U.S. patent application number 13/394874 was filed with the patent office on 2012-07-05 for method and facility for producing oxygen through air distillation.
This patent application is currently assigned to L'AIR LIQUIDE SOCIETE ANONYME POUR L'ETUDE ET L'EXPLOITATION DES PROCEDES GEORGES CLAUDE. Invention is credited to Marie Cognard, Richard Dubettier-Grenier.
Application Number | 20120167622 13/394874 |
Document ID | / |
Family ID | 42238760 |
Filed Date | 2012-07-05 |
United States Patent
Application |
20120167622 |
Kind Code |
A1 |
Cognard; Marie ; et
al. |
July 5, 2012 |
METHOD AND FACILITY FOR PRODUCING OXYGEN THROUGH AIR
DISTILLATION
Abstract
In a method for producing oxygen through the distillation of air
supplied by air at atmospheric pressure so as to produce a first
and second compressed air flow, and through a first purification
unit (5) and a second purification unit (7), the first and second
compressed air flows at different pressures: the first compressed
air flow is sent from a first outlet of the compression means to
the first purifying unit at the first pressure; the first purified
air flow is sent to a column of the column system (15); the second
purified air flow is sent, in an at least partially condensed form,
from the second purifying unit to the column system; an oxygen-rich
liquid is bled off the column system; said oxygen-rich liquid is
vaporized through heat exchange with at least the second purified
air flow.
Inventors: |
Cognard; Marie; (Igny,
FR) ; Dubettier-Grenier; Richard; (La Varenne Saint
Hilaire, FR) |
Assignee: |
L'AIR LIQUIDE SOCIETE ANONYME POUR
L'ETUDE ET L'EXPLOITATION DES PROCEDES GEORGES CLAUDE
Paris
FR
|
Family ID: |
42238760 |
Appl. No.: |
13/394874 |
Filed: |
September 7, 2010 |
PCT Filed: |
September 7, 2010 |
PCT NO: |
PCT/FR2010/051854 |
371 Date: |
March 8, 2012 |
Current U.S.
Class: |
62/645 |
Current CPC
Class: |
F25J 3/04121 20130101;
F25J 2205/62 20130101; F25J 3/0409 20130101; F25J 3/04145 20130101;
F25J 2230/40 20130101; F25J 2230/06 20130101; F25J 2250/42
20130101; F25J 3/04533 20130101; F25J 3/04309 20130101; F25J
3/04018 20130101; F25J 3/04412 20130101; F25J 3/04169 20130101;
F25J 3/04557 20130101; F25J 3/04206 20130101; F25J 3/04957
20130101; F25J 2230/24 20130101; F25J 3/04296 20130101; F25J
2250/40 20130101; F25J 3/04133 20130101; F25J 3/04618 20130101 |
Class at
Publication: |
62/645 |
International
Class: |
F25J 3/04 20060101
F25J003/04 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 10, 2009 |
FR |
0956179 |
Claims
1-14. (canceled)
15. A method for producing oxygen by distilling air in an apparatus
comprising at least one system of columns (15), at least one
exchange line (13), at least one compression means driven by an
electric motor and/or by a steam turbine and supplied with air at
atmospheric pressure to produce one first and one second
pressurized air flow, one first purification unit (5), one second
purification unit (7), the first and second pressurized air flows
leaving the compression means at a first and a second pressure, the
second pressure being higher than the first by at least 0.5 bar,
possibly by at least 5 bar, potentially by at least 10 bar, even by
at least 25 bar, and the second pressure being the highest pressure
of any air flow intended to be fed into the system of columns; in
which method the first pressurized air flow is sent from a first
outlet of the compression means to the first purification unit (5)
substantially at the first pressure in order to produce a first air
flow that is purified in terms of water and in terms of carbon
dioxide, the second pressurized air flow is sent from a second
outlet of the compression means to the second purification unit (7)
substantially at the second pressure in order to produce a second
air flow that is purified in terms of water and in terms of carbon
dioxide, the purified first flow is cooled in the exchange line
(13), possibly at the first pressure, the purified second flow is
cooled in the exchange line (13), possibly at the second pressure,
the purified first air flow is sent from the first purification
unit to one column of the system of columns (15), the purified
second air flow from the second purification unit is sent to one
column of the system of columns (15) at least in partially
condensed form, an oxygen-rich liquid is tapped off from the system
of columns, vaporized, possibly in the exchange line or in an
auxiliary vaporizer (25) by exchanging heat at least with the
purified second flow at the second pressure and is delivered as
product.
