This application is a § 371 of International PCT Application PCT/FR2014/052228, filed Sep. 9, 2014, which claims the benefit of FR1358927, filed Sep. 17, 2013, both of which are herein incorporated by reference in their entireties.
The present invention relates to a process and to an apparatus for producing gaseous oxygen by cryogenic distillation of air.
One subject of the invention is the improvement in the energy performance of an air separation unit producing a gas, generally oxygen, at a pressure above 20 bar a, by vaporization of the main exchanger of liquid oxygen, drawn from the distillation columns and brought to high pressure by means of a pump.
In the units for producing oxygen by vaporization of liquid, the energy efficiency of the plant depends to a large extent on the method used for generating the hot pressurized fluid, generally feed air, which, by condensing toward the cold end of the exchanger, will enable the vaporization of the oxygen by exchange of heat.
U.S. Pat. No. 5,475,980 describes an air separation process in which a portion of the air is compressed in a hot booster and another portion in a cold booster until substantially identical pressure is reached. The cold compression gives rise to an introduction of compression heat into the heat exchanger. However a portion of the air boosted in the cold booster is expanded in an expansion turbine. For this reason, it is not possible to reduce the cold-boosted flow below a certain value since the air available for the expansion would be insufficient.
In certain embodiments of the present invention, the air stream sent to the turbine has not been boosted in the cold booster and thus it is possible to minimize the amount of compression heat.
All the pressures mentioned are absolute pressures.
The invention proposes a particularly effective method for generating this pressurized gas, by the succession of several operations.
According to one subject of the invention, a process is provided for producing gaseous oxygen by cryogenic distillation of air, wherein:
i) all or part of the feed air flow is brought to a pressure P1, at least 5 bar greater than the pressure of the medium-pressure column, by means of a first compressor, the suction temperature T0 of which is between 0 and 50° C., preferably between 5 and 30° C.,
ii) the gas at the pressure P1 is cooled, typically by heat exchange with water, in order to generate an air stream at the pressure P1 and the temperature T1 between 5 and 45° C., preferably between 15 and 25° C.,
iii) a portion of the air compressed in the first compressor undergoes an additional compression step starting from the temperature T1 and pressure P1 to a pressure P2 greater than P1, then is cooled, typically by heat exchange with water, to the temperature T2 where T2 and T1 differ by less than 10° C., typically less than 5° C.,
iv) this cooled portion is then introduced into a heat exchanger of an air separation unit in order to undergo cooling to a temperature below or equal to −100° C.,
v) another portion of the air is introduced at the pressure P1 into a heat exchanger of the air separation unit, optionally that from step iv), in order to undergo cooling therein to a temperature below −100° C., then at least one fraction of this other portion is compressed starting from this cryogenic temperature in a second compressor (4) to a pressure P3 which is either equal to P2, or is less than 5 bar higher or lower than P2,
vi) the fraction thus compressed in the second compressor is sent back to one of the previous exchangers or to the exchanger in order to be cooled therein to a temperature below −100° C.,
vii) at least one portion of the air at the pressure P2 and at least one portion of the air at the pressure P3 and optionally at least one portion of the stream at the pressure P1 are cooled up to the cold end of the exchanger where they are liquefied, then are sent after expansion to at least one distillation column of the air separation unit,
viii) at least 50%, preferably at least 70%, of the total air flow supplies, in gaseous form, at least one distillation column of the unit, after having been expanded in an expansion turbine,
ix) air is separated in the system of columns, and
x) liquid oxygen is drawn from one of the distillation columns, pressurized by means of a pump to the required pressure which is greater than 20 bar abs, vaporized by heat exchange, then reheated in order to be used in the form of gaseous product,
wherein the air is expanded in the expansion turbine starting from the pressure P1 or P2 or from a pressure between P1 and P2.
