METHOD AND APPARATUS FOR SEPARATION AT SUBAMBIENT TEMPERATURE

Abstract

A method for separating a gas mixture at subambient temperature, in which a gas mixture is sent to a heat-insulated chamber, cooled and separated in a column, and placed inside the chamber so as to produce at least two fluids, each of which is enriched with a component from the gas mixture. At least one fluid from the method can be heated inside the chamber or vaporized via heat exchange with at least one heating member including at least one element having magnetocaloric properties and built into a circuit configured to conduct a magnetic flux. The element is alternatingly in thermal contact with a cold source, made up of the fluid to be heated, and a hot source, made up of a source hotter than the fluid to be heated, and variation in the magnetic flux via the magnetocaloric effect generates electrical and/or mechanical energy.

Claims

1-15. (canceled)

16. A process for separating a gas mixture at subambient temperature, wherein the process comprises the steps of: sending a gas mixture to a thermally insulated chamber under conditions effective for cooling and separating the gas mixture within a column that is placed inside the thermally insulated chamber, so as to produce at least two fluids, each of which is enriched with a component of the gas mixture; heating at least one of the two fluids inside the thermally insulated chamber by heat exchange with at least one heating member, wherein the at least one heating member comprises at least one element having magnetocaloric properties and integrated into a circuit configured to conduct a magnetic flux, said at least one element being alternatingly in thermal contact with a cold source made up of the fluid to be heated and a hot source made up of the surrounding environment or another source that is hotter than the fluid to be heated; and generating electrical and/or mechanical energy from the variation in the magnetic flux via the magnetocaloric effect, wherein at least one of the two fluids to be heated being at least one part of the gas mixture.

17. The process as claimed in claim 16, wherein the main component(s) of the fluid to be heated is a fluid selected from the group consisting of air, nitrogen, oxygen, argon, carbon dioxide, methane, helium, hydrogen, carbon monoxide, and combinations thereof.

18. The process as claimed in claim 16, wherein at least one other fluid to be heated is a fluid inside the column.

19. The process as claimed in claim 16, wherein at least one other fluid to be heated is a fluid enriched with a component of the gas mixture originating from the column.

20. The process as claimed in claim 16, wherein the fluid is a liquid.

21. The process as claimed in claim 16, wherein the fluid to be heated is brought into direct contact with the element having magnetocaloric properties.

22. The process as claimed in claim 16, wherein the heat exchange of the heating is carried out through a heat exchanger with a heat-transfer fluid having been in contact with the element having magnetocaloric properties.

23. The process as claimed in claim 16, wherein the heat exchange is carried out through an intermediate heat-transfer circuit with the heat-transfer fluid having been in contact with the element having magnetocaloric properties.

24. An apparatus for separating a gas mixture at subambient temperature, or even cryogenic temperature, comprising a thermally insulated chamber, a heat exchanger and at least one separating column which are placed inside the chamber, a pipe for sending the gas mixture to the heat exchanger for it to cool, a pipe for sending the cooled mixture to the column, means for withdrawing at least two fluids, each of which is enriched with a component of the gas mixture from the column, at least one member for heating at least one fluid from the process, located inside the chamber, wherein the at least one heating member comprises at least one element having magnetocaloric properties and integrated into a circuit capable of conducting a magnetic flux, said at least one element being alternatingly in thermal contact with a cold source made up of the fluid to be heated, or even the liquid to be vaporized, and a hot source made up of the surrounding environment or another source that is hotter than the fluid to be heated and means for generating electrical and/or mechanical energy from the variation in the magnetic flux via the magnetocaloric effect, the fluid to be heated being the gas mixture to be separated.

25. The apparatus as claimed in claim 24, wherein the heating member and/or a cooling member for cooling a fluid from the process and comprising at least one element having magnetocaloric properties is/are placed inside the thermally insulated chamber.

26. The apparatus as claimed in claim 24, wherein the column is a phase separator.

27. The apparatus as claimed in claim 24, wherein the column is an air separation column.

28. The apparatus as claimed in claim 24, wherein the at least one separating column is a simple column having a top condenser and/or a bottom reboiler.

