U.S. patent application number 10/058218 was filed with the patent office on 2002-09-05 for three-column system for the low-temperature fractionation of air.
This patent application is currently assigned to LINDE AKTIENGESELLSCHAFT. Invention is credited to Corduan, Horst, Kunz, Christian, Rottmann, Dietrich.
Application Number | 20020121106 10/058218 |
Document ID | / |
Family ID | 7672117 |
Filed Date | 2002-09-05 |
United States Patent
Application |
20020121106 |
Kind Code |
A1 |
Rottmann, Dietrich ; et
al. |
September 5, 2002 |
Three-column system for the low-temperature fractionation of
air
Abstract
The process and the apparatus are used for the low-temperature
fractionation of air in a three-column system which has a
high-pressure column (5), a low-pressure column (7) and a medial
column (6). Charge air (1, 2, 4) is introduced into the
high-pressure column (5), where it is separated into a first
oxygen-enriched liquid and a first nitrogen fraction (16). At least
a part (19) of the first nitrogen fraction (16) is condensed in a
first condenser/evaporator (8) to form a first liquid nitrogen
fraction (20). A first oxygen-enriched fraction (22) from the
high-pressure column (5) is introduced into the medial column (6),
where it is separated into a second oxygen-enriched liquid and a
second nitrogen fraction (24). At least a part of the second
nitrogen fraction (24) is condensed in a second
condenser/evaporator (25) to form a second liquid nitrogen fraction
(26) and is added as reflux to one of the columns of the
three-column system and/or is obtained as liquid product (64). A
second oxygen-enriched fraction (29, 31) from the high-pressure
column or from the medial column (6) is introduced into the
low-pressure column (7), where it is separated into a third
oxygen-enriched liquid and a third nitrogen fraction. Liquid reflux
nitrogen (54, 60), which has not been formed in the second
condenser/evaporator (25), is introduced into the medial column
(6).
Inventors: |
Rottmann, Dietrich;
(Muenchen, DE) ; Kunz, Christian; (Muenchen,
DE) ; Corduan, Horst; (Puchheim, DE) |
Correspondence
Address: |
MILLEN, WHITE, ZELANO & BRANIGAN, P.C.
2200 CLARENDON BLVD.
SUITE 1400
ARLINGTON
VA
22201
US
|
Assignee: |
LINDE AKTIENGESELLSCHAFT
Wiesbaden
DE
|
Family ID: |
7672117 |
Appl. No.: |
10/058218 |
Filed: |
January 29, 2002 |
Current U.S.
Class: |
62/643 |
Current CPC
Class: |
F25J 3/04393 20130101;
F25J 2235/52 20130101; F25J 2235/50 20130101; F25J 3/04084
20130101; F25J 2250/42 20130101; F25J 3/04884 20130101; F25J
2245/50 20130101; F25J 2200/40 20130101; F25J 2220/42 20130101;
F25J 3/04351 20130101; F25J 3/04678 20130101; F25J 3/04296
20130101; F25J 2245/42 20130101; F25J 3/042 20130101; F25J 3/0406
20130101; F25J 3/04454 20130101; F25J 2250/50 20130101; F25J
2200/32 20130101; F25J 2245/02 20130101; F25J 3/04448 20130101;
F25J 2200/20 20130101; F25J 3/0423 20130101; F25J 3/04303 20130101;
F25J 2250/52 20130101; F25J 3/0409 20130101; F25J 3/04709 20130101;
F25J 3/04212 20130101; F25J 2205/30 20130101 |
Class at
Publication: |
62/643 |
International
Class: |
F25J 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 30, 2001 |
DE |
10103968.9 |
Claims
Patent claims
1. Process for the low-temperature fractionation of air in a
three-column system, which has a high-pressure column (5), a
low-pressure column (7) and an medial column (6), in which process
(a) charge air (1, 2, 4, 1080, 1083, 1084, 1085, 1104, 1113, 1183,
1184, 1190, 1191) is introduced into the high-pressure column (5),
where it is separated into a first oxygen-enriched liquid and a
first nitrogen fraction (16), (b) at least a part (19) of the first
nitrogen fraction (16) is condensed in a first condenser/evaporator
(8) to form a first liquid nitrogen fraction (20), (c) a first
oxygen-enriched fraction (22) from the high-pressure column (5) is
introduced into the medial column (6), where it is separated into a
second oxygen-enriched liquid and a second nitrogen fraction (24),
(d) at least a part of the second nitrogen fraction (24) is
condensed in a second condenser/evaporator (25) to form a second
liquid nitrogen fraction (26) and is added as reflux to one of the
columns of the three-column system and/or is obtained as liquid
product (64), and in which process (e) at least a second
oxygen-enriched fraction (29, 31, 870, 871, 1270, 1271) from the
high-pressure column or from the medial column (6) is introduced
into the low-pressure column (7), where it is separated into a
third oxygen-enriched liquid and a third nitrogen fraction,
characterized in that liquid reflux nitrogen (54, 60, 860), which
has not been formed in the second condenser/evaporator (25), is
introduced into the medial column (6).
