JPH102664A - Low temperature distillating method for air flow of compressed raw material for manufacturing oxygen products of low purity and high purity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for manufacturing oxygen products having two different purities from one plant of air separating process. SOLUTION: Oxygen product 38 of low purity is produced from a normal low purity tower 25 through a low temperature distillation process for compressed raw material air flow 10 and oxygen product 36 of high purity is produced by refining a flow 35 full of oxygen flowing from distrillation facilities 15, 25 with a high purity tower 23. First process flow 30 is supplied to a re- boiler 31 in a low purity tower and then second process flow 21 having a higher pressure than that of first process flow 30 is supplied to a re-boiler 22 of a high purity tower.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

It is an object of the present invention to efficiently and cost-effectively produce two different purities of oxygen from the same air separation plant when only a small amount of high purity oxygen is required. It is. The present invention also provides a method for producing small amounts of crude argon product, if required, in a factory that regularly produces low purity oxygen. This is consistent with the requirements of a new grassroots steel mill based on the COREX steelmaking process.

[0002]

BACKGROUND OF THE INVENTION In the past, there have been two commonly used methods for producing two different purity oxygens from the same facility. One was to build two independent cryogenic trains, one for each purity. This is expensive and complex.
The other is to design the entire factory for high purity,
A main air compressor discharge pressure of a pressure corresponding to the high purity oxygen was required. This is not energy efficient because much of the air only needs to be boosted to a lower pressure corresponding to generating low purity oxygen.

[0003] A number of efficient factories for producing low-purity oxygen are known in the literature. US Patent No. 47
Nos. 0,075, 4,704,148 and 4,936
No. 099 describes a number of very efficient process cycles using multiple reboiler condensers. However, none of these cycles jointly produce a portion of the oxygen product with a purity higher than 95%.

[0004] US Pat. No. 5,515,833 describes:
A cycle is described in which a portion of the expanded gas from the compander is used to reboil the bottom reboiler of a dual reboiler low pressure (LP) column. This cycle uses one double column assembly for the two products. All feed air to the process is compressed at the outlet of the expander to a pressure sufficient to reboil high purity oxygen in the bottom reboiler of the low pressure column. The high pressure nitrogen stream from the top of the high pressure (HP) column is fed to an intermediate reboiler located above the point where low purity oxygen is withdrawn. This is because large volumes of air are forced into the low pressure column to bring boiling for both high and low purity gaseous oxygen products and also for all vapor streams for distillation above the point of low purity oxygen withdrawal. The need to condense in the bottoms reboiler makes the process inefficient in that the recovery of oxygen and especially the recovery of nitrogen cannot be too high. The large amount of air that needs to be condensed in the bottom reboiler of the low pressure column reduces the amount of available liquid nitrogen reflux and negatively affects oxygen recovery. Furthermore,
Most of the air that must be condensed at higher pressures in heat exchange with pure oxygen increases energy consumption and thereby wastes compression energy. This method also makes the low pressure column sized for all feed air, leading to potential production and transport failures.

[0005] US Pat. No. 5,515,833 describes:
Also shown is an argon side arm column connected to the main distillation column between the two oxygen product withdrawal points. This feed point is necessary to eliminate nitrogen from the feed to the side arm column. However, it results in a side arm column feed with very low argon concentration (Ar less than 4%). This makes this distillation much more difficult than when the side arm column feed argon is in the range of 9-14%. For a given oxygen recovery, the argon recovery in the feed to the side arm column is low, resulting in an insufficient argon recovery.

Clearly, there is a need for a more efficient cycle for producing both high and low purity oxygen with high efficiency and ease of operation.

[0007]

SUMMARY OF THE INVENTION The present invention provides a cryogeni stream of a stream containing nitrogen and oxygen for efficiently producing oxygen of at least two levels of purity.
c) For distillation. The first product is a low purity oxygen stream containing less than 97% oxygen (but generally more than 80% oxygen) and the second product is more than 97% oxygen, preferably 99% oxygen. A high purity oxygen product stream containing more than 0.5% oxygen. By employing and modifying a high efficiency process cycle for the production of low purity oxygen according to the present invention, high efficiency is obtained. This high efficiency process cycle comprises at least a distillation column that distills the feed stream to produce low purity oxygen from the bottom and a nitrogen rich stream from the top. At the bottom of the column is a reboiler that condenses the appropriate process stream and supplies a boiling load to the distillation column. According to the invention, a liquid stream whose oxygen concentration is at least equal to that of the above-mentioned feed stream is withdrawn from the bottom of this first column (at the point of the bottom reboiler) or from the point of withdrawal of low-purity oxygen. Is also withdrawn from the point above several separation stages and fed to the top of the side-leg tower. The bottoms of the side leg column are boiled with a suitable process fluid and high purity oxygen product is withdrawn from the bottom of the side leg column. The vapor from the top of the side-leg column is returned to the first column 1, preferably to the same separation stage from which the liquid feed stream is withdrawn.

[0008] If it is desired to produce argon simultaneously, an argon side arm column is installed at a suitable location in the side leg column for producing high purity oxygen, ie, the steam feed from the middle of the side leg column. To the argon side arm column to produce argon from the top of the column and return the liquid stream from the bottom of the column to the side leg column.

The advantage of this method is that the high temperature boil of high purity oxygen is kept to a minimum. Much more heat is supplied where low purity oxygen is produced. This results in substantial energy savings.