29. The apparatus as claimed in claim 24, comprising a heating member comprising an element having magnetocaloric properties for heating the liquid of a bottom reboiler of the column.

30. The apparatus as claimed in claim 24, comprising a cooling member comprising an element having magnetocaloric properties for cooling the top gas of a top condenser of the column.

Description

[0047] Other particularities and advantages will emerge on reading the description hereinafter, given with reference to the figures in which:

[0048] FIG. 1 represents a diagrammatic and partial view illustrating the structure and operation of a first example of a facility for producing gas according to the invention,

[0049] FIGS. 2 and 3 represent diagrammatic and partial views illustrating the structure and the operation of, respectively, a second and a third example of a facility for producing gas according to the invention.

[0050] FIG. 1 shows a process for separating air by cryogenic distillation. In this example, air 1 is compressed in a compressor 3, cooled in a cooler 5 to form a cooled flow 7 and purified in a purification unit 9. The purified air enters a thermally insulated chamber E and cools in a heat exchanger 17. The air cooled at a cryogenic temperature is sent to an intermediate level of a distillation column 23. The distillation column 23 is a simple column equipped with a top condenser 8 and with a bottom reboiler 10. The bottom reboiler 10 is heated by means of a heating member G comprising at least one element having magnetocaloric properties and integrated into a circuit capable of conducting a magnetic flux. The element is alternatingly in thermal contact with a cold source, made up of the liquid to be vaporized in the bottom of the column 23, through the reboiler 10, and a hot source made up of a fluid 4 hotter than the liquid to be vaporized. The variation in the magnetic flux via the magnetocaloric effect in the element generates electrical and/or mechanical energy. This therefore makes it possible either to generate electricity to be exported or to be used in the process, or to generate mechanical energy for driving, for example, a rotating machine of the process or a generator.

[0051] The cooling of the head of the column 23 may also be provided by a cooling member M comprising at least one element having magnetocaloric properties which serves to cool a top condenser 8 of the column. Thus, the gas of the top of the column constitutes the cold source of the cooling organ and the cold source is made up of the surrounding environment through a gas 2.

[0052] FIG. 2 shows an apparatus for separating air by cryogenic distillation. The apparatus comprises a heat exchange line 17 and a double air separation column comprising a medium-pressure column 23 and a low-pressure column 25 thermally connected by means of a reboiler 27.

[0053] Air 1 is compressed in a compressor 3 to a pressure of 5.5 bara. The compressed air is cooled in the cooler 5 so as to form a cooled flow 7 which is purified in order to remove the water and the carbon dioxide in an adsorption unit 9.

[0054] The purified air enters a thermally insulated chamber E and is divided up into four. A part 8A cools to an intermediate temperature of the heat exchanger 17, then is sent to a heating organ G comprising at least one element having magnetocaloric properties and integrated into a circuit capable of conducting a magnetic flux. The element is alternatingly in thermal contact with a cold source, made up of the air 8A at the intermediate temperature of the exchanger, and a cold source 4 made up of the surrounding environment or another source hotter than the air 8A. The variation in the magnetic flux via the magnetocaloric effect generates electrical and/or mechanical energy. The air 8A heated by the member G is sent back to the heat exchanger at a temperature higher than the temperature at which it is withdrawn therefrom. Use is made of the excess frigories available at the level of the oxygen vaporization plateau to produce a doubling of flow (of 8A) in the exchanger in order to try to absorb this cold as much as possible (by improving the exchange diagram), and to convert it into electrical energy.

[0055] A part 8B cools, while entirely passing through the exchange line 17, to a temperature of approximately 170 C. and is mixed with the flow 8A and then sent to the medium-pressure column in gas form. A part 8C cools while entirely passing through the exchange line 17 and then serves as a cold source for the heat pump 31 having a magnetocaloric effect. The remainder 21 is sent to separate a gas form in the column 23.

[0056] The part 8C cools and liquefies by heat exchange in the heat pump 31. The part 8C is divided up into a part 8D which is sent to the medium-pressure column 23 and a part 8E which is sent to the low-pressure column 25.

