EP3137830A1

EP3137830A1 - Method for purifying, cooling and separating a gaseous mixture and associated apparatus

Info

Publication number: EP3137830A1
Application number: EP15759832.7A
Authority: EP
Inventors: Guillaume CARDON; Antony CORREIA ANACLETO; Benoît DAVIDIAN; Erwan LE GULUDEC; Clément LIX; Quentin SANIEZ; Bernard Saulnier
Original assignee: LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2014-04-30
Filing date: 2015-04-30
Publication date: 2017-03-08
Also published as: FR3020669B1; CN106461321A; WO2015166191A1; US20170045291A1; FR3020669A1

Abstract

The invention relates to a method for cooling, purifying and separating a gaseous mixture (1) containing at least one impurity, in which the gaseous mixture is cooled to a temperature no higher than the temperature at which the at least one impurity solidifies in a heat exchanger (3, 3A) having cooling passages, the cooling passages being at least partially covered with a coating and/or physically treated and/or chemically treated, the coating and/or the treatment serving to limit or even to prevent the solidified impurity from forming and/or adhering to a surface of the passages; at least one portion (5B, 19) of the solidified impurity exiting the cooling passages of the heat exchanger is collected; and the gaseous mixture is drawn from the heat exchanger.

Description

The present invention relates to a process for purifying, cooling and separating a gaseous mixture and to a purification and cooling apparatus a gaseous mixture. When a gaseous mixture has to be cooled to a temperature below the liquefaction temperature, or even solidification of one of the gaseous components that it contains, this poses particular problems. If the heat exchanger used for cooling the gaseous mixture is, for example, a plate and fin exchanger comprising passages in which the gaseous mixture cools, these passages may be obstructed by the formation of solids on the walls. passages.

This problem is particularly well known to specialists in air separation because traditionally the air to be distilled was cooled in heat exchangers and the water and carbon dioxide contained in the air were deposited on the walls of the air passages. a first exchanger. Before the clogging of these, the air was directed into another heat exchanger to cool while the first heat exchanger was heated by passing nitrogen to melt and then vaporize the water and remove the dioxide. carbon.

These systems have been abandoned for several decades to be replaced by a purification upstream of the heat exchanger. In this scheme become common, the air is dried and decarbonated by an adsorption process in the purification head and then cooled.

An object of the present invention is to propose an alternative to conventional schemes for purifying and cooling, or even liquefying, a gaseous mixture.

An object of the present invention is to provide an alternative to conventional purification schemes of air separation units and other separation and / or liquefaction units, operating at low temperature. Among these liquefaction units include air liquefaction units (for example for energy storage, liquefaction of a gas produced by separating air, for example nitrogen and liquefaction of natural gas. Other examples of the separation units include for example, the units for separating a mixture of carbon dioxide containing at least 30% of carbon dioxide as well as hydrogen and / or methane and / or oxygen and / or carbon monoxide at room temperature subambient. The separation units may also be cryogenic separation units of mixtures of hydrogen and / or carbon monoxide and / or nitrogen and / or methane, the mixture containing at least 10 mol% of at least one of these components.

Exploration of new surface treatment technologies makes it possible to consider drying and / or decarbonising the air directly in the main exchanger so that the condensed water then frozen and / or the frozen C0 ₂ have a reduced adhesion. they no longer adhere to the walls of the latter and therefore the fouling increases until the air side passages of the exchanger are clogged.

It is known to treat surfaces or cover them with a coating in areas very different from the low temperature separation of a gaseous mixture, in particular to reduce or prevent the adhesion of ice or frost on surfaces. exposed to atmospheric elements, such as airplanes, wind turbines and pylons. These surfaces can also in some cases reduce the amount of ice formed.

A large number of surface treatments reduce the adhesion of ice. These are so-called "passive anti-ice" treatments which are generally based on silicone or fluorocarbon polymers (non-exhaustive list) as described in US-A-2013/0305748.

For example, polytetrafluoroethylene, PTFE, also known as Teflon®, allows low adhesion of ice due to low surface tension as described in MG Ferrick, ND Mulherin, BA Coutermarsh, GD Durell, LA Curtis, TL St. Clair, ES Weiser, RJ Cano, Smith TM, CG Stevenson and EC Martinez, Journal of Adhesion Science and Technology, 26 (2012) 473. The NUSIL ^® R2180 coating based on polysiloxane also significantly reduces the ice adhesion. Similar results were obtained using another amorphous carbon (DLC) coating as described in US-A-8524318. Other examples of coatings for limiting the adhesion of ice on aluminum alloys are reported by Menini et al. Cold Regions Science and Technology, 65 (201 1) 65.

In most cases, these treatments increase the hydrophobicity of the surfaces, which makes it possible to increase the contact angle of the water on these surfaces and thus to reduce the interactions between the water and the surface. Thus, surfaces that reduce ice adhesion are generally hydrophobic or superhydrophobic as described in L. Foroughi Mobarakeh, R. Jafari and M. Farzaneh, Applied Surface Science, 284 (2013) 459.

It is also possible to reduce the adhesion of the ice with heterogeneous surfaces comprising both hydrophobic and hydrophilic zones as described in WO-A-050751 12. In this case, the treatment makes it possible to control the zones well. crystallization of the water, which facilitates the removal of ice with a gas or liquid sweep.

Another type of surface reduces the adhesion of ice, it is the lubricated surfaces. The surface is impregnated with a fluorocarbon-based lubricant such as Krytox® or silicone oils as described in WO-A-2012/100100 and US-A-2006/0281861.

With such surfaces, the ice is in contact with the lubricant, i.e. a liquid phase, thus the adhesion forces are very low. The lubricant also has another advantage, it improves the erosion resistance of the surfaces.

