Process and plant for low-temperature separation of air

Abstract

Described herein is a process for low-temperature separation of air, in which an air separation plant having a first rectification column and a second rectification column is used, the first rectification column being supplied with cooled compressed air and the second rectification column being supplied with liquid from the first rectification column or liquid formed herefrom. In a first condenser-evaporator, head gas from the first rectification column is condensed and liquid from the second rectification column, or liquid formed herefrom, is evaporated, thereby producing a first evaporation product.

Claims

1. A process for the low-temperature separation of air using an air separation plant having a first rectification column and a second rectification column, said process comprising: operating the first rectification column at a pressure level of 9 to 13.5 bar and operating the second rectification column at a pressure level of 5.5 to 8.5 bar, supplying the first rectification column with cooled compressed air and supplying the second rectification column with liquid from the first rectification column or liquid formed herefrom, condensing a first portion of head gas from the first rectification column in a first condenser-evaporator and evaporating liquid from the second rectification column or liquid formed herefrom in the first condenser-evaporator to produce a first evaporation product, condensing head gas from the second rectification column in a second condenser-evaporator and evaporating further liquid from the second rectification column or liquid formed herefrom in the second condenser-evaporator to produce a second evaporation product, decompressing and heating a first portion of the second evaporation product, and removing resultant decompressed, heated first portion of the second evaporation product from the process, and removing a second portion of the head gas from the first rectification column from the process as a pure nitrogen product, wherein a third rectification column, operated at a pressure level of 1.1 to 2.5 bar, is also used in the process, and said process further comprises: condensing in a third condenser-evaporator a second portion of the second evaporation product and evaporating sump liquid from the third rectification column or liquid formed herefrom in the third condenser-evaporator to produce a third evaporation product, supplying at least part of the second portion of the second evaporation product condensed in the third condenser-evaporator to the third rectification column, supplying the third rectification column with non-evaporated further liquid from the second rectification column or liquid formed herefrom, and internally compressing and removing from the process further sump liquid from the third rectification column or liquid formed herefrom as an impure oxygen product.

2. The process according to claim 1, wherein the further sump liquid from the third rectification column has an oxygen content of 85 to 99.8%.

3. The process according to claim 1, wherein at least the second condenser-evaporator is a forced-flow condenser-evaporator.

4. The process according to claim 1, wherein the second condenser-evaporator is operated at an evaporation pressure level of 2 to 5 bar.

5. The process according to claim 4, wherein the first portion of the second evaporation product, which is decompressed by a decompression machine, heated and removed from the process, is supplied to the decompression machine at evaporation pressure level.

6. The process according to claim 1, wherein the liquid from the second rectification column is sump liquid from the second rectification column, and the sump liquid from the second rectification column is evaporated in the first condenser-evaporator to produce the first evaporation product and a non-evaporated residue, and a first portion of the non-evaporated residue is the further liquid from the second rectification column evaporated in the second condenser-evaporator to produce the second evaporation product.

7. The process according to claim 6, wherein the non-evaporated further liquid from the second rectification column supplied to the third rectification column is a second portion of the non-evaporated residue produced in the first condenser-evaporator.

8. The process according to claim 7, wherein (a) the non-evaporated, further liquid from the second rectification column, or the liquid formed herefrom, which is supplied to the third rectification column, and (b) the second portion of the second evaporation product condensed in the third condenser-evaporator, or the portion thereof, which is supplied to the third rectification column, are both supplied to the third rectification column in a head region.

9. The process according to claim 1, further comprising withdrawing liquid from the second rectification column via a side draw and using the withdrawn liquid as the non-evaporated further liquid from the second rectification column or the liquid formed herefrom, which is supplied to the third rectification column.

10. The process according to claim 9, wherein the third rectification column has a first separation section and a second separation section arranged above the first separation section, wherein the non-evaporated further liquid from the second rectification column or the liquid formed herefrom, which is supplied to the third rectification column, is supplied to the third rectification column above the second separation section, and the second portion of the second evaporation product condensed by in the third condenser-evaporator, or the portion thereof, which is supplied to the third rectification column, is supplied to the third rectification column between the first separation section and the second separation section.

11. The process according to claim 1, further comprising liquefying an air stream that has been compressed to a pressure level above a pressure level at which the first rectification column is operated to produce a liquified compressed air stream, decompressing the liquified compressed air stream into the first rectification column.

