U.S. patent application number 15/305849 was filed with the patent office on 2017-02-16 for method for purifying, cooling and separating a gaseous mixture and associated apparatus.
This patent application is currently assigned to L'Air Liquide, Societe Anonyme pour l'Etude et I'Exploitation des Procedes Georges Claude. The applicant listed for this patent is L'Air Liquide, Societe Anonyme pour l'Etude et I'Exploitation des Procedes Georges Claude. Invention is credited to Guillaume CARDON, Antony CORREIA ANACLETO, Benoit DAVIDIAN, Erwan LE GULUDEC, Clement LIX, Quentin SANIEZ, Bernard SAULNIER.
Application Number | 20170045291 15/305849 |
Document ID | / |
Family ID | 51261055 |
Filed Date | 2017-02-16 |
United States Patent
Application |
20170045291 |
Kind Code |
A1 |
CARDON; Guillaume ; et
al. |
February 16, 2017 |
METHOD FOR PURIFYING, COOLING AND SEPARATING A GASEOUS MIXTURE AND
ASSOCIATED APPARATUS
Abstract
The invention relates to a method for cooling, purifying and
separating a gaseous mixture 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 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 prevent the solidified impurity from forming
and/or adhering to a surface of the passages; at least one portion
of the solidified impurity exiting the cooling passages of the heat
exchanger is collected; and the gaseous mixture is withdrawn from
the heat exchanger.
Inventors: |
CARDON; Guillaume; (Poissy,
FR) ; CORREIA ANACLETO; Antony; (Creteil, FR)
; DAVIDIAN; Benoit; (Saint Maur des Fosses, FR) ;
LE GULUDEC; Erwan; (Versailles, FR) ; LIX;
Clement; (Versailles, FR) ; SANIEZ; Quentin;
(Paris, FR) ; SAULNIER; Bernard; (La Garenne
Colombes, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
L'Air Liquide, Societe Anonyme pour l'Etude et I'Exploitation des
Procedes Georges Claude |
Paris |
|
FR |
|
|
Assignee: |
L'Air Liquide, Societe Anonyme pour
l'Etude et I'Exploitation des Procedes Georges Claude
Paris
FR
|
Family ID: |
51261055 |
Appl. No.: |
15/305849 |
Filed: |
April 30, 2015 |
PCT Filed: |
April 30, 2015 |
PCT NO: |
PCT/FR2015/051166 |
371 Date: |
October 21, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25J 3/04187 20130101;
F25J 3/044 20130101; F25J 2205/20 20130101; F25J 2200/74 20130101;
F25J 2230/52 20130101; F25J 2200/40 20130101; F25J 2200/50
20130101; F25J 2210/40 20130101; F25J 2215/04 20130101; F25J
3/04242 20130101; F25J 2205/04 20130101; F25J 2230/32 20130101;
F25J 2205/10 20130101; F25J 2270/908 20130101; F25J 3/04278
20130101; F25J 2220/40 20130101 |
International
Class: |
F25J 3/04 20060101
F25J003/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 30, 2014 |
FR |
1454000 |
Claims
1-16. (canceled)
17. A process for cooling, purifying and separating a gas mixture
(1) containing at least one impurity of a gas mixture, the process
comprising the steps of: cooling the gas mixture containing at
least one impurity to a temperature below or equal to that at which
the at least one impurity solidifies in a heat exchanger, the heat
exchanger comprising at least one exchange body having cooling
passages configured to reduce the adhesion of the solidified
impurity on a surface of the passages; collecting at least one
portion of the solidified impurity leaving the cooling passages of
the heat exchanger and/or at an intermediate level of the heat
exchanger; withdrawing the gas mixture from the heat exchanger;
sending the gas mixture to a system of columns under conditions
effective for separating the gas mixture by cryogenic distillation
to produce at least a first fluid and a second fluid, wherein each
of the first fluid and the second fluid are enriched in one
component of the gas mixture, wherein the cooling passages are at
least partially covered by a coating and/or physically treated
and/or chemically treated, the coating and/or the treatment serving
to at least limit the formation and/or the adhesion of the
solidified impurity on a surface of the cooling passages, and
wherein: i) during substantially the entire time that the
separation by distillation is carried out, the gas mixture is
cooled in each exchange body having cooling passages configured to
reduce the adhesion of the solidified impurity on a surface of the
passages, and/or ii) the first fluid and the second fluid are
reheated in each exchange body having cooling passages designed to
reduce the adhesion of the solidified impurity on a surface of the
passages.
18. The process as claimed in claim 17, wherein the gas mixture is
purified to remove at least one fraction of the at least one
impurity upstream of the heat exchanger, said one fraction
representing between 20% and 95% of the impurity contained in the
gas mixture upstream of the process.
19. The process as claimed in claim 17, wherein at least one
portion of the solidified impurity is collected downstream of the
heat exchanger, by means of a phase separator and/or an endless
screw.
20. The process as claimed in claim 17, wherein the cooled gas
mixture is treated downstream of the heat exchanger and/or at at
least one intermediate level of the heat exchanger in order to
eliminate the impurity in gaseous and/or liquid and/or solid
form.
21. The process as claimed in claim 20, wherein the gas mixture is
cooled in the heat exchanger firstly to a temperature below or
equal to the liquefaction temperature of the at least one impurity
but above its solidification temperature, at least one portion of
the gas mixture is taken out of the exchanger in order to eliminate
a portion of the impurity in liquid form and at least one portion
of the gas mixture containing some impurity is sent back to the
heat exchanger in order to cool the at least one portion of the gas
mixture containing some impurity to the solidification temperature
of said impurity.
22. The process as claimed in claim 20, wherein at least 50% of the
impurity present at the inlet of the heat exchanger, referred to as
the hot end, is eliminated by collecting the impurity downstream of
the heat exchanger after cooling up to the outlet of the exchanger
at the cold end.
23. The process as claimed in claim 22, wherein the hot end of the
heat exchanger is placed at a higher level than that of the cold
end.
24. The process as claimed in claim 17, wherein the hot end of the
heat exchanger is placed at a lower level than that of the cold end
or than that of an intermediate level of the exchanger in the case
of an inverted U-shaped exchanger and at least 50% of the impurity
present in the gas mixture to be cooled is eliminated at the inlet
of the heat exchanger, referred to as the hot end, by collecting
the impurity in solid or liquid form at the hot end of the
exchanger where the impurity drops by gravity after cooling in the
heat exchanger.
