METHOD FOR THE CRYOGENIC SEPARATION OF AIR, AND AIR SEPARATION PLANT

Abstract

A method for the cryogenic separation of air, in which method an air separation plant with a rectification column arrangement is used, which plant has a pressure column, a low-pressure column, a raw argon column and pure argon column. In the method, evaporation gas from a head gas condensation device associated with the raw argon column is partially or completely fed into the low-pressure column in a first feed-in region, whereas evaporation gas from a head gas condensation device associated with the pure argon column and excess liquid from this head gas condensation device are partially or completely fed into the low-pressure column in a shared second feed-in region. In one embodiment, flash gas forming during the expansion of cooling fluid into the head gas condensation device associated with the raw argon column can be partially or completely fed into the low-pressure column in the second feed-in region.

Claims

1. A method for the cryogenic separation of air, in which method an air separation unit with a rectification column arrangement is used, which plant has a pressure column, a low-pressure column, a raw argon column and a pure argon column, wherein using a first proportion of an oxygen-enriched liquid from the pressure column, a first liquid pressure flow is formed, which is expanded while a first flash gas is produced and a first low-pressure liquid remains, using a second proportion of the oxygen-enriched liquid from the pressure column, a second liquid pressure flow is formed, which is expanded while a second flash gas is produced and a second low-pressure liquid remains, the raw argon column is operated using a first head gas condensation arrangement in which head gas of the raw argon column is subjected to condensation with partial evaporation of a first cooling fluid provided using the first low-pressure liquid or a part thereof, the pure argon column is operated using a second head gas condensation arrangement in which head gas of the pure argon column is subjected to condensation with partial evaporation of a second cooling fluid provided using the second low-pressure liquid or a part thereof, a first evaporation gas formed during the partial evaporation of the first cooling fluid or a part thereof and a first excess liquid remaining after the partial evaporation of the first cooling fluid or a part thereof are fed into the low-pressure column, and a second evaporation gas formed during the partial evaporation of the second cooling fluid or a part thereof and a second excess liquid remaining after the partial evaporation of the second cooling fluid or a part thereof are fed into the low-pressure column, the first evaporation gas or the part thereof fed into the low-pressure column is partially or completely fed into the low-pressure column in a first feed-in region, the second evaporation gas or the part thereof fed into the low-pressure column is partially or completely fed into the low-pressure column in a second feed-in region, the second excess liquid or the part thereof fed into the low-pressure column is partially or completely fed into the low-pressure column in the second feed-in region, and the first feed-in region is 5 to 25 theoretical plates below the second feed-in region and the first and second feed-in regions are each regions which do not comprise any separating devices.

2. The method according to claim 1, in which the first flash gas is separated from the first low-pressure liquid in a first phase separation and the second flash gas is separated from the second low-pressure liquid in a second phase separation, wherein the first and second phase separations are carried out in separate first and second phase separators, and in particular the second phase separator is formed by the evaporation chamber of the second head gas condensation arrangement.

3. The method according to claim 1, in which the formation of the first flash gas and the first low-pressure liquid and the production of the second flash gas and the second low-pressure liquid are carried out in a common valve and in a common phase separation and a common phase separator, which is formed in particular by the evaporation chamber of the second head gas condensation arrangement.

4. The method according to claim 1, in which the first flash gas or a part thereof is partially or completely, and separately from the first evaporation gas, fed into the low-pressure column in the second feed-in region, wherein in particular the first flash gas is transferred unthrottled into the low-pressure column after it has been provided in the first phase separation.

5. The method according to claim 1, in which the first evaporation gas or a part thereof is fed together with the first excess liquid or a part thereof as a first two-phase flow into the low-pressure column in the first feed-in region.

6. The method according to claim 1, in which the first low-pressure liquid or the part thereof which is forcibly fed through the one or more condenser evaporators is held in a reservoir which is geodetically arranged above one or more feed-in positions into the one or more condenser evaporators.

7. The method according to claim 5, in which the first evaporation gas and the first excess liquid are discharged from the condenser evaporator as the first two-phase flow without returning the first excess liquid or a part thereof into the one or more condenser evaporators.

8. The method according to claim 4, in which the first flash gas is transferred unthrottled to the low-pressure column after being provided in the phase separation.

