APPARATUS AND METHOD FOR SEPARATING AIR BY CRYOGENIC DISTILLATION

Abstract

An apparatus for separating air, comprising a double column, means for sending air to the purification unit at a pressure that is no more than 1 bar higher than atmospheric pressure, a pipe for sending a first air flow, the first air flow having been purified in the purification unit, to the heat exchanger at a fourth pressure that is no more than 1 bar higher than the second pressure, a pipe for sending the first purified air flow, which has been cooled in the heat exchanger, to the second column for separation, and a booster compressor, the apparatus not comprising any means for depressurizing the first flow.

Claims

1-15. (canceled)

16. An air separation apparatus comprising: a double column with a first column operating at a first pressure and a second column operating at a second pressure, lower than the first pressure, the second column having a bottom reboiler; means for sending nitrogen-enriched gas from the top of the first column to the bottom reboiler and means for sending at least a part of the condensed nitrogen-enriched gas from the bottom reboiler to the top of the first column; a heat exchanger; a purification unit; means for sending air to the purification unit at a third pressure greater than atmospheric pressure by at most 1 bar; a pipe for sending a first flow of air purified in the purification unit to the heat exchanger at a fourth pressure greater than the second pressure by at most 1 bar; a pipe for introducing the first flow of purified air cooled in the heat exchanger into the second column in order to be separated therein, a booster; a pipe for sending a second flow of air purified in the purification unit to the booster; a pipe for sending at least a part of the second flow, compressed by the booster up to a fifth pressure between the first pressure and 1 bar above the first pressure, to the heat exchanger; means for producing refrigeration; a pipe for withdrawing at least one fluid enriched in oxygen or nitrogen from a column of the double column connected to the heat exchanger and a pipe for exiting at least one fluid enriched in oxygen or nitrogen from the heat exchanger as product; and the apparatus not comprising any means of expansion of the first flow and comprising only a single purification unit; wherein the second column comprises an absence of an intermediate condenser, wherein the pipe for introducing the first flow of purified air is connected to the inside of the second column such that the first flow is included in the distillation.

17. The apparatus as claimed in claim 16, in which the means for the production of refrigeration includes at least one of: a turbine for expansion of a part of the second flow, a turbine for expansion of a nitrogen-rich gas originating from the first column, and means for sending a cryogenic liquid from an external source to the double column.

18. The apparatus as claimed in claim 17, in which the turbine for expansion of the part of the second flow is connected to the second column in order to send the expanded air to the second column.

19. The apparatus as claimed in claim 16, in which the means for sending air to the purification unit at the third pressure comprises an absence of any compression means other than a single-stage compressor.

20. The apparatus as claimed in claim 16, further comprising an absence of any means for compression of the first flow.

21. A process for the separation of air by cryogenic distillation using a double column with a first column operating at a first pressure and a second column operating at a second pressure, lower than the first pressure, the second column having a bottom reboiler, in which: a. sending air containing water and carbon dioxide to a single purification unit at a third pressure greater than atmospheric pressure by at most 1 bar; b. separating the purified air into two; c. sending a first flow of air purified in the purification unit to a heat exchanger at a fourth pressure greater than the second pressure by at most 1 bar; d. sending the first flow of purified air cooled in the heat exchanger to the second column, without having expanded the first flow of purified air; e. boosting a second flow of purified air to a fifth pressure between the first pressure and 1 bar above the first pressure, and then sending at least a part of the second flow at the fifth pressure to the heat exchanger and sending the at least a part of the second flow to the first column in gaseous form; f. providing refrigeration; g. at least partially condensing a nitrogen-rich gas from the first column in the reboiler and returning at least a part of the condensed nitrogen to the first column; h. sending a nitrogen-enriched liquid and an oxygen-enriched liquid from the first column to the second column; and i. withdrawing an oxygen-enriched gas or a nitrogen-enriched gas from the double column and reheating said oxygen-enriched gas or said nitrogen-enriched gas in the heat exchanger in order to form a product of the process, wherein the first air flow is sent directly into the second column in order to be separated therein without having been condensed in a condenser.

22. The process as claimed in claim 21, in which the first flow is sent to the second column at a level lower than or equal to the level of arrival of the oxygen-enriched liquid.

23. The process as claimed in claim 21, kept cold by expansion of a part of the second flow in a turbine from the fifth pressure to the second pressure, the part of the air expanded in the turbine preferably representing between 6 vol % and 15 vol %, preferably between 6% and 8%, of the purified air.

24. The process as claimed in claim 23, in which all the second flow is cooled in the heat exchanger down to an intermediate temperature of the heat exchanger, the inlet of the turbine is at the intermediate temperature of the heat exchanger and the part of the second flow sent to the first column is cooled in the heat exchanger down to the cold end of the latter.

25. The process as claimed in claim 21, in which all the air is purified at a pressure which does not exceed 1.5 bara, indeed even does not exceed 1.3 bara.

26. The process as claimed in claim 21, in which the oxygen-enriched gas contains at least 80 mol % oxygen, indeed even at least 90 mol % oxygen, but preferably less than 98 mol % oxygen.

27. The process as claimed in claim 21, in which the first flow represents between 20 vol % and 30 vol % of the purified air flow.

28. The process as claimed in claim 21, in which the second flow represents between 70 vol % and 80 vol % of the purified air flow.

29. The process as claimed in claim 21, in which an oxygen-enriched gas and/or a nitrogen-enriched gas is withdrawn from the double column and it is reheated in the heat exchanger in order to form a product of the process by introducing it or by introducing them at the cold end of the heat exchanger.