In the examples cited so far, surface coatings reduce the adhesion of ice. Another type of surface may be of interest in the context of this invention are so-called "active anti-ice" coatings which can delay the formation of ice.

It is known that the ice formation temperature can be lowered with salt or glycol compounds. It turns out that a similar phenomenon can occur when a polymer compound, usually a hygroscopic polymer is grafted to a surface. This type of coating can lower the ice formation temperature and reduce the amount of ice formed. The most well-known coatings on this subject are of the glycol type (US-A-2010/0086789) but coatings inspired by the structure of the anti-icing proteins have a similar effect as described in L. Makkonen, Journal of Adhesion Science and Technology, 26 (2012) 413.

Finally, some treatments combine two effects: modify the type of frost and decrease its adhesion horn described by J. Chen, R. Dou, D. Cui, Q. Zhang, Zhang Y., Xu F., X. Zhou, This is the case of microstructured surfaces comprising a hydroscopic polymer matrix (based on polyacrylic acid, for example). These surfaces make it easy to remove formed ice and have the advantage of being used as a water lubricant, so the surface is self-lubricating with the moisture contained in the air.

It is also known to limit or even prevent the formation of frost by heating, for example Joule effect or pneumatic pulsation systems.

There are also techniques with a gas flow with a sufficient flow rate or a supply of mechanical and / or electrical energy, which can be combined with a coating and / or a treatment in order to easily remove the impurities whose adhesion has been reduced. .

Those skilled in the art who are specialists in purification and cooling processes or in low-temperature separation or liquefaction processes are not aware of the developments concerning the surface treatments and coatings used to limit or even prevent the formation and / or ice adhesion on a surface. Part of the present invention results from the realization that these techniques can be applied to the cooling and purification field, for example used upstream of a separation or a liquefaction, for example a distillation, at low temperature or other process operating at low temperature.

GB-A-917286 discloses a low temperature separation process in which a gas containing carbon dioxide is cooled by two exchangers in turn, each allowing a heat exchange between only two fluids and each comprising an area designed to prevent carbon dioxide deposition.

In this case, since the passages intended to cool the gas to be separated during a first period also serve to heat a separate gas during a second period, it is necessary to provide in the exchanger the same number of passages and the same type of fins to achieve symmetrical operation during both periods of operation.

The heat exchanger of GB-A-917286 necessarily consists of at least two exchange bodies and can not be monobloc.

A low temperature separation takes place at at most 0 ° C, or at least

-50 ° C or at least -100 ° C, depending on the gaseous mixture to be separated.

The "hot end" is the part of the heat exchanger that is operating at a maximum average temperature. The "cold end" is that part of the heat exchanger that is operating at a minimum average temperature.

A heat exchanger is a single exchange body or a plurality of exchange bodies, capable of performing a heat exchange.

The gaseous mixture to be cooled returns to the hot end of the exchanger and comes out, usually at the cold end.

Generally a heat exchanger is mounted so that its hot end is up and its cold end down. In some cases, as described later, the present invention may require having the hot end at the bottom and the cold end at the top.

The heat exchanger is generally disposed within a thermally insulated cold box. Other elements of a separation apparatus may also be in the cold box, for example, a distillation column.

The conclusions concerning the purification of a gas containing water and CO ₂ are that the purification of the gas by condensation / solidification is more energetically efficient than the adsorption It also makes it possible to eliminate or reduce the size of the apparatus used according to the prior art, for example adsorption purification apparatus. If the purification is carried out at atmospheric pressure, this presents special advantages because being colder at the outlet of the exchanger, it stops even better CO 2 and especially a portion of the secondary impurities, which simplifies or even eliminate downstream purification and / or simplify the design and / or operation of certain downstream equipment (eg vaporizers).

According to one object of the invention, there is provided a method for cooling, purifying and separating a gaseous mixture containing at least one impurity in which the gaseous mixture containing at least one impurity is cooled to an equal temperature. or less than that at which the at least one impurity solidifies in a heat exchanger comprising at least one exchange body having cooling passages designed to reduce the adhesion of the solidified impurity to a surface of the passages, collects at least a portion of the solidified impurity exiting the cooling passages of the heat exchanger and / or at an intermediate level of the heat exchanger and the gas mixture, possibly at least partially liquefied, is withdrawn from the heat exchanger, preferably at the cold end, the gaseous mixture is optionally further cooled and the gaseous mixture is sent to a column system for being separated by low-temperature distillation, or even cryogenic temperature, to produce two fluids, each enriched in a component of the gaseous mixture, characterized in that the cooling passages are at least partially covered with a coating and / or treated physically and / or chemically treated, the coating and / or the treatment serving to limit or even prevent the formation and / or adhesion of the solidified impurity on a surface of the passages and in that

i) during substantially all the time that the separation by distillation takes place, the gaseous mixture cools in each exchange body having cooling passages designed to reduce the adhesion of the solidified impurity to a surface of the passages and / or

ii) the two fluids, each enriched in a component of the mixture, are heated in each exchange body having cooling passages designed to reduce the adhesion of the solidified impurity to a surface of the passages.

