U.S. patent application number 12/730429 was filed with the patent office on 2010-09-30 for process and apparatus for cryogenic air separation.
This patent application is currently assigned to LINDE AG. Invention is credited to Stefan LOCHNER.
Application Number | 20100242537 12/730429 |
Document ID | / |
Family ID | 42106961 |
Filed Date | 2010-09-30 |
United States Patent
Application |
20100242537 |
Kind Code |
A1 |
LOCHNER; Stefan |
September 30, 2010 |
PROCESS AND APPARATUS FOR CRYOGENIC AIR SEPARATION
Abstract
The process and the apparatus in accordance with the invention
relate to cryogenic separation of air in a distillation column
system that has at least one single column (12). A compressed feed
air stream (6, 8) is cooled in a main heat exchanger (9) in
counter-current flow to a first return stream (16, 23) from the
distillation column system. Cooled feed air stream (11) is fed into
the distillation column system. A nitrogen-rich fraction (15) is
produced in the upper region of the single column (12). At least
part (16b) of the nitrogen-rich fraction (15) is condensed in a top
condenser (13), which is constructed as a condenser-evaporator. At
least part (54) of the liquid nitrogen-rich fraction (52) produced
in the top condenser (13) is fed into the single column (12) as
reflux. An oxygen-containing recycle fraction (18a) is drawn off
from the single column (12) in liquid form. The liquid recycle
fraction (18a) is cooled in a counter-current subcooler (100). The
cooled recycle fraction (18b) is evaporated in the top condenser
(13). The evaporated recycle fraction (29) is re-compressed in a
re-compressor (30). The re-compressed recycle fraction (31, 32) is
fed to the lower region of the single column (12). The main heat
exchanger (9) and the counter-current subcooler (100) are formed as
an integrated heat exchanger (102). The first return stream (16,
23) is fed into a group of passages (102) within the integrated
heat exchanger which extend from the cold end thereof to the warm
end thereof, and, in the process, the first return stream is
brought into indirect heat exchange with both the liquid recycle
fraction (18a) and the feed air stream (8).
Inventors: |
LOCHNER; Stefan; (Grafing,
DE) |
Correspondence
Address: |
MILLEN, WHITE, ZELANO & BRANIGAN, P.C.
2200 CLARENDON BLVD., SUITE 1400
ARLINGTON
VA
22201
US
|
Assignee: |
LINDE AG
Muenchen
DE
|
Family ID: |
42106961 |
Appl. No.: |
12/730429 |
Filed: |
March 24, 2010 |
Current U.S.
Class: |
62/644 ;
62/649 |
Current CPC
Class: |
F25J 3/04236 20130101;
F25J 3/044 20130101; F25J 3/04048 20130101; F25J 2200/94 20130101;
F25J 3/04321 20130101; F25J 2250/20 20130101; F25J 2200/72
20130101; F25J 2250/02 20130101; F25J 3/0423 20130101; F25J 2245/02
20130101; F25J 3/04284 20130101 |
Class at
Publication: |
62/644 ;
62/649 |
International
Class: |
F25J 3/04 20060101
F25J003/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 24, 2009 |
DE |
102009014557.5 |
Jun 23, 2009 |
EP |
09008224.9 |
Claims
1. A process for cryogenic air separation in a distillation column
system comprising at least one single column (12), said process
comprising: cooling a compressed feed air stream (6, 8) in a main
heat exchanger (9) in counter-current to a first return stream (16,
23) from the distillation column system, introducing the cooled
feed air stream (11) into said single column (12), removing a
nitrogen-rich fraction (15) from the upper region of said single
column (12), condensing at least part (16b) of the nitrogen-rich
fraction (15) in a top condenser-evaporator (13), introducing at
least part (54) of the condensed liquid nitrogen-rich fraction (52)
from the top condenser-evaporator (13) into said single column (12)
as reflux, withdrawing an oxygen-containing recycle fraction (18a)
from said single column (12) in liquid form, cooling the
oxygen-containing recycle liquid fraction (18a) in a
counter-current subcooler (100), evaporating the cooled
oxygen-containing recycle fraction (18b) in the top
condenser-evaporator (13), re-compressing the evaporated
oxygen-containing recycle fraction (29) in a re-compressor (30),
and introducing the re-compressed recycle fraction (31, 32) into
the lower region of said single column (12), wherein the main heat
exchanger (9) and the counter-current subcooler (100) are formed as
an integrated heat exchanger (101), the integrated heat exchanger
(101) having a first group of passages for said first return stream
(16, 23), which extend from the cold end of said integrated heat
exchanger (101) to the warm end of said integrated heat exchanger
(101), said first return stream (16, 23) being introduced into said
first group of passages (102) at the cold end of said integrated
heat exchanger (101), and flowing through said integrated heat
exchanger (101) to the warm end said integrated heat exchanger
(101) and, during passage through said integrated heat exchanger
(101), said first return stream is brought into indirect heat
exchange with both said liquid recycle fraction (18a) and said the
feed air stream (8), and the cooled feed air stream (11) is
withdrawn from said integrated heat exchanger (101) in completely
gaseous form and is fed into said single column (12) in completely
gaseous form.