16. The method of claim 15, in which the difference in pressure
between the two pressurized air flows is at most 4 bar or possibly
at least 1 bar and at most 3 bar.
17. The method of claim 15, in which the difference in pressure
between the two pressurized air flows is at least 5 bar and at most
30 bar, or possibly at least 15 bar and at most 25 bar.
18. The method of claim 15, in which at least some of the purified
first air flow is sent into the same column of the system of
columns as the purified second air flow.
19. The method of claim 15, in which no part of the second flow is
sent into a reboiler of the system of columns.
20. The method of claim 15, in which the second pressure is higher
than the first by at least 5 bar.
21. The method of claim 15, in which the second pressure is higher
than the first by at least 10 bar.
22. The method of claim 15, in which the second pressure is higher
than the first by at most 25 bar.
23. A facility for producing oxygen by distilling air, comprising
at least one system of columns (15), at least one exchange line
(13), at least one compression means driven by a steam turbine
and/or by an electric motor, the compression means having a first
and a second outlet, one first purification unit (5), one second
purification unit (7), the compression means being designed to be
supplied with air at atmospheric pressure and to produce, from the
first outlet, a first pressurized air flow at a first pressure and
from the second outlet a second pressurized air flow at a second
pressure, the second pressurized air flow being at a pressure that
is higher, by at least 0.5 bar, possibly by at least 5 bar,
potentially by at least 10 bar, even by at least 25 bar, than the
pressure of the first pressurized air flow, a first pipe for
connecting the first outlet to the first purification unit, a
second pipe for connecting the second outlet to the second
purification unit, a third pipe (11) for connecting the first
purification unit to the exchange line, a fourth pipe (9) for
connecting the second purification unit to the exchange line, no
means of boosting the air pressure being connected downstream of
the second purification unit, a fifth pipe connecting the exchange
line to one column of the system of columns, a sixth pipe for
connecting the exchange line to one column of the system of
columns, a pipe (17) for tapping off an oxygen-rich liquid from the
system of columns and for sending to a vaporizer (25), possibly
consisting of the exchange line, means for sending at least part of
the purified second flow to the vaporizer where it condenses and in
which facility there is no means of compressing air between the
first outlet and the first purification unit and there is no means
of compressing air between the second outlet and the exchange line,
or potentially the system of columns.
24. The facility of claim 23, in which the compression means
comprises a first compressor (1) and a second compressor (3), means
for supplying the first compressor and the second compressor with
air at atmospheric pressure, the first and second compressors
possibly being driven by a common steam turbine (39).
25. The facility of claim 23, in which just one of the first and
second air compressors comprises intermediate coolants (isothermal
compression).
26. The facility of claim 25, comprising means for sending air from
the outlet of that one of the two air compressors that does not
have an intermediate coolant to a heat exchanger (31), and means
for sending at least one fluid from the system of columns and/or
water to the exchanger where it is heated up.
27. A method of producing oxygen by distilling air in an apparatus
comprising n systems of columns, where n.gtoreq.2, n exchange lines
(13, 13'), at least one first compressor (1,1') compressing
atmospheric air in order to produce an air flow at a first
pressure, at least one second compressor (3,3') compressing
atmospheric air to produce an air flow at a second pressure, the
first pressure being lower by at least 0.5 bar, possibly by at
least 5 bar, potentially by at least 10 bar, or even by at least 25
bar, than the second pressure, and the second pressure being the
highest pressure of any air pressure intended for distillation, in
which method air at the first pressure is sent from at least one
first compressor to at least one first purification unit (5,5'),
air at the second pressure is sent from at least one second
compressor to at least one second purification unit (7,7'), air at
the first pressure is sent from the first purification unit to at
least two systems of columns (15, 15'), air at the second pressure
is sent from the second purification unit to at least two systems
of columns, and oxygen is produced from at least one of the systems
of columns.
