JP3322416B2 - Low-temperature separation method for air - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a compressed air supply,
It is purified, cooled and divided into a plurality of partial streams and introduced into the high and low pressure stages of a two-stage rectifier, wherein a first partial stream is passed to said high pressure stage and to a second A method for cryogenic separation of air wherein a stream is introduced into said low pressure stage.

[0002]

2. Description of the Related Art Such a method is known from EP-A 0 342 436. In this case, the supply air is initially compressed only to the pressure of the low pressure stage, but is diverted at intermediate pressure into first and second partial flows. Only part of the first partial stream supplied into the high-pressure stage is further compressed. This method allows for very economical compressor utilization. However, it is necessary to remove carbon dioxide, hydrocarbons and water from the second partial stream in its own purifier, generally a molecular sieve. Such molecular sieves require large amounts of regeneration gas due to low pressure. Therefore, this regeneration gas is used for other purposes.
In particular, it cannot be used freely for inexpensive evaporative cooling of cooling water necessary for pre-cooling air.

[0003]

The object of the present invention is therefore to further develop a method of the kind mentioned at the outset, to improve the economics and to achieve a particularly inexpensive air purification. I do.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to supply air at the first high pressure stage to approximately the pressure of the high pressure stage and purify it by adsorption in a purifier, followed by the first and the second. Splitting into a second partial stream, heating the second partial stream by indirect heat exchange with the compressed supply air before feeding it into the low pressure stage to perform work and expand; The problem is solved by using the work obtained in the expansion of the partial stream for the compression of the process stream, in particular of the supply air.

By the method according to the invention as described above,
This makes it possible to treat the entire supply air in a single purification device, in particular at the pressure of the high-pressure stage. In this way, no large equipment costs are required and no additional large low-pressure purifier operating costs are required. The excess compression energy provided to the second substream is recovered in the turbine as partial mechanical work and can be partially converted to cold.

This work is generally provided entirely directly by mechanical coupling to the compressor, but may additionally or alternatively be adapted to drive the generator. The second partial stream is preheated in order to perform an expansion that works in good conditions. The compressed feed air can then be conveniently extracted of heat.

A compressor driven by a turbine, for example, allows a product stream or an intermediate product stream to flow. In general, it is advantageous to use the work obtained during the work expansion to compress the supply air.

Furthermore, in this method, refrigeration can be generated, in which case a third partial stream is branched downstream of the adsorption purification device and post-compressed in a second compressor stage. The work which is subsequently cooled and expanded by work is supplied to the low pressure stage, the work obtained during the expansion performing the work of the third partial stream being taken up in the second compressor stage. A third partial stream can be provided for post-compression. In this case, pressures that are not necessary for the generation of processing refrigeration are likewise utilized.

To convey work and cold, the present invention
Two embodiments are provided.

The first embodiment is adapted to supply to the first compressor stage the work obtained during the expansion with the work of the second partial stream. Since this task is not self-evidently sufficient for driving the air compressor, the shaft connecting the expansion turbine and the first compressor stage must generally be additionally driven by a motor.

In this case, it is advantageous for the heating of the second partial stream before expansion by indirect heat exchange with the supply air after the first compressor stage and before the purification device.

In any case, the supply air must be pre-cooled at this position. Supply air is generally about 25 ° C
Exiting a cooler having a temperature of about 35.degree. C., driven by about 50.degree. C. water and having to be brought to about 10.degree. This is generally done by cold cooling water drawn from external refrigeration equipment or evaporative coolers driven by dry nitrogen. This pre-cooling is passed on to the at least partially purified second partial stream, reducing the cost of the refrigeration installation,
In some cases, nitrogen can be made to serve other purposes.

A second embodiment is such that the work obtained during the expansion to perform the work of the second partial stream is supplied for post-compression of the third partial stream in a third compressor stage. Has become.

This third compressor stage is preferably connected before the second compressor stage so as to increase the pressure difference during the expansion of the third partial flow.