2. Process according to claim 1, characterized in that at least a
part (60) of the liquid reflux nitrogen for the medial column is
formed by at least a part of the first liquid nitrogen fraction
(20, 21).
3. Process according to claim 1 or 2, characterized in that no part
or no significant part of the second liquid nitrogen fraction (26)
formed in the second condenser/evaporator (25) is introduced into
the medial column (6).
4. Process according to one of claims 1 to 3, characterized in that
at least a part of the second liquid nitrogen fraction (26) is
introduced into the low-pressure column (7) by means of static
pressure.
5. Process according to one of claims 1 to 4, characterized in that
a liquid fraction (36, 38, 39) is removed from the low-pressure
column (7) and is evaporated in the second condenser/evaporator
(25).
6. Process according to one of claims 1 to 5, characterized in that
the second oxygen-enriched liquid is boiled by means of a third
condenser/evaporator (28).
7. Process according to claim 6, characterized in that the third
condenser/evaporator is heated by means of gaseous nitrogen (49,
449, 549), which has been compressed in particular in a circulation
compressor (46, 346, 446).
8. Process according to claim 7, characterized in that nitrogen
(50, 54) which has liquefied in the third condenser/evaporator is
introduced into the medial column (6) as liquid reflux
nitrogen.
9. Process according to one of claims 1 to 8, characterized in that
the medial column (6) is operated at a pressure which is higher
than the operating pressure of the high-pressure column (5).
10. Apparatus for the low-temperature fractionation of air, having
a three-column system which has a high-pressure column (5), a
low-pressure column (7) and a medial column (6), and having (a) a
charge-air line (1, 2, 4, 1080, 1083, 1084, 1085, 1104, 1113, 1183,
1184, 1190, 1191), which leads into high-pressure column (5), (b) a
first condenser/evaporator (8) for condensing at least a part (19)
of a first nitrogen fraction (16) from the high-pressure column (5)
to form a first liquid nitrogen fraction (20), (c) a line (22) for
introducing a first oxygen-enriched fraction from the high-pressure
column (5) into the medial column (6), (d) a second
condenser/evaporator (25) for condensing at least a part of a
second nitrogen fraction (24) from the medial column (6) to form a
second liquid nitrogen fraction (26), the liquefaction space of
which is connected, via a reflux line, to one of the columns of the
three-column system or to a liquid product line (64), and having
(e) a charge line (29, 31, 870, 871, 1270, 1271) for introducing a
second oxygen-enriched fraction from the high-pressure column or
from the medial column (6) into the low-pressure column (7),
characterized by a liquid line (54, 60, 860) for introducing liquid
reflux nitrogen into the medial column (6), which is not in flow
communication with the liquefaction space of the second
condenser/evaporator (25).
11. Apparatus according to claim 10, characterized in that the
second condenser/evaporator (25) is arranged at a higher geodetic
level than the top of the low-pressure column (7).
Description
[0001] The invention relates to a process for the low-temperature
fractionation of air according to the preamble of patent claim 1.
In this process, the air is distilled in a three-column system
which has a high-pressure column, a low-pressure column and a
medial column.