12. The process according to claim 1, wherein the third rectification column has 10 to 45 theoretical separating plates.

13. An air separation plant comprising: a first rectification column and a second rectification column wherein the first rectification column is configured to operate at a pressure level of 9 to 13.5 bar and the second rectification column is configured to operate at a pressure level of 5.5 to 8.5 bar, a first line to supply the first rectification column with cooled compressed air and a second line to supply the second rectification column with liquid from the first rectification column or liquid formed herefrom, a first condenser-evaporator for condensing a first portion of head gas from the first rectification column and for evaporating liquid from the second rectification column or liquid formed herefrom, wherein the first condenser-evaporator produces a first evaporation product, a second condenser-evaporator for condensing head gas from the second rectification column and for evaporating further liquid from the second rectification column or liquid formed herefrom, wherein the second condenser-evaporator produces a second evaporation product, an expansion turbine for decompressing a first portion of the second evaporation product, means for heating the first portion of the second evaporation product, and means for removing from the process the first portion of the second evaporation product, and means for removing a second portion of the head gas of the first rectification column from the process as a pure nitrogen product, a third rectification column which is configured to operate at a pressure level of 1.1 to 2.5 bar, a third condenser-evaporator for condensing a second portion of the second evaporation product and for evaporating liquid from the third rectification column or liquid formed herefrom, wherein the second condenser-evaporator produces a third evaporation product, means to supply at least some of the second portion of the second evaporation product condensed in the third condenser-evaporator to the third rectification column, means to supply the third rectification column with non-evaporated further liquid from the second rectification column or liquid formed herefrom, and means to internally compress sump liquid of the third rectification column or liquid formed herefrom and means to remove the internally compressed sump liquid of the third rectification column or liquid formed herefrom from the process as an impure oxygen product.

14. The process according to claim 1, wherein the first rectification column has 50 to 70 theoretical separating plates.

15. The process according to claim 1, wherein the second rectification column has 40 to 60 theoretical separating plates.

16. The process according to claim 1, wherein the first rectification column has 50 to 70 theoretical separating plates, the second rectification column has 40 to 60 theoretical separating plates, and the third rectification column has 10 to 45 theoretical separating plates.

17. The process according to claim 1, wherein the non-evaporated further liquid from the second rectification column that is supplied to the third rectification column is sump liquid from the second rectification column.

18. The process according to claim 1, wherein the non-evaporated further liquid from the second rectification column that is supplied to the third rectification column is supplied to a head region of the third rectification column.

19. The process according to claim 1, wherein the second portion of the second evaporation product condensed in the third condenser-evaporator is supplied to a head region of the third rectification column.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1 to 5 show an air separation plant according to embodiments of the invention in a simplified schematic representation.

(2) In the figures, identical or identically acting elements are in each case designated by identical reference signs and are not explained repeatedly for the sake of clarity. Plant components can in each case also represent corresponding process steps so that the following explanations regarding the air separation plants also relate to corresponding processes. In the figures, liquid material streams are indicated by black (filled) flow arrows, whereas gaseous streams of material are indicated by white (not filled) flow arrows.

DETAILED DESCRIPTION OF THE DRAWINGS

(3) In FIG. 1, an air separation plant according to an embodiment of the invention is shown in the form of a schematic process flow diagram and is designated as a whole by 100.

(4) In the plant 100, feed air or process air P is drawn in via a filter 1 by means of a main air compressor 2. After precooling in heat exchangers (not designated) and in a direct-contact cooler, which is operated with water W, the correspondingly compressed air is supplied to an adsorber station 3, where it is freed from unwanted components, such as water and carbon dioxide. The air is then fed in the form of a feed-air stream a to a main heat exchanger 4 of the air separation plant 100 and is extracted therefrom at the cold end. The feed air stream further on designated by a is supplied to a first rectification column (high-pressure column) 11 of a distillation column system 10 that, in addition to the first rectification column 11, also has a second rectification column (low-pressure column) 12 formed as a double column with the first rectification column 11 and a third rectification column 13.

(5) In the first rectification column 11, a head gas and a sump liquid are formed, wherein the sump liquid from the first rectification column 11 is conducted here completely in the form of a material stream b through a supercooling counterflow heat exchanger 5 and is supplied to the second rectification column 12. A head gas and a sump liquid are formed in the second rectification column 12.

(6) A portion of the head gas of the first rectification column 11 is condensed by means of a first condenser-evaporator 111 (main condenser), which is formed here as a forced-flow condenser-evaporator. A further portion of the head gas is drawn off in the form of a material stream c, conducted through the supercooling counterflow heat exchanger 5 and the main heat exchanger 4, and discharged as a pure nitrogen product C. The condensed portion of the head gas of the first rectification column 11 is recycled in the form of a material stream d into the first rectification column 11.

(7) By means of the first condenser-evaporator 111, a portion of the sump liquid of the second rectification column 12 is also evaporated. The evaporated portion rises in the second rectification column 12.

(8) Head gas of the second rectification column 12, which is supplied in the form of a material stream e to the second condenser-evaporator 121, is condensed by means of a second condenser-evaporator 121. The condensed head gas is partly recycled to the second rectification column 12 and is partly provided as a liquid nitrogen product E. Further head gas of the second rectification column 12 can be withdrawn therefrom in the form of a material stream f, conducted through the supercooling counterflow heat exchanger 5 and the main heat exchanger 4 and provided as a further compressed nitrogen product F.