According to other optional aspects: the gaseous mixture withdrawn contains at least part of the solidified impurity

the gaseous mixture comprises at least one component, preferably a major component, which does not solidify and possibly does not liquefy in the heat exchanger

the gaseous mixture comprises at least two components, preferably major components, which do not solidify and possibly do not liquefy in the heat exchanger

an impurity is a component which does not represent more than 10%, mol or 5% mol or even 1% mol or even 0.1% mol or even 0.01% mol of the gaseous mixture.

the gaseous mixture is purified to remove at least a fraction of the at least one impurity upstream of the heat exchanger, this fraction representing between 20% and 95% of the impurity contained in the gaseous mixture upstream of the process.

the gaseous mixture is not purified to remove at least a fraction of the at least one impurity upstream of the heat exchanger

at least a portion of the solidified impurity is collected downstream of the heat exchanger by means of a phase separator and / or a worm cooling passages are at least partially physically modified, the treatment serving to limit or even prevent the formation and / or adhesion of the solidified impurity on a surface of the passages

the cooled gas mixture downstream of the heat exchanger and / or at least one intermediate level of the heat exchanger is treated to remove the impurity in gaseous and / or liquid and / or solid form.

the cooled gaseous mixture is treated solely downstream of the heat exchanger and not at least at an intermediate level of the heat exchanger in order to eliminate the impurity in gaseous and / or liquid and / or solid form.

the cooled gas mixture is treated solely at at least one intermediate level of the heat exchanger and not downstream of the heat exchanger to remove the impurity in gaseous and / or liquid and / or solid form. the gas mixture is cooled in the heat exchanger first to a temperature less than or equal to the liquefaction temperature of the at least one impurity but above its solidification temperature, the gas mixture is removed from the exchanger to remove a portion of the impurity in liquid form and returns the gaseous mixture containing impurity in the heat exchanger to cool to the solidification temperature thereof.

at least 20%, at least 50% or even at least 70% or even at least 90% of the impurity present at the inlet of the heat exchanger, said hot end, is removed by collecting at least one intermediate point of the heat exchanger after cooling, in solid and / or liquid form

at most 80%, at most 50%, or even at most 30%, or even at most 10% of the impurity present at the inlet of the heat exchanger, called hot end, are removed by collecting it at least once intermediate point of the heat exchanger after cooling, in solid and / or liquid form

at least 50% or even at least 70% or even at least 90% or even at least 99% or even at least 99.9% or even at least 99.99% of the impurity present at the inlet of the exchanger is eliminated of heat, said hot end, by collecting it downstream of the heat exchanger after cooling to the outlet of the exchanger at the cold end.

- at most 50%, or even more than 30%, or even more than 10%, or even more than 1%, or even more than 0.1%,% or even more than 0.01% of the impurity present at the inlet of the heat exchanger, said hot end, by collecting it downstream of the heat exchanger after cooling to the outlet of the cold end exchanger

at least 20%, at least 50% or even at least 70%, or even at least 90% or even at least 99% of the impurity present, is eliminated upstream of the inlet of the heat exchanger, said end hot

at most 80%, at most 50%, or even at most 30%, or even at most 10%, or even at most 1% of the impurity present, is eliminated upstream of the inlet of the heat exchanger, said end hot

the hot end of the heat exchanger is disposed at a higher level than the cold end. the hot end of the heat exchanger is disposed at a lower level than that of the cold end or that of an intermediate level of the exchanger in the case of an inverted U-shaped exchanger and is eliminated at least 50% the impurity, for example water, present in the gaseous mixture to be cooled at the inlet of the heat exchanger, said hot end, by collecting it in solid or liquid form at the hot end of the exchanger where it falls by gravity after cooling in the heat exchanger (because its adhesion to the walls is limited).

the hot end of the heat exchanger is arranged at the same level as the cold end in the case of an inverted U-shaped exchanger

the gaseous mixture is air or a mixture whose main components are hydrogen and / or carbon monoxide and / or methane and the at least one impurity is water and / or carbon dioxide; carbon or a mixture whose main component is carbon dioxide and optionally hydrogen and / or carbon monoxide and / or methane and / or oxygen and / or nitrogen and / or argon and the at least one impurity is water.

at least one surface of the cooling passages has been treated to make it rougher and / or to lubricate and / or to render it hydrophilic and / or hydrophobic and / or hydroscopic and / or hygroscopic so as to limit or even prevent formation and / or the adhesion of solidified impurities, for example ice.

the heat exchanger may comprise passages of which at least one section has a treatment and / or a coating and / or a geometry and / or, in the case of a plate and fin exchanger, a type of fins which differs from that of another section to operate at a lower temperature range.

the heat exchanger may comprise passages of which at least one section has a treatment and / or a coating and / or a geometry and / or, in the case of a plate and fin heat exchanger, a type of fins which differs from that of another section located downstream of an intermediate withdrawal point of solidified impurities.

the gaseous mixture is purified and cooled by a process as described above, optionally further cooled and sent to a column system to be separated by distillation at low temperature or even cryogenic temperature to produce at least one fluid enriched in a component of the gas mixture.

the fluid enriched in a component of the gaseous mixture heats up in the heat exchanger in the warming passages.

the heat exchanger comprises at least one heating passage of a fluid, the at least one heating passage having not been treated or coated to limit or even prevent the formation and / or adhesion of impurities solidified, for example ice.

at least a portion of the solidified impurity exiting the cooling passages of the heat exchanger is returned to the heat exchanger to heat up.

the at least a portion of the solidified impurity is mixed with another gas prior to heating in the heat exchanger.

the at least one heating passage to which the solidified impurities are sent has been treated or coated to limit or even prevent the formation and / or adhesion of solidified impurities, for example ice.

at least a portion of the solidified impurity exiting the cooling passages of the heat exchanger and / or at an intermediate level of the heat exchanger is collected and the gas mixture is liquefied or liquefied by a subsequent step of downstream of the exchanger and / or is separated at a subambient temperature downstream of the exchanger, optionally after removal downstream of the remaining impurity exchanger which would solidify at this subambient temperature.

frigories are provided to the gaseous mixture which cools to at least one intermediate point of the heat exchanger.

coolants are supplied to the gaseous mixture which cools to at least one intermediate point of the heat exchanger, preferably downstream or upstream of a draw-off point of at least a portion of the solidified or liquefied impurity at a intermediate level of the heat exchanger.

