FR3032887A1 - METHOD AND APPARATUS FOR SUBAMBIAN TEMPERATURE SEPARATION - Google Patents

Abstract

In a process for separation of a mixture by separation at subambient temperature, a heat pump using the magnetocaloric effect (60) exchanges heat between a cold source and two hot sources, thereby at least partly contributing the separation energy. and at least a part of the cold necessary to maintain the refrigeration balance of the process, the first cold source being at subambient temperature, the first hot source at a first subambient temperature, the second hot source is at ambient temperature, characterized in that the separation is carried out in a single column (19), the first heat sink being thermally connected to the single column and the first heat source being thermally connected to the single column (19).

Description

The present invention relates to a method and apparatus for separation at subambient temperature, or even cryogenic. The separation may be separation by distillation and / or dephlegmation and / or absorption. The equipment used for this separation will be called "column". Thus a column may for example be a distillation or absorption column. Reduced to its simplest expression, it can be a phase separator. Otherwise a column can also be a device where a dephlegmation takes place. Magnetic refrigeration is based on the use of magnetic materials having a magnetocaloric effect. Reversible, this effect results in a variation of their temperature when they are subjected to the application of an external magnetic field. The optimal ranges of use of these materials are in the vicinity of their Curie temperature (Tc). In fact, the higher the magnetization variations, and consequently the magnetic entropy changes, the higher the changes in their temperature. The magnetocaloric effect is said to be direct when the temperature of the material increases when it is put in a magnetic field, indirect when it cools when it is put in a magnetic field. The rest of the description will be made for the direct case, but the transposition to the indirect case is obvious to those skilled in the art. There are several thermodynamic cycles based on this principle. A typical magnetic refrigeration cycle consists of: (i) magnetizing the material to increase its temperature, (ii) cooling the constant magnetic field material to reject heat, (iii) demagnetizing the material to cool it, and (iv) heat the constant magnetic field material (usually zero) to capture the heat.

A magnetic refrigeration device uses elements of magnetocaloric material, which generate heat when they are magnetized and absorb heat when demagnetized. It can implement a regenerator magnetocaloric material to amplify the temperature difference between the "hot source" and the "cold source": it is called magnetic refrigeration active regeneration. It is known to use the magnetocaloric effect to provide cold to a subambient temperature separation process in EP-A-2551005. US-A-6502404 discloses the use of the magnetocaloric effect (instead of the conventional use of an expansion turbine) to provide cold (necessary to ensure the refrigeration balance of the process) to a cryogenic process of separation of gas from the air, the separation energy being conventionally provided by the pressurized air which makes it possible to operate the vaporizer-condenser of the double column (the low pressure column can be reduced to a simple vaporizer in the case a nitrogen generator). The separation (distillation) is partly under pressure, typically between 5 and 6 bara in the medium pressure column. It has long been known to use the same circuit to provide both heat reboiler of a distillation column and condenser frigories of the same column. US-A-2916888 shows an example for hydrocarbon distillation. FR13 / 58666 describes a separation entirely at very low pressure, the fluid to be separated does not convey the energy (in the form of pressure) used for the separation and for the cold resistance of the process. The energy for the separation and the energy for the cold resistance are provided by heat pumps using the magnetocaloric effect, independently of the fluid to be separated and its pressure. The present invention addresses the problem of simplifying the implementation and reducing the energy consumption of the separation, by combining the so-called "separation" magnetocaloric heat pump with the magnetocaloric heat pump called "refrigeration balance" and using a unique heat transfer fluid circuit, associated with a single pump (or a set of pumps), placed on the side of the hot source called "ambient".