According to other optional aspects of the invention:
According to another subject of the invention, an apparatus is provided for producing gaseous oxygen by cryogenic distillation of air that comprises a system of columns, a first compressor, a second compressor, at least one heat exchanger, means for sending all or part of the feed air flow to the first compressor capable of bringing its pressure to a pressure P1, at least 5 bar greater than the pressure of the medium-pressure column, a first cooler for cooling the gas at the pressure P1, typically by heat exchange with water, in order to generate an air stream at the pressure P1 and the temperature T1 between 5 and 45° C., preferably between 15 and 25° C., means for compressing a portion of the air compressed in the first compressor at the pressure P1 to a pressure P2 greater than P1, a second cooler for cooling the portion of the air at P2, to the temperature T2 where T2 and T1 differ by less than 10° C., typically less than 5° C., means for sending this cooled portion to the or one of the heat exchanger(s) in order to undergo cooling to a temperature below or equal to −100° C., means for introducing another portion of the air at the pressure P1 into the or one of the heat exchanger(s) of the air separation unit, in order to undergo cooling therein to a temperature below −100° C., means for sending at least one fraction of this other portion to the second compressor starting from this cryogenic temperature in a second compressor to a pressure P3 which is either equal to P2, or is less than 5 bar higher or lower than P2, means for sending back the fraction thus compressed in the second compressor to one of the previous exchangers or to the exchanger in order to be cooled therein to a temperature below −100° C., means for sending at least one liquefied gas at the pressure P1 and/or at the pressure P2 and/or at the pressure P3 to at least one distillation column of the air separation unit, an expansion turbine capable of expanding at least 50%, preferably at least 70%, of the total air flow connected to at least one column of the system and means for drawing off liquid oxygen from a column of the system, a pump for pressurizing the liquid and means for sending the pumped liquid to the/one of the heat exchanger(s), characterized in that the expansion turbine is connected to the outlet of the first compressor in order to receive air that originates therefrom but is connected so that it does not receive air from the second compressor.
According to other optional aspects of the invention:
All or part of the feed air flow is brought to a pressure P1, at least 5 bar greater than the medium-pressure column, by means of a compressor, the suction temperature T0 of which is between 0 and 50° C., preferably between 5 and 30° C. At the outlet of the compressor, the gas is cooled, typically by heat exchange with water, in order to generate an air stream at the pressure P1 and the temperature T1 between 5 and 45° C., preferably between 15 and 25° C.
A portion of this stream undergoes an additional compression step starting from the temperature T1 and pressure P1 to a pressure P2 greater than P1, then is cooled, typically by heat exchange with water, to the temperature T2. T2 and T1 only differ by less than 10° C., typically less than 5° C. This flow is then introduced into an exchanger E1 of the air separation unit in order to undergo cooling to a temperature below or equal to −100° C.
Another portion of this stream is introduced at the pressure P1 and at the temperature T1 into an exchanger of the air separation unit, optionally E1, in order to undergo cooling therein to a temperature below −100° C., then at least one fraction of this portion is compressed starting from this cryogenic temperature in a compressor to a pressure equal to P2, or that differs by less than 5 bar from P2. The flow thus compressed is sent back to one of the previous exchangers in order to be cooled therein to a temperature below −100° C.
At least one portion of each of the flows brought to a high pressure is cooled to the cold end of the exchanger where they are liquefied, then are sent after expansion to the distillation columns.
Optionally, a third portion of the flow at the temperature T1 and at the pressure P1 is sent to an exchanger of the air separation unit.
At least 50%, preferably at least 70%, of the total air flow supplies, in gaseous form, the distillation columns of the unit, optionally after having been expanded from one of the pressures mentioned above in an expansion turbine.
Liquid is drawn off from the distillation columns, pressurized by means of a pump to the required pressure, vaporized by heat exchange, in particular during step 4), then reheated in order to be used in the form of gaseous product.
The compression of the pressurized stream starting from the cryogenic temperature as described below takes place in a booster coupled to an expansion turbine.
