 6 and 7. The steam rising in the low-pressure column 4 thus experiences the same pressure loss in both sections 6, 7. The flowing down

Liquid is distributed to the two sections 6, 7 by means of distributors 24, 25. The same amount of liquid is preferably applied to both sections 6, 7. However, in order to optimize the process management, it can make sense to provide different liquid throughputs in sections 6 and 7. The distribution of the rising steam over the two sections 6, 7 is advantageous as a function of the counter-flowing amounts of liquid and the pressure losses in the packing beds 20, 21.

A stream 13 essentially containing argon and oxygen with an argon concentration of 35% is drawn off from the section 7 and introduced into a crude argon column 14 provided with packings. The oxygen-argon mixture is rectified in the crude argon column 14. At the top of the crude argon column 14, the argon formed is condensed in a top condenser 15 and in part obtained as product 16 with a residual oxygen content of less than 10 ppm, and in part 17 is returned to the crude argon column 14 as reflux liquid. Liquid oxygen collects in the sump of the crude argon column 14 and is returned via line 18 to the divided section 7 of the low-pressure column 4.

In the low pressure column 4 are the infeeds of

Bottom liquid 3 separated from the pressure column 2 and turbine air 12 from the argon vent 13. In this way, significantly higher argon concentrations can be set in the argon vent 13 than in columns without a partition.

In Figure 2, an embodiment of the invention is shown in which instead of

Partition 5, a parallel side column 30 is provided. The same elements are provided with the same reference numbers in both figures.

The low-pressure column 4 is designed in this case without a partition. The liquid flowing down from the rectification section 22 is distributed on the one hand by means of the distributor 24 to the beds 20, 21 which form the first section. The second section is implemented by the side column 30. A portion of the liquid flowing down from the packing bed 22 is drawn off from the low-pressure column 4 via line 31 and fed to the side column 30 at the top. Gas formed at the top of the side column 30 is via line 32 above the

Packed bed 21 returned to the low pressure column 4. Correspondingly, liquid is passed from the side column 30 into the low-pressure column 4 by means of the line 33 or gas from the low-pressure column 4 into the side column 30 by means of the line 34. The procedures in the embodiments according to FIGS. 1 and 2 are the same, only in FIG. 2 the rectifying sections 20, 21 of the low-pressure column 4 represent the first section 6 and the side column 30 the second section 7. Correspondingly, the streams 3, 12 are introduced into the low-pressure column 4, while the stream 13 containing argon is removed from the side column 30.

Within the scope of the present invention, the specific, i.e. determines the amount of steam based on the amount of argon product as a function of the argon concentration of the steam. The determined dependency is shown in FIG. 3. An argon product purity of 98.5% and a constant argon yield, i.e. a constant ratio of argon product to the amount of argon in the feed air.

The solid curve shows the theoretical minimum amount of steam with an infinite theoretical number of trays. The dashed curve shows the course of the states calculated for a theoretical number of plates of 50. Both curves have essentially the same course. However, it can be seen from the curve for a finite number of trays that in this case approximately 30 to 40% larger amounts of steam have to be used compared to the theoretical curve.

Both curves show that with increasing argon concentration, less and less steam has to be transferred into the crude argon column 14 in order to obtain the desired purity and amount of argon. However, the curves approach a lower limit value at about 50% argon concentration. At higher

Argon concentrations, or only a slight further reduction in the amount of steam to be supplied, can be expected.

As a result of the decreasing amount of steam with increasing argon concentration in the feed stream to the crude argon column 14, its diameter can be made correspondingly smaller. The reduction in the amount of steam can only be observed up to an argon concentration of about 50%. On the other hand, if the concentration is increased to more than 50%, no further reduction in the amount of steam can be achieved under the present conditions, so that no further reduction in the crude argon column cross section can be achieved. The one with the However, the increase in concentration associated with regulation in the low pressure column increases significantly.

