US20120174625A1

US20120174625A1 - Method and device for producing a gaseous pressurized oxygen product by cryogenic separation of air

Info

Publication number: US20120174625A1
Application number: US13/389,862
Authority: US
Inventors: Thomas Rathbone; Frances Masterson
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 2009-08-11
Filing date: 2010-08-10
Publication date: 2012-07-12
Also published as: EP2464937A2; CN102741636A; WO2011018207A3; RU2012108588A; WO2011018207A2

Abstract

Process and apparatus for producing a pressurized gaseous oxygen product by cryogenic air separation

The process and the apparatus serve for producing a pressurized gaseous oxygen product by cryogenic air separation in a distillation column system which has at least one separating column. Feed air is compressed in an air compressor. A first partial stream (2, 4, 6, 7) of the compressed feed air is expanded (5, 8) while performing work. A second partial stream (3) of the compressed feed air (1) is cooled and liquefied or pseudo-liquefied and subsequently introduced into the distillation column system. A liquid oxygen product stream (51) is removed from the distillation column system, brought to a first increased pressure in the liquid state (52), vaporized or pseudo-vaporized under this first increased pressure by indirect heat exchange (10) with the second partial stream (3) of the compressed feed air, warmed to approximately ambient temperature (10) and finally drawn off as a gaseous product stream (55). The vaporized or pseudo-vaporized oxygen product stream (53) is brought further to a second increased pressure, which is higher than the first increased pressure, in a cold compressor (13). The product stream (54) is warmed to approximately ambient temperature under this second increased pressure (10). At least part of the mechanical energy produced in the work-performing expansion (5, 8) of the first partial stream (3) is used for driving the cold compressor (13).

