U.S. patent application number 09/756167 was filed with the patent office on 2001-06-28 for integrated heat exchanger system for producing carbon dioxide.
Invention is credited to Bonaquist, Dante Patrick, Howard, Henry Edward, Wong, Kenneth Kai.
Application Number | 20010004838 09/756167 |
Document ID | / |
Family ID | 46257401 |
Filed Date | 2001-06-28 |
United States Patent
Application |
20010004838 |
Kind Code |
A1 |
Wong, Kenneth Kai ; et
al. |
June 28, 2001 |
Integrated heat exchanger system for producing carbon dioxide
Abstract
A system for producing carbon dioxide wherein carbon dioxide
feed fluid is first processed in a cooling section of an integrated
heat exchanger before purification in a column, and wherein column
bottom fluid operates within one of an evaporating section and
desuperheating section of the heat exchanger and refrigerant fluid
operates within the other of the evaporating section and
desuperheating section of the heat exchanger.
Inventors: |
Wong, Kenneth Kai; (Amherst,
NY) ; Bonaquist, Dante Patrick; (Grand Island,
NY) ; Howard, Henry Edward; (Grand Island,
NY) |
Correspondence
Address: |
PRAXAIR, INC.
LAW DEPARTMENT - M1 557
39 OLD RIDGEBURY ROAD
DANBURY
CT
06810-5113
US
|
Family ID: |
46257401 |
Appl. No.: |
09/756167 |
Filed: |
January 9, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09756167 |
Jan 9, 2001 |
|
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|
09429611 |
Oct 29, 1999 |
|
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Current U.S.
Class: |
62/617 ;
62/928 |
Current CPC
Class: |
F25J 2215/80 20130101;
F25J 2270/60 20130101; F25J 2270/02 20130101; Y02C 20/40 20200801;
Y10S 62/928 20130101; F25J 2200/70 20130101; F25J 2245/02 20130101;
F25J 3/0266 20130101; F25J 2290/40 20130101; F25J 3/08 20130101;
F25J 2270/90 20130101; F25J 3/0295 20130101; F25J 2200/74 20130101;
F25J 2220/82 20130101; F25J 2270/12 20130101; F25J 2200/02
20130101; F25J 2205/02 20130101; F25J 2205/60 20130101 |
Class at
Publication: |
62/617 ;
62/928 |
International
Class: |
F25J 003/00 |
Claims
1. A method for producing carbon dioxide comprising: (A) passing
carbon dioxide feed fluid through a cooling section of a heat
exchanger having a cooling section, a desuperheating section and an
evaporating section to produce cooled carbon dioxide feed fluid;
(B) passing cooled carbon dioxide feed fluid into a distillation
column and producing carbon dioxide product fluid in the
distillation column; (C) recovering carbon dioxide product fluid
from the lower portion of the distillation column as product carbon
dioxide; and (D) passing carbon dioxide product fluid through one
of the evaporating section and the desuperheating section of the
heat exchanger, and passing refrigerant fluid through one of the
evaporating section and the desuperheating section of the heat
exchanger.
2. The method of claim 1 wherein carbon dioxide product fluid is
passed through the evaporating section of heat exchanger and
refrigerant fluid is passed through the desuperheating section of
the heat exchanger.
3. The method of claim 1 wherein carbon dioxide product fluid is
passed through the desuperheating section of the heat exchanger and
refrigerant fluid is passed through the evaporating section of the
heat exchanger.
4. The method of claim 1 wherein the heat exchanger comprises a
first portion and a second portion with each portion having a
cooling section, a desuperheating section and an evaporating
section, and wherein the carbon dioxide feed fluid passes through
the cooling sections of each of the first and second portions,
carbon dioxide product fluid passes through the evaporating section
of the first portion and the desuperheating section of the second
portion, and refrigerant fluid passes through the desuperheating
section of the first portion and the evaporating section of the
second portion.
5. The method of claim 4 further comprising recovering a vapor
stream containing carbon dioxide from the top of the distillation
column, passing said vapor stream through one or both cooling
sections of the heat exchanger to cool and partially condense said
stream, separating said partially condensed stream into a liquid
condensate stream enriched in carbon dioxide and a carbon dioxide
depleted vapor stream, and passing said carbon dioxide enriched
liquid condensate stream into said distillation column.