In its broadest aspect, the present invention comprises a low purity column for producing a low purity (less than 97%) oxygen product stream and a nitrogen rich stream, wherein the column comprises a suitable first process stream. A method for cryogenically distilling a compressed feed air stream in a distillation facility having a bottom reboiler to condense and provide a boiling load for the column, wherein the oxygen concentration is at least as high as that of the feed to the low purity column. An equal oxygen-rich stream is withdrawn from the distillation facility and rectified in a high purity column to provide a high purity (> 97%) oxygen product stream, the bottoms reboiler heat of the high purity column A second process stream, the second process stream being at a higher pressure than the first process stream.

Typically, the low purity oxygen product stream contains more than 80% oxygen, and preferably contains at least 90% oxygen. The high purity oxygen product stream preferably contains at least 99.5 oxygen.

In a presently preferred embodiment of the present invention, the distillation facility includes a high pressure column and a low pressure column, and (a) feeds at least a portion of the compressed feed air to the high pressure column where the feed air is rectified. (B) supplying at least a portion of the high pressure crude liquid oxygen bottoms to the low pressure column, where the high pressure crude liquid oxygen Rectifying the liquid oxygen bottoms into a low pressure nitrogen top product and a low pressure liquid oxygen bottoms,
(C) condensing at least a portion of the high pressure nitrogen overhead product and returning at least a portion of the condensed high pressure nitrogen overhead product to the high pressure column as reflux, and (d) a low pressure liquid oxygen bottom. At least a portion of the liquid is boiled in a bottom reboiler, in which a suitable first process stream is condensed, (e) a low purity oxygen product stream is withdrawn from the low pressure column, and (f) the oxygen concentration is increased to a high pressure. An oxygen-rich stream at least equal to that of the crude liquid oxygen column bottoms is withdrawn from the distillation facility and fed to a high-purity column, where it is rectified to reduce overhead oxygen vapor and high-purity liquid (G) compressing at least a portion of the high purity liquid oxygen bottoms to a pressure higher than the pressure of the first process stream for boiling the low pressure column. Step Boiled by bottom reboiler by condensation of Seth stream, withdrawing the high purity oxygen product stream from (h) high purity column.

[0013] The process stream to the high purity column for reboiling the bottoms liquid is a further compression of a portion of the compressed feed air. At least a portion of the compressed feed air portion can be supplied to a high pressure column and / or a low pressure column.

Alternatively, the process stream to the high purity column for reboiling the bottoms may be a further compression of at least a portion of the high pressure nitrogen top product.

[0015] The oxygen-rich stream can be withdrawn from the low pressure column, usually from its sump, and preferably, the reduced oxygen overhead vapor is substantially equivalent to the withdrawal of the oxygen-rich stream. At the same point, it is returned to the low pressure column.

Alternatively, the oxygen-rich stream is passed from a high pressure column,
Suitably as part of the high pressure crude liquid oxygen bottoms,
Can be extracted. From the low-pressure column, a vapor stream can be extracted at a point below the supply point of the high-pressure crude liquid oxygen column bottom liquid and supplied to the high-purity column at a point below the supply point of the oxygen-rich stream.

The process stream to the lower pressure column for reboiling the bottoms may be at least a portion of the high pressure nitrogen overhead product or a portion of the compressed feed air. If it is a portion of the compressed feed air, at least a portion of the resulting condensed feed can be fed to a high and / or low pressure column. If the high pressure nitrogen overhead product is not condensed to reboil the low pressure column, at least a portion thereof can be condensed at an intermediate point in the low pressure column.

As mentioned earlier, the argon-rich vapor stream withdrawn from the middle of the high-purity column is separated by the argon column and the argon product stream and the argon-free liquid returned to the high-purity column are returned to the high-purity column. Flow and can be manufactured.

If the high pressure nitrogen overhead product is condensed at an intermediate point in the low pressure column, the oxygen-rich stream is suitably withdrawn from the low pressure column at a point above the intermediate point and The argon-rich vapor stream withdrawn from the middle point of the purity column is separated by an argon column, and an argon product stream,
An argon-free liquid stream can be produced that is returned to the high purity column.

The argon overhead product from the argon column is:
A portion of the high pressure crude liquid oxygen bottoms can be condensed by boiling, and the vaporized high pressure crude liquid oxygen bottoms can be fed to a low pressure column and / or a high purity column.

[0021] A portion of the compressed feed air may be fed to the low pressure column, or a portion of the compressed feed air may be further compressed to a higher pressure than the portion of the main compressed feed air to the high pressure column, and At least a portion of this further compressed feed air portion can be fed to a high pressure column and / or a low pressure column.

At least a portion of the condensed high pressure nitrogen overhead product can be fed as reflux to the low pressure column. Alternatively, all of the condensed high-pressure nitrogen overhead product may be fed to the high-pressure column as reflux, and the side stream withdrawn from the high-pressure column may be used as reflux for the low-pressure column. A portion of this nitrogen-rich side stream may be fed to a high purity column.

If not all of the high pressure nitrogen overhead product is condensed, the remainder can be recovered as product.

The low purity oxygen product stream is boiled by heat exchange with a portion of the compressed feed air supplied to the high pressure column,
The compressed feed air portion can be at least partially vaporized.

The low-purity oxygen product stream and the high-purity oxygen product stream can be withdrawn from the low-pressure column and the high-purity column, respectively, as liquid, and then pressurized, and then heat-exchanged with the main compressed feed air to remove the pressurized oxygen product. Can be made.