Description

The invention relates to a process according to the preamble of patent claim 1.
In the process, an oxygen product stream compressed in liquid form is vaporized against a heat transfer medium and finally obtained as a pressurized gaseous product. This method is also referred to as internal compression. It serves for obtaining pressurized oxygen. In the case of a supercritical pressure, there is no phase transition in the actual sense; the product stream is then “pseudo-vaporized”.
A heat transfer medium under high pressure is liquefied (or pseudo-liquefied if under supercritical pressure) against the (pseudo) vaporizing product stream. The heat transfer medium is often formed by part of the air, in the present case by the “second partial stream” of the compressed feed air.
Internal compression processes are known, for example, from DE 830805, DE 901542 (=U.S. Pat. No. 2,712,738/U.S. Pat. No. 2,784,572), DE 952908, DE 1103363 (=U.S. Pat. No. 3,083,544), DE 1112997 (=U.S. Pat. No. 3,214,925), DE 1124529, DE 1117616 (=U.S. Pat. No. 3,280,574), DE 1226616 (=U.S. Pat. No. 3,216,206), DE 1229561 (=U.S. Pat. No. 3,222,878), DE 1199293, DE 1187248 (=U.S. Pat. No. 3,371,496), DE 1235347, DE 1258882 (=U.S. Pat. No. 3,426,543), DE 1263037 (=U.S. Pat. No. 3,401,531), DE 1501722 (=U.S. Pat. No. 3,416,323), DE 1501723 (=U.S. Pat. No. 3,500,651), DE 253132 (=U.S. Pat. No. 4,279,631), DE 2646690, EP 93448 B1 (=U.S. Pat. No. 4,555,256), EP 384483 B1 (=U.S. Pat. No. 5,036,672), EP 505812 B1 (=U.S. Pat. No. 5,263,328), EP 716280 B1 (=U.S. Pat. No. 5,644,934), EP 842385 B1 (=U.S. Pat. No. 5,953,937), EP 758733 B1 (=U.S. Pat. No. 5,845,517), EP 895045 B1 (=U.S. Pat. No. 6,038,885), DE 19803437 A1, EP 949471 B1 (=U.S. Pat. No. 6,185,960 B1, EP 955509 A1 (=U.S. Pat. No. 6,196,022 B1), EP 1031804 A1 (=U.S. Pat. No. 6,314,755), DE 19909744 A1, EP 1067345 A1 (=U.S. Pat. No. 6,336,345), EP 1074805 A1 (=U.S. Pat. No. 6,332,337), DE 19954593 A1, EP 1134525 A1 (=U.S. Pat. No. 6,477,860), DE 10013073 A1, EP 1139046 A1, EP 1146301 A1, EP 1150082 Al, EP 1213552 A1, DE 10115258 A1, EP 1284404 A1 (=US 2003051504 A1), EP 1308630 A1 (=U.S. Pat. No. 6,612,129 B2), DE 10213212 A1, DE 10213211 A1, EP 1357342 A1 or DE 10238282 A1, DE 10302389 A1, DE 10334559 A1, DE 10334560 A1, DE 10332863 A1, EP 1544559 A1, EP 1585926 A1, DE 102005029274 A1, EP 1666824 A1, EP 1672301 A1, DE 102005028012 A1, WO 2007033838 A1, WO 2007104449 A1, EP 1845324 A1, DE 102006032731 A1, EP 1892490 A1, DE 102007014643 A1, EP 2015012 A2, EP 2015013 A2, EP 2026024 A1, WO 2009095188 A2 or DE 102008016355 A1.
Such internal compression processes have many advantages, but require that part of the feed air is made available under particularly high pressure as a heat transfer medium. Energy must correspondingly be expended for this.
The invention is based on the object of providing a process of the type mentioned at the beginning and a corresponding apparatus that operate particularly favorably in terms of energy.
This object is achieved by the characterizing features of claim 1.
In this case, the pressure increase to the product pressure (the “second increased pressure”) is not entirely carried out in the liquid state but only partly, that is to the lower “first increased pressure”. The rest of the pressure increase is performed after the (pseudo) vaporization in the cold, but gaseous state. This initially appears to be paradoxical, since a main advantage of the internal compression is to substitute the compression in the gaseous state by an increase in pressure in the liquid state. Moreover, the cold compression has the effect of introducing heat into the process that cannot be removed by means of economical coolants such as cooling water, as would be the case with warm compression.
However, it has been found within the scope of the invention that the advantages of this procedure outweigh the likely disadvantages. The (pseudo) vaporization pressure, lying below the final pressure, also allows the pressure of the second partial stream, which supplies the heat, to be chosen correspondingly lower. Furthermore, mechanical energy produced in the process itself is used for driving the cold compressor; for this purpose, particularly the expander for the first partial stream of the feed air is mechanically coupled directly to the cold compressor, for example via a common shaft or a transmission. However, even the apparent disadvantage of an increased temperature when the cold-compressed product stream re-enters the heat exchange has proven to be an advantage. It allows a critical point in the heat exchange diagram to be avoided and particularly efficient heat exchange is achieved overall between feed air to be cooled and returning streams to be warmed. Only the further energy-saving caused as a result brings about the surprisingly high reduction in energy consumption within the scope of the invention.
The inlet temperature of the cold compressor lies, for example, 2 to 50 K, preferably 5 to 10 K, above the (pseudo) vaporization temperature of the product stream under the first increased pressure. The process is particularly favorable when the oxygen product pressure (“second increased pressure”) lies between 20 and 40 bar. The pressure ratio at the cold compressor is preferably 1.4 to 2.1, the “first increased pressure” between 10 and 30 bar.
In principle, the process can be carried out with a single expander. In this case, a dissipative brake, a generator or a warm compressor must be coupled to the expander in addition to the cold compressor in order to produce the cold necessary for the process. Alternatively, a second expander with a suitable process stream may be operated, assuming the task of producing the cold.
The work-performing expansion of the first partial stream is preferably carried out in two expanders connected in parallel or in series. In this case, for example, one of the two expanders may be coupled to the cold compressor and the other to a warm compressor, a generator or a dissipative brake.
If the expanders are connected in series, it is favorable if the first partial stream is warmed up between the two expanders (intermediate warming).
If the expanders are connected in parallel, it is favorable if the two expanders have the same inlet temperature and/or the same inlet pressure and the same outlet pressure and/or the same outlet temperature.
In a special embodiment of the invention, mechanical energy from both expanders is used for driving the cold compressor. Both expanders are therefore mechanically coupled to the cold compressor (and optionally in addition to a warm compressor, a generator or a dissipative brake). Instead of one or two conventional booster turbines, in this case two turbines connected in series are used, mechanically coupled to each other, for example via a common shaft, or a transmission machine. The construction with both turbine wheels in a common housing, driving a common shaft and thus representing a unit, is particularly advantageous. The common shaft drives the cold compressor and optionally a further braking device, for example a dissipative brake, a generator or a warm compressor.
It is favorable if the cooling of the feed air, the liquefaction or pseudo-liquefaction of the second partial stream, the vaporization or pseudo-vaporization of the product stream and the warming of the product stream are carried out in a main heat exchanger. The “main heat exchanger” may be formed by one or more heat exchanger portions connected in parallel and/or in series, for example one or more plate heat exchanger blocks.
The invention also relates to an apparatus for producing a pressurized gaseous product by cryogenic air separation according to patent claims 8 to 13.