6. The method of claim 4 further comprising recovering a vapor
stream containing carbon dioxide from the top of the distillation
column, passing said vapor stream through one or both cooling
sections of the heat exchanger to cool and partially condense said
stream thereby forming a vapor component and a liquid component,
passing the vapor component and the liquid component together or
separately into a second heat exchanger to further cool said liquid
component and further partially condense said vapor component,
recovering from said second heat exchanger a combined stream
comprising said further cooled liquid component and said further
partially condensed vapor component, separating said combined
stream into a liquid condensate stream enriched in carbon dioxide
and a carbon dioxide depleted vapor stream, passing said carbon
dioxide depleted vapor stream and said carbon dioxide enriched
liquid condensate stream through said second heat exchanger to
vaporize said carbon dioxide enriched liquid into a carbon dioxide
enriched vapor and to warm said carbon dioxide depleted vapor
stream by heat exchange therein from said partially condensed vapor
stream, and recycling said carbon dioxide enriched vapor to step
(A) for passing through said cooling section.
7. Apparatus for producing carbon dioxide comprising: (A) a heat
exchanger having a cooling section, a desuperheating section and an
evaporating section, and means for passing carbon dioxide feed
fluid to the cooling section of the heat exchanger; (B) a
distillation column and means for passing carbon dioxide feed fluid
from the cooling section of the heat exchanger to the distillation
column; (C) means for recovering carbon dioxide product fluid from
the lower portion of the distillation column; (D) means for passing
carbon dioxide product fluid from the lower portion of the
distillation column through one of the desuperheating section and
evaporating section of the heat exchanger, and means for passing
refrigerant fluid through one of the evaporating section and the
desuperheating section of the heat exchanger.
8. The apparatus of claim 7 comprising means for passing carbon
dioxide product fluid through the evaporating section of the heat
exchanger, and means for passing refrigerant fluid through the
desuperheating section of the heat exchanger.
9. The apparatus of claim 7 comprising means for passing carbon
dioxide product fluid through the desuperheating section of the
heat exchanger, and means for passing refrigerant fluid through the
evaporating section of the heat exchanger.
10. The apparatus of claim 7 wherein the heat exchanger comprises a
first portion and a second portion with each portion having a
cooling section, a desuperheating section and an evaporating
section, comprising means for passing carbon dioxide feed fluid to
the cooling sections of each of the first and second portions,
means for passing carbon dioxide product fluid to the evaporating
section of the first portion and the desuperheating section of the
second portion, and means for passing refrigerant fluid to the
desuperheating section of the first portion and to the evaporating
section of the second portion.
11. The apparatus of claim 10 wherein the first and second portions
are contained in a single heat exchanger module.
12. The apparatus of claim 10 wherein the first and second portions
are contained in separate heat exchanger modules.
13. The apparatus of claim 10 further comprising means for
recovering a vapor stream containing carbon dioxide from the top of
the distillation column, means for passing said vapor stream
through one or both cooling sections of the heat exchanger to cool
and partially condense said stream, means for separating said
partially condensed stream into a liquid condensate stream enriched
in carbon dioxide and a carbon dioxide depleted vapor stream, and
means for passing said carbon dioxide enriched liquid condensate
stream into said distillation column.
14. The apparatus of claim 10 further comprising means for
recovering a vapor stream containing carbon dioxide from the top of
the distillation column, means for passing said vapor stream
through one or both cooling sections of the heat exchanger to cool
and partially condense said stream thereby forming a vapor
component and a liquid component, means for passing the vapor
component and the liquid component together or separately into a
second heat exchanger to further cool said liquid component and
further partially condense said vapor component, means for
recovering from said second heat exchanger a combined stream
comprising said further cooled liquid component and said further
partially condensed vapor component, means for separating said
combined stream into a liquid condensate stream enriched in carbon
dioxide and a carbon dioxide depleted vapor stream, means for
passing said carbon dioxide depleted vapor stream and said carbon
dioxide enriched liquid condensate stream through said second heat
exchanger to vaporize said carbon dioxide enriched liquid into a
carbon dioxide enriched vapor and to warm said carbon dioxide
depleted vapor stream by heat exchange therein from said partially
condensed vapor stream, and means for recycling said carbon dioxide
enriched vapor to step (A) for passing through said cooling
section.
Description
[0001] This application is a continuation-in-part of U.S.
application Ser. No. 09/429,611, filed Oct. 29, 1999.