[0015] Furthermore, downstream of the purifier, additionally or alternatively, a fourth partial stream is diverted, post-compressed in a fourth compressor stage, subsequently cooled and placed in a high-pressure stage. It is advantageous to supply the work obtained during the expansion with the work of the second partial stream to the fourth compressor stage for the post-compression of the fourth partial stream. The expansion of this fourth partial stream is generally effected by a throttle valve.

In this case, the numbering of the compressor stages is intended to show these distinct differences, and inevitably the second or third compression stage described above when a fourth compressor stage is present. It does not mean that a mechanism must be provided.

However, it has proven advantageous if the third and fourth partial streams are post-compressed in a common third compressor stage. In this case, the third and fourth compressor stages are provided as a single machine at relatively low cost.

A second method of transferring heat to the second partial stream at high pressure is according to a further aspect of the present invention.
Heating the partial stream prior to its expansion by indirect heat exchange with the third and / or fourth partial stream after post-compression in a third or fourth compressor stage. Made up of

Such measures make it possible to adapt these streams particularly well to the inlet temperature of the main heat exchanger, which cools the post-compressed partial streams. The refrigeration obtained before the introduction of the second partial flow into the expansion turbine is supplied particularly efficiently at this location.

Post-compression of the fourth partial stream above the pressure of the high pressure stage is particularly advantageous when obtaining oxygen at an elevated pressure by this method. In this case, according to a further advantageous embodiment of the inventive concept, the liquefied oxygen is withdrawn from the low-pressure stage, brought to a high pressure and evaporated by indirect heat exchange with the post-compressed fourth partial stream. It is done.

In this case, a portion of the air obtained at a pressure higher than the pressure of the high-pressure stage is used for the production of energetically favorable high-pressure oxygen. Oxygen is brought to a high pressure in a liquid state (by a pump or by using a hydrostatic potential) and subsequently evaporated at a high pressure. The high-pressure air is condensed in countercurrent to the air to be evaporated, releasing latent heat. This indirect heat exchange
It is preferably carried out in the main heat exchanger block through which other feed and product streams are also passed.

In this case, it is advantageous if the partially condensed fourth partial stream is subsequently introduced into the high-pressure stage above the first partial stream.

During the heat exchange with the high-pressure oxygen, a large part of the high-pressure air is generally condensed and some pre-separation action can be used, in which case the condensate is converted into at least one theoretical bed ( Boden), especially for 4 to 8 theoretical beds, to be supplied above the air of the remaining high pressure stage.

The process according to the invention provides a process for the production of oxygen (S
auerstoff geringer reinhe
It is particularly advantageous to use it for obtaining it). In this case, the purity of oxygen means 99%, especially 85% to 98% (by volume) or less. 100,000 Nm ³ / h or more, especially 200,000 Nm ³ / h or more, especially up to 20
The advantages of the present invention are particularly apparent in an air separation facility with an air separation of between 0000 and 400,000 Nm ³ / h. The present invention also relates to a GUD- (combined cycle-Anla).
ge) or steelmaking equipment (for example, COREX method) (COR
It is advantageous to carry out the supply in the range of (EX-Verfahren).

[0025]

DETAILED DESCRIPTION OF THE INVENTION The invention and further details of the invention are illustrated in FIG.
And two embodiments which are schematically illustrated in FIG. 2, in which like steps are denoted by the same reference numerals as far as possible.

According to the circuit diagram shown in FIG. 1, air at atmospheric pressure is sucked into the first compressor stage 2 via conduit 1 and
Compressed to a pressure of 乃至 10 bar, especially about 5.65 bar, cooled to 5-25 ° C., especially about 12 ° C., and in a purification device 4 filled with molecular sieves, for example water, carbon dioxide and hydrocarbons Impurities are removed.