[0002] The principles of low-temperature fractionation of air in
general are described in the monograph "Tieftemperaturtechnik"
[low-temperature technology] by Hausen/Linde (second edition,
1985), and in an article by Latimer in Chemical Engineering
Progress (Vol. 63, No.2, 1967, page 35). In the three-column
system, high-pressure column and low-pressure column preferably
form a Linde double column, i.e. these two columns are in
heat-exchanging communication via a principal condenser. (However,
the invention can in principle also be applied to other
arrangements of high-pressure column and low-pressure column and/or
other condenser configurations. In addition to the three columns
mentioned for nitrogen/oxygen separation, further apparatus for
obtaining other components of air, in particular noble gases, for
example for argon recovery, may be provided.) Unlike in the
classical Linde two-column process, in the three-column process not
all the oxygen-enriched liquid which is formed in the high-pressure
column is introduced directly into the low-pressure column, but
rather a first oxygen-enriched fraction from the high-pressure
column flows into the medial column, where it is fractionated
further, generally under a pressure which is between the operating
pressures of high-pressure column and low-pressure column. In the
process, liquid nitrogen (second liquid nitrogen fraction) is
generated from the first oxygen-enriched fraction and is used as an
additional reflux in the three-column system and/or is obtained as
a liquid product. A process according to the preamble of patent
claim 1 is known, for example, from DE 1065867 B, DE 2903089 A or
EP 1043556 A1.
[0003] A three-column process of this type normally offers energy
advantages over the conventional two-column process. However, it
also involves increased complexity, which has drawbacks in
particular if the process has to react relatively quickly to
changes in product demand. Rapid load changes of this nature occur,
for example, in air fractionators which are combined with IGCC
(Integrated Gasification Combined Cycle) plants and supply, for
example, nitrogen for a gas turbine and/or oxygen for a
gasification unit for producing fuel gas for a gas turbine. They
require a high degree of flexibility of the air fractionation
process.
[0004] The invention is therefore based on the object of providing
a process of the type described in the introduction and a
corresponding apparatus which have a particularly high degree of
flexibility.
[0005] This object is achieved by the fact that liquid reflux
nitrogen which has not been formed in the second
condenser/evaporator is introduced into the medial column.
[0006] In the three-column systems which have previously been
customary, the second condenser/evaporator is operated as a top
condenser of the medial column, i.e. the liquid nitrogen produced
in that region forms the reflux for the medial column.
[0007] By contrast, the measure according to the invention does not
initially appear appropriate, since sufficient reflux for the
medial column is available in the form of the condensate from the
second condenser/evaporator, so that additional outlay on supplying
reflux from another source does not appear to promise any benefit.
However, in the context of the invention it has been found that
particularly with the measure described above it is possible to
achieve a significant improvement in the flexibility of the
process.
[0008] This is because, in the event of load changes, the
composition of the impure charge fraction of the medial column (the
"first oxygen-enriched fraction") changes. On account of the
relatively low number of theoretical plates inside the medial
column, this change in concentration also has an effect on the top
product of the medial column, which top product is liquefied in the
second condenser/evaporator. Since a part of the liquid nitrogen
from the second condenser/evaporator, however, is used as liquid
product or as reflux in another column, the fluctuation in
concentration has a direct effect on the purity of the end product
or impairs operation in the other column (for example the
low-pressure column).
[0009] This drawback which has been discovered during research on
the invention is alleviated by the use of liquid nitrogen from a
source other than the second condenser/evaporator as reflux in the
medial column. Since this liquid nitrogen is subject to less
significant fluctuations in concentration, reflux of substantially
constant composition is always available even during a load change,
so that the purity of the nitrogen produced in the medial column
(and therefore of the liquid nitrogen formed in the second
condenser/evaporator) remains substantially constant even in the
event of load changes. Since the dependency of the product purities
on the way in which the plant operates is thereby reduced, the
result is a significantly improved degree of flexibility compared
to the known processes.
[0010] It is advantageous if at least a part of the liquid reflux
nitrogen for the medial column is formed by at least a part of the
first liquid nitrogen fraction. Since the fluctuations in
concentration in the nitrogen product of the high-pressure column
are particularly low, preferably only the nitrogen which has been
liquefied in the first condenser/evaporator is used as reflux for
the medial column. As an alternative or in addition, it is also
possible for other sources of liquid reflux nitrogen to be used,
for example a liquid tank or a nitrogen circuit in which liquid is
formed.