A heat pump is a thermodynamic device for transferring a quantity of heat from a medium considered as "transmitter" said "cold source" from which the heat is extracted to a medium considered as "receiver" said " hot source "where the heat is supplied, the cold source being at a cooler temperature than the hot source. An ambient temperature is the temperature of the ambient air in which the process is located, or a temperature of a cooling water circuit related to the air temperature. A subambient temperature is at least 10 ° C below room temperature, for example below 0 ° C. A cryogenic temperature is below -50 ° C. According to an object of the invention, there is provided a method for separating a mixture, for example gas from air, by separation at subambient temperature or even cryogenic in which at least one heat pump using the effect 15 magnetocaloric heat exchange directly or indirectly between at least one cold source and at least two hot sources thus providing at least partly the separation energy and at least a portion of the cold necessary to maintain the refrigeration balance of the process, the first source at a subambient or even cryogenic temperature, the first hot source at a first temperature that is subambient or even cryogenic, the second hot source at a temperature higher than the first temperature, for example at room temperature, characterized in that the separation is carried out in a single column or set of columns, the first heat sink being thermally connected directly or indirectly to the single column or column of the set and the first hot source being thermally connected, directly or indirectly, to the single column or column of the set. According to other optional features: the heat pump using the magnetocaloric effect transfers, at least partly, heat directly or indirectly from the top of the single column or column of the assembly, preferably by condensing gas from the column or of a column of the assembly, towards the tank of the column or the column of the assembly, preferably by vaporization of liquid from the single column or the column of the assembly, thus providing at least in part the separation energy. the heat pump using the magnetocaloric effect exchanges heat directly or indirectly with at least one second heat sink. The heat pump using the magnetocaloric effect cools or condenses at least partially, directly or indirectly, at least part of the mixture to be separated before it is introduced into the single column or the column of the assembly. the heat pump using the magnetocaloric effect cools or condenses, directly or indirectly, a fluid coming from the single column or from the column of the assembly. the heat pump using the magnetocaloric effect exchanges heat directly or indirectly with at least one third hot source. a liquid is withdrawn from the column or set of columns and vaporized to form a gaseous product under pressure, possibly after pressurization at a higher pressure or after depressurization at a pressure lower than the pressure at which it is drawn off, characterized in at least a part of the heat of vaporisation of the liquid is supplied by the heat pump using the magnetocaloric effect whose third hot source exchanges heat, directly or indirectly, with the liquid which vaporizes. The heat pump using the magnetocaloric effect heats or vaporizes, directly or indirectly, a fluid originating from the single column or from a column of the assembly. a single heat transfer fluid is used in the heat pump using the magnetocaloric effect, the single heat transfer fluid being in contact with at least one magnetocaloric material. - only one circulation pump (or a set of circulation pumps) is used, characterized in that the single circulation pump (or the circulation pump set) operates at a temperature not exceeding 20 ° C ( ± 20 ° C), or 10 ° C (± 10 ° C), or even 5 ° C (± 5 ° C) of that of the second hot source, for example 30 at room temperature. The heat pump using the magnetocaloric effect consists of several regenerators with magnetocaloric materials placed in series and / or parallel. at least one regenerator with magnetocaloric materials comprises an intermediate withdrawal of heat transfer fluid. At least one regenerator with magnetocaloric materials does not see all the flow of heat transfer fluid. at least one regenerator with magnetocaloric materials consists of a single magnetocaloric material characterized by a single Curie temperature. at least one magnetocaloric material regenerator consists of several magnetocaloric materials each having a different Curie temperature. each (or set of) regenerator (s) with magnetocaloric materials may have a natural operating frequency of the magnetocaloric cycle, to allow a better adaptation of the heat transmitted, in particular during a decrease in the process load. the pressure of the single column or columns of the assembly is less than 2 bara, preferably less than 1.5 bara, preferably at least one pressure which differs from the atmospheric pressure only by the pressure losses of the connecting elements the column or columns with the atmosphere. The mixture is air. the heat exchanged at the first hot source differs by more than 20%, or even more than 30%, from the heat exchanged at the first cold source. the heat exchanged at the level of the first hot source differs from less than 20%, or even less than 10%, of the heat exchanged at the level of the first cold source. - The set of columns comprises an argon separation column, the heat pump using the magnetocaloric effect condensing, directly or indirectly, a fluid from the argon separation column. The process produces as final product at least one gas enriched in one component of the mixture. The process produces at least one liquid enriched in one component of the mixture as final product. According to another object of the invention, there is provided an apparatus for separating a mixture, for example air gas, by a subambient or even cryogenic separation process comprising a single column or a set of columns where the subambient or even cryogenic separation is carried out, means for sending a mixture to the column or a column of assembly, means for withdrawing at least one fluid enriched in a component of the mixture of the column, at least one pump to heat using the magnetocaloric effect, exchanging heat 10 directly or indirectly between at least one cold source and at least two hot sources thus providing at least part of the separation energy and at least part of the cold required to maintain the balance sheet refrigerant of the apparatus, the first cold source being at subambient temperature, even cryogenic, the first hot source at a first subambient temperature, the second hot source at a temperature higher than the first temperature, for example at room temperature, characterized in that the first cold source is thermally connected, directly or indirectly, to the single column or to a column of the assembly and the first hot source is thermally connected, directly or indirectly, to the single column or column of the assembly.