25. The process as claimed in claim 17, wherein the gas mixture is:
air with the at least one impurity being selected from the group
consisting of water, carbon dioxide, and combinations thereof, or a
mixture of gases, having a main component selected from the group
consisting of hydrogen, carbon monoxide, methane, and combinations
thereof, with the at least one impurity being selected from the
group consisting of water, carbon dioxide, and combinations
thereof, or a mixture of gases, having the main component of carbon
dioxide and at least a second component selected from the group
consisting of hydrogen, carbon monoxide, methane, oxygen, nitrogen,
argon, and combinations thereof, with the at least one impurity
being water.
26. The process as claimed in claim 17, further comprising the step
of treating at least one surface of the cooling passages thereby
producing a surface that is hydrophobic and/or superhydrophobic
and/or that has hydrophobic and hydrophilic, and/or hygroscopic
zones, in order to at least limit the formation and/or the adhesion
of solidified impurities.
27. The process as claimed in claim 17, wherein the heat exchanger
comprises at least one passage for reheating a fluid, the at least
one reheating passage not having been treated or coated in order to
at least limit the formation and/or the adhesion of solidified
impurities.
28. The process as claimed in claim 17, wherein at least one
portion of the solidified impurity leaving the cooling passages of
the heat exchanger is sent back to the heat exchanger to be
reheated.
29. The process as claimed in claim 17, wherein at least one
portion of the solidified impurity leaving the cooling passages of
the heat exchanger and/or at an intermediate level of the heat
exchanger is collected and the gas mixture finds itself liquefied
or is liquefied by a subsequent step downstream of the exchanger
and/or is separated at a subambient temperature downstream of the
exchanger, optionally after elimination, downstream of the
exchanger, of remaining impurities that would be solidified at this
subambient temperature.
30. The process as claimed in claim 17, wherein frigories are
supplied to the gas mixture which is cooled at at least one
intermediate point of the heat exchanger downstream or upstream of
a point for drawing off at least one portion of the solidified or
liquefied impurity at an intermediate level of the heat
exchanger.
31. The process as claimed in claim 17, wherein the gas mixture is
at least partially liquefied within the heat exchanger and is
withdrawn from the cold end of the heat exchanger.
32. The process as claimed in claim 17, wherein the gas mixture is
cooled downstream and
33. An apparatus for cooling and purifying a gas mixture containing
at least one impurity comprising a heat exchanger comprising at
least one, or even two, exchange bodies, each having cooling
passages designed to reduce the adhesion of the solidified impurity
on at at least one portion of the surface of the passages and
reheating passages, means for sending the gas mixture containing at
least one impurity to be cooled in the cooling passages of the
exchange body or bodies to a temperature below or equal to that at
which the at least one impurity solidifies and means for drawing
off the, optionally at least partially liquefied, gas mixture from
the exchange body or bodies, preferably at the cold end, means for
sending a gas to be reheated in the reheating passages and means
for collecting at least one portion of the solidified impurity
leaving the cooling passages of the heat exchanger and/or at an
intermediate level of the heat exchanger and means for taking the
gas mixture of the at least one impurity out of the heat exchanger,
wherein the cooling passages of each exchange body are at least
partially covered by a coating and/or physically treated and/or
chemically treated, the coating and/or the treatment serving to
limit, or even prevent, the formation and/or the adhesion of the
solidified impurity on a surface of the passages and in that
reheating passages are connected to means for transporting a first
gas to be reheated and other reheating passages are connected to
means for transporting a second gas to be reheated.
34. The apparatus as claimed in claim 33, wherein the number of
cooling passages is not equal to the number of reheating passages
connected to the means for transporting the first gas and the
number of cooling passages is not equal to the number of reheating
passages connected to the means for transporting the second gas.
Description
[0001] The present invention relates to a method for purifying,
cooling and separating a gas mixture and to an apparatus for
purifying and cooling a gas mixture. When a gas mixture must be
cooled to a temperature below the liquefaction temperature, or even
the solidification temperature of one of the gaseous components
that it contains, this poses particular problems. If the heat
exchanger used for cooling the gas mixture is, for example, a
plate-fin exchanger comprising passages in which the gas mixture is
cooled, these passages risk being obstructed by the formation of
solids on the walls of the passages.
[0002] This problem is particularly well known to air separation
specialists since conventionally 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 passages of a first
exchanger. Before the blocking of these passages, the air was sent
to another heat exchanger in order to be cooled while the first
heat exchanger was reheated by passing nitrogen therethrough in
order to melt then vaporize the water and remove the carbon
dioxide.
[0003] These systems were abandoned several decades ago in order to
be replaced by a purification upstream of the heat exchanger. In
this strategy that has become common, the air is dried and
decarbonated by an adsorption process in front-end purification and
then cooled.
[0004] One object of the present invention is to propose an
alternative to the conventional strategies for the purification and
cooling, or even liquefaction, of a gas mixture.
[0005] One object of the present invention is to propose an
alternative to the conventional purification strategies for air
separation units and for other separation and/or liquefaction
units, operating at low temperature. Among these liquefaction
units, mention may be made of air liquefaction units (for example
for storing energy, units for liquefaction of a gas produced by
separating air, for example nitrogen and units for liquefaction of
natural gas. Other examples of separation units comprise for
example the units for separating a mixture of carbon dioxide
containing at least 30% carbon dioxide and also hydrogen and/or
methane and/or oxygen and/or carbon monoxide at subambient
temperature. The separation units may also be units for the
cryogenic separation 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.
[0006] The study of new surface treatment technologies makes it
possible to envisage drying and/or decarbonating the air directly
in the main exchanger in such a way that the water condensed then
frozen and/or the frozen CO.sub.2 have a reduced adhesion or even
so that they no longer adhere to the walls of this exchanger and
therefore so that the clogging increases until the passages on the
air side of the exchanger are blocked.
[0007] It is known to treat surfaces or cover them with a coating
in fields very different from the low-temperature separation of a
gas mixture, in particular to reduce, or even prevent, the adhesion
of ice or frost on metal surfaces exposed to atmospheric elements,
such as aircraft, wind turbines and pylons. These surfaces may
also, in certain cases, reduce the amount of ice formed.
[0008] A large number of surface treatments make it possible to
reduce the adhesion of ice. These are treatments referred to as
"passive anti-ice treatments" which in general are based on
silicone or fluorocarbon polymers (non-exhaustive list) as
described in US-A-2013/0305748.
