METHOD FOR THE LOW-TEMPERATURE SEPARATION OF AIR AND AIR SEPARATION PLANT

Abstract

A method for the low-temperature separation of air using an air separation plant which comprises a rectification column arrangement (10) having a pressure column, a low-pressure column and an argon column, wherein: the low-pressure column comprises a first and a second rectification region (A, B); the argon column comprises a first and a second rectification region (C, D, D1, D2); argon-enriched fluid is removed from the low-pressure column between the first and second rectification region (A, B) thereof and is fed into the first rectification region (C) of the argon column; and argon-depleted fluid is removed from the first rectification region (C) of the argon column (13a, 13b) and is fed into the low-pressure column between the first and second rectification region (A, B) thereof.

Claims

1. A method for the low-temperature separation of air using an air separation plant which comprises a rectification column arrangement having a pressure column, a low-pressure column and an argon column, wherein: the low-pressure column is designed in one or more parts and comprises a first and a second rectification region (A, B), and the argon column is designed in one or more parts and comprises a first and a second rectification region (C, D, D1, D2), between the first and second rectification regions (A, B) of the low-pressure column, a first transfer fluid enriched in argon is removed from the low-pressure column and fed into the argon column in a first transfer quantity below the first rectification region (C) of the argon column, below the first rectification region (C) of the argon column, a second transfer fluid depleted of argon is removed from the argon column and fed into the low-pressure column in a second transfer quantity between the first and second rectification regions (A, B) of the low-pressure column, wherein the air separation plant is operated in a first operating mode and in a second operating mode, a nitrogen product is discharged from the air separation plant in the first operating mode in a larger product quantity than in the second operating mode, a pressure is set in the argon column in a pressure range that in the first operating mode corresponds to a pressure range in which the low-pressure column is operated, or a pressure range that is at least 50 mbar, at least 100 mbar and/or up to 700 mbar or 900 mbar lower, and which in the second operating mode is at least 50 mbar, at least 100 mbar and/or up to 700 mbar or 900 mbar below the pressure range of the argon column in the first operating mode, and in that the rectification column arrangement comprises a pure oxygen column in which a pressure is adjusted in a pressure range that in the first operating mode corresponds to the pressure range in which the low-pressure column is operated, or a pressure range that is at least 50 mbar, at least 100 mbar and/or up to 700 mbar or 900 mbar lower, and which in the second operating mode is at least 50 mbar, at least 100 mbar and/or up to 700 mbar or 900 mbar below the pressure range of the pure oxygen column in the first operating mode, wherein the pure oxygen column is operated with a liquid as the return flow, which is removed from the argon column between the first and second rectification regions (C, D) of the argon column, and wherein a head gas is removed from the pure oxygen column and fed into the argon column between the first and second rectification regions (C, D, D1, D2) of the argon column.

2. The method according to claim 1, wherein a valve that is provided in a line for feeding the first transfer quantity into the argon column is closed in the second operation mode, or more tightly in the second operation mode than in the first operation mode.

3. The method according to claim 1, in which the pressure column and the low-pressure column are connected in a heat-exchanging manner by means of a main condenser, wherein a recirculating stream is formed using head gas from the low-pressure column, which is heated, compressed, cooled again, passed partially or completely through the main condenser and/or partially or completely through a sump evaporator of the pure oxygen column, condensed there at least partially, and fed back into the pressure column and/or the low-pressure column.

4. The method according to claim 1, wherein a product quantity of the nitrogen product that is discharged from the air separation plant in the second operation mode is at least 2.5% less, at least 10% less, or 10% to 60% less than in the first operation mode.

5. The method according to claim 1, wherein, between the first and the second operating mode, the pressure in the low-pressure column is changed by not more than 100 mbar.

6. The method according to claim 1, with which the first rectification region (A) and the second rectification region (B) of the low-pressure column are accommodated in a common column shell in which the second rectification region (B) of the low-pressure column is arranged above the first rectification region (A) of the low-pressure column.

7. The method according to claim 1, with which the first and second rectification regions (C, D) of the argon column are accommodated in separate column shells, and with which the column shell, in which the first rectification region (C) of the argon column is accommodated, is arranged in particular above a column shell of the pure oxygen column and is connected thereto or is designed integrally therewith.

8. The method according to claim 1, wherein the first rectification region (A) of the low-pressure column is accommodated in a first column shell, the second rectification region (B) of the low-pressure column is accommodated in a second column shell, and the first and second column shells are arranged next to one another.

9. The method according to claim 8, with which the first column shell and a column shell of the pressure column are arranged one above the other and are designed in the form of a double column.