28. A facility for producing oxygen by distilling air in an
apparatus comprising n systems of columns, where n.gtoreq.2, n
exchange lines (13, 13'), at least one first compressor (1,1')
compressing atmospheric air in order to produce an air flow at a
first pressure, at least one second compressor (3,3') compressing
atmospheric air to produce an air flow at a second pressure, the
first pressure being lower by at least 0.5 bar, possibly by at
least 5 bar, potentially by at least 10 bar, or even by at least 25
bar, than the second pressure, at least one first purification unit
(5,5'), at least one second purification unit (7,7'), means for
sending air at the first pressure from the first compressor(s) to
the first purification unit(s), means for sending air at the second
pressure from the second compressor(s) to the second purification
unit(s), means for sending air to at least two systems of columns
(15, 15') from the first purification unit(s) and means for sending
air to the two systems of columns from the second purification
unit(s), in which facility there is no compression means between
the first compressor(s) and the first purification unit(s) and
there is no compression means between the second compressor(s) and
the exchange lines, or potentially the systems of columns.
Description
[0001] The present invention relates to a method and to a facility
for producing oxygen by distilling air. The invention applies for
example to the production of very large quantities of oxygen in
which the oxygen pressure required is in a range comprised, for
example, between 5 and 20 bar. The oxygen is produced in one or
more large-sized air distillation units in which it is advantageous
for the liquid oxygen produced in the distillation unit(s) to be
brought to these pressures using pumps and for the liquid oxygen to
be vaporized by exchange of heat with a calorigenic fluid
compressed to a pressure sufficient to allow the oxygen to
vaporize, this calorigenic fluid typically being pressure boosted
air. The always tricky use of oxygen compressors is thus
avoided.
[0002] It is common practice in such air separation units (ASUs)
for air to be compressed at atmospheric pressure in one or more
main air compressor(s) installed in parallel. The air thus
compressed is cooled by refrigeration means, typically in a range
comprised for example between 5 and 40.degree. C. The air thus
cooled is processed in one or more purification unit(s) in which
impurities such as water, CO.sub.2 and hydrocarbons are, for the
most part, eliminated.
[0003] Some of this air thus purified is sent to a pressure booster
where it undergoes an additional compression step, typically to
beyond 10 bar, and for example constitutes a calorigenic fluid used
to vaporize the product or products such as oxygen.
[0004] The production of large quantities of oxygen by ASUs entails
purifying large quantities of air in the purification units and in
order to do that minimizing the size of these purification units
that are able to process a given volume of air.
[0005] The use of purification units of the concentric bed type
makes it possible to reduce the size of these units, something that
can also be obtained by increasing the pressure of the purified air
in these units, or by lowering the temperature thereof.
[0006] U.S. Pat. No. 5,337,570 describes a method in which two air
flows are purified at different pressures, but one of these flows
then has its pressure boosted to a higher pressure so as to be able
to vaporize a pressurized liquid oxygen flow.
[0007] The present invention seeks to alleviate the defects of the
prior art and may make it possible to reduce the cost of
investments by avoiding the addition of any air pressure booster
after the purification unit(s) and instead to have equivalent
compression prior to the step of purifying the air in the
purification unit(s).
[0008] The purification units will process two air flows at two
different pressures, the first air flow at a first pressure of
between 5 and 9 bar or potentially of between 2 and 4 bar and the
second air flow at a second pressure of between 11 and 50 bar or
potentially of between 4.5 and 8 bar.
[0009] One subject of the invention is a method for producing
oxygen by distilling air in an apparatus comprising at least one
system of columns, at least one exchange line, at least one
compression means driven by an electric motor and/or by a steam
turbine and supplied with air at atmospheric pressure to produce
one first and one second pressurized air flow, one first
purification unit, one second purification unit, the first and
second pressurized air flows leaving the compression means at a
first and a second pressure, the second pressure being higher than
the first by at least 0.5 bar, possibly by at least 5 bar,
potentially by at least 10 bar, even by at least 25 bar, and the
second pressure being the highest pressure of any air flow intended
to be fed into the system of columns; in which method the first
pressurized air flow is sent from a first outlet of the compression
means to the first purification unit substantially at the first
pressure in order to produce a first air flow that is purified in
terms of water and in terms of carbon dioxide, the second
pressurized air flow is sent from a second outlet of the
compression means to the second purification unit substantially at
the second pressure in order to produce a second air flow that is
purified in terms of water and in terms of carbon dioxide, the
purified first flow is cooled in the exchange line, possibly at the
first pressure, the purified second flow is cooled in the exchange
line, possibly at the second pressure, the purified first air flow
is sent from the first purification unit to one column of the
system of columns, the purified second air flow from the second
purification unit is sent to one column of the system of columns at
least in partially condensed form, an oxygen-rich liquid is tapped
off from the system of columns, vaporized, possibly in the exchange
line or in an auxiliary vaporizer by exchanging heat at least with
the purified second flow at the second pressure and is delivered as
product.