[0009] For example, polytetrafluoroethylene, PTFE, also known under
the name Teflon.RTM., allows a weak adhesion of ice owing to a low
surface tension as described in M. G. Ferrick, N. D. Mulherin, B.
A. Coutermarsh, G. D. Durell, L. A. Curtis, T. L. St. Clair, E. S.
Weiser, R. J. Cano, T. M. Smith, C. G. Stevenson and E. C.
Martinez, Journal of Adhesion Science and Technology, 26 (2012)
473. The polysiloxane-based NUSIL.RTM. R2180 coating also makes it
possible to significantly reduce the adhesion of ice.
[0010] Similar results have been obtained using another coating
based on (DLC or examples of coatings that make it possible to
limit the adhesion of ice to aluminum alloys are reported by Menini
et al., Cold Regions Science and Technology, 65 (2011) 65.
[0011] In most cases, these treatments increase the hydrophobicity
of the surfaces, which makes it possible to increase the contact
angle of water on these surfaces and therefore to reduce the
interactions between water and the surface. Thus, the surfaces that
make it possible to reduce the adhesion of ice are in general
hydrophobic or superhydrophobic as described in L. Foroughi
Mobarakeh, R. Jafari and M. Farzaneh, Applied Surface Science, 284
(2013) 459.
[0012] It is also possible to reduce the adhesion of ice using
heterogeneous surfaces comprising both hydrophobic and hydrophilic
zones as described in WO-A-05075112. In this case, the treatment
makes it possible to properly control the water crystallization
zones, which facilitates the elimination of the ice with the aid of
a flushing of gas or liquid.
[0013] Another type of surface makes it possible to reduce the
adhesion of the ice, these are lubricated surfaces. The surface is
impregnated with a lubricant which may be based on fluorocarbons
such as Krytox.RTM. or on silicone oils as described in
WO-A-2012/100100 and US-A-2006/0281861.
[0014] With such surfaces, the ice is in contact with the
lubricant, i.e. a liquid phase, thus the adhesion forces are very
weak. The lubricant also has another advantage, it makes it
possible to improve the erosion resistance of the surfaces.
[0015] In the example cited so far, the surface coatings make it
possible to reduce the adhesion of the ice. Another type of surface
that may prove advantageous within the context of this invention
are the coatings referred to as "active anti-ice coatings" that
make it possible to slow down the formation of the ice.
[0016] It is known that it is possible to lower the ice formation
temperature using salt or glycol-type compounds. It turns out that
a similar phenomenon may take place when a polymer-type compound,
in general a hygroscopic polymer, is grafted to a surface.
[0017] This type of coating may lower the ice formation temperature
and reduce the amount of ice formed. The best known coatings in
this regard are of glycol type (US-A-2010/0086789) but anti-frost
coatings inspired by the structure of proteins have a similar
effect as described in L. Makkonen, Journal of Adhesion Science and
Technology, 26 (2012) 413.
[0018] Finally, certain treatments make it possible to combine two
effects: modifying the type of frost and reducing its adhesion as
described by J. Chen, R. Dou, D. Cui, Q. Zhang, Y. Zhang, F. Xu, X.
Zhou, J. Wang, Y. Song and L. Jiang, ACS Applied Materials and
Interfaces, 5 (2013) 4026. This is the case for microstructured
surfaces comprising a hydroscopic polymer matrix (based on
polyacrylic acid for example). These surfaces make it possible to
easily eliminate the ice formed and have the advantage of using
water as lubricant, thus the surface is self-supplied with
lubricant with the aid of the humidity contained in the air.
[0019] It is also known to limit, or even prevent the formation of
frost by heating, for example with the Joule effect or pneumatic
pulsation systems.
[0020] There are also techniques with a gas stream with a
sufficient flow or an input of mechanical and/or electrical energy,
which may be combined with a coating and/or a treatment in order to
easily detach the impurities, the adhesion of which has been
reduced.
[0021] A person skilled in the art who is a specialist in
low-temperature purification and cooling or separation or
liquefaction processes is not abreast with developments relating to
the surface treatments and the coatings used for limiting, or even
preventing the formation and/or the adhesion of ice on a surface. A
portion of the present invention results from the realization that
these techniques may be applied to the field of cooling and
purification, for example used upstream of a separation or a
liquefaction, for example a distillation, at low temperature or
another process operating at low temperature.
[0022] GB-A-917286 describes a low-temperature separation process
in which a gas containing carbon dioxide is cooled by two
exchangers in rotation, each allowing a heat exchange between only
two fluids and each comprising a zone designed to avoid the
deposition of carbon dioxide.
[0023] In this case, as the passages intended to cool the gas to be
separated during a first period are also used to reheat a separated
gas during a second period, it is necessary to provide the same
number of passages and the same type of fins in the exchanger in
order to obtain a symmetrical operation during the two operating
periods.
[0024] The heat exchanger from GB-A-917286 inevitably consists of
at least two exchange bodies and cannot be a monoblock body.
[0025] A low-temperature separation takes place at at most
0.degree. C., or even at at least -50.degree. C., or even at at
least -100.degree. C., depending on the gas mixture to be
separated.
[0026] The "hot end" is the portion of the heat exchanger that is
found operating at a maximum mean temperature. The "cold end" is
that portion of the heat exchanger that is found operating at a
minimum mean temperature.
[0027] A heat exchanger is a single exchange body or a plurality of
exchange bodies, capable of carrying out a heat exchange.
[0028] The gas mixture to be cooled enters at the hot end of the
exchanger and leaves therefrom, generally at the cold end.
[0029] Generally, a heat exchanger is mounted so that its hot end
is found toward the top and its cold end toward the bottom. In
certain cases, as described later on, the present invention may
necessitate placing the hot end at the bottom and the cold end at
the top.
[0030] The heat exchanger is generally placed inside a thermally
insulated cold box. Other elements of a separation apparatus may
also be found in the cold box, for example a distillation
column.
[0031] The conclusions regarding the purification of a gas
containing water and CO.sub.2 are that the purification of the gas
by condensation/solidification is more energetically efficient than
adsorption. It also makes it possible to eliminate or reduce in
size the apparatus used according to the prior art, for example the
apparatus for purification particular advantages since being colder
at the outlet of the exchanger, the CO.sub.2, and especially a
portion of the secondary impurities, are stopped even better, which
makes it possible to simplify, or even eliminate the downstream
purifications and/or to simplify the design and/or the operation of
certain downstream equipment (for example the vaporizers).