FIELD OF THE INVENTION
[0002] This invention generally relates to the recovery of carbon
dioxide from a feed stream.
BACKGROUND ART
[0003] Large scale processing systems for recovering carbon dioxide
from a feed stream are known in the art. Typically such systems are
similar to systems which are used to carry out the cryogenic
separation of air into its components and thus employ heat
exchangers having relatively complicated structures as are
typically required for the rigorous cryogenic separation of air.
Such complicated structures are costly and it would be desirable to
have a system for producing carbon dioxide which can employ a more
advantageous heat exchanger arrangement.
[0004] Accordingly it is an object of this invention to provide a
system for effectively producing carbon dioxide from a feed stream
while employing an improved heat exchanger arrangment from that
employed by conventional carbon dioxide recovery systems.
SUMMARY OF THE INVENTION
[0005] The above and other objects, which will become apparent to
those skilled in the art upon a reading of this disclosure, are
attained by the present invention, one aspect of which is:
[0006] A method for producing carbon dioxide comprising:
[0007] (A) passing carbon dioxide feed fluid through a cooling
section of a heat exchanger having a cooling section, a
desuperheating section and an evaporating section to produce cooled
carbon dioxide feed fluid;
[0008] (B) passing cooled carbon dioxide feed fluid into a
distillation column and producing carbon dioxide product fluid in
the distillation column;
[0009] (C) recovering carbon dioxide product fluid from the lower
portion of the distillation column as product carbon dioxide;
and
[0010] (D) passing carbon dioxide product fluid through one of the
evaporating section and the desuperheating section of the heat
exchanger, and passing refrigerant fluid through one of the
evaporating section and the desuperheating section of the heat
exchanger.
[0011] Another aspect of the invention is:
[0012] Apparatus for producing carbon dioxide comprising:
[0013] (A) a heat exchanger having a cooling section, a
desuperheating section and an evaporating section, and means for
passing carbon dioxide feed fluid to the cooling section of the
heat exchanger;
[0014] (B) a distillation column and means for passing carbon
dioxide feed fluid from the cooling section of the heat exchanger
to the distillation column;
[0015] (C) means for recovering carbon dioxide product fluid from
the lower portion of the distillation column;
[0016] (D) means for passing carbon dioxide product fluid from the
lower portion of the distillation column through one of the
desuperheating section and evaporating section of the heat
exchanger, and means for passing refrigerant fluid through one of
the evaporating section and the desuperheating section of the heat
exchanger.
[0017] As used herein the term "indirect heat exchange" means the
bringing of two fluid streams into heat exchange relation without
any physical contact or intermixing of the fluids with each
other.
[0018] As used herein the terms "upper portion" and "lower portion"
mean those sections of a column respectively above and below the
mid point of the column.
[0019] As used herein the term "column" means a distillation or
fractionation column or zone, i.e. a contacting column or zone,
wherein liquid and vapor phases are countercurrently contacted to
effect separation of a fluid mixture, as for example, by contacting
of the vapor and liquid phases on a series of vertically spaced
trays or plates mounted within the column and/or on packing
elements such as structured or random packing. For a further
discussion of distillation columns, see the Chemical Engineer's
Handbook, fifth edition, edited by R. H. Perry and C. H. Chilton,
McGraw-Hill Book Company, New York, Section 13, The Continuous
Distillation Process.
[0020] Vapor and liquid contacting separation processes depend on
the difference in vapor pressures for the components. The high
vapor pressure (or more volatile or low boiling) component will
tend to concentrate in the vapor phase whereas the low vapor
pressure (or less volatile or high boiling) component will tend to
concentrate in the liquid phase. Distillation is the separation
process whereby heating of a liquid mixture can be used to
concentrate the more volatile component(s) in the vapor phase and
thereby the less volatile component(s) in the liquid phase. Partial
condensation is the separation process whereby cooling of a vapor
mixture can be used to concentrate the volatile component(s) in the
vapor phase and thereby the less volatile component(s) in the
liquid phase. Rectification, or continuous distillation, is the
separation process that combines successive partial vaporizations
and condensations as obtained by a countercurrent treatment of the
vapor and liquid phases. The countercurrent contacting of the vapor
and liquid phases can be adiabatic or nonadiabatic and can include
integral (stagewise) or differential (continuous) contact between
the phases. Separation process arrangements that utilize the
principles of rectification to separate mixtures are often
interchangeably termed rectification columns, distillation columns,
or fractionation columns.