Immediately after the purification device 4, the supply air is branched into a first partial stream 101 and a second partial stream 102. The first partial stream 101 is cooled by heat exchange with the product stream in the main heat exchanger 5 and is cooled in the high-pressure stage 7 of a conventional two-stage rectifier 6.
Supplied within. As product, low pressure stage 8 (operating pressure 1.
From 2 to 1.6 bar, in particular about 1.3 bar), gaseous oxygen 9 and gaseous nitrogen 10 are withdrawn and heated in the main heat exchanger 5 to about ambient temperature. Nitrogen is supplied for regeneration of the molecular sieve of the purifier 4 (conduit 11) and / or conduit 1 for other purposes, for example for cooling the cooling water in the evaporative cooler.
2 can be withdrawn.

The second partial stream 102 is heated by heat exchange with the supply air compressed in the heat exchanger 3 according to the invention, expanded in the turbine 13, cooled and fed into the low-pressure stage 8. . The supply air stream is supplied to the heat exchanger 3 and the purifier 4
In addition, additional cooling can be performed, for example, by indirect heat exchange with water cooled by an evaporative cooler (not shown).

The third partial stream 103 is likewise branched off downstream of the purifier 4, further compressed in the second compressor 14, cooled in the main heat exchanger 5 to an intermediate temperature and thereafter It is expanded in the turbine 15 to generate cold. The work obtained by the expansion of this partial stream is transmitted mechanically to the second compressor 14. Expanded third partial flow 10
3 is adapted to be introduced into the low pressure stage 8 in common with the expanded and cooled second partial stream 102.

FIG. 2 shows an embodiment of the second embodiment of the method according to the invention. In this case, the second partial stream 102 is diverged from the first partial stream 101 at the branch point 21, heated in the heat exchanger 3 'and expanded in the turbine 13'. The work obtained in this case is transmitted to the third compressor 16.

The third partial stream is compressed in a third compressor to a pressure of at least 15 bar, in particular about 20 to 50 bar, and subsequently the second partial stream before being expanded in the heat exchanger 3 '.
Is cooled by heat exchange with the partial stream 102 and then introduced into a second post-compressor 14 connected to a turbine 15.

After the third compressor stage 16 and the heat exchanger 3 ′, a fourth partial stream 104 from the third partial stream 103 is branched (22), cooled in the main heat exchanger 5, and The squeezed expansion is introduced into the stage 7. This fourth partial stream 104
By means of countercurrent heat exchange with the oxygen, the oxygen is evaporated and is withdrawn through the conduit 9 of the low-pressure stage and brought into the pump 17 to a pressure of at least 4 bar, in particular 20 to 100 bar. 4th
The high-pressure air in this partial stream is condensed almost completely by this heat exchange and is fed into the high-pressure stage 7 above the first partial stream 101.

The process according to the invention, in which the feed air is fed directly into the low-pressure stage, ensures that the product oxygen (conduits 23 and 24 in the examples) has a purity of 85 to 98%. It has proven to be economically advantageous when it must. For example, if a 96% oxygen purity is desired, up to 35% of the feed air can be supplied to the second and third substreams 10 without significantly reducing the oxygen yield.
2, 103 can be supplied directly to the low pressure stage.

[0034]

According to the present invention, as described above, the first partial stream of the supply air is supplied to the high pressure stage of the two-stage rectification apparatus, and the second partial stream is supplied directly to the low pressure stage. In a cryogenic air separation process adapted to be introduced, a second partial stream is separated from the remaining feed air after adsorption purification and heated by heat exchange with the compressed feed air to produce a work stream. Is performed, and the work obtained at that time is supplied at least partially to a compressor or the like of supply air,
An excellent method of air separation is provided which improves economics and allows for inexpensive air purification, especially for obtaining moderately pure oxygen.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an example of the first embodiment of the air separation method according to the present invention.

FIG. 2 is a circuit diagram showing an example of a second embodiment of the air separation method according to the present invention.