- Frigories are supplied to the gaseous mixture which is at a temperature between -5 ° C and 5 ° C frigories are supplied to the gaseous mixture which is at a temperature between -20 ° C and -30 ° C

frigories are provided to the gas mixture by removing at least a portion of the gaseous mixture from the heat exchanger and cooling it.

- Frigories are provided to the gas mixture by means of a refrigerant sent to an intermediate level of the heat exchanger.

the gas mixture cools in the heat exchanger permanently

the gaseous mixture cools in the heat exchanger intermittently

the heat exchanger cools the gaseous mixture to the cold end until a temperature below 0 ° C, or even below -50 ° C, or even below -100 ° C.

the gaseous mixture is at atmospheric pressure or a pressure greater than atmospheric pressure

the heat exchanger comprises only one exchange body and is a monobloc exchanger

the heat exchanger comprises at least two exchange bodies the gaseous mixture cools in cooling passages whose number does not equal the number of heating passages connected to the means of transport of the first gas

the gaseous mixture cools in cooling passages whose number does not equal the number of heating passages connected to the means of transport of the second gas.

Each of the above features may be combined with each of the above except in the event of manifest incompatibility.

If the passages of the heat exchanger are treated to limit the deposition of impurities but not to prevent it completely, it will be necessary to remove the solids formed in the passages, for example by heating and / or passing the gaseous mixture at a sufficient flow rate (its nominal flow rate or a higher flow rate) and / or at a high pressure with respect to the flow rate and / or pressure used during cooling or by mechanical means, for example the variation of the gas mixture flow rate or the gas mixture flow rate pulsations, or the vibrations applied directly to the exchanger.

According to one object of the invention, there is provided an apparatus for cooling and purifying a gas mixture containing at least one impurity comprising a heat exchanger having cooling passages of the gas mixture and heating passages of a gas, means for sending the gaseous mixture containing at least one impurity to cool in the heat exchanger to a temperature equal to or less than that at which the at least one impurity solidifies and means for withdrawing the gaseous mixture , optionally at least partially liquefied, of the heat exchanger, preferably at the cold end and means for collecting at least a portion of the solidified impurity exiting the cooling passages of the heat exchanger and / or at a intermediate of the heat exchanger and means for discharging the gas mixture into the at least one impurity of the heat exchanger characterized in that the pa cooling parts are at least partially coated and / or physically treated and / or chemically treated, the coating and / or treatment serving to limit or even prevent the formation and / or adhesion of the solidified impurity to a surface of the passages and in that the apparatus comprisesa single heat exchanger connected to the means for collecting at least a portion of the solidified impurity, the heat exchanger being monobloc. .

According to other optional aspects:

the apparatus comprises heating passages for a first gas and heating passages for a second gas

the apparatus comprises means for purifying the gaseous mixture upstream of the heat exchanger in order to remove at least a fraction of the at least one impurity.

the means for collecting at least a portion of the solidified impurity downstream of the heat exchanger are constituted by a phase separator and / or a worm. the heat exchanger is constituted by at least one plate and fin heat exchanger

the heat exchanger consists of at least two plate and fin heat exchangers made of aluminum or copper or titanium

- The heat exchanger is constituted by at least one coil heat exchanger The heat exchanger is constituted by at least one shell and tube heat exchanger

the apparatus comprises means for treating the cooled gaseous mixture downstream of the heat exchanger and / or at least an intermediate level of the heat exchanger to remove impurity in gaseous and / or liquid form and / or solid.

the hot end of the heat exchanger is disposed at a higher level than the cold end.

the hot end of the heat exchanger is disposed at a lower level than that of the cold end or that of an intermediate level of the exchanger in the case of an inverted U-shaped exchanger and is eliminated at least 50% the impurity, for example water, present in the gaseous mixture to be cooled at the inlet of the heat exchanger, said hot end, by collecting it in solid or liquid form at the hot end of the exchanger where it falls by gravity after cooling in the heat exchanger.

at least one surface of the cooling passages has been treated to make it rougher and / or to lubricate it and / or to have a hydrophobic and / or superhydrophobic surface, and / or with hydrophobic and hydrophilic and / or hygroscopic zones in order to limit or even prevent the formation and / or adhesion of solidified impurities, for example ice.

the surface of a passage may be impregnated with a lubricant or not.

the exchanger comprises at least one heating passage of a fluid and at least one surface of the at least one heating passage has been treated to make it rougher and / or to lubricate it and / or to make it hydrophilic and and / or hydrophobic and / or hydroscopic and / or hygroscopic so as to limit or even prevent the formation and / or adhesion of solidified impurities, for example ice. According to another aspect of the invention there is provided a low temperature distillation or even cryogenic temperature separation apparatus comprising a cooling and purification apparatus as described above as well as a column system and means for send the purified and cooled gas mixture through the cooling and purification apparatus to the column system.

The separation apparatus may not comprise means for cooling the gaseous mixture downstream of the cooling and purification apparatus.

The apparatus may include means for supplying a fluid enriched in a component of the gaseous mixture to heat in the heat exchanger in warming passages.

According to other optional features:

the heat exchanger comprises at least one heating passage of a fluid, the at least one heating passage having not been treated or coated to limit or even prevent the formation and / or adhesion of solidified impurities , for example ice cream.

the apparatus comprises means for sending at least a portion of the solidified impurity exiting the cooling passages of the heat exchanger to the heat exchanger to heat up.

means for mixing the at least a portion of the solidified impurity with another gas prior to heating in the heat exchanger.

The separation and purification apparatus may comprise means for supplying frigories to the gaseous mixture which cools to at least one intermediate point of the heat exchanger.

