DE10216269A1 - Process for recovering argon from air in a rectification system using a low temperature decomposition method comprises removing a stream having a specified argon concentration from a partial section of a rectification section - Google Patents

Abstract

Process for recovering argon from air in a rectification system in which the argon concentration in the stream removed from a second partial section lies between 15% and 50%, preferably between 15% and 40%, especially between 20% and 35%. Process for recovering argon from air in a rectification system using a low temperature decomposition method comprises passing a fluid containing oxygen and argon into the first of the two partial sections of a second rectification section, and removing a stream (13) containing oxygen and argon from the second section (7) of the two partial sections. The argon concentration in the stream removed from the second partial section lies between 15% and 50%, preferably between 15% and 40%, especially between 20% and 35%.

Description

The invention relates to a process for the production of argon Cryogenic air separation in a rectification system that has at least one Air separation column, which has a partition extending in the longitudinal direction of the column has, whereby the air separation column at the level of the partition into a first and a second section is divided, the first section being an oxygen and argon-containing fluid is introduced and the second section Current containing oxygen and argon is withdrawn.

The boiling point of argon is between the boiling points of oxygen and Nitrogen. In the classic low-temperature separation of air through two stages Rectification accumulates the argon in a central area of the low pressure column on. This area is usually used to obtain argon Extracted fraction, which consists essentially of oxygen and argon. This with About 10% argon-enriched fraction is the so-called crude argon column fed in the rectification separation of oxygen and argon is carried out. Argon can be drawn off at the top of the crude argon column and into the bottom of which collects a liquid which essentially contains oxygen, the is then returned to the low pressure column.

In practice, argon purities of over 95% are often required. In which In known processes, the crude argon column is only about 10% argon containing current supplied. In order to achieve the desired high argon purities concentrate and around the head of the raw argon column the desired To be able to draw off the amount of product has to go into the crude argon column considerable Amounts of steam are introduced and rectified in this. Must be correspondingly large the cross-section of the crude argon column can be chosen, creating significant Investment costs arise.

In the field of hydrocarbon production in particular, it is already known use so-called dividing wall columns for the decomposition of ternary mixtures. at a dividing wall column is a part of the column by an in Column longitudinally arranged wall divided into two sections. at Appropriate procedures can be found in the section on one side of the Partition initiated three-component mixture in a single column in three Fractions to be disassembled. The lightest boiling component can be on the head the dividing wall column, the middle boiler on the opposite of the feed Side of the partition and the high-boiling component obtained from the sump become. Compared to a column without a partition, the Partition column at the side draw achieved higher concentrations of the medium boiler become.

In low-temperature air separation, dividing wall columns have so far been used because of their difficult regulation hardly used. A method is described in EP 0 638 778 B1 described for the low-temperature separation of air in a dividing wall column. The The low-pressure column is divided into a central area by a partition. On one side of the partition is fed sump liquid from the pressure column, while the argon-containing fluid is drawn off on the other side of the partition. To better regulate the process, on the side of the partition on which the Bottom liquid is introduced, a waste fluid is removed. The process parameters are chosen so that the argon-containing fluid obtained has an argon concentration of at least 70%.

With a product requirement in the range of 70% argon concentration, the the method described in EP 0 638 778 B1 is the number of theoretical trays reduced in the raw argon column and thus construction height can be saved. However high argon concentrations of, for example, more than 95% are required Advantages of concentrating the withdrawn from the low pressure column and the Fluids supplied to the crude argon column become less and less than 70% argon. This is due to the fact that the majority of theoretical plates in the raw argon column to remove the last percentages of oxygen from the argon are necessary. That is, at high The initial concentration of the crude argon column plays a role in purity introduced fluids play a minor role.

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

This object is achieved by a method of the type mentioned dissolved, the argon concentration in that taken from the second section Current between 15% and 50%, preferably between 15% and 40%, particularly preferably between 20% and 35%.

The invention is based on the knowledge that for a given quantity and Purity of the argon product increases the initial concentration of argon in the current introduced into the crude argon column is a reduction in the amount to be transferred Amount of steam. This is positive in that the cross section of the Raw argon column can be reduced accordingly and costs can be saved.