The present invention also provides an apparatus for producing a low-purity oxygen product and a high-purity oxygen product by low-temperature distillation of compressed raw material air by the method described as the broadest aspect (the method of claim 1). (I) a distillation facility comprising a low-purity column for rectifying compressed feed air and producing a low-purity (less than 97%) oxygen product stream and a nitrogen-rich stream; ii) a bottom reboiler in the low purity column for condensing a suitable first process stream to reboil the low purity column, and (iii) supplying the first process stream to the reboiler. Means, (iv) means for extracting the low-purity oxygen product from the apparatus, wherein the apparatus further comprises the following (v) to (ix).

(V) A high purity column for rectifying an oxygen-rich stream having an oxygen concentration at least equal to that of the feed to provide a high purity (> 97%) oxygen product stream. (Vi) means for withdrawing this oxygen-rich stream from the distillation facility and feeding it to a high purity column. (Vii) a bottom reboiler in the high purity column for condensing a suitable second process stream to reboil the high purity column. (Viii) means for supplying a second process stream to the high purity column reboiler at a pressure higher than the pressure at which the second process stream is supplied to the low purity column reboiler. (Ix) means for withdrawing a high purity oxygen product stream from the apparatus.

In a presently preferred embodiment of this aspect of the apparatus, the distillation facility includes the following (1) to (12).

(1) A high-pressure column for rectifying at least a portion of the compressed feed air into a high-pressure nitrogen overhead product and a high-pressure crude liquid oxygen bottom solution. (2) A low pressure column for rectifying a high pressure crude liquid oxygen bottom liquid into a low pressure nitrogen top product and a low pressure liquid oxygen bottom liquid. (3) A means for supplying at least a portion of the high pressure crude liquid oxygen column bottom liquid to the low pressure column. (4) means for condensing at least a portion of the high pressure nitrogen overhead product and returning at least a portion of the condensed high pressure nitrogen overhead product to the high pressure column as reflux. (5) A bottom reboiler in the low pressure column for condensing a suitable first process stream to reboil the low pressure column. (6) Means for supplying a first process stream to the reboiler. (7) Means for extracting a low purity oxygen product stream from the device. (8) A high-purity column for rectifying an oxygen-rich stream into a vapor having a reduced oxygen content and a high-purity liquid oxygen column bottoms. (9) Means for extracting an oxygen-rich stream from a distillation facility and supplying it to a high-purity column. (10) A bottom reboiler in the high purity column for condensing a suitable second process stream to reboil the high purity column. (11) Means for supplying the second process stream to the high-purity column reboiler at a pressure higher than the pressure at which the second process stream is supplied to the low-pressure column reboiler. (12) Means for extracting a high purity oxygen product stream from the apparatus.

[0030]

BRIEF DESCRIPTION OF THE DRAWINGS The presently preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings. In all the drawings, the same reference numbers are used to indicate the same or equivalent components.

Hereinafter, the principle of the present invention will be described with reference to FIG. Briefly, the high pressure column (15) and the low pressure column (2)
5), and equipment including a side leg tower (23) is used. Low-purity oxygen products (9
5% GOX). High purity oxygen products (99.5%
GOX) is obtained from the bottom of the side-leg column (23), in which the liquid stream (35) from the bottom of the low-pressure column (25) is fed to a portion of the feed air (10) at elevated pressure (10). Distill and boil according to 21). The steam (37) from the top of the side-leg tower (23) is converted to the low-pressure tower (2).
Return to the bottom of 5).

More specifically, clean dry compressed air (1) from the front-end refining facility (1) is used.
0) is divided into three flows (11, 12, 13). The first feed air stream (11) is fed directly to the main heat exchanger (14), where it is cooled to near its dew point and then fed to the high pressure column (15) (11 '). The second raw material air stream (12) is supplied to the compressor side (1) of the compander (17).
6) to the main heat exchanger (14), from which it is withdrawn as a side stream (18) and into a compander (17)
Is supplied to the low-pressure column (25) via the expander side (19). This compander (17) generates refrigeration for the cycle. The third feed air stream (13) is passed through a low pressure booster air compressor (20) to the main heat exchanger (1).
4) where it is cooled to near its dew point.
The resulting cooling stream (21) is fed to a high purity or reboiler (22) at the bottom of the side leg column (23),
The column is reboiled. The liquefied air (24) from the reboiler (22) is supplied to the high-pressure column (15).

Alternatively, part or all of the liquefied air (24) may be supercooled and supplied to the low pressure column (25) instead of the high pressure column (15).

The high-pressure column (15) performs an initial distillation of air to form a liquid oxygen-rich (crude liquid oxygen) stream (2) from the bottom of the column.
6) and a high pressure gaseous nitrogen stream (27)
Cause. The oxygen content of the crude liquid oxygen stream (26) is usually greater than 30%, often greater than 35%. This stream (26) is passed through the subcooler (29) to the low pressure column (25).
Is supercooled by heat exchange with a low-pressure nitrogen stream (28) from the top of the column and then depressurized and fed to an intermediate point of the low-pressure column (25). The warmed low pressure gaseous nitrogen stream (28 ') is further heated in the main heat exchanger (14) and then released to the atmosphere (waste) or recovered as a coproduct stream.

The majority (30) of the high pressure gaseous nitrogen (27) from the top of the high pressure column (15) comprises the low pressure column (25).
Is supplied to the reboiler (31) at the bottom of the column. The condensed nitrogen stream from the reboiler (31) is split to provide two split streams (32, 33). One split flow (32)
Is used to supply reflux to the high pressure column (15), while the other split stream (33) is cooled by a subcooler (29) and then used to supply reflux to the low pressure column (25) .