The separation and purification apparatus may comprise means for supplying frigories to the gaseous mixture which cools to at least one intermediate point of the heat exchanger, preferably downstream and / or upstream of a draw-off point. at least a portion of the impurity solidified or liquefied at an intermediate level of the heat exchanger. The separation and purification apparatus may comprise means for supplying the gas mixture with frigories by removing at least a portion of the gaseous mixture from the heat exchanger.

The separation and purification apparatus may comprise means for supplying frigories to the gas mixture by means of a refrigerant supplied to an intermediate level of the heat exchanger.

In all the separation schemes by liquefaction and condensation of impurities, the challenge is to compensate for the enthalpies of phase changes of the various components by the supply of energy (here cold booster) via external devices to the main exchanger (example: heat pump, cooling unit).

If we do not make extra cold the exchange diagram is removed at the cold end as seen in Figure 1 1.

In the curve of Figure 1 1 one observes the curvature caused by the condensation and the solidification of the water (moist air at 1, 4 bara). Figure 12 is a diagram "compensated" by sufficient cold backups.

The case of Figure 12 is a simulation of the condensation and the solidification of water combined with the solidification of CO ₂ .

The invention will be described in more detail with reference to Figures 1 to 10 which schematically show methods according to the invention.

Here are detailed process diagrams on which the concept of the invention could be applied. These are low pressure, single column air separation unit diagrams. They could be transposed to other separation and / or liquefaction processes, such as cryogenic separation processes for the H ₂ / CO mixture as explained above.

In Figure 1, there is shown a cryogenic distillation air separation method using a plate and finned aluminum heat exchanger 3 and a single distillation column 27. This process allows the production of an enriched liquid in oxygen 43, an oxygen-enriched gas 45 and a nitrogen-enriched gas 47. The use of a plate-and-finned brazed aluminum heat exchanger is not essential. This exchanger can use other technologies and may for example be a wound heat exchanger or a shell and tube heat exchanger.

The air to be separated 1 contains water and carbon dioxide, which must be purified upstream of the distillation. After filtering in a filter F and compression in a compressor C, the compressed air 1 enters the heat exchanger 3 constituted by a single exchange body and called "exchange line" without passing through adsorbent beds typically present in an air separation apparatus. It is conceivable to remove some of the water contained in the air by separating the water that condenses, during compression of the air followed by a cooling step. However, at least 20% of the water present in the ambient air will be removed by passing through the exchanger. The extraction of water on the one hand and the rest of the water and CO2 on the other hand are done at two different places in the exchange line 3. A large part of the water is removed in the form of liquid (about 75% of the water present in the air 1 arriving in the exchanger 3, after compression followed by a cooling step) at a temperature close to 0 ° C: the air 5 is withdrawn at this temperature. separating the air and water 5B in a phase separator 2 and then reinjecting the dried air 5A to finish its cooling and perform the same separation at its exit from the exchange line 3 with the rest of the water and CO ₂ this time, both being solid. To compensate for the latent heat of liquefaction and condensation of impurities, two cold additions are required via two heat pumps, for example at 0 ° C and -25 ° C.

Thus air 7 withdrawn at an intermediate level of the exchange line 3 cools by means of a first heat pump 4 and the cooled air is returned to the exchange line 3.

Then air 1 1 withdrawn at a colder intermediate level of the exchange line 3 cools with a second heat pump 6 fed by a fluid 13. The cooled air 1 1 A is returned to the 'exchange.

The air already purified with water and cooled in two stages contains ice and solid carbon dioxide is sent to a phase separator 17 and ice and solid carbon dioxide 19 are removed. The walls of the cooling passages are treated to limit or prevent the formation and / or adhesion of ice and carbon dioxide on the surfaces, at least in regions where the temperature of the passage is expected to be below the solidification temperature of the water and / or carbon dioxide.

This treatment may be a physical treatment of the surface or the establishment of a coating as described above, for example superhydrophobic. Thus, the solid water and carbon dioxide remain in the air and pass through the exchange line to the cold end before being collected in the second phase separator 17.

Part of the secondary impurities in the air (in particular propane, acetylene, propylene, C4 +, N ₂ O) are also separated in the separator 17 at the cold end of the exchanger, either in solid form or in liquid form.

The purified air 20 is divided into two parts 23, 25. The part 23 is sent to the middle of the simple distillation column 27 where it separates to form nitrogen-enriched gas at the top of the column 47 and a liquid enriched in nitrogen. oxygen 43 in the vat of column 27.

Part 15 of the air is condensed at least partially in a heat exchanger 59 by heat exchange with a fluid flow 57 which cools by means of a heat pump 21 using the magnetocaloric effect.

A cooling fluid 53, typically ambient air or cooling water is supplied to the heat pump 21 using the magnetocaloric effect. Heated water 55 leaves the heat pump 21.

The column comprises a bottom reboiler 29 and a top condenser 31. The reboiler is heated by means of a fluid circuit 41 in connection with a heat pump using the magnetocaloric effect 33. This heat pump using the effect magnetocaloric 33 also serves to cool a fluid 37 which cools the top condenser 31. The fluids 37 and 41 may be the same or different. An oxygen-enriched liquid 43 is withdrawn in the vat from the column 19 and a nitrogen-enriched gas withdrawn via a pipe 47 is heated in the exchanger 3 and does not serve to regenerate a purification unit, since there do not have any. An oxygen-enriched gas 45 is withdrawn in the bottom of the column 27, is heated in the exchanger 3 and is compressed by a compressor 49.

Figure 1a illustrates a variant of Figure 1 in which the heat exchanger 3 is constituted by two exchange bodies 3a, 3b. Each of the bodies 3a, 3b is a plate and fin heat exchanger as described above but other technologies can be envisaged.