[0032] According to one subject of the invention, a process is
provided for cooling, purifying and separating a gas mixture
containing at least one impurity, wherein the gas mixture
containing at least one impurity is cooled to a temperature below
or equal to 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
on a surface of the passages, at least one portion of the
solidified impurity leaving the cooling passages of the heat
exchanger and/or at an intermediate level of the heat exchanger is
collected and the gas mixture, optionally at least partially
liquefied, is drawn off from the heat exchanger, preferably at the
cold end, the gas mixture is optionally cooled again and the gas
mixture is sent to a system of columns in order to be separated by
distillation at low temperature, or even cryogenic temperature, in
order to produce two fluids, each enriched in one component of the
gas mixture, characterized in that the cooling passages are at
least partially covered by a coating and/or physically treated
and/or chemically treated, the coating and/or the treatment serving
to limit, or even prevent, the formation and/or the adhesion of the
solidified impurity on a surface of the passages, and in that
[0033] i) during substantially the entire time that the separation
by distillation is carried out, the gas mixture is cooled in each
exchange body having cooling passages designed to reduce the
adhesion of the solidified impurity on a surface of the passages
and/or
[0034] ii) the two fluids, each enriched in one component of the
mixture, are reheated in each exchange body having cooling passages
designed to reduce the adhesion of the solidified impurity on a
surface of the passages.
[0035] According to other optional aspects: [0036] the gas mixture
drawn off contains at least one portion of the solidified impurity,
[0037] the gas mixture comprises at least one component, preferably
a major component, that is not solidified and optionally that is
not liquefied in the heat exchanger, [0038] the gas mixture
comprises at least two components, preferably major components,
that are not solidified and optionally that are not liquefied in
the heat exchanger, [0039] an impurity is a component that
represents no more than 10 mol % or 5 mol % or even 1 mol %, or
even 0.1 mol %, or even 0.01 mol % of the gas mixture, [0040] the
gas mixture is purified to remove at least one 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
gas mixture upstream of the process, [0041] the gas mixture is not
purified to remove at least one fraction of the at least one
impurity upstream of the heat exchanger, [0042] at least one
portion of the solidified impurity is collected downstream of the
heat exchanger, by means of a phase separator and/or an endless
screw, [0043] the cooling passages are at least partially modified
physically, the treatment serving to limit, or even prevent, the
formation and/or the adhesion of the solidified impurity on a
surface of the passages, [0044] the cooled gas mixture is treated
downstream of the heat exchanger and/or at at least one
intermediate level of the heat exchanger in order to eliminate the
impurity in gaseous and/or liquid and/or solid form, [0045] the
cooled gas mixture is treated only downstream of the heat exchanger
and not at at least one intermediate level of the heat exchanger in
order to eliminate the impurity in gaseous and/or liquid and/or
solid form, [0046] the cooled gas mixture is treated only at at
least one intermediate level of the heat exchanger and not
downstream of the heat exchanger in order to eliminate the impurity
in gaseous and/or liquid and/or solid form, [0047] the gas mixture
is cooled in the heat exchanger firstly to a temperature below or
equal to the liquefaction temperature of the at least one impurity
but above its solidification temperature, the gas mixture is taken
out of the exchanger in order to eliminate a portion of the
impurity in liquid form and the gas mixture containing some
impurity is sent back to the heat exchanger in order to cool it to
the solidification temperature of this impurity, [0048] 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, referred
to as the hot end, is eliminated by collecting it at at least one
intermediate point of the heat exchanger after cooling, in solid
and/or liquid form, [0049] 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, referred to as the hot end, is eliminated by
collecting it at at least one intermediate point of the heat
exchanger after cooling, in solid and/or liquid form, [0050] 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 heat exchanger, referred to as
the hot end, is eliminated by collecting it downstream of the heat
exchanger after cooling up to the outlet of the exchanger at the
cold end, [0051] at most 50%, or even at most 30%, or even at most
10%, or even at most 1%, or even at most 0.1%, or even at most
0.01% of the impurity present at the inlet of the heat exchanger,
referred to as the hot end, is eliminated by collecting it
downstream of the heat exchanger after cooling up to the outlet of
the exchanger at the cold end, [0052] 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, upstream of the inlet of the heat exchanger,
referred to as the hot end, is eliminated, [0053] 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, upstream of the inlet of the heat
exchanger, referred to as the hot end, is eliminated, [0054] the
hot end of the heat exchanger is placed at a higher level than that
of the cold end, [0055] the hot end of the heat exchanger is placed
at a lower level than that of the cold end or than 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 gas mixture to be cooled is eliminated at the
inlet of the heat exchanger, referred to as the hot end, by
collecting it in solid or liquid form at the hot end of the
exchanger where it drops by gravity after cooling in the heat
exchanger (since its adhesion to the walls is limited), [0056] the
hot end of the heat exchanger is placed at the same level as that
of the cold end in the case of an inverted U-shaped exchanger,
[0057] the gas mixture is air or a mixture having, as 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
having, as main component, 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, [0058] at
least one surface of the cooling passages has been treated to make
it rougher and/or to lubricate it and/or to make it hydrophilic
and/or hydrophobic and/or hydroscopic and/or hygroscopic in order
to limit, or even prevent, the formation and/or the adhesion of
solidified impurities, for example ice, [0059] the heat exchanger
may comprise passages, at least one section of which has a
treatment and/or a coating and/or a geometry and/or, in the case of
a plate-fin exchanger, a type of fin that differs from that of
another section that has to operate at a lower temperature range,
[0060] the heat exchanger may comprise passages, at least one
section of which has a treatment and/or a coating and/or a geometry
and/or, in the case of a plate-fin exchanger, a type of fin that
differs from that of another section that is found downstream of an
intermediate point for drawing off solidified impurities, [0061]
the gas mixture is purified and cooled by a process as described
above, optionally cooled again and sent to a system of columns in
order to be separated by distillation at low temperature, or even
cryogenic temperature, in order to produce at least one fluid
enriched in one component of the gas mixture, [0062] the fluid
enriched in one component of the gas mixture is reheated in the
heat exchanger in the reheating passages, [0063] the heat exchanger
comprises at least one passage for reheating a fluid, the at least
one reheating passage not having been treated or coated in order to
limit, or even prevent, the formation and/or the adhesion of
solidified impurities, for example ice, [0064] at least one portion
of the solidified impurity leaving the cooling passages of the heat
exchanger is sent back to the heat exchanger to be reheated, [0065]
at least one portion of the solidified impurity is mixed with
another gas before being reheated in the heat exchanger, [0066] the
at least one reheating passage to which the solidified impurities
are sent has been treated or coated in order to limit, or even
prevent, the formation and/or the adhesion of solidified
impurities, for example ice, [0067] at least one portion of the
solidified impurity leaving the cooling passages of the heat
exchanger and/or at an intermediate level of the heat exchanger is
collected and the gas mixture finds itself liquefied or is
liquefied by a subsequent step downstream of the exchanger and/or
is separated at a subambient temperature downstream of the
exchanger, optionally after elimination, downstream of the
exchanger, of remaining impurities that would be solidified at this
subambient temperature, [0068] frigories are supplied to the gas
mixture which is cooled at at least one intermediate point of the
heat exchanger, [0069] frigories are supplied to the gas mixture
which is cooled at at least one intermediate point of the heat
exchanger, preferably downstream or upstream of a point for drawing
off at least one portion of the solidified or liquefied impurity at
an intermediate level of the heat exchanger, [0070] frigories are
supplied to the gas mixture which is at a temperature between
-5.degree. C. and 5.degree. C., [0071] frigories are supplied to
the gas mixture which is at a temperature between -20.degree. C.