2. A process according to claim 1, wherein said integrated heat
exchanger is a single plate-type heat exchanger block.
3. A process according to claim 1, wherein said single column is
the only distillation column of said distillation column
system.
4. A process according to claim 1, further comprising withdrawing a
further oxygen-containing fraction (14a) from said single column
(12) in liquid form, cooling the further oxygen-containing liquid
fraction (14a) in said integrated heat exchanger (101), evaporating
the cooled further oxygen-containing liquid fraction in the top
condenser-evaporator (13), warming the evaporated further
oxygen-containing fraction (19) in said integrated heat exchanger
(101) in counter-current flow to air, and expanding the warmed
evaporated further oxygen-containing fraction in an expansion
machine (21) to produce work, wherein the temperature of the
further oxygen-containing liquid fraction (14a) as introduced into
said integrated heat exchanger (101) is higher than the temperature
of the cooled feed air stream (11) withdrawn off from said
integrated heat exchanger (101).
5. A process according to claim 4, wherein, before the
work-producing expansion, the warmed evaporated further
oxygen-containing fraction is warmed up in counter-current flow to
air in said integrated heat exchanger.
6. A process according to claim 4, wherein said oxygen-containing
recycle fraction is removed from said single column at an
intermediate point which is located at least one theoretical or
practical plate above the point at which said further
oxygen-containing fraction is removed from said single column
(12).
7. A process according to claim 4, wherein said expansion machine
(21) is coupled mechanically to said re-compressor (30).
8. A process according to claim 1, wherein said re-compressor (30)
is constructed as a cold compressor.
9. A process according to claim 1, wherein said re-compressed
recycle fraction (31) is cooled in said integrated heat exchanger
(101) before being introduced into the lower region of said single
column (12), and said re-compressed recycle fraction (32) is
withdrawn from said integrated heat exchanger (101) in completely
gaseous form and fed into said single column (12) in completely
gaseous form.
10. An apparatus for cryogenic air separation in a distillation
column system, comprising: at least one single column (12), a main
heat exchanger (9) for cooling a compressed feed air stream (6, 8)
in counter-current flow to a first return stream (16, 23) from the
distillation column system, means for introducing a cooled feed air
stream (11) into said single column (12), means for removing a
nitrogen-rich fraction (15) from the upper region of said single
column (12), a top condenser-evaporator for condensing at least
part of the nitrogen-rich fraction, means for introducing condensed
nitrogen-rich fraction (52) from said top condenser-evaporator (13)
into said single column (12) as reflux, means for withdrawing an
oxygen-containing liquid recycle fraction (18a) from said single
column (12), a counter-current subcooler (100) for cooling down
liquid recycle fraction (18a), means for introducing cooled recycle
fraction (18b) into said top condenser-evaporator (13), a
re-compressor (30) for compressing evaporated recycle fraction (29)
from said top condenser-evaporator (13), and means for introducing
re-compressed recycle fraction (31, 32) into the lower region of
said single column (12), wherein said main heat exchanger (9) and
said counter-current subcooler (100) are formed as an integrated
heat exchanger (101), said integrated heat exchanger (101) having a
first group of passages (102) for the first return stream (16, 23),
which extends from the cold end of said integrated heat exchanger
to the warm end of said integrated heat exchanger, the cold end of
said integrated heat exchanger (101) being connected to means for
introducing the first return stream (16, 23) into said first group
of passages, the warm end of said integrated heat exchanger (101)
being connected to means for withdrawing the first return stream
(16, 23) from said first group of passages, the integrated heat
exchanger (101) being constructed so that, during operation, the
first return stream (16, 23) is brought into indirect heat exchange
with both liquid recycle fraction (18a) and feed air stream (8),
and the passages in the integrated heat exchanger (101) are
arranged so that, during operation, cooled feed air stream (11) is
withdrawn from said integrated heat exchanger (101) in completely
gaseous form and is fed into said single column (12) in completely
gaseous form.