According to other optional objects: the pressure of the single column or columns of the assembly is less than 2 bara, preferably less than 1.5 bara, so that the column is or the columns are connected to the column; atmosphere by at least one conduit not including detent means. The apparatus comprises means for withdrawing a liquid product at the head or single column vessel or a column of the assembly. the apparatus comprises means for withdrawing a gaseous product at the head or in the vat of the single column or of a column of the assembly. Figure 1 illustrates the state of the art as described in FR13 / 58666.

The invention will be described in more detail with reference to Figures 2 to 3.

In FIG. 1, a flow of gaseous air 1 is compressed in a compressor 3 and cooled in a cooler 5 to form compressed and cooled air 7. This cooled air 7 is purified in a purification unit 9. to remove water and carbon dioxide and other impurities. The purified air is then cooled in a heat exchanger 11 with 5 plates and fins. The cooled air 14 in the exchanger 11 is divided into two parts 13,15. Part 13 is sent to the middle of a single distillation column 19 where it separates to form nitrogen-enriched gas 41 at the top of column 19 and an oxygen-enriched liquid 29 in the bottom of column 19. Part 15 air is condensed at least partially in a heat exchanger 17 by heat exchange with a fluid flow 23 which cools by means of a second heat pump using the magnetocaloric effect 21. A cooling fluid 51 typically, ambient air or cooling water is supplied to the second heat pump using the magnetocaloric effect 21. The column comprises a bottom reboiler 33 and a top condenser 35. The reboiler (is heated) by means of a fluid circuit 37 in connection with a first heat pump using the magnetocaloric effect 31. This first heat pump using the magnetocaloric effect 31 also serves to cool a fluid 39 which cooled t the top condenser 35. The fluids 37 and 39 may be the same or different. An oxygen-enriched liquid 29 is withdrawn from the bottom of the column 19 and a nitrogen-enriched gas 41 is heated in the exchanger 11 and serves, at least in part, to regenerate the purification unit 9. Is enriched in oxygen is withdrawn in the bottom of the column 19, is heated in the exchanger 11 and is compressed by a compressor 27. In Figure 2, a flow of gaseous air 1 is compressed in a compressor 3 and cooled in a This chilled air 7 is purified in a purification unit 9 to remove water and carbon dioxide and other impurities. The purified air is then cooled in a plate and fin heat exchanger 11. The cooled air 14 in the exchanger 11 is sent to the middle of a single distillation column 19 where it separates to form nitrogen-enriched gas 41 at the top of the column 19 and an oxygen-enriched liquid 29 in the bottom of the column 19. column 19.

