FR3010510A1 - METHOD AND APPARATUS FOR SUBAMBIAN TEMPERATURE SEPARATION - Google Patents

Abstract

In a process for separation of a mixture by separation at subambient temperature, a first heat pump (31), using the magnetocaloric effect, exchanges heat between a cold source at subambient temperature and a hot source at subambient temperature, thereby providing at least partly the separation energy and a second heat pump (21), using the magnetocaloric effect heat exchange between a cold source (15) at subambient temperature and a hot source at room temperature thereby providing at least one part of the cold necessary to maintain the refrigeration balance of the process, the separation being effected in a single column (19) at a pressure of less than 2 bara.

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) heating the material. constant magnetic field material (usually zero) to capture heat. A magnetic refrigeration device uses elements of magnetocaloric material, which generate heat when magnetized and absorb heat when demagnetized. It can implement a magnetocaloric material regenerator to amplify the temperature difference between the "hot source" and the "cold source": it is called active regenerative magnetic refrigeration. It is known to use the magnetocaloric effect to provide cold to a subambient temperature separation process in EP-A-2551005.

US-A-6502404 describes the use of the magnetocaloric effect (instead of the conventional use of an expansion turbine) to provide cold (necessary to ensure the cooling of the process) to a cryogenic separation process of 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 of a nitrogen generator). The separation (distillation) is partly under pressure, typically between 5 and 6 bara in the medium pressure column. The present invention addresses the problem of how to carry out a separation entirely in very low pressure, the fluid to be separated does not convey the energy (in the form of pressure) used for the separation and the cold behavior of the process. The energy for the separation and the energy for the cold resistance are provided by heat pumps, independently of the fluid to be separated and its pressure. It has long been known to use the same circuit to provide both heat to the reboiler of a distillation column and condenser frigories to the same column. US-A-2916888 shows an example for hydrocarbon distillation. A heat pump is a thermodynamic device for transferring a quantity of heat from a medium considered as "emitter" or "cold source" from which the heat is extracted to a medium considered as "receiver" said "source 25 where the heat is supplied, the cold source being at a colder temperature than the hot source. The conventional cycle used in the state of the art for this type of application is a thermodynamic cycle of compression - cooling (condensation) - expansion - heating (vaporization) of a refrigerant.

Figure 12 of the document "ENGINEERING TECHNIQUES - Magnetic Refrigeration 2005" shows a gain of a factor 2 on the coefficient of performance of a refrigeration system using a magnetic cycle compared to the conventional cycle. The separation at low pressure, or almost atmospheric is easier, because of a greater volatility between the components to be separated. By combining this effect with the very good performance of heat pumps using the magnetocaloric effect, a process with a very good separation energy is obtained. Moreover, the low-pressure or even quasi-atmospheric separation makes it possible to simplify the design and the mechanical strength of the equipment of the separating apparatus, thus reducing its cost. 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. A cryogenic temperature is below -50 ° C. According to one object of the invention, there is provided a method for separating a mixture, for example gas from air, by separating at subambient temperature, or even cryogenically in which: a. at least one first heat pump, using the magnetocaloric effect, said heat pump separation, heat exchange directly or indirectly between a first cold source at subambient temperature or cryogenic and a first hot source at subambient temperature or cryogenic thus bringing at least part of the separation energy, and b. at least one second heat pump, using the magnetocaloric effect, called the cooling balance heat pump, exchanging heat directly or indirectly between a second cold source at a first subambient temperature or even a cryogenic temperature and a second hot source at a temperature higher than the first temperature, for example at room temperature, thus providing at least a portion of the cold required to maintain the refrigeration balance of the process, characterized in that the separation takes place in a single column or a set of columns, 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 connecting the or the columns with the atmosphere, the first cold source and the first hot source and connected thermally, directly or indirectly, to the single column or column of the assembly.

