[0001] The present invention relates to a process and an apparatus for the separation of
air by cryogenic distillation. Argon is mostly produced with an air separation process
by distillation at cryogenic temperatures.
[0002] The compressed and purified air is sent to a double column including a first column
operating at a first pressure and a second column operating at a second pressure,
the second pressure being lower than the first pressure. Oxygen enriched liquid and
nitrogen enriched liquid are sent from the first column to the second column. Oxygen
rich fluid is removed from the bottom of the second column and nitrogen enriched gas
is removed from the top of the second column.
[0003] An argon enriched stream, contains nitrogen and oxygen, is removed from an intermediate
point of the second column and separated by cryogenic distillation. The stream typically
contains between 5 and 15 mol% argon. Argon volatility being between those of oxygen
and nitrogen, for a pure argon product, two argon columns are required to get on specification,
typically less than 1 ppm oxygen and nitrogen being required in the argon product,
whilst for a less pure argon product one argon column is sufficient.
[0004] The first column (called crude argon column in the remaining description) removes
oxygen from argon and nitrogen, this separation is the more difficult one due to the
close volatility of oxygen and argon. Such a column is typically 60 meters in height.
The second column (called pure argon column) removes nitrogen from argon; this separation,
much easier, requires only a short column.
[0005] The top product of the crude argon column, free of oxygen, is then sent to the pure
argon column. The reflux of the crude argon column flows down the column and the bottom
liquid is pumped back to the second column.
[0006] Starting-up the crude argon column and converging to the required purity specification
take a long time, on average 18 hours, because of the difficulty of separating argon
and oxygen and because of the relatively small argon input in the crude argon column
in comparison with the required total liquid argon hold-up the packings and distributors.
[0007] During the operation, the main risk of in the crude argon column is a high N2 ingress
from the second column. This will reduce the temperature at the top of the crude argon
column and block the top condenser thus interrupting the flow from the second column
to the crude argon column and the crude argon column will stop.
[0008] The key points to keep in mind regarding the crude argon column are that:
- typically the crude argon column cannot run without the double column of the air separation
unit
- the crude argon column is sensitive to upsets in the second column
- the crude argon column requires a long restart time
[0009] The proposed idea here is a configuration, which allows at least part of the crude
argon column to run at a reduced load in closed loop mode while the remaining part
of the air separation unit is either in cold stand-by or suffering a major upset.
The major advantage is that the crude argon column is ready to produce whenever the
cold stand-by or the upset is over.
[0010] "Cold stand-by" means that the distillation column does not function but remains
at a cryogenic temperature, either because the stand-by duration is so short that
the temperature does not rise above cryogenic temperatures or because refrigeration
is added to the column, for example by adding a cryogenic liquid to the column from
an outside source.
[0011] Having an air separation unit in cold stand-by for few hours may become the rule
in the future, since the energy supply from certain sources, such as renewables, is
intermittent. The proposed solution here aims at adapting the air separation unit
for such conditions, keeping the argon part in operation and ready to use during a
stoppage of the column feeding the crude argon column, at reasonable energy cost.
According to the invention, the crude argon column is kept running using a cycle to
provide reboil to the column, the cycle fluid being an argon enriched gas from the
top of the crude argon column. This presents the advantage of using a fluid present
in the crude argon column, rather than importing a fluid from an external source.
[0012] According to our calculations, comparing the cost of keeping the crude argon column
running and the cost of restarting the crude argon column, it is economical to run
the crude argon column on its own for several days, rather than to restart it. According
to the invention, there is provided a process for the separation of air by cryogenic
distillation in which :
- i) During a first operation mode, compressed and purified air is sent to a first distillation
column operating at a first pressure, an oxygen enriched liquid is sent from the first
distillation column to a second distillation column operating at a second pressure
lower than the first pressure, a nitrogen enriched liquid is sent from the first distillation
column to the second distillation column, the first distillation column being thermally
linked with the second distillation column via a bottom reboiler of the second distillation
column, an oxygen enriched fluid is removed from the bottom of the second distillation
column, a nitrogen enriched gas is removed from the top of the second distillation
column, a feed stream containing between 5 and 15% mol argon is sent from the second
column to the bottom of a crude argon column and a stream containing proportionally
more argon than the feed stream is removed from the top of the crude argon column
and
- ii) During a second operation mode, no air is sent the first distillation column,
no liquids are sent from the first to the second distillation column, no feed stream
is sent from the second distillation column to the crude argon column and no stream
containing more argon than the feed stream is removed from the top of the crude argon
column wherein during the second operation mode, a cycle stream is removed from the
top of the crude argon column, at least part of the cycle stream is used to warm a
bottom reboiler of the crude argon column being thereby condensed to form a condensed
cycle stream, the condensed cycle stream being sent to the top of the crude argon
column and the stream, if present, containing proportionally more argon than the feed
stream removed from the top of the upper section constitutes at most 20% of the flow
of that stream during the first operation mode.