The invention and further details of the invention are explained in more detail below on the basis of exemplary embodiments that are presented in the drawings. The drawings only comprise the essential details of the process and of a corresponding apparatus; in particular, the air compressor and the distillation column system are not represented. The latter is preferably formed by a conventional two-column system for nitrogen-oxygen separation. In the drawings:

FIG. 1 shows a first exemplary embodiment of the invention with a combined machine

FIGS. 2 to 5 show further embodiments, in which only one expander respectively drives the cold compressor.

Components and process steps that correspond to one another bear the same designations in all the drawings.
In FIG. 1, air 1 flows from the main air compressor and the downstream air purification (neither represented) under very high pressure and is divided into a first partial stream 2 (turbine stream) and a second partial stream 3 (throttle stream).
The first partial stream 2 is introduced into a main heat exchanger 10 at the warm end thereof. At an intermediate temperature, the first partial stream is removed again via line 4 and subsequently expanded to an intermediate pressure in a first turbine 5 while performing work. The intermediately compressed air 6 is warmed again in the main heat exchanger 10 (intermediate warming) and fed via line 7 to a second turbine 8 and expanded there from the intermediate pressure to approximately the operating pressure of the high-pressure column of the distillation column system (not represented) while performing work. The exhaust air 9 of the second turbine 8 is fed to the high-pressure column as substantially gaseous feed air.
The second partial stream 3 is passed through the main heat exchanger 10 under very high pressure up to the cold end and thereby supplies the heat for an oxygen product stream vaporizing or pseudo-vaporizing under pressure, which has been removed from the distillation column system in liquid form (51-LOX) and brought to a “first increased pressure” of 19.5 bar in a pump 52. (The other return streams through the main heat exchanger are not represented here.) The cold second partial stream is expanded to approximately high-pressure column pressure in a throttle valve 11 and introduced in liquid form or as a two-phase mixture into one or more columns of the distillation column system.
The two turbines 5, 8 are mechanically coupled, to be precise by a common shaft 12, which drives them both. Also seated on this shaft is a cold compressor 13, which is driven by means of the mechanical energy produced in the turbines and transferred to the shaft 12. The shaft also drives a dissipative brake, a generator or a warm compressor (not represented).
The vaporized product stream 53 is drawn off from the main heat exchanger 10 at an intermediate temperature of approximately 5 to 10 K above the (pseudo) vaporization temperature and fed to the cold compressor 13. There, it is compressed from the “first increased pressure” further to a “second increased pressure” of 33 bar. It leaves the cold compressor (line 54) at a temperature which is 15 to 30 K higher than the inlet temperature and is then fed at a suitable point to the main heat exchanger 10 again and warmed there to approximately ambient temperature. Finally, the pressurized gaseous product (PGOX) is removed from the warm end via line 55.
In the case of FIG. 2, the two expanders are connected in parallel. The first partial stream 4 at the intermediate temperature is in this case divided into two branch streams 204, 207, which are respectively expanded in only one of the turbines 205, 208 while performing work. The two expanded air streams are reunited and passed on via line 9, as in FIG. 1.
Furthermore, the two turbines are designed as two separate machines. The first turbine 205 drives a warm compressor 223 via a first common shaft. This compressor is formed as a re-compressor for the feed air 1 compressed in the air compressor (not represented). There then follows a re-cooler and the re-compressed air is passed via line 201 to the warm end of the main heat exchanger 10. The second turbine 208 drives the cold compressor 13 for the (pseudo) vaporized product stream 53 via a second common shaft.
FIG. 3 differs from FIG. 2 in that not the entire air 1 is re-compressed, but only the second partial stream 303. For this purpose, the feed air 1 compressed in the air compressor is already divided into the first partial stream 2 and the second partial stream 303 upstream of the re-compressor 323, and only the second partial stream 303 is fed to the re-compressor 323. The re-compressed second partial stream 3 is finally passed as before to the warm end of the main heat exchanger 10 and forms the throttle stream.
In FIG. 4, a further modification of FIG. 2 is represented. Here, the compressed feed air is pre-cooled upstream of the re-compressor 223 in an additional group of passages 410 of the main heat exchanger 10, as is explained in more detail in DE 102007042462.
In an analogous way, the exemplary embodiment of Figure differs from FIG. 3 by the additional group of passages 510 of the main heat exchanger.

