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Jan. 7, 1947.
‘
.
w. DENNIS
'
2,413,752
SEPARATION OF THE CONSTITUENTS 0F GASEOUS MIXTURE$
Filed July 28, 1944
2 Sheets-Sheet 1
JCRUBE'
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I
s'rs .nsm
INVENTOR
' [1/6 /¢a 7'11,“ 14‘
'
‘I
BY
‘
ATTORNEYS
. Jan. 7, 1947. '
w, DENNls
2,413,752
SEPQRATION OF THE CONSTITUENTS' OF GASEOUS MIXTURES
Filed July 28, 1944
2 Sheets-Sheet 2
ATTO R N EYS
Patented Jan. 7, 1947
2,413,752
UNITED STATES .PA'II'ENTV OFFICE
2,413,752
SEPARATION OF THE CONSTITUENTS OF
GASEOUS MIXTURES
Wolcott Dennis, Darien, Conn., asslgnor to Air
Reduction Company, Incorporated, New'York,
N. Y.~,> a corporation of New York
.
‘Application July 28, 1944, Serial No. 547,048
,8‘ Claims. . (.01. sz-nasy
1
.. I.
This invention relates to the separation of the
constituents of gaseous mixtures'by liquefaction
2
produce refrigeration and the application \.of a
scrubber to the ?rst expansion engine exhaust
and recti?cation and particularly to the removal
results in a saturated vapor which cannot be
of impurities present in the gaseous mixture with
expanded eliiciently in the second engine due to
out resort to chemical treatment. While intended 5 formation of liquid within the engine vduring ex
primarily for use in the treatment of air, it may
pansion. In order to produce the maximum ex
be utilized in the recovery of the constituents of
pansion work and hence the most refrigerative
other gaseous mixtures.
effect, it is desirable .to admit air to the second
One of the problems in the recovery of oxygen,
engine at the highest practicable temperature.
‘nitrogen, etc., from the atmosphere results from 10 and to avoid excessive pressure drops.
.
the presence of carbon dioxide in the air treated.v
I have discovered that solidi?ed particles of
Since carbon dioxide congeals at the low temper
carbon dioxide, residual moisture, oil and other
atures employed, it interferes with the‘ operation
hydrocarbons may be separated readily from a
unless removed. It is customary to subject the \_ gaseous mixture such as air entering a liquefac
air to treatment in largecaustic towers to remove 15 tion system by the procedure hereinafter de
the carbon dioxide. This introduces considerable
scribed, and that the operation may be conducted
expense and other dii?culties. Oil and hydrocar
‘with great e?lciency. ‘In carrying out, the inven
bon derivatives are introduced in the compressors
tion, the air is initially compressed to a relatively _
employed to raise the pressure of the air, and
high pressure and portions thereof are expanded
since such compounds are not readily removable 20 consecutively with external work. The air is
from the air, they accumulate in the system and‘
subjected between expansions to the scrubbing
?nd their way into the products.
;
action of liquid produced from a portionof the
It is the object of the present invention to pro
‘air to concentrate solidi?ed impurities therein
vide a simple, economical and effective method of
and the liquid containing the impurities is either
, removing impurities from gaseous mixtures and
particularly to ensure the elimination of impuri
vaporized or ?ltered so that the impurities are
separated. The air which is delivered to the rec-'
ties such as carbon dioxide in a liquefaction
ti?er is free vfrom impurities and consequently
method employing successive‘ expansion of air
none of them can accumulate in the liquid oxy
with external work to produce refrigeration.
gen product.
Another object ‘of the invention is the pro 30 The drawings illustrate two procedures by
vision .of a method of producing liquid oxygen
which the solidi?ed carbon dioxide and other
free from impurities and in an efficient manner.
Other objects ‘and advantages of the invention
will be apparent as it is better understood by
reference to the following speci?cation. and the
accompanying drawings, in which
Fig. l is a diagrammatic illustration of an ap
paratus suitable for the practice of_the inven
tion; and
impurities are removed in such a liquefaction
. cycle without interfering materially with the
thermodynamic e?iciency of the method. Both of
these procedures employ a scrubber in which the
exhaust air of the ?rst or high level expansion is
puri?ed by contacting with the lique?ed portion
of the high pressure air after throttling to a lower
pressure. A portion of the scrubbed air is
Fig. 2 is a similar view illustrating a modi?ed 40 warmed up by exchange of heat between the high
form of the apparatus.