10. The method according to claim 8, with which the second rectification region (D) of the argon column is subdivided into a first subregion (D1) and a second subregion (D2), wherein the first rectification region (C) of the argon column is accommodated in a third column shell, the first subregion (D1) of the second rectification region (D) of the argon column is accommodated above the first rectification region (C) of the argon column in the third column shell, and the second subregion (D1) of the second rectification region (D) of the argon column is accommodated in the fourth column shell.

11. The method according to claim 10, with which gas above the first rectification region (A) of the low-pressure column is withdrawn from the first column shell and fed into the second column shell in a first portion below the second rectification region (B) of the low-pressure column and into the third column shell as the first transfer fluid in a second portion below the first rectification region (C) of the argon column, with which liquid is withdrawn from the third column shell below the first rectification region (C) of the argon column and is fed into the first column shell as the second transfer fluid above the first rectification region (A) of the low-pressure column, and with which liquid is withdrawn from the second column shell below the second rectification region (B) of the low-pressure column and is fed into the third column shell below the first rectification region (C) of the argon column.

12. The method according to claim 11, with which a lower end of the second column shell lies geodesically above an inlet position of the first transfer fluid into the third column shell, the first transfer fluid is transferred purely into the third column shell.

13. The method according to claim 1, with which the pressure column is operated at a pressure in an operating pressure range of 9 to 14.5 bar, and with which the low-pressure column is operated at a pressure in an operating pressure range of 2 to 5 bar.

14. An air separation plant which comprises a rectification column arrangement having a pressure column, a low-pressure column and an argon column, wherein: the low-pressure column is designed in one or more parts and comprises a first and a second rectification region (A, B), and the argon column is designed in one or more parts and comprises a first and a second rectification region (C, D, D1, D2), and the air separation plant is configured such that between the first and second rectification regions (A, B) of the low-pressure column, a first transfer fluid enriched in argon is to be removed from the low-pressure column and is to be fed into the argon column in a first transfer quantity below the first rectification region (C) of the argon column, below the first rectification region (C) of the argon column, a second transfer fluid depleted of argon is to be removed from the argon column and is to be fed into the low-pressure column in a second transfer quantity between the first and second rectification regions (A, B) of the low-pressure column, wherein is configured for operation in a first operating mode and in a second operating mode, wherein: the air separation plant is configured to discharge a nitrogen product from the air separation plant in the first operating mode in a larger product quantity than in the second operating mode, and the air separation plant is configured to adjust a pressure in the argon column in a pressure range that, in the first operating mode, corresponds to a pressure range in which the low-pressure column is operated, or a pressure range that is at least 50 mbar, at least 100 mbar and/or up to 700 mbar or 900 mbar lower, and which in the second operating mode is at least 50 mbar, at least 100 mbar and/or up to 700 mbar or 900 mbar below the pressure range of the argon column in the first operating mode, and in that the rectification column arrangement comprises a pure oxygen column, wherein the air separation plant is configured to adjust a pressure in the pure oxygen column in a pressure range that, in the first operating mode, corresponds to the pressure range in which the low-pressure column is operated, or a pressure range that is at least 50 mbar, at least 100 mbar and/or up to 700 mbar or 900 mbar lower, and which in the second operating mode is at least 100 mbar and/or up to 700 mbar or 900 mbar below the pressure range of the pure oxygen column (14) in the first operating mode, wherein the air separation plant is configured for the pure oxygen column to be operated with a liquid as the return flow, which is removed from the argon column between the first and second rectification regions of the argon column, and wherein the pure oxygen column comprises means for removing a head gas that is fed into the argon column between the first and second rectification regions of the argon column.

Description

DESCRIPTION OF THE FIGURES

[0054] FIGS. 1 and 2 illustrate air separation plants according to different embodiments of the present invention.

[0055] In the figures, elements that correspond to one another structurally or functionally are denoted by identical reference signs and, for the sake of clarity, are not repeatedly explained. Explanations relating to plants and plant components apply in the same way for corresponding methods and method steps.

[0056] In FIG. 1, an air separation plant according to an embodiment of the present invention is illustrated in the form of a simplified process flow diagram and is denoted as a whole by 100.

[0057] In the air separation plant 100, air is sucked by means of a main air compressor 1 via a filter 2 and compressed to a pressure level of, for example, about 12.5 bar. After cooling and separation of water, the correspondingly compressed air is freed of residual water and carbon dioxide in an pre-cleaning unit 3, which can be designed in a manner known per se. For the design of the mentioned components, reference is made to the technical literature cited at the outset.