[0010] According to other subjects of the invention; [0011] The
difference in pressure between the two pressurized air flows is at
most 4 bar or possibly at least 1 bar and at most 3 bar. [0012] The
difference in pressure between the two pressurized air flows is at
least 5 bar and at most 30 bar, or possibly at least 15 bar and at
most 25 bar. [0013] At least some of the purified first air flow is
sent into the same column of the system of columns as the purified
second air flow. [0014] No part of the second flow is sent into a
reboiler of the system of columns. [0015] The second pressure is
higher than the first by at least 5 bar. [0016] The second pressure
is high than the first by at least 10 bar. [0017] The second
pressure is higher than the first by at most 25 bar. [0018] The
flow at the second pressure enters one column of the system of
columns and is not used to heat a reboiler of the system of
columns.
[0019] Another subject of the invention is a facility for producing
oxygen by distilling air, comprising at least one system of
columns, at least one exchange line, at least one compression means
driven by a steam turbine and/or by an electric motor, the
compression means having a first and a second outlet, one first
purification unit, one second purification unit, the compression
means being designed to be supplied with air at atmospheric
pressure and to produce, from the first outlet, a first pressurized
air flow at a first pressure and from the second outlet a second
pressurized air flow at a second pressure, the second pressurized
air flow being at a pressure that is higher, by at least 0.5 bar,
possibly by at least 5 bar, potentially by at least 10 bar, even by
at least 25 bar, than the pressure of the first pressurized air
flow, a first pipe for connecting the first outlet to the first
purification unit, a second pipe for connecting the second outlet
to the second purification unit, a third pipe for connecting the
first purification unit to the exchange line, a fourth pipe for
connecting the second purification unit to the exchange line, no
means of boosting the air pressure being connected downstream of
the second purification unit, a fifth pipe connecting the exchange
line to one column of the system of columns, a sixth pipe for
connecting the exchange line to one column of the system of
columns, a pipe for tapping off an oxygen-rich liquid from the
system of columns and for sending to a vaporizer (25), possibly
consisting of the exchange line, means for sending at least part of
the purified second flow to the vaporizer where it condenses and in
which facility there is no means of compressing air between the
first outlet and the first purification unit and there is no means
of compressing air between the second outlet and the exchange line,
or potentially the system of columns.
[0020] According to other aspects of the invention: [0021] The
compression means comprises a first compressor and a second
compressor, means for supplying the first compressor and the second
compressor with air at atmospheric pressure, the first and second
compressors possibly being driven by a common steam turbine. [0022]
Just one of the first and second air compressors comprises
intermediate coolants (isothermal compression). [0023] Means for
sending air from the outlet of that one of the two air compressors
that does not have an intermediate coolant to a heat exchanger, and
means for sending at least one fluid from the system of columns
and/or water to the exchanger where it is heated up.
[0024] Another subject of the invention is a method of producing
oxygen by distilling air in an apparatus comprising n systems of
columns, where n.gtoreq.2, n exchange lines, at least one first
compressor compressing atmospheric air in order to produce an air
flow at a first pressure, at least one second compressor
compressing atmospheric air to produce an air flow at a second
pressure, the first pressure lower by at least 0.5 bar, possibly by
at least 5 bar, potentially by at least 10 bar, or even by at least
25 bar, than the second pressure, and the second pressure being the
highest pressure of any air pressure intended for distillation, in
which method air at the first pressure is sent from at least one
first compressor to at least one first purification unit, air at
the second pressure is sent from at least one second compressor to
at least one second purification unit, air at the first pressure is
sent from the first purification unit to at least two systems of
columns, air at the second pressure is sent from the second
purification unit to at least two systems of columns, and oxygen is
produced from at least one of the systems of columns.