However, such an increase in the argon concentration in the side draw is the Air separation column with a more complicated version of the air separation column and one complex control. It should also be noted that the advantages of Argon concentration in the side vent from the air separation column at high Product requirements become less and less because, as described above, in this The number of theoretical plates in the crude argon column is essentially the same final concentration to be achieved and does not depend on the initial concentration.

Studies have now shown that the minimum amount of steam that the Raw argon column must be fed with for proper functioning increasing argon concentration initially decreases, from an argon concentration of 50% remains the same. That is, further argon enrichment in the side vent to values over 50% brings no further reduction in the crude argon column amount of steam to be introduced and therefore no possibility of another Cross-sectional reduction of the crude argon column with itself. Only the advantage remains a higher argon concentration in the mixture fed to the crude argon column. However, since there are high demands on the argon purity, the number of theoretical Soils in the crude argon column are essentially independent of the Initial concentration is a further increase in the argon concentration in the electricity taken from the air separation column no longer makes sense. As part of the In the present invention, this fact was investigated in more detail and found that an argon concentration between 15% and 50% in that of the air separation column withdrawn electricity is particularly cheap.

In practice, it has been found that a procedure in which the Air separation column a stream with an argon concentration between 15% and 40%, preferably between 20% and 35%, is taken, brings particular advantages.

The stream withdrawn from the air separation column is preferably converted into a Raw argon column headed. The one that essentially contains oxygen Bottom liquid is preferably in the second section of the air separation column returned, that is to say in the section to which the argon-containing fraction also belongs is removed.

The invention is preferably suitable for a rectification system which has a pressure column and has a low pressure column, the partition in the low pressure column is arranged, and wherein in the first section an oxygenated Fluid from the pressure column, preferably bottom liquid, is introduced.

The advantages of the method 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, to be obtained in the raw argon column. The invention is then special advantageous if more than 100 theoretical plates are preferred in the raw argon column between 150 and 200 theoretical plates. In these cases it is Height of the raw argon column anyway due to the high final purity required Number of theoretical floors set. The diameter of the crude argon column can but clearly compared to the conventional process without a dividing wall column be reduced.

Packings for rectification are preferably used in the air separation column. It is advantageous here if the packs are stacked in several Areas, so-called beds, are arranged, with the rectified Liquid and / or the gas to be rectified are collected between two beds and redistributed to the next pack bed. Instead of Packs of other internals or devices for rectification in the Air separation column used, it has also proven itself, collectors and / or To provide distributors at certain intervals in the air separation column, so Counteracting maldistributions in the pillar.

The partition between the two divided areas in the air separation column preferably ends at the top or bottom of a packing bed, or when using other column internals at the top or lower end of the corresponding area, which is collected by a collector / distributor adjacent area is divided. Because there are two pillar areas at these joints anyway, collectors / distributors are arranged when using the partition no additional collectors / distributors are provided. Only the one immediately Collectors / distributors located above the partition must be converted so that he has the liquid in the desired way on the two through the partition divided sections distributed.

The air separation column, in particular, has proven to be particularly favorable the low pressure column of a double column system, in four areas, or at the Use packs in four pack beds to divide and divide the partition to be provided at the level of the second and third area.

In the first and second sections are preferred Mass transfer elements are used that have the same pressure drop for the ascending Cause gas.

The invention and further details of the invention are described below of exemplary embodiments illustrated in the drawings. in this connection demonstrate:

Fig. 1 shows an apparatus for performing the method according to the invention,

Fig. 2 shows the amount of steam to be fed to the crude argon column as a function of its argon concentration and

Fig. 3, the argon recovery as a function of the argon concentration in the crude argon column the supplied steam.

In Fig. 1, the rectifying section of a cryogenic air separation plant is shown with argon recovery. Feed air 1, after cleansing and cooling, introduced into the pressure column second The oxygen-enriched liquid collecting 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 are provided between each two beds for collecting and distributing the liquid flowing downward in the low-pressure column 4 . For reasons of clarity, the collectors / distributors located between the beds 20 , 21 are not shown in FIG. 1.

In a central area 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 packing 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 to the partitioned section 6 via line 3 bottoms 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 .

In sections 6 and 7 , packs with the same specific surfaces are installed. 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 the 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 be very useful to provide different liquid throughputs in sections 6 and 7 . The distribution of the rising vapor over the two sections 6 , 7 is advantageous depending on the counter-flowing quantities of liquid and the pressure losses in the packing beds 20 , 21 .

