JPH076736B2 - Cryogenic rectification method and device using hybrid type argon column - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a cryogenic rectification method and apparatus for separating a feed containing oxygen, nitrogen and argon into an oxygen-rich component, a nitrogen-rich component and an argon-rich component.

[0002]

BACKGROUND OF THE INVENTION An industrial system often used for separating mixtures containing oxygen, such as air, nitrogen and argon is cryogenic rectification. Separation is driven by increasing the feed pressure, which is generally accomplished by compressing the feed in a compressor before it is introduced into the column system. Separation is carried out by passing liquid and gas in countercurrent contact in a gas-liquid contact element in a column or columns, whereby more volatile component or components are passed from the liquid to the vapor. However, the less volatile component or components pass through the liquid from the vapor. As the vapor moves up the column, the vapor becomes progressively enriched with volatile components, while as the liquid flows down the column, the liquid becomes progressively enriched with less volatile components. In general, cryogenic separation is in a main column system that includes at least one column that separates the feed into a nitrogen-rich component and an oxygen-rich component, and feeds from the main column system are enriched with argon and oxygen. It is carried out in an auxiliary argon column which separates the components.

The power cost to operate the feed compressor and thereby drive the separation is the major operating cost for separation. The pressure drop in the system places a heavy burden on feed compression and results in increased feed compression requirements. It is desirable to operate the cryogenic rectification system with the lowest possible pressure drop, thereby reducing the feed compression burden. Furthermore, the lower the pressure level in the column used, the greater the relative volatility between the components. The greater the volatility between the components in the column, the easier the separation, which ultimately increases the argon, oxygen and nitrogen product recovery. The conventional argon column has been operated by filling the entire packing with a small pressure drop.

In the operation of an argon column, a vapor stream having a relatively high argon concentration is withdrawn from the main column system and passed into and elevated in the argon column,
Meanwhile, the argon concentration is gradually enriched. Crude argon product is recovered from the top of the argon column. The vapor raises the argon column due to the pressure gradient between the feed to the argon column and the crude argon product. The pressure of the argon column feed is determined by the main column conditions at the vapor withdrawal point.

[0005]

Operation of an argon column at reduced pressure is subject to two constraints regarding how low operating pressures can be achieved without harm. One constraint is that subatmospheric pressures at the top of the argon column should be avoided to avoid air leaks into the system. Another constraint involves the temperature differential for the top condenser of the argon column. Reducing the pressure at the top of the argon column also results in a lower temperature, thus reducing the temperature difference between the condensing argon and the boiling kettle liquid in the argon condenser. A minimum temperature difference of about 0.7 ° K is required for effective operation of the condenser. When the feed pressure to the argon column is reduced through the use of a valve,
A significant disadvantage arises in that the liquid at the bottom of the argon column, which must be returned to the main column and returned, is no longer at a pressure below the pressure in the main column at the return point. Therefore, repressurization of the liquid is necessary, for example by pump pressurization or by increasing the height of the argon column. This repressurization is costly and results in system inefficiency.

The object of the present invention is therefore to provide oxygen, nitrogen which makes it possible to operate an argon column at a reduced mean pressure without having to repressurize the liquid which is passed from there back into the main column. And a cryogenic separation method for separating a feed containing argon.

Yet another object of the present invention is to provide an argon column in a cryogenic air separation unit comprising a main column system and an auxiliary argon column without the need for increasing the pressure of the liquid passed from the argon column to the main column. It is an object of the present invention to provide a cryogenic separation device capable of operating at a reduced average pressure.

[0008]

The present inventor has found that the configuration of the argon column is modified so that a combination of the lower tray section and the upper packing section is suitable for solving these problems. .

In a method aspect, the invention comprises: (A) feeding a feed comprising oxygen, nitrogen and argon to a main column system comprising at least one rectification column, and (B) in the main column system. Separating the feed into a nitrogen-enriched component and an oxygen-enriched component by countercurrent gas-liquid contact of (C) passing a fluid containing argon and oxygen from the main column system through an argon column. (D) separating the fluid into an argon-enriched component and an oxygen-enriched component by countercurrent gas-liquid contact in an argon column;
Wherein (E) countercurrent gas-liquid contact in said argon column in a gas-liquid contacting element with a tray in the lower part of the argon column and with a packing in the remainder of the argon column. Provided is a cryogenic rectification method carried out in a contact element.