[0025] Another subject of the invention is a facility for producing
oxygen by distilling air in an apparatus comprising n systems of
columns, where n.gtoreq.2, n exchange lines, at least one first
compressor compressing atmospheric air in order to produce an air
flow at a first pressure, at least one second compressor
compressing atmospheric air to produce an air flow at a second
pressure, the first pressure lower by at least 0.5 bar, possibly by
at least 5 bar, potentially by at least 10 bar, or even by at least
25 bar, than the second pressure, at least one first purification
unit, at least one second purification unit, means for sending air
at the first pressure taken from the first compressor(s) to the
first purification unit(s), means for sending air at the second
pressure taken from the second compressor(s) to the second
purification unit(s), means for sending air to at least two systems
of columns from the first purification unit(s) and means for
sending air to the two systems of columns from the second
purification unit(s), in which facility there is no compression
means between the first compressor(s) and the first purification
unit(s) and there is no compression means between the second
compressor(s) and the exchange lines, or potentially the systems of
columns.
[0026] For preference, there is no means of connecting the outlet
of (one of) the first compressor(s) to the outlet of (one of) the
second compressor(s) and/or there is no means of connecting the
outlet of (one of) the first purification unit(s) to the outlet of
(one of) the second purification unit(s).
[0027] Thus, there is an independent circuit supplied by at least
two compressors producing air at the first pressure and an
independent circuit supplied by at least two compressors producing
air at the second pressure, each of the two circuits supplying at
least two independent systems of columns.
[0028] Some embodiments will now be described in relation to the
attached drawings which depict air separation facilities according
to the invention.
[0029] The facility depicted in FIG. 1 is intended to supply oxygen
to one or more iron smelting-reduction unit(s)
(Corex.RTM./Finex.RTM.) or to one or more oxycombustion unit(s) for
example. In the first case, the pressure of the oxygen supplied is
comprised in a range from 5 to 15 bar. In the second case, the
pressure of the oxygen supplied is comprised in a range of 1 to 5
bar (preferably 1 to 2 bar abs).
[0030] The facility comprises one first compressor 1 and one second
compressor 3, installed on the same site, means for supplying the
first compressor and the second compressor with air at atmospheric
pressure, the first and the second compressor being driven by
electric motors and respectively bringing the air to a first
pressure comprised between 2.5 and 8 bar and to a second pressure
comprised between 4 and 30 bar.
[0031] The two separate compressed air flows leaving the two air
compressors are cooled for example using a final coolant, before
being sent into a first and a second purification unit 5 and 7, one
of the air flows being substantially at the first pressure and the
second substantially at the second pressure.
[0032] The purified first air flow is sent into the main exchange
line 13 by means of the pipe 11 and the purified second air flows
is sent into the main exchange line 13 by means of the pipe 9.
[0033] Once it has been cooled in the exchanger 13, the first air
flow is introduced into the system of columns 15, the second air
flow is introduced into the system of columns 15 in at least
partially condensed form after having passed through an auxiliary
vaporizer 25 using an oxygen-rich liquid tapped off from the system
of columns 15 by means of a pipe 17 and a pump 23. The first air
flow introduced into the system of columns 15 is at least partially
introduced into the same column as the second air flow introduced
at least partially condensed into the system of columns 15 (for
example the high-pressure column of a double column comprising a
high-pressure column and a low-pressure column).
[0034] FIG. 2 illustrates a first alternative form of this facility
in which just one of the first and second air compressors comprises
intermediate coolants (isothermal compression) namely the
compressor 1, means for sending air taken from the outlet of that
one of the two air compressors that does not comprise an
intermediate coolant to a heat exchanger 31, and means for sending
at least one fluid taken from the system of columns and/or water to
the exchanger where it is heated up.
[0035] The two compressed air flows leaving the two air compressors
are sent into two purification units 5 and 7, one of them
substantially at the first pressure and the second substantially at
the second pressure.
[0036] The purified first air flow is sent into the main exchange
line 13 by means of pipes 11 and the purified second air flow is
sent into the main exchange line 13 by means of the pipe 9.
[0037] Once it has been cooled in the exchanger 13, the first air
flow is introduced into the system of columns 15, the second air
flow is introduced into the system of columns 15 in at least
partially condensed form after having passed through an auxiliary
vaporizer 25 using an oxygen-rich liquid tapped off from the system
of columns 15 by means of a pipe 17 and a pump 23. The first air
flow introduced into the system of columns 15 is at least partially
introduced into the same column as the at least partially condensed
second air flow 15. The oxygen-rich liquid tapped off from the
system of columns 15 by means of the pipe 17 and which was
vaporized in the auxiliary vaporizer 25 against the purified second
air flow, is introduced into the heat exchanger 31 and allows the
cooling of the air compressed in the compressor 1 comprising no
intermediate coolants.
