METHOD FOR SEPARATING AIR BY CRYOGENIC DISTILLATION

Abstract

A method for separating air by cryogenic distillation is provided, in which, at least one portion of the first oxygen-enriched liquid is sent from a first column to a first vaporizer-condenser where it is partially vaporized in the form of a film at a pressure higher than the second pressure forming a second oxygen-enriched liquid constituting at least 30% of the oxygen-enriched liquid sent to the first vaporizer-condenser and a third oxygen-enriched gas, an argon-enriched fluid is sent from a second column to a third column and the fluid is separated in the column forming an argon-rich flow at the top of the column and an oxygen-rich flow at the bottom of the column and the third oxygen-enriched gas is expanded in a turbine with production of work.

Claims

1-13. (canceled)

14. A method for separating air by cryogenic distillation, in which: i) a flow of compressed, purified and cooled air is sent to a first column operating under a first pressure where it separates forming a first oxygen-enriched liquid and a first nitrogen-enriched flow; ii) at least one portion of the first oxygen-enriched liquid is sent to a first vaporizer-condenser where it is partially vaporized at a pressure higher than a second pressure, forming a second oxygen-enriched liquid and a third oxygen-enriched gas; iii) at least one portion of the first nitrogen-enriched flow is sent to a second column operating under the second pressure, lower than the first pressure; iv) the bottom of the second column is heated by means of a second bottom vaporizer-condenser; v) an argon-enriched fluid is sent from the second column to a third column and the fluid separates in the third column forming an argon-rich flow at the top of the column and an oxygen-rich flow at the bottom of the column; vi) the argon-rich flow condenses in the first vaporizer-condenser; and vii) the third oxygen-enriched gas is expanded in a turbine with production of work, optionally after heating, characterized in that the at least one portion of the first oxygen-enriched liquid partially vaporizes in the first vaporizer-condenser in the form of a film, the third gas exiting via the bottom of the first vaporizer-condenser co-current with the liquid which vaporizes and the second oxygen-enriched liquid constitutes at least 30% of the oxygen-enriched liquid sent to the first vaporizer-condenser.

15. The method as claimed in claim 14, wherein the temperature difference between the oxygen-enriched liquid and the temperature of the liquid exiting at the bottom of the condensation side of the first vaporizer-condenser is lower than 1 C., preferably lower than 0.5 C.

16. The method as claimed in claim 14, wherein the turbine drives a booster on one of the gaseous fluids of the method.

17. The method as claimed in claim 16, wherein the gaseous fluid is the residual gas used for the regeneration of the purification at the top.

18. The method as claimed in claim 14, wherein the turbine drives a generator.

19. The method as claimed in claim 18, wherein the generator turns at the same speed as the turbine

20. The method as claimed in claim 19, wherein the energy of the generator passes into a frequency converter in order to supply the electrical grid at 50 or 60 Hz depending on the country.

21. The method as claimed in claim 14, wherein the turbine drives a booster and a generator, the three being on the same shaft, turning at the same speed.

22. The method as claimed in claim 14, wherein the gas to be expanded is heated by indirect heat exchange with a liquid coming from the first column or from the main exchanger which sub-cools.

23. The method as claimed in claim 14, wherein the argon-rich flow is mixed with the residual fluid of the second column.

24. The method as claimed in claim 14, wherein the gas to be expanded is not heated in a main exchanger where the supply air cools upstream of the expansion.

25. The method as claimed in claim 14, wherein the gas to be expanded is at between 1.7 and 2.7 bar absolute.

26. The method as claimed in claim 14, wherein all the first oxygen-enriched liquid is sent to the first vaporizer-condenser.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawing(s). It is to be noted, however, that the drawing(s) illustrate only several embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it can admit to other equally effective embodiments.

[0035] The FIGURE shows a process diagram for the method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0036] The FIGURE shows a three column apparatus, including a first column K01 operating at a first pressure K01, a second column K02 operating at a second pressure lower than the first pressure, and a column for producing argon K10. The first column K01 is thermally connected to the second column K02 by the bottom condenser E02 of the second column K02 in known manner.

[0037] A flow of air is compressed by a compressor (not shown) to the high pressure, the compressed flow is purified in a purification unit (not shown) and the purified flow is divided into two. The major portion of the air 5 is again separated into two in order to form two flows 5A and 5B. Flow 5A is boosted in a booster 6 coupled to a turbine D01. The air 5A is then cooled in a cooler D01 E, partially cools in the exchange line 9 and is sent to the turbine D01. The expanded air is sent to the second column K02.

[0038] The air 5B is sent to the exchange line 9 where it cools before being sent, in gaseous form, to the bottom of the first column K01.

[0039] The remainder of the air 7 is boosted in a booster 8 to a high pressure. After being cooled in the exchange line 9, the flow is divided in two, one portion 11 being sent to the first column K01 and the remainder 13 to the second column K02 after sub-cooling in E04, both in liquid form.

[0040] Other ways of cooling the air and generating cold can replace these.

[0041] A nitrogen-rich liquid 13 is cooled in the sub-cooler E04 and supplies the second column K02.

[0042] A flow of rich liquid 15 (oxygen-enriched liquid) is withdrawn at the bottom of the first column K01. A portion of the rich liquid supplies a top condenser E10 of the argon column K10. The condenser-vaporizer E10 is used to condense the gas at the top of the argon column K10.