[0011] In the context of the invention, the possibility of a
certain part of the reflux for the medial column being withdrawn
from the second condenser/evaporator, i.e. being produced from the
second nitrogen fraction produced in the medial column, is not
ruled out altogether. This quantity may, for example, amount to up
to 30%, preferably less than 20%, and most preferably less than 10%
of the total reflux used in the medial column. However, it is
particularly beneficial if the reflux in the upper region of the
medial column is formed exclusively or substantially exclusively by
liquid reflux nitrogen which has not been produced in the second
condenser/evaporator. This means that no part or no significant
part (i.e. for example less than 10%, preferably less than 5%) of
the second liquid nitrogen fraction formed in the second
condenser/evaporator is introduced into the medial column.
[0012] As has already been mentioned, in processes known to date,
the second condenser/evaporator has been designed as a top
condenser of the medial column. In this case, under certain
circumstances it is necessary to use a pump in order to introduce
the liquid nitrogen formed there into the low-pressure column. In
the process according to the invention, however, the second
condenser/evaporator may be arranged independently of the position
of the medial column, for example at a higher geodetic level than
the top of the low-pressure column. It is thus possible for liquid
nitrogen from the second condenser/evaporator to be introduced into
the low-pressure column by means of static pressure. It is then
also possible to dispense with a pump if there is no pressure
gradient or only a very low pressure gradient between the
liquefaction space of the second condenser/evaporator and the top
of the low-pressure column.
[0013] The second condenser/evaporator is preferably cooled by a
single coolant, generally an evaporating liquid. The coolant for
the second condenser/evaporator may be formed by a liquid fraction
from the low-pressure column. It can, for example, be withdrawn
from the bottom of the low-pressure column or from an intermediate
point below the point at which the second oxygen-enriched fraction
is introduced.
[0014] The medial column preferably has a bottom evaporator (third
condenser/evaporator), in which the second oxygen-enriched liquid
is boiled. It can--as is known per se--be operated directly with
gaseous nitrogen from the high-pressure column. In many cases,
however, it is more advantageous to compress gaseous nitrogen from
high-pressure column, medial column or low-pressure column in a
circulation compressor to above the high-pressure column pressure
and then to condense this gaseous nitrogen in the third
condenser/evaporator.
[0015] The (circulating) nitrogen, which has been liquefied in the
third condenser/evaporator, may form some or all of the liquid
reflux nitrogen for the medial column.
[0016] As has already been mentioned, the medial column is
generally operated at an intermediate pressure. In certain cases,
however, it is advantageous within the context of the invention for
the medial column to be operated at a pressure which is higher than
the operating pressure of the high-pressure column. This applies,
for example, if the second condenser/evaporator is used to produce
a gaseous pressurized product.
[0017] The invention also relates to an apparatus for the
low-temperature fractionation of air according to Patent claims 10
and 11.
[0018] The invention, as well as further details of the invention,
are explained in more detail below with reference to exemplary
embodiments illustrated in the drawings.
[0019] In the process illustrated in FIG. 1, a first part 2 of
compressed and cleaned charge air 1 is fed to the warm end of a
principal heat exchanger 3. The first part of the air emerges at
the cold end of the principal heat exchanger 3, via line 4, at
approximately dew point temperature and flows to a high-pressure
column 5 immediately above the bottom.
[0020] The high-pressure column 5 is part of a three-column system
which, in addition, comprises a medial column 6 and a low-pressure
column 7. High-pressure column 5 and low-pressure column 7 are in
heat-exchanging communication via a first condenser/evaporator 8,
also known as the principal condenser.
[0021] In the high-pressure column 5, a first nitrogen fraction 16
is produced as top gas and a first oxygen-enriched liquid is
produced in the bottom. A part 17 of the high-pressure column
nitrogen 16 may be heated in the principal heat exchanger 3 and at
least partially obtained as gaseous pressurized product 18. The
remainder 19 is condensed in the principal condenser 8 so as to
form a first liquid nitrogen fraction 20. A part of this liquid
nitrogen is used as reflux in the high-pressure column 5, and
another part is removed from the high-pressure column via line
21.