A portion (34) of the gaseous nitrogen stream (27) withdrawn from the top of the high pressure column (15) is added in the main heat exchanger (14) for recovery as a product (GAN). Warmed up. If no nitrogen product is required, the entire withdrawn high pressure nitrogen stream (27) can be fed to the reboiler (31). However, if large quantities of product nitrogen are required, it is typically more efficient to obtain it from the low pressure column (25).

If very high purity (ppm levels of oxygen) is required, it may be more efficient to reflux the low pressure column (25) with impure liquid nitrogen. In this case, all of the condensed nitrogen stream from the reboiler (31) is supplied to the top of the high pressure column (15), and the low pressure column (25)
Is refluxed from the top of the high-pressure column (15) several stages below, cooled by a supercooler (29), and then cooled to a low-pressure column (2).
This is performed by a side flow (not shown) supplied to 5).

The low-purity liquid oxygen stream (35) is passed through the low-pressure column (2).
5) Withdraw from the liquid pool of the side leg tower (2)
Feed to the top of 3). This low purity oxygen is distilled and boiled in heat exchange with the cooled third feed air stream (21) fed to the reboiler (22). A high-purity gaseous oxygen stream (36) is supplied to the side leg tower (2
The main heat exchanger (1)
4), from which the product (99.5% GOX)
Will be collected as The overhead vapor stream with reduced oxygen content (3
7) is returned from the side leg column (23) to just above the pool in the low pressure column (25). Side leg tower (23)
Raw material (35) for crude liquid oxygen raw material (26 ')
Is extracted from the low-pressure column (25) at a point below the supply point, the oxygen concentration in the liquid feed (35) is higher than that in the crude liquid oxygen feed (26 ').

The low purity oxygen product stream (38) is fed to the low pressure column (2).
5) Withdrawn from the bottom of the tower and supplied to the main heat exchanger (14), from which it is recovered as a product (95% GOX).

In FIG. 1, a separate feed air stream (13) is used to compress the third feed air stream (13) used to reboil the bottoms of the side leg column (23) with the heat exchanger (22). A booster compressor (20) is provided. but,
This feed air stream (13) could be intensified on the compressor side (16) of the compander device (17).

In the embodiment of FIG. 2, the low-purity oxygen stream (38) is withdrawn from the low-pressure column (25) as a liquid stream and is passed through a liquid oxygen boiling vaporizer (210) in the first cooling feed air stream (11). Boil by heat exchange with a part (215), transfer the reboiler (31) to the middle point of the low pressure column (25),
1 in that a further reboiler (211) to which the cooling air stream (212) is supplied is arranged at the bottom of the low-pressure column (25). Next, only the differences between these two facilities will be described.

A small portion of the cooled first feed air stream (11 ') is withdrawn as a split stream (212) and fed to the bottom reboiler (211) of the low pressure column (25). Condensed air (21) from this reboiler (211)
3) is fed to an intermediate point of the high pressure column (15).

The remaining (more) portion (215) of the cooled first feed air stream (11 ') is a liquid oxygen (LOX) boiling vaporizer (210) from the low pressure column (25). Is partially condensed by heat exchange with the low purity liquid oxygen product (38). The resulting two-phase feed air stream (214)
Is then fed to the bottom of the high pressure column (15).

If necessary, the condensed air (213) is
Instead of the above intermediate point, it can be supplied to the high pressure column (15) at the same place as the two-phase feed air (214).
This configuration is simpler, but the efficiency is lower than feeding to an intermediate point.

Reboilers (22, 21) supplied with air
Part or all of the liquefied air from 1) is supercooled (29)
And replace the high pressure column (15) with the low pressure column (2).
5).

At least a majority of the high pressure gaseous nitrogen stream (27) from the top of the high pressure column is relocated to an intermediate location in the low pressure column (25) compared to the installation of FIG. ).

The low-purity liquid oxygen stream (38) withdrawn from the sump of the low-pressure column (25), whose pressure has risen slightly due to its own static head, is supplied to the liquid oxygen boiling vaporizer (21).
0). This oxygen stream (38) is boiled by the cooled first air stream (215) and then recycled to the main heat exchanger (1) for recovery as product (95% GOX).
Heated in 4). The liquid oxygen boiling vaporizer (210) increases the pressure of the low purity oxygen vapor and thus reduces the compression power.

The embodiment of FIG. 3 shows a second feed air stream (12).
Is increased by the compressor (310), and the discharge stream (311) from the expander side (19) of the compander (17) is supplied to the high pressure column (15) instead of the low pressure column (25), and additional raw material air is supplied. (312/313, 312/314) to the low pressure column (25) and / or the high pressure column (15), and the non-refluxed portion (33) of the condensed high pressure nitrogen stream (315) is supplied to the low pressure column (25). Instead of being fed to the gaseous product (GAN), the liquid oxygen boiling vaporizer is omitted, the stream of high-purity oxygen product (36) is withdrawn from the side-leg tower (23) as liquid, and the low-purity oxygen stream (GAN) is removed. 3
8) pressurizing the high purity oxygen stream (36) and the nitrogen product stream (33) using liquid pumps (316, 317, 318) to produce pressurized oxygen and nitrogen products, and the low pressure column (25) Is returned to the side stream (31) from the high pressure column (15).
9) is different from the embodiment of FIG. Next, only the differences between these two facilities will be described.