In contrast to Figure 1, throughout the duration of the distillation, the air 1 is divided into two flow rates, one of which is sent to the body 3a and the other to the body 3b. Each of the bodies has cooling passages designed to reduce the adhesion of the solidified impurity to a surface of the passages. The cooling passages of each body 3a, 3b are at least partially coated and / or physically treated and / or chemically treated, the coating and / or treatment serving to limit or even prevent the formation and / or adhesion of the solidified impurity on a surface of the passages. It is conceivable to use more than two bodies.

Carbon dioxide and / or solidified water (s) is collected for both bodies and sent to a single container 17. The use of several containers is obviously conceivable.

The purified air of the two bodies is mixed to form the flow 20 and continues its treatment as for Figure 1.

The gas 47 is heated simultaneously in the two exchange bodies during the distillation, being divided in two upstream of the bodies 3a, 3b and remixed downstream thereof.

The gas 45 heats up simultaneously in the two exchange bodies during the distillation, being divided in two upstream of the bodies 3a, 3b and remixed downstream thereof.

Since each passage receives only a gas to be heated or a gas to be cooled and the flow rates are not reversed during the distillation, the number of passages dedicated to the cooling of the air is not identical to the number of passages intended to reheat. the gas 47 for a given body.

In Figure 1b is schematically illustrated an exchange body corresponding to a body 3, 3a, 3b of one of the other Figures, where it can be seen that the number of passages dedicated to the cooling of the gaseous mixture, in this case air is not identical to the number of passages dedicated to the heating of the first gas, here nitrogen NR corresponding to nitrogen 47 or the number dedicated to the heating a second gas, here oxygen gas OG.

In the variant of FIG. 2 and those of FIGS. 3 to 9, the heat exchanger 3 is a monoblock heat exchanger which cools all the air intended for distillation during any period during which the distillation takes place. It also heats all the gas from the distillation during any period when the distillation takes place. The extraction of water on the one hand and the rest of the water and CO2 on the other hand are also at two different places in the exchange line 3. Now we remove a large part of the water in solid form (approximately 97% of the water present in the air 1 arriving in the exchanger 3) at a temperature close to -25 ° C, so in solid form. The air 5 is withdrawn at this point by separating the air and the ice 5B in a phase separator 2 and then the dried air 5A is reinjected to finish its cooling. The air sent to the separator 2 has already been cooled upstream by a first makeup of cold at 0 ° C.

Thus air 7 withdrawn at an intermediate level of the exchange line 3 cools first by means of a first heat pump 4 and then is removed from the line to remove the ice. The cooled air 5A returned to the exchange line 3 is cooled again by the second cooler 6.

For the case of Figure 3, the air is first cooled in the exchange line 3, it is removed from the exchange line and water is removed in liquid form in the separator 2, it cools then the purified air 5A in the exchange line, then by a first cooler 4, then in the exchange line 3, then the air is purified to remove the water in the separator 8, it is cooled in the exchange line, then with a second cooler 6 and the air is cooled to the cold end.

Note that in all cases, there may be only one extra cold at the exchange line 3, or not at all, if you are willing to sacrifice energy, the extra necessary cold being brought then to the cold end of the exchanger, where it costs the most. In the variant of FIG. 4, the order of the stages of separation of water, CO ₂ and cold additions is as in FIG. 1. By withdrawing liquid water in a first separation at 0 ° C. this can be used to cool the machines, for example the compressor C.

But in this example, the solids or liquids 19 (the rest of the water, C0 ₂ and other secondary impurities) collected in the separator 17 are sent to the exchange line 3 to bring cold. This makes it possible to recover some of the latent heat, and thus to lighten or even simplify the necessary cold additions

In order not to complicate the exchange line, they can be injected into at least one dry and cold fluid, for example, coming from the cryogenic separation, for example nitrogen 47 to form a mixed flow rate 61. In this case, it It may be prudent to treat at least some parts of the nitrogen passages to be heated to limit or even prevent the deposition of these solids.

Figure 5 illustrates the case where a worm system 17A is used to extract impurities in the form of ice or a mixture of ice / liquid for reinjecting them directly into the products. This replaces the phase separator 17 of the other figures.

Other means can be envisaged to remove the solid impurity, which can be released to the atmosphere. The heat exchanger can cool the gas containing at least one impurity episodically and the impurity can be melted, for example while the heat exchanger is not working.

The solid could also be evacuated by agreeing to lose some of the gaseous mixture that then carries the solid, with pneumatic style transport.

Figure 6 is a variant where all the water and CO ₂ present in the air at the hot end are removed at the cold end of the exchange line. The extra cold can be provided to compensate for the condensation and the solidification of impurities, as well as their cooling along the exchange line with a multitude of heat pumps, here n heat pumps PAC1, PACn powered by flow rates 9, 13. The addition of cold can also be done with a cold temperature slippery. It can also be limited to 1 or 2 colds. In Figure 7, a portion of the impurities is removed by a conventional adsorption separation system A. This portion may comprise between 20% and 95% of an impurity or impurities present (s). Purification can be done by other means than adsorption. Then the fluid purified at least one impurity enters the exchange line where it ends removing the remaining impurities by solidification / liquefaction and final separation. At least one heat pump is always required to compensate for the latent heat of liquefaction and condensation of impurities. The impurities can be reinjected into the products, as seen in FIGS. 4 and 5. In the case where the majority of the impurities to be removed are removed upstream in a conventional system A, the cold filling can be done only at the cold end. of the exchanger 3.

In the variant of Figure 8, another separation system E is used at the outlet of the fan C to remove a portion of the impurities from the flow, for example in the form of a drying wheel. Then the fluid 1 still loaded with impurities enters the exchange line 3. The impurities are removed at two levels and heat pumps compensate for the latent heat of condensation and liquefaction of impurities. Frozen water / solid CO ₂ and solid / liquid secondary impurities are recovered at the cold end without reinjecting it into the products.