[0022] Oxygen-enriched bottom liquid from the high-pressure column
(in this example all of this liquid) is fed via line 22, as first
oxygen-enriched fraction, via a restrictor valve 23, to the medial
column 6 at an intermediate point. In the medial column 6, a second
nitrogen fraction 24 is produced as top gas and a second
oxygen-enriched liquid is produced in the bottom. The top gas 24 is
fed to the liquefaction space of a second condenser/evaporator 25,
where it is condensed to form a second liquid nitrogen fraction 26.
In the example, the latter is added in its entirety as reflux to
the top of the low-pressure column 7, under certain circumstances
after restrictive expansion 27. Even if there is no pressure
gradient or only a slight pressure gradient to the low-pressure
column 7, the second liquid nitrogen fraction 26 flows into the
low-pressure column without being forced. This is due to the
geodetic arrangement of the second condenser/evaporator 25 above
the low-pressure column top which is illustrated in the
drawing.
[0023] The process illustrated in FIG. 1 has a third
condenser/evaporator 28, which is connected as a bottom evaporator
of the medial column 6. The proportion of the bottom liquid of the
medial column 6 which is not evaporated in this
condenser/evaporator 28 is supercooled as second oxygen-enriched
fraction 29 in a countercurrent supercooler 30 and is fed to the
low-pressure column 7 as second oxygen-enriched fraction 31 via a
restrictor valve 32.
[0024] Gaseous nitrogen 33 is extracted from the top of the
low-pressure column 7, is heated in the countercurrent supercooler
30, is passed via line 34 to the principal heat exchanger 3 and is
finally discharged, at approximately ambient temperature, via line
35 as nitrogen product and/or residual gas. Pure or impure oxygen
is obtained in the bottom of the low-pressure column 7 and is
extracted in liquid form via line 36. A pump 37 conveys the liquid
oxygen product via line 38, the countercurrent supercooler 30, line
39 and control valve 40 into the evaporation space of the second
condenser/evaporator 25. Vapour 41 which is produced in this space
is combined with gaseous oxygen 42 which is extracted directly from
the low-pressure column 7. The gaseous oxygen product 43 together
flows to the principal heat exchanger 3 and is ultimately
extracted, at approximately ambient temperature, via line 44. The
oxygen 63 which has remained in liquid form in the second
condenser/evaporator is extracted as liquid product (LOX).
[0025] Liquid nitrogen 21 from the high-pressure column 5 is added,
via line 57, countercurrent supercooler 30, line 58 and restrictor
valve 59, as further reflux to the low-pressure column 7. Another
part 60 of the high-pressure column LIN 21 is restricted (61) and
injected as reflux into the top of the medial column 6.
[0026] The process illustrated in FIG. 1 also has a nitrogen
circuit. To provide this, nitrogen 16, 17, 45 which has been
extracted from the high-pressure column 5 is brought to above the
high-pressure column pressure in a circulation compressor 46, is
recooled (47), is fed to the principal heat exchanger 3 via line 48
and in this heat exchanger is cooled to a temperature which lies
slightly above the temperature of the cold end, and is fed, via
line 49, to the liquefaction space of the third
condenser/evaporator 28. The condensate 50 formed there flows via
line 51 to the countercurrent supercooler 30 and onward, via line
52 and restrictor valve 53, to the top of the high-pressure column.
A part 54 may be added as reflux to the medial column 6 in addition
or as an alternative to the liquid nitrogen 21 which has been
extracted from the high-pressure column. The corresponding
proportions can be set by means of the valves 55 and 61.
[0027] The circulation compressor 46 may also be utilized as a
product compressor, by extracting a high-pressure product 62
upstream or downstream of the recooler 47. A liquid nitrogen
product (LIN) can be extracted from the low-pressure column 7 via
line 64.