and -30.degree. C., [0072] frigories are supplied to the gas
mixture by taking at least one portion of the gas mixture out of
the heat exchanger and by cooling it, [0073] frigories are supplied
to the gas mixture by means of a refrigerant fluid sent to an
intermediate level of the heat exchanger, [0074] the gas mixture is
cooled in the heat exchanger continuously, [0075] the gas mixture
is cooled in the heat exchanger intermittently, [0076] the heat
exchanger cools the gas mixture up to the cold end to a temperature
below 0.degree. C., or even below -50.degree. C., or even below
-100.degree. C., [0077] the gas mixture is at atmospheric pressure
or a pressure above atmospheric pressure, [0078] the heat exchanger
comprises only a single exchange body and is a monoblock exchanger,
[0079] the heat exchanger comprises at least two exchange bodies,
[0080] the gas mixture is cooled in cooling passages, the number of
which is not equal to the number of reheating passages connected to
the means for transporting the first gas, [0081] the gas mixture is
cooled in cooling passages, the number of which is not equal to the
number of reheating passages connected to the means for
transporting the second gas.
[0082] Each of the above features may be combined with each of the
others above except in the case of an obvious incompatibility.
[0083] 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 by passage of the gas mixture at a
sufficient flow rate (its nominal flow rate or a higher flow rate)
and/or at high pressure relative to the flow rate and/or pressure
that are used during the cooling or by mechanical means, for
example by variation of the gas mixture flow rate or pulses of the
gas mixture flow rate, or else vibrations applied directly to the
exchanger.
[0084] According to one subject of the invention, an apparatus is
provided for cooling and purifying a gas mixture containing at
least one impurity comprising a heat exchanger having passages for
cooling the gas mixture and passages for reheating a gas, means for
sending the gas mixture containing at least one impurity to be
cooled in the heat exchanger to a temperature below or equal to
that at which the at least one impurity solidifies and means for
drawing off the, optionally at least partially liquefied, gas
mixture from the heat exchanger, preferably at the cold end and
means for collecting at least one portion of the solidified
impurity leaving the cooling passages of the heat exchanger and/or
at an intermediate level of the heat exchanger and means for taking
the gas mixture of the at least one impurity out of the heat
exchanger, characterized in that the cooling passages are at least
partially covered by a coating and/or physically treated and/or
chemically treated, the coating and/or the treatment serving to
limit, or even prevent, the formation and/or the adhesion of the
solidified impurity on a surface of the passages and in that the
apparatus comprises a single heat exchanger connected to means for
collecting at least one portion of the solidified impurity, this
heat exchanger being a monoblock heat exchanger.
[0085] According to other optional aspects: [0086] the apparatus
comprises reheating passages for a first gas and reheating passages
for a second gas, [0087] the apparatus comprises means for
purifying the gas mixture upstream of the heat exchanger in order
to remove at least one fraction of the at least one impurity,
[0088] the means for collecting at least one portion of the
solidified impurity downstream of the heat exchanger are
constituted by a phase separator and/or an endless screw, [0089]
the heat exchanger is constituted by at least one plate-fin
exchanger, [0090] the heat exchanger is constituted by at least two
plate-fin exchangers made of aluminum or made of copper or made of
titanium, [0091] the heat exchanger is constituted by at least one
coil exchanger, [0092] the heat exchanger is constituted by at
least one shell and tube exchanger, [0093] the apparatus comprises
means for treating the cooled gas mixture downstream of the heat
exchanger and/or at at least one intermediate level of the heat
exchanger in order to eliminate the impurity in gaseous and/or
liquid and/or solid form, [0094] the hot end of the heat exchanger
is placed at a higher level than that of the cold end, [0095] the
hot end of the heat exchanger is placed at a lower level than that
of the cold end or than 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 gas
mixture to be cooled is eliminated at the inlet of the heat
exchanger, referred to as the hot end, by collecting it in solid or
liquid form at the hot end of the exchanger where it drops by
gravity after cooling in the heat exchanger, [0096] 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 surface that is hydrophobic
and/or superhydrophobic and/or that has hydrophobic and
hydrophilic, and/or hygroscopic zones, in order to limit, or even
prevent, the formation and/or the adhesion of solidified
impurities, for example ice, [0097] the surface of a passage may or
may not be impregnated with a lubricant, [0098] the exchanger
comprises at least one passage for reheating a fluid and at least
one surface of the at least one reheating passage has been treated
to make it rougher and/or to lubricate it and/or to make it
hydrophilic and/or hydrophobic and/or hydroscopic and/or
hygroscopic in order to limit, or even prevent, the formation
and/or the adhesion of solidified impurities, for example ice.
[0099] According to another aspect of the invention, an apparatus
is provided for separation by distillation at low temperature, or
even cryogenic temperature, comprising a cooling and purification
apparatus as described above and also a system of columns and means
for sending the gas mixture purified and cooled by the cooling and
purification apparatus to the system of columns.