[0021] As used herein the term "cooling section" means a section of
a heat exchanger wherein a fluid stream releases heat indirectly to
one or more other fluid streams thereby cooling and/or condensing
that stream.
[0022] As used herein the term "desuperheating section" means a
section of a heat exchanger wherein a fluid stream is cooled with
an accompanying decrease in temperature and the heat exchange is
carried out without a phase change, i.e. boiling or
condensation.
[0023] As used herein the term "evaporating section" means a
section of a heat exchanger wherein a fluid stream absorbs heat and
is at least partially vaporized.
[0024] As used herein the term "refrigerant fluid" means a fluid
which absorbs heat and is subsequently compressed and condensed
against another fluid.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a schematic representation of a carbon dioxide
recovery system as one preferred embodiment of the present
invention.
[0026] FIG. 2 is a schematic representation of a carbon dioxide
recovery system as another preferred embodiment of the present
invention.
[0027] FIG. 3 is a schematic representation of a carbon dioxide
recovery system incorporating another preferred embodiment of the
present invention.
[0028] FIG. 4 is a schematic representation of a carbon dioxide
recovery system incorporating yet another preferred embodiment of
the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0029] A first preferred embodiment of the present invention will
be discussed with reference to the single column carbon dioxide
distillation system 130 shown in FIG. 1.
[0030] Feed stream 135, generally comprising at least 95 mole
percent carbon dioxide as well as contaminants such as nitrogen,
oxygen, water, argon, hydrogen, carbon monoxide and methane, enters
a feed stream supply 136. Feed stream supply 136 compresses,
cleans, dries and cools the feed stream using, for example, one or
more compressors, phase separators and heat exchangers to prepare
the feed stream for processing. Although not shown in FIG. 1,
carbon adsorption beds may be used to extract hydrocarbons from the
feed stream. A refrigeration system 160 circulates in streams 161
and 162 refrigerant fluid through feed stream supply 136 to assist
in cooling the feed stream. Refrigeration system 160 may be a
conventional refrigeration system. Examples of suitable refrigerant
fluids include carbon dioxide, chlorodifluoromethane, ammonia and
propane.
[0031] The cooled and dried feed stream exits feed stream supply
136 as stream 140 and enters a single integrated heat exchanger 145
with a temperature of about 40.degree. F. to about 50.degree. F. at
a pressure of about 300 psia to about 350 psia. Heat exchanger 145
comprises a single module having two heat exchanger portions, each
portion having a cooling section, a desuperheating section and an
evaporating section. The feed stream is further cooled within heat
exchanger 145 to a temperature of about -10.degree. F. to about
-20.degree. F. in the cooling section of the first portion and is
substantially liquefied in the cooling section of the second
portion by transferring heat from the feed stream to stream 150 of
carbon dioxide product fluid supplied from a column 165 and passing
in the evaporating section of the first portion, and to stream 155
of refrigerant from refrigeration system 160 and passing in the
desuperheating section of the first portion of heat exchanger
145.
[0032] The cooled carbon dioxide feed stream exits heat exchanger
145 as stream 170 and is introduced into the upper portion of
column 165 to serve as the primary feed source to column 165. The
carbon dioxide feed fluid flows down column 165 while being
contacted with upwardly flowing stripping vapor such that the
concentration of carbon dioxide in the feed fluid descending
through column 165 becomes progressively enriched. Essentially pure
liquid carbon dioxide is produced as carbon dioxide product fluid
in the lower portion of column 165 and is withdrawn from the bottom
of column 165. The stripping vapor is withdrawn from the upper
portion of column 165.
[0033] To provide the stripping vapor, carbon dioxide product fluid
is removed in stream 180 from the bottom of column 165 and is split
into two streams. A first stream 150 is passed into heat exchanger
145 and is vaporized in an evaporating section of heat exchanger
145 at a temperature of about 0.degree. F. to about 10.degree. F.
at a pressure of about 300 psia to about 350 psia as was previously
described. The resulting carbon dioxide vapor is introduced into
column 165 in the lower portion of column 165 and passes counter to
the descending stream of liquid carbon dioxide. Thus, the carbon
dioxide vapor resulting from warming the first stream 150 serves as
the stripping vapor within column 165 to purify the descending feed
stream.