.
level engine exhaust ‘and itself and then passes
When a single column is used to produce. a
to the second or low level expansion engine and
liquid oxygen product the air pressure required to
then after the second expansion to the column
produce the necessary refrigeration may be ma
low pressure recti?er. Sufficient superheat is ob
terially reduced by employing a second expansion 45 tained in the inlet gas to the low level expander
engine or turbine expanding a portion of the
to insure e?lcient expansion at this point.
?rst or high pressure engine exhaust to a lower
The drawings illustrate two procedures for pur
pressure and exhausting this portion into the
i?cation of the impure liquid reaching the bot
column recti?er. In. this way efficient production
tom of the scrubber in which the impurities of _
of liquid oxygen may be carried out at initial air 50 the original air are accumulated. In one case
pressure of about 40 atmospheres.
the impure liquid is ?ltered before admission to,
The use of ?lters for carbon dioxide removal in
the recti?cation column and means are provided
such a method leads to complications in the oper
for draining the impurities from‘ the ?lter from
ation of the plant and to pressure drops which
time to time and backwashing the ?lter cloth
interfere with e?icicnt expansion of the air to 55 when necessary. In the other case the impure
2,418,752
4
.
'
accumulate ‘in the liquid which remains unva
porized in the vaporizer 35 and may be withdrawn
liquid is admitted to a small vaporizer at reduced
pressure and is vaporized by-heat exchange with
4 from time to time through a purge 4'! controlled
condensing puri?ed vapor from the scrubber out
by a valve 48.
let. The vapor produced from the impure liquid _
is admitted to the low pressure recti?er together 5
It will be noted that all of the .air entering the
with the exhaust oi the second engine. From
column .5 through the pipes 42 and 45 has. been
time to time as required the impurities accumupurified initially by scrubbing and subsequently
lating in the vaporizer are purged, '
.
by vaporization of the liquid formed in the lique
Referring to the drawings, 5 indicates a column
7 tier 2|. Impurities which solidity at the tem
. provided with the usual trays 6 and bubblecaps ‘I. l0 perature involved are retained in the vaporizer
At the bottom of the column, a vaporizer section
8 is provided with tubes 9 terminating in aheader
ill to which air is fedthrough a pipe ||. The air
-
'
35, and by purging liquid from the vaporizer at
intervals, such impurities can be withdrawn from
the system. The impurities do not enter the col
umn 5 and consequently the liquid oxygen ac
is'lique?ed in the tubes by heat exchange with " cumulating in the vaporizer 8 is free from such
liquid oxygenac umulating in the vaporizer seo- _
tion 8 from whic the liquid oxygen may be with;
' impurities.
By" expanding the air successively
with external work, it is possible to maintain the
necessary refrigeration to permit operation in the
manner described andto maintain e?icient and
drawn through a pipe l2 controlled by a valve II.
The liquid air is withdrawn through a pipe l4 and
delivered through an expansion, valve l5 to the
economical application of the principles involved.
top of the column 5. As it ?ows downwardly over 20
Referring to Fig. 2; acolumn 55 is provided with
the trays 6, the liquid is progressively enriched in
the usual trays 5| and bubble caps 52. A vaporizer
oxygen. Vapor rich in nitrogen‘ is withdrawn
53 at the bottom of the column is provided with
through the pipe.|5.
'
I
'
tubes 54 and a- header 55 connected to a pipe 56.‘
The air to be separated is initially compressed
Air introduced through.‘ the pipe 55 is lique?ed by
in suitable apparatus (not, shown) to a relatively 25 heat exchangewith liquid oxygen accumulating
high pressure, for example about 40 atmospheres,
in the vaporizer 53 from which it may be‘ with
andafter initial cooling is introduced through a I drawn through a pipe 51 controlled by a valve 58.
pipe l1 to an exchanger l8 where it is further ,Liquid airproduced in the tubes 54 is withdrawn
cooled by heat exchange with the nitrogen eiiiuent 30 through a pipe 59 and expansion valve. 55 and is
from the column 5. The air is withdrawn through
delivered by a pipe 5| to the top of the column 50.