A part (21) of the first raw material air stream (11 ') remaining after the withdrawal of the split stream (212)
5) is fed directly to the bottom of the high pressure column (15).

The second feed air stream (12) is compressed in a high pressure booster air compressor (310) and split into two split streams (312, 320). The larger split stream (312), containing the majority of the compressed air, is fed to the main heat exchanger (14),
It is condensed there and vaporizes the liquid product. As shown in FIG. 3, a part (314) of the liquefied air can be supplied to the high-pressure column (15), and the remaining (313) is cooled by the supercooler (29) and is cooled by the low-pressure column (25). ). However, all of the liquefied air is transferred to the high pressure tower (15).
Alternatively, it could be fed to the low pressure column (25).

The smaller portion of the air from the booster compressor (310), the smaller stream (320), is fed to the compressor side (16) of the compander (17) and to the main heat exchanger (14). After partially cooling with the compander (1
7) is supplied to the expander side (19) to generate refrigeration for the plant. The discharge air (311) of the expander is a part (21) of the cooled first raw material air stream.
5) and fed to the bottom of the high pressure column (15). The feed to the compander may be obtained as a side stream from an intermediate stage of the booster compressor (310) instead of from the discharge side of the booster compressor (310) as shown in FIG.

[0052] Instead of treating the second split stream of feed air (320) with a compander, it may be preferable to simply expand it. In that case, the compander (1
7) is omitted and the partially cooled split stream (320) is supplied from the main heat exchanger (14) to another expander instead of the expander side (19) of the compander (17).

Two booster compressors (20, 310)
It may be advantageous to use a common booster compressor instead. In this case, the compressed third feed air stream (13) required to reboil the side leg column (23) is fed from this common booster compressor or from the discharge product of the common booster compressor. Can be extracted as a side stream.

The impure reflux side stream (319) is withdrawn from the top of the high pressure column (15) several stages below, cooled in a subcooler (29) and then removed from the column of the low pressure column (25). It is fed to the top (319 ').

The high-pressure nitrogen stream (27) withdrawn from the top of the high-pressure column (15) is condensed in the intermediate reboiler (31), and the condensed high-pressure nitrogen stream is divided into a reflux split stream (32) and a product stream (33). And divided into The product stream (33) is pressurized by a liquid pump (318) and then gaseous nitrogen product (GAN)
Is vaporized in the main heat exchanger (14).

The low-purity liquid oxygen stream (38) extracted from the liquid pool of the low-pressure column (25) is also pressurized by the liquid pump (316), and then is supplied with a low-purity gas oxygen product (95% GO).
It is vaporized in the main heat exchanger (14) to be collected as X).

Similarly, the high-purity liquid oxygen stream (36) from the side leg column (23) is pressurized by the liquid pump (317), and then the high-purity gaseous oxygen product (99.5% G
It is vaporized in the main heat exchanger (14) to be collected as OX).

In the embodiment of FIG. 3, the product (GAN, 9
It is not necessary to collect all of the 5% GOX, 99.5% GOX) by vaporization in the liquid pump and main heat exchanger (14). Any combination of liquid and gaseous products from the tower is possible.

The embodiment of FIG. 4 is a simplification of that of FIG. 2, in which the liquid oxygen boiling vaporizer (210) is omitted and the cooled first feed air stream (11 ') The (larger) portion (215) is fed directly to the bottom of the higher pressure column (15). A low purity oxygen product stream (438) is withdrawn from the sump of the low pressure column (25) as a gas rather than as a liquid.

The embodiment of FIG. 5 shows that the feed to the side leg column (23) and the return from it are located above the intermediate reboiler (31) of the low pressure column (25), and the argon side arm column (510) Is different from the embodiment of FIG. Next, only the differences between these two facilities will be described.

In FIG. 5, instead of extracting the feed stream (35) to the side leg column (23) from the liquid pool of the low pressure column (25) as in FIG. 2, an intermediate reboiler ( 31) Pull out from above. Alternatively, the feed stream (35) to the side leg column (23) could be withdrawn below the intermediate reboiler (31), but above the pool of the low pressure column (25). . The vapor stream (37) from the top of the side leg column (23) is preferably returned to this same point of the low pressure column (25). The high purity oxygen product stream (36) exits the bottom of the side leg column (23) as a gas (as in FIG. 2) or as a liquid (as in FIG. 3).
It is extracted.

A side stream (511) of vapor rich in argon is withdrawn from the middle of the side leg column (23), where the nitrogen content of the vapor in the column is low. The nitrogen concentration of this argon-rich vapor side stream (511) is usually less than 1%, preferably less than 0.5%, especially less than 100 ppm. The argon-rich side stream (511) is further distilled in a crude argon column or side arm column (510). The product from this column is largely argon and may contain as little as 4% or as little as 1 ppm oxygen, depending on the number of stages in the column. The side stream (511) can be further purified in any suitable purifier if necessary.
The liquid stream (512) with a reduced amount of argon from the bottom of the side arm column (510) is preferably at the same point where the side stream of vapor (511) is withdrawn, in the middle of the side leg column (23). Returned to Side arm tower (51
The argon at the top of 0) is condensed by boiling a portion (513) of the supercooled crude liquid oxygen in a reboiler (514). The vaporized crude liquid oxygen (515) is supplied to an appropriate point of the low pressure column (25). A portion of the argon stream from the top of the side arm column (510) is recovered as an argon product stream.
Preferably, the argon product stream is reboiler (51
Part (520) of the condensed stream from 4).