[0013] According to other optional features:
- during the first operation mode, a nitrogen enriched gas or liquid is removed from
the top of the second distillation column,
- during the first operation mode, a stream containing proportionally more argon than
the feed stream is removed from the top of the crude argon column for further purification
or for direct use as a product stream
- during the first operation mode, no stream is used to warm the bottom reboiler of
the crude argon column.
- in the second operation mode, the stream containing proportionally more argon than
the feed stream removed from the top of the crude argon column constitutes at most
10% of the flow of that stream during the first operation mode
- during the second operation mode at least part of the cycle stream is compressed in
a compressor having a cryogenic inlet temperature upstream of the reboiler.
- during the second operation mode the condensed cycle stream is pressurized by a pump
before being sent to the top of the crude argon column.
- during the second operation mode, part of the cycle stream is vented or used as a
product.
- -during the second operation mode, part of the cycle stream is condensed in a condenser
other than the bottom reboiler and then sent back to the crude argon column.
- during the second operation mode, any valves on conduits between the second column
and the crude argon column are closed.
[0014] According to another object of the invention there is provided a process for the
separation of air by cryogenic distillation in which :
- i) During a first operation mode, compressed and purified air is sent to a first distillation
column operating at a first pressure, an oxygen enriched liquid is sent from the first
distillation column to a second distillation column operating at a second pressure
lower than the first pressure, a nitrogen enriched liquid is sent from the first distillation
column to the second distillation column, the first distillation column being thermally
linked with the second distillation column via a bottom reboiler of the second distillation
column, an oxygen enriched fluid is removed from the bottom of the second distillation
column, a nitrogen enriched gas is removed from the top of the second distillation
column, a feed stream containing between 5 and 15% mol argon is sent from the second
column to the bottom of a crude argon column having a lower section and an upper section
and a stream containing proportionally more argon than the feed stream is removed
from the top of the upper section of crude argon column and
- ii) During a second operation mode, no air is sent the first distillation column,
no liquids are sent from the first to the second distillation column, no feed stream
is sent from the second distillation column to the crude argon column in two sections
and no stream containing more argon than the feed stream is removed from the top of
upper section, the crude argon column wherein during the second operation mode, a
cycle stream is stream is removed from the top of the crude argon column, at least
part of the cycle stream is used to warm a bottom reboiler of the upper or lower section
of the crude argon column being thereby condensed to form a condensed cycle stream,
the condensed cycle stream being sent to the top of the upper section of the crude
argon column. and the stream, if present, containing proportionally more argon than
the feed stream removed from the top of the crude argon column constitutes at most
20% of the flow of that stream during the first operation mode.
[0015] According to another object of the invention there is provided an apparatus for the
separation of air by cryogenic distillation comprising a first distillation column
operating at a first pressure, a second distillation column operating at a second
pressure lower than the first pressure, the second distillation column having a bottom
reboiler, a crude argon column having a top condenser and a bottom reboiler, a conduit
for sending compressed and purified air to the first distillation column operating
at a first pressure, a conduit for sending an oxygen enriched liquid from the first
distillation column to the second distillation column operating at a second pressure
lower than the first pressure, a conduit for sending a nitrogen enriched liquid from
the first distillation column to the second distillation column, the first distillation
column being thermally linked with the second distillation column via the bottom reboiler
of the second distillation column, a conduit for removing an oxygen enriched fluid
from the bottom of the second distillation column, a conduit for removing nitrogen
enriched gas from the top of the second distillation column, a conduit for sending
a feed stream containing between 5 and 15% mol argon from the second column to the
bottom of a crude argon column, possibly a conduit for removing a stream containing
more argon than the feed stream from the top of the crude argon column characterized
in that it comprises a conduit for sending at least part of a cycle stream to the
reboiler and a conduit for sending a condensed cycle stream from the reboiler to the
top of the crude argon column and means for closing the conduit for sending air to
the first distillation column and/or means for closing the conduit for sending the
feed stream from the second distillation column to the crude argon column.