According to other optional features: the first so-called separation heat pump transfers heat directly or indirectly from the top of the column, preferably by condensing gas from the column, to the column vessel, preferably by vaporizing liquid from the column. the single column; the first so-called separation heat pump transfers heat directly or indirectly to a column of the assembly, preferably by condensing gas in a column of the assembly, to a column of the assembly, preferably by vaporization in a column of the set; - the mixture is air; the second heat pump condenses air directly or indirectly at least partially before introduction of air into the single column or into a column of the assembly; the second heat pump totally or directly condenses part of the air before introducing the part of the air totally condensed in the single column or in a column of the assembly, preferentially above the feed of the rest of the air; the air ; - the process produces as final product at least one gas enriched in a component of the mixture; - the process produces as final product at least one liquid enriched in a component of the mixture; the second heat pump, referred to as the cold storage heat pump, cools or condenses, directly or indirectly, a fluid originating from the single column or from a column of the assembly; at least one fluid to be separated and / or resulting from the separation of the column or column from the assembly is brought into direct contact with the magnetocaloric material of one of the first and second heat pumps; the heat exchange is at least partly carried out between a fluid to be separated and / or resulting from the separation of the column or a column from the assembly and a heat-transfer fluid having been in contact with the magnetocaloric material of a first and second heat pumps through an exchanger; the heat exchange is at least partly carried out between a fluid to be separated and / or resulting from the separation of the column or a column from the assembly and a heat-transfer fluid having been in contact with the magnetocaloric material of a first and second heat pumps through an intermediate heat transport circuit. 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, for example of air gas, to the column or a set column, means for withdrawing at least one fluid enriched in a component a mixture of the column or an assembly column, at least a first heat pump, using the magnetocaloric effect, called the separation heat pump, for exchanging heat directly or indirectly between a first cold source at subambient temperature, even cryogenic and a first hot source at subambient temperature, or even cryogenic thus providing at least partly the separation energy and at least a second heat pump r, using the magnetocaloric effect, called the cooling balance heat pump, for exchanging heat directly or indirectly between a second cold source at a first subambient or even cryogenic temperature and a second hot source at a temperature greater than the first temperature, for example at room temperature, thus providing at least part of the cold necessary to maintain the refrigeration balance of the process, the pressure of the single column or columns of the assembly being less than 2 bara, preferably less than 1.5 bara , so that the column is or the columns are connected to the atmosphere by at least one conduit not comprising expansion means, the first heat sink and the first heat source being thermally connected, directly or indirectly, to the single column or one column of the set. According to other optional objects: the apparatus comprises means for withdrawing a liquid product at the top or single column vessel or a column of the assembly; the apparatus comprises means for withdrawing a gaseous product at the head or The invention will be described in more detail with reference to the figures which illustrate methods according to the invention. 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 plate and fin heat exchanger 11. The cooled air in the exchanger 11 is divided into two parts 13,15. Part 13 is sent to the middle of a single distillation column where it separates to form N-enriched gas at the top of column 19 and an oxygen-enriched liquid in vessel of column 19. Part 15 of air (indirect cold source of the second heat pump) 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 (hot source of the second heat pump), typically ambient air or cooling water is sent to the second heat pump using the magnetocaloric effect 21. The column comprises a The reboiler (the reboiled liquid in the reboiler is the indirect heat source of the first heat pump) is heated by means of a fluid circuit 37 in connection with the reboiler. c, 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 cools the overhead condenser 35 (the condensed gas in the condenser is the indirect cold source of the first heat pump). The fluids 37 and 39 may be the same or different. An oxygen-enriched liquid 29 is withdrawn in the vat from the column 19 and a nitrogen-enriched gas 41 is heated in the exchanger 11 and serves, at least in part, subsequently to regenerate the purification unit 9. A gas 25 oxygen-enriched is withdrawn in the tank of the column 19, is heated in the exchanger 11 and is compressed by a compressor 27. In Figure 2, unlike in Figure 1, the fluids 37, 39 are replaced by flow rates fluids from column 19. Column 19 has no head condenser or bottom reboiler. A portion 29A of the tank liquid (hot source of the first heat pump) vaporizes in the first heat pump using the magnetocaloric effect 31 and is returned to the column in gaseous form. Part 41A of the overhead gas (cold source of the first heat pump) is sent to the first heat pump using the magnetocaloric effect 31 where it condenses. The formed liquid is returned to the top of the column. Similarly, the fluid 15 (cold source of the second heat pump) is sent directly into the second heat pump using the magnetocaloric effect 21 where it condenses at least partially. In Figure 3, unlike Figure 1, the air is not divided in half. The entire flow 7 is cooled by means of a second heat pump using the magnetocaloric effect 21, the calories being discharged by the heat exchanger 17 and the fluid 23 which cools in a second heat pump using the effect As a result, the air is partially condensed in the exchanger 17 and is sent to the column 19. In FIG. 4, the heat transfer between the reboiler 33 and the overhead condenser 35 is carried out as follows. for Figure 1, by a first heat pump using the magnetocaloric effect 31. By cons, a portion 43 of the nitrogen gas at the top of the column is condensed in the heat exchanger 17 by means of a second pump to The condensed nitrogen is returned to the column so that a portion of the condensation at the top of the column is effected by means of the second heat pump using the magnetocaloric effect 21. even as can be seen in FIG. 5, part of the oxygen-enriched gas 26 can be cooled and at least partially condensed in a heat exchanger 17 by means of a fluid circuit 53. The fluid 53 transfers the heat to a second heat pump using the magnetocaloric effect 21, itself cooled by means of a cooling fluid 51, typically ambient air or cooling water.