[0058] A correspondingly formed compressed air stream a is fed from the warm to the cold end through a main heat exchanger 4 and into a pressure column 11 of a rectification column arrangement 10. In addition to the pressure column 11, which comprises a column shell 11, the rectification column arrangement 10 in the shown example comprises a low-pressure column 12 with a column shell 12, a crude argon column divided into two and consisting of the column sections 13a and 13b with column shells 13a and 13b along with a pure oxygen column 14 with a column shell 14 and a pure argon column 15. The pressure column 11 is connected in a heat-exchanging manner to the low-pressure column 12 via a main condenser 16, which can in particular be designed as a multi-level bath evaporator, and a sump evaporator 17 is arranged in the bottom of the pure oxygen column 14. In the example shown, a subcooling heat exchanger 18 is also associated with the rectification column system 10.

[0059] The low-pressure column 12 and the argon column 13a, 13b comprise rectification regions A to D, wherein first and second rectification regions A, B are provided in the low-pressure column 12, and first and second rectification regions C, D are also provided in the argon column. Between the first and second rectification regions A, B of the low-pressure column 12, a first transfer fluid enriched in argon is removed from the low-pressure column 12 in the form of a material stream t1 and fed into the argon column 13a, 13b in a first transfer quantity below the first rectification region C of the argon column 13a, 13b. Below the first rectification region C of the argon column 13a, 13b, a second transfer fluid depleted of argon is removed from the argon column 13a, 13b in the form of a material stream t2 and fed into the low-pressure column 12 in a second transfer quantity between the first and second rectification regions A, B of the low-pressure column 12.

[0060] The pure oxygen column 14 is operated with a liquid as the return flow, which is removed from the argon column 13a, 13b in the form of a material stream r between the first and second rectification regions C, D of the argon column 13a, 13b, and a head gas is removed from the pure oxygen column 14 in the form of a material stream g, which is fed into the argon column 13a, 13b between the first and second rectification regions C, D of the argon column 13a, 13b.

[0061] The pressure column 11 and the low-pressure column 12 are connected by means of the main condenser 16 in a heat-exchanging manner, wherein a recirculating stream c is formed using head gas from the low-pressure column 12, which is passed through the subcooling heat exchanger 18, heated in the main heat exchanger 4, compressed by means of a compressor 5, cooled again in the main heat exchanger 4, passed in part c1 through the main condenser 16 and in part c2 through the sump evaporator 17 of the pure oxygen column 14, at least partially condensed there, and fed back into the pressure column 11 and the low-pressure column 12. Portions of the head gas from the low-pressure column are diverted from the recirculating stream c and discharged in the form of a gas product stream c3 and a liquid product stream c4, wherein the latter can be subcooled by expanding a partial stream c5.

[0062] In contrast to the embodiment illustrated here, the recirculating stream c can also be fed back into the pressure column 11 without diverting the gas product stream c3 on the warm side of the main heat exchanger 4 after cooling in the main heat exchanger 4, in particular substantially completely, without first passing it through the main condenser 16 and/or the sump evaporator 17 of the pure oxygen column 14. In the latter case, as mentioned, gas, in particular head gas, is removed from the pressure column 11 above the feed-in point of the recirculating stream c, which is further purified in this way with respect to the recirculating stream c, and instead of the recirculating stream itself, this can now be passed partially or completely through the main condenser 16 and/or partially or completely through the sump evaporator 17 of the pure oxygen column 14, where it is at least partially condensed, and returned to the rectification column arrangement 10. In the latter case, the nitrogen product can be provided using head gas from the pressure column 11.

[0063] In the embodiment illustrated in FIG. 1, the first rectification region A and the second rectification region B of the low-pressure column 12 are accommodated in the common column shell 12 in which the second rectification region B of the low-pressure column 12 is arranged above the first rectification region A of the low-pressure column 12. Furthermore, the first rectification region C of the argon column 13a, 13b is accommodated in the column shell 13a, and the second rectification region D of the argon column 13a, 13b is accommodated in the separate column shell 13b. The column shell 13a, in which the first rectification region C of the argon column 13a, 13b is accommodated, is arranged above the column shell 14 of the pure oxygen column 14 and is connected thereto or designed integrally therewith.

[0064] Further aspects of the operation of the air separation plant 100 according to FIG. 1 will now be explained, some of which are also realized in the air separation plant 200 according to FIG. 2 in the same or a similar way.