[0043] The rich liquid 15 is partially vaporized in the film vaporizer E10 in the form of a film, in order to form an oxygen-enriched liquid and an oxygen-enriched gas. The vaporized gas exits via the bottom of the condenser-vaporizer E10 co-current with the liquid which vaporizes; only the instantaneously vaporized gas coming from the incoming liquid exits at the top. Indeed, the expansion in the valve just upstream of the vaporizer E10 generates the gas at the inlet of the condenser vaporizer which can represent up to 10% of the liquid 45. The condenser-vaporizer E10 is shown without a housing (cylindrical shell) around it: this signifies that one (or more) brazed aluminum plate heat exchangers are used where hemispherical ends have been welded to the upper and lower ends in order to supply liquid and to recover and separate the gaseous and liquid fractions at the bottom. This condenser-vaporizer E10 could also be placed in a housing.

[0044] In this example, the gas at the top of the hemispherical end at the lower end of the condenser-vaporizer E10 joins the gas generated upstream of the condenser-vaporizer E10 taken from inside the hemispherical end at the upper end of the condenser-vaporizer, and the liquid withdrawn at the bottom of the hemispherical end is sent to the column K02.

[0045] The gas exiting via the bottom of the first vaporizer-condenser, co-current with the liquid which vaporizes, is of order 50% of the liquid 45.

[0046] The oxygen-enriched liquid 38 constitutes at least 30% of the liquid 15 sent to the vaporizer E10. Hence, the condenser-vaporizer E10 is massively purged: this reduces the oxygen concentration of the vaporized fluid and therefore increases the vaporization pressure for a given temperature.

[0047] The temperature difference between the oxygen-enriched liquid 38 and the temperature of the liquid exiting the bottom, condensation-side, of the condenser E10 is lower than 1 C., preferably lower than 0.5 C.

[0048] The liquid 38 is sent to the second column K02 and the gas 43 is heated in the sub-cooler E04 before being expanded in a turbine D07 and then sent as gas 32 to supply the second column K02. Is not absolutely necessary to heat the vaporized liquid 43 coming from the vaporizer E10. It could also be sent directly to the turbine D07, but a two-phase flow would be produced which would need to be managed. If the turbine is on the ground, this requires a separator pot and pump on the liquid fraction; otherwise, the turbine can be sited above the point of injection of the gas 32 into the second column K02 so that the liquid flows with a downward gradient. In this case, a turbine without oiled bearings, in other words with magnetic bearings or rolling bearings or gas bearings, will be used.

[0049] The inlet pressure of the turbine D07 is between 1.7 and 1.9 bar absolute and the second pressure is of order 1.4 bar absolute.

[0050] The remainder 28 of the rich liquid 15 is optionally sent to the second column K02. In the majority of cases, it is preferred to send all of the rich liquid to the vaporizer-condenser E10.

[0051] A nitrogen-rich gas flow 39 is withdrawn at the top of the first column K01 as product.

[0052] A nitrogen-rich gas flow 35 is withdrawn at the top of the second column K02, heats up in the sub-cooler and in the exchanger 9.

[0053] A liquid oxygen flow 33 is withdrawn at the bottom of the second column K02, pressurized by the pump P01 and then vaporizes in the exchange line 9.

[0054] The argon column K10 is supplied at the bottom by an argon-enriched flow 19 coming from the column K02.

[0055] The liquid from the bottom of the argon column 41 is relatively pure oxygen which is pumped in a pump P02, and returned at the bottom of the second column K02.

[0056] An argon flow is withdrawn as product at the top of the column K10. The argon production is not essential.

[0057] It is obviously conceivable to vaporize other liquids in the exchange line.

[0058] The turbine D07 can drive a booster on one of the gaseous fluids of the method.

[0059] This gaseous fluid may be the residual gas used for the regeneration of the purification at the top.

[0060] The turbine can drive a generator.

[0061] The generator can turn at the same speed as the turbine.

[0062] The energy from the generator can pass into a frequency converter in order to supply the electrical grid at 50 or 60 Hz depending on the country.

[0063] The turbine can drive a booster and a generator, the three being on the same shaft, turning at the same speed.

[0064] The gas 43 is heated by sub-cooling a liquid 28 coming from the first column K01 or from the main exchanger E01.

[0065] A portion of the argon-enriched fluid 19 can be condensed in the first vaporizer-condenser (E10).

[0066] The condensed portion of the fluid 19 will then be introduced into the third column K10 at an intermediate level thereof.

[0067] The argon-rich flow 45 can be mixed with the residual fluid 35 of the second column K02. In this case, there is no argon production.

[0068] The second column K02 can contain the vaporizer E10 and/or the column K10. The second column K02 can support the vaporizer E10.

[0069] In any event, the argon produced by the column K10 is not necessarily a product of the apparatus and can be mixed with the residual nitrogen and sent to the atmosphere.

[0070] Alternatively, the liquid sent to the vaporizer-condenser E10 could be partially or totally liquid air 11 or 13 which has come from the compressor 8.

[0071] While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed.

[0072] Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

[0073] The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

[0074] Comprising in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of comprising). Comprising as used herein may be replaced by the more limited transitional terms consisting essentially of and consisting of unless otherwise indicated herein.

[0075] Providing in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

[0076] Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

[0077] Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

[0078] All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.