[0016] The apparatus optionally comprises:
- a compressor for compressing the cycle stream downstream of the removal from the crude
argon column and upstream of the bottom reboiler of the crude argon column.
- a pump for sending at least part of the cycle stream in condensed form back to the
crude argon column.
- a conduit from sending bottom liquid from the crude argon column to the second distillation
column, said conduit being closable via closure means.
- means for venting at least part of the cycle stream.
[0017] The invention will be described in detail with reference to the figures, Figure 1
representing schematically the first and second columns of an apparatus according
to the invention and Figures 2 to 6 representing a crude argon column of an apparatus
according to the invention.
[0018] Figure 1 shows the first and second columns of an apparatus for the separation of
air by cryogenic distillation, designed to be connected to a crude argon column according
to one of Figures 2 to 6.
[0019] During a first operation mode corresponding to normal operation of the air separation
unit, air 101 is compressed in a compressor C01, purified from water and carbon dioxide
in adsorbers R01, R02, cooled in heat exchanger 103 and divided in two. One part of
the compressed and purified air is compressed in a cold compressor V02, cooled in
heat exchanger 103 and divided in two. One part is expanded in a Claude turbine D01
and sent to the first distillation column as gaseous stream 105. The rest 107 is cooled
completely in heat exchanger 103 and sent as a liquid to first column K01.
[0020] Other types of feed air treatment are of course possible (no booster, no cold booster
with a warm booster etc).
[0021] Compressed and purified air 105 is sent to the first distillation column K01 operating
at a first pressure, generally between 4 and 15 bars abs, and is separated in the
first distillation column to form an oxygen enriched liquid at the bottom of the column
and a nitrogen enriched gas at the top of the column. Oxygen enriched liquid 109 is
sent from the first distillation column to a second distillation column K02 operating
at a second pressure lower than the first pressure, generally between 1.2 and 4 bars
abs. Part 113A of the oxygen enriched liquid is sent to a top condenser E1 of the
crude argon column to be vaporized. A nitrogen enriched liquid is sent from the first
distillation column K01 to the second distillation column K02. The first distillation
column K01 is thermally linked with the second distillation column K02 via a bottom
reboiler of the second distillation column. A feed stream 1 containing between 5 and
15% mol argon removed from an intermediate point of the second column K02 is sent
to the bottom of a crude argon column K10, as illustrated in any one of Figures 2
to 6.
[0022] Oxygen enriched liquid 31 from the bottom of the crude argon column is sent back
to the second column K02.
[0023] Oxygen rich liquid 27 is removed from the bottom of the second column K02 and vaporized
in exchanger 103. Nitrogen rich gas 23 from the top of the second column K02 is also
warmed in exchanger 103.
[0024] In Figure 2, column K10 operates at just above atmospheric pressure and stream 3
is compressed to 2.3 bara. During the first operation mode, in normal operation, the
feed stream 1 containing between 5 and 15% mol argon removed from an intermediate
point of the second column K02 to the bottom of the crude argon column K10 in which
it is separated, forming an oxygen enriched stream at the bottom of crude argon column
K10 and an argon enriched stream at the top of the crude argon column.
[0025] The crude argon column K10 has a top condenser E1 and a bottom reboiler E2. The bottom
reboiler E2 does not function during the first operation mode, i.e. during normal
operation. The top condenser E1 functions during the first operation mode, i.e. during
normal operation but not in the second operation mode.
[0026] The top condenser E1 condenses a top gas of the crude argon column and sends the
liquid formed back to the column as a reflux.
[0027] The argon enriched stream at the top of the crude argon column may be in liquid or
gaseous form. It may be removed as a final product (not shown) or it may be sent to
a pure argon column for further purification Part of stream 3 may be produced as a
product stream or may be further purified, this stream, if present, containing constituting
at most 20% of the flow of that stream during the first operation mode. Cooling for
the condenser E1 is provided by stream 113A from the bottom of the first distillation
column K01 or another appropriate fluid.
[0028] During a second operation mode, the double column K01, K02 of Figure 1 does not function.
This may be because of an accidental or deliberate stoppage of the column. For example,
the main air compressor C01 may break down and cause an accidental stoppage. In the
case of deliberate stoppage, when energy for the compressor C01 is not available,
the double column K01, K02 may be closed down in a programmed way, whilst remaining
preferably at cryogenic temperature or at least temperatures below zero, this situation
being known as a "cold standby". In this mode, no air is sent the first distillation
column, no liquids are sent from the first to the second distillation column, no feed
stream is sent from the second distillation column to the crude argon column and no
stream containing more argon than the feed stream is removed from the top of the crude
argon column as a product. Alternatively an argon enriched stream representing at
most 20% of the argon enriched stream removed from the argon column K10 in the first
operation mode is removed from the argon column in liquid or gaseous form.