(9) Liquid collected at the head of the second rectification column 12 in a liquid retention device can be recycled in the form of a material stream g by means of a pump 6 through the supercooling counterflow heat exchanger 5 and to the first rectification column 11 (back pumping). At this point, a partial stream of the material stream used to form the liquid nitrogen product E can also be supplied, which is decompressed for the supercooling of the liquid nitrogen product E.

(10) By means of a second condenser-evaporator 121, further sump liquid from the second rectification column 12 is evaporated and supplied in the form of a material stream h to the second condenser-evaporator 121 after it has previously been conducted through the supercooling counterflow heat exchanger 5.

(11) By means of a decompression machine 7, which can be coupled to a simple brake or a generator, a first portion of the further sump liquid from the second rectification column 12 evaporated by means of the second condenser-evaporator 121 is decompressed in the form of a material stream i, is heated, before and after the decompression, in the supercooling counterflow heat exchanger 5 and in the main heat exchanger 4, and is removed from the process, i.e., discharged to the atmosphere A and, as needed, used as a regeneration gas in the adsorber station 3.

(12) By means of a third condenser-evaporator 131, which is formed as a sump evaporator of the third rectification column 13, a second portion of the further sump liquid from the second rectification column 12 evaporated by means of the second condenser-evaporator 121 is condensed in the form of a material stream k. In the third condenser-evaporator 131, sump liquid of the third rectification column 13 is also evaporated.

(13) At least some of the second portion, condensed by means of the third condenser-evaporator 131, of the further liquid from the second rectification column 12 evaporated by means of the second condenser-evaporator 121 is supplied to the third rectification column 13. The third rectification column 13 is further supplied in the form of a material stream I with non-evaporated further liquid from the second rectification column 12. Sump liquid of the third rectification column 13 is internally compressed in the form of a material stream m by means of a pump 8 and removed from the process as an internally compressed oxygen product M.

(14) In the air separation plant 100 according to FIG. 1, the non-evaporated further liquid from the second rectification column 12, which is supplied in the form of the material stream I to the third rectification column, is sump liquid of the second rectification column 12. The latter is also supplied to the third rectification column 13 in a head region, like the second portion, condensed by means of the third condenser-evaporator 131, of the further liquid from the second rectification column 12 evaporated by means of the second condenser-evaporator 121, or the portion thereof, which is supplied to the third rectification column 13. An additional supply of liquid nitrogen X is likewise illustrated.

(15) In the air separation plant 200 according to FIG. 2, which illustrates a further embodiment of the present invention, this supply takes place differently. Liquid of a material stream n, which is withdrawn from the second rectification column 12 via a side draw, is used here as a non-evaporated further liquid from the second rectification column 12, which is supplied to the third rectification column 13.

(16) In the air separation plant 200 according to FIG. 2, the third rectification column 13 has a first separation section 13a and a second separation section 13b arranged above the first separation section 13a, wherein the non-evaporated further liquid from the second rectification column 12, which is supplied to the third rectification column 13, i.e., the material stream n, is supplied to the third rectification column 13 above the second separation section 13b, and wherein the second portion, condensed by means of the second condenser-evaporator 131, of the further liquid from the second rectification column 12 evaporated by means of the second condenser-evaporator 121, or the portion thereof, which is supplied to the third rectification column 13, i.e., the material stream k, is supplied to the third rectification column 13 between the first separation section 13a and the second separation section 13b.

(17) In the air separation plants 100 and 200 according to FIGS. 1 and 2, the cooled compressed air that is supplied to the first rectification column 11 is exclusively gaseous, cooled or pre-liquefied compressed air that has been compressed in the main air compressor 2 to no longer the pressure level at which the first rectification column 11 is operated.

(18) In the air separation plant 300 according to FIG. 3, which illustrates a further embodiment of the present invention, this air supply takes place differently. The cooled compressed air that is supplied to the first rectification column 11 comprises here the gaseous, cooled compressed air of material stream a, which has been compressed to no longer the pressure level at which the first rectification column 11 is operated, but additionally also liquefied air of a material stream o, which has been compressed by means of a recompressor 9 to a pressure level above the pressure level at which the first rectification column 11 is operated, and which is subsequently liquefied in the main heat exchanger 4 and decompressed into the first rectification column 11.

(19) In contrast to the air separation plants illustrated above, in the air separation plant 400 according to FIG. 4, which illustrates a further embodiment of the present invention, no liquid collected at the head of the second rectification column 12 in a liquid retention device is recycled to the first rectification column 11. The partial stream of the material stream used to form the liquid nitrogen product E, which is decompressed for supercooling the liquid nitrogen product E, can nevertheless be supplied to the first rectification column 11 (not shown).

(20) The material stream c is heated here without being conducted beforehand through the supercooling counterflow heat exchanger 5. Therefore, the supercooling counterflow heat exchanger 5 typically does not have a corresponding passage. The passage for the liquid, which is collected according to the plants illustrated above at the head of the second rectification column 12 in a liquid retention device and recycled to the first rectification column 11, is also typically omitted, even if both passages are still rudimentarily illustrated in FIG. 4.