[0038] The facility depicted in FIG. 3 represents a second variant,
intended for supplying oxygen to an iron smelting-reduction unit
(Corex.RTM./Finex.RTM.). The pressure of the oxygen supplied is
comprised in a range from 5 to 15 bar (preferably from 8 to 12 bar
abs).
[0039] The facility comprises a first compressor 1 and a second
compressor 3, means for supplying the first compressor and the
second compressor with air at atmospheric pressure, the first and
second compressors being driven by a common steam turbine 39 and
respectively bringing the air to a first pressure of between 4 and
7 bar and to a second pressure of between 10 and 30 bar.
[0040] The two compressed air flows leaving the two air compressors
are sent into two purification units 5 and 7, one of them
substantially at the first pressure and the second substantially at
the second pressure.
[0041] A first portion of the purified first air flow is sent into
the main exchange line 13 by means of the pipes 11 and the purified
second air flow is sent into the main exchange line 13 by means of
the pipe 9.
[0042] The second portion of the purified first air flow is sent
into the compressor 33 of a booster turbine by means of the pipe
29, before being cooled in the main exchange line 13 and then
expanded in the turbine part 35 of the booster turbine. The air
expanded in the turbine 35 is sent into the system of columns via
the pipe 41.
[0043] The purified second air flow, once cooled in the exchange
line, is introduced into the system of columns 15 by means of the
pipe 43.
[0044] As in the other cases, the first air flow introduced into
the system of columns 15 is introduced at least partially into the
same column as the second air flow introduced at least partially
condensed into the system of columns 15.
[0045] FIG. 4 illustrates a third alternative form derived from
FIG. 3 in which just one of the first and second air compressors
(the compressor 3) comprises intermediate coolants (isothermal
compression), comprising means for sending air from the outlet of
that one of the two air compressors that does not have an
intermediate coolant to a heat exchanger and means for sending
water to the exchanger where it heats up.
[0046] FIG. 5 describes a fourth variant of the facility described
in FIG. 1, in which the two compressors are combined into one and
the same machine 3, for example an axial-radial compressor.
[0047] FIG. 6 describes an additional variant in which n facilities
described in FIG. 1 are interconnected. This figure, for the sake
of clarity, shows the case n=2: thus it shows two facilities as
described in FIG. 1, interconnected by means of the pipes 45 and 47
on the one hand, and 49 and 51 on the other. Thus, the pipe 45
connects the outlet of the compressor 1 and that of the compressor
1', and the pipe 47 connects the outlet of the compressor 3 and
that of the compressor 3'; the pipe 49 connects the outlet of the
purification means 7 with that of the purification means 7', and
finally, the pipe 51 connects the outlet of the purification means
5 with that of the purification means 5'.
[0048] The first of the two interconnected facilities comprises a
first and second compressor 1 and 3, the second facility comprises
a first and a second compressor 1' and 3'. The first compressors 1
and 1' and the second compressors 3 and 3' are supplied with air at
atmospheric pressure, the first and second compressors being driven
by electric motors and respectively bringing the air to a first
pressure comprised between 2.5 and 8 bar and to a second pressure
comprised between 4 and 30 bar.
[0049] The air flows pressurized by the compressors 1 and 1' on the
one hand, and 3 and 3' on the other, are cooled for example using a
final coolant before being sent into the first purification units 7
and 7' on the one hand, and into the second purification units 5
and 5' on the other, the air flows being substantially at the first
pressure on the one hand in the case of the flows taken from the
compressors 1 and 1', and substantially at the second pressure on
the other hand in the case of the flows taken from the compressors
3 and 3'.
[0050] The facility comprises a pipe 45 connecting the first air
flows compressed by the first compressors 1 and 1', and a pipe 47
connecting the second air flows compressed by the second
compressors 3 and 3'. The facility also comprises a pipe 49
connecting the first air flows purified by the purification means 7
and 7', and a pipe 51 connecting the second air flows purified by
the purification means 5 and 5'.
[0051] The system of columns 15 in all the figures may comprise
just one column, a conventional double column or a triple column
with a high-pressure column, an intermediate-pressure column and a
low-pressure column, amongst others.
* * * * *