METHOD AND PLANT FOR LOW TEMPERATURE FRACTIONATION OF AIR

Abstract

A SPECTRA process for low-temperature fractionation of air is proposed, in which bottoms liquid from an additional second rectification column used to obtain oxygen is evaporated in a second condenser evaporator arrangement. In this second condenser evaporator arrangement, gas that has been evaporated beforehand in a first condenser evaporator arrangement, which is used for condensation of tops gas from a first rectification column, is partially condensed after recompression. The invention also relates to a corresponding plant.

Claims

1. A process for the low-temperature fractionation of air, in which an air fractionation plant having a first rectification column, a second rectification column, a first condenser evaporator arrangement, and a second condenser evaporator arrangement is used, wherein the process comprises that the first rectification column is fed with air and operated at a first pressure level, and the second rectification column is fed from the first rectification column and operated at a second pressure level below the first pressure level, wherein tops gas of the first rectification column is obtained as a nitrogen product and discharged from the air fractionation plant, and bottoms liquid of the second rectification column is obtained as an oxygen product and discharged from the air fractionation plant, a first and a second material stream below the first pressure level are formed in the first condenser evaporator arrangement by evaporating liquid from the first rectification column, and further tops gas of the first rectification column is condensed in the first condenser evaporator arrangement and returned to the first rectification column as a return flow, the first material stream is formed with a first oxygen content, and the second material stream is formed with a second oxygen content above the first oxygen content, the first material stream or a part thereof is subjected to recompression to the first pressure level and is fed into the first rectification column, and the second material stream or a part thereof is subjected to work-performing expansion and is discharged from the air fractionation plant, bottoms liquid of the second rectification column is evaporated in the second condenser evaporator arrangement, and the first material stream or the portion thereof which is subjected to the recompression to the first pressure level and is fed into the first rectification column, after the recompression to the first pressure level and before being fed into the first rectification column, is subjected to partial liquefaction at least to the portion in the second condenser evaporator arrangement and is fed into the first rectification column in the form of a two-phase stream, and tops gas of the second rectification column is supplied to a work-performing expansion.

2. The process according to claim 1, in which the tops gas of the second rectification column is supplied, upstream of its expansion, to the second material stream or the portion thereof which is subjected to the work-performing expansion and is discharged from the air fractionation plant.

3. The process according to claim 1, in which tops gas of the second rectification column is subjected to a work-performing expansion separately from the second material stream or the portion thereof which is subjected to the work-performing expansion and is discharged from the air fractionation plant.

4. The process according to claim 1, in which the first material stream or the portion thereof which is subjected to the recompression to the first pressure level, first material stream or the portion thereof which is subjected to the recompression and is fed into the first rectification column is liquefied in the partial liquefaction in the second condenser evaporator arrangement to give 5 to 30 mol %, and in particular 15 to 25 mol %.

5. The process according to claim 1, in which the first material stream or the portion thereof which is subjected to the recompression to the first pressure level is conducted completely through the second condenser evaporator arrangement.

6. The process according to claim 1, in which a first fraction of the first material stream or the portion thereof which is subjected to the recompression to the first pressure level and is fed into the first rectification column is conducted through the second condenser evaporator arrangement, liquefied there at least to a predominant extent, and fed into the first rectification column, and in which a second fraction of the first material stream or the portion thereof which is subjected to the recompression to the first pressure level and is fed into the first rectification column is fed into the first rectification column without being conducted through the second condenser evaporator arrangement.

7. The process according to claim 1, in which the first rectification column is operated at a first pressure level of 7 to 14 bar, and in which the second rectification column is operated at a second pressure level of 3 to 7 bar.

8. The process according to claim 7, in which the first material stream or the portion thereof which is subjected to the recompression to the first pressure level and is fed into the first rectification column is brought during the recompression to a third pressure level, which corresponds to at least the first pressure level, wherein the partial liquefaction takes place at the first pressure level.

9. The process according to claim 7, in which the first material stream or the portion thereof which is subjected to the recompression to the first pressure level and is fed into the first rectification column is transferred to the first rectification column without a pump.

10. The process according to claim 1, wherein, for the recompression of the first material stream or the portion thereof which is subjected to the recompression to the first pressure level and is fed into the first rectification column, one or more compressors is or are provided, and in which, for the work-performing expansion of the second stream or the portion thereof which is subjected to the work-performing expansion and is discharged from the air fractionation plant, one or more expansion machines are provided which is or are coupled to the one or more compressors.

11. The process according to claim 1, in which the tops gas of the first rectification column has a content of in each case less than 1 ppb oxygen, carbon monoxide, and/or hydrogen and a content of less than 10 ppm argon on a volume basis.

12. The process according to claim 1, in which the bottoms liquid of the second rectification column has a content of less than 10 ppb argon and/or 5 ppm methane on a volume basis.

13. The process according to claim 1, in which all of the cooled compressed air to be fractionated in the process is fed into the first rectification column 11 in gaseous form.