9. The method according to claim 4, wherein the second evaporation gas or the part thereof fed into the low-pressure column in the second feed-in region is combined with the second excess liquid or the part thereof fed into the low-pressure column in the second feed-in region to form a second two-phase flow which is fed into the low-pressure column in the second feed-in region.

10. The method according to claim 5, in which the first two-phase flow is passed between the first head gas condensation arrangement and the low-pressure column through a throttle valve.

11. The method according to claim 6, in which there is passing between the head gas condensation arrangement and the low-pressure column into a phase separator in which the first evaporation gas and the first excess liquid are separated from each other, wherein the evaporation gas is passed between the phase separator and the low-pressure column through a throttle valve.

12. The method according to claim 11, in which the throttle valve is completely open at least temporarily during operation.

13. The method according to claim 11, in which the liquid level in the phase separator is measured and the amount of first cooling fluid introduced into the first head gas condensation arrangement is adjusted as a function of the measured value.

14. The method according to claim 13, in which the amount of liquid produced in the phase separator is quantitatively controlled.

15. The method according to claim 11, in which the head gas condensation arrangement comprises a heat exchanger block and said heat exchanger block is arranged in the interior of the phase separator, in which the first evaporation gas and the first excess liquid are separated from each other.

16. The method according to any of claim 10, in which the throttle valve is adjusted such that the temperature of the first cooling fluid is preferably at least 0.1 K above the triple point temperature of argon upon entering the first head gas condensation arrangement.

17. An air separation plant with a rectification column arrangement having a pressure column, a low-pressure column, a raw argon column and a pure argon column, wherein the air separation plant is configured to, using a first proportion of an oxygen-enriched liquid from the pressure column, form a first liquid pressure flow and expanded said first liquid pressure flow while a first flash gas is produced and a first low-pressure liquid remains, using a second proportion of the oxygen-enriched liquid from the pressure column, form a second liquid pressure flow and expand said second liquid pressure flow while a second flash gas is produced and a second low-pressure liquid remains, operate the raw argon column using a first head gas condensation arrangement and subject this head gas of the raw argon column to condensation with partial evaporation of a first cooling fluid provided using the first low-pressure liquid or a part thereof, operate the pure argon column using a second head gas condensation arrangement and subject this head gas of the pure argon column to condensation with partial evaporation of a second cooling fluid provided using the second low-pressure liquid or a part thereof, feeding a first evaporation gas formed during the partial evaporation of the first cooling fluid or a part thereof and a first excess liquid remaining after the partial evaporation of the first cooling fluid or a part thereof into the low-pressure column, and feeding a second evaporation gas formed during the partial evaporation of the second cooling fluid or a part thereof and a second excess liquid remaining after the partial evaporation of the second cooling fluid or a part thereof into the low-pressure column, characterized by means which are configured: to partially or completely feed the first evaporation gas or the part thereof fed into the low-pressure column into the low-pressure column in a first feed-in region, to partially or completely feed the second evaporation gas or the part thereof fed into the low-pressure column into the low-pressure column in a second feed-in region, and to partially or completely feed the second excess liquid or the part thereof fed into the low-pressure column into the low-pressure column in the second feed-in region, wherein the first feed-in region is 5 to 25 theoretical plates below the second feed-in region and the first and second feed-in regions are each regions which do not comprise any separating devices.

18. The air separation unit according to claim 17, comprising means which are configured to partially or completely, and separately from the first evaporation gas, feed the first flash gas or a part thereof into the low-pressure column in the second feed-in region.

Description

DESCRIPTION OF THE FIGURES

[0059] FIG. 1 illustrates an air separation plant according to a non-inventive embodiment in a simplified representation.

[0060] FIGS. 2 to 4 illustrate air separation plants according to embodiments of the invention with separate phase separation of the two liquid pressure flows in a simplified representation.

[0061] FIG. 5 is a sectional representation from FIGS. 3 and 4.

[0062] FIG. 6 shows a further embodiment of the invention with common phase separation of the two liquid pressure flows in the evaporation chamber of the top condenser of the pure argon column.

[0063] FIGS. 7 to 10 show further embodiments of the invention with additional measures downstream of the top condenser of the raw argon column.

[0064] 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 units and unit components apply in the same way for corresponding methods and method steps.

DETAILED DESCRIPTION OF THE DRAWINGS

[0065] In FIG. 1, an air separation plant according to a non-inventive embodiment of the present invention is illustrated in the form of a simplified process flow diagram and is denoted as a whole by 90.