[Explanation of symbols]

 2 First compressor stage 3 Heat exchanger 3 'Heat exchanger 4 Purifier 5 Main heat exchanger 6 Two stage rectifier 7 High pressure stage of two stage rectifier 6 8 Low pressure stage of two stage rectifier 6 Reference Signs List 9 oxygen 10 nitrogen 13 turbine 13 'turbine 14 second compressor 15 turbine 16 compressor 17 pump 21 branch point 101 first partial flow 102 second partial flow 103 third partial flow 104 fourth partial flow

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-64385 (JP, A) JP-A-58-194711 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F25J 1/00-5/00

Claims (11)

(57) [Claims] (1)It has a high pressure stage (7) and a low pressure stage (8)
In the method of separating air at low temperature with a two-stage rectifier (6)
hand, The supply air (1) is approximately high in the first compressor stage (2).
Compress to the pressure of the pressure stage, After pre-cooling the compressed supply air, it is compressed and purified.
Adsorbed in the purification device (4) to obtain the supply air
Purify by The compressed, purified supply air is passed through a first partial stream (10
1) and a second partial stream (102), Heating said second partial stream by indirect heat exchange (3,3 ')
And Cooling the second partial stream and compressing the process stream (2,16)
The heated second part to perform the work for
Expand the flow (13, 13 '), Introducing said expanded second partial stream into a low pressure stage (8); Introducing said first partial stream into a high pressure stage (7)
Low temperature separation method of air. 2. The indirect heat exchange of said second partial stream (3, 3).
The heating according to 3 ') comprises compressed unpurified supply air and
Compressed to cool compressed compressed supply air
Unpurified supply air or compressed and purified supply air
2. The method according to claim 1, wherein
Way. 3. A third downstream side of said adsorption and purification device (4).
Of the second compressor stage (1)
4), which is post-compressed, subsequently cooled (5), expanded to perform work (15) and fed into the low-pressure stage (8), The work obtained during the expansion (15) performing the work of the third partial stream is supplied for the post-compression of the third partial stream in the second compressor stage (14). 3. The method according to claim 1 or claim 2 , wherein 4. The expansion (1) performing the work of the second partial flow.
Claim 1 work obtained during 3) is characterized in that it is adapted to be supplied for driving the first compressor stage (2), in claim 2 or claim 3 The described method. 5. Indirect heat exchange with the supply air before the expansion of the second partial stream, after the first compressor stage (2) and before the purification device (4). This second
5. The method according to claim 4 , wherein the heating of the partial stream is performed. 6. The expansion (1) performing the work of the second partial flow.
3. The process according to claim 1, wherein the work obtained during 3 ') is supplied for post-compression of said third partial stream in a third compressor stage (16). 3. The method described in 3 . 7. A fourth partial stream (104) is diverted downstream of said purifier (4), post-compressed in a fourth compressor stage (16) and subsequently cooled (5). The work supplied to the high pressure stage (7) during the expansion (13 '), which performs the work of the second partial flow, is obtained in the fourth compressor stage (16). the method according to any one of claims 1 to claim 6, characterized in that it is made it takes to be supplied for the compression after the fourth partial flow. 8. A fourth part downstream of said purifier (4).
The split stream (104) is branched off and in the fourth compressor stage (16)
At the high-pressure stage
(7), wherein the work of the second partial flow is
The work obtained during the inflation (13 ') performed is the fourth pressure
Post-compression of said fourth partial flow in a compressor stage (16).
And the third
7. The method as claimed in claim 6 , wherein the fourth partial stream is post-compressed in a common third compressor stage (16). 9. The heating of the second partial stream is performed prior to its expansion, after the third and / or after compression in the third or fourth compressor stage (16). the method according to any one of claims 6 to 8 characterized in that it is carried out by 4 indirect heat exchange with a partial stream of (3 '). 10. Liquefied oxygen is withdrawn (9) from said low pressure stage (8), brought to high pressure (17) and indirect heat exchange (5) with said post-compressed fourth partial stream (104). The method according to any one of claims 6 to 9 , wherein the method is evaporated. 11. The fourth partial stream (104) is at least partially condensed during indirect heat exchange with the oxygen to be evaporated, and is subsequently condensed above the first partial stream (101). The method according to claim 10 , wherein the method is adapted to be introduced into the high-pressure stage (7).