[0034] A second stream 185 of the carbon dioxide product fluid
removed from the bottom of column 165 is passed through flow
control valve 190 and into heat exchanger 145. The second stream
185 is subcooled in a desuperheating section of heat exchanger 145
to a temperature of about -10.degree. F. to about -20.degree. F. in
heat exchanger 145 by transferring heat to a refrigerant stream 195
supplied from refrigeration system 160 across a valve 200 and
passing in an evaporating section of heat exchanger 145.
[0035] After exiting heat exchanger 145, a subcooled second stream
205 is split into two streams. A first stream 210 of the subcooled
second stream 205 recovered as product carbon dioxide having a
carbon dioxide concentration of up to 99.9 mole percent or
more.
[0036] A second stream 215 of the subcooled second stream 205 is
passed through valve 220 and is sent as 255 to a condenser 225 at a
temperature of about -65.degree. F. to about -55.degree. F. at a
pressure of about 80 psia to about 115 psia. Additionally,
stripping vapor is fed as stream 230 to condenser 225 from the top
of column 165 at a temperature of about -50.degree. F. to about
-15.degree. F. The second stream 215 partially condenses the
stripping vapor to a temperature of about --50.degree. F. to about
-60.degree. F. The partially condensed stripping vapor is then
passed as stream 235 from condenser 225 to a phase separator 240.
Condensed impure liquid carbon dioxide from the bottom of phase
separator 240 is returned as stream 245 to the top of column 165
for further processing. Waste gas from the top of phase separator
240 is vented as stream 250 to the atmosphere. The liquid carbon
dioxide fed as stream 255 to vent condenser 225 to cool and
condense the stripping vapor exits reflux condenser 225 as stream
260 and is passed through valve 265 and returned as stream 270 to
feed stream supply 136.
[0037] Heat exchanger 145 in the first preferred embodiment
illustrated in FIG. 1 is a single, integrated brazed aluminum
plate-fin type heat exchanger. By way of explanation, a plate-fin
type heat exchanger includes at least three heat conductive plates
separated by predetermined distances. The separations between
adjacent plates provide passages through which fluids flow. These
passages may be filled with heat conductive structures, such as
metal fins, to facilitate heat transfer from one passage to
another. Thus, a warm fluid flowing in one passage may efficiently
transfer heat to a colder fluid flowing in an adjacent channel.
[0038] A relatively large number of passages may be easily created
in a plate-fin type heat exchanger to allow a relatively large
number of fluids to participate in heat transfer operations. For
example, heat exchanger 145 of the present invention includes
sufficient passages to allow heat exchanger 145 to cool and liquefy
the entering feed stream from about 45.degree. F. to about
-20.degree. F., vaporize a refrigerant stream at about -25.degree.
F., subcool a portion of a product stream from about 0.degree. F.
to about -20.degree. F., and partially vaporize a remaining portion
of the column bottoms. Heat exchanger 145 thus provides the
advantage of replacing multiple heat exchangers with a single
integrated unit. Further, within heat exchanger 145 of the present
invention unfavorable temperature differences are minimized. Less
piping and related structures are required because the above-noted
heat exchange operations are performed within a single integrated
core.
[0039] Another preferred embodiment of the carbon dioxide recovery
system of the present invention is illustrated in FIG. 2. This
preferred embodiment provides, among other features, a carbon
dioxide distillation system 570 having a single unit incorporating
a heat exchanger into a distillation column.
[0040] The preferred embodiment illustrated in FIG. 2 uses a feed
stream supply 575 for receiving a carbon dioxide feed stream 580
and compressing, cleaning, drying and cooling the feed stream.
[0041] The carbon dioxide feed stream exits feed stream supply 575
as stream 585 and enters a brazed aluminum plate-fin type main heat
exchanger 590 located below a distillation unit 595 of a
distillation column 600. At this stage, the feed stream has a
temperature of about 40.degree. F. to about 50.degree. F. and a
pressure of about 300 psia to about 350 psia. Main heat exchanger
590 includes a first heat exchanger portion 605 and a second heat
exchanger portion 610 separated by a partition 615. The feed stream
585 entering first heat exchanger portion 605 is cooled by passage
through the cooling section of heat exchanger portion 605 to a
temperature of about 5.degree. F. to about 15.degree. F. by
exchanging heat with column bottoms contained in the evaporating
section of heat exchanger 605. Liquid refrigerant 625 from
refrigeration supply 620 is subcooled in the desuperheating section
of heat exchanger 605 and also against boiling carbon dioxide
product fluid.