Description
SUMMARY OF THE INVENTION
[0001] The invention relates to a process for cryogenic air
separation which has at least one single column, wherein: [0002] a
compressed feed air stream is cooled down in a main heat exchanger
in counter-current flow to a first return stream (i.e., returned
from the distillation column system to the main heat exchanger),
[0003] the cooled feed air stream is fed into the single column,
[0004] a nitrogen-rich fraction is produced in the upper region of
the single column, [0005] at least part of the nitrogen-rich
fraction is condensed in a top condenser, which is constructed as a
condenser-evaporator, [0006] at least part of the liquid
nitrogen-rich fraction produced in the top condenser is fed into
the single column as reflux, [0007] an oxygen-containing liquid
recycle fraction is drawn off from the single column in liquid
form, [0008] the liquid recycle fraction is cooled down in a
counter-current subcooler, [0009] the cooled liquid recycle
fraction is evaporated in the top condenser, [0010] the evaporated
recycle fraction is re-compressed in a re-compressor, and [0011]
the re-compressed recycle fraction is fed to the lower region of
the single column.
[0012] Similar processes with residual gas recycling are known from
DE 2261234, U.S. Pat. No. 4,966,002, U.S. Pat. No. 5,363,657, U.S.
Pat. No. 5,528,906, U.S. Pat. No. 5,934,106, U.S. Pat. No.
5,611,218, U.S. Pat. No. 5,582,034, US 2004244417, DE 19909744 A1,
DE 19919933 A1, DE 19954593 A1, US 2007204652 A1, DE 102006027650
A1 and EP 1995537 A2. In this case, and also in U.S. Pat. No.
4,966,002 and U.S. Pat. No. 5,582,034, a counter-current subcooler
is used, in which the liquid oxygen-containing recycle fraction is
"subcooled", i.e. cooled below its boiling point.
[0013] Here, "single column" is understood to mean a distillation
column which is operated in a uniform pressure range--which means
here that the pressure difference between top and bottom of the
column is based exclusively on the pressure loss of the vapour
rising in the column--and in which both the feed air is fed in as
main feed fraction and also the nitrogen product is produced in the
form of part of the nitrogen-rich fraction accumulating in the
upper region of the column. Double-column or triple-column
processes for nitrogen/oxygen separation are therefore not covered.
However, a pure oxygen column, which is connected to the single
column and is operated as a pure stripping column, is not ruled
out.
[0014] Processes and apparatuses for the cryogenic separation of
air are described in general terms in Hausen/Linde,
Tieftemperaturtechnik, 2nd Edition 1985, Chapter 4 (pages 281 to
337).
[0015] An aspect of the invention is to provide a process of the
type mentioned above, as well as a corresponding apparatus, which
are economically particularly beneficial.
[0016] Thus, in accordance with the invention, there is provided a
process of the type mentioned above wherein (references numerals
refer to those of the FIGURE): [0017] the main heat exchanger (9)
and the counter-current subcooler (100) are formed as an integrated
heat exchanger (101), [0018] the integrated heat exchanger (101)
having a first group of passages for the first return stream (16,
23), which extends from the cold end of the integrated heat
exchanger (101) to the warm end of the integrated heat exchanger
(101), [0019] the first return stream (16, 23) is introduced into
this group of passages (102) at the cold end and flowing through
the integrated heat exchanger (101) as far as the warm end thereof,
[0020] the first return stream (16, 23) being brought into indirect
heat exchange with both the liquid recycle fraction (18a) and with
the feed air stream (8) in the integrated heat exchanger (101), and
[0021] the cooled feed air stream (11) being withdrawn from the
integrated heat exchanger (101) in completely gaseous form and
being fed into the single column (12) in completely gaseous
form.
[0022] Surprisingly, the use of an integrated heat exchanger, which
combines the functions of a main heat exchanger and a
counter-current subcooler, permits any pre-liquefaction of the air
to be avoided. As a result, all of the air fed to the column is
able to rise and participate in the rectification. Thus, the
separation effect becomes higher and, overall, the process
according to the invention is therefore particularly beneficial.
The precise layout of the integrated heat exchanger depends on the
boundary conditions of the individual case and must be defined for
each plant by using the usual calculation tools of the process
engineer.