The embodiment of FIG. 6 differs from that of FIG. 3 in that the side leg column (23) is not connected to the low pressure column (25) and an argon side arm column (510) is added. Next, only the differences between these two facilities will be described.

In FIG. 6, the feed to the side leg column is extracted from the low-pressure column (25) instead of the supercooled nitrogen-rich impure reflux (319) to the top of the side leg column (23). To provide a portion (610) of
And it is provided by feeding a supercooled portion (611) of the reflux (26) of the crude liquid oxygen to the low pressure column (25) to an intermediate point of the side leg column (23).

The vapor stream (612) from the top of the side-leg tower (23) is a reduced oxygen waste and the reduced oxygen (2) from the top of the low pressure column (25) (2)
8) is mixed.

The high purity oxygen product (36) is withdrawn from the bottom of the side leg column (23) as a liquid (as in FIG. 3) or as a gas (as in FIG. 2).

The argon-rich vapor side stream (511) is:
It is extracted from the middle part of the side leg tower (23) where the nitrogen content of the steam in the tower is low. The nitrogen concentration of this argon-rich vapor side stream (511) is usually less than 1%, preferably less than 0.5%, especially less than 100 ppm. This argon-rich side stream (511) is further distilled in a side arm column (510). The product from this column is largely argon and may contain as little as 4% or as little as 1 ppm oxygen, depending on the number of stages in the column. The side stream (511) can be further purified in any suitable purifier if necessary. The reduced argon liquid stream (512) from the bottom of the side arm column (510) is preferably a vapor side stream (51).
At the same place where 1) was extracted, the side leg tower (2
3) Returned to the middle. The argon at the top of the side arm column (510) is condensed by boiling a portion (513) of the supercooled crude liquid oxygen in the reboiler (514). Evaporated crude liquid oxygen (61
3) is fed to a suitable point in the side leg tower (23). A portion (520) of the condensed argon stream from reboiler (514) is recovered as an argon product stream.

In some other variants of the method of FIG. 6, the vapor stream is fed to the low pressure column (25) with the crude liquid oxygen feed (2).
It can be extracted from the stage below the supply point of 6) and supplied to the side leg tower (23) at a point below the supply point of the vaporized crude liquid oxygen (613).

FIG. 7 shows a side arm tower (510).
The vaporized crude liquid oxygen (713) from the top of the column is supplied to the low-pressure column (25), and the vapor stream (711) extracted from a portion of the low-pressure column (25) below the point where it is supplied
Is supplied to the side leg tower (23).

In all of the above embodiments, it is possible to use nitrogen instead of air to reboil the side leg column. For example, a nitrogen product stream (GAN) is compressed by a low pressure booster compressor (20) instead of a third feed air stream (13). Low temperature (c) in the main heat exchanger (14)
After cooling to ryogenic temperature, the compressed nitrogen product stream is passed through a side-leg tower (23).
To the reboiler (22). The obtained condensed nitrogen can be supplied to any appropriate point of the high-pressure column (15).

In all of these embodiments, the pressure of the feed air from the pre-installation (1) is only the pressure required to boil low-purity oxygen. This is consistent with the low pressure of a double reboiler cycle. Only the portion of the air required to make the side leg oxygen is compressed to the pressure required to boil high purity oxygen. This reduces the compression power beyond the cycle in which all of the feed air is used to make high purity oxygen, and US Pat.
Compared to the cycle of No. 33.

The new cycle of the present invention also makes it possible to reduce the size of the low pressure column (25). If the side leg columns (23) are not connected as in FIG. 6, the overall diameter of the low pressure column (25) will be smaller because it does not purify the entire air stream. It also makes it possible to reduce the number of stages that have to be large in diameter, since the large main towers (15, 25) no longer need to make high-purity oxygen.

By withdrawing the feed (511) to the side arm tower (510) from an intermediate point in the side leg tower (23), the feed is rich in argon (typically 6 to 22 Ar). %, Preferably 9 to 15
%). This not only simplifies and shortens the side arm column beyond the cycle of U.S. Pat. No. 5,515,833, which must start from a feedstock with a significantly reduced argon (typically less than 4% Ar). , Make the argon recovery much higher.

[Brief description of the drawings]

FIG. 1 illustrates a first (basic) embodiment of the present invention.

FIG. 2 illustrates a second embodiment of the present invention using a liquid oxygen boiling vaporizer for low purity oxygen products.

FIG. 3 illustrates a third embodiment of the present invention for making pressurized oxygen and nitrogen products using a liquid pump.

FIG. 4 is a diagram showing a fourth embodiment of the present invention in which the embodiment of FIG. 2 is simplified and the liquid oxygen boiling vaporizer is omitted.

FIG. 5 is a diagram showing a fifth embodiment of the present invention in which the embodiment of FIG. 2 is modified by incorporating a crude argon side arm column.

FIG. 6 is a modification of the embodiment of FIG. 3 incorporating a crude argon side arm column and showing a sixth embodiment of the present invention having a side leg column disconnected from the low pressure column.