A stream 13 containing essentially argon and oxygen with an argon concentration of 35% is withdrawn from 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 resulting argon is condensed in a head condenser 15 and recovered as the product in part 16 with a residual oxygen content of less than 10 ppm, given up to the part 17 as a reflux liquid again to the crude argon column fourteenth Liquid oxygen collects in the sump of the crude argon column 14 and is returned via line 18 to the section 7 of the low-pressure column 4 .

In the low-pressure column 4 , the feeds of bottom liquid 3 from the pressure column 2 and turbine air 12 are separated from the argon vent 13 by the partition 5 . In this way, significantly higher argon concentrations can be set in the argon vent 13 than in columns without a partition.

In the context of the present invention, the amount of steam to be fed to the crude argon column 14 was determined as a function of the argon concentration of the steam by means of simulations. The determined dependency is shown in FIG. 2. An argon product purity of 98.5% and a constant argon yield were assumed.

The solid curve shows the theoretical minimum amount of steam at infinite theoretical number of trays. The dashed curve shows the course of the one theoretical number of soils from 50 calculated states. Both curves have essentially the same course. From the curve for finite number of trays, however, is too deduce that in this case about 30 to 40% of the theoretical curve larger amounts of steam must be used.

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 approximately 50% argon concentration. At higher argon concentrations, no or only a slight further reduction in the amount of steam to be supplied is to 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. However, 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 over 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. However, the regulatory effort in the low-pressure column associated with the increase in concentration 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 with 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.

In Fig. 3, the argon recovery is shown as a function of the concentration of the argon fed into the argon column vapor. The solid curve shows the calculated values for a short partition, the dashed curve for a long partition.

The solid curve shows that the argon yield is in one area essentially between 10 and 25% argon concentration in the fed steam remains constant. The curve breaks off at 25%, since with the assumed Partition length no higher argon concentrations can be achieved. At a longer partition, which is used to calculate the dashed curve was also in the range of higher argon concentrations over 30% up to 90% determine essentially constant argon yield. An increase in Accordingly, argon concentration does not have a negative effect on the yield.

Claims (11)

1. A method for the production of argon by low-temperature separation of air in a rectification system which has at least one air separation column which has a dividing wall running in the longitudinal direction of the column, whereby the air separation column is divided into a first and a second section at the height of the dividing wall, the first Section is introduced a fluid containing oxygen and argon and a stream containing oxygen and argon is withdrawn from the second section, characterized in that the argon concentration in the stream ( 13 ) withdrawn from the second section ( 7 ) 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 stream ( 13 ) taken from the second section ( 7 ) is fed to a crude argon column ( 14 ). 3. The method according to claim 2, characterized in that bottom liquid from the crude argon column ( 14 ) in the second section ( 7 ) of the air separation column ( 4 ) is returned. 4. The method according to any one of claims 2 or 3, characterized in that argon with a purity of more than 95%, preferably more than 98%, is obtained in the crude argon column ( 14 ). 5. The method according to any one of claims 2 to 4, characterized in that argon is obtained with an oxygen content of less than 10 ppm in the crude argon column ( 14 ). 6. The method according to any one of claims 2 to 5, characterized in that the crude argon column ( 14 ) has more than 100, preferably 150 to 200 theoretical plates. 7. The method according to any one of claims 1 to 6, characterized in that packs for rectification are used at least in part in the air separation column ( 4 ). 8. The method according to claim 7, characterized in that the air separation column ( 4 ) has a plurality of regions ( 19 , 20 , 21 , 22 ) arranged one above the other, the fluid containing oxygen and argon being collected and / or distributed between two regions, and the partition ( 5 ) ends at the top or bottom of one of the areas ( 20 , 21 ). 9. The method according to claim 8, characterized in that the air separation column has four areas ( 19 , 20 , 21 , 22 ) and that the partition ( 5 ) extends over the second and third areas ( 20 , 21 ). 10. The method according to any one of claims 1 to 9, characterized in that in the air separation column ( 4 ) gaseous rising oxygen and argon-containing fluid in the first and in the second section ( 6 , 7 ) experiences the same pressure loss. 11. The method according to any one of claims 1 to 10, characterized in that the rectification system has a pressure column ( 2 ) and a low pressure column ( 4 ), the partition ( 5 ) being 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 ).