In the case of FIG. 9, for a gaseous mixture 1 charged with water in gaseous form, the water in liquid and / or solid form flows countercurrently from the flow of gas 1, the incoming airflow 1 from the bottom of the exchanger 3, contrary to conventional operation (one can also imagine an inverted U-shaped heat exchanger configuration, with hot end and cold end at the bottom, and an intermediate point at the top).

Indeed, by solidifying and / or liquefying, the water becomes heavier and falls against the current of the gas that cools. It comes out in liquid form at the hot end of the exchanger 3.

This variant does not use phase separators but generally requires cold input to the exchange line.

Conversely, the cold flow rates 45, 47 enter at the top of the exchange line and exit at the bottom. For clarity, the figure is drawn as if the water and / or ice 19 descended through a passage other than the passage through which they are entered, present in the air.

In fact, water and / or ice 19 will exit through the same passage through which they entered.

In the variant of FIG. 10, for a mixture containing water, the exchange line 3 of FIG. 9 is divided into two (exchange line 3 and 3A) in order to draw off the water between the two. an intermediate temperature. Thus the cooled air in the line 3 with a cold supply of the cooler 4 is separated in the phase separator to remove a portion of the water 5B. The rest of the water and / or ice falls down lines 3 and 3A. The at least partially purified air is cooled in the exchange line 3A with a cold supply of the cooler 6 and then cooled in the line 3A again. The phase separator 17 is not present in this particular case.

For the case where the exchange line is divided into two exchange bodies in series, the two lines 3,3A can be built with the same technology or different technologies (plate heat exchanger and fins, coil exchanger, heat exchanger calender). Similarly if the exchange lines are of the same technology, they do not necessarily have the same construction and may differ in the size of the passages, the number of passages, the type of coating and / or treatment used to limit the deposit solids, the type of fins used, the material in which they are built, etc.

These eleven examples all relate to the separation of air by distillation in a single column. The invention can be applied to the cryogenic separation of air by any known column system, other than that described and using any means of producing known cold, other than those described.

The air separation apparatus may for example be a double air separation column producing at least one gaseous product and / or at least one liquid product.

The invention can also be applied to the purification and cooling of other gaseous mixtures having at least one impurity liable to solidify during cooling. An impurity is a component which does not represent more than 10%, mol or 5% mol or even 1% mol or even 0.1% mol or even 0.01% mol of the gaseous mixture.

It applies in particular to other gas mixtures, for example mixtures of carbon dioxide containing for example at least 30% of carbon dioxide and water. In this case, the passages of the exchange line are treated to limit or even prevent the deposition of water and the pressure and temperature are chosen to avoid deposition of CO ₂ . Such a mixture can be separated in a process of Figures 1 to 10 by changing the operating temperatures.

For all the figures, the supply of cold, if any, can be carried out with any known and adapted means (for example, magneto-caloric cooler, conventional compression-expansion refrigeration unit, turbine).

In the figures, a part of the gaseous mixture leaves the exchange line to be cooled in the element bringing cold while the rest of the gaseous mixture continues cooling in the exchange line. The portion cooled by the cold supply then mixes with the rest of the mixture that has not left the exchange line.

It is also possible to take all the gas mixture from the exchange line to send it to the element bringing the cold and return the cooled mixture in the exchange line.

In the examples of the figures, it is seen that part or more parts 7, 1 1 of the air exit the exchanger 3 to be cooled and returned (flows 7A, 1 1 A) to the exchanger. It is obviously possible in all or part of the cases to use a heat transfer fluid in a closed circuit that transfers heat from the heat exchanger 3 to the cooling means 4,6 and returns to the heat exchanger for bring cold.

In any case, it is conceivable to provide an ultimate purification downstream of the exchanger and, where appropriate, downstream of the phase separator or worm, to remove the remaining impurities in the mixing rate 20. In all cases, the heat exchanger 3 may comprise passages of which at least one section has a treatment and / or a coating and / or a geometry and / or a type of fins in the case of a plate heat exchanger. and fins which differs from that of another section to operate at a lower temperature range.

For example, the heat exchanger passage section at a temperature between 20 ° C to 0 ° C will be treated or coated in one way and that at a temperature between 0 ° C to -60 ° C will be treated in another way. The treatment or coating may be selected to suit the type of physical phenomenon change (gas-liquid, gas-solid, liquid-solid), or type of impurities concerned (eg water / carbon dioxide).

The heat exchanger 3 may comprise passages of which at least one section has a treatment and / or a coating and / or a geometry and / or a type of fins in the case of a plate and fin heat exchanger which differs that of another section located downstream of an intermediate withdrawal point of solidified impurities.

The heat exchanger may consist of at least two heat exchangers of different materials, for example a brazed aluminum heat exchanger and a brazed copper heat exchanger.

For all the examples, during substantially all the time that the separation by distillation takes place, the gaseous mixture cools in each exchange body having cooling passages designed to reduce the adhesion of the solidified impurity to a surface of the crossings

Claims

claims

Process for cooling, purifying and separating a gaseous mixture (1) containing at least one impurity of a gaseous mixture in which the gaseous mixture containing at least one impurity is cooled to an equal or lower temperature to that at which the at least one impurity solidifies in a heat exchanger (3,3A, 3a, 3b) comprising at least one exchange body having cooling passages designed to reduce the adhesion of the solidified impurity on one surface of the passages, at least a portion (5B, 10B, 19) is collected of the solidified impurity exiting the cooling passages of the heat exchanger and / or at an intermediate level of the heat exchanger and withdrawing the gaseous mixture, possibly at least partially liquefied from the heat exchanger, preferably at the cold end, the gaseous mixture is optionally further cooled and the gaseous mixture is sent to a colon system nes (27) to be separated by low temperature distillation, or even cryogenic temperature, to produce two fluids (43, 45, 47), each enriched in a component of the gaseous mixture characterized in that the cooling passages are at least partially covered coated and / or physically treated and / or chemically treated, the coating and / or treatment serving to limit or prevent the formation and / or adhesion of the solidified impurity on a surface of the passages and in that than

2. Method according to claim 1 wherein the gas mixture (1) is purified to remove at least a fraction of the at least one impurity upstream of the heat exchanger (3, 3A, 3a, 3b), this fraction representing between 20% and 95% of the impurity contained in the gas mixture upstream of the process.