[0023] Besides this, the integration according to the invention
simplifies the design considerably with respect to the pipework.
Since the counter-current subcooler is given a substantially larger
cross section as a result of the integration in the main heat
exchanger, the liquid streams that flow in counter-current relation
to the gas streams are offered an optimum heating surface area. It
is merely necessary for a heat exchanger to be supported and piped
in the coldbox. The absolute number of headers of the two heat
exchangers decreases. The gas streams (residual gas to the turbine,
product nitrogen, residual gas from the turbine) from the top of
the coldbox do not have to be led via two fixed points
(counter-current subcooler and main heat exchanger). Expansion
loops can be dispensed with; the integrated solution permits a pipe
run with minimized pipe stresses.
[0024] The integration of main heat exchanger and counter-current
subcooler is certainly known from air separation processes having
two or more columns for nitrogen/oxygen separation. However, this
measure has not previously been applied to processes of the type
mentioned above, since the manufacturing outlay for a particularly
long integrated heat exchanger did not appear to be justified in
single column processes. The surprising effect of the avoidance of
pre-liquefaction of the air was previously unknown.
[0025] In principle, any heat exchanger type can be used as an
integrated heat exchanger in the process according to the
invention, for example a helically coiled heat exchanger or else a
straight pipe exchanger. However, the use of a plate-type heat
exchanger, in particular a brazed aluminium plate heat exchanger,
is particularly beneficial. In this case, the integrated heat
exchanger is formed by a single plate-type heat exchanger
block.
[0026] It is particularly cost-effective if the single column
constitutes the only distillation column of the distillation column
system.
[0027] In order to generate refrigerating capacity, a further
oxygen-containing fraction can be expanded, producing work. Thus,
for example, the process can further comprise: [0028] withdrawing a
further oxygen-containing fraction (14a) in liquid form from the
single column (12), [0029] this further oxygen-containing liquid
fraction (14a) is cooled down in the integrated heat exchanger
(101), [0030] the cooled further oxygen-containing fraction is
evaporated in the top condenser (13), [0031] the evaporated further
oxygen-containing fraction (19) is warmed in the integrated heat
exchanger (101) in counter-current flow to air, and [0032] the
warmed further oxygen-containing fraction is expanded in an
expansion machine (21) to produce work, and [0033] the temperature
of the liquid further oxygen-containing fraction (14a), as it is
introduced into the integrated heat exchanger (101), is higher than
the temperature of the cooled feed air stream (11) as it is
withdrawn from the integrated heat exchanger (101).
[0034] The integrated heat exchanger is also used for the
subcooling of the further oxygen-containing fraction, in that the
liquid further oxygen-containing fraction is cooled down in the
counter-current subcooler before its evaporation. The integration
according to the invention makes it possible to introduce the
further oxygen-containing liquid fraction into the heat exchanger
above the temperature of the air removal. The temperature
difference is, for example, 0.2 to 5 K. This contributes to the
avoidance of the pre-liquefaction.
[0035] In addition, before being subjected to work-producing
expansion, the evaporated further oxygen-containing fraction is
warmed up by counter-current heat exchange with air in the
integrated heat exchanger.
[0036] The further oxygen-containing fraction can, for example,
have the same composition as the recycle fraction. In this case,
the two fractions can be led in common lines and passages until
after the top condenser.
[0037] Alternatively, the oxygen-containing recycle fraction is
removed from the single column at an intermediate point which is
located at least one theoretical or practical plate above the point
at which the further oxygen-containing fraction is removed. In this
case, separate lines and separate passages must be provided for the
two fractions in the top condenser and possibly in the
counter-current subcooler.
[0038] Advantageously, the expansion machine is coupled
mechanically to the re-compressor. As a result, the mechanical
energy obtained during the work-producing expansion is used for
re-compression. This is preferably the only energy source for the
drive of the re-compressor.
[0039] It is beneficial if the re-compressor is constructed as a
cold compressor. Here, a "cold compressor" is understood to mean an
apparatus in which the gas to be compressed is fed in at a
temperature which lies considerably below the ambient temperature,
in general below 250 K, preferably below 200 K.
[0040] It is also beneficial if, in the process according to the
invention, the re-compressed recycle fraction is cooled in the
integrated heat exchanger before being introduced into the lower
region of the single column, the re-compressed recycle fraction
being drawn off from the integrated heat exchanger in completely
gaseous form and led into the single column in completely gaseous
form. The recycle fraction is therefore also free of
pre-liquefaction and participates in the rectification in the
single column completely as rising vapor. Therefore, the
pre-liquefaction is avoided completely in both feed streams to the
single column, namely in the feed air and in the recycle
fraction.
