PROCESS AND PLANT FOR CRYOGENIC SEPARATION OF AIR

Abstract

A process for cryogenic separation of air using an air separation plant configured as a high air pressure air separation plant is provided, wherein of the air initially compressed several partial air streams are formed which are at least in part further compressed, cooled in a main heat exchanger and expanded before being introduced into the column system. The partial air streams include a first partial air stream and a second partial air stream whose air is compressed in parallel in a first warm booster and a second warm booster and thereafter expanded in a first expander and a second expander mechanically coupled to the first booster and to the second booster, respectively. A corresponding air separation plant is also part of the present invention.

Claims

1. A process for cryogenic separation of air using an air separation plant comprising a column system with a pressure column operated at a pressure in a first pressure range and a low-pressure column operated at a pressure in a second pressure range below the first pressure range, wherein the column system, and thereof at least the pressure column, is supplied with compressed air, all air being supplied to the column system being compressed to a pressure in a third pressure range at least 5 bar above the first pressure range, and of the air compressed to the first pressure range, several partial air streams being formed which are at least in part further compressed, cooled in a main heat exchanger and expanded before being introduced into the column system, the partial air streams include a first partial air stream whose air is, at least in part, in the order indicated and in a single pass, compressed to a pressure in a fourth pressure range above the third pressure range in a first booster being operated with an inlet temperature of more than 0 C., cooled in the main heat exchanger, expanded in a first expander mechanically coupled to the first booster to a pressure in the first pressure range, and introduced into the pressure column, the partial air streams include a second partial air stream whose air is at least in part, in the order indicated and in a single pass, supplied at a pressure in a fifth pressure range being above or corresponding to the third pressure range to a second expander, expanded in the second expander to a pressure in a sixth pressure range between the first and the fifth pressure range, further expanded to a pressure in the first or second pressure range, and introduced into the column system, the air of the second partial air stream is at least in part cooled before being expanded to the pressure in the sixth pressure range in a first cooling step and at least in part cooled after having been expanded to the pressure in the sixth pressure range in a second cooling step, the first and second cooling steps being performed using the main heat exchanger, internally compressed gaseous oxygen is produced in and withdrawn from the process at an absolute pressure between 3 and 9 bar, and the air separation plant is operated without a turbine expanding air of the first partial stream and/or air of the second partial stream into the low pressure column.

2. The method according to claim 1, wherein the fifth pressure range is above the third pressure range, wherein at least a part of the air of the second partial air stream is, before being expanded in the second expander, compressed to the pressure in the fifth pressure range in a second booster mechanically coupled to the second expander, the second booster being coupled with an inlet temperature of more than 0 C.

3. The method according to claim 1, wherein the partial air streams include a third partial air stream whose air is at least in part liquefied in the main heat exchanger, expanded to a pressure in the first or second pressure range and introduced into the column system.

4. The method according to claim 1, wherein the air of the third partial air stream is, at least in a first operation mode, at least in part compressed to the pressure in the fourth pressure range in the first booster and liquefied in the main heat exchanger at the pressure in the fourth pressure range.

5. The method according to claim 4, wherein the air of the third partial air stream is, in a second operation mode, at least in part liquefied in the main heat exchanger at the pressure in the third pressure range.

6. The method according to claim 5, wherein, in the second operating mode at least the 1.1-fold and up to the 3.0-fold amount of internally compressed gaseous oxygen is withdrawn from the air separation plant as compared to the first operating mode and wherein, in the second operating mode, at most the 0.5-fold amount of liquid oxygen is withdrawn from the air separation plant as compared to the first operating mode.

7. The process according to claim 1, wherein liquid products are withdrawn from the air separation plant, wherein a ratio of an equivalent value characterizing a total amount of the liquid products to a total amount of the internally compressed gaseous oxygen is in a range from 0.6 to 1.6, the equivalent value corresponding to the sum of all liquid nitrogen products, all liquid oxygen products multiplied by a factor of 1.08, and all liquid argon products multiplied by a factor of 0.8, all values being expressed in normalized cubic meters per hour.

8. The process according to claim 1, wherein the first pressure range is from 4 to 7 bar, the second pressure range is from 1 to 2 bar, the third pressure range is from 15 to 28 bar, the fourth pressure range is from 20 to 38 bar, the fifth pressure range is from 20 to 45 bar and the sixth fifth pressure range is from 9 to 21 bar absolute pressure.

9. The process according to claim 1, wherein, from the air compressed to the third pressure range, a relative proportion of 0.6 to 0.8 is provided as the first partial air stream and a relative proportion of 0.15 to 0.30 is provided as the second partial air stream.