3. Method according to one of the preceding claims wherein is collected at least a portion of the solidified impurity downstream of the heat exchanger (3, 3A, 3a, 3b), by means of a phase separator ( 17) and / or an endless screw (17A).

4. Method according to one of the preceding claims wherein the cooled gaseous mixture is treated downstream of the heat exchanger (3, 3A, 3a, 3b) and / or at least an intermediate level of the heat exchanger to remove the impurity (5B, 10B) in gaseous and / or liquid and / or solid form.

5. Method according to claim 4 wherein the gas mixture (1) is cooled in the heat exchanger (3, 3A, 3a, 3b) first to a temperature less than or equal to the liquefaction temperature of the at least one impurity but greater than its solidification temperature, at least a portion of the gaseous mixture (5) of the exchanger is removed to remove a portion of the impurity in liquid form (5B, 10B) and return the at least a portion of the gaseous mixture containing impurity in the heat exchanger for cooling to the solidification temperature thereof.

6. Method according to claim 4 or 5 wherein at least one eliminates

50% of the impurity present at the inlet of the heat exchanger (3, 3A, 3a, 3b), said hot end, by collecting it downstream of the heat exchanger after cooling to the outlet of the exchanger with the cold end.

7. The method of claim 6 wherein the hot end of the heat exchanger (3, 3a, 3b) is disposed at a higher level than the cold end.

8. Method according to one of claims 1 to 7 wherein the hot end of the heat exchanger (3, 3a, 3b) is disposed at a lower level than the cold end or that of an intermediate level. of the exchanger in the case of an inverted U-shaped exchanger and at least 50% of the impurity, for example water, present in the gaseous mixture to be cooled at the inlet of the heat exchanger is eliminated, said hot end, by collecting it in solid or liquid form at the hot end of the exchanger where it falls by gravity after cooling in the heat exchanger.

9. Method according to one of the preceding claims wherein the gas mixture (1) is air or a mixture having for main components hydrogen and / or carbon monoxide and / or methane and the at least one impurity is water and / or carbon dioxide or a mixture whose main component is carbon dioxide and optionally hydrogen and / or carbon monoxide and / or methane and / or oxygen and / or nitrogen and / or argon and the at least one impurity is water.

10. Method according to one of the preceding claims wherein at least one surface of the cooling passages has been treated to have a hydrophobic surface, and / or superhydrophobic, and / or with hydrophobic and hydrophilic zones, and / or hygroscopic, so to limit or even prevent the formation and / or adhesion of solidified impurities, for example ice.

1 1. Method according to one of the preceding claims, in which the heat exchanger (3) comprises at least one heating passage of a fluid, the at least one heating passage having not been treated or coated for limit or even prevent the formation and / or adhesion of solidified impurities, for example ice

12. Method according to one of the preceding claims wherein at least a portion of the solidified impurity exiting the cooling passages of the heat exchanger is returned to the heat exchanger to heat up.

13. Method according to one of the preceding claims wherein is collected at least a portion of the solidified impurity leaving the cooling passages of the heat exchanger and / or at an intermediate level of the heat exchanger and the mixture gas is liquefied or is liquefied by a subsequent step downstream of the exchanger and / or is separated at a subambient temperature downstream of the exchanger, possibly after removal downstream of the remaining impurity exchanger which would solidify at this subambient temperature.

14. Process according to one of the preceding claims, in which frigories are supplied to the gaseous mixture which cools to at least one intermediate point of the heat exchanger (3), preferably downstream or upstream of a point of contact. withdrawing at least a portion of the solidified or liquefied impurity at an intermediate level of the heat exchanger.

15. Apparatus for cooling and purifying a gas mixture containing at least one impurity comprising a heat exchanger (3) comprising at least one or two exchange bodies (3, 3A, 3a, 3b), each having cooling passages designed to reduce the adhesion of the solidified impurity to at least a portion of the surface of the passages and the heating passages, means for sending the gaseous mixture containing at least one impurity to cool in the passages of cooling the exchange body or bodies to a temperature equal to or lower than that at which the at least one impurity solidifies and means for withdrawing the gaseous mixture (15), optionally at least partially liquefied, the exchange body or bodies, preferably at the cold end, means for sending a gas to heat up in the heating passages and means (2, 8, 17, 17A) to collect at least one part of the solidified impurity exiting the cooling passages of the heat exchanger and / or at an intermediate level of the heat exchanger and means for discharging the gas mixture into the at least one impurity of the heat exchanger. characterized in that the cooling passages of each exchange body are at least partially coated and / or physically treated and / or chemically treated, the coating and / or treatment serving to limit or even prevent the formation and / or the adhesion of the solidified impurity to a surface of the passages and in that heating passages are connected to means for transporting a first gas (47, NG) to be heated and other s warming passages are connected to means for transporting a second gas to be heated (45, OG).

16. Apparatus according to claim 15 wherein the number of cooling passages is not equal to the number of heating passages connected to the first gas transport means (47, NG) and the number of cooling passages is not equal to the number of heating passages connected to the transport means of the second gas (45, OG). .