Method and device for recovering high-pressure oxygen and high-pressure nitrogen

Abstract

The method and device according to the invention provide for recovery of high-pressure oxygen and high-pressure nitrogen by low-temperature separation of air in a distillation-column system. This system comprises a high-pressure column, a low-pressure column, and a main condenser. A first air feed stream is cooled at a first subcritical pressure in a main heat exchanger to approximately dew point and introduced at least partially into the high-pressure column. A second air feed stream is brought to a second, supercritical, pressure, cooled, depressurized, and introduced at least partially into the distillation-column system. A first partial stream of the second air feed stream is cooled in the main heat exchanger, and a second partial stream is cooled in a high-pressure heat-exchanger system. The first and second partial streams are then merged and work-expanded in a liquid turbine.

Claims

1. A method for recovering high-pressure oxygen and high-pressure nitrogen by low-temperature separation of air in a distillation-column system comprising a high-pressure column (4) and a low-pressure column (5), which are in heat-exchange connection via a main condenser (6) which is a condenser-evaporator, said method comprising: Cooling a first air feed stream (100, 101) at a first, subcritical, pressure, which is less than 1 bar above the operating pressure of said high-pressure column (4), in a main heat exchanger (2), and introducing (3) the cooled first air feed stream into said high-pressure column (4), Cooling a second air feed stream (200) at a second, supercritical, pressure, and subsequently depressurizing and introducing the cooled second air feed stream into said distillation-column system, Pressurizing (17) a liquid oxygen stream (16) from said low-pressure column (5), in the liquid state, to a first product pressure which is higher than the operating pressure of said low-pressure column, heating said liquid oxygen stream (16) at the first product pressure in a heat-exchanger system (11, 12) having at least two helically-wound heat exchangers connected in series, and ultimately recovering as a high-pressure oxygen product stream (18), Pressurizing (20) a liquid nitrogen stream (19) from said high-pressure column (4) or from said main condenser (6), in the liquid state, to a second product pressure which is higher than the operating pressure of said high-pressure column (4), heating said liquid nitrogen stream (19) at the second product pressure to approximately ambient temperature, and ultimately recovering as a high-pressure nitrogen product stream (21), Cooling a first partial stream (210) of said second air feed stream (200) by indirect heat exchange in said main heat exchanger (2), Cooling a second partial stream (202, 221) of said second air feed stream (200) in said heat-exchanger system (11, 12), Merging said first partial stream (211) and said second partial stream (221) of the second air feed stream downstream from their cooling to form a merged second air feed stream, Wherein the heating of the liquid nitrogen stream (19) that is pressurized in liquid form is performed in said main heat exchanger (2) by indirect heat exchange with said first air feed stream (100) and said first partial stream (210) of said second air feed stream (200), Wherein said merged second air feed stream is depressurized in a liquid turbine (13) before said merged second air feed stream is introduced (205, 3) into said distribution-column system, a third partial stream (230) of said second air feed stream (200), cooled to an intermediate temperature in said heat-exchanger system, is branched off from the second partial stream (206) of said second air feed stream between the two helically-wound heat exchangers (11, 12) of said heat-exchanger system, and introduced into the main heat exchanger (2) at an intermediate point and further cooled therein, and after said third partial stream (230) is branched off from said second partial stream, the remainder of the second partial stream (206) of the second air feed stream is further cooled in said heat-exchanger system (12), said method further comprising cooling a third air feed stream (300) at a third pressure which is above said first, subcritical, pressure and below said second, supercritical, pressure, in said main heat exchanger (2), removing the cooled third air feed stream from said main heat exchanger at an intermediate point, expanding the cooled third air feed stream, and introducing the cooled and expanded third air feed stream into said high-pressure column (4), and wherein the entirety of said cooled first air feed stream, said cooled second air feed stream, and said cooled and expanded third air feed stream are introduced into said high-pressure column (4).