FIG. 7 is a modification of the embodiment of FIG. 6, showing a seventh embodiment of the present invention in which a low pressure column is combined with both a side arm column and a side leg column.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Feed air 14 ... Main heat exchanger 15 ... High pressure tower 16 ... Compander compressor 17 ... Compander 19 ... Compander expander 20 ... Low pressure booster compressor 22 ... Reboiler 23 ... Side leg tower 25 ... Low pressure tower 29 ... Excess Cooler 31 ... Intermediate reboiler 210 ... Liquid oxygen boiling vaporizer 211 ... Bottom reboiler 310 ... Compressor 316,317,318 ... Liquid pump 510 ... Argon side arm tower 514 ... Reboiler

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[Procedure amendment]

[Submission date] August 25, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0024

[Correction method] Change

[Correction contents]

The low purity oxygen product stream is boiled by heat exchange with a portion of the compressed feed air supplied to the high pressure column,
The compressed feed air portion can be at least partially condensed .

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0027

[Correction method] Change

[Correction contents]

(V) a high purity column for rectifying an oxygen-rich stream having an oxygen concentration at least equal to that of the feed to the low purity column to provide a high purity (> 97%) oxygen product stream; . (Vi) means for withdrawing this oxygen-rich stream from the distillation facility and feeding it to a high purity column. (Vii) a bottom reboiler in the high purity column for condensing a suitable second process stream to reboil the high purity column. (Viii) the second process stream to the high purity column reboiler, means for supplying at a pressure higher than the pressure which the first process stream is supplied to the low purity column reboiler. (Ix) means for withdrawing a high purity oxygen product stream from the apparatus.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0029

[Correction method] Change

[Correction contents]

(1) A high-pressure column for rectifying at least a portion of the compressed feed air into a high-pressure nitrogen overhead product and a high-pressure crude liquid oxygen bottom solution. (2) A low pressure column for rectifying a high pressure crude liquid oxygen bottom liquid into a low pressure nitrogen top product and a low pressure liquid oxygen bottom liquid. (3) A means for supplying at least a portion of the high pressure crude liquid oxygen column bottom liquid to the low pressure column. (4) means for condensing at least a portion of the high pressure nitrogen overhead product and returning at least a portion of the condensed high pressure nitrogen overhead product to the high pressure column as reflux. (5) A bottom reboiler in the low pressure column for condensing a suitable first process stream to reboil the low pressure column. (6) Means for supplying a first process stream to the reboiler. (7) Means for extracting a low purity oxygen product stream from the device. (8) A high-purity column for rectifying an oxygen-rich stream into a vapor having a reduced oxygen content and a high-purity liquid oxygen column bottoms. (9) Means for extracting an oxygen-rich stream from a distillation facility and supplying it to a high-purity column. (10) A bottom reboiler in the high purity column for condensing a suitable second process stream to reboil the high purity column. (11) means for supplying the second process stream to the high purity column reboiler at a pressure higher than the pressure at which the first process stream is supplied to the low pressure column reboiler. (12) Means for extracting a high purity oxygen product stream from the apparatus.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Jeffrey Alan Hopkins United States, Pennsylvania 18052, Whitehall, Pellicles Place 1225, Apartment 6 (72) Inventor Rakesh Agrowol United States, Pennsylvania 18049, Emaus, Commonwealth Drive 4312 (72) Inventor Ku Junguo United States of America, Pennsylvania 18051, Vogelsville, White Birch Circle 8121

Claims (16)