[0100] The separation apparatus may not comprise means for cooling
the gas mixture downstream of the cooling and purification
apparatus.
[0101] The apparatus may comprise means for sending a fluid
enriched in one component of the gas mixture to be reheated in the
heat exchanger in reheating passages.
[0102] According to other optional features: [0103] the heat
exchanger comprises at least one passage for reheating a fluid, the
at least one reheating passage not having been treated or coated in
order to limit, or even prevent, the formation and/or the adhesion
of solidified impurities, for example ice, [0104] the apparatus
comprises means for sending at least one portion of the solidified
impurity leaving the cooling passages of the heat exchanger to the
heat exchanger in order to be reheated, [0105] means for mixing at
least one portion of the solidified impurity with another gas
before being reheated in the heat exchanger, [0106] the at least
one reheating passage to which the solidified impurities are sent
has been treated or coated in order to limit, or even prevent, the
formation and/or the adhesion of solidified impurities, for example
ice.
[0107] The separation and purification apparatus may comprise means
for supplying frigories to the gas mixture which is cooled at at
least one intermediate point of the heat exchanger.
[0108] The separation and purification apparatus may comprise means
for supplying frigories to the gas mixture which is cooled at at
least one intermediate point of the heat exchanger, preferably
downstream and/or upstream of a point for drawing off at least one
portion of the solidified or liquefied impurity at an intermediate
level of the heat exchanger.
[0109] The separation and purification apparatus may comprise means
for supplying frigories to the gas mixture by taking at least one
portion of the gas mixture out of the heat exchanger.
[0110] The separation and purification apparatus may comprise means
for supplying frigories to the gas mixture by means of a
refrigerant fluid sent to an intermediate level of the heat
exchanger.
[0111] In all the strategies for separation by liquefaction and
condensation of the impurities, the issue is to compensate for the
phase change enthalpies of the various constituents by input of
energy (here refrigeration make-up) via devices external to the
main exchanger (example: heat pump, refrigerating unit).
[0112] If no refrigeration make-up is made, the exchange graph is
moved apart at the cold end as is seen in FIG. 11.
[0113] In the curve from FIG. 11, the curvature caused by the
condensation then the solidification of water (moist air at 1.4
bara) is observed. FIG. 12 is a graph that is "compensated for" by
sufficient refrigeration make-ups.
[0114] The case of FIG. 12 is a simulation of the condensation then
the solidification of water combined with the solidification of
CO.sub.2.
[0115] The invention will be described in greater detail by
referring to FIGS. 1 to 10 which schematically represent processes
according to the invention.
[0116] Detailed here are process diagrams to which the concept of
the invention could be applied. They are diagrams of a
single-column, low-pressure air separation unit. They could be
transposed to other separation and/or liquefaction processes, such
as cryogenic separation processes for the H.sub.2/CO mixture as
explained above.
[0117] Represented in FIG. 1 is a process for separating air by
cryogenic distillation using a brazed aluminum plate-fin heat
exchanger 3 and a single distillation column 27. This process
enables the production of an oxygen-enriched liquid 43, an
oxygen-enriched gas 45 and a nitrogen-enriched gas 47. The use of a
brazed aluminum plate-fin heat exchanger is not essential. This
exchanger may use other technologies and may for example be a coil
exchanger or a shell and tube exchanger.
[0118] The air to be separated 1 contains water and carbon dioxide,
which must be purified upstream of the distillation. After
filtering through 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 referred to as an "exchange line" without
passing through beds of adsorbents conventionally present in an air
separation apparatus. It can be envisaged to eliminate a portion of
the water contained in the air by separating the water that is
condensed, during the 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
the water on the one hand then the remainder of the water and the
CO.sub.2 on the other hand are carried out at two different
locations in the exchange line 3. A large portion of the water is
removed in liquid form (around 75% of the water present in the air
1 on arriving in the exchanger 3, after compression followed by a
cooling step) at a temperature close to 0.degree. C.: the air 5 at
this location is drawn off by separating the air and the water 5B
in a phase separator 2 then the dried air 5A is reinjected in order
to finish the cooling thereof and to carry out the same separation
at its outlet from the exchange line 3 with the remainder of the
water and the CO.sub.2 this time, the two being solid. To
compensate for the latent heat of liquefaction and of condensation
of the impurities, two refrigeration make-ups are necessary via two
heat pumps, for example at 0.degree. C. and at -25.degree. C.
[0119] Thus air 7 drawn off at an intermediate level of the
exchange line 3 is cooled by means of a first heat pump 4 and the
cooled air is sent back to the exchange line 3.
[0120] Next air 11 drawn off at a colder intermediate level of the
exchange line 3 is cooled by a second heat pump 6 supplied by a
fluid 13. The cooled air 11A is sent back to the exchange line.
[0121] The air already purified of water and cooled in two steps 15
contains ice and solid carbon dioxide and is sent to a phase
separator 17 and the ice and the solid carbon dioxide 19 are
removed.
[0122] The walls of the cooling passages are treated in order to
limit, even prevent, the formation and/or the adhesion of ice and
of carbon dioxide to the surfaces, at least in the regions where
the temperature of the passage is anticipated to be below the
solidification temperature of the water and/or of the carbon
dioxide.
[0123] This treatment may be a physical treatment of the surface or
the installation of water and solid 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.
[0124] A portion of the secondary impurities of the air (in
particular propane, acetylene, propylene, C4+, N.sub.2O) are also
separated in the separator 17 at the cold end of the exchanger,
either in solid form, or in liquid form.
[0125] The purified air 20 is divided into two portions 23, 25. The
portion 23 is sent to the middle of the single distillation column
27 where it is separated to form nitrogen-enriched gas 47 at the
top of the column and an oxygen-enriched liquid 43 at the bottom of
the column 27.
[0126] The portion 15 of the air is condensed at least partially in
a heat exchanger 59 by heat exchange with a flow of fluid 57 that
is cooled by means of a heat pump 21 using the magnetocaloric
effect.
[0127] A cooling fluid 53, typically ambient air or cooling water
is sent to the heat pump 21 using the magnetocaloric effect.
Reheated water 55 leaves the heat pump 21.
[0128] The column comprises a bottom reboiler 29 and an overhead
condenser 31. The reboiler is heated by means of a fluid circuit 41
in connection with a heat pump 33 using the magnetocaloric effect.