2. The method according to claim 1, wherein said third partial stream (231) is merged with said first partial stream (211) and said second partial stream (221) downstream of said main heat exchanger (2) and upstream from said liquid turbine (13).

3. The method according to claim 1, wherein the first product pressure is higher than 100 bar.

4. The method according to claim 3, wherein the first product pressure is higher than 110 bar.

5. The method according to claim 3, wherein the first product pressure is between 105 and 135 bar.

6. The method according to claim 1, wherein the second product pressure is lower than 100 bar.

7. The method according to claim 6, wherein the second product pressure is lower than 90 bar.

8. The method according to claim 7, wherein the second product pressure is between 30 and 80 bar.

9. The method according to claim 1, wherein the second, supercritical pressure is lower than the first product pressure.

10. The method according to claim 9, wherein the second, supercritical pressure is less than 100 bar.

11. The method according to claim 10, wherein the second, supercritical pressure is less than 90 bar.

12. The method according to claim 10, wherein the second, supercritical pressure is between 60 and 90 bar.

13. The method according to claim 1, wherein first subcritical pressure is between 5.0 and 6.0 bar.

14. The method according to claim 13, wherein first subcritical pressure is between 5.3 and 5.7 bar.

15. The method according to claim 1, wherein said third partial is introduced into the main heat exchanger at a temperature of between 220 and 120 K.

16. The method according to claim 15, wherein said third partial is introduced into the main heat exchanger at a temperature of between 190 and 150 K.

17. The method according to claim 1, wherein the intermediate point at which said third partial stream (231) is introduced into said main heat exchanger (2) is closer to the cold end of said main heat exchanger (2) than the intermediate point at which said cooled third air feed stream is removed from said main heat exchanger (2).

18. The method according to claim 1, wherein said third pressure of said third air feed stream (300) is 53 to 61 bars.

19. The method according to claim 1, wherein said cooled third air feed stream (300) is removed from said main heat exchanger at temperature that is higher than the intermediate temperature of the third partial stream (230) of the second air feed stream.

20. The method according to claim 1, wherein the following gas streams are heated in said main heat exchanger: a low pressure gaseous pure nitrogen (22, 23) removed from the top of said low-pressure column (5), a low pressure gaseous impure nitrogen (24, 25) removed from an intermediate point of said low-pressure column (5), and gaseous nitrogen (26, 27) removed from the top of said high-pressure column (4).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The inventive process and apparatus, as well as further aspects of the invention, are explained in more detail below based on an embodiment which is diagrammatically depicted in the FIGURE.

(2) All of the air is compressed in a main air compressor to a first, subcritical pressure of 6 bar and then precooled and purified (not shown). The purified feed air 1 is divided up into a first air feed stream 100, a second air feed stream 200, and a third air feed stream 300.

(3) The first air feed stream 100 is introduced at this first pressure into a main heat exchanger 2, and it completely flows through the latter from the hot to the cold end. The first air feed stream 101, cooled to approximately its dew-point temperature, is then introduced via line 3 into the high-pressure column 4 of a distillation-column system, which in addition has a low-pressure column 5 and a main condenser 6. The two columns, as depicted, are arranged above one another as a standard double column arrangement; as an alternative, they could stand beside one another. Generally, the operating pressure of the high-pressure column is around 4.9 to 7.0 bars, preferably 5.3 to 6.1 bars, and the general operating pressure of the low-pressure column is around 1.1 to 2.3 bars, preferably 1.2 to 1.4 bars

(4) The second air feed stream 200 is compressed in a first secondary compressor 7, cooled in a first secondary condenser 8, further compressed in a second secondary compressor 9 to a second, supercritical pressure of 85 bar, and then cooled a second secondary condenser 10. Thereafter, the second air feed stream 200 is divided at 201 into a first partial stream 210 and a second partial stream 202. The first partial stream 210/211 of the second air feed stream 200 also completely flows through the main heat exchanger 2 from the hot end up to the cold end. The second partial stream 220/221 of the second air feed stream does not flow through the main heat exchanger 2 at all. The latter is cooled completely in a high-pressure heat-exchanger system, which is formed in the embodiment from two helically-wound heat exchangers 11, 12, which are arranged in separate shells.