[0057] The invention could also apply to processes for separating other mixtures. For example in FIGS. 1 and 2, the air could be replaced with a mixture containing, as main components, methane and nitrogen and/or carbon dioxide.

[0058] A liquid enriched with oxygen 33 is withdrawn from the bottom of the medium-pressure column 23, cooled in the sub-cooler 43 and sent to the low-pressure column 25. A liquid enriched with nitrogen 35 is withdrawn from the top of the medium-pressure column 23, cooled in the sub-cooler 43 and sent to the top of the low-pressure column 25.

[0059] Air 11 is boosted in a booster 13, cooled in the exchange line 17, expanded in the turbine 15 and sent to the low-pressure column 25.

[0060] A nitrogen-rich gas 45 is withdrawn from the top of the low-pressure column 25, heated in the sub-cooler 43 and in the exchange line 17 and sent at least partly to the regeneration of the purification 9. Nitrogen-rich gas 49 is withdrawn from the top of the medium-pressure column 23, and heated in the exchange line 17 and serves as product. Liquid oxygen 47 is withdrawn from the low-pressure column 25, pressurized by a pump 29 and partially heated in the exchange line 17. The heated liquid is then removed from the exchange line 17, at least partially vaporized in the heat pump 31 and sent back to the exchange line 17, either for finishing the vaporization and heating, or solely for heating.

[0061] FIG. 3 illustrates a process for separating by distillation a carbon dioxide-rich gas mixture in order to produce a gas product enriched with carbon dioxide. A gas mixture 3 containing at least 60% of carbon dioxide and also at least one light impurity, which may be oxygen, carbon monoxide, nitrogen, argon, hydrogen or at least two of these constituents, is separated so as to form a fluid that is richer in carbon dioxide. The gas mixture comes from a source 1A which may be an oxycombustion unit followed by purification units in order to remove the water and other contaminants, such as dust, SO.sub.x or NO.sub.x. The source 1A may be a compressor. The gas mixture 3A is compressed as required for example at a pressure above 6 bar ABS. The pressurized gas mixture 3A is sent into a thermally insulated chamber E and is cooled in a brazed aluminum plate heat exchanger 5A. The cooled gas mixture is, as required, treated in a separating means 7A. This separating means 7A may be made up of a phase separator or several phase separators in series in order to increase the carbon dioxide content of the gas mixture upstream of the column 10A, for example in order to reach at least 80% of carbon dioxide for the liquid from a phase separator. The separating means 7A may alternatively or additionally comprise a distillation column, for example a column for removing NO.sub.x, or else an exchanger for at least partially cooling the gas mixture or a fluid derived from a part of the gas mixture.

[0062] The carbon dioxide-enriched liquid 9A is sent to the top of the low-temperature separating column 10A. The top gas 13A is withdrawn at the top of the column and is enriched with light components with respect to the liquid 9A. It heats in the exchanger 5A.

[0063] The bottom liquid contains more than 90% of carbon dioxide and is separated into three parts. A part 12A is sent to a heating member G comprising at least one element having magnetocaloric properties and integrated into a circuit capable of conducting a magnetic flux. The element is alternatingly in thermal contact with a cold source, made up of the liquid to be vaporized 12A, and a hot source 4A made up of the surrounding environment or another source that is hotter than the liquid 12A. The variation in the magnetic flux via the magnetocaloric effect generates electrical and/or mechanical energy. The heat produced by the member G makes it possible to vaporize the liquid 12A and the vaporized liquid is sent back to the bottom of the column 10A.

[0064] The remainder of the bottom liquid 11A is divided in two so as to form a part 15A and a part 19A. The part 15A is expanded in a valve 17A and vaporizes, then heats in the heat exchanger so as to form a carbon dioxide-rich gas product. The remainder 19A is sent to an intermediate level of the heat exchanger 5A, vaporizes therein and then heats so as to form a carbon dioxide-rich gas product, optionally combined with the first CO.sub.2-rich gas product, after compression, thereby forming the part 23A.

[0065] For all the figures, the variation in the magnetic flux via the magnetocaloric effect in the element can generate electrical energy to be exported or to be used in the process. Otherwise or additionally, the variation can generate mechanical energy for driving, for example, a rotating machine of the process or a generator.