[0066] Air separation plants of the type shown are often described elsewhere, for example in (see above), Industrial Gases Processing, Wiley-VCH, 2006, in particular section 2.2.5, Cryogenic Rectification and in conjunction with FIG. 2.3A. For detailed explanations regarding structure and operating principle, reference is therefore made to corresponding technical literature. An air separation plant for use of the present invention can be designed in a variety of ways. As mentioned, the present invention can in principle be applied to all process circuit topologies with argon recovery, regardless of the type of refrigeration or the type of product compression.

[0067] The air separation plant 90 shown by way of example in FIG. 1 has, among other things, a main air compressor 1, a pre-cooling device 2, a cleaning system 3, a secondary compressor assembly 4, a first booster turbine 5, a second booster turbine 6, a main heat exchanger 7, pumps 8 and 9 and a rectification column system 10. In the example shown, the rectification column system 10 comprises a classic double-column assembly made up of a pressure column 11 and a low-pressure column 12 and a raw argon column 13 and a pure argon column 14. The raw argon column 13 and the pure argon column 14 have head gas condensation arrangements 13.10 and 14.10, referred to here as first and second head gas condensation arrangements, each of which comprises a reflux or bath condenser evaporator.

[0068] In the air separation plant 90, a feed air flow is sucked in and compressed by means of the main air compressor 1 via a filter (not labeled). The compressed feed air flow is supplied to the pre-cooling device 2 that is operated with cooling water. The pre-cooled feed air flow is cleaned in the cleaning system 3. In the cleaning system 3, which typically comprises a pair of adsorber vessels used in alternating operation, the pre-cooled feed air flow is largely freed of water and carbon dioxide.

[0069] Downstream of the cleaning system 3, the feed air flow is divided into subflows. The air of the feed air flow is cooled in the main heat exchanger 7 in a fundamentally known manner. In the example illustrated here, two so-called turbine flows are formed in the corresponding turbines. In this case, the booster unit of the turbine booster 6 is designed as what is known as a cold booster, i.e., it is fed with already cooled air from the main heat exchanger 7. Air which has been completely cooled in the main heat exchanger 7 is expanded in a liquefied state via throttle valves, which are not separately labeled, and fed into the rectification column system as what are known as throttle flows.

[0070] An oxygen-enriched liquid bottom fraction and a nitrogen-enriched gaseous top fraction are formed in the pressure column 11. The oxygen-enriched liquid bottoms fraction is drawn off from the pressure column 11 and expanded in proportions into the evaporation chambers of the reflux or bath condenser evaporators in the head gas condensation arrangements 13.10 and 14.10. Gas proportions formed by the expansion and evaporation against the head gas of the raw or pure argon column 13, 14 are fed into the low-pressure column 12, as is the case here with unevaporated liquid.

[0071] The operation of the air separation unit 90 illustrated here is of common knowledge in this technical field and reference is made to the technical literature cited. The raw argon column 13 is usually fed from the low-pressure column 11, while the pure argon column 14 is usually fed from the raw argon column 13.

[0072] FIGS. 2 to 4 shows air separation plants according to embodiments of the invention and labeled with 100, 200 or 300.

[0073] In all cases, an oxygen-enriched liquid drawn off from the pressure column 11 is labeled with A. Using a first proportion thereof, a first liquid pressure flow B is formed, which is expanded while a first flash gas is obtained and a first low-pressure liquid remains in a valve not separately labeled.

[0074] In the embodiments 100 and 200 according to FIGS. 2 and 3, in which identical reference signs are used as before for the sake of simplicity, a previously described forced-flow condenser evaporator 13.12 is used in the first head gas condensation arrangement 13.10, next to which a separate phase separator 13.11 is arranged. The first low-pressure liquid is forced out thereof by the pressure of the forming liquid column through evaporation passages of the forced-flow condenser evaporator 13.12; the first flash gas can be drawn off as illustrated with C. The embodiments 100 and 200 differ from one another substantially in that the turbine booster 6 is not present in the embodiment 200 of FIG. 3.

[0075] In the embodiment 300 according to FIGS. 2 and 3, a reflux or bath condenser evaporator 13.12 is used in the first head gas condensation arrangement 13.10, in which a phase separator 13.11 is integrated. The first low-pressure liquid flows out of the phase separator 13.11 into the evaporation chamber of the reflux or bath condenser evaporator 13.12; the first flash gas can be drawn off as also illustrated by C.