10. The process according to claim 2 wherein, from the air compressed to the third pressure range, a relative proportion of 0.05 to 0.15 is provided as the third partial air stream.

11. The process according to claim 1, wherein the air of the second partial air stream is at least in part liquefied in the main heat exchanger before being expanded to the pressure in the first pressure range or in the second pressure range and thereafter being introduced into the column system.

12. The process according to claim 1, wherein the air of the first partial air stream is at least in part cooled in the main heat exchanger to a temperature in a temperature range between 132 and 92 C. before being expanded in the first expander and wherein the air of the second partial air stream is at least in part cooled in the first cooling step to a temperature in a temperature range between 30 and 30 C. and in the second cooling step to a temperature in a temperature range between 87 and 47 C.

13. The process according to claim 1, wherein gaseous nitrogen withdrawn from the pressure column is heated in the main heat exchanger and thereafter compressed to a product pressure.

14. An air separation plant comprising a column system with a pressure column adapted to be operated at a pressure in a first pressure range, a low-pressure column adapted to be operated at a pressure in a second pressure range below the first pressure range, a first booster adapted to be operated with an inlet temperature of more than 0 C., a first expander mechanically coupled to the first booster, a second expander, and a main heat exchanger, wherein the air separation plant comprises means adapted to supply to the column system, and thereof at least to the pressure column, compressed air, to compress all air being supplied to the column system to a pressure in a third pressure range at least 5 bar above the first pressure range, to form, of the air compressed to the pressure in the first pressure range, several partial air streams, and to at least in part further compress, cool in the main heat exchanger and expand before being introduced into the column system said partial air streams, the partial air streams include a first partial air stream, and the air separation plant comprises means adapted to subject the air of the first partial air stream at least in part, in the order indicated and in a single pass, to a compression in the first booster to a pressure in a fourth pressure range above the third pressure range, to an expansion in the first expander to a pressure in the first pressure range, and a cooling in the main heat exchanger before said expansion to the pressure in the first pressure range, and to an introduction into the pressure column after said expansion to the pressure in the first pressure range, the partial air streams include a second partial air stream, and the air separation plant comprises means adapted to subject the air of the second partial air stream at least in part in the order indicated and in a single pass, to an expansion from a pressure in a fifth pressure range being above or corresponding to the third pressure range, in the second expander to a pressure in a sixth pressure range between the first and the fifth pressure range, to a further expansion to a pressure in the first or second pressure range and to an introduction into the column system, the air separation plant is adapted to cool the air of the second partial air stream at least in part before being expanded to the pressure in the sixth pressure range in a first cooling step and to cool the air of the second partial air stream at least in part after having been expanded to the pressure in the sixth pressure range in a second cooling step, and to perform the first and second cooling steps using the main heat exchanger, the air separation plant comprises means which are adapted to produce in and withdraw from the air separation plant internally compressed gaseous oxygen at an absolute pressure between 3 and 9 bar, and the air separation plant is adapted to be operated without a turbine expanding air of the first partial stream and/or air of the second partial stream into the low pressure column.

15. The air separation plant according to claim 14, wherein a second booster is provided which is adapted to be operated with an inlet temperature of more than 0 C. and which is mechanically coupled to the second expander, wherein the second booster is adapted to compress at least a part of the air of the second partial air stream to the pressure in the fifth pressure, the fifth pressure range being above the third pressure range.

Description

SHORT DESCRIPTION OF THE FIGURES

[0066] FIG. 1 illustrates an air separation plant according to a particularly preferred embodiment of the present invention.

[0067] FIG. 2 illustrates an air separation plant according to a further particularly preferred embodiment of the present invention.

[0068] FIG. 3 illustrates an air separation plant according to a further particularly preferred embodiment of the present invention.

[0069] FIG. 4 illustrates an air separation plant according to a further particularly preferred embodiment of the present invention.

[0070] Hereinafter, explanations relating to methods and steps thereof shall equally apply to apparatus adapted to carry out such method.

EMBODIMENTS OF THE INVENTION

[0071] FIG. 1 illustrates an air separation plant 100 according to a particularly preferred embodiment of the present invention.

[0072] Air separation plants of the type shown are described elsewhere, for example in H.-W. Hring (eds.), Industrial Gases Processing, Wiley-VCH, 2006, in particular Section 2.2.5, Cryogenic Rectification. For detailed explanations of the structure and function, additional reference is made to the relevant technical literature. An air separation plant for the application of the present invention can be designed in a variety of ways, provided it comprises the features claimed.