This heat pump 33 using the magnetocaloric effect also serves to
cool a fluid 37 which cools the overhead condenser 31. The fluids
37 and 41 may be identical or different. An oxygen-enriched liquid
43 is drawn off at the bottom of the column 19 and a
nitrogen-enriched gas drawn off via a pipe 47 is reheated in the
exchanger 3 and is not used to regenerate a purification unit since
there is none. An oxygen-enriched gas 45 is drawn off at the bottom
of the column 27, is reheated in the exchanger 3 and is compressed
by a compressor 49.
[0129] FIG. 1a illustrates a variant of FIG. 1 in which the heat
exchanger 3 is constituted by two exchange bodies 3a, 3b. Each of
the bodies 3a, 3b is a plate-fin exchanger as described above but
other technologies may be envisaged.
[0130] Unlike FIG. 1, throughout the duration of the distillation,
the air 1 is divided into two flows, one of which is sent to the
body 3a and the other to the body 3b. Each impurity on a surface of
the passages. The cooling passages of each body 3a,3b are at least
partially covered by a coating and/or physically treated and/or
chemically treated, the coating and/or the treatment serving to
limit, or even prevent, the formation and/or the adhesion of the
solidified impurity on a surface of the passages. It can be
envisaged to use more than two bodies.
[0131] The solidified carbon dioxide and/or the (solidified) water
is collected for both bodies and sent to a single container 17. The
use of several containers can obviously be envisaged.
[0132] The purified air from both bodies is mixed to form the flow
20 and continues its treatment as for FIG. 1.
[0133] The gas 47 is reheated simultaneously in the two exchange
bodies during the distillation, being divided into two upstream of
the bodies 3a, 3b and remixed downstream of these bodies.
[0134] The gas 45 is reheated simultaneously in the two exchange
bodies during the distillation, being divided into two upstream of
the bodies 3a, 3b and remixed downstream of these bodies.
[0135] As each passage only receives one gas to be reheated or one
gas to be cooled and the flows are not reversed during the
distillation, the number of passages dedicated to cooling the air
is not identical to the number of passages intended to reheat the
gas 47 for a given body.
[0136] Illustrated schematically in FIG. 1b is an exchange body
corresponding to a body 3,3a,3b of one of the other figures, where
it is possible to observe that the number of passages dedicated to
the cooling of the gas mixture, here air, is not identical to the
number of passages dedicated to the reheating of a first gas, here
nitrogen NR corresponding to the nitrogen 47 or to the number
dedicated to the reheating of a second gas, here gaseous oxygen
OG.
[0137] In the variant from FIG. 2 and those from FIGS. 3 to 9, the
heat exchanger 3 is a monoblock heat exchanger that cools all the
air intended for the distillation throughout the period where the
distillation takes place. It also reheats all the gas originating
from distillation throughout the period where the distillation
takes place. The extraction of the water on the one hand then the
remainder of the water and the CO.sub.2 on the other hand are also
carried out at two different locations in the exchange line 3.
However, a large portion of the water is removed in solid form
(around 97% of the water present in the air 1 on arriving in the
exchanger 3) at a temperature close to -25.degree. C., therefore in
solid form. The air 5 is drawn off at this location by separating
the air and the ice 5B in a phase separator 2 then the dried air 5A
is reinjected in order to finish the cooling thereof. The air sent
to the separator 2 has already been cooled upstream by a first
refrigeration make-up at 0.degree. C.
[0138] Thus air 7 drawn off at an intermediate level of the
exchange line 3 is cooled firstly by means of a first heat pump 4
and then is removed from the line in order to remove the ice. The
cooled air 5A sent back to the exchange line 3 is again cooled by
the second cooler 6.
[0139] For the case of FIG. 3, the air is firstly cooled in the
exchange line 3, it is taken out of the exchange line and water in
liquid form is removed in the separator 2, next the purified air 5A
is cooled in the exchange line, then by a first cooler 4, then in
the exchange line 3, next 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 up to the cold end.
[0140] It should be noted that in all cases, there may be only a
single refrigeration make-up at the exchange line 3, or even none
at all, if one is ready to sacrifice energy, the necessary
refrigeration make-up then being introduced at the cold end of the
exchanger, where it costs the most.
[0141] In the variant from FIG. 4, the order of the steps of
separation of water and CO.sub.2 and of refrigeration make-ups is
as for FIG. 1. By drawing off liquid water in a first separation at
around 0.degree. C., this liquid water can be used to cool the
machines, for example the compressor C.
[0142] But in this example, the solids or liquids 19 (the remainder
of the water, the CO.sub.2 and other secondary impurities)
collected in the separator 17 are sent to the exchange line 3 in
order to provide refrigeration thereto. This makes it possible to
recover a portion of the latent heat, and therefore to reduce, or
even simplify the necessary refrigeration make-ups.
[0143] In order not to complicate the exchange line, they may be
injected into at least one dry and cold fluid, for example
originating from the cryogenic separation, for example the nitrogen
47 in order to form a mixed flow 61. In this case, it may be
prudent to treat at least certain portions of the nitrogen
reheating passages in order to limit, or even prevent, the
deposition of these solids.
[0144] FIG. 5 illustrates the case where an endless screw system
17A is used in order to extract the impurities in the form of ice
or a mixture of ice/liquid in order to reinject them directly into
the products. This replaces the phase separator 17 from the other
figures.
[0145] Other means may be envisaged for removing the solid
impurity, which may be released to the atmosphere. The heat
exchanger may cool the gas containing at least one impurity
periodically and the impurity may be melted, for example while the
heat exchanger is not operating.
[0146] The solid could also be evacuated by consenting to lose a
portion of the gas mixture that then transports the solid, with a
pneumatic style transportation.
[0147] FIG. 6 is a variant where all of the water and CO.sub.2
present in the air at the hot end are removed at the cold end of
the exchange line. The refrigeration make-up may be provided to
compensate for the condensation and the solidification of the
impurities, and also the cooling thereof throughout the exchange
line with a multitude of heat pumps, here n heat pumps PAC1, PACn
supplied by cooling flows 9, 13. The refrigeration make-up may also
be made with a sliding cold temperature. It may also be limited to
1 or 2 refrigeration make-ups.