[0028] In the process, refrigeration is produced by work-performing
expansion 14 of a part of the charge air. To do this, a second part
9 of the charge air 1 is compressed further in a recompressor 10
and, after recooling 11, flows via line 12 likewise to the warm end
of the principal heat exchanger 3. The second part of the air is
removed again from the principal heat exchanger 3 at an
intermediate temperature via line 13, is expanded in a
work-performing manner to approximately low-pressure column
pressure in a turbine 14 and is blown (15) into the low-pressure
column 7. The turbine 14 is mechanically coupled to the
recompressor 10.
[0029] The operating pressures of the columns (in each case at the
top) are as follows:
[0030] High-pressure column 5 for example 3.5 to 17 bar, preferably
approximately 12 bar
[0031] Medial column 6 for example 3.5 to 17 bar, preferably
approximately 9 bar
[0032] Low-pressure column 7 for example 1.3 to 7 bar, preferably
approximately 3 bar
[0033] In the process shown in FIG. 2, the medial column 6 is
dimensioned in such a way that the nitrogen 24 produced therein is
sufficient to produce the entire gaseous oxygen product by
evaporation of the bottom liquid of the low-pressure column 7 in
the second condenser/evaporator 25. The bottom product of the
low-pressure column 7 is extracted in liquid form via the line 36.
The liquid oxygen is passed into the second condenser/evaporator 25
via 37, 38, 30, 39, 40. The vapour 41 produced in this
condenser/evaporator forms the entire gaseous oxygen product 43,
44. No gaseous oxygen is removed directly from the low-pressure
column 7. It is thus possible--depending on the operating pressure
of the medial column 6--for all the gaseous oxygen product to be
obtained at a pressure which is higher than the operating pressure
of the low-pressure column 7. (In this case, the crude oxygen has
to be pumped out of the high-pressure column 5 to the medial column
6--cf. for example FIG. 7.) In this way, which is a type of
internal compression, the release pressure of the gaseous oxygen
product is increased without a gas compressor (external
compression) being required. Naturally, it is additionally possible
to provide an oxygen compressor which brings the warm oxygen
product 44 to an even higher pressure (combination of internal
compression and external compression).
[0034] In the context of this procedure, it is possible for the
pressure in the gaseous oxygen product 41, 43, 44 to be made
flexible by means of the operating pressure of the second
condenser/evaporator 25. On the one hand, it is possible, by
suitably designing medial column 6 and condenser/evaporator 25, to
adapt a specific process to the desired steady-state product
pressure and/or to inexpensive oxygen compressors for further
compression in the gaseous state. On the other hand, it is also
possible to vary the oxygen pressure in the lines 41, 43, 44 while
the plant is operating without having to change the operating
pressures of high-pressure column 5 or low-pressure column 7. A
variation of this type may be carried out, for example by suitably
setting the valves 40, 61, 55 and 23. (If the product pressure of
the oxygen is above the operating pressure of the low-pressure
column 7, the delivery head of the pump (not shown) in line 22 also
has to be correspondingly changed).
[0035] FIG. 3 differs from FIG. 2 in that gaseous nitrogen 33, 34,
345 from the low-pressure column 7 is fed to the circulation
compressor 346 instead of high-pressure column nitrogen. Although
this increases the outlay on energy for operation of the circuit,
it means that there is more liquid nitrogen available as reflux, so
that the reflux is improved in particular in the upper section of
the low-pressure column 7.
[0036] While the variants of the invention which have been shown
above have a warm circulation compressor 46, 346, the nitrogen
circuit in FIG. 4 is driven by a cold compressor 446. A part 445 of
the gaseous nitrogen 16 from the high-pressure column is branched
off at column temperature and is fed to the circulation compressor
446. The compressed circulating nitrogen 449 is passed directly
into the liquefaction space of the third condenser/evaporator 28.
The cold compressor circuit is advantageous in particular at a
relatively low operating pressure of the medial column 6, i.e. at a
pressure which is not far above the low-pressure column pressure.
In this case, the cold compressor only has to overcome a relatively
low pressure difference of, for example, 0.3 to 1.0 bar, preferably
approximately 0.5 bar.