[0073] The air separation plant 100 shown in FIG. 1 comprises, among other things, a main air compressor 1, an absorber skid 2, a main heat exchanger 3, an expansion turbine 4 coupled to a booster 5, i.e. a booster turbine, an expansion turbine 6 coupled to a booster 7, i.e. a further expansion turbine, internal compression pumps 8.1 and 8.2, a counter-stream subcooler 9 and a column system 10.

[0074] In the example shown, the distillation column system 10 comprises a classical double column arrangement consisting of a high-pressure column 11 and a low-pressure column 12 as well as a raw argon column 13 and a pure argon column 14.

[0075] In the air separation plant 100, a feed air stream formed from atmospheric air A is aspired and compressed by means of the main air compressor 1 via a filter not individually labelled. The air separation plant is operated on the basis of a high-pressure process, and therefore the air is compressed to a pressure in a correspondingly high pressure range which is referred to as third pressure range before. The compressed feed air stream, still indicated A, is optionally pre-cooled in a pre-cooling unit not shown in specific detail and thereafter purified in adsorber skid 2 in a manner known per se.

[0076] A partial stream B of the compressed and purified air stream A is further compressed in the booster 5 coupled to the expansion turbine 4 to a pressure in a pressure range above the initial pressure range, which is referred to as a fourth pressure range before. The booster 5 and the expansion turbine 4 were referred to as a first booster and first expansion turbine before, respectively. The booster 5 is operated as a warm booster as defined above.

[0077] A partial stream C of the partial stream B, referred to as first partial air stream before, is, at the pressure in the fourth pressure range in this specific example, partially cooled in the main heat exchanger 3 before being expanded in the first expansion turbine 4 and introduced into the pressure column 11. Expansion in the first expansion turbine 4 is performed to a pressure in a pressure range at which the pressure column 11 is operated and which is referred to as a first pressure range hereinbefore.

[0078] Another partial stream D of the partial stream B, referred to as third partial air stream before, is, at the fourth pressure range, fully cooled and liquefied in the main heat exchanger 3 before being expanded using a valve not individually labelled to a pressure in the first pressure range and introduced into the pressure column 11. Alternatively, the last expansion step may mentioned be also performed to a pressure in a pressure range at which the low-pressure column 12 is operated, this pressure range being referred to as a second pressure range before, in which case the third partial air stream may be introduced into the low pressure column 12.

[0079] A further partial stream E of the compressed and purified air stream A, which is referred to as second partial air stream before, is, in the example shown here, further compressed in the booster 7 coupled to the expansion turbine 6 to a pressure in a pressure range also being above the initial pressure range, which is referred to as a fifth pressure range before, and thereafter cooled and liquefied in the main heat exchanger 3 before being expanded in the expansion turbine 6, reintroduced into the main heat exchanger 3, further cooled therein, and introduced into the pressure column 11. The booster 7 and the expansion turbine 6 were also referred to as second booster and second expansion turbine before, respectively, and the cooling steps in the main heat exchanger 3 before and after the expansion in the expansion turbine 6 as first cooling step and second cooling step. The booster 7 is, like the booster 5, operated as a warm booster as defined above. Be it noted that the booster 7 can also be omitted, in non-inventive alternatives, in which case the expansion turbine 6 may also be coupled to an electric generator or a brake instead. In such a case, furthermore, the second partial air stream is provided to the first cooling step at a pressure in the third pressure range.

[0080] Expansion in the second expansion turbine 6 is performed to a pressure in a pressure range above the first pressure range and below the third and fifth pressure range, which is referred to as sixth pressure range hereinbefore. Thereafter, the second partial stream E is expanded using a valve not individually labelled to a pressure in the first pressure range. Partial streams D and E, i.e. the third and second partial air streams mentioned before, are combined in the example shown before being introduced into the pressure column 11. As for partial air stream D, also the partial air stream E may alternatively be expanded to a pressure in the second pressure range instead of the first pressure range, in which case the partial air stream E may also be introduced into the low pressure column 12.

[0081] In the high-pressure column 11, an oxygen-enriched liquid bottom fraction and a nitrogen-enriched gaseous top fraction are formed. The oxygen-enriched liquid bottom fraction is, as known per se, withdrawn from the high-pressure column 11, partly used as heating medium in a sump vaporizer of the pure argon column 14 and fed in defined proportions into a top condenser of the pure argon column 14 and a top condenser of the raw argon column 13. Fluid evaporating in the evaporation chambers of the head condensers of the raw argon column 13 and the pure argon column 14 is combined and transferred to the low-pressure column 12, such as are purge amounts of liquid remaining in these evaporation chambers.