[0148] In FIG. 7, a portion of the impurities is removed by a
conventional adsorption separation system A. This portion may
constitute between 20% and 95% of an impurity or of the impurities
present. The purification may be made by means other than
adsorption. Next, the fluid purified of at least one impurity
enters the exchange line where the removal of the remainder of the
impurities by solidification/liquefaction compensate for the latent
heat of liquefaction and condensation of the impurities. It is
possible to reinject the impurities into the products, as seen for
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
refrigeration make-up may be made solely at the cold end of the
exchanger 3.
[0149] In the variant from FIG. 8, another separation system E is
used at the outlet of the fan C in order to remove a portion of the
impurities of the flow, for example in the form of a drying wheel.
Next, 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
the impurities. The frozen water/solid CO.sub.2 and solid/liquid
secondary impurities are recovered at the cold end without
re-injecting them into the products.
[0150] In the case from FIG. 9, for a gas mixture 1 loaded with
water in gaseous form, the water in liquid and/or solid form flows
counter-current to the flow of gas 1, the stream of air 1 entering
through the bottom of the exchanger 3, contrary to the conventional
operation (it is also possible to imagine an inverted U-shaped
exchanger configuration, with hot end and cold end at the bottom,
and an intermediate point at the top).
[0151] Indeed, by solidifying and/or liquefying, the water becomes
heavier and falls counter-current to the gas, which is cooled. It
emerges in liquid form at the hot end of the exchanger 3.
[0152] This variant does not use phase separators but generally
needs supplies of refrigeration at the exchange line.
[0153] Conversely, the cold flows 45, 47 enter through the top of
the exchange line and exit through the bottom.
[0154] For greater clarity, the figure is drawn as if the water
and/or the ice 19 descended through a passage other than the
passage through which they entered, present in the air.
[0155] In fact, the water and/or the ice 19 will exit through the
same passage through which they entered.
[0156] In the variant from FIG. 10, for a mixture containing water,
the exchange line 3 from FIG. 9 is divided into two (exchange line
3 and 3A) in order to draw off the water between the two at an
intermediate temperature. Thus the air cooled in the line 3 with a
supply of refrigeration from the cooler 4 is separated in the phase
separator in order to remove a portion of the water 5B. The
remainder of the water and/or of the ice falls toward the bottom of
the lines 3 and 3A. The at least partially purified air is cooled
in the exchange line 3A with a supply of refrigeration from the
cooler 6 and is then cooled in the line 3A again. The phase
separator 17 is not present in this particular case.
[0157] For the case where the exchange line is divided into two
exchange bodies in series, the two lines 3,3A may be constructed
with the same technology or different technologies (plate-fin
exchanger, coil exchanger, shell and tube exchanger). Similarly, if
the exchange lines are of the same technology, they do not
necessarily have the same construction and may differ by the
dimensions of the passages, the number of passages, the type of
coating and/or treatment used to limit the deposition of solids,
the type of fins use, the material out of which they are
constructed, etc.
[0158] These eleven examples all relate to the separation of air by
distillation in a single column. The invention may be applied to
the cryogenic separation of air by any known system of columns,
other than that described and using any known means of producing
refrigeration, other than those described.
[0159] 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.
[0160] The invention may also be applied to the purification and
cooling of other gas mixtures having at least one impurity capable
of solidifying during the cooling. An impurity is a component that
represents no more than 10 mol % or 5 mol % or even 1 mol %, or
even 0.1 mol %, or even 0.01 mol % of the gas mixture.
[0161] It is applied in particular to other gas mixtures, for
example to mixtures of carbon dioxide containing for example at
least 30% carbon dioxide and water. In this case, the passages of
the exchange line are treated in order to limit, or even prevent,
the deposition of the water and the pressure and the temperature
are chosen in order to avoid the deposition of CO.sub.2. A mixture
of this type may be separated in a process from FIGS. 1 to 10 by
modifying the operating temperatures.
[0162] For all the figures, the supply of refrigeration, if there
is any, may be carried out with any known and suitable means (for
example, magnetocaloric cooler, compression-expansion conventional
refrigerating unit, turbine).
[0163] In the figures, a portion of the gas mixture leaves the
exchange line in order to be cooled in the element supplying
refrigeration while the remainder of the gas mixture continues its
cooling in the exchange line. The portion cooled by the supply of
refrigeration is then mixed with the remainder of the mixture which
has not left the exchange line.
[0164] It is also possible to take the entire gas mixture out of
the exchange line in order to send it to the element supplying
refrigeration and send back the cooled mixture to the exchange
line.
[0165] In the examples from the figures, it is seen that a portion
or several portions 7, 11 of the air leave the exchanger 3 in order
to be cooled and sent back (flows 7A, 11A) to the exchanger. It is
also possible in all or some of the cases to use a heat transfer
fluid in a closed circuit which transfers heat from the heat
exchanger 3 to the cooling means 4,6 and returns to the heat
exchanger in order to supply refrigeration thereto.
[0166] In all cases, it can be envisaged to provide a final
purification downstream of the exchanger and, where appropriate,
downstream of the phase separator or endless screw, in order to
eliminate the remaining impurities in the flow of mixture 20.
[0167] In all cases, the heat exchanger 3 may comprise passages, at
least one section of which has a treatment and/or a coating and/or
a geometry and/or a type of fin, in the case of a plate-fin
exchanger, that differs from that of another section that has to
operate at a lower temperature range.
[0168] For example, the passage section of the exchanger that is at
a temperature between 20.degree. C. and 0.degree. C. will be
treated in one way or will have a coating of one type and the
passage section that is at a temperature between 0.degree. C. and
-60.degree. C. will be treated in another way. The treatment or
coating may be chosen in order to adapt to the type of physical
phenomenon change (gas.fwdarw.liquid, gas.fwdarw.solid,
liquid.fwdarw.solid), or else the type of impurities in question
(for example water/carbon dioxide).
[0169] The heat exchanger 3 may comprise passages, at least one
section of which has a treatment and/or a coating and/or a geometry
and/or a type of fin, in the case of a plate-fin exchanger, that
differs from that of another section that is found downstream of an
intermediate point for drawing off solidified impurities.
[0170] The heat exchanger may be constituted by at least two heat
exchangers made of different materials, for example one brazed
aluminum exchanger and one brazed copper exchanger.
[0171] For all the examples, during substantially the entire time
that the separation by distillation is carried out, the gas mixture
is cooled in each exchange body having cooling passages designed to
reduce the adhesion of the solidified impurity on a surface of the
passages.
* * * * *