In Figure 6, column 19 has a top condenser 35 but no bottom reboiler. All air for the column is cooled by means of a heat exchanger 11, then a heat exchanger 17 where it is at least partially condensed, a fluid 23 and a second heat pump Using the magnetocaloric effect 21. As in FIG. 1, only a portion of the air can pass into the heat exchanger 17. The nitrogen 41 heats up and is compressed by a compressor 42. the column is first heated in the heat exchanger 53, where it is at least partially vaporized and then in the exchanger 11. A fluid circuit 55 cools in the exchanger 53 and recovers heat at the first heat pump using the magnetocaloric effect 31. The overhead condenser is cooled as in FIG. 1. In FIG. 7, the column has neither a condenser nor a reboiler. All the air 7 cools in the heat exchanger 11, then a heat exchanger 17 where it is at least partially condensed by means of a second heat pump using the magnetocaloric effect 21, as for the As in FIG. 1, only a portion of the air can pass into the heat exchanger 17. Alternatively, all or part of the air can be directly sent to the second heat pump using the heat exchanger. magnetocaloric effect 21. The tank liquid 37 is entirely sent to a first heat pump using the magnetocaloric effect 31 where it vaporizes at least partially. The vaporized flow 37A then warms up in the heat exchanger 11 and serves at least partially to the regeneration of the purification unit 9. The overhead gas is divided in two, a portion 41 being heated and compressed and the rest 41A being sent to the first heat pump using the magnetocaloric effect 31 where it is at least partially condensed, forming the flow 41B which is sent to the top of the column.

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 méthane.10

Claims (10)

REVENDICATIONS1. Process for separating a mixture, for example gas from air, by subambient or even cryogenic separation in which a) at least a first heat pump (31), using the magnetocaloric effect, called a heat pump separation, heat exchange directly or indirectly between a first cold source (39, 41A) at subambient temperature, or even cryogenic and a first hot source (37, 29A, 55) at subambient temperature, or even cryogenic, thus providing at least in part the energy of separation and b) at least one second heat pump (21), using the magnetocaloric effect, called refrigerant balance heat pump, exchange of heat directly or indirectly between a second cold source (15, 23, 53) at a first subambient or even cryogenic temperature and a second hot source (51) at a temperature above the first temperature, for example at room temperature e, thereby providing at least a portion of the cold necessary to maintain the refrigeration balance of the process characterized by the fact that the separation takes place in a single column (19) or a set of columns, 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 pressure losses of the elements connecting the column or columns with the atmosphere, the first cold source and the first heat source being thermally connected, directly or indirectly, to the single column or column of the assembly. 2. Method according to claim 1, wherein the first heat pump (31), said separation transfers heat directly or indirectly from the head of the single column (19) or a column of the assembly, preferably gas condensation of the column or column of the whole, to the column or column of the whole column, preferably by vaporization of liquid from the single column or column of the whole . 3. Method according to one of the preceding claims, wherein the mixture is air. 4. The method of claim 3, wherein the second heat pump (21) condenses directly or indirectly at least partially the air before introduction of air into the single column (19) or in a column of the assembly. . The method according to claim 3, wherein the second heat pump (21) totally or directly condenses part of the air before introducing the part of the air that is totally condensed in the single column (19) or in a column of the set, preferentially above the supply of the rest of the air. 6. Method according to one of the preceding claims, wherein the second heat pump (21), said cold balance cool or condense directly or indirectly a fluid from the single column (19) or a column of the together. 7. Method according to one of the preceding claims, wherein at least one fluid to be separated and / or from the separation of the column (19) or a column of the assembly is put in direct contact with a magnetocaloric material. one of the first and second heat pumps (31, 21), 8. Method according to one of the preceding claims, wherein the heat exchange is at least partly carried out between a fluid to be separated and / or from the separation of the column (19) or a column of the whole and a coolant having been in contact with a magnetocaloric material of one of the first and second heat pumps (31,21), through an exchanger (17). 9. Method according to one of the preceding claims, wherein the heat exchange is at least partly carried out between a fluid to be separated and / or from the separation of the column (19) or a column of all and a coolant having been in contact with a magnetocaloric material of a first and second heat pump (31, 21) through an intermediate heat transfer circuit. Apparatus for separating a mixture of gases from the air 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 takes place means for sending a mixture of gases from the air to the column or a column of the assembly, means for withdrawing at least one fluid enriched in a component of the mixture of the column, at least a first heat pump (31) , using the magnetocaloric effect, called the heat pump separation, to exchange heat directly or indirectly between a cold source at subambient temperature or cryogenic and a hot source at subambient temperature, or even cryogenic, thus providing at least partly the separation energy and at least one second heat pump (21), using the magnetocaloric effect, called the cooling balance heat pump, for exchanging heat directly or indirectly between a cold source at a first subambient temperature or even a cryogenic temperature and a hot source at a temperature higher than the first temperature, for example at room temperature, thereby providing at least a portion of the cold required to maintain the refrigeration balance of the process , the pressure of the single column or columns of the assembly being less than 2 bara, preferably less than 1.5 bara, so that the column is or the columns are connected to the atmosphere by at least one conduit (41) not including expansion means, the first heat sink and the first heat source being thermally connected, directly or indirectly, to the single column or column of the assembly.