[0029] Specific means, such as valves, may be provided for closing a conduit to prevent
air being sent to the first distillation column and/or a conduit for sending the feed
stream from the second distillation column to the crude argon column and/or a conduit
for sending bottom liquid from the crude argon column to the second distillation column,
during the second operation mode.
[0030] Stream 113A is not sent to the condenser E1 during the second operating mode. During
shut-down of a double column (K01, K02), the argon column (K10) keeps functioning
or is in a ready to function state, using a cycle stream (3) to heat a bottom reboiler
(E2) of the argon column.
[0031] However, if the crude argon column remains in a state of operation, the purities
of the fluids within the column remain stable or at least do not increase beyond an
acceptable extent. A cycle stream 3 containing more argon than the feed stream, for
example 80 to 99,5% mol argon or even up to 99,9% argon and less than 1ppm 02, is
removed from the top of the crude argon column K10, is sent to a heat exchanger E4,
compressed in a compressor C, cooled in a cooler R using cooling water forming a cooled
stream 5, cooled in heat exchanger E4 and then used to warm a bottom reboiler E2 of
the crude argon column. The cycle stream is condensed in the bottom reboiler E2 to
form a condensed cycle stream, the condensed cycle stream being sent to the top of
the crude argon column after pressurization in a pump P.
[0032] If this cycle stream were not used, the liquid hold-up on the distributors and packings
of the crude argon column would fall to the bottom of the column and time would be
required to reestablish the liquid levels and the purity profile on restarting the
crude argon column K10.
[0033] The use of the cycle stream to provide reboil for the crude argon column ensures
that the liquid levels are maintained within the column at least to some extent. The
use of the cycle stream to provide vapor and reflux to the crude argon column ensures
that the purity profile is maintained along the crude argon column
[0034] Part of stream 3 may be produced as a product stream or may be further purified,
this stream, if present, containing constituting at most 20% of the flow of that stream
during the first operation mode.
[0035] It may be necessary to provide some additional refrigeration during the second operation
mode to compensate for E4 and P loss of cold and to subcool stream 8 in order to limit
the downstream flash of stream 9
[0036] The crude argon column K10 of Figure 3 differs from that of Figure 2 in that part
3A of the cycle gas 3 warmed in heat exchanger E3 is sent to the compressor C and
part 3B is vented. Thus in the second operation mode, the gas is warmed and then divided
in two, one part being compressed and the rest vented. In Figure 3, there is a vent
due to the fact that the cold losses and the flash are not compensated. This specific
run case of Fig3 will last until a low level at the bottom of the K10 column is reached
in the second operating mode.
[0037] In FIG 4 in both modes, column K10 operates at just above atmospheric pressure and
stream 3 is compressed to 2.3 bara in compressor C so to be able to be condensed in
reboiler E2. Typically stream 3 is compressed to between 0,2 and 2 bar above the pressure
of the argon column K10.
[0038] In Figure 4, the exchanger E3 is not used. In the second operation mode, the cycle
gas 3 is sent directly to the compressor C via valve V2 and then divided into parts
13A, 13B. Stream 13A is condensed in condenser E5 against a liquid nitrogen stream,
by opening valve V3 using for example a PIC at the top of the column K10. Streams
13A downstream the condenser E5 and 13B are sent to a common phase separator S and
gas from the phase separator is sent to the bottom reboiler E2 to be condensed. The
condensed stream from E2 is sent to the separator S and the liquid 8 from the separator
is pressurized in the pump P before being sent back to the column K10 viva valve V4
as two-phase stream 9. The pump P is required to overcome the hydrostatic pressure,
column K10 being over 60m in height.
[0039] During the first operation mode, the cycle gas is not used to reboil the crude argon
column K10 and so the compressor C and pump P do not operate, for all of Figures 2
to 4.
[0040] Typically valve V2 control the flow 3, the column pressure is controlled via valve
V3 and the level of separator S is controlled with valve V4.
[0041] A stream of argon enriched gas or liquid is produced from the top of column K10 (not
shown).
[0042] During the second operation mode, the crude argon column K10 may be separated from
the double column K01,K02 by closing valves on the conduit for sending the feed gas
1 to the crude argon column K10 and on the conduit for sending the bottom liquid from
the crude argon column K10 to the second column K02.