[0041] According to an apparatus aspect, the invention provides an
apparatus for cryogenic air separation in a distillation column
system, comprising: [0042] at least one single column (12), [0043]
a main heat exchanger (9) for cooling a compressed feed air stream
(6, 8) in counter-current flow to a first return stream (16, 23)
from the distillation column system, [0044] means (such as conduits
or piping) for introducing the cooled feed air stream (11) into the
single column (12), [0045] means (such as conduits or piping) for
removing a nitrogen-rich fraction (15) from the upper region of the
single column (12), [0046] a top condenser for condensing at least
part of the nitrogen-rich fraction, the top condenser being
constructed as a condenser-evaporator, [0047] means (such as
conduits or piping) for introducing the liquid nitrogen-rich
fraction (52) produced in the top condenser (13) into the single
column (12) as reflux, [0048] means (such as conduits or piping)
for withdrawing an oxygen-containing recycle fraction (18a) from
the single column (12) in the liquid state, [0049] a
counter-current subcooler (100) for cooling down the liquid recycle
fraction (18a), [0050] means (such as conduits or piping) for
introducing the cooled recycle fraction (18b) into the top
condenser (13), [0051] a re-compressor (30) for compressing the
evaporated recycle fraction (29) from the top condenser (13), the
re-compressor (30) being constructed, for example, as a cold
compressor, and [0052] means (such as conduits or piping) for
introducing the re-compressed recycle fraction (31, 32) into the
lower region of the single column (12), wherein [0053] the main
heat exchanger (9) and the counter-current subcooler (100) are
formed as an integrated heat exchanger (101), [0054] the integrated
heat exchanger (101) having a first group of passages (102) for the
first return stream (16, 23), which extends from the cold end to
the warm end of the integrated heat exchanger, [0055] the cold end
of the integrated heat exchanger (101) being connected to means
(such as conduits or piping) for introducing the first return
stream (16, 23) into the first group of passages, [0056] the warm
end of the integrated heat exchanger (101) being connected to means
(such as conduits or piping) for withdrawing the first return
stream (16, 23) from the first group of passages, [0057] the
integrated heat exchanger (101) being constructed in such a way
that, during operation, the first return stream (16, 23) is brought
into indirect heat exchange with both the liquid recycle fraction
(18a) and the feed air stream (8), and [0058] the passages in the
integrated heat exchanger (101) are arranged in such a way that,
during operation, the cooled feed air stream (11) is withdrawn from
the integrated heat exchanger (101) in completely gaseous form and
is fed into the single column (12) in completely gaseous form.
BRIEF DESCRIPTION OF THE DRAWINGS
[0059] The invention and further details, such as features and
attendant advantages, of the invention are explained in more detail
below on the basis of an exemplary embodiment which is
diagrammatically depicted in the drawing, and wherein:
[0060] FIG. 1 shows an embodiment of the device according to the
invention.
DETAILED DESCRIPTION OF THE DRAWINGS
[0061] Atmospheric air 1 is taken in by an air compressor 3, via a
filter 2, and compressed to an absolute pressure of 6 to 20 bar,
preferably about 9 bar. After flowing through a re-cooler 4 and a
water separator 5, the compressed air 6 is cleaned in a cleaning
device 7. The cleaning device 7 has a pair of containers which are
filled with adsorption material, preferably a molecular sieve. The
cleaned air 8 is cooled down to somewhat above the dew point in a
main heat exchanger 9 and finally led into a single column 12 as a
completely gaseous feed air stream 11.