[0037] In the event of a particularly low medial column pressure,
it is under certain circumstances possible to dispense with the
circulation compressor altogether, so that the third
condenser/evaporator 28 is heated directly by gaseous nitrogen 549
from the high-pressure column, as shown in FIG. 5.
[0038] In the process shown in FIG. 6, the medial column 6 is
operated at a higher pressure than in FIG. 5. (The medial column
pressure may be equal to the high-pressure column pressure, may be
up to 2 bar lower or may be up to 13 bar higher. The medial column
pressure is preferably about 2 bar higher than the high-pressure
column pressure.) The bottom liquid 22 of the high-pressure column
is brought to a correspondingly high pressure by means of a further
pump 665. The valve 23 at the location of feed into the medial
column 6 is used only for control purposes. As a result of the
higher operating pressure, the pressure in the top product 24 of
the medial column 6 and therefore in the second
condenser/evaporator 25 also rises. It is thus possible to achieve
a correspondingly higher product pressure in the gaseous oxygen 41,
43, 44. Since the condensed liquid 26 is also at a higher pressure
than that of the high-pressure column, it can be fed into the high
pressure column via line 626, preferably after prior supercooling
666 against the liquid oxygen 638 which has been pumped (37) to
high pressure.
[0039] FIG. 7 differs from FIG. 6 in that gaseous nitrogen 33, 34,
345 from the low-pressure column 7 instead of high-pressure column
nitrogen is fed to the circulation compressor 346. Although this
increases the outlay on energy for operation of the circuit, there
is also more liquid nitrogen available as reflux, thus improving
the reflux in particular in the upper section of the low-pressure
column 7.
[0040] In a similar manner to FIG. 5, in FIG. 8 the bottom
evaporator (third condenser/evaporator) 28 of the medial column 6
is operated directly with gaseous nitrogen 16, 549 from the top of
the high-pressure column 5. All the condensate 851 which is formed
there is returned to the top of the high-pressure column 5.
However, the reflux for low-pressure column and medium-pressure
column is extracted below a mass transfer section 867, which has
one to ten theoretical or practical plates. In this way, it is
possible for liquid nitrogen which is low in readily volatile
impurities such as helium, neon or hydrogen to be removed via line
821. A first part 860 is added as liquid reflux nitrogen to the top
of the medial column 6. The remainder 857 is supercooled (30) and
added (858, 859) to the low-pressure column 7 at its top. As a
result, it is possible to produce high-purity (in particular
virtually helium-, neon- and hydrogen-free) nitrogen in the medial
column 6 and the low-pressure column 7. In FIG. 8, the liquid
nitrogen produced 864 is extracted from the high-pressure column 5
or from the principal condenser 8.
[0041] In FIG. 8, the second condenser/evaporator 25 is cooled by
means of the bottom liquid 29, 868, which has been supercooled in
30 and expanded in 869, from the medial column 6 ("second
oxygen-enriched liquid"). The vapour 870 which is thus formed as
well as the proportion 871 which remains in liquid form are
introduced into the low-pressure column 7 at suitable locations.
The liquid nitrogen 26 which is obtained in the second
condenser/evaporator 25 is cooled in the countercurrent supercooler
30 and is added to the low-pressure column 7 via line 872 and valve
27. The liquid oxygen product 863 is extracted directly from the
bottom of the low-pressure column 7.
[0042] In the variant shown in FIG. 9, an additional mass transfer
section 967 is arranged in the low-pressure column, this section
having one to ten theoretical or practical plates. The reflux
liquids 57, 60 for the low-pressure column 7 and the medial column
6 are in this case, as in FIG. 1, removed directly from the top of
the high-pressure column via line 21. The liquid nitrogen 972 which
is obtained in the second condenser/evaporator 25 from the top gas
of the medial column and is then supercooled is restricted (927)
and injected below the mass transfer section 967. In this way,
fluctuations in concentration in the medial column 6 have less
effect on the purity of the products of the low-pressure column 7,
in particular on the liquid nitrogen product 64. Impure nitrogen is
extracted from an intermediate point of the low-pressure column 7
via the lines 973, 974 and 975 and is heated to approximately
ambient temperature in the heat exchangers 30 and 3.
[0043] FIG. 10 shows a conventional internal compression process.