[0043] It may be possible to operate during the second operation mode without closing any
valve on the conduit for sending the feed gas 1 to the crude argon column K10, thus
the valve will not necessarily be present or may have a particularly low pressure
drop.
[0044] Part of stream 3 may be produced as a product stream or may be further purified,
this stream, if present, containing constituting at most 20% of the flow of that stream
during the first operation mode.
[0045] In these examples, the crude argon column K10 is comprised of a single column section,
however it will be appreciated that the crude argon column may comprise two to four
column sections.
[0046] Figures 5 and 6 show the example where the crude argon column is divided in two sections
K10.1 and K10.2, K10.1 corresponding to the lower part of the crude argon column and
K10.2 the upper part.
[0047] During the first operation mode for Figures 5 and 6, argon enriched gas 1 is sent
from the second column K02 to the bottom of column K10.1, gas from the top of column
K10.1 is sent to the bottom of column K10.2, liquid from the bottom of column K10.2
is sent to the top of column K10.1 and an argon rich product is removed at the top
of column K10.2, under the top condenser E1. During the first operation mode, bottom
reboiler E2 at the bottom of column K10.1 in Fig 5 and the bottom of column K10.2
in Fig 6 does not operate. A stream of argon enriched gas or liquid is produced from
the top of column K10.2 (not shown).
[0048] During the second operation mode, for Figure 5, argon enriched gas 1 is not sent
from the second column K02 to the bottom of column K10.1, however gas from the top
of column K10.1 is sent to the bottom of column K10.2, liquid from the bottom of column
K10.2 is sent to the top of column K10.1. No argon rich product is removed at the
top of column K10.2, under the top condenser E1. During the second operation mode,
bottom reboiler E2 at the bottom of column K10.1 in Fig 5 operates. Gas from the top
of the column K10.2 is compressed in compressor C condensed in reboiler E2 to form
condensed stream 7 which is pumped in pump P and sent to the top of column K10.2.
Thus both columns K10.2 and K10.1 are in operation. During the second operation mode,
for Figure 6, argon enriched gas 1 is not sent from the second column K02 to the bottom
of column K10.1, gas from the top of column K10.1 is not sent to the bottom of column
K10.2, liquid from the bottom of column K10.2 is not sent to the top of column K10.1.
No argon rich product is removed at the top of column K10.2, under the top condenser
E1. During the second operation mode, bottom reboiler E2 at the bottom of column K10.2
in Fig 6 operates. Gas 3 from the top of the column K10.2 is compressed in compressor
C condensed in reboiler E2 to form condensed stream 7 which is pumped in pump P and
sent to the top of column K10.2. Thus only column K10.2 is in operation.
[0049] Part of stream 3 may be produced as a product stream or may be further purified,
this stream, if present, containing constituting at most 20% of the flow of that stream
during the first operation mode.
1. Process for the separation of air by cryogenic distillation in which :
i) During a first operation mode, compressed and purified air is sent to a first distillation
column (K01) operating at a first pressure, an oxygen enriched liquid (109) is sent
from the first distillation column to a second distillation column (K02) operating
at a second pressure lower than the first pressure, a nitrogen enriched liquid (115)
is sent from the first distillation column to the second distillation column, the
first distillation column being thermally linked with the second distillation column
via a bottom reboiler (43) of the second distillation column, an oxygen enriched fluid
(27) is removed from the bottom of the second distillation column, a nitrogen enriched
gas (23) is removed from the top of the second distillation column, a feed stream
(1) containing between 5 and 15% mol argon is sent from the second column to the bottom
of a crude argon column (K10) and a stream (3) containing proportionally more argon
than the feed stream is removed from the top of the crude argon column and
iii) During a second operation mode, no air is sent the first distillation column,
no liquids are sent from the first to the second distillation column and no feed stream
is sent from the second distillation column to the crude argon column wherein during
the second operation mode, a cycle stream (3) is removed from the top of the crude
argon column, at least part of the cycle stream is used to warm a bottom reboiler
(E2) of the crude argon column being thereby condensed to form a condensed cycle stream
(7), the condensed cycle stream being sent to the top of the crude argon column and
the stream, if present, containing proportionally more argon than the feed stream
removed from the top of the crude argon column constitutes at most 20% of the flow
of that stream during the first operation mode.
2. Process according to Claim 1 wherein during the first operation mode, no stream is
used to warm the bottom reboiler (E2) of the crude argon column.