[0082] The gaseous nitrogen-rich head product is, on the one hand, withdrawn from the head of the high-pressure column 11, liquefied in a main condenser, which creates a heat-exchanging connection between the high-pressure column 11 and the low-pressure column 12, and refed as a reflux into the high-pressure column 11. A further part is internally compressed in pump 8.1, heated in the main heat exchanger, and provided as an internally compressed gaseous nitrogen product GAN IC. A yet further part is subcooled in the subcooler 9 and expanded into the low pressure column 12. Furthermore, a part or the gaseous nitrogen-rich head product is, in the form of a stream indicated F, heated in the main heat exchanger 3 in gaseous form and in parts provided as seal gas SG and compressed in a compressor 20 for gaseous nitrogen arranged downstream of the warm side of the main heat exchanger.

[0083] An oxygen-rich liquid bottom fraction and a nitrogen-rich gaseous top fraction are formed in the low-pressure column 12. The former is partially pressurized in liquid form in the pump 8.2, heated in the main heat exchanger 3, and made available as an internally compressed gaseous oxygen product ICGOX 1. A further part is at least in part subcooled in the subcooler 9 and provided as a liquid oxygen product LOX. A liquid nitrogen-rich stream is withdrawn from a liquid retention device at the head of the low-pressure column 12 and is discharged as liquid nitrogen product LIN from the air separation unit 100. A gaseous nitrogen-rich stream withdrawn from the head of the low pressure column 12 is passed through subcooler 9 and the main heat exchanger 5 and provided as nitrogen product LPGAN at the pressure of the low pressure column 12. Furthermore, a stream is withdrawn from the low-pressure column 12 from an upper section and, after heating in the main heat exchanger 3, is used as so-called impure nitrogen in the pre-cooling unit not shown, or, after heating by means of an electric heater, as a regeneration stream in the adsorption skid 2. It is thereafter vented to the atmosphere ATM.

[0084] The operation of the argon system comprising the raw argon column 13 and the pure argon column 14 is generally known and will not be explained in more detail. Using the argon system, a liquid argon product LAR is provided, while mainly nitrogen from the top of the pure argon column may be vented to the atmosphere.

[0085] In a specific example, the air stream A may be provided in an amount of about 139,700 normalized cubic meters per hour and at a pressure of about 21.50 bar (third pressure range) while the further compression in the booster 5 is performed to a pressure of about 31.6 bar (fourth pressure range). Partial air stream D, i.e. the first partial air stream, is, in this example, formed in an amount of about 11,000 normalized cubic meters per hour. In the first turbine 4, an amount of work corresponding to about 1,688 kilowatts is provided. In the example, the partial air stream E, i.e. the second partial air stream, may be compressed in the second booster 7 to a pressure of about 37.5 bar (fifth pressure range). Partial air stream E is, in this example, formed in an amount of about 31,750 normalized cubic meters per hour. In the second turbine 6, an amount of work corresponding to about 742 kilowatts is provided. The outlet pressure of the second turbine 6 (fifth pressure range) is, in the example, about 13 bar.

[0086] As to the air products provided, in the example just mentioned, pressurized gaseous nitrogen PGAN may be provided in an amount of about 19,200 normalized cubic meters per hour, wherein this pressurized gaseous nitrogen PGAN is supplied to the compressor 20 at a pressure of about 5.1 bar. Internally compressed nitrogen GAN IC is provided in an amount of about 1,160 normalized cubic meters per hour and at a pressure of about 61 bar. The internally compressed oxygen ICGOX 1 is, in the example, provided in an amount of about 18,500 normalized cubic meters per hour and at a pressure of about 4.8 bar. Liquid oxygen LOX is provided in an amount of about 7,600 normalized cubic meters per hour while liquid argon LAR is provided in an amount of about 992 normalized cubic meters per hour. Liquid nitrogen LIN is provided in an amount of about 8,200 normalized cubic meters per hour.

[0087] Further fluid streams may be provided and treated as desired, one non-limiting example being illustrated in form of stream X.

[0088] FIG. 2 illustrates an air separation plant 200 according to a further particularly preferred embodiment of the present invention.

[0089] In contrast to the air separation plant 100 illustrated in FIG. 1, the first booster 5 may be bypassed in the air separation plant 200 according to FIG. 2, as illustrated with a stream D.1, which is provided instead of stream D.2, such that air of the partial air stream D may be taken directly from the air stream A, i.e. at the first pressure level. This bypass is realized by closing a valve 202 while opening a valve 201 and preferably realized in an operating mode referred to as second operating mode before. By opening valve 202 while closing valve 201 instead, essentially the operation as illustrated in FIG. 1 for air separation plant 100 before is realized by providing stream D.2 and not stream D.1, this operating mode being referred to as a first operating mode before.