The column comprises a bottom reboiler 33, a top condenser 35 and an intermediate condenser 17. A heat pump using the magnetocaloric effect 6032887 8 consists of several regenerators with magnetocaloric materials 61, 62, 63, 64, 65 and 66 connected in series (and / or parallel), through which circulates a heat transfer fluid 23 set in motion by a single circulation pump 27 (or a single set of circulation pumps). The heat pump using the magnetocaloric effect 60 is thermally connected, directly or indirectly, to two cold sources and two hot springs. The coolant 23 cools in the exchanger 51 by direct or indirect heat exchange with the second hot source, typically ambient air or cooling water. It is then cooled again in the magnetocaloric material regenerators 66, 65, 64, 63 and 62. It is heated in the intermediate condenser 17 by direct or indirect heat exchange with the second heat sink, partly condensing the gas in column 19. It is then again cooled in the magnetocaloric material regenerators 61 and 62. It is reheated in the overhead condenser 35 by direct or indirect heat exchange with the first cold source, partially condensing gas at the top of the column 19. It is then reheated in the regenerator with magnetocaloric materials 62 and then in the reboiler 33 by direct or indirect heat exchange with the first hot source, by vaporizing a portion of the liquid in the bottom of the column 19. It is then again reheated in the magnetocaloric material regenerators 63, 64, 65 and 66.

An oxygen-enriched liquid 29 is withdrawn from the bottom of the column 19 and a nitrogen-enriched gas 41 warms up in the exchanger 11 and serves, at least in part, to regenerate the purification unit 9. A gas The oxygen-enriched fraction is withdrawn from the column 19, is heated in the exchanger 11 and compressed by a compressor 27. In FIGS. 2 and 3, the number of regenerators with magnetocaloric materials (six, five) is here illustrative. It can be adjusted according to the thermal gradients to be generated in each part of the heat pump using the magnetocaloric effect 60, in particular by varying their length. A generator may also have an intermediate withdrawal to send the heat transfer fluid make a direct or indirect thermal exchange with the first hot source and / or the second cold source. Each (or set of) regenerator (s) with magnetocaloric materials may have a natural frequency of operation of the magnetocaloric cycle, to allow a better adaptation of the heat transmitted, in particular during a drop in the process load. With respect to FIG. 1, the process has been simplified, in particular by eliminating the circulating pump for the heat transfer fluid of the heat pump using the magnetocaloric effect 31, called separation, placed at cryogenic temperature, by pooling it with the circulating pump of the heat transfer fluid of the heat pump using the magnetocaloric effect 21, called cooling balance. In addition, the electrical power of the suppressed circulation pump no longer modifies the refrigeration balance of the process, which allows to gain energy. Finally, the method of FIG. 2 makes it possible to decouple the heat exchanged between the top condenser 35 and that of the bottom vaporizer 33 of the column 19, offering an additional degree of freedom to optimize the distillation, and thus reduce the electrical consumption. . FIG. 2 differs from FIG. 3 in that the intermediate condenser 17 is omitted, the heat pump using the magnetocaloric effect 60 then being connected thermally, directly or indirectly, to a cold source and to two hot sources. The invention is described herein in the air separation application at cryogenic temperature. It is obvious that the invention also applies to other separations at subambient temperatures for example at the separation of a mixture containing carbon monoxide and / or hydrogen and / or nitrogen and / or methane. 25

Claims (16)