[0076] In all cases, using a second proportion of the oxygen-enriched liquid from the pressure column 11, a second liquid pressure flow D is formed, which is expanded while a second flash gas is obtained and a second low-pressure liquid remains, wherein the second flash gas is labeled in each case with E.

[0077] The raw argon column 13 is thus operated here in each case using a first head gas condensation arrangement 13.10 in which head gas of the raw argon column 13 is subjected to condensation with partial evaporation of a first cooling fluid provided using the first low-pressure liquid or a part thereof.

[0078] The pure argon column 14 is operated using a second head gas condensation arrangement 14.10 in which head gas of the pure argon column 14 is subjected to condensation with partial evaporation of a second cooling fluid provided using the second low-pressure liquid or a part thereof.

[0079] A first evaporation gas formed during the partial vaporization of the first cooling fluid or a part thereof and a first excess liquid remaining after the partial evaporation of the first cooling fluid or a part thereof are fed into the low-pressure column 12 in both embodiments 100, 200 and 300 according to FIGS. 2, 3 and 4, as illustrated by F and G.

[0080] Likewise, a second evaporation gas formed during the partial evaporation of the second cooling fluid or a part thereof and a second excess liquid remaining after the partial evaporation of the second cooling fluid or a part thereof are fed into the low-pressure column 12, as illustrated by H and I.

[0081] Differences between the embodiments 100 and 200 according to FIGS. 2 and 3 on the one hand and the embodiment 300 according to FIG. 4 on the other hand result from the embodiments of the condenser evaporator 13.12 in the first head gas condensation arrangement 13.10. Its evaporation chamber is designed as a bath evaporator in FIG. 4. In the embodiment 300 according to FIG. 4, the first evaporation gas F is drawn off from the evaporation chamber separately from the first excess liquid G (and separately from the first flash gas C). In the embodiments 100 and 200 according to FIGS. 2 and 3, the first evaporation gas F and the first excess liquid G are discharged together in the form of a two-phase flow. The liquefaction chamber of the condenser evaporator 13.12 can be designed as a reflux condenser, as shown in FIG. 4, or conventionally as a classic pass-through condenser.

[0082] The first evaporation gas F or the part thereof fed into the low-pressure column 12 is always partially or completely fed into the low-pressure column 12 in a first feed-in region, in particular at a common position with the first excess liquid G.

[0083] The second evaporation gas H or the part thereof fed into the low-pressure column 12, on the other hand, is partially or completely fed into the low-pressure column 12 in a second feed-in region. Likewise, the second excess liquid I or the part thereof fed into the low-pressure column 12 is partially or completely fed into the low-pressure column 12 in the second feed-in region. The first flash gas C or a part thereof is partially or completely, and separately from the first evaporation gas F, fed into the low-pressure column 12 in the second feed-in region.

[0084] A transfer flow from the raw argon column 13 to the pure argon column is additionally labeled with T in FIG. 4 and is also present in the other embodiments.

[0085] FIG. 5 shows a sectional representation from FIGS. 3 and 4 with corresponding reference signs. Reference is made in this context to the explanations above.

[0086] FIG. 6 shows the upper ends of columns 10, 13 and 14 very schematically. The method the same as in FIG. 2 or FIG. 3, but no separate separator is used as the phase separator of the first liquid pressure flow B, nor is a separator installed in the evaporation chamber of the head gas condensation arrangement 13.10 (raw argon top condenser) as in FIGS. 4 and 5, but simply the evaporation chamber of the second head gas condensation arrangement 14.10 (pure argon top condenser).

[0087] For this purpose, the two liquid pressure flows B and H are expanded together downstream of the bottom evaporator 600 of the pure argon column 14 in valve 601 and fed together via line 602 into this evaporation chamber of the second head gas condensation arrangement 14.10, which acts as a common phase separator. The first flash gas C is drawn off via line 603, together with the second evaporation gas E produced in the condenser evaporator 14.10. The first cooling fluid K is drawn off from the evaporation chamber of the second head gas condensation arrangement 14.10 together with the second excess liquid I via line 604 and fed separately into the evaporation chamber of a first head gas condensation arrangement (13.10) for the purpose of partial evaporation. The first head gas condensation arrangement (13.10) is designed as a forced-flow evaporator on the evaporation side. The remaining fluids to and from the first head gas condensation arrangement (13.10) are conducted as shown in FIGS. 2 and 3.