3. Process according to Claim 1 or 2 wherein during the second operation mode at least
part of the cycle stream is compressed in a compressor (C) having a cryogenic inlet
temperature upstream of the reboiler (E2).
4. Process according to any preceding claim wherein during the second operation mode
the condensed cycle stream (7) is pressurized by a pump before being sent to the top
of the crude argon column (K10).
5. Process according to any preceding claim wherein during the second operation mode,
part (3B) of the cycle stream (3) is vented or used as a product.
6. Process according to any preceding claim wherein during the second operation mode,
part (13A) of the cycle stream is condensed in a condenser (E5) other than the bottom
reboiler (E2) and then sent back to the crude argon column.
7. Process according to any preceding claim wherein during the second operation mode,
any valves on (V1) conduits between the second column (K02) and the crude argon column
(K10) are closed.
8. Process for the separation of air by cryogenic distillation in which :
i) During a first operation mode, compressed and purified air (105, 107) is sent to
a first distillation column (K01) operating at a first pressure, an oxygen enriched
liquid (109) is sent from the first distillation column to a second distillation column
(K02) operating at a second pressure lower than the first pressure, a nitrogen enriched
liquid (115) is sent from the first distillation column to the second distillation
column, the first distillation column being thermally linked with the second distillation
column via a bottom reboiler (43) of the second distillation column, an oxygen enriched
fluid (27 is removed from the bottom of the second distillation column, a nitrogen
enriched gas (23) is removed from the top of the second distillation column, a feed
stream (1) containing between 5 and 15% mol argon is sent from the second column to
the bottom of a crude argon column (K10) having a lower section (K10.1) and an upper
section (K10.2) and a stream (3) containing proportionally more argon than the feed
stream is removed from the top of the upper section of crude argon column and
iii) During a second operation mode, no air is sent the first distillation column,
no liquids are sent from the first to the second distillation column, no feed stream
is sent from the second distillation column to the crude argon column in two sections
and no stream containing more argon than the feed stream is removed from the top of
upper section, the crude argon column wherein during the second operation mode, a
cycle stream (3) is removed from the top of the crude argon column, at least part
of the cycle stream is used to warm a bottom reboiler (E2) of the upper or lower section
of the crude argon column being thereby condensed to form a condensed cycle stream
(7), the condensed cycle stream being sent to the top of the upper section of the
crude argon column and the stream, if present, containing proportionally more argon
than the feed stream removed from the top of the upper section constitutes at most
20% of the flow of that stream during the first operation mode.
9. Apparatus for the separation of air by cryogenic distillation comprising a first distillation
column (K01) operating at a first pressure, a second distillation column (K02) operating
at a second pressure lower than the first pressure, the second distillation column
having a bottom reboiler (43), a crude argon column (K10) having a top condenser (E1)
and a bottom reboiler (E2), a conduit for sending compressed and purified air (105,
107) to the first distillation column operating at a first pressure, a conduit for
sending an oxygen enriched liquid (109) from the first distillation column to the
second distillation column operating at a second pressure lower than the first pressure,
a conduit for sending a nitrogen enriched liquid (115) from the first distillation
column to the second distillation column, the first distillation column being thermally
linked with the second distillation column via the bottom reboiler (43) of the second
distillation column, a conduit for removing an oxygen enriched fluid (27) from the
bottom of the second distillation column, a conduit for removing nitrogen enriched
gas (23) from the top of the second distillation column, a conduit for sending a feed
stream (1) containing between 5 and 15% mol argon from the second column to the bottom
of a crude argon column, possibly a conduit for removing a stream containing more
argon than the feed stream from the top of the crude argon column characterized in that it comprises a conduit for sending at least part of a cycle stream to the reboiler
and a conduit for sending a condensed cycle stream from the reboiler to the top of
the crude argon column and means for closing the conduit for sending air to the first
distillation column and/or means for closing the conduit for sending the feed stream
from the second distillation column to the crude argon column.
10. Apparatus according to Claim 9 comprising a compressor (C) for compressing the cycle
stream (3) downstream of the removal from the crude argon column (K10) and upstream
of the bottom reboiler (E2) of the crude argon column.
11. Apparatus according to Claim 9 or 10 comprising a pump for sending at least part of
the cycle stream (7) in condensed form back to the crude argon column (K10).
12. Apparatus according to Claim 9, 10 or 11 comprising a conduit from sending bottom
liquid from the crude argon column (K10) to the second distillation column (K10),
said conduit being closable via closure means.
13. Apparatus according to any of Claims 9 to 12 including means for venting at least
part (3B) of the cycle stream.