(5) At 204, the three partial streams (the third partial stream is described below) of the second air feed stream are recombined and then work-expanded in a liquid turbine 13 to the operating pressure of the high-pressure column (approximately 6 bar). The liquid turbine is braked by a generator 14. The resultant work-expanded second air feed stream 205 is introduced into the high-pressure column 4 in a predominantly liquid state.

(6) A third partial stream 230 of the second air feed stream 200 is cooled to an intermediate temperature of 165 K together with the second partial stream 220 in the hot helically-wound heat exchanger 11, and then removed from helically-wound heat exchanger 11 via line 203. At 206, the third partial stream 230 is split off (branched off) from the second partial stream 220, and the third partial stream 230 is then fed to the main heat exchanger 2 at an intermediate point that corresponds to its temperature. The third partial stream 230 is ultimately cooled in the main heat exchanger 2 up to the cold end thereof. The completely cooled third partial stream 231 removed from the cold end of the main heat exchanger 2 is combined at 204 with the remainder of the second air feed stream (i.e., the first and second partial streams).

(7) Together with the second air feed stream 200, a third air feed stream 300 is further compressed to a third pressure of, for example, 49 to 61 bars, preferably 53 to 57 bars, e.g., 55 bar, in the secondary compressor 7 and at this pressure enters into the hot end of the main heat exchanger 2. At a temperature that is somewhat higher than the intermediate temperature of the third partial stream 230 of the second air feed stream, the third air feed stream 301 is removed from the main heat exchanger 2 and work-expanded in an air turbine 15 to approximately the operating pressure of the high-pressure column 4. The air turbine 15 drives the second secondary compressor 9. The resultant turbine-depressurized third air feed stream 303 is introduced in gaseous form into the high-pressure column 4 via line 3.

(8) A liquid oxygen stream 16 from the low-pressure column 5 is brought in an oxygen pump 17 in the liquid state to a first product pressure that is approximately 115 bar, in this exemplary embodiment. The liquid oxygen stream 16 is heated at this first product pressure to approximately ambient temperature in the high-pressure heat-exchanger system 12/11, and is ultimately recovered as a high-pressure oxygen product stream 18. The oxygen flows through the interior of the helically-wound pipes of the heat exchangers 11 and 12, and the second air feed stream 202 or 206 flows through the shell thereof.

(9) A liquid nitrogen stream 19 removed from the high-pressure column 4 (it could also be removed from the main condenser 6) is brought in the liquid state to a second product pressure in a nitrogen pump 20 (this second product pressure is approximately 80 bar in this exemplary embodiment). The pressurized liquid nitrogen stream is then heated at this second product pressure to approximately ambient temperature, and is ultimately recovered as a high-pressure nitrogen product stream 21.

(10) In addition, the following gas streams are heated in the main heat exchanger 2: a low pressure gaseous pure nitrogen 22/23 removed from the top of the low-pressure column 5, a low pressure gaseous impure nitrogen 24/25 removed from an intermediate point of the low-pressure column 5, and pressurized gaseous nitrogen 26/27 removed from the top of the high-pressure column 4.

(11) A portion of the low-pressure nitrogen 23, 25 can be used for regeneration of the purification unit for the charging air (not shown). The heated pressurized gaseous nitrogen can be used as seal gas 28 and/or as a medium-pressure product 29.

(12) Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

(13) The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

(14) From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.

(15) The entire disclosures of all applications, patents and publications, cited herein and of corresponding European patent application No. 13000875.8, filed Feb. 21, 2013, are incorporated by reference herein.