The invention, in an apparatus aspect, comprises (A) a main column system comprising at least one rectification column having a gas-liquid contacting element, (B) a gas-liquid contacting element comprising a tray in the lower part and the balance. And an argon column having a gas-liquid contacting element with packing in (C), and (C) a cryogenic separator comprising means for providing fluid from the main column system into the lower portion of the argon column.

DEFINITION OF TERMS The term "column" as used herein refers to a column or zone for carrying out distillation or fractional distillation, that is, separation of a fluid mixture by countercurrent contact of liquid and gas phases. Means a contacting column or zone which provides, for example, by contacting the vapor and liquid phases in a series of vertically spaced trays or plates mounted in the column or in packing elements packed in the column. Be implemented. Further details of the distillation column can be found in R. R., published by McGraw-Hill Book Company. H.
See Perry et al., "Chemical Engineers Handbook," pages 13-3, continuous distillation process. The term "double column" as used herein refers to a column composed of a high pressure column and a low pressure column, in which the upper end of the high pressure column is brought into contact with the lower end of the low pressure column in a heat exchange relationship. A more detailed discussion of the double tower can be found in "The Separation of Gases", Chapter VII, "Industrial Air Separation," by Ruheman, Oxford University Press (1949).

As used herein, an "argon column" is a column that progressively enriches with argon by countercurrently contacting an upwardly flowing vapor with a descending liquid and recovers the argon product from the column. Say.

"Indirect heat exchange" means bringing two fluid streams into a heat exchange relationship without physical contact between fluids or mutual mixing. "Gas-liquid contact element" refers to equipment used within the column to promote mass transfer or component separation at the gas-liquid interface in a two-phase countercurrent flow. A "tray" is a substantially flat plate with an opening and a liquid inlet and outlet that is placed in a column that allows liquid to flow across the plate as vapor flows through the opening, allowing mass transfer between two phases. A plate that is called. "Packing" is a defined form, dimension used as internal packing in a column to provide a surface area for a liquid to enable mass transfer at the gas-liquid interface in a two-phase countercurrent flow. And any shape having a solid or hollow body.
"Chaotic packing" refers to packing in which the individual members have no particular orientation with respect to each other or the column axis. "Organized packing" refers to packing in which the individual members have a particular orientation with respect to each other or the column axis. By "theoretical stage" is meant the ideal contact between the upwardly flowing vapor and the downwardly flowing liquid into one stage so that the outgoing flow is in equilibrium.

[0014]

The tray in the lower part of the argon column not only functions as a gas-liquid contact means to effect mass transfer between the ascending vapor and the descending liquid, but the argon column operates at a lower average pressure level. Acts as a means to create a pressure reduction at the inlet of the argon column. Therefore, most of the benefits from low pressure operation, such as improved resolution, are realized while at the same time allowing the return of fluid from the argon column to the main column system without the need for its pressurization.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The method and apparatus of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, oxygen, such as air,
A feed 1 containing nitrogen and argon is passed through a filter 2 to remove dust and other particulate matter. The filtered feed (air) 3 is generally 4.9 to 13.3 kg / cm ² absolute pressure (70 to
Compressed to a pressure in the range of 190 psia). The compressed feed (air) 5 is passed through a weak purification 6 to remove high boiling impurities such as water, carbon dioxide and hydrocarbons. The purified compressed feed (air) 7 is cooled in the heat exchanger 8 to near the liquefaction temperature by indirect heat exchange with the product and waste streams from the column. Purified,
The compressed and cooled feed (air) 9 is then
It is introduced into the first tower 10 which is a high pressure tower of the main tower system which is a double tower type. Other main tower systems that can be used with the present invention include single towers, as well as two or more towers arranged in series. The tower 10 is generally 4.2 to 12.6 kg / c.
It is operated at a pressure in the range of m ² absolute pressure (60-180 psia). A small portion 40 of the feed (air) is withdrawn from the middle of the heat exchanger 8 and expanded in the turbine 41 and into the post low pressure column 13 below the nitrogen withdrawal point but below the argon column feed. It is introduced at a point above the extraction point. These extraction points will be described in detail below. The tower 13 is here the low-pressure tower of the double tower main tower system.