a pipe l9 and a portion thereof diverted through
It ?ows downwardly over the trays 5|, becoming
a pipe 20 to a lique?er 2| where the air is further
enriched in oxygen. An eiliuent consisting prin
cooled and lique?ed by‘ heat exchange with, the
cipally of nitrogen is withdrawn'through a pipe 52.,
nitrogen eiiiuent. The liquid from the lique?er 2|
The air to be separated, initiallycompressed to I
is delivered by a pipe 22 through an-expansion
a relatively high pressure for example 40 atmos
valve 23 whereby the pressure is reduced to ap
pheres, is introduced through a pipe 53 to an ex-'
proximately. 5 atmospheres. The liquid ?ows
changer 54 where it is cooled by heat exchange
through a pipe 24 to a scrubber 25 having trays
with _ the e?iuent nitrogen.
It is withdrawn
26 and bubble caps 21.
_
through a pipe 55, and a portion is diverted by
The remainder of the air is delivered through 40 pipe 55 to a lique?er 51 where the air is further
a pipe 28 to anexpansion engine 29 where it is
cooled and lique?ed by heat exchange with the
expanded with external work to a suitable pres
eiiluent nitrogen. The liquid is delivered by a
sure for example about 5 atmospheres. From the
pipe 58 to an expansion valve 39 whereby the
engine, the expanded air passes through a pipe 30 45 pressure is reduced, for example to' about 5 at
to an exchanger 3| wherein it is further cooled
v mospheres, at which pressure the liquid is deliv
by heat exchange-with air from the scrubber 25.
ered by a pipe 10 to a scrubber 1| having trays
Leaving the exchanger 3 i, the air is delivered by a
12 and bubble caps 13.
‘
pipe 32 to the bottom' of the scrubber '25 and
The
remainder
of
the
air
is
delivered
through
passes upwardly through the trays 26 in contact 50 a pipe 14 to an expansion engine ‘I5 where it is
with the liquid air supplied through the pipe 24.
expanded with external work to a suitable pres
Impurities in the gaseous phase air accumulate in
sure, for example about 5 atmospheres. , Thence
the liquid which is withdrawn through a pipe 33. '
the air travels through a pipe 15 to an exchanger
The liquid passes through an expansion valve 34
where'it is further cooled by heat exchange
whereby the pressure is reduced to approximately 55 ‘ll
with vapors from the scrubber ‘I |.- The air is de
1 atmosphere, at which pressure the liquid is de
livered through a pipe 18 to the bottom of the
livered through a pipe 35 to a vaporizer 36.
s upwardly through the
The vapor phase air escaping from the scrubber " scrubber ‘H and passe th a liquid. Impurities.
trays
12
in
contact
wi
25 through a pipe 31 is separated into two parts,
in the air are thus transferred to the _
one of which is delivered by a pipe 38 to the ex so present
liquid
in
which they accumulate. The liquid con
changer 3| wherein it is. warmed by heat ex ' taining the
impurities is delivered through a pipe
change with expanded air from the engine 29.
‘it and ‘expansion valve 80 to a pipe 8| which is
The vapor phase air is withdrawn through a pipe
connected to a ?lter 82 including a ?lter element
39 and delivered to an expansion engine 40 where
83 oi! any suitable material which will prevent
it is expanded with external work to a pressure of 65 passage or solid particles of carbon dioxide and
approximately 1 atmosphere. From the engine 40
the like while permitting the liquid to escape.
the low pressure air is delivered through pipes 4|
The vapor phase air from the scrubber 1|‘ is
and 42 to the upper level of the column 5.