A nitrogen-enriched gas from the medium-pressure column is expanded in a turbine in order to achieve this compression.
The power supplied by the turbine differs significantly from the power required by the cryogenic compressor, so that a system of supplying (respectively extracting) additional (respectively surplus) power is incorporated between the turbine and the booster, either directly on the common shaft of the turbine/booster, or by means of a gearbox.
The flows at the pressure P2 which are generated are re-mixed in the exchanger of the air separation unit so as to form only a single flow at the pressure P2.
These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings. It is to be noted, however, that the drawings 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.
The invention will be described in a more detailed manner by referring to the figures that represent processes according to the invention.
For simplification, the figures do not show the air separation apparatus which comprises at least one double column comprising a medium-pressure column and a low-pressure column, the top of the medium-pressure column being thermally coupled with the bottom of the low-pressure column. Air is sent to the medium-pressure column and optionally to the low-pressure column. Reflux liquids enriched in oxygen and in nitrogen are sent from the medium-pressure column to the low-pressure column.
An oxygen-enriched liquid is drawn off from the bottom of the low-pressure column and is vaporized in the exchanger where the air is cooled.
In
A portion of this stream undergoes an additional compression step in a compressor 2 starting from the temperature T1 and pressure P1 to a pressure P2 greater than P1, then is cooled in a cooler R3, typically by heat exchange with water, to the temperature T2. T2 and T1 differ by less than 10° C., typically less than 5° C. This cooled flow 19 is then introduced into a heat exchanger 9 of the air separation unit in order to undergo cooling to a temperature below or equal to −100° C.
Another portion 17 of this flow is introduced at the pressure P1 and at the temperature T1 into the exchanger 9, in order to undergo cooling therein to a temperature below −100° C. Then a fraction 21 of the portion 17 is compressed starting from this cryogenic temperature in a compressor 4 to a pressure P3 equal to P2. The flow thus compressed is sent back to the exchanger E1 in order to be cooled therein to a temperature below −100° C.
A portion 43 of the flow 19 and a portion 27 of the fraction 17, 23 are cooled up to the cold end of the exchanger 9 where they are liquefied, then are sent after expansion in the valves V1, V2 to the double column.
At least 50%, preferably at least 70%, of the total air flow 11 supplies, as flow 25 in gaseous form, the distillation columns of the unit. A portion 25 of the air at the pressure P1 is expanded in an expansion turbine 3. The expansion turbine has an inlet temperature lower than that of the compressor 4.
Liquid oxygen 29 is drawn from the low-pressure column, pressurized by means of a pump 31 to the required pressure, vaporized by heat exchange in the exchanger 9, then reheated in order to be used in the form of gaseous product.
Medium-pressure nitrogen 37 originating from the medium-pressure column is reheated in the exchanger 9, is expanded in the turbine 7 and is sent as flow 39 to be mixed with the low-pressure nitrogen 33 in order to form the flow 35. The flow 35 is reheated in the exchanger 9.
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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.
The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.
“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.
“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.
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.
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.
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.
Number | Date | Country | Kind |
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13 58927 | Sep 2013 | FR | national |
Filing Document | Filing Date | Country | Kind |
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PCT/FR2014/052228 | 9/9/2014 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2015/040306 | 3/26/2015 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
5475980 | Grenier et al. | Dec 1995 | A |
20060277944 | Le Bot | Dec 2006 | A1 |
20090064714 | Rottmann | Mar 2009 | A1 |
Number | Date | Country |
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102007014643 | Sep 2007 | DE |
2 015 012 | Jan 2009 | EP |
2 369 281 | Sep 2011 | EP |
2 597 409 | May 2013 | EP |
2 943 408 | Sep 2010 | FR |
Entry |
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International Search Report and Written Opinion for PCT/FR2014/052228, dated May 4, 2015. |
Number | Date | Country | |
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20160231053 A1 | Aug 2016 | US |