[Claims] 1. An oxygen product stream of low purity (less than 97%) (3%).
8) and a low-purity column (2) producing a stream rich in nitrogen (28).
5) in which a suitable first process stream (30, 212) is condensed to provide a boiling load for the column (25).
1) A method for cryogenic distillation of a compressed feed air stream (10) in a distillation facility (15, 25), wherein the oxygen concentration is at least as high as that of the feed (26 ') to the low purity column (25). An equal oxygen-rich stream (35,611) is withdrawn from the distillation facility (15,25) and rectified in a high purity column (23) to provide a high purity (> 97%) oxygen product stream (36). The bottoms reboiler heat of the high purity column (23) is then transferred to a suitable second process stream (21).
Of this second process stream (21)
At a higher pressure than the first process stream (30, 212). 2. The distillation facility includes a high pressure column (15) and a low pressure column (25), and (a) removing at least a portion (11) of the compressed feed air (10) from the high pressure column (15). Where the feed air (11) is rectified into a high pressure nitrogen top product (27) and a high pressure crude liquid oxygen column bottoms (26); (b) the high pressure crude liquid At least a portion of the oxygen bottoms (26) is fed to the low pressure column (25), where the high pressure crude liquid oxygen bottoms (26) is rectified to obtain a low pressure nitrogen top product (26). And (c) condensing at least a portion (30) of the high-pressure nitrogen overhead product (27) to obtain a low-pressure liquid oxygen bottom product. Returning at least a portion (32) of the to the high pressure column (15) as reflux, (d) (E) condensing a suitable first process stream (30, 212) in the bottom reboiler (31, 211) to condense the first process stream (30, 212) in the reboiler; The pure oxygen product stream (38) is passed through the low pressure column (2).
(F) the oxygen concentration is above the high pressure crude liquid oxygen bottom liquid (26)
An oxygen-rich stream (26, 3
5) is withdrawn from the distillation equipment (15, 25) and supplied to the high-purity column (23), where it is rectified and the overhead vapor (37) with reduced oxygen content and the high-purity liquid oxygen column (G) compressing at least a portion of the high purity liquid oxygen column bottoms to a pressure higher than the pressure of the first process stream (30, 212) for boiling the low pressure column (25). 2. A high purity oxygen product stream (36) is withdrawn from said high purity column (23) by boiling the bottom reboiler (22) by condensing the appropriate second process stream (21). The described method. 3. The process stream to the bottom reboiler (22) of the high purity column (23) is a further compressed portion (21) of the compressed feed air (10).
The described method. 4. The process stream to the bottom reboiler (22) of the high purity column (23) is fed to the high pressure nitrogen top product (2).
7) at least a part of a further compression of
The method of claim 2. 5. The process according to claim 2, wherein the oxygen-rich stream (35) is withdrawn from the low-pressure column (25). 6. The overhead vapor having a reduced oxygen content (37).
6. The process according to claim 5, wherein the oxygen is returned to the low pressure column (25) at substantially the same point as the oxygen-rich stream (35) is withdrawn. 7. The method according to claim 5, wherein the oxygen-rich stream (35) is withdrawn from a sump of the low-pressure column (25). 8. The process according to claim 2, wherein the oxygen-rich stream (611) is a part of the high pressure crude liquid oxygen bottoms (26). 9. A vapor stream (711) is withdrawn from a point of the low-pressure column (25) below a point where the high-pressure crude liquid oxygen column bottom liquid (26) is supplied, and the oxygen stream of the high-purity column (23) is extracted. The method according to claim 8, wherein the feed is supplied to a point below the point of supply of the rich stream (611). 10. The bottom reboiler (21) of the low pressure column.
The process stream to 1) is a portion (212) of the compressed feed air (10) and condenses at least a portion (30) of the high pressure nitrogen overhead product (27) to the low pressure column (25). The method according to any one of claims 2 to 9, wherein the method is carried out with a reboiler (31) at an intermediate position of (1). 11. The oxygen-rich stream (35) is withdrawn from a point above the middle reboiler (31) of the low pressure column (25) and from a middle point of the high purity column (23). Argon-rich vapor stream (51
11) Separating 1) in an argon column (510) to produce an argon product stream and a reduced argon liquid stream (512), and returning this liquid stream to the high purity column (23). the method of. 12. The low pressure column (25), comprising the distillation installation according to claim 2, wherein all of the condensed high pressure nitrogen overhead product (27) is fed as reflux to the high pressure column.
Reflux from the high pressure column (15).
The method according to any one of claims 2 to 11, wherein the method is performed in 9). 13. The method according to claim 12, wherein a portion (610) of the nitrogen-rich side stream (319) is fed to the high-purity column (23). 14. An apparatus for producing a low-purity oxygen product and a high-purity oxygen product by distilling a compressed raw air (10) at a low temperature according to the method of claim 1, and (i) compressed raw air (10). Column for rectifying a low-purity (<97%) oxygen product stream (38) and a nitrogen-rich stream (28)
Distillation apparatus (15, 25) comprising 5); (ii) the low purity column (25) for condensing a suitable first process stream to reboil the low purity column (25).
(Iii) means for supplying the first process stream to the reboiler (27, 30, 11, 212); (iv) the low purity oxygen from the apparatus. Means for extracting the product (38), comprising:
To (ix). (V) for rectifying an oxygen-rich stream having an oxygen concentration at least equal to that of the feed (26 ') to the low purity column (25) to provide a high purity (> 97%) oxygen product stream; (Vi) withdrawing the oxygen-rich stream from the distillation facility (15, 25) and removing it from the high-purity column (23)
(35, 26, 611) (vii) the high-purity column (23) for condensing a suitable second process stream and boiling the high-purity column (23)
(Viii) The high-purity tower reboiler (22) is supplied with the second process stream, and the first process stream is supplied to the low-purity tower reboiler (31, 211). (20, 21) means for supplying at a pressure higher than the pressure at which the high purity oxygen product stream is withdrawn from the apparatus (36). 15. The distillation equipment according to the following (1) to (1).
15. The device according to claim 14, comprising (12). (1) A high-pressure column (15) for rectifying at least a part of the compressed feed air (10) into a high-pressure nitrogen overhead product and a high-pressure crude liquid oxygen bottom solution. A low-pressure column for rectifying the high-pressure crude liquid oxygen bottom liquid into a low-pressure nitrogen top product and a low-pressure liquid oxygen bottom liquid (25) (3) The above-mentioned high-pressure crude liquid oxygen bottom liquid Means (2) for supplying at least a portion of the mixture to the low pressure column (25).
(6) 29) (4) for condensing at least a portion of the high pressure nitrogen overhead product and returning at least a portion of the condensed high pressure nitrogen overhead product to the high pressure column (15) as reflux. Means (27, 31, 32) (5) Bottom reboiler (31, 211) in said low pressure column (25) for condensing a suitable first process stream to bring said low pressure column (25) to boiling (6) means (27, 30, 11, 2) for supplying the first process stream to the reboiler (31, 211).
12) (7) Means for extracting a low-purity oxygen product stream (38) from the apparatus. (8) Oxygen-rich stream is rectified to reduce the oxygen content of the overhead vapor (37) and high-purity liquid. High-purity column (23) for use as oxygen column bottom liquid (9) Means for extracting a stream rich in oxygen from the distillation equipment (15, 25) and supplying it to the high-purity column (23) ( 26, 35) (10) The high-purity column (2) for condensing a suitable second process stream and boiling the high-purity column (23).
3) The bottom reboiler in (22) (11) The high purity column reboiler at a pressure higher than the pressure at which the first process stream is supplied to the low pressure column reboiler (31, 211) (22) Means for feeding (20, 21) (12) Means for withdrawing the high purity oxygen product stream from the apparatus (36) 16. Apparatus according to claim 15, comprising the components required to carry out the individual method according to any one of claims 3 to 13.