[0065] Sump liquid is removed from the pressure column in the form of a material stream s and, after passing through the subcooling heat exchanger 18 and partial use as a heating medium in a sump evaporator of the pure argon column 15, is fed into liquid baths of the top condensers of the argon column 13a, 13b and the pure argon column 15. The gas formed there and the corresponding flushing quantities are fed into the low-pressure column 12 in the form of material streams s1 to s3. Gas from above the first rectification region C of the argon column 13a, 13b and head gas from the pure oxygen column g is transferred to the corresponding part 13b of the argon column 13a, 13b below the second rectification region D, as already mentioned in part. The sump liquid accrued here is returned by means of a pump 18 to the corresponding part 13a of the argon column 13a, 13b above the first rectification region A and, as mentioned, to the pure oxygen column 14.

[0066] The argon column 13a, 13b, designed here as a crude argon column, and the pure argon column 15 are operated as is generally known from the field of argon production. Therefore, reference is made to the relevant technical literature. In particular, a pure argon stream p is removed from the pure argon column 15 in liquid form, which is internally compressed and discharged as a gaseous argon pressure product. A pure oxygen stream o is withdrawn in liquid form from the bottom of the pure oxygen column 14, which can be stored in a tank system (not shown), for example.

[0067] A gas stream t can be withdrawn from the low-pressure column 12 below the first rectification region A, subjected to any dilution gas stream v, heated in the main heat exchanger 8, expanded to an intermediate temperature by means of a residual gas turbine 8 braked by a generator G, for example, and released to the atmosphere or heated and used in the pre-cleaning unit 3. As illustrated in the form of the material stream o1, pure oxygen can be evaporated in the main heat exchanger and released as a corresponding pure oxygen product.

[0068] For further features of the air separation plant 100 illustrated in FIG. 1, reference is again made to the relevant technical literature.

[0069] FIG. 2 illustrates a simplified representation of an air separation plant 200 according to a further embodiment of the invention.

[0070] In the air separation plant 200 according to FIG. 2, the first rectification region A of the low-pressure column 12a, 12b is accommodated in a first column shell 12a, the second rectification region B of the low-pressure column 12a, 12b is accommodated in a second column shell 12b, and the first and second column shells 12a, 12b are arranged next to one another. The first column shell 12a and the column shell 11 of the pressure column 11 are arranged one above the other and are designed in the form of a double column. The second rectification region D of the argon column 13a, 13b is subdivided into a first subregion D1 and a second subregion D2, wherein the first rectification region C of the argon column 13a, 13b is accommodated in a third column shell 13a, the first subregion D1 of the second rectification region D of the argon column 13a, 13b is accommodated above the first rectification region C of the argon column 13a, 13b in the third column shell 13a, and the second partial region D1 of the second rectification region D of the argon column 13a, 13b is accommodated in the fourth column shell 13b.

[0071] As illustrated in FIG. 2, gas in the form of a material stream k above the first rectification region A of the low-pressure column 12a, 12b is withdrawn from the first column shell 12a, and a first portion in the form of a material stream k1 below the second rectification region B of the low-pressure column 12a, 12b is fed into the second column shell 12b, and a second portion in the form of a material stream k2 below the first rectification region C of the argon column 13a, 13b is fed into the third column shell 13b as the first transfer fluid.

[0072] Liquid is withdrawn from the third column shell 13b in the form of a material stream m below the first rectification region C of the argon column 13a, 13b and fed into the first column shell 12a above the first rectification region A of the low-pressure column 12a, 12b as the second transfer fluid, and liquid is withdrawn from the second column shell 12b in the form of a material stream n below the second rectification region B of the low-pressure column 12a, 12b and fed into the third column shell 13a below the first rectification region C of the argon column 13a, 13b. A lower end of the second column shell 12b is arranged geodesically above a feed-in position of the first transfer fluid into the third column shell 13a, so that the first transfer fluid is transferred into the third column shell 13a purely by gravity.

[0073] The pure oxygen column 14 is operated with a liquid as the return flow, which is removed from the argon column 13a, 13b in the form of a material stream r between the first and second rectification regions C, D of the argon column 13a, 13b, and a head gas is removed from the pure oxygen column 14 in the form of a material stream g, which is fed into the argon column 13a, 13b between the first and second rectification regions C, D of the argon column 13a, 13b.

[0074] For further details regarding the design and mode of operation of the air separation plant 200 in accordance with FIG. 2, reference is made to the explanations for FIG. 1 and the air separation plant 100 and to technical literature.

[0075] The air separation plant 100 according to FIG. 1 and the air separation plant 200 according to FIG. 2 are operated in a first operating mode and in a second operating mode, wherein a nitrogen product formed in the low-pressure column 12 after its compression in the compressor 5 is discharged from the air separation plant 100, 200 in the second operating mode in a smaller product quantity than in the first operating mode in the form of a material stream c3, and in the second operating mode, the first transfer quantity of the material stream t1 or k2, that is to say of the first transfer fluid, is adjusted to a lower value than in the first operating mode.