REVENDICATIONS1. Process for separating a mixture, for example gas from air, by subambient or even cryogenic separation in which at least one heat pump using the magnetocaloric effect (60), exchanges heat directly or indirectly between at least one cold source and at least two hot sources thus providing at least part of the separation energy and at least part of the cold necessary to maintain the refrigeration balance of the process, the first cold source being at subambient temperature, or even cryogenic, the first hot source at a first subambient or even cryogenic temperature, the second hot source at a temperature higher than the first temperature, for example at room temperature, characterized in that the separation is carried out in a single column (19) or a set of columns, the first cold source being thermally connected, directly or indirectly, to the column e single or a column of the set and the first hot source being thermally connected, directly or indirectly, to the single column or the column of the assembly. 2. The method of claim 1 wherein the heat pump using the magnetocaloric effect (60) transfers, at least in part, heat directly or indirectly from the head of the single column (19) or the column of the together, preferably by condensation of gas from the column or the column of the assembly, towards the column or column of the column of the assembly, preferably by vaporization of liquid from the single column or the column of the together, thus at least partly contributing the energy of separation. The method of claim 1 or 2 wherein the heat pump using the magnetocaloric effect (60) exchanges heat directly or indirectly with at least one second heat sink. 3032887 11 4. The method of claim 3 wherein the heat pump using the magnetocaloric effect (60) cools or condenses at least partially, directly or indirectly, at least a portion of the mixture to be separated before its introduction into the single column (19). or column of the set. 5 5. The method of claim 3 wherein the heat pump using the magnetocaloric effect (60) cools or condenses, directly or indirectly, a fluid from the single column (19) or a column of the assembly. 10 6. Method according to one of the preceding claims wherein the heat pump using the magnetocaloric effect (60) exchanges heat directly or indirectly with at least a third hot source. 7. The method of claim 6 wherein a liquid is withdrawn from the separation unit and vaporized to form a gaseous product under pressure, optionally after pressurization to a higher pressure or after depressurization at a pressure lower than the pressure at which it is withdrawn, characterized in that at least a part of the heat of vaporization of the liquid is supplied by the heat pump using the magnetocaloric effect (60) whose third heat source exchanges heat, directly or indirectly, with the liquid that vaporizes. The method of claim 6 wherein the heat pump using the magnetocaloric effect (60) heats or vaporizes, directly or indirectly, a fluid from the single column (19) or column of the assembly. 25 9. Method according to one of the preceding claims wherein a single heat transfer fluid is used in the heat pump using the magnetocaloric effect (60), the single heat transfer fluid being in contact with at least one magnetocaloric material. 3032887 12 The method of claim 9 wherein a single circulation pump (27) (or a set of circulation pumps) is used, characterized in that the single circulation pump (27) (or the circulation pump assembly) ) operates at a temperature of at most 20 ° C, or 10 ° C, or even 5 ° C of that of the second hot source, for example at room temperature. 11. Method according to one of the preceding claims wherein the heat pump using the magnetocaloric effect (60) consists of several regenerators with magnetocaloric materials placed in series and / or parallel. 10 12. Method according to one of the preceding claims wherein the pressure of the single column or columns of the assembly being less than 2 bara, preferably less than 1.5 bara, preferably at least one pressure which differs from the atmospheric pressure only by the losses of the elements 15 connecting the column or columns with the atmosphere. 13. Method according to one of the preceding claims wherein the mixture is air. 20 14. Method according to one of the preceding claims wherein the heat exchanged at the first hot source differs by more than 20%, or even more than 30%, of the heat exchanged at the first cold source. 15. Method according to one of the preceding claims 1 to 13 wherein the heat exchanged at the first hot source differs from less than 20%, or even less than 10%, of the heat exchanged at the first source. cold. Apparatus for separating an air gas mixture by a subambient or even cryogenic separation process comprising a single column (19) or a set of columns where the subambient or even cryogenic separation is carried out. means for sending an air gas mixture to the column or an assembly column, means for withdrawing at least one fluid enriched in a component of the column mixture, at least one heat pump using the magnetocaloric effect (60), exchanging heat directly or indirectly between at least one cold source and at least two hot sources, thereby providing at least part of the separation energy and at least part of the cold required to maintain the refrigeration balance of the apparatus, the first cold source being at subambient temperature, even cryogenic, the first hot source at a first temperature subambient or cryogenic, the second hot source being at a temperature higher than the first temperature, for example at room temperature, characterized in that the first cold source is thermally connected, directly or indirectly, to the single column or to a column of the assembly and the first hot source is thermally connected, directly or indirectly, to the single column or column of the assembly. 15