30. The process as claimed in claim 21, in which the first air flow and/or the part of the second flow intended for the first column is cooled in the heat exchanger down to a temperature at least 5° C. above its dew point.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0057] 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.

[0058] The FIGURE shows an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0059] The invention will be described in a more detailed manner with reference to the FIGURE.

[0060] FIG. 1 represents a process for the separation of air by cryogenic distillation according to certain embodiments of the invention.

[0061] An apparatus for the separation of air by cryogenic distillation comprises a double column with a first column K3 operating at a first pressure and a second column K4 operating at a second pressure, lower than the first pressure, the second column having a bottom reboiler M. The second column K4 does not contain an intermediate condenser.

[0062] In this example, the first pressure is 4.5 bara and the second pressure is 1.13 bara.

[0063] A nitrogen-enriched gas is sent from the top of the first column to the bottom reboiler M and at least a part of the condensed nitrogen-enriched gas from the bottom reboiler is sent to the top of the first column.

[0064] Air at atmospheric pressure is filtered in a filter A, compressed by a blower B having a single stage at a pressure at most 1 bar, preferably at most 0.5 bar, above atmospheric pressure, cooled by a cooling means C and purified of water and carbon dioxide in a single purification unit D in which the air 4 enters at a third pressure greater than atmospheric pressure by at most 1 bar, preferably by at most 0.5 bar. The purification unit comprises two adsorbent beds used alternately to purify the air, one bed purifying the air while the other is regenerated.

[0065] The air purified in the unit D is divided into two in order to form two flows 6,8. The air 8 is neither compressed nor expanded and is at a pressure which differs from the second pressure by a pressure equal to the pressure drops in the pipes and the heat exchanger G.

[0066] Preferably, the first flow 8 represents between 20 vol % and 30 vol % of the flow 4 and the second flow 6 represents between 70 vol % and 80 vol % of the flow 4.

[0067] Thus, the air 8 is sent directly from the purification unit to the second column K2 to be separated therein, entering the column in entirely gaseous form. The air 8 is cooled in the heat exchanger G down to a temperature at least 5° C. above its dew point.

[0068] The flow 6 is boosted in a booster E, cooled in a cooler F and sent to the heat exchanger G. The booster E boosts the air 6 up to a fifth pressure between the first pressure and 1 bar above the first pressure. The air 6 is divided into two parts 30,32 at an intermediate level of the exchanger. The air 30 leaves the exchanger at an intermediate temperature of the latter, for example −125° C., is expanded in a turbine 28 down to the second pressure and enters in gaseous form, mixed with the flow 8, to be separated in the second column K4.

[0069] The flow 30 can represent between 6 vol % and 15 vol %, preferably between 6% and 8%, of the air 4.

[0070] The air 32 is cooled down to the cold end of the exchanger G and is sent to the bottom of the first column K3 in essentially gaseous form in order to be separated therein. The air 8 is cooled in the heat exchanger G down to a temperature at least 5° C. above its dew point.

[0071] An oxygen-enriched liquid flow 34 is withdrawn at the bottom of the first column and sent to a level of the second column which is above the air inlet. Alternatively, the air can enter the second column at the same level as that of the arrival of the liquid 34.

[0072] The expanded liquid 34 can be separated in a phase separator: the liquid resulting from the phase separator is sent to the column K4 and the vapor phase can be mixed at the inlet of air 8,30 into the column K4.

[0073] A flow of liquid nitrogen 35 is withdrawn from the top of the first column and sent to the top of the second column.

[0074] Gaseous nitrogen 36 is withdrawn at the top of the second column K4 and is heated in the subcooler S and subsequently in the exchanger G. A part 14 of this gas is used to regenerate the purification unit D.

[0075] Gaseous oxygen 29 is withdrawn at the bottom of the second column K4. The flow 29 preferably contains at least 80 mol % oxygen, indeed even at least 90 mol % oxygen, but preferably less than 98 mol % oxygen.

[0076] It will be noticed that the process does not produce any liquid flow as final product. The process does not produce any liquid flow to be vaporized in order to form a final gaseous product, optionally under pressure. It is, however, possible to produce a small amount of final gaseous product in this way, which can optionally be mixed with the main gaseous product.

[0077] Furthermore, a small flow of liquid might be produced.

[0078] In an alternative form, the air 8 and/or the air 30 can be subcooled in the sub cooler S and then be introduced into the second column K4. Otherwise, the mixture of the flows 8 and 30 can be subcooled in the subcooler S and then be introduced into the second column K4.

[0079] In the example described, the flow 29 is a flow of gaseous oxygen which is heated in the heat exchanger G from the cold end of the exchanger G. Alternatively, the flow 29 can be a flow of oxygen-rich liquid pressurized to a pressure above that of the second column K4. The liquid 29 is vaporized either in a dedicated vaporizer (not illustrated) or in the heat exchanger G. The liquid 29 can be vaporized by heat exchange with all the air 32 in order to partially condense the air 32, which will subsequently be sent to the bottom of the first column K3. Otherwise the liquid 29 can be vaporized by heat exchange with a part of the air 32 in order to completely condense this part of the air 32. The condensed air will subsequently be sent to the bottom of the first column K3 or to an intermediate point of the first and/or of the second column.

[0080] Otherwise, a part of the purified air can be boosted in a booster to a pressure greater than that of the first column K3 in order to vaporize the liquid 29.

[0081] 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. 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.

[0082] The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

[0083] “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.

[0084] “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.

[0085] 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.

[0086] 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.

[0087] 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.