Also, the number of theoretical plates in the crude argon column 14 cannot be significantly reduced by increasing the argon concentration in the steam 13 to be supplied at a desired product purity of 98.5%, since the number of plates is not due to the final concentration to be achieved at high product purities is determined by the initial concentration.

The low-pressure column 4 is operated according to the invention in such a way that an argon concentration of 45% is achieved in the side draw 13. At this concentration, the amount of steam introduced into the raw argon column 14 can be minimized and the diameter of the raw argon column 14 can be reduced in accordance with the amount of steam.

FIG. 4 shows the argon yield as a function of the argon concentration of the vapor fed into the argon column. The solid curve shows the calculated values for a short partition, the dashed curve for a long partition. The number of trays in the low pressure column was kept constant.

The solid curve shows that the argon yield remains essentially constant in a range between 10 and 25% argon concentration in the supplied steam. The curve breaks off at 25% because no higher argon concentrations can be achieved with the assumed partition wall length. In the case of a longer partition wall, which was used to calculate the dashed curve, an essentially constant argon yield can also be found in the range of higher argon concentrations above 30% to 90%. Accordingly, increasing the argon concentration does not have a negative effect on the yield.

Claims

claims

1. A method for the production of argon by low-temperature separation of air in a rectification system which has three rectification sections arranged in series, the first and the second as well as the second and the third rectification sections being connected to one another on the gas and liquid side, and the second rectification section has two sections, which are not connected to one another on the gas and liquid sides and are flowed through in parallel, a fluid containing oxygen and argon being introduced into the first of the two sections and a stream containing oxygen and argon being withdrawn from the second of the two sections, characterized in that that the argon concentration in the stream (13) taken from the second subsection (7, 30) is between 15% and 50%, preferably between 15% and 40%, particularly preferably between 20% and 35%.

2. The method according to claim 1, characterized in that the rectification system has at least one air separation column (4) with three rectification sections (19, 20, 21, 22) arranged in series, the second rectification section (20, 21) having a dividing wall running in the longitudinal direction of the column (5), whereby the air separation column (4) at the level of the partition (5) is divided into a first (6) and a second section (7).

3. The method according to claim 1, characterized in that the rectification system has at least a first air separation column (4) and a second column (30), the gas and liquid side with at its upper and lower ends

Intermediate locations of the first air separation column (4) are connected, the section (20, 21) located between the intermediate locations of the first air separation column and the second column (30) forming the two subsections.

4. The method according to claim 3, characterized in that the oxygen and argon-containing stream (13) is removed from the second column (30).

5. The method according to any one of claims 1 to 4, characterized in that the stream (13) taken from the second subsection (7, 30) is fed to a crude argon column (14).

6. The method according to claim 5, characterized in that bottom liquid from the crude argon column (14) in the second section (7, 30) is returned.

7. The method according to any one of claims 5 or 6, characterized in that argon with a purity of more than 95%, preferably more than 98%, is obtained in the crude argon column (14).

8. The method according to any one of claims 5 to 7, characterized in that argon is obtained with an oxygen content of less than 10 ppm in the crude argon column (14).

9. The method according to any one of claims 5 to 8, characterized in that the crude argon column (14) has more than 100, preferably 150 to 200 theoretical plates.

10. The method according to any one of claims 1 to 9, characterized in that in the rectification sections (19, 20, 21, 22) at least partially packs are used for rectification.

11. The method according to claim 10, characterized in that the oxygen and argon-containing fluid is collected and / or distributed between two rectification sections (23, 24, 25, 26, 27).

12. The method according to any one of claims 1 to 9, characterized in that the rising in the rectification system gaseous, containing oxygen and argon fluid in the first and in the second section (6, 7) the same

Experiences pressure loss.

13. The method according to any one of claims 1 to 12, characterized in that the rectification system has a pressure column (2) and a low pressure column (4), wherein the partition (5) is arranged in the low pressure column (4), and wherein in the first section (6) an oxygen-enriched fluid (3) is introduced from the pressure column (2).