[0062] The operating pressure of the single column 12 (at the top)
is 6 to 20 bar, preferably about 9 bar. Its top condenser is cooled
with an oxygen-containing recycle fraction 18a, 18b and a further
oxygen-containing fraction 14a, 14b. The further oxygen-containing
fraction 14a is drawn off from the bottom of the single column 12,
the recycle fraction 18a from an intermediate point some practical
or theoretical plates further above the bottom of the single column
12. Before they are fed 14b, 18b into the top condenser 13, both
fractions 14a, 18a are cooled down in a counter-current subcooler
100. The main heat exchanger 9 and counter-current subcooler 100,
according to the invention, are formed by an integrated heat
exchanger 101, which is implemented here as a single plate-type
heat exchanger block. The height difference between the exit of the
stream 14a from the single column 12 (more precisely the liquid
level at the bottom of the column) and the entry into the
integrated heat exchanger 101 should in principle be chosen such
that the proportion of gas as a result of the expansion lies below
5% by volume. If, in a departure from this, the proportion of gas
is higher than 5% by volume, a perforated plate is fitted in the
header over the entire region above the point of entry of the
two-phase mixture into the passages. The pressure loss across the
perforated plate is chosen such that the gas bubbles are
distributed over all the passages. The two-phase mixture is then
fed into the integrated heat exchanger (101), first transversely
with respect to the other streams (possibly with one or more
deflections), in which the gas proportion is condensed completely,
that is to say the adjacent passages are correspondingly colder in
every operating case. After the initial transverse flow, the fluid
streams flows counter-current to the other streams.
[0063] The main product from the single column 12, gaseous nitrogen
15, 16 is drawn off at the top and, as first return stream, is led
through a group of passages 102 which extend from the cold end to
the warm end of the integrated heat exchanger. In the process, the
recycle stream (16) in the region of the counter-current subcooler
100 comes into indirect heat exchange with the two
oxygen-containing fractions 14a, 18a and then, in the region of the
main heat exchanger 9, into indirect heat exchange with the feed
air stream 8. Via a line 17, it is finally drawn off at
approximately ambient temperature as a gaseous pressurized product
(PGAN).
[0064] The remainder 16b of the gaseous nitrogen 15 is condensed
completely or substantially completely in the top condenser 13.
Part 53 of the condensate 52 from the top condenser 13 can be
removed as liquid nitrogen product (PLIN); the remainder 54 is
introduced into the top of the single column as reflux.
Non-condensed constituents can be drawn off via a purge line
90.
[0065] The recycle fraction 18b is evaporated in the top condenser
13 under a pressure of 2 to 9 bar, preferably about 4 bar, and
flows in gaseous form via line 29 to a cold compressor 30, in which
it is re-compressed approximately to a pressure which is sufficient
to feed it back into the single column. The re-compressed recycle
fraction 31 is cooled down to column temperature again in the
counter-current subcooler 100 and fed to the single column 12 at or
near the bottom in completely gaseous form via line 32.
[0066] The further oxygen-containing fraction 14b is evaporated in
the top condenser 13 under a pressure of 2 to 9 bar, preferably
about 4 bar, and flows in gaseous form via line 19 to the cold end
of the integrated heat exchanger 101. There, in the region of the
counter-current subcooler 100, it comes into indirect heat exchange
with the two liquid oxygen-containing fractions 14a, 18a and then,
in the region of the main heat exchanger 9, into indirect heat
exchange with the feed air stream 8. It is removed from the main
heat exchanger 9 again (line 20) at an intermediate temperature and
is expanded to about 300 mbar above atmospheric pressure, producing
work, in an expansion machine 21 which, in the example, is
constructed as a turbo-expander. The expansion machine is coupled
mechanically to the cold compressor 30 and a braking device 22
which, in the exemplary embodiment, is formed by an oil-filled
brake. The expanded further fraction 23 is warmed up to about
ambient temperature in the integrated heat exchanger 101. The warm
further fraction 24 is blown off into the atmosphere (line 25)
and/or used in the cleaning device 7 as regeneration gas 26, 27,
possibly following heating in the heating device 28.
[0067] As mentioned above, the further oxygen-containing fraction
(14a, 14b) can, for example, have the same composition as the
oxygen recycle fraction (18a, 18b). For example, these two
fractions can be removed from column 12 as a single stream, for
example the stream (14a, 14b), and introduced as a single stream
into top condenser 13. Thereafter, the streams are divided into two
streams (19) and (29).
[0068] In the exemplary embodiment, the top condenser 13 is
constructed as a forced-flow evaporator. Alternatively, a bath
evaporator or falling film evaporator can be used.
[0069] The entire disclosure[s] of all applications, patents and
publications, cited herein and of corresponding German Application
No. 10 2009 9014557.5, filed Mar. 24, 2009 are incorporated by
reference herein.
[0070] The preceding examples can be repeated with similar success
by substituting the generically or specifically described reactants
and/or operating conditions of this invention for those used in the
preceding examples.
[0071] From the foregoing description, one skilled in the art can
easily ascertain the essential characteristics of this invention
and, without departing from the spirit and scope thereof, can make
various changes and modifications of the invention to adapt it to
various usages and conditions.
* * * * *