[0042] The carbon dioxide feed stream and the carbon dioxide
product fluid surrounding first heat exchanger 605 pass through
partition 615 and into second heat exchanger portion 610. Within
second heat exchanger 610 the feed stream is substantially
condensed by passing through the cooling section of second heat
exchanger 610. The latent heat of feed condensation is imported to
the refrigerant in the evaporating section of second heat exchanger
610. After condensation in second heat exchanger 610, the feed
stream has a temperature of about -20.degree. F.
[0043] To provide refrigerant to the evaporating section of second
heat exchanger 610, the refrigerant leaves first heat exchanger
605, passes in stream 630 across a valve 635 and is re-introduced
into distillation column shell 600 at a location below partition
615. The refrigerant then collects at the bottom of column 600 and
surrounds second heat exchanger 610 at a temperature of about
-25.degree. F.
[0044] The refrigerant surrounding second heat exchanger 610 is
vaporized by the condensing carbon dioxide feed stream. At this
stage, the refrigerant vapor has a temperature of about -25.degree.
F. The refrigerant vapor passes through a demister 640 to remove
liquid droplets and exits column 600 to be recycled as stream 627
through refrigeration supply system 620. The refrigerant also
provides product subcooling of stream 650.
[0045] The cooled and liquefied feed stream exits second heat
exchanger 610 as stream 645 and is fed to the upper portion of
distillation unit 595. The liquid feed stream thus becomes the
primary feed stream descending through distillation unit 595 for
purification. The liquid cooled carbon dioxide feed stream is
enriched in distillation unit 595 by contacting a counterflowing
stripping vapor to become almost pure carbon dioxide product fluid.
After flowing down distillation column 595, the liquid carbon
dioxide product fluid collects above partition 615 and surrounds
first heat exchanger 605 in the evaporating section of heat
exchanger 605. The carbon dioxide product fluid surrounding first
heat exchanger 605 contributes to cooling the carbon dioxide feed
stream passing through the cooling section of first heat exchanger
605, and a portion of the carbon dioxide product fluid passes
through partition 615 through a pipe and through second heat
exchanger 610, as previously discussed. After passing through
second heat exchanger 610, the carbon dioxide product fluid exits
column 600 as stream 650 and passes through valve 655 for recovery
as product carbon dioxide.
[0046] A portion of the carbon dioxide product fluid surrounding
first heat exchanger 605 is vaporized by indirect heat exchange
with the carbon dioxide feed stream passing through the cooling
section of first heat exchanger 605. The resulting carbon dioxide
vapor passes into distillation unit 595.
[0047] The stripping vapor collects at the top of distillation
column 600 after passing countercurrently to the descending carbon
dioxide feed fluid in distillation unit 595. The stripping vapor is
then fed as stream 660 from the top of the distillation column 600
into a secondary heat exchanger 665 at a temperature of about
-10.degree. F. to about -20.degree. F. Secondary heat exchanger 665
cools and partially condenses the stripping vapor to a temperature
of about -40.degree. F. to about -60.degree. F. The partially
condensed stripping vapor drains as stream 670 directly into a
phase separator 675 by way of piping. Waste gas from the top of
phase separator 675 passes as stream 680 through secondary heat
exchanger 665, across a valve 685 and is vented directly to the
atmosphere. Impure carbon dioxide liquid is withdrawn as stream 690
from the bottom of phase separator 675, passes through valve 695
and through secondary heat exchanger 665. The carbon dioxide liquid
is subsequently passed through valve 700 and as stream 701 is
passed into feed compression and prepurification unit 575.
[0048] The preferred embodiment illustrated in FIG. 2 provides many
advantages. For example, incorporating most of the heat transfer
and mass transfer functions of a carbon dioxide distillation system
into a single unit reduces the necessary piping and equipment for
producing essentially pure carbon dioxide from a feed stream. Thus,
this embodiment of the present invention reduces the complexities
and costs of producing carbon dioxide from a feed stream.
[0049] Additional preferred embodiments are shown in FIGS. 3 and 4
and are described below.