[0088] Compared to FIGS. 2 to 4, this results in lower manufacturing costs for the plant and a smaller footprint, and therefore also smaller boxes for the insulating cold box and its filling with insulating material such as perlite.

[0089] FIG. 7 shows, also schematically, a further development based on FIG. 6. However, the further development can also be applied to FIGS. 2 and 3, in which the first head gas condensation arrangement (13.10) also has a forced-flow evaporator. In FIG. 7, there is a valve (throttle valve) or flap 703 in the descending pipe 703 of the two-phase flow 701. Said valve or flap is usually fully open during normal operation. During special operating situations, for example during partial load operation, the two-phase flow can be throttled to increase the pressure and thus the temperature in the first head gas condensation arrangement (13.10). This effectively prevents the argon from freezing and ensures particularly stable operation. The valve can be pressure-controlled (or alternatively temperature-controlled)

[0090] FIG. 7 also shows the corresponding control elements. The following meanings apply: [0091] FIC-Flow Indication and Control [0092] LIC-Liquid Indication and Control [0093] PIC-Pressure Indication and Control

[0094] The data lines between the measuring and actuating elements are shown as dashed lines in FIG. 7 (and also in FIGS. 8 and 9).

[0095] FIC1 controls the supply of second excess liquid I to the low-pressure column 12. FIC2 controls the supply of condensate from the first head gas condensation arrangement (13.10) as a function of the feed quantity for the raw argon column. PIC1 controls the pressure on the evaporation side of the second head gas condensation arrangement (14.10). LIC1 controls the quantity of first cooling fluid flowing into the first head gas condensation arrangement (13.10). LIC2 controls the total quantity of coolant via the bottom level measurement in the high-pressure column.

[0096] FIC2 controls the evaporator performance (by backing up the liquid into block 13.10 and covering part of the condensation surface).

[0097] The liquid proportion in flow 701 is optionally calculated and adjusted by FIC1.

[0098] Alternatively, particularly stable operation can be achieved by using an additional phase separator 804 to separate the two-phase flow 701 into the first evaporation gas F and the first excess liquid G. This variant is shown in FIG. 8. The first evaporation gas F is then passed through a throttle valve 803, which is arranged between the phase separator 804 and the low-pressure column 12, in a similar way to the liquid above.

[0099] The control is also shown in FIG. 8. PIC1 and LIC2 have the same function as in FIG. 7. The pressure on the evaporation side of the second head gas condensation arrangement (14.10) can optionally be controlled with PIC2.

[0100] Alternatively, instead of PIC2, a TIC (Temperature Indication and Control) controller can be used to control the temperature of the first cooling fluid as it enters the first head gas condensation arrangement (13.10). LIC3 controls the quantity of first cooling fluid flowing into the first head gas condensation arrangement (13.10), but in this case as a function of the value of the fill level in the phase separator 804. The quantity of second excess liquid I flowing to the low-pressure column is adjusted by means of LIC4 as a function of the liquid level on the evaporation side of the pure argon condenser. There are also FIC3 and FIC4 controllers in the lines for the second excess liquid G and the raw argon, which is transferred to the pure argon column 14. The FIC3 controller is particularly important here. This means that the liquid proportion in the flow 701 can be controlled directly (and not determined by calculation) and dry evaporation in the condenser can be avoided.

[0101] FIG. 9 is a simplified illustration of a particular embodiment of the invention according to FIG. 8. Here, the heat exchanger block of the first head gas condensation arrangement 13.10 is arranged inside the phase separator 804, in which the first evaporation gas and the first excess liquid are separated from each other. The first head gas condensation arrangement does not lose its character as a forced-flow evaporator. Rather, the liquid to be evaporated continues to flow forcibly and the line at LIC3 and the header on the heat exchanger block into the evaporation passages and is not drawn in from the liquid bath of the separator 804 as would be the case with a bath evaporator.

[0102] FIG. 10 is very similar to FIG. 8. In this case, however, the valve 803 is controlled as a function of the feed quantity into the raw argon columns.

[0103] The special measures of FIGS. 7 to 10 can also be applied to the overall methods of FIGS. 2 and 3, for example with a separate phase separator for the first liquid pressure flow or with one integrated into the head gas condensation arrangement.