Claims

1. A process for producing a pressurized gaseous oxygen product by cryogenic air separation in a distillation column system which has at least one separating column, in which process

feed air is compressed in an air compressor,

a first partial stream (2, 4, 6, 7) of the compressed feed air is expanded (5, 8) while performing work,

a second partial stream (3) of the compressed feed air (1) is cooled and liquefied or pseudo-liquefied and subsequently introduced into the distillation column system,

a liquid oxygen product stream (51) is removed from the distillation column system, brought to a first increased pressure (52) in the liquid state, vaporized or pseudo-vaporized under this first increased pressure by indirect heat exchange (10) with the second partial stream (3) of the compressed feed air, warmed to approximately ambient temperature (10) and finally drawn off as a gaseous product stream (55), characterized in that

the vaporized or pseudo-vaporized oxygen product stream (53) is brought further to a second increased pressure, which is higher than the first increased pressure, in a cold compressor (13) and

the product stream (54) under this second increased pressure is warmed to approximately ambient temperature (10), wherein

at least part of the mechanical energy produced in the work-performing expansion (5, 8) of the first partial stream (3) is used for driving the cold compressor (13).

2. The process as claimed in claim 1, characterized in that the work-performing expansion of the first partial stream (2, 4, 6, 7) is carried out in two expanders (5, 8) connected in parallel or in series.

3. The process as claimed in claim 2, characterized in that the first partial stream (6) is warmed between the two expanders connected in series (10).

4. The process as claimed in claim 2, characterized in that the two expanders connected in parallel have the same inlet temperature and/or the same inlet pressure.

5. The process as claimed in claim 4, characterized in that the two expanders connected in parallel have the same outlet pressure and/or the same outlet temperature.

6. The process as claimed in claim 2, characterized in that mechanical energy of both expanders (5, 8) is used for driving the cold compressor (13).

7. The process as claimed in claim 1, characterized in that the cooling of the feed air, the liquefaction or pseudo-liquefaction of the second partial stream, the vaporization or pseudo-vaporization of the product stream and the warming of the product stream are carried out in a main heat exchanger.

8. An apparatus for producing a pressurized gaseous oxygen product by cryogenic air separation

with a distillation column system which has at least one separating column,

with an air compressor for compressing feed air,

with a first expander for the work-performing expansion (5, 8) of a first partial stream (2, 4, 6, 7) of the compressed feed air,

with means for cooling and liquefying or pseudo-liquefying a second partial stream (3) of the compressed feed air (1),

with means for introducing the liquefied or pseudo-liquefied first partial stream into the distillation column system,

with means for removing a liquid oxygen product stream (51) from the distillation column system, bringing it to a first increased pressure (52) in the liquid state, vaporizing or pseudo-vaporizing it under this first increased pressure by indirect heat exchange (10) with the second partial stream (3) of the compressed feed air, warming it to approximately ambient temperature (10) and finally drawing it off as a gaseous product stream (55), characterized by

a cold compressor (13) for further increasing the pressure of the vaporized or pseudo-vaporized oxygen product stream (53) to a second increased pressure, which is higher than the first increased pressure, by

means for warming (10) the product stream (54) under this second increased pressure to approximately ambient temperature and by

means for transmitting at least part of the mechanical energy produced in the work-performing expansion (5, 8) of the first partial stream (3) to the cold compressor (13).

9. The apparatus as claimed in claim 8, characterized by a second expander (8) for the work-performing expansion of the first partial stream (2, 4, 6, 7), which is connected to the first expander (5) in parallel or in series.

10. The apparatus as claimed in claim 8, characterized by means for warming (10) the first partial stream (6) between the two expanders connected in series.

11. The apparatus as claimed in claim 8, characterized in that the two expanders connected in parallel have the same inlet temperature, the same inlet pressure, the same outlet pressure and/or the same outlet temperature.

12. The apparatus as claimed in claim 8, characterized by means for transmitting mechanical energy from both expanders (5, 8) to the cold compressor (13).

13. The apparatus as claimed in claim 8, characterized in that the cooling of the feed air, the liquefaction or pseudo-liquefaction of the second partial stream, the vaporization or pseudo-vaporization of the product stream and the warming of the product stream are carried out in a main heat exchanger.