'
withdrawn through a pipe 84 and a portion there
The remainder of the vapor, phase air is de
of is delivered to the .exchanger 11 for heat ex-'
livered through a pipe 43 to a coil 44 .in the va
porizer 35. It is further. cooled in vaporizing
liquid in the vaporizer 35 and is delivered through
_ a pipe 45 to the pipe H at the bottom of the col- '
umn 5. The vapor from the vaporizer 35 escapes
70 change with the air from'the expansion engine
75. The vapor phase air is withdrawn through a
pipe 85 and delivered to an expansion engine 85
where it is expanded with external'work to a
suitable pressure, for example about 1 atmos- '
through apipe 46 and joins the expanded air en; 75 phere. Thence it is delivered through pipes 81
tering the column through the pipe 42., Impurities
2,413,702
5
6
and 88 to an upper level of the column 50. The
balance of the vapor phase air from the scrubber
‘II is delivered through a'pipe 89 to the pipe 56
to provide liquid in the column 50.
with external work, scrubbing the expanded por
tion with the lique?ed portion to remove impuri
ties therefrom, expanding ‘some of the scrubbed
The liquid air, free from solid impurities, which
the remainder of the scrubbed gaseous mixture
and rectifying the expanded, scrubbed gaseous
mixture by contact with the lique?ed remainder
of the scrubbed gaseous mixture, separating from
the liquid ‘containing impurities a fraction free
10 from such impurities, delivering it to the recti?
cation, and purging liquid in which impurities
passes the ?lter element 83 is delivered throughia
pipe 90 and expansion valve 9| to a pipe 92 which
is connected to the pipe 88. The liquid enters
the column with the air expanded in the expan
sion engine 88.
-
'
.
gaseous mixture with external work liquefying
In order to free the ?lter 82, and the ?lter ele
ment 83, from accumulated impurities, a purge
have accumulated.
“
93 provided with a valve 94 permits escape of
3. Theiimethod of separating the constituents
liquid when the valve 94 is opened. During purg
of gaseous mixtures by liquefaction and recti?ca
ing, the valves 80 and 9| may be closed, and air' 15 tion which comprises compressing and cooling the
or other gas under pressure may be introduced ~
gaseous mixture liquefying a portion of the com
through a pipe 95 controlled by a valve 96 which
pressed and cooled gaseous mixture by heat ex
is closed in normal operation. The gas under
change with a separated constituent, expanding
pressure forces any particles from the surface of
the remaining portion of the gaseous mixture
the ?lter element 83 so that they are discharged 20 with external work, scrubbing the expanded por
with the liquid.
tion with the lique?ed. portion to remove impuri
To avoid shut-down of the entire operation,
ties therefrom, expanding some of the scrubbed
the scrubber ‘ll may be of su?icient size to ac- ‘
cumulate a surplus of liquid. After purging, the
valves 80 and M may be re-opened and the ac
gaseous mixture with external work liquefying ‘
the remainder of the scrubbed gaseous mixture
cumulated liquid discharged into the ?lter, thus
permitting immediate resumption of normal op
eration. As in the preceding embodiment of the
and rectifying the expanded, scrubbed gaseous
mixture by contact with the liquefied remainder
of the scrubbed gaseous mixture, separating from
the liquid containing impurities a liquid fraction
invention, the procedure utilizes successive ex
pansion of the air with external work. All of the
air entering the column 50 is previously freed
from impurities such as carbon dioxide. Hence
none of these impurities can accumulate in the
recti?cation, and purging liquid in which im
purities have accumulated.
4. The method of separating the constituents
free from such impurities, delivering it to the _
of air by liquefaction and recti?cation which
liquid oxygen which is withdrawn through the
comprises compressing and cooling the air, lique
pipe 51.
fying a portion of the compressed and cooled air
by heat exchange with a separated constituent,
expanding the remaining portion of the air with
-.
-
The procedures as described afford numerous
advantages, particularly in the production of high
purity oxygen liquid, and especially in plants de
signed to produce large quantities of such liquid.
A double column may be employed in this process
if the air pressure is suf?ciently increased to
match the amount of liquid produced with the
external work, scrubbing the expanded portion
with the lique?ed‘ portion to remove impurities
thereform, expanding some of the scrubbed ‘air
with external work liquefying the remainder of
the scrubbed air and rectifying the expanded,
scrubbed air by contact with the lique?ed re
ability of the column to rectify the air. However,
at 40 atmospheres air pressure and with efficient
mainder of the scrubbed air and purging liquid .
expansion engines a single column is sufficient to 45 air in which impurities have accumulated.
rectify the liquid product and a double column
5. The method of separating the constituents
is unnecessary.