[0050] One such embodiment comprises recovering a vapor stream
containing carbon dioxide from the top of the distillation column,
passing said vapor stream through one or both cooling sections of
the heat exchanger to cool and partially condense said stream,
separating said partially condensed stream into a liquid condensate
stream enriched in carbon dioxide and a carbon dioxide depleted
vapor stream, and passing said carbon dioxide enriched liquid
condensate stream into said distillation column.
[0051] With reference to FIG. 3, overhead gas stream 660 is
directed to an additional pass through heat exchanger 610. The
stream is cooled and partially condensed to -15 to -20.degree. F.
and exits as stream 700. Stream 700 is phase separated in vessel
701. Condensate stream 702 which is enriched in carbon dioxide is
directed to a mechanical pump 703 where it is pressurized to a
pressure greater than the presure in column 595. The pressurized
condensate stream is then directed to the upper section of column
704. Alternatively, stream 704 can be directed into column feed
pipe 645. The vapor derived from vessel 701 contains residual light
gas contaminants and is directed to an atmospheric vent through
pipe 705, valve 706 and pipe 707.
[0052] The advantage posed by the arrangement shown in FIG. 3 stems
from the fact that a separate heat exchanger is not required to
obtain an increased fraction of carbon dioxide from the feed
stream. This arrangement reduces total package height and
eliminates the separate vent exchanger, refrigerant, piping and
controls.
[0053] Another embodiment comprises recovering a vapor stream
containing carbon dioxide from the top of the distillation column,
passing said vapor stream through one or both cooling sections of
the heat exchanger to cool and partially condense said stream
thereby forming a vapor component and a liquid component, passing
the vapor component and the liquid component together or separately
into a second heat exchanger to further cool said liquid component
and further partially condense said vapor component, recovering
from said second heat exchanger a combined stream comprising said
further cooled liquid component and said further partially
condensed vapor component, separating said combined stream into a
liquid condensate stream enriched in carbon dioxide and a carbon
dioxide depleted vapor stream, passing said carbon dioxide depleted
vapor stream and said carbon dioxide enriched liquid condensate
stream through said second heat exchanger to vaporize said carbon
dioxide enriched liquid into a carbon dioxide enriched vapor and to
warm said carbon dioxide depleted vapor stream by heat exchange
therein from said partially condensed vapor stream, and recycling
said carbon dioxide enriched vapor to step (A) for passing through
said cooling section.
[0054] With reference to FIG. 4, a carbon dioxide refrigerated vent
condenser is incorporated into the process. In this arrangement,
condensate stream 702 is directed through valve 800 and through
pipe 801 into vent condenser 802. Vapor stream 705 is directed
through valve 706 and through stream 707 and is rejoined with
stream 801. Alternatively, stream 700 could be introduced into
exchanger 802 directly. However, phase separator 701 is included in
order to provide separate liquid and vapor streams which can be
distributed individually within exchanger 802. If this were not
done it is possible that maldistribution of liquid and vapor could
occur within exchanger 802 reducing its overall efficiency. The
combined stream emerges further cooled and further partially
condensed as stream 803. Stream 803 is then phase separated in
vessel 804. Condensate stream 805 is pressure reduced in valve 806
and directed to exchanger 802 via pipe 807. Stream 807 is
substantially vaporized and emerges as gas stream 808 which can be
recycled to feed compression train 575 (as previously noted in
regard to FIGS. 1 and 2) for compression and subsequent additional
carbon dioxide recovery. A residual vent gas stream 809 is taken
from vessel 804 and warmed in exchanger 802 and vented to
atmosphere through pipe 810, valve 811 and pipe 812.
[0055] The advantage posed by the embodiment of FIG. 4 stems from
the fact that it is more suitable for lean feed streams (lower
carbon dioxide content, <97% CO.sub.2). Stream 803 is
cooled/condensed to -60.degree. F. and consequently significant
additional carbon dioxide can be recovered as product.
[0056] In addition, the embodiment of FIG. 4 offers the option of
eliminating the additional mechanical pump 703 shown in FIG. 3.
This saves cost and increases process reliability.
[0057] While the present invention has been described with respect
to what is considered to be the preferred embodiments, the
invention is not limited to the disclosed embodiments. To the
contrary, the invention is intended to cover various modifications
and equivalent arrangements included within the spirit and scope of
the appended claims. The scope of the following claims is to be
accorded the broadest interpretation so as to encompass all such
modifications and equivalent structures and functions.
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