14. Air fractionation plant having a first rectification column, a second rectification column, a first condenser evaporator arrangement, and a second condenser evaporator arrangement and configured to feed the first rectification column with air and to operate it at a first pressure level, and to feed the second rectification column from the first rectification column and to operate it at a second pressure level below the first pressure level, to obtain tops gas of the first rectification column as a nitrogen product and discharge it from the air fractionation plant, and to obtain bottoms liquid of the second rectification column as an oxygen product and discharge it from the air fractionation plant, to form a first and a second material stream below the first pressure level in the first condenser evaporator arrangement by evaporating liquid from the first rectification column, and to condense further tops gas of the first rectification column in the first condenser evaporator arrangement and return it to the first rectification column as a return flow, to form the first material stream with a first oxygen content and the second material stream with a second oxygen content above the first oxygen content, to subject the first material stream or a portion thereof to recompression to the first pressure level and to feed it into the first rectification column, and to subject the second material stream or a portion thereof to expansion and to discharge it from the air fractionation plant, to evaporate bottoms liquid of the second rectification column in the second condenser evaporator arrangement, to subject the first material stream or the portion thereof which is subjected to the recompression to the first pressure level and is fed into the first rectification column, after the recompression to the first pressure level and before the feed into the first rectification column, to partial liquefaction at least to the portion in the second condenser evaporator arrangement and to feed it into the first rectification column in the form of a two-phase stream, and to supply tops gas of the second rectification column to a work-performing expansion.

15. Air fractionation plant according to claim 14, having means which are configured to carry out a process for the low-temperature fractionation of air, in which an air fractionation plant having a first rectification column, a second rectification column, a first condenser evaporator arrangement, and a second condenser evaporator arrangement is used, wherein the process comprises that the first rectification column is fed with air and operated at a first pressure level, and the second rectification column is fed from the first rectification column and operated at a second pressure level below the first pressure level, wherein tops gas of the first rectification column is obtained as a nitrogen product and discharged from the air fractionation plant, and bottoms liquid of the second rectification column is obtained as an oxygen product and discharged from the air fractionation plant, a first and a second material stream below the first pressure level are formed in the first condenser evaporator arrangement by evaporating liquid from the first rectification column, and further tops gas of the first rectification column is condensed in the first condenser evaporator arrangement and returned to the first rectification column as a return flow, the first material stream is formed with a first oxygen content, and the second material stream is formed with a second oxygen content above the first oxygen content, the first material stream or a part thereof is subjected to recompression to the first pressure level and is fed into the first rectification column, and the second material stream or a part thereof is subjected to work-performing expansion and is discharged from the air fractionation plant, bottoms liquid of the second rectification column is evaporated in the second condenser evaporator arrangement, and the first material stream or the portion thereof which is subjected to the recompression to the first pressure level and is fed into the first rectification column, after the recompression to the first pressure level and before being fed into the first rectification column, is subjected to partial liquefaction at least to the portion in the second condenser evaporator arrangement and is fed into the first rectification column in the form of a two-phase stream, and tops gas of the second rectification column is supplied to a work-performing expansion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0063] FIG. 1 shows an air fractionation plant according to an embodiment of the invention.

[0064] FIG. 2 shows an air fractionation plant according to an embodiment of the invention.

[0065] FIG. 3 shows an air fractionation plant according to an embodiment of the invention.

[0066] FIG. 4 shows an air fractionation plant according to an embodiment of the invention.

[0067] In the figures, elements corresponding functionally or structurally to one another are indicated by identical reference signs and, only for the sake of clarity, are not repeatedly explained below.

DETAILED DESCRIPTION OF THE DRAWINGS

[0068] FIG. 1 illustrates an air fractionation plant 100 in the form of a schematic plant diagram. The central component is a rectification column system 10 having a first rectification column 11, a second rectification column 12, a first condenser evaporator 111, and a second condenser evaporator 121.

[0069] The first rectification column 11 is operated at a first pressure level, and the second rectification column 12 is operated at a second pressure level below the first pressure level. As mentioned, the first and second condenser evaporators 111 and 121 can each be part of a first or second condenser evaporator arrangement. A first and second condenser evaporator 111, 121 is discussed below simply for the sake of clarity.

[0070] By means of a main air compressor 1 of the air fractionation plant 100, air is sucked in from the atmosphere A via a filter (not separately designated) and compressed. After cooling in an aftercooler (likewise not designated separately) downstream of the main air compressor 1, the feed air stream a formed in this way is further cooled in a direct contact cooler 2 operated with water W. The feed air stream a is then subjected to cleaning in an adsorber unit 3. For further explanations in this context, reference is made to the technical literaturefor example, in connection with FIG. 2.3A in Haring (see above).

[0071] After cooling in the main heat exchanger 4, the feed air stream a is fed into the first rectification column 11. In a conventional process, a portion of the feed air stream a would be fed into the first rectification column 11, whereas a further portion would be routed through the second condenser evaporator 121, which is arranged in a lower region of the second rectification column 12, and evaporated by means of the bottoms liquid of the second rectification column 12. This further portion would be partially condensed in the second condenser evaporator 121 and then likewise fed into the first rectification column 11.