In the column 10, the feed (air) is separated into a nitrogen-enriched vapor and an oxygen-enriched liquid by rectification. Nitrogen-enriched vapor 11 is passed from column 10 through conduit means to a main condenser 12 which is preferably located in the second column 13. The main condenser 12 may also be physically located outside the wall of the column 13. In the main condenser 12, the nitrogen-enriched vapor 11 is condensed by indirect heat exchange with the bottom liquid of the column 13 that reboils. The resulting nitrogen-enriched liquid 14 is passed as reflux to column 10 through conduit means. A portion of the resulting nitrogen-enriched liquid, generally in the range of 20-50%, is
Passed to No. 3 at or near its top.

Oxygen-enriched liquid 16 is withdrawn from the first column 10 and passed into a post argon column overhead condenser 17,
Here, it is partially evaporated by indirect heat exchange with the top vapor of the argon column. The vapors and liquids produced are passed into the column 13 as streams 18 and 42, respectively, below the nitrogen withdrawal point and above the argon column feed withdrawal point.

The second column 13 is at a lower pressure than the first column 10 and generally 0.8 to 3.2 kg / cm ² absolute pressure (12
Operated at pressures in the range of ~ 45 psia). In the second column 13, the fluid introduced therein is separated into a nitrogen-enriched component and an oxygen-enriched component by rectification, which can be recovered as a nitrogen product and an oxygen product, respectively. Oxygen products can generally be recovered as a gas and / or liquid having a purity of greater than about 99%. The gaseous oxygen product is withdrawn from the second column 13 at a point above the main condenser 12, passed through the heat exchanger 8 as stream 19 and stream 2
Collected as 0. The nitrogen product, which generally has a purity of greater than about 99.9%, flows from the top of second column 13 to stream 22.
As heat, passed through heat exchanger 8 and stream 24
Will be collected as. A waste nitrogen stream 25, which facilitates the operation of the separation system, is also withdrawn from the second column, passed through the heat exchanger 8 and discharged as stream 23. Stream 25 is withdrawn from the second column 13 at a point above the point at which the nitrogen enriched stream is introduced.

FIG. 1 illustrates one preferred arrangement in which all gas-liquid contact elements in column 10 are trays 44 and all gas-liquid contact elements in column 13 are packing 43. . The gas-liquid contact elements in column 10 can also all be packings or a combination of trays and packings. The gas-liquid contact elements in column 13 can also be all trays or a combination of trays and packing. Such a combined arrangement for column 13 may be such that the column portion between the inlet of stream 40 and the outlet of stream 25 comprises trays and the balance of the gas-liquid contacting element is packing. The packing can be either disordered or organized packing. However, structured packing is preferred over chaotic packing. Examples of structured packings include the Stemman packings described in US Pat. No. 2,047,444, Trans.
Instn. Chem. Engrs. , 41, 1963
Goodloe filling described in US Pat. Nos. 4,186,159 and 4,296,05.
There are more recently developed and more efficiently organized packings such as those described in No. 0.

The separation system of the present invention further includes the production of crude argon. Returning to FIG. 1, stream 26 is tower 1
It is extracted from the middle point of 3. At this point, the argon concentration is at or near the maximum level in the column, typically 10-20%. Stream 26 is generally and preferably first
It is a steam flow as illustrated in the figure. The majority of the remainder of stream 26 consists of oxygen while nitrogen may be present in stream 26 at a concentration of less than 1%.

Stream 26 is passed from the main column system through conduit means to the lower portion of argon column 27. The argon column is generally 0.8-3.2 kg / cm ² absolute pressure (12-4
Operated at pressures in the range of 5 psia). The vapor becomes progressively enriched with argon by flowing up the argon column 27 and countercurrent with the falling liquid.

The argon-enriched vapor is passed from the argon column 27 to the top condenser 17 where it is partially condensed by indirect heat exchange with the partially vaporized oxygen-enriched liquid 16. The partially condensed argon-enriched fluid 29 produced is separated by the separator 3
Passed through 0. Argon-enriched vapor 31 is recovered from separator 30 as crude argon product, which generally has an argon concentration of greater than 96%, while liquid 32 is passed from separator 30 into argon column 27 as a descending fluid. The liquid that collects at the bottom of the argon column 27 and has an oxygen concentration above that of stream 26 is passed into second column 13 as stream 33. The vapor flow through the argon column 27 is provided by the pressure difference between the pressures of stream 26 and 28.