of air by liquefaction and recti?cation which com
Various changes may be made in the form and
prises compressing and cooling the air, liquefy
arrangement of the apparatus employed without
ing a portion of the compressed and cooled air by
departing from the invention or sacri?cing the 5 O heat exchange with a separated constituent, ex
advantages thereof.
pandirrg the remaining portion of the air with
I claim:
‘
external work, scrubbing the expanded portion
' 1. ‘The method of separating the constituents
‘ with the lique?ed portion to remove impurities
of gaseous vmixtures by liquefaction and recti?ca
therefrom, expanding some of the scrubbed 'air
tion which comprises compressing and cooling the 55 with external work liquefying the remainder of
gaseous mixture liquefying a portion of the com
the scrubbed air and rectifying the expanded,
pressed and cooled gaseous mixture by heat ex
scrubbed air by contact with the lique?ed re
change with a separated constituent, expanding
mainder of the scrubbed air, separating from the
the remaining portion of the gaseous mixture
liquid air containing impurities a fraction free
with external work, scrubbing the expanded por 60 from such impurities, delivering it to the recti
tion with the lique?ed portion to remove impuri
?cation and purging liquid air in which impuri
ties therefrom, expanding some of the scrubbed
ties have accumulated.
gaseous mixture with external work, liquefying
6. The method of separating the constituents
the remainder of the scrubbed gaseous mixture
of- air by liquefaction and recti?cation which
65
rectifying the expanded, scrubbed gaseous mix
comprises compressing and cooling the air, liquee
ture by contact with the lique?ed remainder-of
fying a portion of the compressed and cooled
the scrubbed gaseous mixture, and purging liquid
air by heat exchange with a separated constitu
in which impurities have accumulated.
ent, expanding the remaining portion of the air
2. The method of separating the constituents
with external work. scrubbing the expanded por
of gaseous mixtures by liquefaction and recti? 70 tion with the lique?ed portion to remove impuri
cation which comprises compressing and cooling
ties therefrom, expanding some of the scrubbed
the gaseous mixture liquefying a portion of the
air with external work liquefying the remainder
compressed and cooled gaseous mixture by heat , of the scrubbed air and rectifying the expanded,
exchange with a separated constituent, expand
scrubbed air by contact with the lique?ed re—
ing the remaining portion of the gaseous mixture
mainder'of the scrubbed air, vseparating from
i
r
2,413,752
8. The method of separating the constituents
oi gaseous mixtures by liquefaction and recti?
cation which comprises compressing and cooling
the rect?cation and purging liquid air in which’
the gaseous mixture, liquefying' a portion ,0! the
impurities have accumulated.
7. The method of separating the constituents 5 compressed and cooled gaseous mixture by heat
exchange with gaseous products of vtl'ie separa
of gaseous mixtures by liquefaction and recti?
tion, expanding the remaining portion with ,ex
the liquid air containing impurities a liquid im
tion tree from such impurities, delivering it to
cation which comprises compressing and cooling
the gaseous mixture, liquefying a portion of the
ternal work, scrubbing the expanded portion with
the lique?ed portion to concentrate impurities
compressed and cooled gaseous mixture by heat
exchange with gaseous products of the separa 10 in the liquid portion, vaporizing most of the re
sulting impure ‘liquid by heat exchange with
tion, expanding the remaining portion with ex
part of the scrubbed vapor and withdrawing the
remainder of the impure liquid together with
the impurities, heating the remainder of the
‘scrubbed vapor by exchange with unscrubbed
15
ing the impurities, subjecting a traction of the
gas from they ?rst expansion, expanding this
scrubbed vapor to heat exchange with the un
scrubbed expanded ‘gas,,expanding the scrubbed. , scrubbed and heated remainder and subjecting
it and the vapor produced from the impure
and heated fraction to the recti?cation pressure
liquid
to recti?cation.‘
,. liquetying the remainder of the scrubbed gaseous
‘
WOLCOTI‘ DENNIS. mixture and rectifying the expanded, scrubbed 2o
gaseous mixture'by contact with the lique?ed
remainder of the scrubbed gaseous mixture.
ternal work, scrubbing the expanded portion with
the lique?ed portion to concentrate impurities
in the liquid fraction, separating and withdraw
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