[0072] Tops gas of the first rectification column 11 is discharged from the air fractionation plant 100 in the form of a material stream d as a nitrogen product B or sealing gas C. In contrast, bottoms liquid of the second rectification column 12 is discharged in the form of a material stream e as an oxygen product D. It is also possible, for example, to feed into so-called run tanks for later evaporation for the provision of an internally compressed oxygen product D.

[0073] In the first condenser evaporator 111, a first material stream g and a second material stream h below the first pressure level (for this purpose, a corresponding expansion in particular takes place in valves which are not denoted separately) are subjected to evaporation in the specific embodiment illustrated here. Further tops gas of the first rectification column 11 is condensed in the form of a material stream i in the first condenser evaporator 111 and returned to the first rectification column 11 as a return flow. As illustrated here in the form of a material stream k, a portion can also be supercooled in a supercooler 5 and provided as liquid nitrogen F. A material stream I heated thereby is treated as explained in more detail below. A further discharge in the form of a purge stream m or P may also be provided. A possible feed of liquid nitrogen (LIN injection) is denoted by Q.

[0074] The first material stream g is formed using liquid taken from the first rectification column 11 with a first oxygen content, and the second material stream h is formed using liquid (in particular, bottoms liquid) taken from the first rectification column 11 with a second oxygen content above the first oxygen content.

[0075] After its evaporation or partial evaporation in the first condenser evaporator 111, gas of the first material stream g is subjected in a compressor 6 to recompression to the first pressure level and fed into the first rectification column 11. A portion indicated by a dashed line can also be returned to compression in the compressor 6. A portion of the material stream g can also be discharged into the atmosphere A in the form of a material stream n.

[0076] After its evaporation or partial evaporation in the first condenser evaporator 111, gas of the second material stream h is partially expanded by a throttle 9 in the example illustrated here, then combined with tops gas, which is taken in the form of a material stream o from the second rectification column 12, subjected to parallel further expansion in expansion machines 7 and 8, and, after heating in the main heat exchanger 4, used as regeneration gas in the adsorber unit 3 or released to the atmosphere A, and thus discharged from the air fractionation plant 100.

[0077] The expansion machine 7 is coupled to the compressor 6, and the expansion machine 8 is coupled to a generator G. In each case, a different number of corresponding machines or a different type of coupling may also be used. An (oil) brake (not separately designated) may also be provided.

[0078] The second rectification column 12 is fed with a side stream p of the first rectification column 11, which is fed into the second rectification column in an upper region. By means of the second condenser evaporator 121, a first portion of the first material stream g or a corresponding part thereof, after its evaporation or partial evaporation in the first condenser evaporator 111 and after its recompression in the compressor 6, is also conducted as a partial stream b and subjected to partial condensation. Correspondingly formed liquid or two-phase mixture, further denoted by b, is transferred to the first rectification column 11 without a pump. A second portion of the first material stream g or a corresponding part thereof, after evaporation or partial evaporation thereof in the first condenser evaporator 111 and its recompression in the compressor 6, is transferred into the first rectification column 11 as a material stream c in gaseous form and likewise without a pump, without being conducted through the condenser evaporator 121.

[0079] In the otherwise substantially identical or comparable air fractionation plant 200 according to FIG. 2, the first material stream g or a corresponding part thereof, after its evaporation or partial evaporation in the first condenser evaporator 111 and its recompression in the compressor 6, is conducted completely through the second condenser evaporator 121, is partially condensed there, and is transferred to the first rectification column 11 as a two-phase stream, now denoted by z, without a pump. In contrast to the embodiment according to FIG. 1, no throttling of the material stream h at a valve 9, as illustrated above, is carried out here. In this way, the maximum potential can be realized: If the stream h is not throttled, no energy is thereby destroyed, and the powers of both turbines are greater, which is manifested as an energy advantage. This is due in particular to the fact that the partial liquefaction of the stream g allows a higher operating pressure in the second rectification column 12. Accordingly, the throttling of the stream h can either be completely dispensed with (as illustrated in FIG. 2), or this throttling can be noticeably reduced (as not shown separately).

[0080] In the air fractionation plant 300 according to FIG. 3, which is otherwise substantially identical or comparable to the air fractionation plant 100 according to FIG. 1, a portion of the material stream h is fed to the material stream d via a throttle 9, before it is heated in the main heat exchanger 3 and expanded in the turbine 8. The remainder of material stream h is likewise heated in the main heat exchanger 4, but expanded in particular in the turbine 7. After combining the expanded material streams, these are combined, heated again in the main heat exchanger 4, and discharged from the plant 300.

[0081] In the air fractionation plant 400 according to FIG. 4, it is provided, in contrast, for example, to the air fractionation plant 100 illustrated in FIG. 1, that the tops gas from the second rectification column in the form of the material stream d be subjected to a work-performing expansion in the turbine 8 separately from the material stream h.