The gas-liquid contacting element inside the argon column 27 comprises at least one tray in the lower part of the argon column. In the broadest embodiment of the present invention, the lower portion of the argon column constitutes 50% below the height of the argon column, wherein the concentration of argon in the vapor and liquid contacted during operation is generally below 75%. . In a preferred embodiment of the invention, the lower part of the argon column constitutes 25% below the height of the argon column, wherein the argon concentration in the vapor and liquid which are in contact during operation is generally below 50%. In a more preferred embodiment of the present invention, the lower part of the argon column constitutes 10% below the height of the argon column, wherein the argon concentration in the vapor and liquid contacted during operation is generally below 25%. In this lower part of the argon column, the gas-liquid contact elements are all trays 45, as illustrated in FIG. The gas-liquid contact element in the remainder of the argon column, where the argon concentration generally exceeds the concentrations specified above, contains packing 46. Preferably the packing is a structured packing.

The number of trays in the lower portion of the argon column can range from a minimum of approximately 1-5 trays to a maximum of approximately 20-30 trays. The number of trays is defined by the tray pressure drop per theoretical plate, the packing pressure drop per theoretical plate, the number of theoretical plates specified between the point at which vapor is withdrawn for feeding to the upper overhead argon column, and Depends on the number of theoretical plates specified in the argon column. The number of trays used should not be so great that the pressure at the top of the argon column drops below atmospheric pressure. This is because there is a risk of contamination of the argon product due to air leaks. The number of trays should not be so great that the pressure of condensing argon vapor at the top of the argon column and thus the temperature is too low for the effective heat transfer performance of the argon condenser. Typically, up to about half of the theoretical plates in an argon column make up trays that do not cause these problems. It enables the operation of the argon column at an average pressure that is lower than the pressure of the column, which is operated entirely with packing, and at the same time the pressure of the main column at the point where fluid is withdrawn for entry into the argon column from the main column. A sufficient number of trays are used to allow the bottom pressure of the argon column to be maintained at about the same pressure.

The fluid passed into the argon column from the main column system is passed into the lower part of the argon column where the gas-liquid contact elements consist of trays, preferably as illustrated in FIG. It is important that the feed stream to the argon column is introduced there from the bottom. Thus, the upwardly flowing vapor stream in the argon column experiences a pressure drop while passing through the trayed compartment, thus establishing a significant pressure gradient in the lower part of the column. The use of packing in the upper section of the argon column reduces the pressure gradient across the rest of the column.
Due to the use of trays at the bottom of the argon column, the pressure at the bottom of the argon column is not different from the pressure of the incoming stream from the main column system, and thus the pressure from the argon column, such as stream 33 in FIG. Liquid can be returned to the main column system without the need for pressurization such as pump pressurization or the addition of a liquid head.

The combined use of trays and packing in an argon column allows operation of the argon column at a low average pressure level compared to the pressure achieved with all packing in the argon column. Thus, the benefit from the improved relative volatility of argon to oxygen at lower pressures allows for improved argon separation and recovery without introducing operational problems at the top or bottom of the argon column. To do.

Any suitable type of tray may be used in the present invention. Examples thereof include sieve trays, bubble cap trays, valve trays and the like. Although trays that produce higher pressure drops per tray are preferred as described herein, the benefits of the present invention are obtained with the use of fewer trays in the argon column. For example, a suitable tray may include a sieve tray with a small effective hole area.

[0028]

FIG. 2 illustrates the pressure profile of a conventional argon column, an argon column with a feed pressure reducing means such as a valve, and the hybrid argon column of the present invention. Referring to FIG. 2, line AB is
1 illustrates the pressure profile of a conventional argon column with all packings placed across the height of the argon column. Line C-D-E illustrates the pressure profile of a conventional, fully packed Argon column where the feed pressure was reduced prior to introduction into the column. Lines A-D-E illustrate the pressure profile of the hybrid (hybrid) argon column of the present invention. As can be seen, the pressure at the top of the hybrid argon column is the same as that of the reduced feed pressure column. However, the pressure at the bottom of the hybrid argon column is
The pressure in the tower with reduced feed pressure is exceeded. Therefore, most of the benefit of the low pressure is realized by the use of a hybrid argon column, while also allowing the return of fluid from the argon column to the main column system without the need for its pressurization.