[0090] The second operating mode particularly corresponds to an increased formation of internally compressed oxygen ICGOX 1 on cost of formation of liquid oxygen LOX. For example, production of internally compressed oxygen ICGOX 1 may, in the second operating mode, be increased to an amount of about 26,000 cubic meters per hour while production of liquid oxygen may be reduced to an amount of about 100 normalized cubic meters per hour. (Production amounts in the first operating mode may essentially correspond to those discussed before for air separation plant 100.) As a result of decreased liquid production the total amount of the air supplied in the form of the air stream A is not reduced, stream A being e.g. provided in an amount of about 141,500 normalized cubic meters per hour, but its pressure is reduced to e.g. about 17.4 bar absolute pressure. This means that the first booster 5 might not be able to cope with the significantly increased volume of air supplied to it. Here the bypass D.1 via valve 201 comes into play, reducing the load on the first booster 5.

[0091] In said second operating mode, and in the air separation plant 200, the air stream A may be provided in an amount of about 141,500 normalized cubic meters per hour and at a pressure of about 17.4 bar (third pressure range) while the further compression in the first booster 5 is performed to a pressure of about 23.1 bar (fourth pressure range). In the first turbine 4, an amount of work corresponding to about 1,331 kilowatts is provided. In the example, the partial air stream E, i.e. the second partial air stream, may be compressed in the second booster 7 to a pressure of about 24 bar (fifth pressure range). Partial air stream E is, in this example, formed in an amount of about 24,000 normalized cubic meters per hour. In the second turbine 6, an amount of work corresponding to about 344 kilowatts is provided. The outlet pressure of the second turbine (sixth pressure range) is, in the example, about 12.6 bar. The third partial air stream D is formed in an amount of about 22,500 normalized cubic meters per hour.

[0092] As to the air products provided, in said second operating mode, and in the air separation plant 200, pressurized gaseous nitrogen PGAN may be provided in an amount of about 19,200 normalized cubic meters per hour, wherein this pressurized gaseous nitrogen PGAN is supplied to the compressor 20 at a pressure of about 5.3 bar. Internally compressed nitrogen GAN IC is provided in an amount of about 1,160 normalized cubic meters per hour and at a pressure of about 61 bar. The internally compressed oxygen ICGOX 1 is, in the example, provided in an amount of about 26.00 normalized cubic meters per hour, as mentioned already, and at a pressure of about 4.8 bar. Liquid oxygen LOX is provided in an amount of about 100 normalized cubic meters per hour, as also mentioned, while liquid argon LAR is provided in an amount of about 992 normalized cubic meters per hour, low pressure gaseous nitrogen LPGAN is provided in an amount of about 10,500 normalized cubic meters per hour, and liquid nitrogen is provided in an amount of 10,200 normalized cubic meters per hour.

[0093] As thus can be seen, the second operation mode may be used to provide the other air separation products except internally compressed oxygen ICGOX 1 and liquid oxygen LOX, in essentially the same amounts.

[0094] In other words, the air of the third partial air stream (D) is, in a first operation mode of the air separation plant 200 and in the air separation plant 100, at least in part compressed to the pressure in the fourth pressure range in the first booster 5 and liquefied in the main heat exchanger 3 at the pressure in the fourth pressure range. In contrast, the air of the third partial air stream D is, in a second operation mode of the air separation plant 200, but not in the air separation plant 100, at least in part liquefied in the main heat exchanger 3 at the pressure in the third pressure range.

[0095] FIG. 3 illustrates an air separation plant 300 according to a further particularly preferred embodiment of the present invention.

[0096] In the air separation plant 300, liquid oxygen internally compressed using pump 8.2 is, before being heated in the main heat exchanger 3, split into two partial streams and, after being passed through the main heat exchanger 3, provided in the form of two different fraction of internally compressed oxygen, ICGOX 1 and ICGOX 2.

[0097] FIG. 4 illustrates an air separation plant 400 according to a further particularly preferred embodiment of the present invention.

[0098] As illustrated in FIG. 4, the partial stream E of the compressed and purified air stream A, which is referred to as second partial air stream herein is not further compressed in a booster such as the booster 7 shown before. That is, the fifth pressure range referred to above in this case corresponds to the third pressure range. The expansion turbine 6 is, in the example illustrated in FIG. 4, mechanically coupled to a generator G.