(The remainder of the process corresponds to FIG. 9.) All the
oxygen product 1036 is extracted in liquid form from the
low-pressure column 7. That proportion 1076 which is not discharged
as liquid product 863 flows to a pump 1077, where it is brought to
the desired product pressure. Via high-pressure line 1078, the
liquid stream flows to the principal heat exchanger 1079, where it
is evaporated (or--if it is at supercritical
pressure--pseudo-evaporated). The heating means used for this
purpose is a third air stream 1080, which is brought to the
pressure required for this purpose in a recompressor 1081 with
recooler 1082 and is fed via line 1083 to the warm end of the
principal heat exchanger 3. The liquefied or supercritical
high-pressure air 1084 is fed into the high-pressure column 5 at a
suitable point via line 1085 and/or into the low-pressure column 7
via the lines 1086 and 1087.
[0044] As an alternative or in addition to the oxygen internal
compression, it is also possible for nitrogen 1088 from the
high-pressure column 5 to be internally compressed by means of a
pump 1089 and to be evaporated (or--if it is at supercritical
pressure--pseudo-evaporated) in the principal heat exchanger 3.
[0045] It is possible to improve the heat exchange operation in the
principal heat exchanger 3 by means of a two-turbine process, as
illustrated in FIG. 11. In this case, not only the air stream 1184
required for the internal compression but also two air streams 1113
and 1190/1191, which are expanded (expansion machines 1114 and
1192) in a work-performing manner to approximately the operating
pressure of the high-pressure column 5, are compressed further in
the recompressor. The turbine-expanded air streams are fed,
together with the direct air 2, to the bottom of the high-pressure
column 5 via line 1104. The internal-compression air 1184 and the
air 1113 for the cold turbine 1114 are recompressed together in two
series-connected recompressors which are driven by the turbines
1114, 1192.
[0046] The fact that air is not blown into the low-pressure column
7 in the process shown in FIG. 11 also enables argon to be obtained
by means of the process steps illustrated in dashed lines. A crude
argon column 1102 is in communication with the low-pressure column
7 via the lines 1100 and 1101. At the top of this crude argon
column 1102, gaseous crude argon 1103 is formed, a first part 1105
of which is condensed in a top condenser 1104 and is added as
reflux to the top of the crude argon column. The remainder 1106 is
extracted as gaseous product and, if appropriate, is processed
further. The top condenser 1104 is cooled by a part 1107 of the
supercooled bottom liquid 1131 of the medial column 6.
[0047] In FIG. 12, the supercooled bottom liquid 31 of the medial
column 6 is restricted (32) and injected directly into the
low-pressure column 7 in a similar manner to that illustrated in
FIG. 1. The second condenser/evaporator 25 is operated using a part
1293/1294 of the bottom liquid 1222 of the high-pressure column 5.
The vapour 1270 which is formed in the second condenser/evaporator
25 as well as the proportion 1271 which remains in liquid form are
introduced into the low-pressure column 7 at suitable points.
Otherwise, FIG. 12 does not differ from FIG. 8. This method of
cooling the second condenser/evaporator 25 can also be employed in
any of the processes illustrated in FIGS. 9 to 11.
[0048] Naturally, further combinations of the specific features of
the exemplary embodiments illustrated in the drawings are possible
within the scope of the invention.
[0049] The processes illustrated are particularly suitable for
combination with an IGCC process with gas turbine. The air 1 may be
compressed in a dedicated air compressor and/or may be completely
or partially extracted from a compressor coupled to the gas
turbine. At least some of the products (oxygen 44 if appropriate
for a gasification unit; nitrogen 18, 62, 35 if appropriate for
increasing the mass flow in the gas turbine and for reducing the
formation of NO.sub.x) are fed to the IGCC process, if appropriate
after further compression.
[0050] 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. Also, the preceding specific embodiments are to
be construed as merely illustrative, and not limitative of the
remainder of the disclosure in any way whatsoever.
[0051] The entire disclosure of all applications, patents and
publications, cited above and below, and of corresponding German
application 10103968.9, are hereby incorporated by reference.
[0052] 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.
* * * * *