By using the method and apparatus of the present invention, cryogenic air separation can now be performed with improved argon recovery. In a double column system, the gas-liquid contact element of the low pressure column can consist essentially of packing, thus reducing the pressure drop through the column and reducing feed pressure requirements. In addition, packing is also used in the argon column to improve argon recovery. Moreover, by providing a gas-liquid contact element consisting of a tray in the lower part of the argon column, the required pressure gradient is provided in the argon column without causing a pressure state below atmospheric pressure at the top of the argon column. A suitable vapor upflow is allowed while at the same time maintaining sufficient pressure to return liquid from the argon column back to the main column system without the need for additional pressurization at the bottom of the argon column.

In the method and apparatus of the present invention, the tray in the lower portion of the argon column serves two functions. These trays act as a means to create a pressure reduction at the inlet of the argon column so that the argon column can operate at lower average pressure levels. At the same time, they act as gas-liquid contacting means that effect mass transfer between the ascending vapor and the descending liquid in the argon column.

Although specific embodiments of the present invention have been described in detail, those skilled in the art will appreciate that many modifications can be made within the scope of the invention.

[Brief description of drawings]

FIG. 1 is a schematic flow diagram of one embodiment of the present invention having a double tower main tower system.

FIG. 2 is a graph showing the relationship between the height and pressure of three types of argon towers.

[Explanation of sign]

1 Feed 2 Filter 4 Compressor 6 Purifier 8 Heat Exchanger 9 Purified, Compressed and Cooled Feed 10 First Tower (High Pressure Tower) 11 Nitrogen Enriched Steam 12 Main Condenser 13 Second Tower (Low Pressure) 14) Nitrogen-enriched liquid 16 Oxygen-enriched liquid 17 Argon top condenser 18, 42 Generated vapor and liquid 20 Oxygen product 24 Nitrogen product 25 Waste nitrogen 26 Fluid containing argon and oxygen (crude argon withdrawal stream) 27 Argon Tower 29 Partially Condensed Argon Enriched Fluid 30 Separator 31 Argon Enriched Vapor Product 32 Liquid 33 Flow to Second Column 45 Tray 46 Packing

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Michael James Rocket Ferry Road, Grand Island, New York, USA 2133 (72) Inventor James Robert Dray Kenford, New York, USA Heartford Avenue 267 (56) References JP-A-1-244269 (JP, A) JP-A-59-4871 (JP, A) JP-A- 1-312382 (JP, A) JP-A-59-24168 (JP, A)

Claims (6)

[Claims] 1. A cryogenic rectification process comprising: (A) supplying a feed comprising oxygen, nitrogen and argon to a main column system comprising at least one rectification column, and (B) a main column system. Separating the feed into a nitrogen-enriched component and an oxygen-enriched component by countercurrent gas-liquid contact within the reactor;
(C) passing a fluid containing argon and oxygen from the main column system through the argon column, and (D) countercurrent gas-liquid contacting the fluid in the argon column with an argon-enriched component and an oxygen-enriched component. And (E) countercurrent gas-liquid contacting in said argon column in a gas-liquid contacting element with a tray in the lower part of the argon column and in the remainder of the argon column. Cryogenic rectification method, characterized in that it is carried out in a gas-liquid contact element with packing. 2. A vapor in which the lower part of the argon column is in contact.
And a part where the liquid has an argon concentration of 25% or less.
The method according to claim 1. 3. A patent in which the packing comprises a structured packing.
The method according to claim 1. 4. A cryogenic rectification apparatus comprising (A) gas-liquid contact
A main tower system comprising at least one rectification tower having tactile elements.
Stem, (B) Gas-liquid with tray in lower part
Gas-liquid contact with contact element and filling at the rest
An argon column having a touch element, and (C) the main column system
Fluid from the column into the lower part of the argon column
Cryogenic rectification device comprising means. 5. The height of the argon column is the lower part of the argon column.
The device according to claim 4, which constitutes 10% below the
Place 6. A patent in which the packing comprises a structured packing.
The device according to claim 4.